High Efficiency Speaker Asylum

Need speakers that can rock with just one watt? You found da place.

Return to High Efficiency Speaker Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Of course we all know that low mass cones = "fast bass"

66.51.146.158
Posted on January 9, 2009 at 09:41:36
Richard BassNut Greene
 copied from the old Adire Audio website several years ago -- sorry that three charts didn't survive the cut & paste to here:

Woofer Speed
By Dan Wiggins
There's a common misconception out there, that heavy woofers must be "slow", and light woofers must be "fast". If a woofer A's moving mass is higher than woofer B's, then woofer A is probably going to be sloppy, or slow and inaccurate. Can't keep up with the bass line. Woofer A simply can't respond as fast as woofer B.

There's also this concept that the "acceleration factor" (BL/Mms) is an indicator of woofer speed/transient response. High BL, combined with a low Mms, should give great transient response, right?

Well, on surface these might sound like logical assumptions. However, they are in fact incorrect! More to the point, moving mass has precious little to do with woofer speed or signal response! And we'll prove it...
Go back to good old Newtonian physics... We're going to start with the famous law:

F=ma (eq 1)

Or force equals mass times acceleration. Anyone who's been through introductory physics (or watched a bit of PBS) should be familiar with the equation above. It's pretty much the bedrock equation of Newtonian physics - it's number 2 of the Big 3 Newtonian equations (the first being about interia, and the third being about complementary/opposed actions).

Now, let's look at a loudspeaker... What do we have? We have a coil of wire which creates an alternating magnetic field which interacts with the static magnetic field in the gap (see our page on DVC subs for a bit more information on this). How does the alternating magnetic field of the coil come into being? Well, the magnetic field is created by passing a current through the voice coil.

As the current through the voice coil changes, the magnetic field created by the coil changes. This field interacts with the static magnetic field of the permanent magnet, and you get a force - the cone moves in and out. Just like two permanent magnets will attract/repel each other depending upon how they are oriented. And a bigger current means more force. Just like bigger/stronger permanent magnets mean stronger attraction/repulsion.

Additionally, what if we make the field of the permanent magnet stronger? Well, that's call the B field in the gap. Increase B, we increase the force as well. Or, what if we could somehow make the magnetic field from the voice coil stronger? We can - increase the number of turns of the voice coil (increase the Length of the wire in the gap). Guess what - in both cases, we increased the BL of the speaker (yes, this is the BL of the T/S parameters - now you know where it comes from!).

Now, let's go back to equation 1... Let's define each of the terms in that equation so we know what we're talking about:
F= Force
m = mass (moving mass)
a = acceleration

So, what is the Force (NO Star Wars jokes, please!). From above, we see that the force on the cone is the motor force factor (BL) times the current. So, let's rewrite equation 1 in these terms that are applicable to the loudspeaker:

BLi = ma (eq 2)

So, the Motor Force Factor BL times the current i equals the moving mass of the driver m times the acceleration of the driver a. Note that we have italicized i and a. There's a reason for it!

Now, back to the original question - transient response of a driver. What is transient response? Simply a measure of how fast the driver can respond to the input signal. That means that - inherently - there is a time dependency on the driver. How much TIME elapses before the driver responds. So, let's look at equation 2, and cancel out all terms that are not based on time. After all, if a quantity is time-invariant, then it won't affect time-variant effects like transient response (think of this as a simple offset).

Or, to put it in an analogy, does the 1/4 mile time of a vehicle depend upon where you start? No, the distance over which you measure is still 1/4 mile. So whether you start in front of your house and go straight 1/4 mile, or motor on down to the dragstrip and go 1/4 mile doesn't really affect the car's 1/4 mile time. The 1/4 mile time is strictly dependent on how fast the car can accelerate from a dead stop over a 1/4 mile length.

So, looking at equation 2 we see that:
BL is time invariant, assuming small excursions (assume an ideal motor with a flat BL curve; I know, most drivers don't have that, but assume that it does, like our XBL2 enabled motors). So BL is essentially a constant.

i is the current into the driver (we used italics to indicate a parameter that is time-variant). This is the music, or test tone sweep, or whatever signal is coming from the amp. It's an AC waveform so by definition it changes with time.

m is mass. Well, if the moving mass of the driver is changing as you operate, you've got big problems! The weight of the cone, dustcap, former, voice coil, surround, and spider are pretty much fixed. The don't change either. So m is essentially a constant.

a is the acceleration. This is what we're after. After all, the rate of change of acceleration IS the transient response - it's what dictates how fast the driver can change speed, which also means it dictates how fast the driver can move from position to position. And note that it's in italics, too. After all, acceleration in the time-variant parameter we care about here!

So, let's rewrite equation 2, and replace the time-invariant parameters with a simple "C" to indicate a constant (a parameter that does not change with time):

Ci = Ca (eq 3) or i :: a (eq 4)

(note: the "::" symbol is the mathematical symbol for proportionality; that is, i is proportional to a).

Interesting! This says that the change in acceleration of a driver - how fast it can change position - is strictly a function of the current through the driver. In fact, if you could make the current change infinitely fast, then the driver would accelerate infinitely fast, and we'd have infinite transients - zero time to change between states. Infinite frequency response.

So, now that we know that current is the driving force (pun somewhat intended) behind driver acceleration changes, let's look at what limits how fast we can ramp current through the driver. Because if we are not restricted in how fast we can change the current, then we are not restricted in how fast the driver can accelerate - transient response is not limited at all.

So, back to that loudspeaker model... A loudspeaker is a coil of wire wound on a former that attaches to the cone. The current flows through the coil, creating an alternating magnetic field that interacts with the static magnetic field of the permanent magnet. So, what could limit current flow? Well, what does a voice coil look like?

How about an inductor? You know, those coils of wire (hey, isn't that what a voice coil is) that you use in crossovers? Guess what - a voice coil IS an inductor! In fact, an inductor stores its energy in the magnetic field (as opposed to a capacitor which stores its energy in the electric field). It is this magnetic field of the voice coil "inductor" that interacts with the permanent magnet field we talked about above. Hey, a loudspeaker is an inductor hung on the end of a cone in a static magnetic field!

So, what about an inductor will alter the way current flows? Well, inductors don't like to have the current flowing through them change. They like to hold the current constant. They will allow you to change the current flowing in them, but the bigger the inductor (or, the higher the measured inductance) the longer it will hold the current before it starts to change (I'll leave it to the reader to go research inductance on their own, to learn why this happens).

So, the voice coil is an inductor. And we see that inductors don't like to change current. But we also see from equation 4 above that we need to change the current if we want to change the acceleration. So, the voice coil doesn't want us to change the current. How good is it at holding the current? Depends upon the inductance! The higher the inductance of the driver, the longer it can hold the current flowing through it. Which means the more time elapses before it starts to respond to the amplifier's applied voltage. Which means we have slower transient response.

Guess what - we just answered the original question! It turns out that transient response of a woofer is not a function of the moving mass, as is commonly espoused (one of the most infamous audio myths). In actuality, it is based upon the inductance of the driver. And the greater the inductance, the slower the driver - the lower the transient response.

So let's put this to the test - let's add some mass to a driver, and also increase the inductance to see what happens. Out to the lab! This is what we did:

- Used a prototype Extremis 6-8 (8 Ohm 6.5" woofer). Note that we had Klippel data measured by the good Dr. Wolfgang Klippel himself at CES 2004.

- Added mass was 28.5 grams (Mms of the Extremis 6-8 is 24.39 grams per Klippel). Mass added to dustcap only; none was placed on the cone itself (all within the diameter of the former).

- Added inductance was a 10 AWG, 0.47 mH inductor (inductance of the Extremis 6-8 is 0.6 mH per Klippel)

We left the driver mounted in our test baffle, which is 48" square. Driver centered on baffle (not flush mounted), anechoic (no box). Nearest reflective surface is 6 feet from the speaker, for good results down to 90 Hz.

Test gear used was:

- Praxis measurement system
- M Audio Audiophile USB sound card
- AudioControl MP200 test mic and preamp (last cal at factory November 2002 - time to get another cal!)
- QSC PLX3402 amplifier

We measured the impulse response of the driver raw, with 28.5 grams added (more than doubled the moving mass), and with 0.47 mH in series (78% increase in inductance). In other words, we more than doubled the mass, and didn't double the inductance. So the mass - if it really limits transient response (and hence frequency response) should really stand out compared to the inductive changes.

Here's what the impulse tests show:



Raw image dump from Praxis. Red is the raw driver - nothing added. Blue is the driver with 28.5 grams mass added. Green is the driver (no added mass) with the inductor in series.

Now, look at the time of the peaks. I've set the markers where the raw driver has its turn-on transient peaks. The mass (blue line) corresponds nicely. The inductor (green line) has a delay in the negative AND positive peaks.

Here's a zoomed in view of the start (note the sampling time is ~21 microseconds, a 48 kHz sampling rate):

You can clearly see that the raw and mass loaded transient peaks - first negative and first positive peaks - occur at the same time. The inductively loaded (green) peaks are definitely delayed in time. As one would expect!

Now, how would this translate to frequency response? Here's a graph of the raw (unsmoothed, wide gate) frequency response for the same 3 cases:

Note the red and blue - raw and mass loaded, respectively. They are pretty much equal from 700 Hz and up (I assume we all accept the Fourier transforms, and that the Fs/efficiency of the driver is affected by the added mass, accounting for the differences down low.

Now look at the green. It is 5+ dB down at 4+ kHz. The high frequency - the transient part of transient response - is reduced! The inductance cut the high frequency extension - mass did not!

Mass isn't the problem - inductance is. So if you want faster transient response, ignore that moving mass parameter that some manufacturers push - look at the inductance! And if they don't list the inductance, ask yourself why - is there something they don't want to show? Inductance is the key to driver transient response - ask for it when transient response comes up!
.
.
.
.
.
.
.
.
.
.
.




Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"

 

Hide full thread outline!
    ...
Flaws in logic and experimental setup., posted on January 9, 2009 at 11:18:32
sser2
Audiophile

Posts: 2571
Location: Pittsburgh USA
Joined: July 30, 2003
 Error in logic. Because for a GIVEN driver mms and BL are constant, it is erroneously assumed that these parameters do not affect acceleration (which is the same as transient response). But in fact, they do. If we compare DIFFERENT drivers, those having lower mms and higher BL will have higher acceleration at the same current, and faster transient response. That is, as common sense tells us, a sub with higher BL and lower mms will have tighter bass.

Error in experimental setup. Because pulse response is unfiltered, it is difficult to tell what this experiment is actually measuring. That extra mass is added directly to the former does not mean that the coil-former-additional mass entity is absolutely rigid. In fact, it is not. At certain high frequency mechanical breakup will occur that will effectively exclude the additional mass. In other words, at high frequencies the added mass will not affect transient response. And what frequencies we are talking about in the experiment described - nobody knows.

That driver's inductance affects transient response has been known for centuries. However, the inductance is important for a full range driver, but not as important for a sub.

 

RE: Of course we all know that low mass cones = "fast bass", posted on January 9, 2009 at 11:48:57
freddyi
Audiophile

Posts: 3852
Joined: December 6, 2001
 FWIW here's ~ ground plane of two woofers with 40Hz resonance, one a JBL M151 and the other A B&C with ~twice the mass of the JBL- I guess anything could be "blended" to get some semblance of "fast" including bandpass boxes but this heavy cone woofer sounds kinda lifeless in my piddling - -perhaps they work well in the hands of folks like Geddes

 

A flaw in your logic?, posted on January 9, 2009 at 13:53:52
Richard BassNut Greene
 YOU WROTE
"That driver's inductance affects transient response has been known for centuries. However, the inductance is important for a full range driver, but not as important for a sub."

MY QUESTION:
Why would low inductance suddenly become less important under 80Hz. (subwoofer driver) then it was over 80Hz.?
.
.
.
YOU WROTE:
" ... as common sense tells us, a sub with higher BL and lower mms will have tighter bass."

MY STATEMENT:
Tighter compared to what?

Your sentence about "tighter bass" ignores the effect of the enclosure design on the decay of a bass note, potential problems from integration of up to three drivers playing a bass note, and the much larger effect of room acoustics.

The driver's motor and cone mass are just some of many factors in obtaining "tighter bass" -- and far from the most important factor in an ordinary home listening room: Control of room bass resonances.
.
.
.
.

.
.
.
.

Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"

 

RE: Flaws in logic and experimental setup., posted on January 9, 2009 at 14:24:18
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 Hi
For the first order approximation, Richard and Dan W, are correct.

While an acoustically small woofer has piston motion and flat response, only it's efficiency and low corner are effected by say adding mass to the motor.

This discussion with Dan actually began on the "bass list" in the mid 90's.
For discussion, I glued a lead ring to the VC former on a driver i had already measured and then measured again with the doubled mass and posted about the results.
The hf and so speed of response was unchanged as was the shape of the response curve in the top half of its range.
The reason is the acoustically small woofer is already an acceleration based system, adding mass doesn't add a "corner" because the mass is already dominating where the response is flat. Adding more mass only pushes the existing corner downward.

The series L on the other hand is the dominant thing and by accident people have associated "slow" woofers with ones that have a lot of mass BUT the cause is strong motor with a lot of turns which produces a lot of series L, not the mass.

Now, to be sure, if you put the driver in a horn where a velocity response not acceleration is desired, then mass produces a low pass corner. That mass corner is primarily what limits the hf power response of all compression drivers (and then add a series L).
Hope that helps
Tom Danley
Danley Sound Labs



 

RE: Of course we all know that low mass cones = "fast bass", posted on January 9, 2009 at 20:26:05
mah


 
F=ma, thus

a=F/m

Using the same driver with heavier cone, F unchanged and m increased, the resulting acceleration is less.

Of course this is a very basic explanation and applies to the loudspeaker operating in its piston mode.

There is a detailed mathematical explanation of loudspeaker driver functions at http://en.wikibooks.org/wiki/Engineering_Acoustics
Section 1.5 looks at cone mass.

mah

 

Stored energy, posted on January 9, 2009 at 23:58:25
Timebasedistortion


 
In physics, resonance is the tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's resonance frequencies (or resonant frequencies). At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy. When damping is small, the resonance frequency is approximately equal to the natural frequency of the system, which is the frequency of free vibrations. Resonant phenomena occur with all types of vibrations or waves: there is mechanical resonance, acoustic resonance, electromagnetic resonance, and resonance of quantum wave functions. Resonant systems can be used to generate vibrations of a specific frequency, or pick out specific frequencies from a complex vibration containing many frequencies.

Resonance was discovered by Galileo Galilei with his investigations of pendulums beginning in 1602.

 

I can hardly wait for, posted on January 10, 2009 at 18:47:27
unclestu52
Dealer

Posts: 6982
Location: Hawaii
Joined: March 5, 2005
 Porsche and Ferrari to come with their 10 ton sports car models. Maybe they'll be competitive in formula one racing, too.


Stu

 

RE: A flaw in your logic?, posted on January 10, 2009 at 19:29:58
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 "Your sentence about "tighter bass" ignores the effect of the enclosure design on the decay of a bass note" "The enclosure design would have a minimal effect on the bass frequency response deviations measured at your seat, except that using a port or passive radiator design would extend the bass a little lower than a non-ported design." Well, Richard these quotes from your fingers........... one can't have it both ways......... no one has two left tongues. Is this pretzel logic, or are you now making an attempt to argue something you don't even believe, perhaps you have something to unsay? I care not what sort of bass makes your socks roll up and down but coherence in thought is appreciated..........never mind you ignoring my previous point of wave launch and sound propagation {how it ties in with corner horns using the walls as part of a speaker cabinet} coherence.......... the sound NOT bouncing again and again. Fast Fourier analysis may elucidate or relieve you of your earnestness for arguing. You say you are a meter reader...........fine. Learn what to measure. Or forget measurements and enjoy the music. Me? I'm more of a fly by the seat of the pants sort of engineer ........... I respect empirical knowledge. Lewis and Clark didn't say to the Indian guide ....... "Go over that hill, have a look and come back ....tell us what you see.......... then we will write it down.">smile< Relax, Rich........... it's a bad day when I don't learn something. You admitting you are wrong OR do not know ........would only show this guy you have some class.


"The Sound of One Hand Clapping is Crashing by Design" HKM

 

RE: I can hardly wait for, posted on January 11, 2009 at 06:23:51
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 Funny but you have missed the key point.

If Porsche were making a road roller, then they would make it heavy.
In other words, a proper design accounts for the intended use.

The fact is, if one makes a low mass driver with a strong motor and reaches a "constant velocity response", then as a direct radiator the response will be tipped upward.

While this will sound like a "fast" woofer, it is also NOT flat in its response, does not replicate the spectrum of the input signal.
It is the lack of the lower frequency components that makes it sound "fast" to ones ears.

For the acoustically small woofer, to have flat response, then it HAS to be an acceleration device, a device who's moving mass dominates it's motion.

I know in light of popular loudspeaker folk lore it seems impossible, but a direct radiating woofer is not like a sports car, it operates in the acceleration domain, not velocity(as one associates with a car).
Best,
Tom Danley


 

RE: Stored energy, posted on January 11, 2009 at 06:35:19
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 This is correct.
What might no be clear is "that" resonance is what defines the low corner of the response of a sealed box woofer.
It is the combination of moving mass and the box and suspension compliance which form the mass and spring in this example of two order resonance..
The damping the motor apply s then defines the Q of that resonance, if the Q is over about .6, then it does begin to "store" energy relative to the above band.

Best,
Tom

 

RE: A flaw in your logic?, posted on January 11, 2009 at 06:56:08
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 You do bring up a co-related point if talks about "what it sounds like", the enclosure type does effect what happens with "time".

From a physics point of view vs loudspeaker folk lore one can say several things.
A woofer's acoustic phase defines when the sound is produced relative to "zero degrees" on the input signal.
If one measures "time" one finds the sound above the low corner at the corner and the sound below it are produced at distinctly different times.

For example, with a vented box or passive radiator alignment, one finds the output in the region of the low corner is delayed by about 180 degrees in phase relative to well above Fb.
The vented (or passive radiator) box IS an inverter, it has a delay at Fb which approximates 1/2 wl at Fb.

The higher the enclosure order, the greater the difference in time (relative to the wavelength) will be comparing above resonance to "at" resonance to below resonance.

People often prefer the sealed alignment over the vented box saying it sounds tighter. It can do that for several reasons, one, it has a sloped non-flat response which is tricking your ears, alternately, one might also hear the larger time dispersion of the higher order system which "spreads" the energy out in time more.

Personal issues with Richard aside, this IS how the systems in question work physically.
Best,
Tom Danley





 

RE: The point..., posted on January 11, 2009 at 08:45:12
Dave-A
Audiophile

Posts: 14286
Joined: May 30, 2000
 at least from a listener POV, is that no single driver can accurately and adequately reproduce bass notes....both the dynamic lead edge and the big blooming afternote.

At least my experience indicates that and I am hardly alone.

The car analogy addresses the shortfall of typical high mass dynamic woofers. The bandwidth argument addresses the weakness of small low mass LF drivers. Intelligent placement and horn loading aside, the problem remains.

The question is at what freq does that lead edge dynamic become irrelevant enough to not matter? Without direct experience, one won't know the answer....and it all becomes academic.

Later
D

 

RE: The point..., posted on January 11, 2009 at 08:56:50
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 To this.......... I have Never heard any transducer replicate a trombone accurately.............Horns come close >smile<
"The Sound of One Hand Clapping is Crashing by Design" HKM

 

RE: The point..., posted on January 11, 2009 at 09:59:31
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 Hi Dave

Richard’s post was about “fast bass”, not the difficulty producing the entire bandwidth or producing it coherently in time.

I would partially disagree, one driver can produce all the bass notes, if your willing to wear a good set of headphones. The issue is the acoustic power one needs for “in room” speakers is orders of magnitude larger and hence much more difficult.

Also, if you read my post, “time” is another issue to consider one that is talked about but not addressed in hifi mostly, how much a speaker spreads the input signal out in time DOES have an impact on what it sounds like even if the magnitude is flat.
Here the vast majority of loudspeakers stink, they are dispersive in time.

You mention Horns, they can be less dispersive in time than direct radiators, the ones we make at work like the SH-50 are much less so than a normal multiway speaker, sufficient to preserve / reproduce the input wave shape like a square wave over a wide range.
Bass horns can also be much better than a direct radiator in that regard but in each case, just being a horn doesn’t make it so.
Best,
Tom Danley

 

And, don't forget..., posted on January 11, 2009 at 10:33:04
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 ...one driver can produce all the bass notes, if your willing to wear a good set of headphones.

or, employ a large enough yet virtually massless electrostatic driver. I measure flat 25 hz response (actually with a touch of rise) in my room with SL U-1s.

rw

 

RE: And, don't forget..., posted on January 11, 2009 at 10:40:16
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 Ah yes, good example.

 

They just won't do 100 db+ very easily :) -nt, posted on January 11, 2009 at 10:56:56
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 rw

 

RE: Stored energy, posted on January 11, 2009 at 14:02:28
Timebasedistortion


 
Fun tool to play with filters and envelopes.
Check the "sounds" library for some examples.

 

On the contrary,, posted on January 11, 2009 at 14:34:19
unclestu52
Dealer

Posts: 6982
Location: Hawaii
Joined: March 5, 2005
 a sports car by nature is constantly accelerating and decelerating, and a lighter overall mass makes them more responsive to changes in the relative velocity. Bonneville Salt Lake speedsters are, on the other hand, with their miles long acceleration strips before the timing traps are much more immune to mass differences. Definitely not so with formula race cars and such, even with their 6 or 7 speed transmissions.

Drivers are the same way: the audio signal being fed them are constantly changing in both amplitude and frequency. A lighter driver with the lower mass can adapt to these changes much more quickly. Most music I listen to does not consist of a pure sine wave monotone. Most cars on a road do not move at constant speed.

You are undoubtedly correct in stating that "faster" woofers have a higher frequency balance, however. In the creation of a "fast" woofer, the bass harmonics are generally much more easily heard. While many will relegate those harmonics to the midrange drivers, I find that many of the harmonic structures lie within the realm of the woofer. Take 30 Hz tone for example: the second harmonic is 60 Hz and the third harmonic is 120 Hz, both well within the range of many subs.

Slow woofers are often heard in automotive installations: those having those one note bass drone, with very little definition of the tonal qualities of bass instrument. True bass in real life with acoustic instruments never have that kind of quality and the bass of a real instrument has a surprising amount of harmonic structure inherent in their overtones.

It is true that even a heavy cone can be overcome by a larger and more powerful motor assembly, Electrostatics perhaps are the best example with their very high motor strength per mass area.

A road car, like a speaker, needs both an engine and brakes. Both need to be balanced in order to achieve ultimate performance to changing demands of a road or a complex music waveform. Lighter masses enable a driver to adapt to the changing amplitude and frequencies much faster in that there is simply less inertial mass to overcome.

Also in the study quoted, bear in mind that the researchers did not mention what input they used in the QSC amplifier. The phone jack input is phase inverted in relation to the terminal strip or the XLR (pin 2 hot convention). That may have a significant contribution to the maximum volumes achieved if using an impulse test. Also by the same token, a steady state sine wave versus a modulated signal can yield very different results.

I do base my observations on some experimentation I have done with single full range drivers. No instrumentation but simple listening determined the results: all one needs is to purchase a large quantity of raw drivers in which to swap out the modified units. I cut out dust caps and achieved significantly quicker speaker response to music. Drilling out the pole pieces helped even though the dust caps were still removed, eliminating the theory that pressure relief under the dust cap could have been a factor. Plugging the hole drilled indeed did nothing to the sound of that driver. Removal of the dust cap did not significantly affect the lower frequency response of the driver, it did clear up the harmonic structure, however.

I have also noted this in reconing JBL and Altec drivers. and in testing them before gluing on their dust caps. The bass harmonic structure is more extended, giving evidence of your statement that the tonality changes, however, I still hear the same bass fundamentals, simply the increase in the upper harmonic structure. In that part I would very much disagree with your statement that the bass is eliminated.

Stu

 

danger danger Will Robinson; long post, posted on January 11, 2009 at 17:38:38
tomservo
Manufacturer

Posts: 8192
Joined: July 4, 2002
 Hi

To explain why the car analogy is not such a good one, we need to dig deeper.
The radiator portion of the speaker in this case is a cone of some diameter.
AS the wavelength being produced is the speed of sound divided by the frequency, one can see the "acoustic size" of the radiator changes as a function of frequency and also for a woofer, the radiator is tiny compared to the wavelength.

We want to radiate sound into the air, that radiation is “work” a dissipation of power into a resistance (space). If one looks at the chart for a piston’s radiation resistance, one finds it is a curve.
Note the curve shown here for radiation resistance as a function of radiation size vs WL.

http://www.vxm.com/NXT.html

For a woofer that is acoustically small, it resides on the sloped part of the curve, this means that as the frequency climbs, it’s efficiency as a radiator increases as well.
This curve IS also the response one would measure IF one drive the radiator as a Velocity source, in other words in the domain one thinks about a car in, the domain we live in.
What it also shows is that once the radiator reaches a certain size, the radiation resistance stops changing. A full size horn raises the efficiency to a high value by coupling that high load from the flat portion of the resistance to the very small radiator which would normally be far down on the sloped portion of the curve.


As the radiation resistance decreases as the frequency falls, one must drive the radiator in a different domain if one wants flat response.
That domain is acceleration, where a constant Velocity system halves its excursion when the frequency doubles, acceleration based system decreases by a factor of four instead of two if the frequency is doubled.

For an acoustically small woofer with flat response, mass driven by the BL (Newtons of force per Amp) while driven through the Rdc provides a constant acceleration force against a fixed mass. This makes the response flat in the face of the changing radiation resistance.

In the case of a horn, the radiation, seeing a constant load or resistance needs to have a Velocity profile and here the mass DOES cause a ‘low pass” filter effect, exactly as imagined or with the car analogy.

You mention of car subwoofers is directly relevant here too.
I explained how the mass actually makes the small direct radiators response flat and does not have any impact on the high frequency or speed of response.

Electrically, the moving mass reflected through the Voice coil is acting like a capacitor driven through the electrical resistance. This makes an RC low pass filter so far as Voltage. In an electrodynamic motor, it’s velocity is exactly proportional to the back emf Voltage. Back EMF is the voltage a motor produces when in motion (when driven is a generator), it is a voltage exactly proportional to the Velocity and force sensitivity (BL) of the motor.
Thus, the falling Velocity / Voltage across the moving element ( the C ) also reflects the acceleration response discussed earlier.

The low frequency corner of this system is defined by a spring force, which is in parallel with the mass, this spring is the total compliance. That is made of the driver and box spring forces in parallel and electrically this spring looks like an inductor in parallel with the mass capacitor.
If one wants a small box and a large cone, one sees a very stiff spring.
Mr. Timebasedistortion posted a good link to this resonance.
http://www.audioasylum.com/forums/hug/messages/13/139713.html

Anyway, if one also wants a low resonance, the ONLY way is by having a “enough” moving mass to give that pitted against the strong spring force.
So far so good, nothing that effects the speed of response or hf response…..yet.

The large mass also requires a very strong motor, one that produces a lot of force per amp (BL). This BL can also bee seen as meters of wire in the gap times the gap flux intensity.
A large motor strength, requires a long length of wire, wire wound into a coil.
Even a straight wire has series inductance, looks like the resistance with a tiny L in series. As soon as you wind it into a coil, the inductance along its length couples back into itself, “mutual inductance” and now instead of X micro henrys per foot, the inductance goes up proportional coil size and to the turns squared. Lots of turns means lots of mutual inductance AND a much larger series L.
(I have glossed over par to of this, the more complicated explanation which involves the coil resistance with L setting the low corner and where the R fits in motor strength and BL)

Now, the series L is a low pass filter in either acceleration or velocity, it rolls off the force delivered as the frequency increases by decreasing the current delivered to the coil.
Most car woofers have about the largest coil one can use, large enough so that the series L’s low pass filter effect is limiting how high the driver can go, rolling off as low as 80Hz or so all by itself.

So would this woofer sound slow?
Remember part of what can make the woofer sound slow is if the response is peaked anywhere. If the low or high corner has a Q or shape greater than say .6 or so, it will have increasing “storage” or ring.
So lets say the low corner is well behaved then what?

Well it could, it sure would if one compared it to another woofer that went up much higher.
On the other hand, if you took that driver that went much higher and drove it with a filter that made it have the same response as the other one, it probably wouldn’t sound much different at all.
I guess what I mean is what ever the low pass corner is, it may or may not be an issue at all, depending what you needed the driver to do (what range).

Now if you are concerned about “time” it is acoustic phase you need to consider.
If you created an impulse that is a broadband signal and fed it to a speaker, one finds that while the input was an instantaneous burst, the different frequency components come out at different times.
This is the area I have been fascinated with and correcting this issue can be quite audible.
The comments about the SH-50 above would give you some idea what making this issue better (and some others) sounds like.

Basically the time spreading issue, combining at crossover and directivity are where many “hifi” speakers usually fail very dismally regardless of looks, cost and exotica.
I have to laugh sometimes, the stuff looks great but don’t they know how sound works, did they measure anything here to see what it does or where the sound goes??.

Anyway, this ended up being kind of long, I hope it makes sense.
Best,
Tom Danley


 

RE: And, don't forget..., posted on January 12, 2009 at 05:10:05
theaudiohobby
Audiophile

Posts: 4674
Joined: January 16, 2003
 "employ a large enough yet virtually massless electrostatic driver"

Actually its virtually massless electrostatic driver membrane, Big difference.

Music making the painting, recording it the photograph

 

Yes, my comments are in context with the discussion, posted on January 12, 2009 at 08:42:29
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 We're all referring to the understood concept of moving mass, aren't we? I am no more considering the mass of an electrostat's stators or frame than anyone else would a cone's magnet structure or basket.

rw

 

Tell me what drugs you are taking so I can take them and hopefully understand your post, posted on January 12, 2009 at 09:14:24
Richard BassNut Greene
 The enclosure type has a minimal effect on bass frequency response under 80Hz. measured at one listening seat, other than the bass frequency response extension from using a port or passive radiator.

Any enclosure design can suffer from poor engineering, resulting in audible problems.

Assuming no design errors, subwoofer enclosure sound quality differences are not likely to be audible without good control of room bass resonances.

After room bass resonances ARE controlled, a listener MIGHT be able to hear sound quality differences among subwoofers.

Because subwoofers are only used for a limited one or two-octave range, the sound quality differences at normal volumes are MUCH easier to hear with test tones, such as sinewave tones and bass tone bursts, and may not be audible at all with ordinary music.

Your continued defense of corner horns, with which I have a lot of experience, is like repeatedly shooting yourself in the foot.

Any speaker placed in a room corner of a typical rectangular room in a home, will fully excite all room modes, which will cause the largest possible deviations from a flat bass frequency response.

You want the roughest possible bass frequency response in a rectangular room = place your speaker in a corner and sit in the opposite corner!

And please use English in future posts: If you are knowledgable about a subject, which seems unlikely based on your verbal ramplings, then you should be able to write about that subject using simple easy-to-understand sentences.
.
.
.
.

Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"

 

RE: Tell me what drugs you are taking so I can take them and hopefully understand your post, posted on January 12, 2009 at 12:51:03
Timebasedistortion


 
Ehh, what kind of drugs are you using???
They seem to be very strong...

 

RE: The point..., posted on January 12, 2009 at 15:25:43
Retsel
Audiophile

Posts: 1238
Joined: April 17, 2000
 Exactly!!!

I discovered this by trying out a set of Lowther drivers with a treatment called Enabl and comparing them to a set of Lowther drivers without such treatment. The Enabl-treated drivers have a series of dashes along the outer boundaries of the drivers' cones, and a coating over the entire driver. Based on the theory that all added mass is bad, one would think that the added mass would hurt the drivers' ability to reproduce music. The coating on the drivers did the exact opposite by making the drivers more dynamic, transparent and more focused by improving the "time response" of the driver (more of the sound left the driver at the same time which led to these improvements).

Retsel

 

Um, er , touche' NT, posted on January 12, 2009 at 21:02:20
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 nt
"The Sound of One Hand Clapping is Crashing by Design" HKM

 

RE: thanks, however your response raises an interesting point, posted on January 13, 2009 at 03:01:55
theaudiohobby
Audiophile

Posts: 4674
Joined: January 16, 2003
 Thanks for the clarification, your comments raised a interesting issue, is an electrostatic diaphragm really "virtually massless" in comparison to modern tweeter dome materials? Its less dense however the differences in mass are probably trivial as an electrostatic membrance covers a much wider area.

Music making the painting, recording it the photograph

 

You make the call, posted on January 13, 2009 at 06:31:21
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 In absolute terms, the total mass of the 2.5 micron Sound Lab diaphragms (for full range operation) is a fraction of the air it moves. It is that fact on which I base my assessment. These diaphragms are also quite a bit thinner than other popular full range electrostats such as the Quad 57 at 12 microns and Acoustats at 17 microns.

...in comparison to modern tweeter dome materials?

Have you ever taken a dynamic speaker apart? Remember that all dome tweeters are moving coil designs having not one, but three components: the dome, the spider and the coil. The primary moving mass component is not the dome that you see - rather it is the hidden coil of wire that drives it. Which is many times more massive than ultra thin "sandwich wrap" alone.

As an aside, this is a similar discussion to differences among phono cartridge types. It is here where the moving coils reign. The coil of (~ 20 micron) wire "motor" is likewise less massive than the more common moving magnet designs. Imagine if there were moving magnet speakers. Talk about sluggish bass!

rw

 

RE: MCs having less moving mass, posted on January 13, 2009 at 07:49:04
ckowal
Audiophile

Posts: 410
Location: Montreal
Joined: October 27, 2002
 I never understood the claims that MC phono cartridges have less moving mass than MM. If you take the time to actually look at them, it's clear that the tiny magnets on MMs are much lighter than the coil windings on MCs. I'm sure this is the reason why MMs typically track better and with less tracking force than MCs. The better sound of MCs must be for another reason than the questionable claim that they have less moving mass. This seems to be some sort of widespread misinformation.

 

You may find individual cases, posted on January 13, 2009 at 08:19:05
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 where that is so, but I stand behind my statement. Old MC designs like the Denon 103 family (had one myself years ago) may support that notion, but newer ones, however, use far lighter wire. It is the number of turns that determines output, not mass.

Typically, MC designs also offer much higher frequency response as a result. YMMV.

rw

 

RE: You make the call, posted on January 13, 2009 at 09:50:06
Tom Brennan
Audiophile

Posts: 5853
Joined: January 2, 2000
 John Eargle claimed that the boundry layer of air must be added to the mass of the ES diaphragm and that ESs aren't really as massless as many assume. Also note that ESs have weak motors and power to weight may be poorer than dynamic drivers. A Ford Focus has lower mass than a Mustang GT but the GT accelerates better, brakes better too.

Maybe my talk about power to weight and Estats talk about mass really have little to do with things anyway; I'm used to think I knew how speakers worked but now I realize I know jack-shit and I no longer worry about it.

What I am sure of is the best speakers I've heard were either horns or ESs.

 

RE: You make the call, posted on January 13, 2009 at 09:58:57
theaudiohobby
Audiophile

Posts: 4674
Joined: January 16, 2003
 "In absolute terms, the total mass of the 2.5 micron Sound Lab diaphragms (for full range operation) is a fraction of the air it moves"

Therein lies the rub isn't it? The acoustic load seen an electrostatic diaphragm is an order of magnitude larger than that of a 'dynamic' tweeter.

Music making the painting, recording it the photograph

 

Every speaker moves air!, posted on January 13, 2009 at 10:22:13
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 That's how they work. I doubt anyone would dispute what that JBL engineer said. As for me, I find that a relatively small pocket of surrounding air has far less mass than a stiff paper spider and a spool of copper wire! I'll go out on a limb here and suggest that I truly believe that I could more readily detect the presence of any spider/cone assembly placed in my hand than the weight of the all the air around it. Try it yourself!

Also note that ESs have weak motors...

That is most certainly true and accounts for their relative inefficiency. Unlike dynamic speakers having voice coils and radiating cones, however, ALL of the radiating area is uniformly driven. Concerns over cone stiffness to ensure the majority of the area (which is not driven) doesn't flap about too much independently is a non-issue.

Maybe my talk about power to weight and Estats talk about mass really have little to do with things anyway...

They address different aspects of speaker performance. I find the bass timbre of planars is more lifelike than any other kind of speaker. This I attribute to their lower mass and single driver coverage of a wider frequency range. What I really value most about my speakers is their inherent coherency - which is something that as I mentioned elsewhere seems to be a unique advantage of the Danley designs. Consequently, I would really like to hear the SH-50s sometime.

rw

 

And still..., posted on January 13, 2009 at 10:25:00
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 The acoustic load seen an electrostatic diaphragm is an order of magnitude larger than that of a 'dynamic' tweeter.

the effective mass remains far less. That's why various engineers continue to wrestle with the tweeter moving mass issue using exotic materials like beryllium and diamonds.

rw

 

RE: You may find individual cases, posted on January 13, 2009 at 11:04:21
ckowal
Audiophile

Posts: 410
Location: Montreal
Joined: October 27, 2002
 Look at the magnets on a MM stylus. They are tiny specks. They are typically smaller than the cores that MCs wrap the coils around, never mind the coils themselves. There are MMs that track extremely well at under 1g tracking force, no MC I've ever seen can do this.

There may be some MCs that track better than some MMs, but the best tracking MMs are clearly better trackers than the best tracking MCs.

The better frequency response and sound of MCs must be due to another factor than moving mass. It probably has something to do with the electro mechanical damping (or loading) used on MMs, but I'm not an expert.

 

RE: Every speaker moves air!, posted on January 13, 2009 at 11:36:10
theaudiohobby
Audiophile

Posts: 4674
Joined: January 16, 2003
 "ALL of the radiating area is uniformly driven...This I attribute to their lower mass and single driver coverage of a wider frequency range. What I really value most about my speakers is their inherent coherency - "

How a membrane where respective sections are driven to different resonant frequencies with different response curves to achieve full-range can be deemed as inherently coherent or term uniformly driven is somewhat bemusing. IMO full-range soundlabs are sophisticated multiway speakers.

oh well..

Music making the painting, recording it the photograph

 

Easy, posted on January 13, 2009 at 12:49:23
E-Stat
Audiophile

Posts: 37584
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 One electrical signal driven by
One electrostatic motor radiated by
One diaphragm.

Do you get the recurring theme here? I won't belabor these facts with you any further.

rw

 

RE: The facts never changed, posted on January 14, 2009 at 01:41:53
theaudiohobby
Audiophile

Posts: 4674
Joined: January 16, 2003
 Do you get the recurring theme here?

Got it from day 1, you however do not get mine, its a multifaceted diaphragm with each facet exhibiting different response curve i.e. multiway. You are hung up on a single diaphragm theme as if that is what defines a multiway device.

I won't belabor these facts with you any further.

Why belabor them, the soundlab is/was always a multiway speaker.

Music making the painting, recording it the photograph

 

RE: And still..., posted on January 14, 2009 at 16:28:24
theaudiohobby
Audiophile

Posts: 4674
Joined: January 16, 2003
 You've got your knickers in a twist here...

the effective mass remains far less

No...

That's why various engineers continue to wrestle with the tweeter moving mass issue using exotic materials like beryllium and diamonds.

err....those exotics materials share another common feature i.e. they are very stiff, the goal is increasing rigidity whilst also reducing the effective mass.

Music making the painting, recording it the photograph

 

RE: danger danger Will Robinson; long post, posted on January 16, 2009 at 00:11:24
Steve Schell
Manufacturer

Posts: 1440
Location: So. California
Joined: December 16, 2001
 Tom... thank you! We are lucky to have you here.

 

Page processed in 0.087 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]