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In Reply to: RE: 105db/meter NON horn loaded speakers posted by used-hifi on April 21, 2017 at 18:37:54
Multiple drivers for each pass band. It's not a particularly difficult task, you'll just end up with a very large box.
Follow Ups:
-unless you are going by sensitivity spec only.
That spec does not tell the full story. Efficiency (1 watt/1 meter) tells more.
In the case of paralleling multiple drivers, the total system efficiency remains exactly the same. This is because the one watt gets distributed over the multiple drivers. So if there are 8 drivers, each gets 1/8th watt.
In a nutshell, by using multiple drivers you can increase the sensitivity (if they are in parallel; if in series the sensitivity goes down with each added driver) but the actual efficiency is the same as if you had one driver only.
Radiating efficiency does go up as the number of drivers is increased. However, the upper -3dB frequency goes down by a factor of 0.7 with each doubling of drivers, so the law of diminishing returns is in effect, and eventually you reach a maximum system efficiency of some 25% with direct radiators. This was long ago quantified by Don Keele in his AES preprint on the efficiency of moving coil drivers. Were this not the case with sufficient drivers you could exceed 100% efficiency, and then you wouldn't need a cold fusion reactor to provide the power for the system.
"then you wouldn't need a cold fusion reactor to provide the power for the system. "
Hahahahahahaha! THAT was funny!
:)
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Lobing isn't an issue with a vertical line array.
"There are cases such as line arrays where lobing is actually a desirable effect by placing many identical drivers in a column which deliberately provokes lobing. This is done to convert a spherical waveform of a single driver into a cylindrical one, with a narrow, vertical direction. The main reason people started building such line arrays was to be able to intelligibly transmit human speech in highly reverberant spaces like churches by avoiding sound being projected onto ceilings and floors.
This only works in a narrow frequency band and line arrays tend to be highly collared when listened to off axis."
"Line arrays have uneven sound quality and response in the middle and high frequencies, despite what their manufacturers would want you to hear. That's because they usually have discontinuities at the edges of each driver unit, and because they don't go from floor to ceiling. All this results in interferences that cloud up the sound quality. It's simple to hear: just play some pink noise on the speaker, and listen up and down from the middle of the line array. You will notice a swishing in the sound, proving that the spectrum changes. Problem is that depending on which row you sit in a tiered theaters, you will get a different experience, none if which is probably right in the first place."
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Lobing resolves into a coherent wave front with distance, so it's not an issue other than at close listening distances. This shows how it occurs:
[url]http://www.acoustics.salford.ac.uk/feschools/waves/diffract4.htm[/url]
The other issues you quoted also occur close in to the array, not at appropriate listening distances. My assumption is that your quoted source is a manufacturer that does not make line arrays.
Edits: 04/22/17
"Note however that once we get to a reasonable distance from the grating, towards the right of the simulation window, the waves from each slit have added back up into a large plane wave by Huygen's principle. "
What constitutes (and how do you calculate it) a "reasonable distance"?
Don't we all listen at "close distances" in our living rooms?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
> What constitutes (and how do you calculate it) a "reasonable distance"?
That depends on the frequency and the driver spacing. If it was a major issue Don Keele's CBT array wouldn't work. It does, but to function at typical living room distances there's an awful lot of very small drivers for the requisite CTC distance.
Yes, Huygens rule does show a final summation however, each source radiates independently and in the array each radiates with its own dispersion angle just as it would operating alone.
Also, the longer or more curved you make a line, the more energy is radiated to the sides.
No one here is going to buy any of our stuff at work so i will link a paper that deals with multiple sources etc with systems on a larger scale than a living room. Some of it uses a modeling program called Direct which is free and has some theoretically perfect examples one can play with as shown here.
Tom,
I know that article is about 5 years old, but it says a lot for the line array vs. point source argument. I actually recommend that someone at your shop revisit that article for grammar/spelling and reducing a little wordiness, condensing it down a bit further--but keeping the excellent figures and their textual explanations. I think that might induce more people to read it. I found it most convincing, but I had to keep myself reading it to get to the end.
I know many others have mentioned the line array problem and how bad they actually sound in real life. A bunch of guys that I know have been looking for the reasons "why not line arrays" and "why point sources" to help focus on point source horn designs. That article has the meat for the big venue commercial sound crowd.
What's less known is why the point source design works so well in small rooms. I'm not sure that I've seen you clearly enumerate why point source loudspeakers designed for the large venues also do so well in small rooms. That would be an interesting discussion. There's a story there. Perhaps I'll break tradition and start a thread on that subject.
JMTC.
Chris
"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."; Jack Dinsdale, May 1974
Hi
I believe there are a number of things which enter into this. Instead of the most obvious things, the most "un-obvious" thing is that our hearing system is VERY different in several ways than a measurement system and here is one thing invisible to a single microphone but clearly audible to the ear.
For example it is possible to have two sets of loudspeakers, eq' to have the same magnitude and phase and if you listen to one, they both sound VERY similar yet when you have pairs, they produce very different results with stereo images. In one case with such recording that has a strong mono phantom (same signal to both speakers) you get a strong phantom image and are unaware of a right and left speaker while the other case, you still hear a phantom image but you can also clearly hear the right and left speakers.
In this case, you are hearing elements of "how" the loudspeaker radiates and when there is sufficient difference between what reaches the right and left ear when facing the 1 speaker, your hearing system can localize it's position. Lacking those contradicting spatial cues, the hearing system instead hears a source coming from directly in front of you in stereo or with just one, it is hard to tell how far away the speaker is when your eyes are closed, your ears choose the depth sound in the recording instead of the speakers location. This is the area I am fascinated with, so is co-worker Doug Jones and I have tried to apply what I see to our large scale loudspeakers at work.
If you have headphones handy, try the link below for a speaker I was testing on Friday which "acts like" a single driver simple source (taken at 100 meters).
https://www.dropbox.com/s/0tjs1mvmy451xcw/20170428113326.mts?dl=0
Secondly, reflections from close by the speakers also impart a spatial signature on everything the speaker produces and these also conflict with the signal you want, giving you cues that weaken or conflict with the image in the recording. Often putting absorption on the side walls where the strongest reflections would be from has a marked improvement in image. One can easily hear how much or if the room has a strong effect by setting the stereo up outside at approximately the same geometry as indoors and spend some time listening, normally the stereo image is vastly better outdoors although typically the bass is less. Fwiw, this is a great excuse to have a BBQ or picnic get together.
The point is, if you have speakers large enough to have significant and consistent forward directivity, then much less energy is going to hit the side walls and the near field where the direct sound is louder than the reflected sound is larger (good juju). This factor is critical in larger scale sound where the cubic volume works against absorptive surface area and the Hopkins Stryker equation shows intelligibility goes down with increasing number of sources and up with increasing source directivity. This is why essentially all of our products at work are large horns to maximize directivity to specific angles.
The cool part of constant directivity, one can move off axis and the spectral balance doesn't change just the spl.
It has been possible to use this combination of aim angle and height in stadiums where speakers are in the scoreboard and have only a + - 2dB variation in loudness over the entire stadium and as the consultant said "it sounds the same everywhere".
The reason high output systems can work very well in the home is because nearly all of the things loudspeakers do wrong or add to the signal increase faster with level than the input signal's portion does. Loudspeakers are more like tube amplifiers than SS, here the distortion and non linearity are nearly all related to level. It has long been said "headroom is your friend" and it's especially true if/when dynamics are a concern. The success also depends on if it sounds good to begin with etc..
Hope that make sense
Tom
if its as easy as you say why has there not any built?
can you be more specific more on the design exact drivers etc...
Line arrays with that kind of sensitivity have been built since the 1940s, when they were referred to as column speakers.
Kidding, but that's the most recent "big name" line array I remember & have heard.
That's what I remember about those-the gentleman promoting it kept saying that over and over. Actually more like THUNderous bass.
Only a little horn:
Sorry it's 10db short of the 105db mark
You know, used-hifi, Bill Fitzmaurice gave you the correct and quite practical to implement answer to your question right off. You might have said thank you instead of continuing to act as though you had asked the unanswerable question.
Sorry don to not live up to your expecstions and no he didn't answer my question!
like already said Multiple drivers for each pass band.
If one driver has 87dB/2.83 volt sensitivity two will have 93dB, four will have 99dB sensitivity, eight will have 105dB sensitivity, so it's as simple as that...if your amp will drive a 1 ohm load. Assuming it won't then you have to use a combination of series and parallel wiring to keep the impedance within a useful range, and that means even more drivers.
OTOH with a large enough horn you can reach 30Hz with 105dB sensitivity with one driver.
I've always been confused by that.
2.83 volts across 8 ohms is one watt.
2.83 volts across 4 ohms is two watts.
2.83 volts across 2 ohms is four watts.
If you have a speaker that will give 87db from one watt and you add another in parallel you get 90db from one watt. Add three (for a total of 4) and you get 93db from one watt, not 99db.
What am I mis-understanding?
I am going to guess that it's because I think in terms of tube amplifiers.
I think of using the 8 ohms tap for one speaker and the 4 ohms tap for two speakers and the 2 ohm tap for four speakers so the amplifier does not output twice the power just because the load impedance has decreased every time the load impedance is halved. In fact it stays the same because the load seen by the output devices stays the same.
Now that leads me to the idea of series/parallel.
The power output of a transistor amplifier only doubles when the load impedance halves so if the speakers are wired series/parallel, to keep the load impedance at 8 ohms, then four speakers vs. one would be 93db vs. 87db even for a SS amp. You would only get to 99db if all four were in parallel.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I am like Tre' in being a bit (a great big bit?) confused on this subject. I accepted the idea that doubling the number of drivers increases efficiency by 6 dB decades ago When Dr. Joe d'Appolito was writing for Speaker Builder. He always stated that doubling the number of drivers increased efficiency by 6dB. I assume he knew what he was talking about. Am I confusing efficiency and sensitivity.If Bill Fitzmaurice or someone else who has a good understanding of this subject could offer a more comprehensive explanation it would be very much appreciated.
Edits: 04/24/17
Hi Don
When two equal sources are about ¼ wavelength apart or less, they "feel" each other's radiation pressure (aka mutual coupling) and add coherently into one new source. In that process, you have doubled power handling (having two drivers now) AND increased radiation efficiency because with coherent addition comes an effectively larger radiator.
BUT when two sources are more than ¼ wl apart, they begin to radiate independently and by ½ wl separation they are independent sources and now when you go from one to two, you go up 3 dB because you no longer have mutual coupling that had raised the efficiency previously.
That increase in sensitivity has a practical upper limit at around 25% efficiency which would be about 106dB 1w1m. O
ne can see a difference between independent radiation and coherent coupling by inverting one of the drivers in each temporarily.
In the close coupled case where they add to become one source, the two sources nearly completely cancel each other out, with more than ¼ wl spacing, only the radiation pattern changes when you invert one because they are two independent sources, not one.
Doubling the driver count parallel wired increases voltage sensitivity by 6dB, not efficiency. It doubles efficiency, which is 3dB of the sensitivity increase. It halves the impedance, giving the other 3dB voltage sensitivity increase. If you double the driver count series wired the double radiation efficiency still gives you an additional 3dB of sensitivity, but the doubled impedance takes that 3dB away, for a net unity gain. But you don't keep getting a doubling of efficiency with every doubling of drivers. 25% efficiency is about it with direct radiators, usually reached with between 16 and 32 drivers.
Here is how I look at it.Doubling the number of drivers (in and of itself) increases the driver sensitivity by 3db.
Now take into account that when the drivers are wired in parallel then the impedance is halved.
With a transistor amplifier (at least in theory) the output power will double when the load impedance is halved.
So with twice an many drivers (wired in parallel) the total increase in system sensitivity is 6db.
To say all of that a different way,
When you double the number of drivers (from one to two) it increases the sensitivity by 6db (twice the power gives 3db and twice the cone area gives another 3db).
BUT if you only provide one watt the net increase is only 3db because each driver is only getting 1/2 watt (twice the cone area gives 3db but we're not providing twice the power so 3db is the net increase).
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/24/17 04/24/17
Answers on line array sensitivity can be found in my Near Field Line Array white paper.
SPL calculations are on page 17-18.
Jim
"For example, two speakers connected in
parallel and mounted within a wavelength center-to-center spacing would yield up to a 6dB increase in SPL. 3dB from the increase in acoustical energy and 3 dB from the reduction in impedance."That's what I said and what Bill said.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/25/17
Well with two sources a half wl apart, you get +6dB over one on axis only.
Think about a polar plot, the diameter is level vs angle and the area within the polar circle summed is the total acoustic power.
Two sources that far apart produce a figure 8 pattern who's peak value is +6dB on axis but the area enclosed by the polar circle is only 3 dB more than each source individually.
Move those sources to less than 1/4 wl apart and now you have a circle who's diameter is +6dB and the total energy is now 6dB greater than one was.
acoustic power
1+1=2
or
1+1=4
depends on the spacing and location
nt
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