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I must confess technical ignorance on this issue thus the need to inquire here. There is a demonstration of the KEF Blades on YouTube. The woofer cones are visibly pulsating. I have never seen any woofer cone movement on any loudspeaker I have owned including ADS L810's, ADS L1590's, PMC's, Avalon Eidolons or my current Gallo Ref 3.5's.
I have observed similar movement on Audio Physic Calderas' 8 inch woofers in 1998 in an audio shop. I do not remember hearing any distortion artifacts as a result of this movement. However, observing these obvious excursions was disconcerting enough to pass on a purchase.
It appears to me that such an effect is a result of a driver reaching its design limits versus a driver with no visible movement but I may stand corrected here.
Follow Ups:
I couldn't see the woofer cones actually moving, but the most eye-popping bass demo I ever saw was at a Tower of Power concert a few yeas back at the Minnesota Zoo's outdoor amphitheater.
They had a couple of big JBL bass bins laying on the ground horizontally on either side of the stage, and one of the security crew was sitting on one of them, facing the crowd to keep an eye on things. His legs were dangling in front of the horn's mouth, at least I believe it was a horn but couldn't tell because the grill cloth was hiding whatever was in there.
Anyhow I was about 25 feet away from this guy and even from that distance I could see his blue jeans flutter in time with the kick drum, and there was no wind that night so this wasn't being caused by any act of nature. That was some SERIOUS bass!
My personal feeling on this is that, except in rare circumstances, most midbass drivers do not need to heave all that much unless tuned exceptionally low or equalized to go below their natural range. In the good old days, with 12" woofs in three ways, you would often see more excursion, especially with vinyl due to subsonic noise. The need for high excursion 5" and 6" drivers is beyond me, except perhaps in some near-field monitoring situation where a sub would be wrong for some very compelling reason(s).
For me, I would not want a 2-way with a 6" or 7" woofer chuffing away trying to reproduce sub bass. I don't want the driver reproducing my midbass and the better half of my mids flopping around like a fish on bath salts.
My favorite designs (these days) are ported or sealed midbass drivers that pass off the workload to a sub between 55 and 65Hz.
They just sound so much better to me, and subs crossed in that low (at 24db/octave) are easy to implement.
CHeers,
Presto
Hi, Presto:
One need not even revert to "the good old days" to see the phenomenon. All turntables produce some rumble. Better ones produce less. Depending on the spectrum and amplitude of the rumble, visibility will be more or less pronounced. Aside from possible harm to a woofer, reduction in effective amplifier power can occur given the power wasted to drive a woofer at frequencies below audibility (varies according to woofer design).
Some pre-amps used to include a switchable "rumble filter" to help avoid the issue. The filter on my pre-amp is -3db at 17 Hz, dropping below at 12 db/octave.
Jeremy
Oh yeah, that's true. Some music is also bad for subsonics - some electronic, dance and hip hop music that uses samples of analog recordings, or effects that change frequency can often result in extreme excursion. In fact, the car guys have special "test CD's" that are specially made *just* to provide over the top excursion.
But you're right - there are many sources of subsonics and not just mediocre turn table setups!
I even had "foot prints" on one recording where someone walked across a stage floor or platform and it was picked up - you could see the woofs going "thud thud thud". At first I thought there was someone upstairs and ran up. I played it again, and sure enough, that guy was back upstairs again. Then I realized it was on the recording.
Back when CD's first came out, some CD players also created substantial subsonics, but this was a very short-lived effect.
Neat stuff.
Subsonic filters are a good idea...
Cheers,
Presto
Yeah. There are even LPs notorious for recorded-on rumble from subways below the auditoria. I don't think I own one of those, but I do have a store-bought casette tape with very low frequency noise recorded (or at least imprinted on the tape) in addition to the music. I have no idea of its source.
Best,
Jeremy
.., were those of some small B & W DM601 speakers being played quite loudly. It's possible that those yellow kevlar drivers had me partially hypnotized, but I do remember being astounded...
Edits: 04/21/15 04/21/15
Here I am wondering how to make my yellow Kevlar drivers to move properly. I have the 685.
Cheers
Bill
My B&W PM-1 woofers flopped around quite noticeably when playing vinyl.
Right John.....I had B&W 802's (I think..some time ago) with woofers that slowly pushed, out, then sucked in. At the time I was near an airport, and an electrician told me that it was my system's reaction to radar....When I got rid of the B&W's the woofer excursions stopped from my new speakers.
It is genuinely surprising that you haven't seen this before.
Maybe you don't listen to music with a bass drum?
Or perhaps you're not used to seeing driver movement because you're looking at the drivers head-on rather than from the side as is the case with the Blades?
In any case, it's totally normal.
It is possible I never saw this effect because I did not observe a driver at 90 degrees. The Audio Physic Caldera I gave as an example had side firing woofers. However, my Gallo Ref 3.5's have side firing 10" woofers and I do not see any pronounced cone movement. I do have program material with a variety of low frequencies including classical, jazz, film soundtracks and some test discs.
I introduced this topic hoping to explore it due to my technical ignorance. I wish to thank everyone who contributed to this topic with their observations, insights, experience and technical knowledge. Your time and attention is very much appreciated.
Something you may want to read about is distortion levels and waterfall graphs of drivers. You would be surprised to what level you would have to push some drivers to start distorting.I have no idea about this particular cones. But you usually do see more "action" with a more rigid or light reflective type material.
But yes cones move. even your silk dome tweeters shimmy and shack.
Edits: 04/21/15
You will notice a difference between the excursion of a sealed and a ported woofer at very low frequencies. A port adds to the output of the woofer at it's tuning frequency, but below that it begins to subtract from the output and acts more like an open baffle (mixing the woofer's front and rear wave in the room = cancellation). The woofers will then be restricted only by the stiffness of their suspensions so they will move more than sealed woofers which must push against a limited volume of air.It's probably worth doing some reading on sealed vs ported enclosures if you want to better understand what you're seeing. But in a nutshell:
Sealed: Speaker LF output falls off gently starting at a higher frequency. LF excursion is limited by the spring created by the enclosure space.
Ported: With the assistance of the port output, the speaker LF output remains flat to a lower frequency than sealed. Below that, the speaker output drops off more quickly than sealed. LF excursion is only limited by the enclosure above the region of the port resonance.
Edits: 04/21/15 04/21/15 04/21/15
is a measurement of the maximum (safe) movement of a speaker cone. It varies from speaker to speaker. The environment plays the biggest role ie sealed box v ported for instance. The back pressure of a sealed box allows for much greater cone movement for instance than a ported box.
Man my old Ezekiel metal cone sealed box woofers really moved a lot.
E
T
But below resonance there is nothing to control a driver in a ported box and low frequency garbage can overdrive a woofer in a ported box badly. That's not true in a sealed box.
Xmax tells you when the coil is leaving the magnetic gap and the waveform will be increasingly compressed beyond this point (distortion). Xlim is when you hit the physical limits of cone travel.
Edits: 04/20/15 04/20/15
I had always thought there was an linear xmax and a mechanical xmax where linear was the limit before performance suffers and mechanical is limit before bad things happen.
E
T
I've just finished building a little speaker using a driver that has an Xmax of +-5mm and an Xdamage of +-9.25mm according to its spec sheet.
From all the spec sheets I've seen Xmax is always maximum linear excursion usually in +- mm while Xlim, Xmech or Xdam all mean the same thing: Max excursion before permanent damage to the driver. It is frequently but not always listed as a peak-to-peak measurement to make it look better.
Both are not always specified and different speaker manufacturers have specified it differently but the common Xmax spec is usually linear excursion and Xlim or Xmech is the mechanical limit (occasionally XmaxL and XmaxM).
Give us a time into the video please.
"There is a demonstration of the KEF Blades on YouTube. The woofer cones are visibly pulsating."
While skipping through the video, I didn't see any close-ups of the woofer motion. Would you please point to a mm:ss point where the video shows what you're talking about? Thanks.
Also, "House13". Are you at all involved with the "GeekHouse" featured in the video?
:)
Please expand the video to fill your display. Look carefully during the following time window: 7:20 through 7:28 and 9:00 through 9:15 minutes in.
The black woofers against the same color enclosure makes for very poor contrast. However, if you concentrate exclusively on the woofers and ignore the visual distractions in the room you will see definite pronounced diaphragm movement.
I have no affiliation with the "Geek House."
...
The damping factor on the amps being used in the Video is 1200.
?
Normally, speakers move too fast for us to see, and so they appear to stay fairly stationary and instead become blurry on large excursions.
Cameras sample the view and will produce effects like wheels appearing to turn backwards. Another thing they do is alter the way speakers look when moving since they will occasionally catch the cone at its maximum point and display it there for 1/30th of a second or so.
I do not have the technical knowledge to disagree with your statement. I was not present during the video and have not seen or heard KEF Blades in person. However, I was present multiple times when the Audio Physic Calderas were playing. I observed significant cone movement in those $18K (1998) loudspeakers.
Let's slay one dragon at a time.
Where in the KEF video do you see the woofers doing what you describe?
> Where in the KEF video do you see the woofers doing what you describe?
Very good question! I think the guy is a troll. He is probably advertising for KEF.
I watched the whole stupid video once and different parts of it several times. The only woofer movement I saw was between 7:17 and 7:29, which was caused by a bass drum in the music. It wasn't woofer pumping. I think the guy is a troll. YMMV
Best regards,
John Elison
How could I be promoting a product I am critical of? Please define what you mean by "troll" and how you honestly think I fit that definition? I am looking for an answer to what I perceive as a possible speaker design flaw in a forum of experienced audiophiles. Why do you have a problem with this?
The bass drum effect on cone movement is exactly my point. There should be no apparent movement in my experience with other loudspeakers. My explanations and examples are pretty clear and if you still miss my point maybe you are the idiot!
normal questions are looked at as abnormal and the reverse is too true, too.
(you don't even know who the moderators are, too, until you memorize their funny-dummy name)
roger wang
> I must confess technical ignorance on this issue
>
> I have never seen any woofer cone movement on any loudspeaker I have owned
>
> I have observed similar movement on Audio Physic Calderas' 8 inch woofers in 1998 in an audio shop.
>
> However, observing these obvious excursions was disconcerting
>
> It appears to me that such an effect is a result of a driver reaching its design limits versus a driver with no visible movement but I may stand corrected here.I think I understand you very clearly: You are ignorant and inexperienced, and you think something is wrong with woofers that exhibit visible movement. Allow me to correct you.
There is absolutely nothing wrong with the movement of the woofers in the video of the KEF Blades. They are supposed to move like that when reproducing a powerful bass drum, especially when connected to 400-watt Parasound monoblock amplifiers.
Good luck,
John Elison
Edits: 04/20/15
you are wrong to accuse, and should say so.
roger wang
A bass drum is a tight membrane designed to flex easily, whereas a speaker cone is designed to be a rigid as possible for the frequencies where it will be used. That's the key- these woofers don't experience cone break-up and reduction until they're pushed up into the midrange. At bass frequencies you can consider them to be an almost perfect piston.There are formulas for how much a given size speaker with a given cabinet alignment must extend to produce the desired SPL. Ported speakers can move quite a bit below port resonance. Some speakers roll off before they get to frequencies requiring large excursions. I'm sure your old speakers can be analyzed as to why they didn't appear to move much, but there are many small woofers which move large volumes of air with minimal distortion.
Edits: 04/20/15
Well, all I can say is different drivers are designed for different situations. One usually must employ large woofers for low bass response because one of the difficulties of driver design is making a small woofer move far enough to produce low bass while still remaining linear and accurate. You may simply be seeing some expensive woofers strutting their stuff.
Edits: 04/20/15
If your woofer is visibly moving slow enough to see, it is because there are ultra low frequencies present in the music, which are undesirable and unnecessary. Normally, you don't see the woofer moving at the lowest audio frequencies because it would be moving too fast to be more than a blur. However, if the source is a vinyl record played on a turntable, this often results in the visible movement you are describing. You can eliminate this by using a high-pass rumble filter. Another way to eliminate this problem with vinyl is to buy speaker with acoustic suspension woofers. That's what I do because anytime you observe woofer pumping, it will always be causing increased intermodulation distortion, which is undesirable.
Good luck,
John Elison
My woofers have always been fine, that is, free of any perceptible or visual cone movement and I have been an audiophile for over 50 years. My issue is with multiple drivers having a relatively high total radiating surface visibly flapping sloppily away without stop.
The demonstration in the video I provided does not use an analog playback source. Those are $30K speakers. With that kind of excursion I question how any reasonable design tolerances can be properly maintained or a uniform radiation pattern.
> The demonstration in the video I provided does not use an analog playback source.
How do you know? I make digital recordings of all my favorite vinyl. I have hundreds of digital recordings of vinyl and they all make ported speakers pump. I bought a little pair of B&W PM-1 speakers before I bought my Thiel CS3.7, and the B&W PM-1's pump like mad with digital recordings of vinyl. The Thiels have a sealed enclosure with a passive radiator and they don't pump.
"The Thiels have a sealed enclosure with a passive radiator"
Doesn't the presence of a passive radiator make the Thiels bass reflex speakers? They simply use a passive radiator instead of the air in a port to take advantage of the back wave from the woofer.
JE
The Thiel woofer and passive radiator act like an acoustic suspension speaker when playing vinyl. There isn't much low frequency movement or pumping at all. Compared to the ported woofer in my B&W speaker, the Thiel CS3.7 is virtually motionless.
With all respects, "what a speaker acts like," i.e. a person's subjective conclusions from their observations, is not determinative of the type of speaker it is.
Your Thiels are bass reflex speakers, albeit ones that use a passive radiator instead of a slug of air in a port for their reflex tuning.
Any woofer will have a characteristic roll off in its low frequency extension. In general terms, whether used in a sealed box enclosure or in a reflex box, a woofer can be made that will provide the same amount of energy. That is, there will be the same amount of "area under the curve." You cannot make bass energy out of nothing. A well made bass reflex speaker takes some of the area under the curve that is extreme bass and moves it higher in frequency. This has the effect of moving the bass roll off lower in frequency, giving more apparent bass, but rolling off the bass much more steeply thereafter. A sealed box will have deeper bass, but the bass will not seem as prominent.
Below is a link to a Stereophile Review (bless JA, all the work he puts in, and his generosity in publishing these reviews!) that shows your Thiels to have a classic bass reflex roll-off. I'm sure the bass you experience in your room is deep, tight and tuneful.
JE
You are free to believe anything you want, but the Thiel's enclosure is sealed. That is a fact.
I agree, your speakers are sealed. They are also bass reflex speakers.
I said your speakers were: "bass reflex speakers, albeit ones that use a passive radiator instead of a slug of air in a port for their reflex tuning." A passive radiator will not work unless the speaker is "sealed." However, using a passive radiator to augment the bass gives the speaker a bass-reflex alignment.
Again, look at that Stereophile review. Figure six shows how both the woofer and the passive radiator contribute to the overall bass response. The passive radiator's power comes from the back, or reflex, wave of the woofer. Remember, we cannot create bass out of nothing.
Note how at the frequencies where the passive radiator (the red trace) is at its highest, the frequencies of the woofer (the blue trace) are at their lowest. This would also happen if the speaker had a woofer and a port. In one case, the woofer would be causing a diaphragm to vibrate, in the other a column of air.
Note also how steeply the overall frequency response rolls off below the "elbow" in the curve. A true "sealed box" (in acoustic terms) design would have a shallower roll off, but one that had an "elbow" higher in frequency.
This is really all academic and has nothing to do with how a speaker sounds. I'm sure there are stellar and infernal examples of both designs to be had. I'm also pretty sure your Thiels sound great. Enjoy them, even if they are not an "acoustically sealed" box!
JE
You're right; they sound great!
Another think I like about them is the woofer and passive radiator don't respond to ultra low frequencies when playing vinyl.
Thanks,
John Elison
Hey John,
As knowledgeable as you are in several areas, Jaundiced Ear is correct on this point. Whether a port-and-duct or a passive radiator, the design is bass reflex.
:)
Regardless of how they're labeled, the only thing that matters to me is how my Thiel speakers perform. With regard to woofer pumping from vinyl they perform like acoustic suspension speakers. All ported speakers I've owned exhibited significant woofer pumping when playing vinyl records, but the Thiels don't. Apparently, passive radiators provide the best of both worlds.
Best regards,
John Elison
nt
I expected the Thiels to pump with vinyl, but they don't, so I'm happy.
John,
This probably has nothing to do with having a passive radiator rather than a port. A system that is direct coupled all the way from cartridge to driver should pump from vinyl regardless of driver loading. If it doesn't, it's likely that something in your signal path is not direct coupled. Probably your phono stage or line stage. But Thiel's use a complex crossover, so there might be a series cap in there.
Dave
You should be happy with them whether they pump on vinyl or not!
JE
JE
You can see in the video that a laptop is used as a source not a turntable. Perhaps the cone excursion is due to a port implementation. However, referring to an earlier example I gave, the Audio Physic Caldera, exhibiting the behavior under discussion, was an infinite baffle. I also believe that a passive radiator is considered a variation of a bass reflex port in loudspeaker design.
Of the loudspeakers I have owned, the ADS were both infinite baffles, the PMC used a transmission line, the Avalon a long vertical tube and the Gallo is an infinite baffle. None of these loudspeakers exhibited any perceptible cone excursions. I cannot feel otherwise that such dramatic cone excursions are sources of distortion of varying magnitude.
Obviously, everything I've said has fallen on deaf ears.
Yes, woofer pumping causes distortion.
Woofer pumping is a result of low frequency signals impressed onto the music as from a turntable. Speakers don't pump on their own.
Just because the music is being played through a computer does not mean it wasn't originally recorded from a turntable.
If this isn't clear to you then you must be an idiot.
You do not need to call me an idiot. Name calling is not appropriate here and I am offended by it. Your point of reference was unclear. You made no distinction between the program material and the equipment reproducing it in your statement.
One could see in the video that the front end was a computer not a turntable. It certainly is possible that the program material was originally analog. I have used analog front ends with some of the loudspeakers I have owned and never experienced any visible woofer cone excursions.
> You do not need to call me an idiot. Name calling is not appropriate here and I am offended by it.
You're right! I apologize.
I have used analog front ends with some of the loudspeakers I have owned and never experienced any visible woofer cone excursions.
Turntables can cause excessive woofer pumping because the phono cartridge reproduces very low frequency signals resulting from record warps as well as the inherent low frequency arm/cartridge resonance. Woofer movement from these types of signals is not desirable and causes increased intermodulation distortion.
The woofer movements in the video of the KEF Blade speakers were produced by a powerful bass drum, which is normal when listening at loud levels. That kind of woofer diaphragm movement is not a problem unless it exceeds the woofer's maximum excursion distance at which point it will cause distortion. However, it didn't appear to be distorting in the video and it didn't sound like it was distorting when I played it on my main system.
Again, I apologize for calling you an idiot.
Best regards,
John Elison
It's pretty obvious in the video that this is digitally sourced stuff being used as a demo. The pumping is just the bass in the song and not the random movement from vinyl.
and set Rumble Filter off.
Dance like heck and nearly no sound (depending on speaker bass alignment)
necessarily indicative of a driver reaching its design limits. Excursion is quite normal when reproducing bass from the first couple of octaves.
As for me, I cannot think of a woofer that does not visibly move to some degree when playing low bass. That's how it moves air!
Woofer movement?A band I see regularly added a Roland 808 bass sample to their arsenal via trigger, and without the FOH guy's prior knowledge (or sound check for level).
They shared in the repair costs of a JBL 18" speaker. The engineer said that in his many years of live sound work, he had never seen a speaker cone so distended. It was literally touching the heavy metal grille of the dual 18" SR sub cab.
"He 'launched' that bastard", was how he described it ...
http://mindseyemusic.blogspot.com/
Edits: 04/22/15
My dispute is with the very large degree of cone movement. This loudspeaker has four 9 inch bass drivers. I have had speakers, as in the example I gave in my first post, using only one driver with no perceptible cone motion. However, I have seen this effect in cheap mid-fi and PA loudspeakers even with multiple low frequency drivers.
I cannot understand the necessity for such large cone movement in a multiple driver system versus the absence of the effect in a loudspeaker with only one bass driver. Certainly the quality and quantity of the bass is not diminished in any way in my experience with such loudspeakers as the Avalon Eidolon with an 11 inch or the Gallo Ref 3.5 with a 10 inch woofer.
large woofer movements were normal, whether or not any bass instruments were playing. It depended on how warped your LP was. Preamps used to have low filter switches specifically intended to roll off extreme low frequencies to damp out such movement.
JE
Look at the specs of any woofer. You will see a value for Xmax, usually in mm. A modern sub driver will have quite a bit of cone movement.
.
Yes, I know. This post should have been a level higher.
we're on the same page.
While stats dominate my two music systems, the Polk LSi speakers in the bedroom and HT sure move. Along with the vintage Advents I use periodically in the garage when playing something with 20-80 hz content.
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