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In Reply to: RE: Observable Woofer Cone Movement posted by House13 on April 20, 2015 at 12:48:43
> 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.
Follow Ups:
"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.
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