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Multi-Way Conventional loudspeakers with crossovers

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Old 13th September 2007, 03:08 AM   #1971
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Hi AInFLA, John K.

“Wouldn't it be a bit more objective to subject the hifi drivers to similar testing as you do for the pro drivers, than cast judgement leafing through a catalog? I don't totally disagree with you about looks being important for hifi drivers, as they are aimed at audiophiles, who hear with their eyes as much (if not more?) than their ears. But with no data, your statement seems rather subjective. Plus sound quality that is blaring loud enough for public address won't always cut it within the confines of a living room. Different audience requirements.”

Several answers;
While at Intersonics my job was to develop new kinds of transducers, “officially” these were for acoustic levitation but I also develop the Servodrive woofer and Phoenix Cyclone rotary woofer and some others while there. I guess from that perspective, I cannot under emphasize that damping is a very important quantity and is not associated with some of the cool looking cone materials.
If looks weren’t apparently more important than sound in some cases, then drivers with nasty behavior wouldn’t be sold based on a “New cone technology”.
It has been a while since I measured any, but I don’t see that they have changed fundamentally since then and if I were building something that used them, I would sample the ones I was interested in.

Your mention of a blaring pa system is spot on in a way.
Most of all the things that are wrong with speakers, get worse as the volume is increased and as the size and complexity of the speaker system increases and also as the room size increases. Often the sale of speakers in this kind of situation is based on hearing side by side demonstrations in the venue. If you can demonstrate better sound, you get the sale most of the time. That kind of puts the focus on better sound and is why I went the way I did.

“What about the low Q resonances within the soft cone drivers passband? What about the flexing and bending of the cone? None pistonic operation? Especially the ultra low mass ones required for HE (pro drivers) attached to powerful motors?
The cone breaking up inside it's passband? A lossy medium is best for signal preservation? Or hiding things?
What if the goal is reproduction of acoustic instruments, not paper cone-compression driver-amplified box speaker-live sound rock concert? Tom, isn't it best to give both sides of the story? Soft, flexy paper cones are without sin?
Is Dr. Toole's research (CMMD) just a marketing gimmick? Thiel?
Last time I checked, there were no paper processed fiber compression drivers. Has that changed?”

Well, all the horn style speakers I build, like the SH-50, only operate the drivers in the piston band. In fact, to reduce distortion, each cone driver feeds into the horn through an acoustic low pass filter comprised of the air volume trapped beneath the cone and a hole which connects to the horn. This low pass filter in front of the driver is above the low pass crossover point and has the effect of attenuating the harmonic distortion the driver produces which comes out above crossover frequency.

With a TEF, one can see a driver which is transitioning to non-piston motion, the old
TEF-10 /12 machines (which were much better in time than the modern ones) one could see the small change in time taking place in a mid range soft dome that had nice smooth response, as the dome de-coupled.
I would think that if you can, you would want to avoid that kind of operation (non-piston) at least where your ears are most sensitive, more or less 300Hz – 3KHz
Bottom line, if you have a mound of acoustic gain between the motor and the net radiation, you magnify the nonlinearity and sub multiples of that F.
On the other hand, if that acoustic gain is in the middle of the band and is broad (low Q) enough, then that can (if eq’d flat) can lower distortion by reducing the drive / excursion of the motor (who’s non-linearity is tied largely to motion).
This is what horns do (one thing), a bass horn that raises the drivers sensitivity by 10dB can reduces its excursion for a given SPL to 1/3 the direct radiator case.

Your comment about compression drivers is related to using metal dome tweeters too.
A dome in a compression driver is one case where strength to weight is a controlling factor as the radiator as mass is more important than in a direct radiator tweeter.
Here, metal or mylar domes are used. A good one inch exit dome type compression driver will have a dome stiff enough (to act like a piston) to reach 17-20KHz before the first resonant mode. Realistically, if you’re an adult, your hearing rolls off before 20KHz and then drops like a rock above 20KHz. I’m not talking about can you detect anything up there under the best case but rather can you hear anything up there under normal conditions, no.
As a result, distortion produced at 5KHz and above has to be at an enormous level to be detectable at all. Similarly peaks and dips associated with breakup, that high, are not generally detectable.
This is not what Earl Geddes is on about, that (HOM’s) are a variable that on one given horn, may make 5 different compression drivers with similar end responses all sound different.

“What if the goal is reproduction of acoustic instruments?”
An ideal reproducer reproduces whatever it is asked to, without alteration in any way.
Like John K. said so well “Door bells and tuning forks should ring, not driver cones.”
No one can convince me that what we have no is so close that we can all give up.
Then there is the recording process and how the speaker interacts with the room, layers which make what the ideal speaker needs to do, less clear.

John K, those are beautiful speakers (all of them).
You obviously have a real knack with math too, very cool.
Again the dogs wish to go, so I must.
Best,

Tom Danley
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Old 13th September 2007, 04:21 AM   #1972
jlsem is offline jlsem  United States
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Quote:
I think one difference between us is that I'm no longer interested in SEAS, Vifa Peerless, ScanSpeak, etc. They've had 15 years to respond to the vacuum-tube subculture and the constantly-expressed demand for substantially higher efficiency, and have done their best to ignore it and hope it would go away. Well, it hasn't, there's only been a trivial 1~2 dB change in efficiency in more than a decade, and to me, the mainstream audiophile drivers sound worse than what they were making 15 years ago.
This is the best loudspeaker forum post I've read yet.

John
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Old 13th September 2007, 11:43 AM   #1973
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Originally posted by jholtz



Hi AJ,

I believe that speaker pictured belongs to John Pastuck and was present at the 2004 Iowa DIY Event. It and Salk Sound HT3's were a few tenths apart in the voting for best sound in the unlimited class. I did not hear the ringing John speaks of but I like metal drivers and don't care for the 8545's. They are very nice speakers.

Jim

Yes, those are John P's speakers. He did a really nice job building them. I think he is in your camp.

The thing about the metal cone mids isn't the ringing per say. As I showed in the CSD plots, with regard to the basic frequency response, it can be shaped given that the breakup is a linear phenomenon. It's the potential for excitation by harmonics of lower frequencies and the resulting "amplification" there of, or excitation from other acoustic sources that is the problem, or so I believe. Response shaping doesn't do anything for these effects since they are introduced independent of the crossover.

I tried to investigate the possibility of acoustic excitation. I set up a second speaker very close to a W18 and played swept sine waves around the resonant frequency to see if the resonance could be excited acoustically while monitoring the W18 voice coil voltage on a scope. The results were inconclusive. I probably should have looked directly at the cone with a laser but I don’t have access to that kind of equipment anymore since I retired. However, there is something going on with the Seas Excel metal cones (at least the W18 and W22 which I have played with) which catches my ear with long term listening. I find the same problem with other metal cones that I have looked at. Trying to quantify the cause is difficult. It's easy to identify what I hear, much harder to quantify why it is heard. Could be some of: A causes B which (speculatively) results in C, therefore A is the problem.

Anyway, the Seas metal cones are very smooth in the pass band but I find that they add a "zip" to the sound that I identify with the resonance (though I could be mistaken), even when carefully addressed in the crossover. And to me this takes something away form what is otherwise excellent. This may be exacerbated by the application since as a dipole mid the W18 is being pushed to the limits, excursion wise. I also think they just sound thin and weak in the lower midrange, but thats a hole other story. Like I said, the 8545 isn’t perfect, but I find the colorations in it more pleasing to my ear than dissonant. There is no question that the W18 and the SS sound different and you’re not the only one who prefers the W18. But I bet you like a Steinway compared to a Baldwin.

Thanks for the kind words about the performance of the system at the Iowa DIY. I think John has done additional tuning of the woofer so it probably sounds better now.
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Old 13th September 2007, 01:48 PM   #1974
soongsc is offline soongsc  Taiwan
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I agree from looking at this data, resonance in most drivers can be equalized; however, due to the fact that resonances occur after the first refleced wave in the cone, an equalized driver will never sound as good as the driver without this resonance. Since we may never be able to do this kind of comparison in reality, knows what we may be missing.
Quote:
Originally posted by john k...


I have to disagree with you here. The resonance in most drivers are a linear phenomenon and as such can be equalized. The problem is as Tom said, that while they can be equalized to response correctly to input signals that doesn't solve the problem of them being excited by distortion components generated as harmonis of lower input frequencies. For example, here is a CSD of a naked Seas W18

Click the image to open in full size.

Now, here is a CSD of a 2nd order band pass active filter;

Click the image to open in full size.

Lastly, here is a CSD of the W18 equalized to have the same 2nd order band pass response;

Click the image to open in full size.

It isn't perfect but clearly the resonance at 500, 800, and 5k Hz are not present. The point is that linear systems can always be corrected by response shaping. It is the nonlinearities that cause the problems.

Now, some one asked aboy Floyd Tool. All I can say about that is, for example, a 1st order band pass response has a transfer function given by

TF = (s/Q)/ (1 + S/Q + s^2).
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Old 13th September 2007, 02:22 PM   #1975
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It is the nonlinearities that cause the problems
Dr Geddes wrote that non-linear distortions in compression drivers are not the problem. Here my equalised Jordan:

Click the image to open in full size.

I don't hear this pre and post ringing - did the test with minimum and linear phase passband filters.
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Old 13th September 2007, 02:48 PM   #1976
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Quote:
Originally posted by jzagaja


Dr Geddes wrote that non-linear distortions in compression drivers are not the problem. Here my equalised Jordan:

Click the image to open in full size.

I don't hear this pre and post ringing - did the test with minimum and linear phase passband filters.
Can you remember what sample rate these were running at? What driving amplifier did you use? and what kind of speaker cable runs?
Since these are composed impulses from MLS signals, the pre-ringing is related with the mathematics and is normally not heard. I have discovered though, that when the drivers have good top end frequency extention and can reveal very good detail, the pre-ringing is shown.

I'm not sure whether the equalized performance is better or not, but my guess is there will be some coloration that may or may not be preferable.
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Old 13th September 2007, 04:19 PM   #1977
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Sample rate was 48K (approx. 200 us/div), Pioneer SF-21 amplituner (unknown topology, legato link DAC), Digigram 440VX, cable OFC 2 x 2,5mm2. Cumulative spectral decay of above. I can only say for sure I hear less high frequencies. Which is better - I can't tell. I've never had positive results with DSP. Maybe it's time to visit Dr Brueggmann in Gelsenkirchen HiFi show this November?

I can run direct impulse measurement with 500K sample rate. How short step pulse should be, 50us? Or better calculate impulse response from a step function? Do you know that Shoeps presented on AES conference deconvolving techniques for microphone impulse response estimation? Two microphones and one full range speaker.
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Old 13th September 2007, 04:25 PM   #1978
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Since these are composed impulses from MLS signals, the pre-ringing is related with the mathematics and is normally not heard
This was a long sine sweep de- convolution - Cooledit and Aurora plug-ins.

I don't hear this passband ringing filters on music:

http://audiostereo.lukarnet.com/gfx/800000/808072_1.gif

... except the case when you play the ringing tail alone.
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Old 13th September 2007, 04:36 PM   #1979
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Originally posted by jzagaja
Sample rate was 48K (approx. 200 us/div), Pioneer SF-21 amplituner (unknown topology, legato link DAC), Digigram 440VX, cable OFC 2 x 2,5mm2. Cumulative spectral decay of above. I can only say for sure I hear less high frequencies. Which is better - I can't tell. I've never had positive results with DSP. Maybe it's time to visit Dr Brueggmann in Gelsenkirchen HiFi show this November?

I can run direct impulse measurement with 500K sample rate. How short step pulse should be, 50us? Or better calculate impulse response from a step function? Do you know that Shoeps presented on AES conference deconvolving techniques for microphone impulse response estimation? Two microphones and one full range speaker.
Normally when I try to listen for improvements above 10KHz, cymbals and tambourines are good candidates. More ringing does make the high frequencies seem less, especially if the ringing is 15KHz or above.

For impulse signals, I would expect the shorter impulse you can output that the amp can handle, the more ideal it would probably be.

I would be interested in reading that Shoeps presentation, is there anyplace it can be found?
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Old 13th September 2007, 04:48 PM   #1980
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I've sent you this paper on email. The author said this approach works best on Manger transducer as an exciter but you can use any wide band driver without crossover and "zeroes in your step response". What he means by that? The disadvantage is you rely on reference microphone.


I apologize for small off-topic.
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