Beyond the Ariel

Re: Re: Re: Different VC wire

gedlee said:

John, this comment about the Lowthars would seem to contradict your opinion that you can put permeable metals in the gap. Comments?


Well you can put anything you'd like in the gap. It doesn't mean it has benefits. Their claim is that as the signal is stopped, the ferric material helps to pull the cone instantly back to center. That is all good, but this effect of pulling back to center would not only happen when there is no signal. It would happen all the time. I'm not exactly sure how it would look, but it is an additional force factor applied to the coil that is not supposed to be there.

John
 
Re: Re: Re: Re: Different VC wire

John_E_Janowitz said:



Well you can put anything you'd like in the gap. It doesn't mean it has benefits. Their claim is that as the signal is stopped, the ferric material helps to pull the cone instantly back to center. That is all good, but this effect of pulling back to center would not only happen when there is no signal. It would happen all the time. I'm not exactly sure how it would look, but it is an additional force factor applied to the coil that is not supposed to be there.

John


The magnet force acts like a nonlinear spring, just like a progressive stiffness spider. But my point is that IF they are using ferric materials in the gap (and I cannot confirm this) and they are NOT having voice coil centering problems, THEN your comment about the the radial forces being unstable does not seem to be a factor. Which was what I alluded to when I commented about how little NI is required.

That there are other forces is undeniable. That these forces would be nonlinear is also undeniable. That they are inherently bad, is not so obvious. I can show you cases where a nonlinear system sounds a lot better than a purely linear one. Its the type of nonlinearity that matters NOT if there is one or not. The idea that all distortion is bad is simply not true. Otherwise there would not be tube amps.
 
Re: Re: Re: Re: Re: Different VC wire

gedlee said:

The magnet force acts like a nonlinear spring, just like a progressive stiffness spider. But my point is that IF they are using ferric materials in the gap (and I cannot confirm this) and they are NOT having voice coil centering problems, THEN your comment about the the radial forces being unstable does not seem to be a factor. Which was what I alluded to when I commented about how little NI is required.

That there are other forces is undeniable. That these forces would be nonlinear is also undeniable. That they are inherently bad, is not so obvious. I can show you cases where a nonlinear system sounds a lot better than a purely linear one. Its the type of nonlinearity that matters NOT if there is one or not. The idea that all distortion is bad is simply not true. Otherwise there would not be tube amps.

Regarding the first point, you are looking at a Lowther which is very low mass on the coil and very low excursion. There is also a tiny gap plate and the amount of ferric material would be very small to coat the entire coil even. Now take a driver that travels 15-20mm, has multiple times the motor strength, a coil that is 10x as long, a 3/4" thick gap plate, etc. Figure in the same proportion of ferric material and there is much more overall in there.

Regarding point 2, I don't want to get into a debate on that one as I know your thoughts on this. IMO though, anything added to or subtracted from the original signal should not be there. My goal is always to reproduce the original signal as accurately as possible. There are already enough non-linearities to deal with regarding motor design, suspension design, etc. Why attempt to add another one that doesn't have to be there?

John
 
Re: Re: Re: Re: Re: Re: Different VC wire

John_E_Janowitz said:
Why attempt to add another one that doesn't have to be there?

John

Because it can make the ones that you can't get rid of less audible.

Seeking perfection in a loudspeaker is rather a waste of time don't you think? The idea to to optimize the tradeoffs. I do that, but you need to know whats audible and whats not to tradeoff. You can't just say "Get rid of them all." Thats poor engineering.
 
for those interested in the DDS waveguides which have also been mentioned here, we just got a pair today. Unfortunately they are not at all useable.

DDSwaveguid-3.jpg


DDSwaveguid-2.jpg


DDSwaveguid-1.jpg


They are way off center, no way to bolt a compression driver to it even. I'm not sure how they could even send one of these out.

John
 
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Re: Re: Re: Re: Re: Re: Re: Different VC wire

gedlee said:


Because it can make the ones that you can't get rid of less audible.

Seeking perfection in a loudspeaker is rather a waste of time don't you think? The idea to to optimize the tradeoffs. I do that, but you need to know whats audible and whats not to tradeoff. You can't just say "Get rid of them all." Thats poor engineering.


Then we need to design some 2nd harmonic back in :D

IMHO - getting rid of as much garbage as possible is the reason I designed these drivers. Last thing I will do is to create more distortion to mask other types of distortion (unless of course its a guitar speaker)
 
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Re: Re: Re: Re: Re: Different VC wire

gedlee said:
The magnet force acts like a nonlinear spring, just like a progressive stiffness spider. But my point is that IF they are using ferric materials in the gap (and I cannot confirm this) and they are NOT having voice coil centering problems, THEN your comment about the the radial forces being unstable does not seem to be a factor.


Radial forces are a factor in every driver, otherwise we could run the softest suspension possible without fear of voice coil rubbing over time.
 
Thanks for the CSDs for that combo.
I guess you made similiar meas. for the DDS horn (e.g. corresponding to the ones you posted here)

Would it be too much to ask to share those ?

Florian,
Here is the equivalent DDS measurement with the BMS 4552ND. This is a standard DDS (no resin or sand) and came from DDS prior to the transition to the new manufacturing location.

4552DDSCSD.jpg
[/IMG]

Soongsc,
Sorry, no impulse files on this PC, only screen shots.
BR
Paul
 
John_E_Janowitz said:

As Nick mentioned, I think the best thing would be to get a pair in your hands to evaluate. That way you can get the data you need under your measurement conditions. Let me know if you'd want to do that.

John

I'll take you up on it, but not for several weeks yet - no open baffle to measure and audition them. That is pending contacts and negotiations with local cabinet-builders. Thanks for the info on what you've found rebuilding Altecs - they certainly built a lot of those things.

As you may have ascertained, I'm not a JBL fan at all - something about the sound I've never liked, going back to my first (terrible) job as a hifi salesman, and pushing those L100's and L200's out the door. I seemed to be the only guy in Southern California that didn't like them. In LA around 1972, Rock-N-Roll Was King, and the louder and more raucous the better - thus the huge success of the L100's, Cerwin-Vegas, Phase Linear and Crown quasi-complementary amplifiers.

Even as far back as 1972, the majority of customers strongly preferred the loudest and most raucous sound possible - they thought that was "High Fidelity". Little did I suspect it would get worse - the Los Angeles Boom Car craze was still ten years in the future. I was very very glad to leave the City of the Angels for the cleaner air of Portland in 1973. After living in the industrial wasteland of the Pomona/Claremont/Upland area for six years, seeing the beautiful green trees of the Northwest was a revelation.

P.S. As you might guess, the phrase "City of the Angels" is spoken by current and former Angelenos in the most ironic tone possible - LA's reputation for depravity and corruption goes back to the days of Raymond Chandler, who remains to this day the best chronicler of the inner character of the city.
 
Cooling plugs

moray james said:
...There has also been a fair bit of work done with regards to heat pumping out the pole to an external sink plate. If you are running your pole at saturation then you can afford to stuff some copper into it and scoot it out the back to a plate on the outside of the cabinet. Big massive copper phase plugs or pole extenders will also draw some heat away from the VC.

That's been my approach. I took some heat (forgive the pun) from some people about wicking heat from the pole piece using aluminum cooling plugs attached to a heat sink panel outside the box. Some felt that forced air cooling was the only thing that worked for loudspeaker cooling. But it was very obvious from my measurements that a LOT of heat was built-up in the motor core, and that tends to cook the adhesive from the voice coil, eventually causing failure.

Forced air convection cooling is fine, but at high frequencies there is little cone motion to pump the air. This is also true when the driver is horn loaded, as that tends to reduce excursion as well. In both cases, airflow through the cooling vents is stalled and loses some of its effectiveness at cooling the voice coil.

Two things tend to heat the motor core. One is direct heating from magnetic loss. Another is heat radiated from the voice coil into the pole piece. Both causes heat the core and it can easily get hot enough to boil water. It's a huge thermal mass, steel surrounded by ceramic, so heat stays in like a thermos bottle. That's a hellish environment for the voice coil to work in. It tends to shift the thermal bias of the voice coil, making its local ambient temperature higher and higher. It increases resistance which changes electro-mechanical parameters. It makes it take less input power to raise the voice coil above its safety margin. And as I said, it eventually cooks the voice coil adhesive and causes it to fail.

I had initially investigated a forced air cooling system for a large basshorn I was making a few years back. After some investigation, it was clear to me that the place I needed to focus my attention on was this heat buildup in the motor core. So I eventually came up with the cooling plug/plate idea, and it worked so well I applied for a patent for it.

 
By the way, when the reader follows the heroic descriptions of the heat-removal techniques used in the professional world, they might think, "oh, this doesn't apply to me, I'm listening at levels hundreds of times lower than a PA system".

Oh, but it does. As mentioned earlier, the voice-coil heats up almost instantaneously, but takes much longer to cool down. Any methods that improve cooling decrease the time-constant of the cool-down process, a very desirable goal even for nonprofessional use. If the cool-down time can be shortened several-fold by professional cooling techniques, that is a major accomplishment.

It always has to be kept in mind the actual emissive area of a voice-coil is really small, a lot smaller than the heat-sink of a transistor amplifier. Not only that, the heat-sink of a Class AB amplifier is only dissipating a small fraction of the total power of the amplifier, while 95~99% of the power of the amplifier is ending up as heat on the (much smaller) voice-coil.

The abysmally low efficiency of loudspeakers is exactly the reason we have to deal with getting rid of all this heat. In a very direct sense, the more efficient the loudspeaker, the less heat there is on the VC for a given SPL. It is easy to forget that a modest-seeming 1 dB gain in efficiency translates to a 20% reduction in power sent to the voice coil.
 
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Lynn Olson said:
As you may have ascertained, I'm not a JBL fan at all - something about the sound I've never liked


Something we both agree on, I have never heard a JBL sound good raw on the bench. EV with the smaller 2.5" coils and the Altecs with the underhung were both the best, but also both had the worse power handling compared to the big stuff.
 
Re: Cooling plugs

Wayne's heat exchanger does have some benefits. The phase plug and additional shorting ring in the TD Apollo motors have a similar goal in mind. Having ridges on the outside of the backplate or top plate to increase surface area will also help remove heat to the outside world. Eminence uses a heatsink at the front of the driver in their Kilomax series to help cool the core as well. CGN uses ridges on the outside of their motor to increase the surface area in their Beehive motor.

It's all a process of optimizing as much as possible. We use high temperature coils that can handle more power to start with. Typical coils wound with adhesive will fail about 375F. Those that are dipped and baked at 550F like ours will handle temperatures slightly higher without failure. Then the shorting rings help pull short term heat quickly from the coil and into the core. That is the first step. If you can't get the heat away from the coil first, there is no need to worry about cooling the core. Once you get the heat away from the coil you can further increase heat transfer with a device like Wayne's, or something along the lines of the phase plug we use. The phase plug helps bring air to outside world where the cone movement can help disperse it, Wayne's heat exchanger helps disperse heat out the back of the cabinet in his system. One way or another you need to get the heat out of the enclosure though to really be effective.

John
 
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Lynn Olson said:
The abysmally low efficiency of loudspeakers is exactly the reason we have to deal with getting rid of all this heat. In a very direct sense, the more efficient the loudspeaker, the less heat there is on the VC for a given SPL. It is easy to forget that a modest-seeming 1 dB gain in efficiency translates to a 20% reduction in power sent to the voice coil.


Agreed. Considering most drivers are <1 ~ 5% efficient that is 95-99% of amp output power being used for heating directly at the voice coil.
 
Lynn Olson said:
As you might guess, the phrase "City of the Angels" is spoken by current and former Angelenos in the most ironic tone possible - LA's reputation for depravity and corruption goes back to the days of Raymond Chandler, who remains to this day the best chronicler of the inner character of the city.

As we are talking audio here, we might add Ry Cooder (Chavez Ravine) as a chronicler of LA business/politics.

Sheldon
 
To me Lynnes point about efficiency is the most important. If you don't have to pump as much power in - virtually all of which goes into heat - then you have far less of a heat problem to begin with for a given SPL. In a home, thermal failure is pretty far down the list and not much of an issue for reliability. In Pro its everything.