Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Beyond the Ariel
Beyond the Ariel
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th May 2008, 09:22 PM   #3811
Lynn Olson is offline Lynn Olson  United States
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
Quote:
Originally posted by John_E_Janowitz

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.
  Reply With Quote
Old 30th May 2008, 09:40 PM   #3812
FlorianO is offline FlorianO  Sweden
diyAudio Member
 
Join Date: Aug 2006
Paul,

Quote:
Originally posted by Paul W
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.
Many thanks yet again. Highly appreciated (and nonetheless insightful)
  Reply With Quote
Old 30th May 2008, 09:43 PM   #3813
Wayne Parham is offline Wayne Parham  United States
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
Default Cooling plugs

Quote:
Originally posted by moray james
...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.
  Reply With Quote
Old 30th May 2008, 09:44 PM   #3814
badman is offline badman  United States
diyAudio Member
 
badman's Avatar
 
Join Date: Sep 2003
Location: Sunny Tustin, SoCal
Quote:
Originally posted by John_E_Janowitz
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.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

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
Impressively hideous!
__________________
"The dawn of Bose created the "Man Cave" and reduced testoterone levels worldwide by 18.5 per cent" Peteleoni
  Reply With Quote
Old 30th May 2008, 10:04 PM   #3815
Lynn Olson is offline Lynn Olson  United States
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
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.
  Reply With Quote
Old 30th May 2008, 10:06 PM   #3816
nickmckinney is offline nickmckinney  Barbados
diyAudio Member RIP
 
Join Date: May 2008
Quote:
Originally posted by Lynn Olson
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.
  Reply With Quote
Old 30th May 2008, 10:08 PM   #3817
John_E_Janowitz is offline John_E_Janowitz  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Green Bay, WI
Send a message via MSN to John_E_Janowitz
Default 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
  Reply With Quote
Old 30th May 2008, 10:09 PM   #3818
nickmckinney is offline nickmckinney  Barbados
diyAudio Member RIP
 
Join Date: May 2008
Quote:
Originally posted by Lynn Olson
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.
  Reply With Quote
Old 30th May 2008, 10:14 PM   #3819
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally posted by Lynn Olson
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
  Reply With Quote
Old 30th May 2008, 10:22 PM   #3820
gedlee is online now gedlee  United States
diyAudio Member
 
gedlee's Avatar
 
Join Date: Dec 2004
Location: Novi, Michigan
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.
__________________
Earl Geddes Gedlee Website
  Reply With Quote

Reply


Beyond the ArielHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 04:47 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki