| Heat Reduction [message #62464] |
Fri, 08 July 2005 02:48  |
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 Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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Hi all,
It's been a while since I've been on this board. I've been very busy with several projects, and have barely had time to respond to things on my own BBS. But I've done some pretty exciting things that I'd like to pass on to you.
Some of you may recall that I was working on a cooling system for speakers. I was mostly motivated in a cooling system for one of my own basshorn designs, but I always had in mind that I'd like it to be compatible with the LABhorn and any others possible. That would make it more useful for more people.
You can do a search here and probably find some of the discussions about the cooling system. There were other conversations along these lines in my forum too.
I'm too tired to write in detail all the things I discovered, but you can find it in the Pi Speakers forum and others on AudioRoundTable.com. A good link is http://www.AudioRoundTable.com/PiSpeakers/messages/17309.htm l . That shows a couple of the systems I tested.
Cutting to the chase, I found that the cooling vent airflow in the LAB12 driver is almost completely obstructed when a boundary is placed within about 1/4". Further away, and the port flows freely, but when you get under a threshold distance, cooling vent airflow practically stops. So since the LABhorn design places the LAB12 very close to this limit, some builders have probably experienced thermal failures. I imagine some builders have spaced it far enough and others haven't.
I found that a ducted heat exchanger arrangement works well for carrying heat away, but it is complicated. A much simpler method works well, and is easy to implement on the LABhorn. Basically, you just put an aluminum tube in the vent hole and bolt it onto the aluminum side covers. Cross-drill the hole so the vent can breathe and the heat is conducted through the tube into the aluminum access panel. Heat transfer is much more effective than without the tube.
See http://www.AudioRoundTable.com/PiSpeakers/messages/17334.htm l for more info.
Wayne Parham
[Updated on: Wed, 26 October 2005 20:12]
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: Heat Reduction [message #62493 is a reply to message #62464 ] |
Fri, 08 July 2005 07:40  |
Brad Litz
Messages: 96
Registered: April 2004 |
Nothing Better To Do |
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[quote title=Wayne Parham wrote on Fri, 08 July 2005 02:48]
"Cutting to the chase, I found that the cooling vent airflow in the LAB12 driver is almost completely obstructed when a boundary is placed within about 1/4". Further away, and the port flows freely, but when you get under a threshold distance, cooling vent airflow practically stops. So since the LABhorn design places the LAB12 very close to this limit, some builders have probably experienced thermal failures. I imagine some builders have spaced it far enough and others haven't."
The V3.0 cabinet has lots of cooling port clearance due to the larger rear chamber.
Brad Litz
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| Re: Heat Reduction [message #62881 is a reply to message #62601 ] |
Sun, 10 July 2005 16:35 |
sheldon harris
Messages: 285
Registered: July 2005 |
Has No Life |
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very interesting!
not only for a lab sub,but for other drivers as well.i'm about to build some 3way horn loaded tops,and the idea of an aluminum pannel with the extension to the pole piece is begining to look like part of my plans.
The things we would do in the quest to attain the highest Levels of Sound! the Pressure that is!
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| Re: Heat Reduction [message #62987 is a reply to message #62464 ] |
Mon, 11 July 2005 09:54 |
Darin Bradfield
Messages: 37
Registered: June 2005 |
Should Get Out More |
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Well if i was going to do it this is how i would. Messed around quite a bit with transferring heat while making amplifiers.
The yellow is aluminium.
The red is magnet.
I don't know why you would only want to collect head through the center of the magnet when you can take it off of the back as well, and then there are the fin's... Why not collect heat out of the air as well and transfer it to the outside of the box? It would be best to have fin's on the outside of the cab as well, but these would probably get into the road while transporting the speaker.
Attachment: HeatSink.jpg
(Size: 23.80KB, Downloaded 618 time(s))
[Updated on: Mon, 11 July 2005 10:26]
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| Re: Heat Reduction [message #62989 is a reply to message #62464 ] |
Mon, 11 July 2005 09:57 |
Darin Bradfield
Messages: 37
Registered: June 2005 |
Should Get Out More |
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didnt seem to atach the file last time.
Attachment: HeatSink.jpg
(Size: 48.26KB, Downloaded 131 time(s))
[Updated on: Mon, 11 July 2005 09:59]
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| Re: Heat Reduction [message #63042 is a reply to message #62601 ] |
Mon, 11 July 2005 17:37 |
Mark Seaton
Messages: 142
Registered: April 2004
Location: Chicago, IL |
Has No Life |
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| Wayne Parham wrote on Fri, 08 July 2005 15:46 |
Even when surrounded by refrigerated air, the pole piece gets really hot, enough to cook meat.
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Hi Wayne,
I have seen some drivers with metal phase plugs with heatsinking effects where the phase plug would get quite warm/hot with a moderate, continuous drive level. I also recall the transfer of heat to the pole is dependent on the design and geometry of the motor. I haven't taken a look at where the heat goes in the LAB12 driver when driven with a continuous signal. What signal and level was required to reach the temperatures you refer to? Did you take any specific temperature measurements? Of course the ulitmate test is shift in Re, as this is the best indicator of heat in the coil. Did you take any measurements of this?
It might be interesting for someone with LAB subs to take a measurement of DCR immediately after giving the subs a workout for a while, preferrably in a more typical application. Of course ALL drivers will suffer thermal compression to some degree with extended duration use, the question is of course comparatively how much?
Regards,
Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." - Daniel H. Burnham
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| Re: Heat Reduction [message #63091 is a reply to message #63042 ] |
Mon, 11 July 2005 23:09 |
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Wayne Parham
Messages: 302
Registered: November 2004 |
Has No Life |
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We measured in several conditions and with several different cooling systems, and we are still in the process of testing.
The reason I reported this here, is that it is a simple thing to do and very effective. The rear chamber of a basshorn is small and easily superheated. To give you an idea how hot things get, we measured the LAB12 speaker in free air, temperature at 72 degrees Fahrenheit. This is a considerably cooler operating environment than a small sealed chamber with no ventillation.
We generated a test signal for 20 minutes and then measured temperatures after that period of time. The speaker was presented a 40VRMS, 40Hz signal cycled 15 seconds on, 15 seconds off, ambient temperature of 72 degrees in free air. This is a fairly conservative level, less than 400WRMS when running and plenty of cool down time between signal bursts. But even at this level, there was a noticeable burning smell and a considerable amount of heat produced. The driver is not at its thermal or mechanical limits though, so it is not at risk of failure.
The center pole piece measured 165 degrees Fahrenheit under these relatively mild operating conditions. It actually rises a couple of degrees over the course of the 15 second on time, then after the signal shuts off, it quickly rises another two or three degrees to a maximum of about 170 degrees. It then begins to cool, and over the course of the next 15 seconds, it drops about five degrees back to the 165 degree point.
I wouldn't be surprised if you measure the same thing inside a LABhorn, with its small sealed motor chamber, you'll probably find the pole piece is hot enough to boil water.
We considered running at 400WRMS continuous, with no cooldown cycle every 15 seconds but we did not want to risk damaging the woofer. We will do destructive tests later.
More information can be found in the web pages below. There are some measurements there, and more are being added as we have time to setup and test. Pyrometer measurements of the voice coil with and without the cooling device will be posted shortly.
Most of my work is in regards to the 12Pi hornsub, but I have made it a point to make the cooling system compatible with many other basshorns too. I think it's an important feature, and always had compatibility and ease of implementation two of the design goals. Since all it takes to make this work is the addition of an aluminum tube, it's about as easy to implement as you can get.
It appears to be enormously effective at removing heat from the motor chamber. This is exciting, since having cool air surrounding the voice coil is important. Getting heat out of the pole piece and magnet keeps them from being heat soaked and prevents average voice coil temperatures from continually rising to the point of failure. I'm expecting system power ratings to double, but we'll not know for sure until we've built the prototype horn with the cooling device, so we can test the entire system. We'll find out soon enough.
http://www.AudioRoundTable.com/ProSpeakers/messages/220.html
http://www.AudioRoundTable.com/PiSpeakers/messages/17387.htm l
http://www.AudioRoundTable.com/PiSpeakers/messages/17334.htm l
http://www.AudioRoundTable.com/PiSpeakers/messages/17309.htm l
http://www.AudioRoundTable.com/PiSpeakers/messages/15873.htm l
[Updated on: Sat, 27 August 2005 01:54]
Wayne Parham
π Speakers
PiSpeakers.com
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| Re: Destructive test [message #71571 is a reply to message #71085 ] |
Fri, 26 August 2005 18:10 |
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Dave Rickard
Messages: 2622
Registered: April 2004
Location: The Wild West |
Has No Life |
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Looks like a winner. Congratulations, and thanks for sharing.
Dave
Dave
Yorkville dealer
The wrong piece of gear, at the right price, is still the wrong piece of gear.
"If you don't have good stuff at each end of the signal chain, (mics and speakers) what you use in between is just turd polish."--Dave Dermont
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