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Re: Speaker Voice Coil Cooling System - Heat Sink [message #47238 is a reply to message #47237] Fri, 01 July 2005 00:11 Go to previous messageGo to next message
ToFo is currently offline  ToFo
Messages: 219
Registered: May 2009
Master
YUP!

Anyways, I am glad I haven't built subs yet. I am real happy about all of these recent developments. I am not only going to shake up the living room. I now have DJ and live duty to think about. Loud enough mid/high for the size crowd I'm looking at is no mystery, but with todays expectations of bass performancve this sort of development could make a difference. Real world stuff like me using my little trailer, or having to borrow/rent a bigger trailer and/or truck.

Low and loud PI subs = tasty treats!

Keep the coolness coming,

Thomas

P.S. I did a party with just my Theater 4's and my Brothers Theater 3's and a little help from 1200 watts. We had people asking what made it sound so sweet. cool huh?



Re: Speaker Voice Coil Cooling System - Heat Sink [message #47254 is a reply to message #47236] Sat, 02 July 2005 21:03 Go to previous messageGo to next message
bgavin is currently offline  bgavin
Messages: 6
Registered: May 2009
Esquire
Computer processors specifically use copper to wick the heat away from the core, then use aluminum fins to dissipate that heat to the atmosphere.

Copper has a superior heat transfer coefficient, and aluminum has a superior heat dissipation function.

Re: Speaker Voice Coil Cooling System - Heat Sink [message #47258 is a reply to message #47254] Sun, 03 July 2005 00:08 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

You could build it out of copper instead of aluminum if you wanted to do that. Either is better than none.

The pole piece of a loudspeaker pushed to its limits gets very hot. The air rushing back and forth in the vent is not heated much at all, but the magnet gets hotter and hotter, with the center pole and front pole piece getting the hottest. The air inside the cabinet can become hot, in which case the air surrounding the voice coil is hot too. So the idea is to transfer the heat into some kind of heat exchanger and get it out of the box.


Thermal limits vs Excursion Limits [message #47362 is a reply to message #47238] Fri, 22 July 2005 12:18 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

I'm very excited about this cooling device. It is turning into a very simple and inexpensive option, less than half the cost of the woofer. So we are anticipating being able to increase the power handling enough to represent doubling the number of woofers at a cost of half that of the woofers. That's two times the punch for half the cost!

I don't know if you've followed the threads, because I've had discussions here, on the AudioRoundTable.com ProSpeakers forum and on ProSoundWeb. But the amount of heat we've been able to dissipate is significant.

I'm still testing, so I'm just leaking information out right now as I get it. We're building a prototype horn now, to test the device as it will be used rather than on a bench. But what we have found out so far is startling.

There has been a common misconception that excursion was the primary cause of failure, and that power levels could be increased some four-fold when horn loaded. But that is not true. While horn-loading increases efficiency, it doesn't do it enough to turn all electrical energy into kinetic energy so heat is still a big problem. In fact, it may be worse because of the confined spaces the drivers are used in and the fact that horns reduce excursion which reduces vent air movement.

There has been another common misconception that heat is carried away mostly by air conduction or convection, and that radiation is not significant. The idea seems to be that if the voice coil were hot enough to be radiant, it would be such a problem that this possibility is overlooked. But the fact is that is the way most voice coil heat is transferred, by black body radiation into the pole piece, and not by convection or conduction into the surrounding air. The best thing you can do to remove heat is to conduct it away from the pole piece, so the voice coil is in the coolest environment possible. Of course, keeping the air cool is also important for the same reason.

Sure, you can over-extend the driver by feeding it a 20Hz signal at 45 volts, but it will sound like an engine running without oil and it will fail very quickly. When a driver is sent a signal that moves to beyond xmech, it suffers mechanical interference. You're basically beating the driver to a pulp and damage is quick and certain. This can happen from a quick burst of low frequency energy. The solution is high-pass subsonic filtering. As for continuous use at high power levels, the real culprit is heat, not excursion.

Thermal limits are less obvious than mechanical limits. A voice coil failure is usually the result of long term exposure to heat. You could fuse the coil by a quick burst of energy, but that's not what usually happens. The normal failure mode is failure of the glue that holds the voice coil in place. Voice coil heat expands the metal and also weakens the glue. Eventually, the over-heated voice coil shifts enough to rub or come undone entirely. Once a part of it moves away, it can fuse or flex break so sometimes it fails that way too.

To give you an idea how hot things get, we measured the LAB12 driver in free air, temperature at 72º Fahrenheit. This is a considerably cooler operating environment than a small sealed chamber in a basshorn.

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 72º 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 165º 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 170º. It then begins to cool, and over the course of the next 15 seconds, it drops about five degrees back to the 165º point.

I wouldn't be surprised if you measure the same thing inside a basshorn with a 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.

The cooling system 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.

The venting techniques used to cool drivers are good, but it is just as important to keep the metal surrounding the voice coil cool too. Especially in the case of basshorns with small back chambers, doing something to get the heat out of the box is important for long-term high-power use. And the same piece used to conduct heat out of the motor structure might be used as a shorting ring as well, which serves to reduce harmonic distortion. So this is a very exciting concept indeed.


Re: Thermal limits vs Excursion Limits [message #47372 is a reply to message #47362] Sat, 23 July 2005 01:32 Go to previous messageGo to next message
ToFo is currently offline  ToFo
Messages: 219
Registered: May 2009
Master
I am excited as well. Many times I have simulated with various long excursion drivers, only to find that some don't do xmax in band until 2x thermal power in the desirable boxes. I was beginning to wonder about the designers intensions. Now you're talking about getting all the travel these drivers promise, and not replacing them all the time. I know all too well about frozen, open and detached VC's. The shop I used to work at sold competition car audio as well as hi-fi. I have seen VC's deform into the gap, but I never saw a "backplated" coil or ripped suspension in a good box.

I really want to build a pair of these horns your working on. I have done enough simulation and real world stuff in the last few years to already see the potential. I want subs that can modulate my voice.(so please test that capacity while you are torturing the prototype)

Thomas

Re: Thermal limits vs Excursion Limits [message #47375 is a reply to message #47372] Sat, 23 July 2005 10:11 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

If you'd like, I'll send you the plans for the 12π basshorn. You'll need five sheets of Baltic Birch, two LAB12 drivers and two of the cooling plates. I've got the best prices on Eminence drivers of anyone I know of, so I've got you covered on the LAB12s. You can either have a local machine shop make the parts for the cooling plate or you can get them from me. I sent out quote requests to about 50 machine shops across the country and I think I found a pretty good deal, especially when buying in moderate quantities. All told, you're looking at $500-600 in materials costs (wood, speakers, aluminum and machining), depending on the price of wood in your area.


Re: Speaker Voice Coil Cooling System - Heat Sink - Photos [message #47430 is a reply to message #47258] Wed, 03 August 2005 23:23 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

Here are some photos of the prototype device:

http://www.pispeakers.com/Basshorn/Cooling_Device_Vent_Pipe.jpg
Cooling plug

http://www.pispeakers.com/Basshorn/Cooling_Device_Vent_Pipe_Closed_End.jpg
Top View

http://www.pispeakers.com/Basshorn/Cooling_Device_Vent_Pipe_Open_End.jpg
Bottom View


The prototype was made using a piece of 6061 aluminum tubing, lathed down to fit into the woofer cooling vent. It is sized to fit snug, not so snug that it is difficult to insert cold but when the aluminum heats up, it expands more than the iron of the pole piece, so it is difficult to move unless it is cold.

The top section is not lathed down, which acts as a stop. Holes are cross-drilled so that vent air is free to pass. An aluminum plug is fitted into the top and is press fit and pinned in place. It is threaded to accept the bolt for mounting the heat exchanger, which doubles as an access panel on basshorns.

Production units will probably be a one-piece design, cut from a billet of aluminum on a CNC machine. It will depend which is more cost effective. The two-piece design is fine, as long as the slug in the top is press fit so the interface is good for thermal transfer. The two-piece design is probably more labor intensive, so we'll see.

http://www.pispeakers.com/Basshorn/12Pi_Cooling_Plug.gif
If you have a shop, you can build these for very little money. McMaster-Carr sells the aluminum tubing, and you only need a few inches per speaker. Measure the depth of the center pole, and cut it so that the length matches when fully inserted. Then drill holes in the top so cooling air passes through and press fit an aluminum slug to seal the hole. Drill and tap the top and viola! You have a heat transfer tube that will cool the motor a lot better than air cooling alone would do.

If you don't have a machine shop, contact me and I'll get some prices for you. I'll probably make these available on the shopping cart soon, and we'll add sizes for popular models as time allows.

When installing the device, be sure to use heat conductive grease. It is very important that the interface between the pole piece on the motor and the cooling plug is good. You want a lot of surface area contact, so the entire length of the cooling plug should be inserted and it should be covered with conductive grease. You also want the interface between the cooling plug and the heat exchanger to be good, so use conductive grease there too, and snug the panel down well. Both surfaces should be straight and smooth to maximize contact surface area.

http://www.pispeakers.com/Basshorn/Conductive_Grease_in_Vent.jpg
Heat conductive grease on pole piece, in vent hole



I would suggest removing the paint from the pole piece inside the vent hole with sandpaper. It is painted black, and this may prevent the cooling plug from sliding freely, as well it may restrict heat flow.

Use very fine sandpaper, like 600 grit, and rub slowly. Make a few swipes and remove the sandpaper and check your surface. Wipe it clean with your finger to see if you've removed the paint and see shiny metal.

Once you're through the paint, stop. It goes pretty quick. If you sand the metal, the tiny filings will stick to the surface. So wipe it down pretty good after you're done.

Next, cover the surface with heat conductive grease. This will both protect the exposed metal and serve to improve heat transfer. Apply it as a thin uniform film. Insert the clean cooling plug and pull it right back out. Inspect the tube to see where you have contact. It will be white where there is contact and not where there isn't. If the tube is white all along it's surface, reapply the film and reinsert. if not, apply a slightly thicker film and try again.

The point of this is to make sure there is plenty of conductive grease and that there is no space between tube and pole piece that isn't filled with conductive grease. We want contact all along the surface. But we don't want so much grease on the pole piece that the cooling plug pushes it down into the area behind the dust cap.

Once the cooling plug is inserted, you can mount the speaker in the cabinet, and then mount the heat exchanger onto the cooling plug.

http://www.pispeakers.com/Basshorn/Cooling_Device_Vent_Pipe_Inserted.jpg
Cooling plug inserted, ready to attach to the heat exchanger


http://www.pispeakers.com/Basshorn/Heat_Tube_and_Plate.jpg
Heat conductive grease applied to cooling plug prior to attaching heat exchanger plate


http://www.pispeakers.com/Basshorn/Heat_Plate_Boltdown.jpg
Fastening the plate to the cooling plug


http://www.pispeakers.com/Basshorn/Heat_Exchanger_Assembled.jpg
Heat exchanger assembled and ready


http://www.pispeakers.com/Basshorn/Heat_Exchanger_Installed.jpg
Heat exchanger assembly inserted in woofer

Re: Speaker Voice Coil Cooling System - Heat Sink - Photos [message #47439 is a reply to message #47430] Fri, 05 August 2005 21:39 Go to previous messageGo to next message
Monomer is currently offline  Monomer
Messages: 18
Registered: May 2009
Chancellor
Ahhh, and they say a picture is worth a thousand words....

yup, I'm going to throw one together. Maybe even make a nice SW drawing just for the hell of it.

does it have to use the giant heat exchanger plate? I plan one using this on a Tuba30slim, where the access panel would be one large chunk of alumn. (a very expensive chunk of alumn.)

Re: Speaker Voice Coil Cooling System - Heat Sink - Photos [message #47440 is a reply to message #47439] Sat, 06 August 2005 01:20 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)

Anything can function as a heat exchanger, but it's best to have a lot of surface area. A wide plate or even better, one with fins or grooves machined into it is best.

I'm using the access panels as heat exchangers, just like you've described. You can have them machined out of 5052 alloy and not get beat up too bad on the price.

We've taken bids from several machine shops across the country and Canada and gotten prices that range from about $50.00 to over $300.00. I'm planning to have the plates and heat tubes made in quantity to get the costs down. Unless you use the most expensive machine shops, even if you do it in single quantity, your cost shouldn't be more than about half the cost of the woofer, even if precision machined. If you do the machining yourself, the cost is even less.

Let us know how yours works out.


Re: Speaker Voice Coil Cooling System - Heat Sink - Photos [message #47442 is a reply to message #47440] Sat, 06 August 2005 10:23 Go to previous messageGo to previous message
Monomer is currently offline  Monomer
Messages: 18
Registered: May 2009
Chancellor
I was planning on DIY, the shop I work in has a lathe and a vertical mill.

thats still one large peice of alumn.

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