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Author Topic: Cooling fan (Patent 4757547)  (Read 10685 times)

robwells

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Re: Cooling fan (Patent 4757547)
« Reply #20 on: September 18, 2006, 08:01:49 pm »

Michael Hedden Jr. wrote on Mon, 18 September 2006 00:53

Didn't I see this in a Jason or Freddy movie or maybe it was that classic "Race with the Devil" where everyone screams run, run for your lives, it's back, the attack of the cooling plug thread!  

Mike Hedden




surely 'Grant Rider' = 'Wayne Parham' ?

Laughing
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Wayne Parham

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Re: Cooling fan (Patent 4757547)
« Reply #21 on: September 19, 2006, 05:19:01 pm »


Rob, I don't know that I need to bother with a reply but I have no trouble making my own points.  I don't know if PSW has trouble with sockpuppets, but they're easy enough to identify by IP or even better by MAC ID.  For what it's worth, it looks to me like Grant is pretty open minded.
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Wayne Parham
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Kerry Stansbury

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Re: Cooling fan (Patent 4757547)
« Reply #22 on: October 10, 2006, 08:35:03 pm »

The Eighteen Sound 15LW1401 does have vents around the spider, a pole vent and six vent holes direct from the voice coil gap. I don't know how much additional forced air would improve it's performance. It is rated at 7000 watts peak! I am currently using a pair of Eighteen Sound 18LW1400's 18" drivers, and they seem to be able to withstand a lot of abuse. I performed some spl comparisons using a frequency generator and an amplifier rated at 1500 watts into 8 ohms operating it just under clipping. With this continuos signal, The 18LW1400 performed fine as did an Aura NRT18-8, Which has a vented spider and pole. The JBL 2242 I tested had only 3 vent holes going directly to the gap which also have some pretty restrictive looking screens on them and no other vents. The JBL smelled like an overheated electrical component within 10 seconds into the test. I hope it didn't damage it, I haven't noticed any after effects "YET". I think with all of the ventilation on the eighteen sound and some other company's drivers like RCF, it may not be nessesary for additional air. I am in the process of trying out a Eighteen sound 15LW1401 which I will be operating at up to 2000 watts. If it fails on me, I will do some forced air testing. I think If you filtered air into the 6 gap vents with just enough to cause the air to move through the gap and out the spider and pole vents, you wouldn't have any problems with pressurization or distortion. Any thoughts on this?
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Rolling Thunder

Wayne Parham

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Re: Cooling fan (Patent 4757547)
« Reply #23 on: October 11, 2006, 10:56:45 am »


Kerry Stansbury wrote on Tue, 10 October 2006 19:35

The Eighteen Sound 15LW1401 does have vents around the spider, a pole vent and six vent holes direct from the voice coil gap. I don't know how much additional forced air would improve it's performance.

That's the best vent arrangement, in my opinion.  The center pole vent has passage to the gap in the front plate, and air flows through the gap to radial vents in the back plate.  Cone motion produces a lot of airflow through vents arranged like this.  I'm not sure that adding a fan makes sense, especially with the added complexity and cone offset from the pressure differential it produces.
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Tom Danley

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Re: Cooling fan (Patent 4757547)
« Reply #24 on: October 11, 2006, 05:30:12 pm »

Hi Kerry, Wayne, all

The idea with forced air cooling is that the air that is swept away after being heated carries away energy which would other wise accumulate, causing a temperature rise.
If you look around, you will see air transfer is the most common method available, everything from your car’s radiator to the heat sinks in your amplifiers use this approach, the air carries away the heat energy.  
A typical V-8 car radiator can dump about 50KW of heat and its not that big, it just takes airflow..

Look at the link below which shows the effect of forced air cooling on a DC servomotor.  This motor is similar to that used in a Servodrive and has stationary magnets with a rotating hollow wire armature (very similar to a Voice coil). These motors only have a cooling air path on the outside of the armature where the air path in my cooling Patent is on both the inside and outside of the VC.
In the Servodrives with power cooling (using this patent), cold air was taken in at one edge of the enclosure and hot air expelled at the other, the motor was not in the driver compression chamber.
On the VC drivers licensed under this Patent, the heat once removed from the VC, heated the enclosure and its aluminum back panel.
In the loudspeakers using the approach shown in the patent, they were able to get more than a factor of two in steady state power handing.

For this to work, it is critical for the air to flow thru the magnetic gap (intimate turbulent contact with the VC) as radiation is a poor mechanism at safe VC temps.  Holes that allow air to bypass this path truly defeat the function.   Also, doing it this way, one avoids any significant offset, which is a problem the other ways it could be done.  As I have explained, this way avoids the radiator area feeling any pressure from the cooling system..

Scroll to the bottom of this link and look at the permissible dissipated power and thermal resistance as a function of air flow.  Keep in mind, these are real Watts and not Loudspeaker Watts but the change would be similar (approaching a factor of four improvement). Also keep in mind, the air path is only on one side of the cup armature.
http://www.pacsci.com/support/low_inertia_pmdc/lowinertia55n msupport.html

Hope this helps.

Tom Danley
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Wayne Parham

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Re: Cooling fan (Patent 4757547)
« Reply #25 on: October 14, 2006, 09:56:28 pm »


Tom, I'm curious:  Has any company you've worked for ever manufactured a voice coil driven speaker with a cooling system as shown in this patent?

Tom Danley wrote on Wed, 11 October 2006 16:30

If you look around, you will see air transfer is the most common method available, everything from your car’s radiator to the heat sinks in your amplifiers use this approach, the air carries away the heat energy.


One of the key things in both of these examples is surface area.  Both are designed to maximize surface area using fins.  They also both use conduction or radiation to carry heat to the fins.

One of the things that reduces the effectiveness of air cooling on loudspeakers is the fact that voice coil surface area is so small.  Some have used conductive formers and other things in an attempt to improve this, but the surface area still remains small.  Cooling vents are certainly worth using, but the fact remains that the relatively small surface area of the voice coil limits the amount of heat that can be removed.  That's why I've suggested that air cooling be augmented by other cooling mechanisms.

Tom Danley wrote on Wed, 11 October 2006 16:30

A typical V-8 car radiator can dump about 50KW of heat and its not that big, it just takes airflow.


Actually, the radiator is huge in terms of surface area.  The whole structure is designed to maximize surface area.

Tom Danley wrote on Wed, 11 October 2006 16:30

Look at the link below which shows the effect of forced air cooling on a DC servomotor.  This motor is similar to that used in a Servodrive and has stationary magnets with a rotating hollow wire armature (very similar to a Voice coil). These motors only have a cooling air path on the outside of the armature where the air path in my cooling Patent is on both the inside and outside of the VC.


Forced air cooling makes sense in a loudspeaker with a motor that is isolated from the diaphragm.  As long as the motor is pneumatically sealed so the pressure from the forced air lines doesn't offset the cone, that's fine.  But in a speaker with a voice coil, the cone is in the same area as the gap.  Unless the speaker is designed with some kind of seal, whatever pressure is placed on the gap is also placed on the cone.  Whether this pressure is positive or negative, on the front or the back, there is still a pressure and that causes offset.

Patents filed after yours have addressed this problem.
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Wayne Parham
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Tom Danley

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Re: Cooling fan (Patent 4757547)
« Reply #26 on: October 15, 2006, 12:17:59 pm »

Hi Wayne

When I came up with this idea, some 20 years ago now, Intersonics had allowed me to pursue the Servodrive woofer concept but for most of the time I was specifically prohibited from using “conventional” drivers in any design.  
Keep in mind they were a NASA flight hardware contractor, not a speaker company, my real job was working on that stuff much of the time..
They did license the technology to a company in Canada who’s principal in now head of R&D at Harmon Motive.  Also, they did talk to several big companies about licensing but the high license fee and rate the owner asked for stopped that.
I did however build a couple conventional drivers using this and the company that licensed it sold a number of products using it.

I suppose you would have had to have been there to see the setup / measured results to see how effective it is.

You say “They also both use conduction or radiation to carry heat to the fins.”
Actually radiation is not a significant part of transferring heat from either a transistor or engine block to the radiator, it is conduction.  Even amplifier heatsink convection is a conduction driven mechanism, when the air in contact is heated, it rises.

You say “One of the things that reduces the effectiveness of air cooling on loudspeakers is the fact that voice coil surface area is so small. Some have used conductive formers and other things in an attempt to improve this, but the surface area still remains small. Cooling vents are certainly worth using, but the fact remains that the relatively small surface area of the voice coil limits the amount of heat that can be removed. That's why I've suggested that air cooling be augmented by other cooling mechanisms”

Your still missing a major concept here.
Consider your surface area argument and then consider that the motor that I linked has less exposed area than one could have with a modest sized VC.  Even so, a vary large increase of heat capacity is demonstrated in its measurements via passing air directly across the hot conductors.
Like the loudspeaker, the problem is not cooling off the case but cooling off the part producing heat which is much much hotter.   

You keep dwelling on cone offset, perhaps your also missing part of the concept here.
Off set force is equal to area times pressure.
Lets say you had a peak pressure of  2 inches H2O, (this is also a pressure of .074 PSIG).
This pressure if applied as I had shown in the Patent, is applied at the VC pocket.
Lets say you had a 2.5 inch ID VC with a 2.3in ID which yields a piston area of  .753 sq/in on which that pressure is applied.
This results in a peak off set force of  about  25 Gms which to put in perspective for a LAB-12, is about 1/6 the offset force on the system “IF” it were simply mounted facing up or down.
As you can see from the shape of the thermal resistance graph for the DC Servomotor, the most rapid increase in PHC happens when you start moving the air not at its highest flows.

You say “Patents filed after yours have addressed this problem.”
So far as I know, we (Intersonics inc) were the first company to “eliminate” power compression,  when I presented my AES paper on “eliminating power compression”,  Doug B from JBL presented right after one of the first papers to acknowledge its existence.
Later Patents may mention this first one seeing “problems” but I am not away of any of these other approaches resulting in reduction in power compression this one delivered on the Servodrives or in the VC versions Bond Acoustics sold back then.
You can bet you will see the idea of directly cooling the vc with forced air again, it works.

Tom Danley

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Kerry Stansbury

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Re: Cooling fan (Patent 4757547)
« Reply #27 on: October 15, 2006, 12:32:18 pm »

Tom's design is a start, but forcing air into the pole vent will always cause pressurization against the dust cap and effect the speakers performance. Also, there is no positive air exchange on the voice coil itself, only on the inside of the former. The voice coil will have air pumped back and forth through it, but some of the air will be hot air trapped between the voice coil and the spider. there will be some air drawn away by the fan at the bottom of the voice coil, but I feel it would not be that much of an improvement considering the downside of pressurization.
On the other hand, If you have vents like those that go directly to the voice coil gap, a pole vent and vents around the spider (Like those in "18 Sound" loudspeakers design) You could filter and force air through the gap vents, it would pass directly by the voice coil and the inside of the voice coil former, providing maximum air exchange. The air would the exit the pole vent and the spider vents causing no pressurization as long as you didn't try to pump to much air through.
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Rolling Thunder

Tom Danley

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Re: Cooling fan (Patent 4757547)
« Reply #28 on: October 15, 2006, 02:55:39 pm »

Hi Kerry

Look again at the drawing, the air connection is at the rear VC pocket, NOT the center pole vent.
In most speakers, one has to drill to this spot (as in the ancient photo earlier in this thread).
If a vacuum is used, then the air path is “in” the center pole vent AND through the spider, into the magnetic gap on the inside and outside. The air flows between the iron and the copper wire on the outside and the iron and former on the inside, then, out the back.

There is no resultant air pressure on the dust cap or cone, the only net force on the system is caused by the cooling pressure and end area of the VC (OD area – ID area).
Some drivers now are made with a vent to this location, like some B&C drivers but the ones I have seen also have a matching set of holes on the front plate.
These defeat the idea when a fan is used as the front holes give a much easier air flow path which doesn’t involve scrubbing up against the hot VC in the gap.
To reach the same gap pressure with these vents, a much larger fan would be needed.

Lastly, one other advantage of the fan system is that its pressure is related to input Voltage where an excursion based (self cooling) system, one finds where heating is greatest, the motion is often least.
Best,

Tom Danley
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Mike {AB} Butler

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Re: Cooling fan (Patent 4757547)
« Reply #29 on: October 16, 2006, 11:07:51 am »

Alright Tom I see the ILP/Gladstone module (hehe)  Very Happy  What was that doing as part of the testbed? (John H., feel free to chime in..)
I used Gladstone modules and different amps for all sorts of testbeds. They were fine when they worked.. but could fail spectacularly..
Cool to see some early years photos.. I wished I had a few of our first servo'd sub developments in 1980..
Regards,
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Mike Butler,
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