Air Exchange rate and subwoofer enclosures (for cooling purposes) - diyAudio
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Old 14th March 2013, 02:39 AM   #1
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Default Air Exchange rate and subwoofer enclosures (for cooling purposes)

Tapped horns have the advantage on cooling here, where the magnets of the drivers are right at the exit, closest to ambient air, correct?

In a ported box, at high output, near the drivers Xmax, does the air inside the enclosure actually "exchange"? Or is the air just being pushed in and out of a port, but not bringing fresh air into the enclosure?

Sealed boxes obviously are at a disadvantage here. But does that hold true for a horn where the motor of the driver is in an enclosed chamber? I'm guessing it does as well. Maybe not as much as a sealed enclosure because Xmax will be less and SPL will be greater for a given input voltage, so energy wasted as heat would be less in a horn. M

And that brings me to this: how many drivers fail thermally due to improper cooling as opposed to over excursion / physical damage?

Once power compression occurs, and amps are pushed harder, the drivers voice coil continues to heat up...for a subwoofer without cooling near the motor, this does not seem like a good time!

Last edited by m R g S r; 14th March 2013 at 03:50 AM.
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Old 14th March 2013, 03:35 AM   #2
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I'd say correct on all counts. The 12π sub uses special cooling plug and plate. Shame most big companies don't care about cooling, but they can sell replacement drivers easily that way
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Old 14th March 2013, 07:39 AM   #3
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Re: sealed enclosures... invert the driver.
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Old 14th March 2013, 06:20 PM   #4
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If you made a plug like Wayne has on the Pi sub, I wonder if you could use some heat transfer pipes like modern CPU coolers do? They have vacuum/fluid filled copper pipes. You could have them brazed to a plug, then run to panels for air cooling outside cabinet.
Wayne's plug and heatsink idea works perfect, as the woofer is close to the back wall...
Not sure how this would work on a larger enclosure.
It would work on a PPSL for one of the drivers, as the woofer magnet can be close to a side wall, and the heat sink would make a nice access panel for the woofer...
There was a trend many years ago of water cooled subwoofers. I think bazooka may still make them.
I guess no one really liked the idea, so it never took off like watercooling of computers.
I know Cerwin Vega has cooling panels on the front of some of their subs, but I don't know how the heat sink is attached to the woofer/voicecoil...
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Old 14th March 2013, 09:12 PM   #5
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Quote:
Originally Posted by m R g S r View Post
1)Tapped horns have the advantage on cooling here, where the magnets of the drivers are right at the exit, closest to ambient air, correct?

2)In a ported box, at high output, near the drivers Xmax, does the air inside the enclosure actually "exchange"? Or is the air just being pushed in and out of a port, but not bringing fresh air into the enclosure?

3)Sealed boxes obviously are at a disadvantage here. But does that hold true for a horn where the motor of the driver is in an enclosed chamber?

4)And that brings me to this: how many drivers fail thermally due to improper cooling as opposed to over excursion / physical damage?
1) Yes.

2) There is usually some net air exchange due to the port and the driver suspension being non-linear.
Since heat rises, having ports on the upper portion of an enclosure is a definite advantage in heat exchange.

3) Yes and yes, the reason Wayne made a metal heat exchanger to get the heat of the Lab 12 out of the box.
However, different drivers do not exchange heat at the same rate. When testing a pair of Lab 12s in a TH, the pair heat up far more with about 1/4" the power per driver than the B&C 18SW115.
The B&C vent effectively removes most of the heat from the voice coil, while the Lab 12 seemed to be conducting most of the heat to the magnet assembly, leaving the voice coil to cook.
From Wayne's claim of double the power handling using his heat exchanger, using the heat exchanger would still be less effective than the B&C cooling.
I have always put the vent side of Lab 12s on the throat side of FLH to allow the magnet and vent some access to outside air.

4) If proper HP filters are used, the majority of driver failures are thermal.
That said, high compression ratios used in horns put far more pressure on the cone when reaching X max than a BR, the ratio of mechanical failure to thermal is higher when lightweight cones are put in TH than BR.

Art
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Old 14th March 2013, 11:00 PM   #6
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You might be interested in this also.

Quote:
In the Volt Radial, the chassis is fixed to the magnet centre pole and doubles as a giant heat sink. It is mounted on the surface of the enclosure and is thus always ventilated, an effect augmented by the movement of the cone. The magnet benefits from conduction cooling as well, and may also be rear vented to add to the overall benefit. This system typically runs at half temperature, power for power of conventional loudspeakers. Put another way, a conventional speaker starting a session at the same output as a Volt Radial may sound only half as loud at the end. And we have the figures to prove it!

http://www.voltloudspeakers.co.uk/About_Us/about_us.htm
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Old 15th March 2013, 03:56 PM   #7
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Hmmm..
This brings up an idea.
I work in an R&D lab (Heat Engines) and have to instrument everything.
It is just in my blood after so many years.
I am going to assemble a sub using a Lab 12 driver this weekend.
.
If I put a thermocouple on the speaker, what location might yield the best information.
I could put an unshielded bead thermocouple right in the cooling vent path and measure the temperature of the cooling air flow.
Or, I could attach a thermocouple to the motor structure.
.
Any opinions?
I would imagine that manufacturers have done this many times.
.
This exercise may not prove much, but I am just curious.

Thanks,
Dave
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Old 15th March 2013, 04:55 PM   #8
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Quote:
Originally Posted by Shadydave View Post
If I put a thermocouple on the speaker, what location might yield the best information.
I could put an unshielded bead thermocouple right in the cooling vent path and measure the temperature of the cooling air flow.
Or, I could attach a thermocouple to the motor structure.
Dave,

The point of most interest is the voice coil temperature, unfortunately neither the magnet structure or the vent are very indicative of the actual voice coil temperature.
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Old 15th March 2013, 04:59 PM   #9
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Quote:
Originally Posted by Zero D View Post
You might be interested in this also.

l
"Put another way, a conventional speaker starting a session at the same output as a Volt Radial may sound only half as loud at the end. And we have the figures to prove it!"
Link didn't work, but to sound "half as loud" would require thermal compression of 10 dB, you would have to search for really poor drivers to find that much thermal compression.
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Old 17th March 2013, 01:26 AM   #10
Zero D is offline Zero D  United Kingdom
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@ weltersys

Not sure why the link didn't work ? As i just C/P'd the page i was viewing, which was fine. But you found it
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