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Author Topic: Is the 12pi Subwoofer an upgrade to the LAB?  (Read 24242 times)

Ivan Beaver

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #30 on: July 13, 2006, 07:57:53 pm »

Wayne Parham wrote on Thu, 13 July 2006 14:24


 Bass is bass, and power is power.  

Power is usually expressed in continuous numbers-ie sine waves.  Music is very dynamic, without the continuous nature of sine waves.

I have no doubt that the cooling exchanger will help with long term power (assuming it is able to dissapate it into the air), but we are talking about music.

I would like to see multiple failure tests conducted (differences between drivers issue) with the EXACT same musical signal applied to each (with and without exchanger) as see what the differences are.  Sine wave tests don't impress me,, unless you consider that music?
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

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dB Audio & Video Inc.
Danley Sound Labs

Pascal Pincosy

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #31 on: July 13, 2006, 08:10:45 pm »

I have never even heard a LABsub at full volume, and I certainly have zero experience with Wayne's heat exchanger. I'm also annoyed by Wayne's claiming that his heat exchanger is the cure-all for problems with LABsubs, especially when that problem is obviously overexcursion of the drivers and has nothing to do with heat buildup. Come on Wayne, please! You are repeatedly spamming the board with your product and it's out of line.

However I have plenty of experience blowing up sub drivers  Rolling Eyes . And I can say with certainty that long-term thermal buildup is a killer. Run your subs for 8 hours straight with a compressed signal well above RMS and you will slowly roast voice coils. The heat created by the motor has to go somewhere. In a sealed chamber there's no where for the heat to go. That's why open-basket designs like the Bassmaxx subs and Danley's tapped horns can provide better long-term performance. The heat is being wicked away by the surrounding air instead of being contained in an insulated chamber. I see no reason why Wayne's heat exchanger wouldn't do the same thing ie wick heat away from the motor.

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Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #32 on: July 14, 2006, 01:19:04 am »


Actually, all music is composed of sine waves.  The test signal I used is pretty similar to what a loudspeaker is subjected to during a live performance, in fact, it wasn't as brutal because it had several cooldown periods, not a constant signal.  Use whatever test signal you want, the device with a heat exchanger still vastly outperforms one without.
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Wayne Parham
π Speakers
PiSpeakers.com

Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #33 on: July 14, 2006, 01:33:38 am »


I'm about sick of being accused of "spamming" when what I've done is to provide my engineering skills, my mechanical engineer's skills, my test results, my designs and photographs of the build-up process free of charge.  What I've done is to provide freely available plans for a high performance basshorn, and to mention that here.  I've responded to people that have asked about 12Pi basshorns.  And I've given LABhorn owners information about a compatible part they can make and install on their horns to improve them.  If that's disagreable spamming, then what in the world is this forum even here for?

By the way, the problem isn't heat build-up in the rear chamber.  It's heat build-up in the motor, radiated into the pole piece and stored in the ceramic and metal.  Open back designs suffer too, because the heat build-up is in the motor.  You have to wick the heat out of the motor.  Perhaps you'll consider this information "spamming" or maybe you'll dismiss it as being unsupported, in which case I encourage you to duplicate my work, test my claims and see for yourself.  Or don't, whatever.
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Wayne Parham
π Speakers
PiSpeakers.com

Andy Peters

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #34 on: July 14, 2006, 03:02:38 am »

Wayne Parham wrote on Thu, 13 July 2006 22:19

Actually, all music is composed of sine waves.


Techno is primarily sine waves, and since I don't do drugs, I find it boring.  Desperately dull.  Ugh.

Seriously, though, many of us understand Fourier transforms.  I think that Ivan's point is that there's a difference between running a 75 Hz pure tone into a sub cabinet at crush and running the kick drum and bass-E-string-every-quarter-note.  The duty cycle differs, for one, and I'm sure you know that.

Quote:

The test signal I used is pretty similar to what a loudspeaker is subjected to during a live performance, in fact, it wasn't as brutal because it had several cooldown periods, not a constant signal.  Use whatever test signal you want, the device with a heat exchanger still vastly outperforms one without.


Now I'll put on my engineer's hat.  Have you measured the heat-transfer efficiency of your heat sink and of the whole system?  Seems to me that there will be a positive effect through the conduction cooling, but you're still heating the inside of the cabinet (esp. if the cabinet is stuffed with insulation), limiting overall heat-transfer efficiency.  I suspect that there's little, if any, convection (other than the cone moving), so in practical terms, the benefit may not be all that great.   The only way to know for sure is to instrument the motor structure, the heat sink and a couple of locations inside the cabinet.  A handful of thermocouples or RTDs and an Omega logger will do the trick.

And along those lines, can you quantify the statement, "the device with a heat exchanger still vastly outperforms one without"?  I'd like to know what your test set-up is like, and I'm sure that others may wish to duplicate your results.

Perhaps the motor heatsink is like those metal things you can buy for your computer memory.  Yeah, they're heat sinks, but moving the heat a sixteenth of an inch from the chips makes little difference if you don't remove the heat from the heatsink.  These things are little more than a placebo.

-a
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Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #35 on: July 14, 2006, 03:28:07 am »


Read the posts that show the heat exchanger construction.  It is described in great detail, enough that you can build one and install it.  Also shown are test results, conditons, setup, etc.

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Wayne Parham
π Speakers
PiSpeakers.com

Matt Jordan

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #36 on: July 14, 2006, 05:24:40 am »

 Confused This place used to be fun. Get off your high horse and bake me a nice meatloaf. We are all in this together. Remember?
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Matt Jordan
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John Roberts {JR}

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #37 on: July 14, 2006, 10:16:44 am »

Andy Peters wrote on Fri, 14 July 2006 02:02



Now I'll put on my engineer's hat.  Have you measured the heat-transfer efficiency of your heat sink and of the whole system?  Seems to me that there will be a positive effect through the conduction cooling, but you're still heating the inside of the cabinet (esp. if the cabinet is stuffed with insulation), limiting overall heat-transfer efficiency.  I suspect that there's little, if any, convection (other than the cone moving), so in practical terms, the benefit may not be all that great.   The only way to know for sure is to instrument the motor structure, the heat sink and a couple of locations inside the cabinet.  A handful of thermocouples or RTDs and an Omega logger will do the trick.

And along those lines, can you quantify the statement, "the device with a heat exchanger still vastly outperforms one without"?  I'd like to know what your test set-up is like, and I'm sure that others may wish to duplicate your results.

Perhaps the motor heatsink is like those metal things you can buy for your computer memory.  Yeah, they're heat sinks, but moving the heat a sixteenth of an inch from the chips makes little difference if you don't remove the heat from the heatsink.  These things are little more than a placebo.

-a


Is an engineers hat that floppy little job worn by the guy driving the train?

OK back on topic. You can measure the rise in VC temp non-invasively. Copper has a pretty well established temperature coefficient, so by comparing the cold or room temp VC resistance to hot VC resistance you can impute how hot the VC is or isn't getting. This mechanism could even be used in smart powered speakers to detect and manage power compression.

Getting heat out of VC is a classic problem and there are lots of patents covering sundry approaches. You are quite correct that a major problem is getting the heat out of the box. Hi/lo ports allow for some natural convection and asymmetrical ports that bias airflow direction could pump cool air though a box. Any number of approaches help to some degree, and some can compliment each other. None AFAIK is a magic bullet.

There has also been much work done to make VC adhesives and materials more tolerant of extreme temperatures but this doesn't mitigate the power compression caused by the resistance rise.  

JR  
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Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #38 on: July 14, 2006, 12:19:44 pm »

My first prototype used a venting system as you've described.  The diaphragm motion was ducted into two ports, each that introduced turbulent flow in one direction but allowed laminar flow in the other.  My thought was to duct heated air out through a heat exchanger, returning cool air into the system.  Unidirectional flow was required so that a hot air slug didn't move back and forth along the duct.


The venting arrangement worked extremely well for introducing unidirectional flow.  The real problem was that even with motor temperatures well above 150
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Wayne Parham
π Speakers
PiSpeakers.com

Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #39 on: July 16, 2006, 01:04:26 am »

http://audioroundtable.com/images/Laughing_Felix.gif
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Wayne Parham
π Speakers
PiSpeakers.com

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