Crazy idea for a powered sub

[John Roberts]

Re: Crazy idea for a powered sub

It would be cool if you could find a way to make the port air supplement the fan cooling.

Already done, AFAIK Jon Risch (at Peavey) got a patent for that years ago... You need to give two ports slightly asymmetrical resistance to airflow in opposite directions, so the natural AC air movement in the ports gets rectified (so to speak) and turns into DC overall flow in one and out the other.

You can do this a little more simply by mounting one port low and the other high to take advantage of natural convection.

FWIW lots of smart folks have been thinking about such things for a while now, but keep thinking, it's good exercise for the gray muscle, and surely there are more ideas out there yet to be discovered, and the best ones are painfully simple, after you figure them out.

JR

 

[Tim Duffin]

Re: Crazy idea for a powered sub

Already done, AFAIK Jon Risch (at Peavey) got a patent for that years ago... You need to give two ports slightly asymmetrical resistance to airflow in opposite directions, so the natural AC air movement in the ports gets rectified (so to speak) and turns into DC overall flow in one and out the other.

You can do this a little more simply by mounting one port low and the other high to take advantage of natural convection.

FWIW lots of smart folks have been thinking about such things for a while now, but keep thinking, it's good exercise for the gray muscle, and surely there are more ideas out there yet to be discovered, and the best ones are painfully simple, after you figure them out.

JR

Was that patent then sold to JBL in the 90's? The technique of designing a port to be both a port and an effective active heat sink has been used on the Eon since its inception. I don't recall any peavey powered products using the technology.

 

[John Roberts]

Re: Crazy idea for a powered sub

Was that patent then sold to JBL in the 90's? The technique of designing a port to be both a port and an effective active heat sink has been used on the Eon since its inception. I don't recall any peavey powered products using the technology.

You made me look this up...

Hard to sell a patent to JBL in the '90s since it only issued in 2003, but I can't imagine Peavey selling a patent to a competitor like that.
Patent US6549637 - Loudspeaker with differential flow vent means - Google Patents

I am not a speaker expert like some here (?), but I suspect there is a whole wing of the patent office dedicated to variants on cooling loudspeakers with their own activity. AFAIK Jon's idea was unique, at least it seemed new to me at the time.

I did find 2 design patents for a JBL EON issued to Harmon in 2009/10 but as you surely know design patents are for look and shape, Jon's patent is a utility patent for a device or mechanism that performs a novel function.
Patent USD609214 - Loudspeaker - Google Patents
Patent USD595694 - Loudspeaker front face - Google Patents

I couldn't find any protected technology in the JBL eon but I am not an expert on JBL. My recollection from back when they were new, was that they did some different mechanical arrangement of amplifier heatsink and speaker driver superstructure that made reconing or replacing drivers a hassle, but again all second hand info, I never got very close to one.

JR

 

[Tim Weaver]

Re: Crazy idea for a powered sub

AFAIK, the eons just put heat sinks in the port area that would be cooled by the turbulent air. In this case it doesn't matter which way the air flows, as long as it flows. The Peavey device used a trick port setup that created one-way airflow by using 2 different tuned ports, each flowing one way. This allowed the heat to be "carried away" from the speaker (or amp). The way Jon did that was by having little vanes in the port that were more aerodynamic in one direction vs the other. Kind of like the barb on a fish hook. It goes in, but it won't come out.

 

[John Roberts]

Re: Crazy idea for a powered sub

AFAIK, the eons just put heat sinks in the port area that would be cooled by the turbulent air. In this case it doesn't matter which way the air flows, as long as it flows. The Peavey device used a trick port setup that created one-way airflow by using 2 different tuned ports, each flowing one way. This allowed the heat to be "carried away" from the speaker (or amp). The way Jon did that was by having little vanes in the port that were more aerodynamic in one direction vs the other. Kind of like the barb on a fish hook. It goes in, but it won't come out.

While I'm not a speaker expert, I know a little about heat sinks, and wiggling the same air back and forth is not the same as simple air flow. It does lower the thermal resistance from heat sink that nearby ambient air from the extra repeat collisions with the same air molecules, and presumably increases the effective heat sink length by the period of the air volume's wave motion back and forth. So definitely something. If the wavelength of the moving air is long relative to the heatsink distance from the port mouth, it could involve cooler outside air that would turn over, so that could work a little better yet.


JR

 

[Gene Hardage]

Re: Crazy idea for a powered sub

I'm surprised that vibration has not been mentioned by anyone yet. It's well known amongst bass players that bass amps last longer when placed on a piece of foam. That 21 is gonna beat the snot out of your amp. It will rattle it apart way ahead of schedule.

 

[Ivan Beaver]

Re: Crazy idea for a powered sub

I'm surprised that vibration has not been mentioned by anyone yet. It's well known amongst bass players that bass amps last longer when placed on a piece of foam. That 21 is gonna beat the snot out of your amp. It will rattle it apart way ahead of schedule.

With the Danley JH90-origionally it was going to be self powered. But it didn't take long before the internal pressures actually started cracking the circuit boards in the amps. So that idea was ditched.

We do have a dealer in Europe who is running his JH90's with custom "piggy back" amps that hang off the back (with foam isolators to damp the vibration) and they work well for him.

The powered stuff works to a point-but when the physical demands get extreme-"other" things start to happen.

So as usual "it depends".

 

[John Roberts]

Re: Crazy idea for a powered sub

With the Danley JH90-origionally it was going to be self powered. But it didn't take long before the internal pressures actually started cracking the circuit boards in the amps. So that idea was ditched.

We do have a dealer in Europe who is running his JH90's with custom "piggy back" amps that hang off the back (with foam isolators to damp the vibration) and they work well for him.

The powered stuff works to a point-but when the physical demands get extreme-"other" things start to happen.

So as usual "it depends".

Since they manage to put circuit boards on rockets and send them into space, I suspect that vibration is manageable, with adequate accommodation. I doubt "internal pressure" alone would impact FR4 while a span of PCB with massive components, insufficiently secured and allowed to flex sympathetically with sound vibrations could fatigue and fail over time.

This is not a new concept for designers. Regarding bass guitar amps, years ago when we did a reliability review (at my old day job) of all products in the context of extending our warranty, I don't recall the instrument amps having any higher or lower historical failure experience. Over decades in a given business the design engineers learn from failures and adjust their design practices to deliver required reliability. It is no secret that the orientation and mounting of tubes inside tube amps accounts for sonic interaction. This used to be much worse in the bad really old days. I have the remains of an old Western Electric (32C?) amp, that had the gain stage tubes mounted inside a sealed padded compartment and balanced on a knife edge, actually two needle screw points. This was all of a 10W or so amp, but that was a bunch of power for the time.

Powered boxes are actually a pretty mature technology, while extending the frequency range lower, and output level louder will increase the forces acting on the components. For active electronics SMD is more robust than old TH technology and more tolerant of vibration stresses. Relatively massive passive crossover components have always been an issue about securing reliably and accounting for unintended resonances with how the PCBs are secured.

JR

PS I don't doubt that Ivan experienced problems, only that such issues should be manageable in dedicated designs. I can imagine it not being worth the trouble to pursue for low-modest volumes.

 

[Tim Weaver]

Re: Crazy idea for a powered sub

The amp in my design will be in a separate chamber that will not be pressurized by the driver. There will be vibrations, but I don't see how the vibrations involved could be an order of magnitude worse than in an amp sitting in a rack 12 inches away from the same sub. We do that every day when using amp racks.

I know of a couple of companies that set small amp racks between subs and the tops. Those amps have been working fine for years. In fact, QSC has said that placing amps on top of the subs would be fine and not void any warranties.

 

[kristianjohnsen]

Re: Crazy idea for a powered sub

While I'm not a speaker expert, I know a little about heat sinks, and wiggling the same air back and forth is not the same as simple air flow. It does lower the thermal resistance from heat sink that nearby ambient air from the extra repeat collisions with the same air molecules, and presumably increases the effective heat sink length by the period of the air volume's wave motion back and forth. So definitely something. If the wavelength of the moving air is long relative to the heatsink distance from the port mouth, it could involve cooler outside air that would turn over, so that could work a little better yet.

JR

Wouldn't the hot air have a tendency to rise every time it has exited the speaker, and then be replaced by cooler air from below the port when blow turns to suck?

 

[John Roberts]

Re: Crazy idea for a powered sub

Wouldn't the hot air have a tendency to rise every time it has exited the speaker, and then be replaced by cooler air from below the port when blow turns to suck?

Yes, I hinted at that, but that depends on where the heat sink and localized hot air is relative to the port mouth and cooler free air, and amount of displacement. Clearly any hot air that goes fully outside the cabinet will diffuse and mix with cooler ambient air. The coherence of this volume of port air is not expected to maintain much past the port mouth.

My judgement is that this does not automatically deliver a high percentage of air turnover, but any turnover with outside air is useful.

JR

 

[kristianjohnsen]

Re: Crazy idea for a powered sub

Yes, I hinted at that, but that depends on where the heat sink and localized hot air is relative to the port mouth and cooler free air, and amount of displacement. Clearly any hot air that goes fully outside the cabinet will diffuse and mix with cooler ambient air. The coherence of this volume of port air is not expected to maintain much past the port mouth.

My judgement is that this does not automatically deliver a high percentage of air turnover, but any turnover with outside air is useful.

JR

I suppose that the presence of a back hole through many woofer magnets supports this observation also.