Subwoofer Amplifier cooling..A concern (1 Viewer)

[Richard_s]

Don't know if this is a real concern just thought I would pass on an observation.



I had a SA-WM40 Sony subwoofer that I returned. I did the Polyfill tweak and yes it did tighten the bass quite a bit as well as got a few more Hz at the low end. great subwoofer for the money just did not seem to have enough power fro my large room.



I now have a PB12 and along the way it was recommended that this too might want to be polyfilled. I find that the PB12 at least for me is very quick, goes low enough and is tight so I am not planning to polyfill.



Here is my concern don't know if it is a real issue just passing my thoughts on. This may be true for any subwoofer of similar construction. I am worried about potential overheating (or reduced life) of the amplifier in the PB12. The SA-WM40 has its amplifier vented with louvers on the back of the unit so polyfill would have little or no efect on the ability of the amplifier to cool itself. The PB12 has the amplifier totally inside the case and it appears to me that this design uses the heat dissipation to the inside of the unit to cool itself and the rear port just helps the cooling. If this design was polyfilled it might cause the amplifier to run too hot[/b}



Just an unsubstantialed but possible concern I wanted to pass on.

 

[Harold_C]

The port isn't going to do diddly to cool an amplfier as there is little or no actual exchange of air from a port.

If the amp is totally enclosed by the subwoofer cabinet, it must be a very high efficiency switching amplifier or it will overheat and blow up. High efficiency switching amps are inexpensive and generate very little heat.

 

[Phil Iturralde]

Harold_C is on target, read JBL'S NEW POWERBASS™ SERIES SUBWOOFERS DELIVER OUTSTANDING BASS PERFORMANCE AND VALUE IN HOME-THEATER AND MUSIC SYSTEMS (partial quote)

The PB12 and PB10 both utilize JBL's exclusive Class-D digital-amplifier technology, which operates in Class-D mode and uses digital-switching amplifier technology for exceptionally high power output with high efficiency and dramatically reduced distortion, even when reproducing no-holds-barred action-movie soundtracks at high-volume listening levels.

Phil

 

[John Garcia]

Both the PB10 and PB12 have previously been noted for amplifier failures. I have a friend who had this happen roughly 6 months after getting his PB10. JBL claims to have solved this issue, which likely does not have to do with cooling, but rather quality control or bad components in the amp assemblies. If you stuff the sub and it fails, you will not be able to claim "normal operation" for warranty.

With the Sony, you are loosing a bit of efficiency by stuffing it, meaning more power would be required to drive it to the same level.

 

[Richard_s]

John:

Yes the Sony output was reduced by 4db when I polyfilled it. I unstuffed it before I returned it.

If you have a problem with the JBL and need service I would just pull out the stuffing. I did not glue or staple the stuffing into the Sony and that appeared to work. I bought a polyfill at walmart that seemed to hold together real well. When stuffed in it seemed to hold in place real well (not sure if it would have worked loose over time though but it was held in place quite well). They had a different polyfill that was slick "teflon" like feel that stuff would not hold in place.

On the heat dissipation issue I don't disagree its just that the design may be such that the amplifier still needs a path to cool. The nice thing about Class D amplifiers vs. AB type is that they are up to 80% efficient but this is at full power. At lower powers their efficiency falls off. Like you say maybe its not an issue.