I've got a pair of 15-inch PhaseTech Octave 1.0 (240watt) subs that "sound GREAT" during typical Home Theater playback . Each performs @ 105db @ 25Hz and I have measured 109db using both in parallel which (needless to say provides "butt-thumping" effects to those action scenes) but the issue I am experiencing is that these "sometimes" generate that tragic low level "Huuuuummmmmmm" when left in normal playing positions.

It's not in the cone itself but rather appears to be in either the Amp or the cross-over controls on the rear or the unit. This can occur during a quite scene of a movie which is irritating. Notes that these are equipped with the "auto-cutoff" that is 'suppose" to shut them down when not in use. Please note that this "condition" has been going on for 4 to 5 years so unless the amps are already "dead", I don't think this is a "dying condition" (but I may be simply too ignorant in this area to know this).

Right now my (temporary) fix is to "fiddle with the cross-over settings until the hum goes away (turning it back up slowly and stopping "just before" the hum returns or turning them comletely off then back on again (and this doesn't always work either).

I would like to understand what (exactly) is going on and also understand if this is some basic "pot" issue that could be resolve by simply replacing the dial-style cross-over and/or gain switch or if it might require a more extensive "Amplifier appendectomy". I've thought about taking these to one of the "speaker doctors" but they want $100 just to look at them and to be honest, I'd rather just fix them myself (if I can).

Since they work "most of the time" (i.e. are OK for kids movies and decent for adult movies), I am not really that interested in playing someone a lot (i.e. $100 to look at them + another $200 for an new amp...) to fix them but rather am looking to understand what I can do (myself) to address the issue. In the past I have replaced amps (in college) in speakers in the past and use to build the Heathkit stuff so soldering and using an Ohm meter is no problem.

What do you guys think I can do to figure out how to "stop the hummmmm"?

Are the subs powered from different outlets than the rest of your equipment?

There could be some difference in the grounding levels - that might explain the hum.

Audioquest has some specialized subwoofer cables with the grounding lugs as part of the cable assembly.

You may want to try disconnecting one of the subs and only use one with one of these interconnects.

Just a thought...

Are the subs powered from different outlets than the rest of your equipment?

There could be some difference in the grounding levels - that might explain the hum.

Audioquest has some specialized subwoofer cables with the grounding lugs as part of the cable assembly.

You may want to try disconnecting one of the subs and only use one with one of these interconnects.

Just a thought...

Thanks for the quick reply. Yes, I currently run only one sub at any one time until I get this issue worked out. Yes, each has an isolated power connection (separate circuits). One is at one end of the room (opposite all gear and phase-controlled to match the other) and one is near the rack-mounted audio gear which is actually terminated in a separate closet adjacent to the HT room and has it's own dedicated circuits.

As an FYI - I have stacked these subs one atop another and connected them to a common circuit as well as connected them to the same circuit the rest of the gear is connected to with no effective change so I really do think it's an internal amp/cross-over/pots issue. I may "give in" and just take one into the Speaker doctor but would be interested in any online troubleshooting guides I could reference to troubleshoot a speaker like this. Anyone know of anything like this online?

If I do replace anything, I figure I would also need to get a similar control capable of the same 24db slope function this currently uses. PS - I also have direct access to a local "components' store than has stuff like this (I use to work there about 20 years ago).

Thanks for the quick reply. Yes, I currently run only one sub at any one time until I get this issue worked out. Yes, each has an isolated power connection (separate circuits). One is at one end of the room (opposite all gear and phase-controlled to match the other) and one is near the rack-mounted audio gear which is actually terminated in a separate closet adjacent to the HT room and has it's own dedicated circuits.

As an FYI - I have stacked these subs one atop another and connected them to a common circuit as well as connected them to the same circuit the rest of the gear is connected to with no effective change so I really do think it's an internal amp/cross-over/pots issue. I may "give in" and just take one into the Speaker doctor but would be interested in any online troubleshooting guides I could reference to troubleshoot a speaker like this. Anyone know of anything like this online?

If I do replace anything, I figure I would also need to get a similar control capable of the same 24db slope function this currently uses. PS - I also have direct access to a local "components' store than has stuff like this (I use to work there about 20 years ago).

You may be right...if they hum with nothing connected to them (except for power, of course) then it is probably internal.

http://www.avsforum.com/avs-vb/showthread.php?t=322698

Craig

Craig - Thanks for the Hum link. After going back to the systems and doing these test I appear to have two separate issues. One of the systems does appear to be experiencing some type of grounding loop (as it ONLY hums when connected to the receiver) however the other hums irregardless of any connections.

Update - Connected the sub's power and the Receiver's power to the same circuit via an Triplite Isobar. 99.5% of the hum is now gone. This required me running the Sub's power cable through the component rack in order to get into the other room but at least I know that this resolves that issue. Thanks.