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[BrianWalther]

Got issue I haven't been able to find the answer for:

I'm running 2 cabs each with one 15" Peavey Black Window 8Ω speaker Max Power: 1,000 watts program.

The Spec sheet for the power amp I have states:
Stereo Mode:                         Continuous Average Output Power Per Channel
8Ω EIA 1kHz 0.1%THD           280W
4Ω EIA 1kHz 0.1%THD           450W

Bridge Mono Mode                 Continuous Average Output Power
8Ω EIA 1kHz 0.1%THD           900W


The Bridge Mode section of the manual for the poweramp states:
This mode is for those who need high level output. It combines the power of both channels to produce the maximum amount of power the unit can handle. Make sure your speaker can handle higher wattage this mode offers. Remember, the minimum impedance requirement is 4 ohm.

My question is...  Can I safely run the two 8Ω cabinets in parallel and draw a 4Ω load from the amp in bridge mode even though the spec sheet doesn't mention 4Ω loads on the spec sheet but does say in the manual that minimum impedance requirement is 4Ω?

Any help would be greatly appreciated.

[Mal Brown]

Call the amp vendor...

[Tim McCulloch]

Got issue I haven't been able to find the answer for:

I'm running 2 cabs each with one 15" Peavey Black Window 8Ω speaker Max Power: 1,000 watts program.

The Spec sheet for the power amp I have states:
Stereo Mode:                         Continuous Average Output Power Per Channel
8Ω EIA 1kHz 0.1%THD           280W
4Ω EIA 1kHz 0.1%THD           450W

Bridge Mono Mode                 Continuous Average Output Power
8Ω EIA 1kHz 0.1%THD           900W


The Bridge Mode section of the manual for the poweramp states:
This mode is for those who need high level output. It combines the power of both channels to produce the maximum amount of power the unit can handle. Make sure your speaker can handle higher wattage this mode offers. Remember, the minimum impedance requirement is 4 ohm.

My question is...  Can I safely run the two 8Ω cabinets in parallel and draw a 4Ω load from the amp in bridge mode even though the spec sheet doesn't mention 4Ω loads on the spec sheet but does say in the manual that minimum impedance requirement is 4Ω?

Any help would be greatly appreciated.

Try it and see what happens.  Seriously.

Will it make sound?  Yes.  Will it be suitable for your purpose?  Only you can answer that after you hear it in Real World Use.

[John Roberts {JR}]

If you already own the amp and speakers try it. If you don't seek out someone who does and ask for their experience.

In general amplifier designers expect bad behavior from customers so worst case might be less power than expected if the amp shuts down prematurely or throttles back.

JR

[Jeremy Young]

Generally speaking, bridging an amplifier into a low-impedence subwoofer load is not typically thought of as a "reliable" solution.  It will work your amplifier hard, and if the amp doesn't specifically state the output at 4-ohm bridge or 2-ohm stereo, I wouldn't do it at a gig. 

Before I knew better, I used to run 4-ohm bridge-mode to subs on some cheap Alto amps and they would thermal and shut off if I gave them any reasonable level.  Running stereo was easier on the amp and I still got to the same level without the silences between.

If I had to guess, the spec sheet doesn't list the wattage rating in 4-ohm bridge mode because the distortion spec is higher than the others without de-rating it to a less-than-appealing number for the marketing folks to approve.  Keep in mind, you're not running 1Khz signals through your subwoofers (where those output numbers are taken from) so actual continuous output at low-frequencies will be limited by the current handling capabilities of the power supply.

If we ASSUME that the output is somewhere around 1,800 watts at 4-ohm bridge, that would put 900 watts into each cabinet (the program power).  That's 29.5 dBw.  Run in stereo 8-ohm, you'd get 280 watts per cabinet, or 24.5 dBw (so about 5dB less output theoretically).  Whether or not you actually see 1,800 watts from it in bridge mode without it overheating is the question. 

If you have the gear at your fingertips, give it a try.  You will see an increase in the amplifier sensitivity when you bridge it, meaning it will seem louder with the same amount of input signal but the maximum level you can send it before clipping will be equally reduced.  Let us know how it goes!

[BrianWalther]

Thanks for the input everyone.  Yeah, I have the gear already so I might give it a try just to see what happens.  It's just a stop gap for a gig this weekend until I get my new amps delivered.  Most likely I'll just stick with running stereo to be safe.  The thump factor isn't too important for this gig. 

[Mike Caldwell]

What make and model is the amp.

Remember speaker impedance will change based on the the box there in and the frequencies they are operated at.

Also as the voice coil heats up the impedance will increase resulting in less output and then you turn the system up to compensate resulting in more heating, aka power compression, aka blown speakers.

[BrianWalther]

What make and model is the amp.

Remember speaker impedance will change based on the the box there in and the frequencies they are operated at.

Also as the voice coil heats up the impedance will increase resulting in less output and then you turn the system up to compensate resulting in more heating, aka power compression, aka blown speakers.

It's just a cheap Phonic MAX1500Plus power amp I have laying around. Got a last minute booking and we wanted to add a little more bottom end to our JBL 225s.

[Stephen Kirby]

The amount of current a given amp will supply is fixed.  You're looking at a numbers game.  By halving the load, you get twice the "watts".  The actual energy moving speaker cones doesn't change.  The lack of a 2 ohm rating or 4 ohm bridges would suggest that the amp has some pretty serious limitations.  Even the famous QSC knockoffs have 2 ohm ratings.

As for extra low end oomph, not likely.  For two compounding reasons.  On either side of the port tuning frequency most speaker systems have fairly significant dips in impedance.  Meaning, right where you want your oomph, the amp is already working harder than you think it is.  Halving the load by paralleling or bridging puts things well below where the amp is rated to perform.  It will probably make noise until it goes into thermal shutdown, but the distortion and lack of cone control will result is much less apparent "oomph" than before the little math game.

[BrianWalther]

The amount of current a given amp will supply is fixed.  You're looking at a numbers game.  By halving the load, you get twice the "watts".  The actual energy moving speaker cones doesn't change.  The lack of a 2 ohm rating or 4 ohm bridges would suggest that the amp has some pretty serious limitations.  Even the famous QSC knockoffs have 2 ohm ratings.

As for extra low end oomph, not likely.  For two compounding reasons.  On either side of the port tuning frequency most speaker systems have fairly significant dips in impedance.  Meaning, right where you want your oomph, the amp is already working harder than you think it is.  Halving the load by paralleling or bridging puts things well below where the amp is rated to perform.  It will probably make noise until it goes into thermal shutdown, but the distortion and lack of cone control will result is much less apparent "oomph" than before the little math game.

Kindof what I was thinking but wasn't sure.  Thanks again everyone for the advice.  I'll just wait until I get my new amps in the next couple weeks to worry about it. :-)

[ProSoundWeb Community]