Will I blow something up?

[Early B.]

Just got a Behringer A500 pro amp to power my DIY sub. It's supposed to crank out 500 watts at 8 ohms in bridged mode. The manual says I should only use an 8 ohm speaker in bridged mode, but my woofer is 4 ohm. What problems could I encounter? Will I blow up the amp or the woofer if I continue to do this?

Thanks.

[Dennis Gardner]

You'll burn up the amp. 200-250 at 8 ohms will be plenty, or hurry up and build another sub to run in series.

Edit: I looked at the manual for the A500 and your amp is rated 230WPC into 4 and 160 into 8 and you are right, it warns all throughout not to hook it up bridged under 8 ohms.

[Early B.]

Thanks, Dennis.

OK, so what if I run the amp in stereo mode and only use one channel?

[heiney9]

Yes, most amps that are bridgeable don't like 4 ohm loads. So I'd say if it says only use with an 8 ohm load that's what I'd do. Some of your higher end mono's might be able to run a 4 ohm load, but probably not the Behringer.

Worse cas is you'll eventually ruin the amp.

[Dennis Gardner]

Its ok to drive 1 channel of a stereo amp. I do it all the time with Peavey, Behringer, Mackie, Crown etc. I do a few installs into as low as 2 ohm loads, but only while in stereo mode and only while driving a single channel.

[RuSsMaN]

What about adding a 4ohm resistor inline on the pos, and running bridged? Sure, it would kill efficiency a little, but the impedance would be squared away.

[Early B.]

What about adding a 4ohm resistor inline on the pos, and running bridged?

If you can tell me exactly what to do, I'll try it. What does "inline" mean? And does "pos" mean the "positive terminal," "point of sell," or "piece of shit?"

[Dennis Gardner]

What about adding a 4ohm resistor inline on the pos, and running bridged? Sure, it would kill efficiency a little, but the impedance would be squared away.

Running series resistors does raise the impedance that the amp will see, (a 4 ohm resistor and 4 ohm speaker in series will be an 8 ohm load) I would take great care doing it with a subwoofer since it drastically lowers the damping ability of the amp to control the driver and we all know how important this can be for good subwoofer/amp combo. This is an accepted method of impedance matching for older full range drivers or modern mids, but todays sensitive tweeters and huge subs deserve well matched amps.

[RuSsMaN]

True, I was thinking this was a sealed box job, and the cabinet and motor structure should be handling the damping on their own.

Bottom line is, forget the bandaids (like I mentioned), and just do it right from the get go. If the amp you have doesn't cut it - get one that will.

Right on Dennis.

Cheers,
Russ

[Early B.]

Tried it in stereo with 1 channel. Works like a charm. I'm good.

Thanks.

[Early B.]

One more thing -- no more plate amps for me. For basically the same piece of change, one can get a pro amp or monoblock (Marantz, Outlaw, NHT, etc.)that will provide a better sound than plates.

This Behringer has more control of the woofer and, therefore, offers a cleaner sound. The plate amp sounded like it had a nervous condition, in comparison. You know -- sort of reckless and twitchy, even though it was one of the better ones on the market.

[Dennis Gardner]

Glad it worked out for you. I'm going to have to bring a pro amp home some day to try in place of my plate amp on my dual Shiva sub.

[Early B.]

I'm going to have to bring a pro amp home some day to try in place of my plate amp on my dual Shiva sub.

Hmmm. Can you rig your dual Shiva sub for a 2-channel amp, where each woofer is powered by a single channel?:eek:

[Dennis Gardner]

My Shivas are dual 8 ohm voice coils so when paralleled then in series, the single channel amp sees 8 ohms. Using 2 channels, the amps would see 4 ohms each.

http://www.adireaudio.com/Files/TechPapers/DualVoiceCoilWiring.pdf