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rockford power bd

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=19808
Printed Date: May 18, 2025 at 1:30 PM


Topic: rockford power bd

Posted By: Ketel22
Subject: rockford power bd
Date Posted: October 08, 2003 at 3:04 AM

why is it that the 2channel bd series amp are stable at 2ohm stereo and 4ohm mono and not 2ohm stereo and 1ohm mono?



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Replies:

Posted By: fuseblower
Date Posted: October 08, 2003 at 8:33 AM

The norm for most 2 channel amps is that they stable @ 2 ohm stereo and 4 ohm mono.




Posted By: wvsquirrel
Date Posted: October 09, 2003 at 3:28 AM
The way I've always remembered it is when you take a stereo amp and bridge the 2 channels into 1, you are doubling the resistance to that 1 channel (combining 2 into 1). I know that's not the best way to remember it (and I don't think it's the proper technical way either), but it's close enough for us amatures to keep it straight for the most part!

So (2) 2ohm Stereo channels bridged would normally equate to (1) 4ohm Mono channel. Just like (2) 4ohm Stereo channels bridged would normally equate to (1) 8ohm Mono channel.

The same works in reverse too...
If you wanted a 2ohm Mono stable Class A/B amp, then by classical theory it would have to be at least 1ohm Stereo stable. If you wanted a 1ohm Mono stable Class A/B amp, then by classical theory it would have to be at least .5ohms Stereo stable.

It's really all in the internal circuitry though. Some companies (like Audiobahn) have designed circuitry that will allow a 1ohm mono bridge on some of their non Class-D amps without having to be .5ohm Stereo stable.

Others (like JBL) have designed "reverse-bridges". Where the amp has 2 distinctive sets of speaker outputs like a 2-channel Class A/B amp would look, but they are actually already combined inside the amp to make (1) Mono channel. So it's not really a true Class D, and not really a Class A/B either. But it is always referred to as a Mono amplifier because there is no defined Left and Right output, only Mono output from both channels (kinda like putting a Y-adapter on an RCA cable). I've read it was an "ease of wiring" thing, but it's still a little confusing the first time you see it.

To further answer your question about the RF BD series (or any RF amp for that matter)...
RF does not make a 1ohm stable amp in either Class A/B, Class D, or Class BD at this time. I read an RF Tech document a while ago that said they may be developing a 1ohm stable Class D or Class BD amp in the future, but nothing would be ready for some time.

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Squirrel
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