Old 2 channel amps and the OHM bridging

[mjoekingz28]

Say you have two 4 ohm subs. You can run them straight stereo at 4ohm. Or you could series them to 8 ohms then bridge them, or you could paralled them into 2 ohms and bridge them.

I ised to hear alot that bridging causes the amp to see half. Is it possible to have a bridged load at stereo. I just sometimes wonder when I see power ratings like 100X2 @2 ohms and 200X1 @ 4ohm mono.

Mainly I am asking the correlation between mono and bridge.

I used to have a US200 amp and would parallel two 4ohm subs and then bridge them ( right positive left negative) and I assumed a 1ohm load. They were later replaced with two dvc 4ohms that were paralled into 1 ohm then bridged into what I thought was a 1/2 ohm load.

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[Boomin_tahoe 5,000+ posts]

So what's the question?

 

[n2audio 5,000+ posts]

A lot of beginners, for one reason or another, have the belief that bridging cuts impedance in half. That's not really the case.

Example amp -- 100x2 at 4 ohms stereo. 200x2 at 2 ohms stereo. 400x1 at 4 ohms bridged/mono.

So a pair of 4 ohm speakers on each channel would get 100w each according to the 100x2 at 4 ohm stereo rating.

If you took ONE of the subs and bridged the amp to it you'd have the 400w (400x1 at 4 ohms bridged/mono).

So EFFECTIVELY, when an amp is bridged -- each channel sees half the load, i.e. each channel operates as though it is running a 2 ohm load - even though the sub is actually 4.

If you took the two 4 ohm subs, wired parallel (for 2 ohms) and bridged the amp you'd have a 2 ohm bridged/mono load which would be a problem for most standard 2 channel amps. They'd eventually shut down from over-current or thermal protection. Unless, of course, the amp is specifically capable of 2 ohms mono/1 ohm stereo.

If you wired them in series for 8 ohms and bridged the sub would see ~200w as it would be the 4 ohm stereo power combined into the bridged channel.

 

[mjoekingz28]

Thanks n2audio!

My old US-200 was 1 ohm stable. As I said I ran two 4ohm Vega 12s parallel to it, then bridged it. So, 4 and 4 is two ohm, and then bridging it makes it mono......so, 2ohm mono!

Then, my cousin put DVC 4ohm Vegas on it... So, 4 and 4 is 2 and 4 and 4 is 2 ...then 2 and 2 is 1 and then it is bridged(which I gather is just another word for mono, in general) so we had a 1 ohm mono load at the amp.

That amp was great, the only problem it gave me in the 18 years I had it (I recently gave it back to the audio center where I purchased it in 1998) was the terminal block whereyou screw in the speaker wire stripped because I had all the connections going into there instead of daisy chaining.

Yeah, it would pop a fuse from time to time, but I kept a few maxi 60a fuses on hand and would simply exchange and go back to full tilt- even in summer with the amp improperly mounted in the trunk with inadequate airflow.

Once we tried the subs in a car with a more solid trunk, I remember playing a certain bass track and was unable to swallow my drink because the bass was very heavy.

Anyways, thanks for the answers. I have lots of questions, uncertainties, and probably some misconceptions about the world of car audio!

Here is a statement from a US Amps manual from 2001.

"Remember, when you bridge your amplifier, each channel 'sees' one half of the load, hence at 4 ohms bridged each channel is operating at 2 ohms,............."

So, it seems when a company says 1 ohm stable they mean that at stereo and/or at 2 ohm monaural.