Axiom Home Page Forums General Discussion Advice from Axiom Owners 80's or 60's????

You are most welcome.Let us know what Rotel has to say about it.

Worf, when you bridge two amp sections to drive one speaker the result is that twice the amount of voltage is being supplied to the speaker, and since one form of Ohm's law is I=E/R(current equals voltage divided by resistance), when the voltage is doubled the current(at least theoretically)is also doubled. This is the same as if the voltage remained the same but the resistance or impedance of the speaker was cut in half. So, it's sometimes said that the bridged amplifier "sees" a 4 ohm load(with 8ohm speakers)or a 2 ohm load(with 4ohm speakers), which isn't really correct since the speaker stays the same, although the extra current load on the amplifier is as if the speaker impedance was lowered.

Don't know what Rotel will say, but that's a fine amp(even if it doesn't have a "British sound")and apparently the resulting current hasn't caused it to shut down.

In reply to:

---

So, it's sometimes said that the bridged amplifier "sees" a 4 ohm load(with 8ohm speakers)or a 2 ohm load(with 4ohm speakers), which isn't really correct since the speaker stays the same, although the extra current load on the amplifier is as if the speaker impedance was lowered.

---

That sounds like a little double talk to me.You say the speaker impedance stays the same but the extra current load on the amplifier is as if the speaker impedance was lowered.Then when using an amp in bridged mode the amp does act as if the impedance of the speaker has been lowered.When I talked to Parasound about doing this very same thing they told me that it would be like the cutting speakers load in half.

I'm not sure what the confusion is over. 2 amps in series = 2 times applied voltage. V proportional to 'I' implies 2x the current. Power proportional to 'I' squared implies 4 times the power.

The load never changes, the currents are doubled through the system.

If you just had one amp with double the normal current it would be as if the normal resistance was lowered by a factor of 2.

edit* Ha, that was pretty poorly stated!

Ok, got a response from Rotel and it isn’t pretty. I will let you read it for your self.

“Basically, the amplifier is bridged so that now it sees 2 ohm speakers instead of 4 ohm speakers. This will generate a lot of heat from the unit. In the long run the heat could eventually cause the amplifier to fail or, depending on how hard you drive the system, something to blow up. If you can keep the amp cool enough during use then you will notice that it works but your distortion rating when running in bridged mode plus 4 ohm speakers is going to be about eight times greater than normal.”

This gave me some major concern, so I decided to check if I had done any damage. I turned all the bridging off and checked each of the channels. The first one was DEAD (Oh No!!!). The other 5 seemed OK (whew!!!). Well I popped the cover off (love that power supply) and found a fried fuse. A quick trip to Radio Shak and I am up and running again. However, instead of bridging, I am bi-amping the M80’s (as per Rotel's recomendation inplace of bridging). I would say the difference is subtle (better), but it is noticeable. And because the 976 has variable gain controls on the front, I can customize the volumes of the highs and lows. I think Axiom got the crossovers in the M80's correct, because I perfer the sound with both being neutral. However it is nice to be able to tweak it a little.

Interesting to me all the huge money spent on exotic speaker cables and inter-connects when the signal still has to travel through a glass tube with a wire in it about .5 millimeters in dia; called a fuse.

Anyway Rick, thanks for the heads up. This probably saved me a lot of grief down the road.

Does anybody know how the math works on this? If I have an amplifier delivering 100 watts into 4 ohms and I bi-amp the speakers does that give me 200 watts?

That does help clear things up for me.

Oh by the way, to tell you the truth, I couldn't define British Sound from any other countries sound (except maybe Japan), I just know what I like and what I can afford. My preference for Rotel is similar to my preference for Axiom. Large bang for the buck, well built good quality products, regardless of where it is designed or manufactured.

Thanks

If you're biamping with 100 watt amplifiers, your speakers are getting 100 watts. Biamping doesn't double the power, just splits it between the woofers and tweeters/mids.

Ken is correct. Also, the only thing traveling through the fuse is electricity from the wall. It's totally outside the audio loop, so you can breathe easy.

Hmmm, but maybe you're onto something here. I can start a business that sells audiophile grade amplified fuses and make a mint!!

IsoClean Audio Grade Fuse Review. HA!

I haven't read it, but I did read about them in the thread here. The amount of crap that people buy into is amazing.

any reviewer of fuses that puts this combination of words in this particular order, "I also inserted the fuses in the opposite direction and in all instances, noted increased glare and brightness. As I said earlier, you can easily determine the proper orientation by ear." ought to be tarred and feathered. I continue to find it amazing that people actually buy into this crap...