Bi-amp = 2 times the power? (1 Viewer)

[Ken Custodio]

If you bi-amp a set of front speakers, are you essentially doubling the watts to your speakers or is it the same watts, since one channel goes to the tweeter and one goes to the woofer?

 

[RobertR]

I biamp my front speakers using a 5 channel amplifier. I have a 400 watt channel going to the midrange/tweeter and a 400 watt channel going to the woofers. Yes, that's a doubling compared to connecting a single 400 watt channel to each speaker.

 

[Steve Zimmerman]

I don't think it's necessarily a doubling of power. First off, you're splitting the pre-amp output and second, and unless you're using two separate amplifiers for the biamping you're still essentially drawing power from the same pool in many cases.

Even if it *is* a doubling of power, that's only 3dB of extra extension at the highest volume.

When I bought my first 5-channel amplifier I couldn't stand the thought of "wasting" two unused channels, so I "fool's" biamped for a while. Then I went back to using one channel per and, frankly, I feel rather embarrassed for having spent the extra money on cables and Y-connectors.

--Steve

 

[Wayne_T]

Robert, I agree. Now what happens to the impedance of the speaker? i.e., if I have an 8 ohm speaker, and I remove the bridge from the terminals, do I have two 8 ohm loads? Or two 4s? Or two 16's?

 

[Wayne_T]

Steve, if you were connecting two separate channels from your five channel amp to separate terminals on your speaker, then you were biamping that speaker. I don't know why you would call that "fool's" biamping. Please explain.

 

[Wayne A. Pflughaupt]

Now what happens to the impedance of the speaker? i.e., if I have an 8 ohm speaker, and I remove the bridge from the terminals, do I have two 8 ohm loads? Or two 4s? Or two 16's?

The speaker’s nominal impedance, as measured at the speaker terminals, is determined as much by resistor networks used in the passive crossover as the impedance of the drivers. In all likelyhood you will see the same impedance for the lows and tweets independently as you see when they are strapped.

Regards,
Wayne A. Pflughaupt

 

[Wayne_T]

Thanks Wayne for the answer on the impedance question. Makes sense to me.
So "fool's" biamping is an elitist term for what ordinary folks would call passive biamping?
Steve, I wouldn't dismiss the benefits of passive biamping or be embarassed about doing it. It is strongly recommended in my speaker manuals, and my own experience validates that. I guess it could be somewhat dependant on the internals of the speaker though, so some might benefit more than others. At the very least, you do get double the power which I think is always an improvement.

 

[Steve Zimmerman]

Wayne_T, I'm no elitist and if it works for you then great.

However, not all speaker manufacturers think passive biamping is a worthwhile endeavor and you will only get double the power if your amplifier is designed a particular way.

--Steve

 

[RobertR]

I should mentioned that my speakers use TRUE biamping, as they make use of an electronic crossover and there are two electrically separate terminals for the mid/tweets and woofers. The nominal impedance for each section is 4 ohms. I forgot to mention that the amp delivers 800 watts per channel into 4 ohms, so my front speakers have a whopping 3200 watts available to them.

 

[Steve Zimmerman]

That's a lot, Robert. Three questions: (1) How far away from the speakers do you sit, (2) What is the efficiency of the speakers in dB, and (3) What is the wattage rating of the speakers?

10000% of the recommended daily allowance of vitamin C makes for, well, expensive urine.

--Steve

 

[RobertR]

Steve:
1. about 11 ft.
2. 92 dB/1 meter/1 watt
3. 500 watts for the mid/tweeter section and 500 watts for the woofer section. Since the bass response is rated flat down to 16 Hz, I feel no need for a subwoofer.

 

[Steve Zimmerman]

Well that means one of two things... No ear drums or a small jock. Ha ha ha. Sounds like some wild speakers.

--Steve

 

[KeithH]

Biamping does not double the power. Bridging can, depending on the amp design. In bridge mode, an amp is used to drive one speaker, and the power may be doubled.

 

[KeithH]

Regarding bridging, here is what www.whathifi.com out of the UK says:

Each drive unit of a speaker is driven by a separate amp channel, so a pair of two-way speakers needs two stereo amps, and two runs of cable to each speaker. See biwiring.

 

[Wayne_T]

Keith, with all due respect biamping does double (or at least approximately double) the power to the speaker. If I connect both sides of a 200W/channel amp to a speaker, it now gets 400W. I will believe that until someone can tell me where the second 200W vanished to.

 

[RichardMA]

True biamping need not mean using a digital crossover.
You can use an outboard passive crossover with separate
sections for each driver. My centre is tri-amped,
the woofer (10") driven by a 100wpc Marantz monoblock,
the midrange driven by a Antique Sound tube amp and the
tweeter driven by another identical tube amp.
The idea of biamping with an electronic crossover at
the "line level" is that most speakers aren't bi-wirable
and don't have separate crossovers for each driver. So
do though. The problem with the line-level electronic
crossover is (again) the need to split the output.
But if you tri-amp, you are likely to have to do this too.
In my setup, I have two centre outputs from my Sony preamp
and I split one to do the amping to the midrange and tweeter.

 

[KeithH]

Wayne, What Hi*Fi? did a cover article on biamping stereo amps last year. In it, they said that biamping does not double the power as is usually believed. I have the issue in the house and when I find it, I will post their exact statement.

 

[Wayne A. Pflughaupt]

If I connect both sides of a 200W/channel amp to a speaker, it now gets 400W. I will believe that until someone can tell me where the second 200W vanished to.

It’s academic, really. For instance, if a speaker is rated for 200 watts, you don’t really gain anything by feeding it 400 watts via biamping.

It seems senseless to biamp using two channels of the same amp unless you are running out of power. Typically this is not the case.

Aside from that, the only good reason I can see for biamping: If you auditioned two amplifiers and decided “I like the way the mids sound with this one, but I like the way the highs sound with that one,” then passive biamping might give you the best of both.

But for the most part I can’t see any advantage of biamping using identical amps.

Regards,
Wayne A. Pflughaupt

 

[Steve Zimmerman]

But for the most part I can’t see any advantage of biamping using identical amps.

Or, even worse, consider biamping using a single 5-channel amplifier that has only one or two transformers. If the two channels you connect to the speaker both come from the same internal supply of power inside the amp then using both of the channels gives you no more reserve power than using a single channel.

--Steve