bi-amping speakers?

B

bikemig

Audioholic Chief
I recently bought a NAD T-747 AV receiver. It's my first AV receiver and I'm happy with it. I'm currently auditioning some floorstanding speakers to go with it. Here's my question, I am only buying one pair of speakers and will not be using surround (partially for space reasons, partially because it works for me since I am mainly interested in music and only secondarily in movies). That means that that surround back amplifier channels can be reassigned to bi-amp the front left and right speakers. I've been reading a bit about (passive) bi-amping on the web and there isn't much agreement on whether it is worth it. I guess the real test is to try it out and see what I think. What are the pros and cons of bi-amping speakers?
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
Pros: There isn't any:eek:

Cons: There isn't any Pros.:D

The more complex the wiring, the more chances of something going wrong. For example, if one set of speaker cable is wire out of phase or one wire is loose or one of the extra amp channels is defective, that may screw up your sound.

This is the case of More is Less.

Besides, all those channels inside the same amp share the same power supply. Thus, you are not gaining anything. For example, in 2Ch you may get 150WPC x 2. But if you run 4Ch continuosly, you may get 75WPC x 4.:D
 
B

bikemig

Audioholic Chief
From what I've read online about this topic, there seems to be little agreement on whether there is any value to bi-amping speakers. That said, the NAD T-747 is rated at 60 watts per channel (this is using NAD's conservative ratings) unless it is bi-amped in which case it is rated at 110 watts. Apparently the surround back amplifier channels can be reassigned to power the front left and right speakers if I bi-amp them.
 
jeffsg4mac

jeffsg4mac

Republican Poster Boy
From what I've read online about this topic, there seems to be little agreement on whether there is any value to bi-amping speakers. That said, the NAD T-747 is rated at 60 watts per channel (this is using NAD's conservative ratings) unless it is bi-amped in which case it is rated at 110 watts. Apparently the surround back amplifier channels can be reassigned to power the front left and right speakers if I bi-amp them.
Your talking about passive bi-amping which is a complete waste time and wire. You would still only be getting 60watts to the woofers and 60watts to the tweeters. That is not the same as 110watts. Now if you were actively bi-amping with an electronic x-over that is a completely different animal.

Unless you are physically bridging two channels into one you are not getting a power increase. If you want or need more power then get a bigger amp. It is that simple.
 
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lsiberian

lsiberian

Audioholic Overlord
I'd not advise it. Keep things as simple as possible.
 
M Code

M Code

Audioholic General
I would double check with NAD that the 747 is capable of bi-amping..
Many AVRs are not..

Just my $0.02... ;)
 
B

bikemig

Audioholic Chief
The NAD is capable of bi-amping and yes I am talking about passive bi-amping. I am getting the idea, though, that it would be a waste of time . . . .
 
P

PENG

Audioholic Slumlord
In theory passive bi-amping allow you to separate the low and high frequencies in the wires but that most likely would not produce audible effects. However, if you are only using two speakers, bi-amping should at least get you lower distortion at a given SPL level you are listening to especially consider the fact that it is a NAD, i.e. the power supply should be reasonably robust.
 
jeffsg4mac

jeffsg4mac

Republican Poster Boy
However, if you are only using two speakers, bi-amping should at least get you lower distortion at a given SPL level you are listening to
Yes maybe, but then again that too is probably not audible.
 
B

bikemig

Audioholic Chief
Your talking about passive bi-amping which is a complete waste time and wire. You would still only be getting 60watts to the woofers and 60watts to the tweeters. That is not the same as 110watts. Now if you were actively bi-amping with an electronic x-over that is a completely different animal.

Unless you are physically bridging two channels into one you are not getting a power increase. If you want or need more power then get a bigger amp. It is that simple.
I don't need a bigger amp for my set-up but when I've listened to different amps with the same speakers, I've noticed a difference in SQ when played at the same volume. I guess what I don't understand is why bi-amping is different than simply getting a more powerful amp.
 
O

oppman99

Senior Audioholic
I don't need a bigger amp for my set-up but when I've listened to different amps with the same speakers, I've noticed a difference in SQ when played at the same volume. I guess what I don't understand is why bi-amping is different than simply getting a more powerful amp.
Because passive biamping with an AVR does not increase the amount of power the AVR will output. Internally, the extra channels on the AVR are drawing power from the same source. It's like hooking up a simple battery, wire and lightbulb. Connecting two wires from each terminal to the bulb will not make the bulb glow brighter (i.e. draw more power). The current flow will not increase. (Ok, technically there is a minute change in resistance, but it's not significant.)
 
P

PENG

Audioholic Slumlord
I don't need a bigger amp for my set-up but when I've listened to different amps with the same speakers, I've noticed a difference in SQ when played at the same volume. I guess what I don't understand is why bi-amping is different than simply getting a more powerful amp.
Bi-amping may get you more power as long as the power supply is not the limiting factor and the amps are. This is even less so for two way speakers because the tweeter does not take or need much power relative to the bass driver(s). A more powerful amp will give you more power period, no question, no doubt, at least for the bass drivers that can use the power.

Even if you disregard the power issue, bi-amping is different because in that case the cable for the bass drivers will carry mostly the low frequency signals while the cables for the tweeter and mid range driver (in some cases) will carry mostly high frequency signals so theoretically the tweeter (and the mid range driver in some cases) will not be influenced by the effects of the much higher low frequency signal currents. The debatable part is whether such theoretical differences are audible. Most posters here seem to say "no", but if you are one of those people who can hear, or think you can hear the difference between amps, cables etc., then may be you should go ahead and try it and find out for yourselves.
 
P

PENG

Audioholic Slumlord
Because passive biamping with an AVR does not increase the amount of power the AVR will output. Internally, the extra channels on the AVR are drawing power from the same source. It's like hooking up a simple battery, wire and lightbulb. Connecting two wires from each terminal to the bulb will not make the bulb glow brighter (i.e. draw more power). The current flow will not increase. (Ok, technically there is a minute change in resistance, but it's not significant.)
You are correct only if you assume the power supply is the limiting factor such as some $300 entry level AVRs that has power supply in them that are really designed to deliver their specified rated power for two channel driven only.

In the case of using only 2 channel (4 if bi-amp) of a 7 channel NAD 747 receiver I would bet the power supply is not quite the limiting factor. As such, using two amps to power each of the two front speakers should in fact give them more power, obviously not twice as much because the MF and HF driver (or in the case of two way speakers, jus the HF) drivers don't take as much power as the bass drivers. I agree the difference in power gain may be insignificant especiallly for two way speakers. In my case, if I biamp, one amp will feed the MF and HF, the two together does draw 30% or more of the total so there is more gain but again it depends on how robust the power supply is.
 
TLS Guy

TLS Guy

Audioholic Jedi
I don't need a bigger amp for my set-up but when I've listened to different amps with the same speakers, I've noticed a difference in SQ when played at the same volume. I guess what I don't understand is why bi-amping is different than simply getting a more powerful amp.
You could get more power, but only with the right speakers.

Lets take a three way with a crossover between woofer and band pass at 400 Hz. This is the acoustic power divide. Lets assume the terminals when the jumpers are removed go the low pass filter, on the bass which powers the woofer. Then the other set of terminals will go to the band pass and high pass filters. Remember filters are in parallel with each other, until you remove the jumpers, then they are isolated.

Lets assume that the music program is pretty evenly split either side of the power divide.

As long as the amps can maintain full power at the same time, then you will have doubled the power and gained a small 3 db in output. It will not sound twice as loud.

Now if the program switches for a moment to where there is a lot of content below 400 Hz and much less above 400 HZ, a common scenario, then the bass amp my clip and the HF amp will sit idly by and not be able to come to the aid of the LF amp. This is why an amp twice the power is less likely to clip, than two amps biamping.

Now lets take the more usual situation these days of a two, or two and a half way speaker with a crossover to tweeter around 2.5 kHz. The exact number is not important as it will be well above the power divide at 400 Hz.

Now when you remove the jumpers, the lower terminals supply the woofer and the upper terminals just the tweeter.

Now the bass amp is delivering practically all the power. The amp to the high pass filter, supplying the tweeter provide relatively a minute amount of power. When the bass amps clip the HF amps can do nothing to help. The HF amp will deliver an insignificant amount of power.

You will not get a measurable increase in spl. As far as HF and LF current in wires is concerned, I really doubt this has any effect, and if it does, is way below the threshold of being audible.

So you see, in the situation of most speakers discussed on these forums, you get absolutely no benefit from biamping. To get a benefit you need to be able to access a set of filters with a crossover point between 350 and 500 Hz. That restricts you to three ways, with a woofer/band pass crossover accessible. And by the way, I have seen a number of three ways where the accessible filters are the LF/band pass on the lower terminal and the high pass on the upper. This does not help you one bit if you are contemplating passive biamping.
 
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