Bi-amping

jdhdiggs

Let's keep this one on the up and up and no name calling. Here's the premise on bi-amping:

200W + 200W = 400W

New Premise:

200W + 200W = 200W (Okay, maybe a bit more around the crossover)

Reasoning: Both Amps are generating full range signal but pushing seperate "halfs" of a speaker. If you are trying to generate a loud 80Hz signal, how much power can you push to it? Only 200W... Virtually any signal can only have 200W directed to it. Same as if you only had one amp...

Lets say that a signal causes a clip due to the extreme bass on the amp driving the woofer section, what happens up top? The top amp is till trying to produce the full range signal but pushing it into a brick wall (AKA Crossover) I'm guessing that the clipping signal is still present and you will blow your tweeter. This one is the more confusing since the amp is seeing an infinate resistance leading to 0 amps on the circuit... This is the piece I'm missing.

At this point, the only purpose to bi-amping that I see is that you can tailer amps to the specific strengths.

Add an external X-over before the amps and it's a totally different ballgame. Then you could put a 5W SET on the top and 500W down below and have great results.

Let the debate begin, and remember, we're all freinds here and keep thinking in dynamic power...

madmax

The fault you have is when the bass is clipped the treble will not be affected. You are saying the treble amp is trying to produce full range. That is not true. The amp delivers into a resistance. There is infinite resistance at the bass frequencies because of the crossover therefore the amp will have no power output at those frequencies. The tweeters will have a much lower resistance and will therefore draw more power from the amp.

As a matter of fact just consider a single amp and the crossed over speakers. What you are looking at is say an 8 ohm speaker from 20 to 20khz. Now, disconnect the woofer. What you have now is an 8 ohm load from maybe 1khz to 20khz. That will obviously pull less power from the amp since it is not the full range that the amplifier is rated at.

This is the reasoning for filtering above 40khz or so in an amplifier. Even though you cannot hear things this high it can still pull a lot of power out of an amplifier which could have been used in the frequency range you can hear.

madmax

jdhdiggs

Yup max, thanks for confirming my stream of caca. If you read it again, I think I finally concluded that the "upper" amp wouldn't clip. This adds a +1 to bi-amping in that you can protect your tweets a bit better. However, I do maintain that the amp is "trying" to produce the full range signal, since that was the input. It just cannot push the signal anywhere.

I guess I would need to see the cause of the clip. I'd say the most common cause, you'd be right. I'm wondering if someone turned up the gain to high and an amp that can handle only 70V on the rail gets called to produce say 110V. Even though the resistance is infinate, would this cause a short and pop the tweet... I don't know about this one... Is this when the magic smoke goes away?

The biggest reason that I brought this whole question up is the herd of people using secondary channels on their receivers as extra power, or those who think to 100W amps will give them as much power as a 200W amp. Just not seeing it from a dynamic perspective...

steveinaz

In my experiences, and my way of thinking, you've got to be "of deep pockets" to bi-amp correctly, and then live with what you spent versus what you gained; which in my opinion, isn't much at all.

Of course, I'd have to be at the "if you have to ask, you can't afford it" level in my life to even consider the proposition. That ain't happening. If I ever do get to that point, I'll hire live musicians to play the "family room."

Personally, I have tried both bi-wiring and bi-amping, and I don't like either. I'd rather spend that money on upgraded speakers and a better core amplifier. Bi-wiring is especially a paradox to me; High-end speakers that have outstanding crossover networks don't need bi-wiring; and the cheap speakers that include bi-wireable binding post benefit "zero" from their use because the crossover isn't as good as it should be to begin with. lets face it, most sub-$1000/pr speakers are bi-wireable because consumers equate bi-wire capability with "high-end" audio; not because there is any audible improvement in their use.

My opinion.

madmax

Again,
The amp does not push anything. It only allows the speakers to pull current out of it. If at a given frequency the resistance is high you pull nothing out of it at that frequency. Now, lets get to the name calling!
madmax

jdhdiggs

Ah, so the perfect amp acts as a voltage source only , got it you ****!

BTW, I always have viewed voltage as trying to push something similar to water on a damn. That's more of what I mean. If the resistance is high enough, the water doen't go anywhere. Just a stupid thing in my head that won't go away...

now why haven't there been any takers on the 2+2=2?

madmax

Originally posted by jdhdiggs
I'm wondering if someone turned up the gain to high and an amp that can handle only 70V on the rail gets called to produce say 110V. Even though the resistance is infinate, would this cause a short and pop the tweet...

If the resistance is infinite then the receiver pulls no current which means it receives no power. You cannot blow up a tweeter with zero power. For example, if you disconnect the speaker totally from the amp you can not blow up the speaker. This is because the resistance between the speaker and amp is infinite.
madmax

madmax

I'll take on the 2 + 2 = 2 thing too.

Lets say you have the speaker crossed over at the perfect point where half the energy goes to the lows and the other half of the energy goes to the highs. At this point if you biamp then 2+2=4.

In the real world the treble section tends to draw less current than the bass when crossed over at the normal frequencies where the bass speaker lets off and the treble takes over. Bass tends to draw a lot more current than the treble. It just takes more power to move a big cone further at a slow rate than it does to move a small cone less distance at a faster rate. Now you are no longer crossing over at the equal power point. What you may end up with is 2+2=3.143 or whatever. That is because one amp runs out of power before the other one peaks.

BTW, this works out great because you can clip a bass speaker somewhat with no problem but the tweeters go quickly when clipped.

madmax

jdhdiggs

Voltage sources draw no power until the resistance is less than infinate.

Other than that, got it.

On your second post, a real world audio signal would never be like that (200W top, 200W below) in that the energies involved would destroy the tweeter or your ears.

Remember, ever octave up requires 1/2 the power for the same dB level (Or is it 1/4, can't remember) so you would never see that under "normal" listening. Granted, you could use a computer to make pink noise wave and crank that into clipping, but that would be the only way your going to push more than 1 amplifiers worth of power at the volume where clipping would occur. So in our test case on real world material, you might push 202 or so.

The fact is that musical energy is not half up top and bottom. I guess if you designed a speaker with the x-over at 60Hz, you might have something.

Real world man, real world...

PUNK! (just for you MM)

And yes, I'm just trying to be difficult! (Real world though, I think you'd agree that the amps are not directly additive unless a perfect pink noise signal is generated.)

madmax

Originally posted by madmax
In the real world the treble section tends to draw less current than the bass when crossed over at the normal frequencies where the bass speaker lets off and the treble takes over.
madmax

As I said punk, REAL WORLD! The 1/2 and 1/2 scenario was only used for example...

madmax

jdhdiggs

As the all powerful Dogbert would say: BAH!

And yes, this is good to get my post count up since I'm severely slacking...

HBombToo

I'll up the anty on the post count:D

Toxis

but here's the problem I see with bi-amping. Both amps are still being fed full range signals and are amplifying the full range signal. So all you're basically doing is making the x-over in the speaker work a little bit harder to get the same aftermath. I like the concept of bi-amping but without an electronics x-over before the amps, I do not see the point personally. Just because there's a crossover in the speaker that's "taking out unwanted frequencies" to the specific driver does not have any effect on what frequencies the amplifier is amplifying. Now if you had an electronic x-over, than I can understand it because now the amplifier is only amplifying a lot smaller spectrum of sound thus creating better sound quality within it's frequency band with little/no clipping.

Please correct me if I'm wrong, but personally, I just don't see how it can be any other way...

jdhdiggs

Originally posted by HBombToo
I'll up the anty on the post count:D

+1

As for Toxis' question, queue Madmax... He explained it already, in a bit better terms than I would

RuSsMaN

I have my Spendor's bi-amped right now. Using a 120w/ch Conrad Johnson Solid State amp, and an 8w/ch Radii tube amp.

Run the numbers on that one.

Cheers,
Russ

jdhdiggs

Yeah Russ, but you also don't listen to the thing a stupid loud levels.

My guess is the 120W will crap the bed before the Radii with real world content.

Why don't you try it out?