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Old 15th July 2004, 06:44 AM   #1
Jennice is offline Jennice  Denmark
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Default Heat sinking power per frequency ???

Hi everybody,

I've given the following some thought, and would like to hear oppinions from others on this...:

You take an ordinary solid-state amplifier, and it's heat sink.
This amplifier drives the full frequency range, thus delivering power to both tweeter and woofer (given a simple 2 way system).
Power to the entire audio spectrum is coming from one power amplifier stage.

What if one wasd to make a amall-signal low-pass / high-pass filter, so that the same amplifier would now only have to handle part of the frequency spectrum, and consequently only deliver power to the woofer OR the tweeter. Provided a certin power spectrum (power per frequency), the resulting energy needed from the amplifier to drive only one unit (with correspondingly limited frequency spectrum), should be lower. Accordingly, heat dissipation should be lower, too.

Should this be the case, my goal would be to mount two output stages on the same heat sink, and let each handle one driver unit with limited bandwidth. The total energy needed over the audio bandwidth should be the same, given the same accoustic power is coming from the speaker. If the same amount of energy is sent to the speaker (but by differnt amplifier output stages), the waste energy to be dissipated by the heat sink should be the same, too (apart from idle power of the extra output stage).

Is this theory correct or where is the error...?

Jennice
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Old 15th July 2004, 07:46 AM   #2
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Let's see, you have a given original output that has a certain efficiency (and thus dissipated power). Then you split the signal and adjust til it sounds the same. Speakers are getting the same signal, amplifiers are the same (assuming they aren't more efficient due to the restricted bandwidth, which isn't going to be the case since they both span far more than maybe 10% of the center frequency), power out 1 + 2 = total, dissipation 1 + 2 = total. Sounds right to me.

The real advantage of biamping is smaller amplifiers (since the power is shared) and no crossover networks at the speakers to mess up and confuse them. I wouldn't bother with tubes since it's more bother to make an amp.

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Old 15th July 2004, 08:53 AM   #3
Jennice is offline Jennice  Denmark
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Indeed, my point was to build the amplifier (solid state circuit) specifically for bi-amping the speakers. By doing it this way, I use the same heat sinks as a single full-range-amplifier, but make it host for two amplifier circuits. Thus, I'd share the power supply and heat sinks, as the handled power - in my world - would be roughly the same as for a single, full-range, amplifier stage.

I know... bias currents etc will give some losses, but still it should be possible in my world. I just want to make sure that my world is not corrupted (in this regard )

You mention something about the amplifier bandwidth. Why is that a concern in regards to energy dissipation, when they're only playing in 20-2000 Hz and 2000 Hz - 20KHz range, respectively. In theory, they should both be able to work full range, but if they are not given a full range signal, then the energy diddipated when playing music shouldn't be full range either. (in total, yes, but I'm thinking individually.)

End effect would be that I'd end up with fewer transformers, un-needed (?? that's what I'm trying to find out) heat sinks and PSU's etc., by designing directly for bi-amping.

Jennice
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Old 15th July 2004, 10:11 AM   #4
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Assuming reasonably efficient amplifiers I think this will work ok. There is the added advantage of increased loudspeaker efficiency which will reduce (slightly) the load on amplifier and psu for a given spl.
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Old 15th July 2004, 10:17 AM   #5
Jennice is offline Jennice  Denmark
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Why do I get higher speaker efficiency from bi-amping? Is there really that much loss in a passive cross-over, or why?

Jennice
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Old 15th July 2004, 07:46 PM   #6
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My bandwidth comment applies to radio circuits where a very limited bandwidth (let's see, +/-10kHz on a 1MHz radio signal is 1%?) allows higher efficiency by operating class C, as the distortion harmonics are not passed due to the resonant output circuitry. (Or instead, a selected harmonic can be passed to make a multiplier stage.) Since you're still covering a number of octaves, not to mention the amplifier design being essentially the same, thus the available BW is the same, then no, no advantage can, or has, been taken by the BW reduction.

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Old 16th July 2004, 06:19 AM   #7
Jennice is offline Jennice  Denmark
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Sch3mat1c,

I'm talking audio frequencies here... nothing with modulated HF.
My consideration is about tnergy, not instant power.
My consideration is as follows:
You supply an amplifier with 20Hz - 20KHz noise.
This signal is amplified, and send to a 2-way speaker, which has internal cross-over at (for the sake of argument) 2kHz.
Energy goes to both the woofer (20-2000Hz) and the tweeter (2k - 20kHz). This system will have losses ("E_loss_fullrange"), which are handled by the heat sink.

Now, suppose we built two identical amplifiers.
One is fed with noise in the band 20-2000Hz. This amplifier will have waste energy "E_loss_LP" to be handled by a heat sink.
This amplifier is directly connected to an identical woofer as in the 2-way speaker.

The other amplifier is fed a noise signal 2k-20kHz, and will have loss energy "E_loss_HP" for its heat sink. The amplifier is connected directly to a tweeter that is identical to the tweeter in the 2-way speaker.

Now, my claim is, that since the total energy sent to the seperate speaker units is the same as is sent to the combined 2-way speaker, the loss energies to the heat sinks should be the same (apart from idle dissipation):

E_loss_fullrange = E_loss_LP + E_loss_HP


Please say why you dont think this is the case.

Jennice
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Old 16th July 2004, 06:53 AM   #8
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Yeah yeah, I know what you're talking about and you're probably confused by my terms. Actually, this very sentence:

Quote:
My consideration is about tnergy, not instant power.
Is exactly switched around! Funny how language works. Well, I learned in Physics class that energy is stored and released, power is energy in action. You charge a capacitor over a certain time with a certain power flow during that time (power is integrated (calculus-ey) by the cap into energy; likewise, power is the derivative, that is, change in energy over time). Instant power, although it is a true term (say you discharge that cap into a screwdriver: instantaneous power is through the roof as the energy is dissipated in a short period of time), I think you meant it more in terms of a sudden energy release.
Your concern is power.

Unless you *do* know what you're talking about, and I'm confused as hell

Class C resonant circuits work just as well at audio frequencies, you could make a woofer electrically tuned to 100 +/- 1Hz. It would boom to no end of course, because music demands variable frequency (the above would only work at 99 to 101Hz, anything outside wouldn't be heard at all) and short time periods (a drum beat would make that ring like a bell!).

Anyway, I originally said:

Quote:
Speakers are getting the same signal*, amplifiers are the same, power out 1 + 2 = total, dissipation 1 + 2 = total. Sounds right to me.
*In terms of what they did originally. You have a crossover at speaker or line level. Same thing.


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Old 16th July 2004, 10:58 AM   #9
Jennice is offline Jennice  Denmark
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Oh, boy.. this is getting deep ;-)

Anyway.. do we agree that there's no problem sharing this same heat sink?

Jennice
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