Bi-Wiring & Bi-Amping - Page 4 - AVS Forum
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post #91 of 105 Old 12-15-2013, 03:08 PM
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Originally Posted by bemoore View Post

Maaaayyyybe. IMO, years ago, someone in marketing decided that a rating of 100 watts sounded much more impressive than a rating of 28 volts, and thus, power ratings were born. I don't know for sure, though. Just speculation.
That seems reasonable
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Just as power it not the only significant number, either. And I see WAY more emphasis on power than I do voltage.
I agree. But I would translate "power" as current, therefore amperage.

Wattage is a product of power and voltage.
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post #92 of 105 Old 12-15-2013, 03:21 PM
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Originally Posted by bemoore View Post

If you're comparing the output of the low amp in an active bi-amp system vs the amp output with a full range signal, the voltage swing will not be the same.
Not IME, which, where acoustical engineering in general and loudspeaker design in particular are concerned, one might call extensive. There won't even be all that much difference in the current draw in a single amp system versus bi-amp with the low frequency amp, since the woofer draws most of the current in a single amp system, often as much as 90%. But where there is a difference it will be in the current draw, not the voltage swing, as SPL is directly proportional to cone excursion, and cone excursion is directly proportional to voltage swing. Removing whatever voltage swing the tweeter requires won't change how much voltage swing the woofer requires to reach a given SPL.

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post #93 of 105 Old 12-15-2013, 03:53 PM
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Originally Posted by Bill Fitzmaurice View Post

But where there is a difference it will be in the current draw, not the voltage swing, as SPL is directly proportional to cone excursion, and cone excursion is directly proportional to voltage swing. Removing whatever voltage swing the tweeter requires won't change how much voltage swing the woofer requires to reach a given SPL.
The two are inseparable. V = A*R.

If the current goes down, and the resistance stays the same, then the voltage *must* go down.

As I understand it: the various frequency wave-forms will sum. So if I have an 8V 100Hz wave, and an 8V 1000Hz wave, then (where peaks meet) I will have some >8V peaks.

If I separate these two waves with an active crossover, then my peaks in each amp will by 8V again. Contrary to what Bill says, I *do* lower my voltage swings (as measured going into the crossover) because I'm not summing as many frequencies.

Where I think Bill is right is that this may not make a lot of *practical* difference; as the vast bulk of the voltage is being delivered to a single driver anyway (the woofer).
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post #94 of 105 Old 12-15-2013, 04:20 PM
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Originally Posted by JerryLove View Post

The two are inseparable. V = A*R.

JL, just because there is an equivalency equation out there doesn't mean you get to use it indiscriminately, you have to understand what it means. For instance, you can have a voltage and zero current, why? Because voltage measures the electrical potential difference between two points. That's all it is, nothing more, it doesn't require a current between the two points and therefore they are not "inseparable".
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As I understand it: the various frequency wave-forms will sum. So if I have an 8V 100Hz wave, and an 8V 1000Hz wave, then (where peaks meet) I will have some >8V peaks.

If I separate these two waves with an active crossover, then my peaks in each amp will by 8V again. Contrary to what Bill says, I *do* lower my voltage swings (as measured going into the crossover) because I'm not summing as many frequencies.

So? When calculating total SPL of the speaker you still include both amps and therefore you would sum the voltage of both amps and again would be over 8v. Or to get the same SPL with a single driver you'd have to push the amp for that driver past 8v. You have to understand what the other person is saying,.
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post #95 of 105 Old 12-15-2013, 07:23 PM
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Originally Posted by ien2 View Post

When calculating total SPL of the speaker you still include both amps and therefore you would sum the voltage of both amps and again would be over 8v..
You would sum the current draw of the two amps, but not the voltage swing. The low frequency driver/amp and high frequency driver/amp operate as parallel voltage driven systems, not series. If both are driven at 8v the total voltage swing is 8v, just as a pair of 1.5v batteries parallel wired still deliver a total of 1.5v.
As for 'summing of frequencies', nothing of the sort occurs.

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post #96 of 105 Old 12-15-2013, 07:35 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

You would sum the current draw of the two amps, but not the voltage swing. The low frequency driver/amp and high frequency driver/amp operate as parallel voltage driven systems, not series. If both are driven at 8v the total voltage swing is 8v, just as a pair of 1.5v batteries parallel wired still deliver a total of 1.5v.
As for 'summing of frequencies', nothing of the sort occurs.
ien2 is talking about amplifying two frequencies through a single amp. Bill is talking about amplifying each freq through it's own amp (bi-amping).

If two signals of differing frequencies are present on the same wire, then the voltages WILL sum, unless one's a harmonic of the other, and they're phase locked.
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post #97 of 105 Old 12-15-2013, 07:48 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

You would sum the current draw of the two amps, but not the voltage swing. The low frequency driver/amp and high frequency driver/amp operate as parallel voltage driven systems, not series. If both are driven at 8v the total voltage swing is 8v, just as a pair of 1.5v batteries parallel wired still deliver a total of 1.5v.
As for 'summing of frequencies', nothing of the sort occurs.

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Originally Posted by bemoore View Post

ien2 is talking about amplifying two frequencies through a single amp. Bill is talking about amplifying each freq through it's own amp (bi-amping).

If two signals of differing frequencies are present on the same wire, then the voltages WILL sum, unless one's a harmonic of the other, and they're phase locked.


Bah, i must have closed my browser before my edit went through. I wasn't clear, that was my fault and for what i originally wrote Bill's correction is right.
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post #98 of 105 Old 12-15-2013, 07:51 PM
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Originally Posted by bemoore View Post

If two signals of differing frequencies are present on the same wire, then the voltages WILL sum, unless one's a harmonic of the other, and they're phase locked.
If you have x volts at 100 Hz and y volts at 200Hz you don't end up with x+y volts, you have x volts at 100Hz and y volts at 200Hz. I'm not schooled in every field of electronics, so I can't say that your statement is untrue in any application, but it does not work that way in audio,

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post #99 of 105 Old 12-15-2013, 08:45 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

If you have x volts at 100 Hz and y volts at 200Hz you don't end up with x+y volts,
Yes, you do, unless, as I've already mentioned, the frequencies are harmonics.
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Originally Posted by Bill Fitzmaurice View Post

you have x volts at 100Hz and y volts at 200Hz.
200Hz is a harmonic of 100Hz. Try shifting one of those frequencies by 10%.
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I'm not schooled in every field of electronics, so I can't say that your statement is untrue in any application, but it does not work that way in audio,
It works in any electrical circuit. Once the signal reaches the driver, and becomes a sound wave, I don't know how it works. But while the signals are electrical, you will have voltage peaks at x + y volts. This may not be obvious in the frequency domain, like on a spectrum analyzer or audio analyzer. Look at the signals on an oscilloscope.
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post #100 of 105 Old 12-15-2013, 09:24 PM
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Originally Posted by bemoore View Post

Yes, you do, unless, as I've already mentioned, the frequencies are harmonics.
200Hz is a harmonic of 100Hz. Try shifting one of those frequencies by 10%.
It works in any electrical circuit. Once the signal reaches the driver, and becomes a sound wave, I don't know how it works. But while the signals are electrical, you will have voltage peaks at x + y volts. This may not be obvious in the frequency domain, like on a spectrum analyzer or audio analyzer. Look at the signals on an oscilloscope.

Actually harmonics don't matter any. Since we are dealing with an alternating current, as long as both amps aren't playing at the same frequency (where you now have to see how they are synced) at some points it'll be cumulative. However nearly all time it'll be a fraction of the total sum. Again this would the case where the amps are combined before reaching the drivers. This was the mistake I meant to clarify before. So this would only be the case where the amps are say connected to the same wire, or if the bridge between the terminals on the speaker are left intact. But my edit was supposed to take that part out since it really isn't bi-amping at the point.
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post #101 of 105 Old 12-16-2013, 07:01 AM
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Originally Posted by bemoore View Post

Once the signal reaches the driver, and becomes a sound wave, I don't know how it works.
I do. This is how voltages combine in audio/loudspeaker circuits:

If you run a 3v signal at 100Hz this is what you get:

3v100Hz.jpg

If you run a 3v signal at every frequency this is what you get:

3v.jpg

That’s 3 volts at every frequency, not 3+3+3+3 etc.

This relates to SPL in this fashion, first showing a 2.83v signal at 100Hz:

2.83v100Hz.jpg

Expand that same 2.83v signal to every frequency and you get this:

2.83v.jpg

The reason you don’t get a uniform SPL across the spectrum is the differing sensitivity of the speaker to each frequency. But the voltage of the input signal would be uniform. If you split that chart at, say, 3kHz, with the left portion being the woofer, the right portion being the tweeter, the voltage required for each driver to reach the given SPL remains 2.83 v, whether the source is one amplifier with the signal divided passively by an internal passive crossover, or two amplifiers, with the signal divided actively prior to being amplified.

As a side note, when you take a FR measurement you’re not measuring decibels, you’re measuring the voltage output of the measurement microphone at each individual frequency point of the sweep. That voltage is extrapolated to arrive at the SPL.
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Look at the signals on an oscilloscope.
We almost never look at an oscilloscope in the loudspeaker design field, as it's for the most part irrelevant. Judging by your posts you seem to have a strong EE background. That's a good stepping stone to the more specialized field of Acoustical Engineering, but they're not the same thing, and not everything taught in EE necessarily applies to AE.

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post #102 of 105 Old 12-16-2013, 08:01 AM
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Quote:
Originally Posted by bemoore View Post

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Originally Posted by Bill Fitzmaurice View Post

You would sum the current draw of the two amps, but not the voltage swing. The low frequency driver/amp and high frequency driver/amp operate as parallel voltage driven systems, not series. If both are driven at 8v the total voltage swing is 8v, just as a pair of 1.5v batteries parallel wired still deliver a total of 1.5v.
As for 'summing of frequencies', nothing of the sort occurs.
ien2 is talking about amplifying two frequencies through a single amp. Bill is talking about amplifying each freq through it's own amp (bi-amping).

If two signals of differing frequencies are present on the same wire, then the voltages WILL sum, unless one's a harmonic of the other, and they're phase locked.

What actually happens is that the largest instantaneous peak voltage will be the sum of the two peak voltages. but most of the time the voltages will sum to be less than that.

This is 100 Hz and 200 Hz mixed 1 to 1



This is 100 Hz and 202 Hz mixed 1 to 1



They both have crest factors (ratio of peak to average) of 6 dB which is 3 dB less than a pure sine wave. That means that either has half the average power of a pure sine wave with the same peak amplitude. So when you start talking about how multiple sine waves mix, and sum the results are complex - each is a "depends on" situation.
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post #103 of 105 Old 12-16-2013, 08:41 AM
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You're looking in the frequency domain. You will not see the summing effect looking the frequency domain. You must look in the time domain. I.e. with an oscilloscope.
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Originally Posted by Bill Fitzmaurice View Post

If you run a 3v signal at every frequency this is what you get:
If you run a 3V signal at every frequency, what you get is infinite power. You can't have a signal at EVERY frequency simultaneously. Your frequency response plots show the result of sweeps, in which, at any point in any sweep, only one frequency is being passed, and one frequency is being measured. I'm familiar with the process. It's the same as with network analyzers, with which I'm very familiar.

The entirety of your argument and examples involve passing one frequency at a time, which is NOT what we're discussing.
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post #104 of 105 Old 12-16-2013, 09:56 AM
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Originally Posted by bemoore View Post

You can't have a signal at EVERY frequency simultaneously..
As a matter of fact, you do. We don't measure response as a totality, we measure one frequency at a time, but that's only because the limitations of the measurement gear means that we have to chart each frequency as a separate entity, connecting the dots as it were after taking the individual measurements. Our ears don't have that limitation, so they do listen to what is a signal at every frequency simultaneously. The electrical difference between having one frequency versus all frequencies receiving signal at the same point in time isn't seen in voltage swing, it's seen in current draw.

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post #105 of 105 Old 12-16-2013, 10:30 AM
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Originally Posted by Bill Fitzmaurice View Post

As a matter of fact, you do. We don't measure response as a totality, we measure one frequency at a time, but that's only because the limitations of the measurement gear means that we have to chart each frequency as a separate entity, connecting the dots as it were after taking the individual measurements. Our ears don't have that limitation, so they do listen to what is a signal at every frequency simultaneously. The electrical difference between having one frequency versus all frequencies receiving signal at the same point in time isn't seen in voltage swing, it's seen in current draw.
This measurement gear limitation you speak of... also affects the equipment that generates, processes, amplifies, filters, etc, audio signals (or any electrical signal, actually). This equipment is not capable of generating, amplifying, etc, EVERY signal in the audio band simultaneously. It defies the laws of physics.
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The Laws of Physics aren't swayed by opinion.
Oh, I see you like irony.

Look up Superposition as applied to electronics.
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