TH 15" flat response to 35Hz (-3dB) - By LORDSANSUI - Page 3 - diyAudio
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Old 9th November 2016, 06:48 AM   #21
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Quote:
Originally Posted by Brian Steele View Post
Yes it does. And that's why basically every audio company quotes a 2.83V reference for their speaker products. It takes literally seconds with a voltmeter to check the output voltage from an amp to confirm that it's 2.83V. And amplifier gain is adjusted by Volts, NOT Watts. I don't have to sit down and work out what voltage I have to set the amplifier to in order to meet your "1 Watt" reference, which apparently has now been changed, by your subsequent note below, LOL. So which should I use now - Re, or measured minimum impedance in the passband?
Amp gain is set with a volume knob, not by volts or watts. Measuring the voltage is simple but the better way if you want to compare equivalent power is to adjust voltage based on minimum impedance in the passband.

Re is almost always very close to the minimum impedance in the passband, so as a shortcut you can just adjust voltage in reference to Re.


Quote:
... which now requires taking an impedance response curve and reading off Rmin, then using that to calculate what "1 Watt" would be at that frequency (and that frequency alone, because impedance will be different at every other frequency) rather than simply setting the voltage at the amp to 2.83 V. How is that more sensible as a reference?
So what if you have to measure impedance? If you want to make an equivalent power comparison you have to do what is required to do that.

This is more sensible as a reference because it's much closer to equal power input.

How does it make any sense to do an equal power comparison of two very different speakers at 2.83V?

If I have a speaker that has 1.4 ohms Re, 1 watt referenced to Re would be 1.1V.
If I have a speaker that has 16 ohms Re, 1 watt referenced to Re would be 4V.
MEASURING THEM BOTH AT 2.83V IS NOT EQUAL POWER, NOT EVEN CLOSE. It doesn't tell you much of anything at all about the speaker to measure everything at 2.83V.

Last edited by just a guy; 9th November 2016 at 06:51 AM.
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Old 9th November 2016, 09:45 AM   #22
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Originally Posted by just a guy View Post
MEASURING THEM BOTH AT 2.83V IS NOT EQUAL POWER, NOT EVEN CLOSE. It doesn't tell you much of anything at all about the speaker to measure everything at 2.83V.
I've already shown you that "equal power" is a myth. It is a made-up parameter. Made up by you. The impedance of any subwoofer does not remain constant through its operating frequency range and your "equal power" assumption is based on a fixed impedance, which does not reflect any subwoofer alignment that I know about. I haven't even mentioned yet how your "minimum impedance" adjustment (which you had to do "on the fly" in this discussion, seeing that it was readily apparent that your previous suggestion to base it on a driver's Re made no sense) also makes no sense because how would you account for sealed subwoofer systems which usually show their minimum impedance OUTSIDE of their usual operating range? You're basing your whole argument on a made-up parameter, which negates the entire argument.
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Old 9th November 2016, 10:57 AM   #23
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Interesting design Lord S, look forward to seeing you progress!

JaG, Brian is correct, Re is only applicable to one frequency, and a constant current source frequency sweep will give a single resonance peak at that frequency. For "real world" comparisons, it is much more appropriate to measure sensitivity, and a constant voltage source is used to do this. Hence the standardization of 2.83V, an arbitrary value that reflects 1W into an ideal frequency independent constant 8ohm load, (that no driver ever is!).

If you want to explore this further, I recommend a copy of "Testing Loudspeakers" by Joseph D'Appolito, a great book everyone should have on their shelf.
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Old 9th November 2016, 10:59 AM   #24
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I have to say i'm kind of with JAG on this one, comparing systems is more "fair" using minimum impedance in the passband...

5 ohm minimum impedance and 8 ohm minimum impedance would both be called "8 ohms nominal" this can make it look like the 5 ohm cab 2dB's more sensitive. While in fact the other cab is just drawing 2dB's less power. On a 2ohms stable amplifier you could connect 3 of the 5 ohms cabs, or 4 of the 8 ohms. So it's not equal power, but it is equal power in minimum impedance! There is no reason to compare 2 different systems with equal power, across the entire band.

If you'd have the same cab, same driver, just different Re (with BL and Le adjusted as well, same motor), you'll find the total impedance will scale with the Re. So it's not just the load @ minimum impedance that is lower, it's the load across the entire band.

I really love the comparisons of the Prosound Shootouts of 2007 http://audioroundtable.com/ProSpeake...sages/486.html
Power based on minimum impedance.

Last edited by carneoleon; 9th November 2016 at 11:02 AM.
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Old 9th November 2016, 11:06 AM   #25
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But you can't just take the driver's minimum impedance as the system's minimum impedance. The enclosure design could alter that radically, so you need to use the measured enclosure impedance graph, (in the appropriate pass band) to rate the impedance the amp sees.
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Old 9th November 2016, 11:10 AM   #26
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Absolutely!! Quoting myself: "using minimum impedance in the passband... "

That's also what the did in the shootout I linked
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Old 9th November 2016, 11:29 AM   #27
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And when do you do that? After building/simulating the system.
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Old 9th November 2016, 11:38 AM   #28
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Fortunately hornresp (and others) can simulate impedance. So you can check the minimum impedance, adjust Eg accordingly and compare it to other simulated systems

And to get back to the Vtc Atc stuff, just add it to the sim and you'll have an accurate simulation of your current design. Compare it to you current sim (so with compensation, thus without Vtc) and see if it even makes a difference.
Based on that you can add your pieces of wood if necessary. Or change the drawings as xoc1 suggested in post 9 and get a bit extra extension, or shave a few cm from you cabinet size
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Old 9th November 2016, 12:16 PM   #29
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Originally Posted by carneoleon View Post
Fortunately hornresp (and others) can simulate impedance. So you can check the minimum impedance, adjust Eg accordingly and compare it to other simulated systems
Indeed, I think we're actually agreeing here. Re is of no import in itself. System minimum impedance within passband is. The best way of getting that is with a constant voltage source simulation. Yes?
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Old 9th November 2016, 12:21 PM   #30
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I'd say:

Amplifier is a voltage and current source, the amount of power you can have from a system is amplifier dependent. If you plug two subs at the same amplifier one of them will play loud and is the one that has lower impedance and this is the reason that all amplifier gives more power with 4 ohm then 8 ohm. Simple as that.

The driver are divided basically at two classes 4ohm and 8ohm, so if you are comparing two system at the same class it really make sense to me to compare at specific voltage and see what shows higher SPL, if one company can reach lower Re for a given driver then others so it has some credits, they can play with all parameter and Re is one of then.

I think we should never forget that the power will always be limited by the amplifier. And efficiency is produce more SPL at the same power. Comparing the same class.

In the past we were limited in terms of electronic components so to have more power it was easy to rise the voltage. Now you can increase power increasing current source.

Power = Voltage x current (simple way)

Quote:
Originally Posted by just a guy View Post

If I have a speaker that has 1.4 ohms Re, 1 watt referenced to Re would be 1.1V.
If I have a speaker that has 16 ohms Re, 1 watt referenced to Re would be 4V.
MEASURING THEM BOTH AT 2.83V IS NOT EQUAL POWER, NOT EVEN CLOSE. It doesn't tell you much of anything at all about the speaker to measure everything at 2.83V.
This doesn't make sense, 1,4 ohm and 16 ohm are part of different classes, if it was 4,7 ohm against 5,6 ohm, I see no problem to compare both @ 2,83V and 4,7 will have some advantage regarding electric power but it doesn't means that the SPL curve will be better.

Example using car subject:
Wouldn't you compare two engine sold as 2L ? in fact one can be 1,84L and the other 2,1L.
If one of then is normal aspirated and the other is turbo, will you still compare them?
What do think is more efficient?
And the others technologies like variable valve train ans so on, all of then will impact the engine efficiency.

Compare things at the same class is the simple and easiest way to go;
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