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Old 6th April 2013, 06:52 AM   #11
abcdmku is offline abcdmku  United States
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j.michael droke, I gave both speakers 40v. Then played sine waves at 20,30,40,50,70, and 100Hz. I'd say the "21" (2985) 50hz to 100hz 102.5+-0.5db" is more of 99dB. I think the dual 2954's lower resistance gives it the edge.

bentoronto, That was my initial fear of getting the 21", but they do use a rather beefy cone.
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Old 6th April 2013, 02:15 PM   #12
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Location: Toronto and Delray Beach, FL
Originally Posted by abcdmku View Post
bentoronto, That was my initial fear of getting the 21", but they do use a rather beefy cone.
Hate to seem churlish after you've bought driver but I think this forum should record ideas for the future too.

Sure, you can make a cone out of strong stuff but the various trade-offs of resonant freq, weight, motor, stiffness, etc. lead me to a rough preliminary impression that 15 or 12 inches is biggest-optimum, today, maybe. I also believe you gotta start with a resonance down near 20 and that is "line in the sand" for bass; hard to make a driver suspension and cone weight combo that achieves that for a big driver.

With the advance of technology, maybe 18 and 21 really are better than I imagine today or in the near future.

HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio
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Old 6th April 2013, 06:52 PM   #13
OscarS is offline OscarS  United States
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unless you log the voltage going into each speaker, together with the impedance curve to see the resistance at one particular frequency, you don't really know if you're feeding them the same power. Even then, it could easily be attributed to alignment differences, as you can't possibly have the same exact alignment for both considering one has dual drivers.

..and that monkey business of "doubling Xmax"? what for? Just to use the P-P version of Xmax? Quantitatively, that sort of thing is useless for when you just want to compare relative swept volume. Sd * Xmax is enough (assuming MCMs specs are correct, which they are likely not). One Vd divided by the other is enough to compare them on a percentage basis.

Last edited by OscarS; 6th April 2013 at 06:57 PM.
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Old 7th April 2013, 05:17 AM   #14
abcdmku is offline abcdmku  United States
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I know I didn't have to double the Xmax, but the cone moves two ways. Therefore I doubled it.
The reason I gave both speakers the same voltage is because I wanted the power to be relative to the amp, not the speaker. If the speaker is exactly 4 ohms it would then get 200w at 40v, whereas if the speaker is 8ohm it will only get 100w. If that amp can do 80v then in regards to the amp it is only at 50%.
I know that isn't the normal way to test speakers, but for what I'm doing it is relevant. I did do a test where both speakers got 10w, 50w, then 300w. The dual 18's where still louder for all three.
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Old 7th April 2013, 08:21 AM   #15
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hmm.... intresting test but if you do not mind, its pointless.
with these drivers, at least.
none of them are realy subs to be honest. anything that starts to fall at 50-ish hz is a medicore bass unit.
i would choose 2 smaller drivers, the motoric power vs mass to move ratio would be better.
smaller cones have a better stiffnes than larger ones.
but, interference between 2 cones makes 100% summing of them impossible.
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Old 8th April 2013, 04:13 PM   #16
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Power = E^2/R
E = voltage
R = impedance
So 40 * 40 = 1600/4 ohms = 400 Watts
40*40 = 1600/8 ohms = 200 Watts

best to start off correct,
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Old 9th April 2013, 04:23 AM   #17
abcdmku is offline abcdmku  United States
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