multidriver multi impedance multicell

[valhallax]

dont know if anyone noticed the two boxes in front of the 210 in my christmas pick..but im fairly certain santa lives in oklahoma. my other 515e's showed up from bill, reconed and beautiful. gonna throw my other 210's together, after much gathering of parts. i will wire the 2 16 ohm 515's parrallel to get an 8 ohm load, this way i can use my 809 crossovers. the horn for these will be 1005's with dual throats. now, i have 4 8ohm 288's and 4 16 ohm 288's. by running one of each per side i should be just over the 8 ohm requirement for this crossover, run in parrallel. my question is..wiil the 8 ohm driver play louder than the 16 in the same circuit? these are for the garage and will be driven by an altec 711 reciever only.

[bfish]

Hi John,

I don't know about Santa, but there are lots of equally nice folks from Oklahoma for sure!

Originally posted by valhallax:
...my question is..wiil the 8 ohm driver play louder than the 16 in the same circuit?...

<font size="2" face="Verdana, Helvetica, sans-serif">Yes it will. For any multi-driver combo, no matter the wiring scheme, the impedances should be closely matched on all drivers.

If you're just using a pair of 288s per side, use the 16s wired parallel for a proper load for the 8 ohm XO, and balanced output from all drivers.

If you're shooting for 4 per horn...(whew)...a series/parallel scheme with all 8 ohm drivers will sum at 8 per side with uniform output from all. The same s/p scheme with 4x16s will sum at 16.

S/P for 4 drivers is acheived by wiring 2 pairs each in parallel, and connecting the pairs in series (+ to -).

[valhallax]

if i do mix impedance in a parrallel circuit..say one driver with a dcr of 5.4 and another with 12.2, giving me a total resistance of 8.8 ohms.. can anyone speculate the drivers independent db output? perhaps i could use this in a line array of horns where a 8 cell horn clearly has a higher out put than a 15 cell horn, thus equalling them out a bit?

[bfish]

Half the impedance = twice the current = twice the power dissipated at any given drive voltage = 3dB.

[valhallax]

hey bfish..whoa..slow down a minute. im not following you there. my 5.4 ohm driver will see a 8.8 ohm load, uh.. this is all purely theoretical at any rate, as ive done as youve suggested, by running the 16ohm drivers in parrallel. however learning along the way. my 16 ohm drivers have new diaphragms from bill and i was reluctant to use them in the garage, was where this whole thing started. through the day, ive had to go over my 8 ohm drivers as 3 had loose phase plugs and one needed the conversion kit. built a couple horn sleds.. still need to get my old 515e's out of my 816 cabs that i use for rear in my surround. will replace them with some nice 418's. but back to the math. can you please clarify a bit for me?

[bfish]

OK, to start with, forget about the DC resistance unless you plan to drive them with DC. Impedance is what matters to an AC audio signal.

If you connect an 8 ohm driver and a 16 ohm driver to a common voltage source, the 8 ohm driver will dissipate twice the power as the 16 ohm one will. It will be that way no matter if they're in series or parallel. The only difference the wiring scheme will make is the total impedance load seen by the source, which is 5.3333 ohms for parallel or 24 ohms for series.

So, with one driver dissipating twice the power as the other, the difference in output would be 3dB between the two.

When the acoustic output of such a mismatch combines in the Y adapter, there are likely to be further complications, but I'm not sharp enough to predict them.

Seems like there's always somone here with the wrong impedance 'frams for their system, maybe you could do a swap that would be mutually beneficial.

[bfish]

Just a thought, since you may need to attenuate the HF anyway, you could parallel a 16 ohm power resistor with a 16 ohm driver, effectively making it an 8 (sort of).

Added;

That would only work if you only used the 16 ohm drivers. If combined with the 8s, it would increase the output difference to 6dB, as an extra 3dB would be burnt up in the resistor.

<font color="#FFFFFF" size="1">[ December 26, 2007 10:32 PM: Message edited by: bfish ]</font>

[valhallax]

is then an 8ohm driver twice as loud, no matter the voltage source? say 75 watts at 8 ohms and 75 watts at 16 ohms?

[bfish]

Nope, 75 watts through either will produce ~equal acoustic output.

Added;

It's all simple Ohm's Law, just substitute impedance for resistance.

<font color="#FFFFFF" size="1">[ December 26, 2007 11:30 PM: Message edited by: bfish ]</font>