How To Measure Subwoofer Impedance?

[okcchad]

Does anyone know an easy way to do this? I've read some articles but they all involve creating some sort of device with a resistor to place in series with the sub.

I ask because I bought a Fi Q series sub (12") that was to be dual 1 ohm (paper work shipped with the sub says dual 1 also). I paired it with a Hi-Fonics Brutus 1208 which lists 900 W output @ 2 ohm. In this setup the sub has never seemed as loud as I expected. Not just a little quieter than expected, but probably 1/2 the expected output.

The Brutus eventually went out (haven't figured out why, but have my RMA to get it fixed) so I conducted a little experiment. I connected the sub up to my home receiver for 1 quick test. A) I do not expect this home amp to drive a 2 ohm signal, it is not very expensive (like $120 purchased 6 - 8 years ago). the sub was only marginally louder than the home sub.

What does anyone thing? Is it possible I was shipped a dual 2 ohm by accident? The Brutus is rated at 400W @ 4 ohm. If yes, then the "numbers" would start to add up for me. Having a dual 2 ohm is fine since I can run the Brutus at 1 ohm and get 1100 watts out, which should be fine as I rarely push the system to its limits.

Let me know what you think.

[Mosin]

Gain settings, H/U settings. What kind of box did you have it in?

Let it break in.

[okcchad]

Yeah, it's been in place for a few months now. Hasn't changed much, although as I got more used to it the sound levels seemed to taper off.

I've been playing with all the different settings the whole time. Any change I make to get more output (increase gain, increase bass EQ on amp, up volume on HU, etc.) just gets me distortion. I've done pretty much everything except bust out a voltmeter and get crackin with some measurements. Which is why I made this thread. I tried searching but all I could really find was some wiring diagrams and some methods for measuring amplifier output.

I guess one other possibility is that the amp may have just been bad from the start. First amp I've ever had go bad and I was way kinder to this amp than the ones I had in the 90s.

As for the box, its in a sealed box mostly because that's what I had some experience with. Sure ported would get me more output, but I just don't see that being the difference between my expectations based upon past equipment and what I'm getting from this setup. On this topic, another comparison to throw out there. My friend has 1 10' sub running on a 300W amp (forget the brands), I'm pretty sure his is noticeably louder than my 12" running on the supposed 900W. At best they were of equal volume.

[Boon]

I would suggest the amp was bad. See if you can try the sub on your friend's setup, as long as his amp is good at 2 ohms.

Don't read too much into the performance on the home receiver. Some home amplifiers have serious current limiting circuitry if they detect that they're running way under rated impedance.

[E a r t h]

I guess it's time to bust out the dmm. How did you wire it up? I hope not in parallel. Anyway, put your dmm on each coil. If it is a D1 sub, each coil should read around .7 ohm cold, give or take a tenth. Or put the probes on the speaker output of the amp for total DCR

Oh yeah, I don't know why you would want the D1 if you're trying to put a 1ohm load on the amp. that sub would either be, 2ohm in series or, .5 ohm in parallel

Edited October 31, 2008 by Earthman