bkolfo4 Posted January 16, 2010 Report Posted January 16, 2010 Thanks for clearing that up, I've also been wondering why all my coils read 1.4 ohm on the DMM, but i suppose thats normal with dual 1 subs, right? If your coil reads 1.4, it is a 2 ohm coil. If you are talking about 2 coils in series read 1.4, then it is a Dual 1 ohm sub. Current system: 1997 Blazer - (4) Customer Fi NEO subs with (8) American Bass Elite 2800.1s Previous systems: 2000 Suburban - (4) BTL 15's and (4) IA 40.1's = 157.7 dB at 37 Hz. 1992 Astro Van - (6) BTL 15's and (6) IA 40.1's = 159.7 dB at 43 Hz.
bkolfo4 Posted January 16, 2010 Report Posted January 16, 2010 The DMM measures DC resistance. It is not the same thing as impedance. It is the resistance of the coil with a DC current applied. Playing the sub with any type of AC signal is impedance. The speaker coil is just a big inductor, which causes impedance to vary with AC signals applied at different frequencies. Rated impedance is an average impedance taken from several points within the driver's operating range. According to the International Electrotechnical Commission (IEC), the lowest impedance of the speaker should be within 80% of the rated impedance (so a coil rated as 2 ohms can have frequencies that the impedance drops to 1.6 ohms if rated per the spec, but of course just like amp's power rating I am sure many of them are not). But even if they do not rate them this way, the minimum impedance will not be lower than the DCR. This is why competitors look at DCR. Even if a cold coil is burped at a frequency of minimum impedance, it will still be at or above DCR. When playing music, the amplifier will see at least the rated impedance most of the time, as it is playing several frequencies at the same time, not a sine wave at one frequency (once again, assuming the coil is rated correctly). There is also the factor of heat. The speaker coils heats up and the DCR and impedance both increase. When you put the sub in a box, the impedance changes again. New resonant frequencies are introduced due to port tuning, back pressure on the cone, etc. This is what people refer to as "impedance rise", although it is really more a change to the impedance due to other physical reactions with the cone that is attached to the coil (inductor). 99% of the time, the impedance of the coil playing music in a box is well above the rated impedance. Look at resonant frequency - The impedance can easily be 4X the rated impedance. But there are also still dips in the impedance, even in the box - this is why you cannot just assume an amplifier will work using a lower rated impedance sub due to "impedance rise". If you are going to try to get away with this, you really need to know the capability of the amplifier and measure the true impedance of your setup over the operating frequency range to make sure there are no dips in the impedance that the amplifier cannot handle. . . There is a lot more to impedance than can be explained here, but there are a lot of people that are very confused with the terms DCR, Rated Impedance, and "Impedance Rise". Sorry for the long rant, just get tired of seeing "Fi subs are only .7 and 1.4 ohms, not 1 and 2 ohms", when the truth is under normal conditions playing music, your amp is more than likely seeing much more than even 1 or 2 ohms. . . Current system: 1997 Blazer - (4) Customer Fi NEO subs with (8) American Bass Elite 2800.1s Previous systems: 2000 Suburban - (4) BTL 15's and (4) IA 40.1's = 157.7 dB at 37 Hz. 1992 Astro Van - (6) BTL 15's and (6) IA 40.1's = 159.7 dB at 43 Hz.
BITLD Posted January 16, 2010 Report Posted January 16, 2010 Good post Brian, I've been wanting to clear this up for sometime myself. Thanks. www.BladeICE.com UK/European Distributors Ascendant Audio Fi Car Audio XS Power KnuKonceptz.co.uk Facebook Youtube Channel
E a r t h Posted January 16, 2010 Report Posted January 16, 2010 it's always going to be hard for alot of people to understand especialy if they haven't had any formal electronics training
Ndnkobra Posted January 17, 2010 Report Posted January 17, 2010 If your coil reads 1.4, it is a 2 ohm coil.If you are talking about 2 coils in series read 1.4, then it is a Dual 1 ohm sub. Well i check the same terminals on one side of the speaker and it reads 1.4, and its SUPPOSED to be a dual 1 ohm sub.
bkolfo4 Posted January 17, 2010 Report Posted January 17, 2010 Well i check the same terminals on one side of the speaker and it reads 1.4, and its SUPPOSED to be a dual 1 ohm sub. Make sure your meter shows 0.0 when you touch the two leads together. . . Current system: 1997 Blazer - (4) Customer Fi NEO subs with (8) American Bass Elite 2800.1s Previous systems: 2000 Suburban - (4) BTL 15's and (4) IA 40.1's = 157.7 dB at 37 Hz. 1992 Astro Van - (6) BTL 15's and (6) IA 40.1's = 159.7 dB at 43 Hz.
Ndnkobra Posted January 17, 2010 Report Posted January 17, 2010 Make sure your meter shows 0.0 when you touch the two leads together. . . Oh wow i made a pretty noob mistake by not doing that, thanks man. the multimeter doesnt go all the way down to 0, just .7 so its fairly off (its a cheap meter). If i were to take the difference then it would be .7
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