Firstly impediance rise. I've heard many people say that its the enemy, others say that as long as you can wire your speakers down low enogh it is a great thing.

The reason, i've been led to believe, for this is that the higher the impediance rise the more efficiently your sub is playing at a frequency.

I can't see exactly how this works, if it isn't bs then at a guess i would say it has something to do with the back emf?

Also for testing purposes is it ok to do burps at half power, I've heard things about the resonant frequency changing in relation to power but once again i just can't see how things would be different when burping at half power as opposed to full power.

More to follow, just researching at the moment.

cheers

Lindsay

I would have thought impedance rise would have more to do with the temperature of the VC and nothing to do with Back EMF. Back EMF is controlled by the Damping factor of your amp from what I understand.

ive also heard that boxes can effect imp. rise also.

yes there is something else, model a sub in a ported box, fiddle with the box volume and tunning freq and watch the impediance plot change. Hmm i would rather not touch on VC temp atm, we will assume that this is for a split second burp on a normal temp coil.

yeh back emf le, dampening factor all over it but i just couldn't htink what would cause impediance rise. It was sort of the only thing that i thought might relate to it!! Cheers anyways mate

Impedance Rise will make the amplifier less efficient at higher frequencies, as amps tend to make more power at lower impedances. It's directly related to the inductance of the coil, and the resonance of the box. There is also an impedance peak at the tuning frequency of a ported box, but this has a different effect, and is related to the Q of the box and the Q of the woofer. A larger box will have less impedance peak at resonance, and so higher SPL. got to watch excursion though.

Burping at various levels will have different results, as various bits of the car have different resonance, you need to find the one which resonates the most at the desired SPL. i.e. the VR wagon has peak resonance at 46Hz with 140+ dB and 56Hz up to about 135 dB. That point, above 135 dB, is where the 46Hz resonance becomes equal or higher amplitude than the 56Hz.

you may find the frequency moves about a bit +/- 10Hz as you go up in level, but one particular frequency will stand out at the higher SPL. This is where you should tune the box.

absolute gold, thanks mate.

when you get a chance do you think you could go more indepth as to how the le effects the rise, how changing box volume will effect the rise and why? Is efficiency gained as impediance increases? Also i have noted that the impediance rise of a ported box does not always happen at the tuning freq.

So say i had a huge impediance rise (30 Ohms) and my amp made 2000wrms @ 1 ohm but only 66 @ 30 ohms (2000/30), ceritus paribus would the spl level be the same?

The impedance peak can also be affected by the loading in the vehicle, I've had the tuning frequency drop on spl enclosures by up to 10hz when loaded in the car.