Using passive xover on sub


2010-07-25 5:48 am
HI all first post on the forum so i appoligise if it is in the wrong area.

I'm chasing some info about crossovers i have a yammy amp which is able to run two sets of front speakers and i also have a spare sub laying around (the amp in it blew) my question is if i put a basic xover in between the out put of the amp and the sub at say 80hz there shouldnt be any problems?? the impediances match up and the speaker can handle the out put of the amp i currently have a 12 inch but would like to put this 10 inch to good use and this is the most cost effective way i can think of

cheers in advance

here are links to parts express low pass filters at 80 hz for both 4 ohm and 8 ohm speakers for less than $20 each.
but you only mentioned that you have "front" outputs, which i imagine would be left and right channels. which means if you were to hook this sub to your amp it would be through either the left or right channel, which means that you are only playing one side of the low end response. unless you are using a dvc sub, where you could connect one voice coil to the left and the other voice coil to the right. but then you would need to buy two low pass filters.
in addition, by using a low pass filter on your sub you are wasting about 30% of the power that your amp is putting into your sub. so i would agree with dave, it would be best to buy a cheap sub plate amp that will deliver a mono low frequency signal to the sub and deliver the filtered signals to a left and right output where you can attach your current speaks to. all done without wasting power. parts express has a 70 watt sub amp like this for about $70.
but it's your call. hope this helped.

80 Hz Low Pass 4 Ohm Crossover | ...(4 ohm)
80 Hz Low Pass 8 Ohm Crossover | ...(8 ohm)
It has to be said, too, that the PE crossovers, valid alternative that they are, do not use the big and expensive parts needed to give highest possible sound quality.
A bipolar electrolytic and a modest (iron, ferrite?, can't tell) cored inductor are not great ingredients for HQ LF.
Also, every passive crossover's response is heavily affected by changes in the driver impedance within several octaves either side if the nominal XO frequency. LPFs at ~100Hz are usually on the upper slope of the driver / systems LF resonance(s) and the results are rarely anything like you might be hoping for.
If you can accomodate it, go the active route. Even a modest plate sub amp will give you much more or the 'thump' that you expect from a sub than ANY passive crossover. :)
Kepp in mind that when using passive x-overs at these frequencies, an impedance-correction is a must, especially when dealing with sub-drivers with a high Le... An active X-Over does a sooo much better job than a simple passive xover like the one linked above... ANd even if one would go through all the trouble to compensate everything "going wrong" in a passive x-over, it still would be inferiour to a active-solution.
In Europe, active-xovers of very high quality are sold for around 30,--, doing it yourself is a matter of a few bucks.... A plate Amp (aka "subwoofer-modul" in Germay) with everything you need can be bought under 100 Euros, when on sale, sometimes 60 euros is possible.