Normal Cutoff for Subwoofers

[diarav]

Hi,
What is the normal cutoff frequency provided for subwoofers?
I see various values of 130Hz, 150Hz , 200Hz.

I am planning a HT set up and if I add a LP filter to the sub, I am concerned that any subwoofer signals from my DVD player exceeding the set frequency will get cut off.

So is there a standard Frequency for subwoofer cutoff ?

Thanks

[richie00boy]

For a music sub, the upper frequency will be determined by your main speakers - how low they play.

For a home cinema sub where you are using full range main speakers and the sub is driven from the LFE output of a 5.1 signal, no filtering is needed as the soundtrack is already filtered.

[diarav]

Thanks for your response richie00boy !

Actually I am including a separate 2 chan input for other sources, and converting this to a 5.1 out using a surround sound decoder circuit. So I might as well include the filter at this stage and send the 5.1 signals from my DVD player directly to the amps.

Still would a freq of 200 Hz be good or is it better to go for a lower/higher value?

Thanks

[croat47]

It you can get to 100Hz with your mains, that would be better than say 200. The directionality, and therefore the "locatability" of the source increase above ~100Hz.

[richie00boy]

So the DVD output is discrete 5.1 which takes care of that. You are left with needing to derive a filtered signal for listening to the stereo source. As said before this will be dependent on your main speakers.

You are building your own surround decoder? This is analogue I would imagine, so will not actually work very well on stereo signals unless they are Prologic encoded. Even then, the sub channel is as before, just filling in your main speakers so again the filter will be dependent on them.

To be honest, if my assumption above is correct, you are wasting your time really building the decoder. You might as well just use stereo for music, and discrete 5.1 from DVDs. Or does your DVD player only have stereo outs and you are building a Prologic decoder and won't have discrete one at all?

[diarav]

Hi ,

My surround sound decoder is from ESP's site.

http://sound.westhost.com/project18.htm

This is primarily to fill up the surround speakers, subwoofer and center speakers and will be used on stereo sources only. The filters will be applied after that and then sent to the amps.

I might as well give it a try and depending on the outcome, keep it or discard it.

Thanks.

[richie00boy]

In that case, you should take the sub feed from the summed left and right channels and apply a filter to suit the roll-off of your main front speakers.

I would advise against expecting surround sound from stereo sources, merely ambient rubbish. It should be OK for DVDs with Prologic sound though, although I'm not sure if they still encode Prologic on the stereo soundtracks these days.

[diarav]

Hi,
Thanks for your response richie00boy.

Yes, I am aware of the limitations of this type of stereo to "surround" system.

This being my first project, I just want to try something, before I venture into bigger projects.

Thanks.

[nunayafb]

Originally posted by croat47
It you can get to 100Hz with your mains, that would be better than say 200. The directionality, and therefore the "locatability" of the source increase above ~100Hz.

This is generally true however you have to keep in mind that subs are usually placed far away from the mains, or off to the side. If you center the sub between the mains (or place a sub under each main) and maintain a fairly decent time alignment then the only criteria for xover is the power response of the sub(the mains roll-off too of course).

[Thack]

200hz starts to get buzzy. These days mains are so small that a sub is needed. I always thought there was a cross-over built into the subs so it wouldn't pass any frequency above 250Hz or so.