Low Pass Frequency?

[diydestruction]

Hiya,

I've got a Sony DB1070, and some TEAC 5.1 Speakers, had a look on the back of the Sub and theres a Low Pass Frequency knob ranging from 50Hz - 250Hz. Where should it be set? As its not mention in the Manual (if you can call it that! :))

Any help much appreciated!

Thanks

[Marcw]

Hi, as I understand it (and how I have my set-up configured) is that the frequency cut off should be ever so slightly higher than the lowest frequency your speakers will reproduce. For example, my B&W speakers extend down to 50Hz so I set my sub crossover at 55hz, this means that at 50 - 55hz my speakers and sub can both produce bass. Above 55 hz the job is left to my speakers, below 50 hz the sub is doing it's job alone. This doesn't take into account the bass management facilities of 5.1 sound, ie, where is your bass routed on your processor / amp? Then all you need to worry about is setting the sub volume correctly...

Make sense? If anyone knows different then please let me know.

Marc.

[Neon]

Good answer! All I would add is that you should then listen to it and adjust. You are aiming for a smooth transition. It all depends on how your mains roll off and, as Marcw states, where your LFE is routed on your amp (IMO best to remove this from your mains if you've got a sub).

[diydestruction]

thanks!

gonna have a play about with it now! though another problem (?) I think I'm experiencing is everytime I turn the Sub off after watching a movie, it "pops" before switching off.... dunno if thats suppose to happen...

anyway, thanks again...

[Marcw]

No probs. With regard to the "popping" sound, I sometimes get that with my sub too but not always. If you're worried about blowing a speaker then one way around it is to turn the volume all the way down on the sub's internal amp (assuming it's an active sub) then power it off. Make sure you remember what it was set to before though! Personally it doesn't bother me too much as it only happens very occasionally.

Marc.

[pjweston]

Note that in terms of the amp.'s bass management features mentioned by Marcw, the speaker frequency response is only an issue if you've set the (front) speakers to 'large' and told the amp. to send bass to both speakers and sub. (not sure of the exact Sony terms for this). If all of your speakers are set to 'small' then simply set the sub. to 250Hz and let the Sony filter out the higher frequencies.

I'd also add one minor caveat to Marcw's comments...

If you're setting the low pass based on the front speaker's frequency response then I'd recommend setting it 5-10Hz lower rather than a little higher. If you set the low pass a little higher than the speaker's low end then some bass frequencies will get additional amplification causing the bass to sound uneven. Setting it a little lower ensures that just as the main speaker's frequency response is rolling off, the sub is rolling on (for the want of a better term :) ).

[MikeK]

Hmmm, not sure I'd agree ther PJ.

The lower frequency quoted for a speaker is most often the -3dB point (ie the frequency at which the sonic output is down by half).
Likewise, the frequency setting on the rear of a sub, should be the point at which the subs output is down by 3dB. (ie if you set for 70Hz, the sub's xover should roll the output off so that it's 3dB down at 70Hz)
So you should set them the same. If you set it lower (although many sub's can't be set below 50Hz in any case), then you may end up with a "hole" in the bass response.
Don't forget too, that the figures quoted for speakers are those expected in an anechoic chamber - the in-room response may be quite different, due to a variety of factors. That's why a set of speakers can sound fab round at the shop, but only average when you set them up at home (those curtains draped on the walls aren't there for show :) )

However, forget all that theory - the chances are the speaker manufacturer is a few Hz optimistic anyway, and it's doubtful whether the dial on the back of the sub is that accurate either.
Use it as a starting point, and then have a fiddle about until it sounds best. :)

[Beddie]

As I understand it, the "best" option for home cinema is to turn the sub to the highest setting, as the amp does the crossover thing for you.

This should not depend on whether you set your speakers to large or small, but it would make a difference if you set bass to output to both fronts and sub. Why you would do that I don't know though.

This would not be the same for hi-fi though, as the correct crossover point would be needed to avoid a bass hump or hole.