A question on low pass filters

[Vaughan]

I think the reason why I disagree with the "lowering crossover if you have a floorstander" option is that the information voiced by the speaker at, let's say, 40 hz will not exactly be cancelled by the subwoofer provided it's also reproducing 40 hz content in the LFE channel.

But if both channels are different with different information contained therein then it is highly improbable that cancellation (or reinforcement) can happen. Just my thoughts on it.

--Regards,

[richie00boy]

I see what you are saying, I'm making the assumption the sub is running of the front left+right mixed, not some kind of LFE signal.

[Vaughan]

Yes. Exactly.

I still have no idea why I see people use the subwoofer low pass filter instead of using the crossover in the AVR. I've encountered so many setup's where the crossover control on the sub is at 80 hz but then in the AVR, crossover is set to 80 hz, speakers set to small.

People don't realize that they are adding two low pass filters in series. I even tried test tones today and found that the level of the tones go down dramatically when set to 80 hz (and 80 hz low pass filter used at the back of sub).

Once the crossover control is set to maximum freq, there is greater output. Just shows you how much cancellation goes on.

--Regards,

[phreeky82]

My new setup (to be), which I'm slowly in the process of having a go at - haven't actually bought the parts yet, still thinking about options, will be:

- AVR x-over set to 80Hz (50Hz, 80Hz, 100Hz, .... are my options)
- Floor standers are bi-amped, MTM section using AVRs mains output, Woofer a separate amp.
- The AVRs sub setting turned off, mains on "Large", other speakers set to "Small", so all bass (+LFE channel) will go to mains
- The mains pre-outs will go through an active x-over @ 60Hz or so, < 60Hz to sub, > 60Hz to woofers.

Advantages I can see:
- The woofers in the mains (8"s) sound nicer for tight bass and music etc, but cannot deliver truly deep bass. The sub doesn't sound great at the higher bass freq. In a sense it's the best of both worlds.
- The surrounds/centre etc will effectively be high-passed at 100Hz (or maybe 80Hz) allowing for a smaller speaker - bit of a compromise really. The bass to them will be split between the mains woofers and the sub.
- The mains will effectively be high-passed at 60Hz.

The disadvantages:
- The "Large" setting for the mains means that a full-range signal is sent to the MTM config, with my only solution (currently in use for testing) being a passive high-pass. For testing purposes I'm using a cap on the MTM section and a coil on the W @ 225Hz, it seems to cope well.............is significant power being wasted by not having a receiving driver for all frequencies there????
- Cost, I have to build an active stereo 2-way (looking at the Rod Elliot stuff at present)

Does this sound like a worth while adventure, or a waste of time (the money is quite insignificant)? Considering I already had all the passive components, the only cost is the active 2-way and I'm sure I'd find a use for that if I don't like this new setup.

[richie00boy]

Well it comes down to if you want it for music or films. For music you should not use the LFE signal, just take the fullrange signal from left and right, so then you would set the appropriate crossover blend (usually lower than 80Hz) with the sub control.

In fact you can do films this way too if your amp can route the LFE channels to front left and right. That's what I do.

[brsanko]

the crossover in the receiver is in the preamp ciurcut and so does not react the way you are describing with the crossover in the subwoofer. I would think it would merely increase the slope and not affect the frequency. I'm guessing though I may be wrong. And whether or not the front speakers and the sub are playing the same information is dependant on the settings on your receiver. I would assume if you set the front speakers to large and the other speakers to small the receiver would send the bass information from the LFE channel(duh) and the surround and center channel but not from the fronts. I have B&W DM220's in my front channels with two 8" woofers each so they are capable of decent bass performance and the rest of my speakers are very small but I still set the fronts to small because this take a great strain off of them and leave more power for clean and clear midrange. Not only that but the lower the excurtion of your woofer the lower your over all distortion. So if you're Sub is well placed so as not to make it obvious that the bass is not comming from the main speakers your better off setting your front speakers to small IMHO.