Riddle Me This: LPF, LFE & Crossovers

[petrichor]

I've recently been fiddling with bass management settings on my receiver, and, despite having searched & read extensively on the subject, a few things are still unclear to me in the context of a 5.1 setup.

1. In general, how much buffer should there be between a speaker's lowest rated frequency response and the HPF crossover setting? Setting at 80hz seems to be the magic number, but I imagine this varies based on the speaker. (My mains are rated to 40hz & center/surrounds to 65hz. Set the filter at 80 and 100, respectively, for a ~40hz buffer?)

2. Why would one want to send a full-range signal to mains, i.e. set them to "large", when used in conjunction with a sub? (I've read, in several places, that you pretty much always want to set mains to "small" just in order to establish H/LPF crossovers. Is this true?)

3. Finally, a less theoretical puzzler: For experiment's sake, instead of just my mains, I set all my speakers to "large" supposing that bass would be louder, if more muddled, boomy, & bad with them all thumping in the 60-100hz range (where the crossover had previously been). Instead, surprisingly, it was far quieter. Is this due to the receiver, rated at 65w/7 channels, running out of steam? Wave cancellation? Placement? Clueless here.

Thanks much in advance!

 

[Grador]

3. Unless you set your receiver for "double bass" [terminology varies by manufacturer] when you set all the speakers to large you are having them play the bass that they were intended to and NOT sending it to the subwoofer. The subwoofer would just be getting the LFE track. With them set to small you are having your subwoofer handle this bass instead, which it is more capable of doing, and chances are you have it set a little "hot." If you turn on double bass having everything set to large might make it louder overall.

Wave cancellation and placement could also be issues here.

 

[Steve81]

1. In general, how much buffer should there be between a speaker's lowest rated frequency response and the HPF crossover setting? Setting at 80hz seems to be the magic number, but I imagine this varies based on the speaker. (My mains are rated to 40hz & center/surrounds to 65hz. Set the filter at 80 and 100, respectively, for a ~40hz buffer?)

There's no real magic number; 80Hz would be a reasonable starting point for all the speakers in your setup, and you can fine tune from there. Some people suggest a buffer since a HPF isn't a brick wall, i.e. a speaker crossed at 80Hz will still receive some content at 40Hz and even 20Hz, albeit at a much reduced level.

As one example to the contrary, THX guidelines call (or called as the case may be) for a sealed speaker rated down to 80Hz with a 12dB/octave acoustic roll off beyond that. When combined with the 12dB/octave HPF filter, you'd get a fairly steep rolloff of 24dB/octave below 80Hz and the speaker was expected to be robust enough to play up to reference levels without strain or distortion for a specific room size (depending on the cert in question).

2. Why would one want to send a full-range signal to mains, i.e. set them to "large", when used in conjunction with a sub?

Under most if not all circumstances, I'd recommend against it. Even with true full range speakers, i.e. speakers that go down to 20Hz or below, there are advantages to rerouting bass to a dedicated subwoofer(s), i.e. consistency.

3. Finally, a less theoretical puzzler: For experiment's sake, instead of just my mains, I set all my speakers to "large" supposing that bass would be louder, if more muddled, boomy, & bad with them all thumping in the 60-100hz range (where the crossover had previously been). Instead, surprisingly, it was far quieter. Is this due to the receiver, rated at 65w/7 channels, running out of steam? Wave cancellation? Placement? Clueless here.

If you're setting your speakers to large, and they can't reproduce those low bass frequencies, they're simply not being reproduced.

 

[psbfan9]

I've recently been fiddling with bass management settings on my receiver, and, despite having searched & read extensively on the subject, a few things are still unclear to me in the context of a 5.1 setup.

1. In general, how much buffer should there be between a speaker's lowest rated frequency response and the HPF crossover setting? Setting at 80hz seems to be the magic number, but I imagine this varies based on the speaker. (My mains are rated to 40hz & center/surrounds to 65hz. Set the filter at 80 and 100, respectively, for a ~40hz buffer?)

2. Why would one want to send a full-range signal to mains, i.e. set them to "large", when used in conjunction with a sub? (I've read, in several places, that you pretty much always want to set mains to "small" just in order to establish H/LPF crossovers. Is this true?)

3. Finally, a less theoretical puzzler: For experiment's sake, instead of just my mains, I set all my speakers to "large" supposing that bass would be louder, if more muddled, boomy, & bad with them all thumping in the 60-100hz range (where the crossover had previously been). Instead, surprisingly, it was far quieter. Is this due to the receiver, rated at 65w/7 channels, running out of steam? Wave cancellation? Placement? Clueless here.

Thanks much in advance!

There seems to be no specific xover setting rule for a buffer. Here at AH they say the xover should be set 10hz over the speakers lowest xover rating, others say it should be 30hz over. Your speakers are rated to 40hz, so try setting them to 50hz and go up from there.

The 80hz setting is what is recommended by THX for optimal movie track reproduction.

I had my mains set to 'large' and at times, music and movies would sound 'cluttered' at higher volumes. When set to large no low frequency's will be out put by the sub unless double bass is turned. So if you have a sub, let it do what it's made to do and handle the lower frequency's.
Now, all my speakers are xover at 60hz, and to me it sounds good.

Keep in mind these xover settings are suggestions/starting points, and not written in stone. You have to do some tweaking and find the sound that suits you.
Good luck

 

[petrichor]

3. Unless you set your receiver for "double bass" [terminology varies by manufacturer] when you set all the speakers to large you are having them play the bass that they were intended to and NOT sending it to the subwoofer. The subwoofer would just be getting the LFE track. With them set to small you are having your subwoofer handle this bass instead, which it is more capable of doing, and chances are you have it set a little "hot." If you turn on double bass having everything set to large might make it louder overall.

Wave cancellation and placement could also be issues here.

Let me clarify, as I forgot to mention an important bit in my OP: I was testing without the sub, both times, and only manipulating the HPF.

Setup: 5.0 with 40hz mains & 65hz center/satellites. No sub. Amp is an HK, 65w/channel @ 7 channels.

A. (louder bass): Only mains set to "large." Satellites & center using a 100hz crossover.
B. (quieter bass): All speakers set to large. No crossover at the receiver; full range signals across the board.

I would think B. would be louder due to more reproduction in the 65-100hz range, but in fact it was the opposite with A. being louder (just the mains). Thoughts?

 

[j_garcia]

Power handling is better with it crossed over because the signal is crossed BEFORE being amplified. In setup B you are amplifying things that 3 of the speakers are not capable of reproducing and with the x-over applied, that bass is redirected to the mains.

 

[petrichor]

Power handling is better with it crossed over because the signal is crossed BEFORE being amplified. In setup B you are amplifying things that 3 of the speakers are not capable of reproducing and with the x-over applied, that bass is redirected to the mains.

Makes sense!

 

[petrichor]

Another thought: Is the least amount of overlap between mains & a sub optimal? I.e., setting the main's HPF and sub's LPF to the same value?