What's the word on mixing bass?

[leadbelly]

Originally posted by JasonB
There are always exceptions, but if you are using a quality subwoofer, crossed over and located properly and not overdriving it it should not be an issue. If you are using a cheap subwoofer, to high of a crossover, poor placement, or are overdriving it then yes I could see that the harmonic distortion generated by the subwoofer could draw attention to itself and cloud the stereo image.

Keep paddling, but I think you're drowning. How about a little science and numbers thrown in with your handwaving generalities? For music, I'd take a stereo set of the "cheap" subs in your example every time over a single "quality" sub. That's the beautiful thing about this forum, to have an open mind and not regurgitate the self-serving justifications for compromise of the mass market products.

[JasonB]

Originally posted by leadbelly


Keep paddling, but I think you're drowning. How about a little science and numbers thrown in with your handwaving generalities? For music, I'd take a stereo set of the "cheap" subs in your example every time over a single "quality" sub. That's the beautiful thing about this forum, to have an open mind and not regurgitate the self-serving justifications for compromise of the mass market products.

I did try a google search for harmonic content of some bass instuments, and believe me if I had found usefull links I would have posted them.

Also, I mentioned the cheap HTIB sub in an earlier post because it was a good real life example of what I had heard and something others may be able to relate to. In the post you are replying to here I never mentioned commercial or DIY subs so I'm not sure why you are even making that last statement, a little self serving on your own part perhaps.

I will still take a single "quality" subwoofer over a pair of "cheap" ones anyday and thats fine if you prefer the opposite. I have never listened to a sytem and thought the lack of "imaging" below 80 hz was poor. However I have listened to several systems where drivers with high harmonic distortion down low have drawn enough attention to themselves to be a distraction.

Jason

[bentoronto]

Never thought I'd hear anybody ever say, Give me two cheap subs instead of one good one.

Bass instruments have very large power outputs in their harmonics, can't be otherwise, outside of electronic "instruments." In fact, a loud tweeter like the marvelous Ionovac and corona wind horns with their bluish bulbs tend to "hog" the directionality all to themselves for just about every instrument.

This is really a place for blind experiments. If you tell a listener, "See that thumbtack on the wall, the woofing is coming from it...." that's where they will localize the sound. Being a super-sensitive (read: arrogant, self-deluded) audiophile (as many of us just happen to be), you can localize the sound from any thumbtack (or mono woofer) in the room anywhere you think is producing the sound. So statements like "I can always tell who's doing the woofing" say more about the lack of objectivity of the tester than about woofing.

[bentoronto]

Another reason for mixing bass, from the world of practical considerations:

With a mixed bass, your electronics takes the full stereo signal, mixes it with no distortion to speak of and puts it through a band-pass filter (AKA high pass filter with sharp subsonic filter).

But when you have two channels, you have two cross-over units and so the upper cross-overs (high-pass) have to track one another in parallel and so do the lower ones (the sub-sonics, well, not as critical).

Getting these low frequency filters to track one another is hard to do, even with a lot of tedious charting and hand-tuning. Moreover, since even little discrepant phase shifts matter a lot at low frequencies, you need to be quite accurate over quite a long stretch of frequencies not just in amplitude but also keeping phase shift tracking together.

I haven't mentioned the mid-range high-pass filter tracking because the issue is the same for mixed as for stereo bass.

Easy to overlook important stuff like that.


Is there any way to return to a old post to edit it?

[owdi]

Originally posted by bentoronto
Is there any way to return to a old post to edit it?

You can only edit your most recent post.

I recently analyzed a few of my favorite songs for stereo bass content. Don't know if I did it right... my process using cooledit:

1. Perform frequency analysis
2. Invert left channel
3. Sum to mono
4. Perform frequency analysis again
5. Compare

I found that the summed signal had plenty of bass content all the way down into the 40's. Thinking back to my process, there is a good chance CoolEdit performed an intelligent sum to save the bass, and my testing was flawed. Well damn, already typed this up so I may as well hit post. :-(

Dan

[bentoronto]

Hooray.... a guy who believes in data.

Not sure I see the flaw in your analysis but if anything it is too sensitive. However, there are logical differences between stereo on the recording and playback practice.

There is not much reason for the recording producer to mix the bass or in any way to separate it to different channels or to try to guess what the hi-fi music lover has for their cross-over points... at least not early in the process. I would think downstream in the process, maybe the HT sound recorders do think in terms of home-users having a single subwoofer and they are likely to bend their sound accordingly.

Disirregardless of finding somewhat independent low frequency stereo channels, it still may be no violation of good reproduction principles to mix them because there may be no "validity" to those differences.

[phase_accurate]

Maybe a useful sidenote:
I have a small PA system that is used for private parties etc every now and then. The tops comprise of a 10" and a horn, crossed-over passively. Then there are two 6th order bandpass "sub"-woofers crossed over actively at 120Hz (the highpasses for the tops are of course active as well). Both channels are summed and then lowpass-filtered in the crossover. So I basically have a mono signal for the bass - although I use a stereo amp for the bass.

To make a long story short. My experience is that I achive the MOST bass when I position both subwoofers close together. But the better integrated and more PRECISE bass is achieved when I place the tops close to the subwoofers (usually the tops standing on the subs).

Regards

Charles

[bentoronto]

Originally posted by phase_accurate

snip

To make a long story short. My experience is that I achive the MOST bass when I position both subwoofers close together. But the better integrated and more PRECISE bass is achieved when I place the tops close to the subwoofers (usually the tops standing on the subs).

Regards

Charles

Interesting. Supports the value of one good woof being better than two poorer ones (putting them together is synergistic, like having one big better one).

About deterioration of the image when woofers are separate from upper-range, it is also a question of how sharp the filtering it. Anything less than say, 24dB/8ave is going to have a lot of sound coming from the woofer even above 240 Hz, which is likely to be detectable/directionalizable (even with normal instrument harmonics present in the mid-range) and would besmirch the image, as you indicate.

Even a nominal 24dB/8ave filter might be down only 18-20 dB at 240 and anything shallower, correspondingly less.

BTW, no distrespect, but awfully hard to test such things objectively (well, subjectively but carefully) when the arrays are sitting there before your eyes.