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Old 2nd February 2008, 08:28 PM   #11
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It's the "inaudible below 140 Hz" thing that I think was dis-proven a while back. Apparently we can detect directionality at low frequencies. Just how low and under what conditions, I'm not sure. No question that room effects at low frequencies confuse the issue beyond belief, and it seems a valid argument for mixing the bass. I don't even have a sub right now, but the few I've built have all been singles. Still, given the right room and conditions, a dual setup might localize drums better- has anybody had both and could you tell the difference?
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Old 3rd February 2008, 02:35 AM   #12
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I am no longer surprised at new scientific findings - today Vitamin E is good for you yesterday, but today, maybe bad for smokers. There's some direction finding with a single ear (even with an immobilized head) and that was a bit of a surprise albeit now 50 yrs ago. So maybe you are right. But I would like to see the basis of your claim that directionality exists much at XX Hz.

To be sure, even woofers make rude noises and hiss and the speaker is detectable in that sense. Likewise, no doubt possible to tell if one or two woofers are playing, the difference between mixed bass and stereo, and so on for basic discrimination tests.

I guess my belief is that iif there were two woofers in a room and your head was more or less steady in one location, you couldn't answer which was playing an 80 Hz note even if you knew they sounded different (which they probably would).

You believe otherwise?
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Old 3rd February 2008, 05:23 PM   #13
JasonB is offline JasonB  Canada
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Quote:
Originally posted by bentoronto

I guess my belief is that if there were two woofers in a room and your head was more or less steady in one location, you couldn't answer which was playing an 80 Hz note even if you knew they sounded different (which they probably would).

You believe otherwise?
I'd for the most part agree with that statement. However there are things that can make subwoofers playing at or below that range easier to localize. It could be harmonic distortion, mechanical noise at higher excursions, or port noise if it's a ported box. I once had a subwoofer using a fairly inexpensive driver and if I pushed the crossover frequency above 120hz the harmonic distortion became strong enough for me to locate the subwoofer. I think that if you are going to go with a single subwoofer in your room there are are several things you could do to make it less easy to localize;

-Keep the crossover frequency as low as your mains will handle
-Use a driver with low harmonic distortion
-Keep the subwoofer between your mains or as close to them as possible.
-Use an adequately sized port to avoid port noise
-Put your subwoofer behind a couch, a stuffed chair, or some other objcect that will absorb some of the higher frequency harmonics
-If you have carpet in your room and the driver is suited to it, build a downfiring subwoofer.
-Use a bandpass enclosure, it will actually filter out some of the mechanical noises and harmonic distortion(I owe credit to Zaph for making this observation) It's even more important to have an adequately sized port in this case since all of your output is through the port.

As far as stereo bass is concerned it's my opinion that the only things that make stereo bass audible as actually being in stereo are the exact same things that you want to avoid in a subwoofer such as harmonic distortion). Even if I am wrong an by chance the human ears can detect very low frequency sounds in stereo there is one other very important point to make. Any instument that makes sound has harmonics, and it will be those harmonics that your ears are able to locate. So unless you listen to recordings made up of low frequency sine waves mixed in stereo then I don't see much of a point to stereo subwoofers.

Jason
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Old 3rd February 2008, 05:50 PM   #14
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Quote:
Originally posted by JasonB
Any instument that makes sound has harmonics, and it will be those harmonics that your ears are able to locate. So unless you listen to recordings made up of low frequency sine waves mixed in stereo then I don't see much of a point to stereo subwoofers.
Unlike the rest of your post, that last part completely misses the point. Harmonics which are present in the source are taken care of by the sub low pass filter; these localizable higher frequencies do not magically make it past the filter because they come from a bass instrument. The distortion of the sub woofer itself, which is in general a relatively large value on the order of 1%, imparts distortion on the sound and makes the sub localizable.
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Old 3rd February 2008, 06:44 PM   #15
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I know I read an article on this several years back, but I've no recollection where. Frankly, the more I think about it, the less I'd trust research on the matter. As said above, the reason being that any sub, even with motional feedback, is going to have some harmonic distortion. The minute the sub emanates anything out of band, you'll be able to localize it. So, it seems to come down to "how do single vs stereo subs sound with music?"
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Old 3rd February 2008, 07:14 PM   #16
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I suppose somebody should mention the reason mixed-bass is a positive benefit: stereo phone cartidges have their vertical rumble cancelled and with benefits to reducing uncorrelated/undesired bass sounds (I may have that garbled). Dunno if summing the bass helps counter any distortions in the digital recording world?

A bigger room would put the woofer further from your ear and so many noise components that are constant (not increasing with sound level) would be inaudible, esp whenever anything loud and bassy is playing. That's a good reason not to use an overly-powerful amp to drive speakers if the absolute noise floor from the amp is correspondingly raised from a small-power but clean amp.

The nice even-harmonic distortion products from the the single woofer would almost certainly be overwhelmed by the very same frequencies made by the source instrument and coming out of the highly localizable upper-range speakers.

If your best single-woofer placement is near your ears, the room is small, the amp is noisy, the woofer distorted, or you have all the money and listening room space in the world... don't go with mixed bass.

Today's favorite bass: Vangelis: Mission to Mars (he also wrote the great music for Chariots of Fire (about Olympic racing... not spaceships). Guess what segment is real loud and bassy?
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Old 3rd February 2008, 08:01 PM   #17
JasonB is offline JasonB  Canada
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Quote:
Originally posted by leadbelly


Unlike the rest of your post, that last part completely misses the point. Harmonics which are present in the source are taken care of by the sub low pass filter; these localizable higher frequencies do not magically make it past the filter because they come from a bass instrument. The distortion of the sub woofer itself, which is in general a relatively large value on the order of 1%, imparts distortion on the sound and makes the sub localizable.
I should have clarified myself a bit better there. I agree that the actual harmonics of the instrument will not make it to the subwoofer, however they will be played by the main speakers. And it will be these harmonics played through the mains that will give you the impression of stereo bass even with a mono subwoofer.

I also agree with your point that it's mainly harmonic distortion that makes it possible to locate a subwoofer playing low frequencies, but I'd be curious to see if a typical subwoofers harmonic distortion would be high enough to mask the natural harmonics of the music that are being played through the mains and ruin the stereo image.

Jason
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Old 3rd February 2008, 08:10 PM   #18
JasonB is offline JasonB  Canada
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Quote:
Originally posted by bentoronto


The nice even-harmonic distortion products from the the single woofer would almost certainly be overwhelmed by the very same frequencies made by the source instrument and coming out of the highly localizable upper-range speakers.

If your best single-woofer placement is near your ears, the room is small, the amp is noisy, the woofer distorted, or you have all the money and listening room space in the world... don't go with mixed bass.

Two excellent points, your comment about the natural harmonics being played be the mains overpowereing the harmonic distortion is what I was I was alluding to in my post above to Leadbelly. And the second point, I've heard cheap subs that come with HTIB systems placed well away from the mains and the highish crossover points and large amount of harmonic distortion really draw attention to their location.

Jason
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Old 4th February 2008, 03:08 AM   #19
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Quote:
Originally posted by bentoronto
The nice even-harmonic distortion products from the the single woofer would almost certainly be overwhelmed by the very same frequencies made by the source instrument and coming out of the highly localizable upper-range speakers.
Quote:
Originally posted by JasonB
Two excellent points, your comment about the natural harmonics being played be the mains overpowereing the harmonic distortion is what I was I was alluding to in my post above to Leadbelly.
You're both dreaming in Technicolor if you think that the harmonic distortion spectra from the sub will mesh so cleanly with harmonics present in the source. Thanks for the chuckle
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Old 4th February 2008, 03:46 AM   #20
JasonB is offline JasonB  Canada
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Quote:
Originally posted by leadbelly




You're both dreaming in Technicolor if you think that the harmonic distortion spectra from the sub will mesh so cleanly with harmonics present in the source. Thanks for the chuckle
Meshing, no.

We both agree that is is harmonics that let the ear determine the location of a low frequency sound. My point is that the natural harmonics of the note played through the main speakers will be much more of an indicator of location to the ear than the harmonic distortion of the subwoofer itself will be. 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.

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