MOVED FROM GEDDES ON WAVEGUIDES
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This is very wrong, I'm afraid. I've said it before and I just tested it again. While it may be true for pure tones, it is NOT true for complex signals.
I just tested this on my system with sharply low passed white noise - about 60dB/octave low pass. Going down by third octaves I could pick direction down to 32Hz.
Below ~160Hz it does get more ambiguous, but location ability does not go away.
There were some spots, like 120Hz, that gave me trouble in my room (nodes), but noise filtered below that was still fairly easy to locate. I did not test below 32Hz as that's the bottom limit for my system.
I can supply the test files if anyone cares to try the same test.
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This is very wrong, I'm afraid. I've said it before and I just tested it again. While it may be true for pure tones, it is NOT true for complex signals.
I just tested this on my system with sharply low passed white noise - about 60dB/octave low pass. Going down by third octaves I could pick direction down to 32Hz.
Below ~160Hz it does get more ambiguous, but location ability does not go away.
There were some spots, like 120Hz, that gave me trouble in my room (nodes), but noise filtered below that was still fairly easy to locate. I did not test below 32Hz as that's the bottom limit for my system.
I can supply the test files if anyone cares to try the same test.
I think it depends on (Dr. Geddes is gunna eyeroll me on this one 😀 ) the harmonic distortion signature of your bass driver. If its distortion is low enough, bass sounds extremely dry. With the typical hi fi drivers what you're localizing is the harmonic. To me the "rules" for subwoofers are a bit different. Obviously multiple subs is the #1 solution. But I run sealed 18" subs and they to me are virtually inaudible below 100hz when EQ'd flat in room until the SPL is very high as it is. Low bass with low distortion is so subtle that if you take it away and aren't paying attention you won't notice anything's missing. One of my subs is actually to the right of me which on paper would be an awful idea. Even when if it's the only sub running I can't localize it crossed at 100hz.
The only time i've ever localized bass, is when there's wierd phasing issues. That's because my ears get an uneven balance.
I don't think distortion in subwoofers is offensive mind you, but I definitely think it's audible as a sonic signature. Others will disagree and that's fine by me.
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Good point, but not with mine. I don't hear the harmonics. Altec 416-8A 15" drivers. I consider it a valid test.
Are they there when you measure - that is content significantly above 100Hz? Doesn't take much to localize.
Sheldon
I'll only know by measuring. Will try to tomorrow. It's possible there are more harmonics than I notice. But from a practical standpoint who uses a 60dB/octave crossover for their subs? The old "subs can't be localized below 100Hz" thing is not true at all in my experience.
IME, I can't localize a sub on any material when it's low passed 24db/oct at 100hz. At 120hz I start to get a sense of "sound is coming from this side of the room. A much bigger issue is that male vocals start to get "aggressive". I think it's a panel resonance on my (tall and pretty well braced but not extremely since it's just a sub) sub.
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I don't think I know the difference! 😀
All I hear is a low rumble. 32Hz is barely there. But I'll have to measure to be sure.
All I hear is a low rumble. 32Hz is barely there. But I'll have to measure to be sure.
It is vented, but it's not really a sub. Low pass for the 15s is about 700Hz, acoustic. I won't rule out that I'm locating the harmonics and will measure to see just how much there is above the cut off frequencies where I low passed.
But also read what I said about the practical side of it. That's important. Probably need to move this to its own thread, as it has little to do with waveguides.
But also read what I said about the practical side of it. That's important. Probably need to move this to its own thread, as it has little to do with waveguides.
I have had two tiny modest size closed box sub's in my little room crossed at 80hz, I cannot locate them. I could locate them more easily individually.
Theoretically, in a small room you should not be able to detect the direction of a very low signal. There must be some explaination.
Take two microphones and space them apart by the ear distance and do a steady state measurement. Then take the difference between these two measurements. This is what is claimed is being detected. I suspect that this difference will be many tens of dB below the signal. I also suspect that something much higher in frequency is happening. This is a case where an extremly small amount of nonlinearity would be detectable.
Take two microphones and space them apart by the ear distance and do a steady state measurement. Then take the difference between these two measurements. This is what is claimed is being detected. I suspect that this difference will be many tens of dB below the signal. I also suspect that something much higher in frequency is happening. This is a case where an extremly small amount of nonlinearity would be detectable.
A 60dB/octave crossover won't reduce HD the sub produces. Whether HD or simple wind noise, they can produce localization artifacts not present in the sub range.
I do agree about LF localization, I can easily discern the direction of LF sounds from idling trucks, generators and such while inside my house (me, not the noise source) even though the LF is 60 or more dB above any upper content.
Also, white noise rolls off the LF regardless of where it is low passed, odd choice of testing sub locality, as white noise as a source would emphasize the upper point of the LP, and a 60 dB/octave filter may have plenty of upper ringing detectable higher.
I used white noise because it was easy. And because it does emphasize the upper range of what's been filtered. I want that band to be most prominent so that i can be sure of the frequency. I could redo with pink.
I can also locate trucks, earthquakes and such outside the house. But that's not a source inside a room, which is what Earl was talking about. Too many people seem to accept that it can't be done at all.
I can also locate trucks, earthquakes and such outside the house. But that's not a source inside a room, which is what Earl was talking about. Too many people seem to accept that it can't be done at all.
Here are the filtered white noise files in MP3 format all inside the zip file. If you want to play. I can also do these from pink noise, if needed.
For whatever reason, when I was using one sub(and a cheap one at that) I never had issues locating my sub. Then I got 2(and dumped the original), and could no longer localized them. I got one nice infinity Cascade 12 and could localize it. Added 2 more other, cheap subs and no longer can.
Every added sub seems to smoother the FR as well.
?
Dan
Every added sub seems to smoother the FR as well.
?
Dan
Griesinger's papers on the subject:
http://www.davidgriesinger.com/overvw1.pdf
http://www.davidgriesinger.com/sfaes.pdf
http://www.davidgriesinger.com/asa05.pdf
I personally can localize bass, but it's dependent on the signal, number of sources and proximity, room, etc.. For the most part it's either an intensity/pressure phenom for me, OR something transient. Typically it's the latter in a very good system with music.
http://www.davidgriesinger.com/overvw1.pdf
http://www.davidgriesinger.com/sfaes.pdf
http://www.davidgriesinger.com/asa05.pdf
I personally can localize bass, but it's dependent on the signal, number of sources and proximity, room, etc.. For the most part it's either an intensity/pressure phenom for me, OR something transient. Typically it's the latter in a very good system with music.
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As Geddes explains, the difference in level between the two ears at say 50 Hz is so low that it may not be possible to localize the source. It must be harmonics up above that allow localization. But harmonics are real too and should not necessarily be ruled out as a mechanism for localizing low frequency sound sources. Just like being able to localize a bass guitar because of the harmonics.
In a small room you can get quite significant differences between the sound level at the two ears, when your head is in a standing wave node. One ear may experience greater changes in pressure than the other. This to me is the most annoying thing about standing waves.
A couple of years ago I had a similar discussion on another forum. Ultimately I decided to take a subwoofer outside and do some experiments in the garden. Contrary to what I expected, I was able to identify the sub's location down to the lowest frequencies. I still don't really understand how that was possible. Maybe it was indeed the harmonics that gave away its location. In a room, it's a different story, though. Room modes are dominant.
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