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When can you localize bass?

post #1 of 29
5/5/12 at 8:45am
Thread Starter 
....the most common answer is 80hz.

But I just went through a test playing only a 50hz tone through the front speakers. I closed my eyes and had my wife randomly choose between playing the 50hz tone from the left or the right speaker. I raised my hand to indicate which speaker I thought it was coming from. Did this 10 times. Results.....I correctly identified where it was coming from every time.

So when people say bass below 80hz cannot be localized, does this mean in context with other sounds at the same time...rather than one specific sine wave tone?

EDIT: More info. I was sitting between both front speakers about 12.5ft away. No subwoofers involved here, mains were set to large and can play into the 30's.
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post #2 of 29
5/5/12 at 9:33am
You have to make sure there is nothing rattling or resonating. I went through a similar test and found resonances in the ductwork which I am having fixed on Monday. I temporarily stopped that and now can't tell. I have two subs (front and back) and to know which is playing, I have to put my hand on them.

Vary the tone 1 Hz at a time to find the peak frequency of problem as you stand near the speaker.

Also, it is possible that your system distorts bass at that frequency and if so, you will hear its higher harmonics. So keep the levels lower and see if that makes a difference.

BTW, kudos to you for testing such assumptions!
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post #3 of 29
5/5/12 at 10:07am
Thread Starter 
Good point about rattles and resonances. I didn't notice any but will do more testing at other frequencies as you suggestdd to see if results are different.

I did run RTA and FFT to check for any harmonics or other issues and they looked good.
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post #4 of 29
5/5/12 at 10:35am
Also note that there's no such thing as reproducing a pure "50Hz" tone. Speakers (and rooms) generate harmonics covering several octaves. Speaker ports also make noises with VLF tones, and "test tones" tend to be at far higher levels than typical audio.

And, although some people may say 80Hz cannot be localized, the truth is that it can - it's just much more difficult. Infrasonic frequencies are almost impossible to localize since they are felt - not heard.
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post #5 of 29
5/5/12 at 10:39am
Quote:
Originally Posted by primetimeguy View Post

....the most common answer is 80hz.

But I just went through a test playing only a 50hz tone through the front speakers. I closed my eyes and had my wife randomly choose between playing the 50hz tone from the left or the right speaker. I raised my hand to indicate which speaker I thought it was coming from. Did this 10 times. Results.....I correctly identified where it was coming from every time.

So when people say bass below 80hz cannot be localized, does this mean in context with other sounds at the same time...rather than one specific sine wave tone?

EDIT: More info. I was sitting between both front speakers about 12.5ft away. No subwoofers involved here, mains were set to large and can play into the 30's.

Generally, what they mean is that it sounds like the bass is coming from your main speakers and not the sub.
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post #6 of 29
5/5/12 at 10:52am
Quote:
Originally Posted by primetimeguy View Post

....the most common answer is 80hz.

But I just went through a test playing only a 50hz tone through the front speakers. I closed my eyes and had my wife randomly choose between playing the 50hz tone from the left or the right speaker. I raised my hand to indicate which speaker I thought it was coming from. Did this 10 times. Results.....I correctly identified where it was coming from every time.

Statements like "bass below 80 Hz" is always nondirectional is overly-broad.

There are in fact a lot of "depends ons".

Quote:


So when people say bass below 80hz cannot be localized, does this mean in context with other sounds at the same time...rather than one specific sine wave tone?

Again, "cannot be localized" is overly general. It depends on the acoustics of the room. It depends on where the listener is situated with respect to the speakers. It depends on where the speakers are situated in the room, and with respect to each other.

Quote:


EDIT: More info. I was sitting between both front speakers about 12.5ft away. No subwoofers involved here, mains were set to large and can play into the 30's.

That is just about a worst case situation. Most of the time you'd be 6-10 feet or more back from a line drawn between the speakers, which would give more acoustical blending of the two sources.

There can be asymmetries in your listening room.

There's also a question about how much nonlinear distortion your speakers have. It's not unusual for speakers to have 1-10% or more THD at 50 Hz. The second harmonic of 50 Hz is 100 Hz, and the third is 150 Hz. If there is audible distortion, then the comparison may really really all about say, 150 Hz, not 50 Hz.
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post #7 of 29
5/5/12 at 11:51am
Thread Starter 
Quote:
Originally Posted by rdgrimes View Post

Also note that there's no such thing as reproducing a pure "50Hz" tone. Speakers (and rooms) generate harmonics covering several octaves. Speaker ports also make noises with VLF tones, and "test tones" tend to be at far higher levels than typical audio.

Agree, it is not a "true tone" but I will try and post the RTA/FFT that I believe show harmonics are not an issue.

As to the volume level, well everything becomes unlocalizable at some volume right. I was in the ballpark of 75db.
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post #8 of 29
5/5/12 at 11:53am
Repeated from a similar thread in 2010...
Quote:
Originally Posted by SoundChex View Post

Quote:
Originally Posted by mgkdragn View Post

Bass below 80 Hz is not directional.. it's low frequency energy. The higher-frequency information provides the directional cues that tell your ear/brain where the sound is coming from. In many cases, the upper-bass octaves of the woofer reproduce those sounds. The typical frequency range for a consumer subwoofer is about 35-200 Hz. Thus, above 80 - 100 Hz, bass is, in fact, directional.

According to this interview with Tomlinson Holman (link), [paraphrasing by me!] "80Hz is two standard deviations below the minimum frequency at which Swedish Radio's most sensitive test panelist could detect directionality" (whatever that really means!) Which suggests to me that for most people (perhaps almost everybody!) the non directional bass regime really extends from 20hz to 160Hz, 320Hz, or even higher . . . and why "good" AVRs allow crossovers well above 80Hz. Plus, if I'm not mistaken, the SDDS (theater) LFE range is up to 330Hz (and I doubt we should draw the inference that SDDS believes 331Hz is directional!?)


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post #9 of 29
5/5/12 at 11:54am
Thread Starter 
Quote:
Originally Posted by arnyk View Post

Statements like "bass below 80 Hz" is always nondirectional is overly-broad.

There are in fact a lot of "depends ons".



Again, "cannot be localized" is overly general. It depends on the acoustics of the room. It depends on where the listener is situated with respect to the speakers. It depends on where the speakers are situated in the room, and with respect to each other.



That is just about a worst case situation. Most of the time you'd be 6-10 feet or more back from a line drawn between the speakers, which would give more acoustical blending of the two sources.

There can be asymmetries in your listening room.

There's also a question about how much nonlinear distortion your speakers have. It's not unusual for speakers to have 1-10% or more THD at 50 Hz. The second harmonic of 50 Hz is 100 Hz, and the third is 150 Hz. If there is audible distortion, then the comparison may really really all about say, 150 Hz, not 50 Hz.


Sorry, I meant I was 12.5ft back from the speakers. Speakers are about 9-10ft apart, 3ft out from the front wall and about 5ft our from side walls. All this in an 18x55ft room and I am at one of the long ends of the room.

I'll try and post RTA/FFT charts that I believe show harmonics are not an issue.
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post #10 of 29
5/5/12 at 11:57am
Thread Starter 
Here are my graphs, RTA first followed by FFT from Omnimic. Showing 50hz tone being played by left speaker in this case. Mic is at main LP about 12.5ft from speaker.

Attachment 245602

Attachment 245603

I can play this tone, the play it in the right speaker and very easily tell which speaker is playing it.
LL
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post #11 of 29
5/5/12 at 12:06pm
Thread Starter 
Quote:
Originally Posted by SoundChex View Post

Repeated from a similar thread in 2010...

2 standard deviations doesn't mean much without knowing the standard deviation itself. If it was 1hz it means it was only 82hz. Doubt that was the case but without more information we can't say for sure.
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post #12 of 29
5/6/12 at 4:59pm
Quote:
Originally Posted by primetimeguy View Post

2 standard deviations doesn't mean much without knowing the standard deviation itself. If it was 1hz it means it was only 82hz. Doubt that was the case but without more information we can't say for sure.

True, but it should still mean at least with the test group, a bit more than 95 percent of the tested population could not identify directionality at 80 Hz.

I thought TH had done additional work on our ability to identify direction of low frequencies, but I have not gone looking for it.

FWIW, when my sub was in the front right corner of my room I could hear sounds a scoming from that corner with the XO at least down to 60 Hz. I suspect an undiagnosed room effect.
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post #13 of 29
5/6/12 at 5:19pm
Thread Starter 
True.

I guess I'm at a loss as to why I can localize a 50hz tone as I didn't think it would be possible. As for a room issue, I think the charts I showed point to that not being the case, right?

I haven't tried other frequencies yet but I find it hard to believe the one freq I chose would be an isolated issue since there is no obvious room vibrations or rattles. And if there was those vibrations/rattles would have to be symmetric on both sides of the room since I can locate the tone in both left and right speakers.
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post #14 of 29
5/6/12 at 7:32pm
Quote:
Originally Posted by primetimeguy View Post

True.

I guess I'm at a loss as to why I can localize a 50hz tone as I didn't think it would be possible. As for a room issue, I think the charts I showed point to that not being the case, right?

I haven't tried other frequencies yet but I find it hard to believe the one freq I chose would be an isolated issue since there is no obvious room vibrations or rattles. And if there was those vibrations/rattles would have to be symmetric on both sides of the room since I can locate the tone in both left and right speakers.

You may be able to localize it when there is too much distortion. It includes components with 50xN Hz frequencies, where N = 1,2,3... You will easily hear direction from wich 150 Hz sound comes from.
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post #15 of 29
5/6/12 at 7:37pm
Thread Starter 
Quote:
Originally Posted by ap1 View Post

You may be able to localize it when there is too much distortion. It includes components with 50xN Hz frequencies, where N = 1,2,3... You will easily hear direction from wich 150 Hz sound comes from.

But my RTA and FFT plots show no audible harmonics
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post #16 of 29
5/7/12 at 1:46am
It'd be nice to have charts from both the R and L speakers to show if the responses picked up at the listening position are identical or not. And people say the responses can differ a few inches apart so it's conceivable each ear is picking up different responses.
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post #17 of 29
5/7/12 at 4:44am
Quote:
Originally Posted by primetimeguy View Post

Here are my graphs, RTA first followed by FFT from Omnimic. Showing 50hz tone being played by left speaker in this case. Mic is at main LP about 12.5ft from speaker.

Attachment 245602

Attachment 245603

I can play this tone, the play it in the right speaker and very easily tell which speaker is playing it.

The speaker's THD shapes up as follows:

Fundamental @ 50 Hz level approx 72 dB SPL

2nd harmonic @ 100 Hz level approx 25 dB SPL, or 47 dB down - 0.3%

3rd harmonic @ 150 Hz level approx 31 dB SPL, or 44 dB down - 0.6%

If we adjust the third harmonic for the difference in the sensitivity of the human ear at an approximate listening level of 50 dB SPL, the ear is about 20 dB more sensitive to the 150 Hz spurious response. If this test involved tones that the ear is equally sensitive to, the third harmonic would be only 24 dB down.

So now an apples-to-apples human perception comparison might be best looked at as one involving only a 24 dB difference which is like 6% THD.

I also looked at the masking of the 150 Hz tone by the 50 Hz tone, and while the data about masking @ 50 Hz that is available to me is fragmentary, there does not seem to be significant masking of the 150 Hz tone by the louder 50 Hz tone.

It is possible that your was test is affected by the harmonic @ 150 Hz.

In fact the performance of this subwoofer is relatively speaking actually pretty good, as music itself provides quite a bit of masking of its nonlinear distortion by naturally being harmonic rich. In fact most instruments that put out strong signals in the 50 Hz range produce more harmonics than fundamental. So, while 0.6 or 6 % THD may look scary on paper, it is not much of a real world problem.
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post #18 of 29
5/7/12 at 5:21am
Thread Starter 
Quote:
Originally Posted by Kilian.ca View Post

It'd be nice to have charts from both the R and L speakers to show if the responses picked up at the listening position are identical or not. And people say the responses can differ a few inches apart so it's conceivable each ear is picking up different responses.

The response is slightly different for each speaker but I'm only listening to one at a time.
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post #19 of 29
5/7/12 at 5:22am
Thread Starter 
Quote:
Originally Posted by arnyk View Post

The speaker's THD shapes up as follows:

Fundamental @ 50 Hz level approx 72 dB SPL

2nd harmonic @ 100 Hz level approx 25 dB SPL, or 47 dB down - 0.3%

3rd harmonic @ 150 Hz level approx 31 dB SPL, or 44 dB down - 0.6%

If we adjust the third harmonic for the difference in the sensitivity of the human ear at an approximate listening level of 50 dB SPL, the ear is about 20 dB more sensitive to the 150 Hz spurious response. If this test involved tones that the ear is equally sensitive to, the third harmonic would be only 24 dB down.

So now an apples-to-apples human perception comparison might be best looked at as one involving only a 24 dB difference which is like 6% THD.

I also looked at the masking of the 150 Hz tone by the 50 Hz tone, and while the data about masking @ 50 Hz that is available to me is fragmentary, there does not seem to be significant masking of the 150 Hz tone by the louder 50 Hz tone.

It is possible that your was test is affected by the harmonic @ 150 Hz.

In fact the performance of this subwoofer is relatively speaking actually pretty good, as music itself provides quite a bit of masking of its nonlinear distortion by naturally being harmonic rich. In fact most instruments that put out strong signals in the 50 Hz range produce more harmonics than fundamental. So, while 0.6 or 6 % THD may look scary on paper, it is not much of a real world problem.

Thanks. I do have a room mode around 150hz, that much I know. So knowing that and what you stated is more fuel for me to try some other frequencies.
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post #20 of 29
5/7/12 at 6:20am
Quote:
Originally Posted by primetimeguy View Post

The response is slightly different for each speaker but I'm only listening to one at a time.

I don't know if this applies, but I have noticed that if the room response to two speakers are different, then sometimes it is possible to hear the room's response along with the direct sound from the speakers. The sound from the speakers may be the same, but the room response creates an audible difference that can be used to discriminate between the two speakers. Since the speakers over all sound is different, it creates the perception of more directional hearing.
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post #21 of 29
5/7/12 at 7:33am
Thread Starter 
Quote:
Originally Posted by arnyk View Post


I don't know if this applies, but I have noticed that if the room response to two speakers are different, then sometimes it is possible to hear the room's response along with the direct sound from the speakers. The sound from the speakers may be the same, but the room response creates an audible difference that can be used to discriminate between the two speakers. Since the speakers over all sound is different, it creates the perception of more directional hearing.

That might make sense listening to actual content, but for my testing where I played one tone from one speaker I don't think it applies.
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post #22 of 29
5/7/12 at 8:43am
Quote:
Originally Posted by primetimeguy View Post

That might make sense listening to actual content, but for my testing where I played one tone from one speaker I don't think it applies.

If definitely applies if you play one tone from one speaker. The speakers are the same but since they can't coexist in the same space, any differences in the space that they are in is potentially audible.
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post #23 of 29
5/7/12 at 9:33am
Thread Starter 
Quote:
Originally Posted by arnyk View Post


If definitely applies if you play one tone from one speaker. The speakers are the same but since they can't coexist in the same space, any differences in the space that they are in is potentially audible.

Ahhh...I'm catching on now, makes sense. :-)
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post #24 of 29
5/7/12 at 2:21pm
Since attempts to present aspects of acoustics that are beyond simple colloquial references result in many here becoming upset, we'll try to keep this simple.

Localization is primarily a function of the interaural-time difference (ITD). This is the difference in time between a signals receipt by one ear and the time the same signal arrives at the other ear.

Interaural time difference (ITD) is a fundamental variable in sound source localization. However, the smaller the ITD distance, the more limited is localization possible based upon the ITD, particularly for long wavelength low-frequency sound.

The smaller the time differential between one's ears, which is exacerbated by increasingly long source wavelengths makes localization of low frequency sources more difficult, but not necessarily impossible.

The irony is that by introducing multiple sources, if the effective gain and ITD of both sources is near equal at the listening position, localization decreases as the differentials in the ITD and gain of the experienced stimuli also decreases.

Conversely, the greater the difference in the perceived binaural differences, the greater the degree of localization that is possible.

Fortunately a few other factors can mitigate such limitations, such as sound intensity differences between the apparent binaural sources. Difference that can be effected in several ways, including by having sources being located in a near field relative to the listener and/or by localized (asymmetrical) reflections that augment the apparent gain from one direction more than another.

The problem with generalizations is that they are just that. Broad sweeping statements that intentionally ignore specific exceptions in order to make a broad sweeping statement. Few generalizations are absolute. So one does well to perform a bit of due diligence in researching any such broad assumptions before acting on them as if they are universally valid.
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post #25 of 29
5/7/12 at 2:39pm
Quote:
Originally Posted by dragonfyr View Post

Since attempts to present aspects of acoustics that are beyond simple colloquial references result in many here becoming upset, we'll try to keep this simple.

Localization is primarily a function of the interaural-time difference (ITD). This is the difference in time between a signals receipt by one ear and the time the same signal arrives at the other ear.

Interaural time difference (ITD) is a fundamental variable in sound source localization. However, the smaller the ITD distance, the more limited is localization possible based upon the ITD, particularly for long wavelength low-frequency sound.

The smaller the time differential between one's ears, which is exacerbated by increasingly long source wavelengths makes localization of low frequency sources more difficult, but not necessarily impossible.

The irony is that by introducing multiple sources, if the effective gain and ITD of both sources is near equal at the listening position, localization decreases as the differentials in the ITD and gain of the experienced stimuli also decreases.

Conversely, the greater the difference in the perceived binaural differences, the greater the degree of localization that is possible.

Fortunately a few other factors can mitigate such limitations, such as sound intensity differences between the apparent binaural sources. Difference that can be effected in several ways, including by having sources being located in a near field relative to the listener and/or by localized (asymmetrical) reflections that augment the apparent gain from one direction more than another.

The problem with generalizations is that they are just that. Broad sweeping statements that intentionally ignore specific exceptions in order to make a broad sweeping statement. Few generalizations are absolute. So one does well to perform a bit of due diligence in researching any such broad assumptions before acting on them as if they are universally valid.

A good read dragonfyr.

Here's what Chris Kyriakakis of Audyssey has to say on the subject:

" ...practical approach came after studying human perception. The mechanisms that we use to determine the direction of arrival of sound depend on the frequency. At high frequencies the wavelength of sound is small and so sound coming from the side is shadowed by our head. That creates a level difference between the sound reaching the ear closest to the source and the ear on the other side. Our brain analyzes these level differences and produces an estimate of where the sound is coming from. But at lower frequencies, the wavelength of sound gets longer and our head is not large enough to produce a level difference at the two ears. Instead, we analyze the difference in time of arrival of sound at the two ears. Sound arrives first at the closest ear and we use that to determine the direction. But even that ability fails us below about 80 Hz. The wavelengths get very large and it was found in listening tests that 80 Hz is the frequency below which most people can not localize the direction of sound."

Full blog here.

And IMHO this phenomenon is not related to sounds coming from speakers and also not related to in-room listening only. Our ears work the same with real world sounds even when we are outside.
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post #26 of 29
5/7/12 at 5:51pm
Thread Starter 
I did a bit more testing today, but it wasn't blind, so more of investigation if you will. I had a disc of other tones but when playing each of those there is an obvious "pop" when the track first starts which is a dead giveaway as to where it is coming from. Checked the 50hz tone from the OmniMic disc and it happens there too. Not sure how I didn't really notice this before. I do recall that the initial "burst" seemed to give it away but after a second or so it was much harder to tell where it was coming from. So my test is unfair. :-(

Time to rethink how to do it without this bias. May have to start tones on mute or low volume and ramp up.
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post #27 of 29
5/8/12 at 4:41pm
Thread Starter 
I haven't had a chance to do more testing as I need another member of the family to help out, but I did do some listening "tests" on my own with actual content. An 80hz crossover just doesn't sound right to me with music. And for movies it tends to have an affect of creating a "wall of bass" in the front as compared to running the mains full range or 40hz crossover. The deep voices at the beginning of all of the Transformers movies all sound better with lower crossovers, the sound seems to come from the center channel as compared to the extreme lows just coming from the front of the room. Not sure how else to explain it.

I understand all the benefits of a higher crossover and the theory it should sound just as good but I just can't seem to prove that in my room....but still working at it.

For reference, here is a plot of running my mains full range (blue,purple), both mains together (green) and the sub with 200hz crossover (red) just to for kicks.

Only thing I can think of is the big difference in response in the 55-75hz range yields a more enveloping effect for some reason as compared to a nice flat response if crossed to the sub.
Attachment 245911
LL
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post #28 of 29
5/16/12 at 7:52pm
Thread Starter 
Been doing a lot more measurements, testing new positions for fronts and subs, and while I don't have my true blind test completed I can now say it is very doubtful I can localize a 50hz tone.

I found loose speaker spikes and other things in the room causing vibrations. When moving my subs around I had one almost right next to me at even at 100hz could hardly tell it was there.

Once I get things all back in there final positions I'll do the blind test but I think I already know the outcome.
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post #29 of 29
5/16/12 at 8:59pm
Good deal. I had my AC vents fixed and like you, it made a huge improvement in secondary noises that bring attention to say nothing of the distortion they add.
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