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Does the crossover rule 1/4 of a wavelenght distance in sound, also apply below the schroeder frequency ?

Tangband

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I have done some experimenting with dsp subwoofers thru the years .
The latest has been done with Genelec SAM monitors and the 7350 subwoofers in an ordinary livingroom.
Before this I have tested one, two or four dsp subwoofer in mono and in stereo. With 4 subwoofers ( 2 in front of the listener and two behind listening position ) the measurements from listening position looks very good, but the sound is much worse than only two stereo subwoofers put in the front.

The theory is saying that one cant hear were the subwoofers are below 200 Hz . With music I find this to be not true . Even with a very steep dsp crossover at 200 Hz and using only one sub, I can easily hear that there is something wrong in the music with only one subwoofer.

In crossover design one often follows the rule of max 1/4 wavelenght distanse from the drivers regarding their crossover frequency If using a 4:th order Linkwitz Riley crossover.
One example is this: a crossover in a two way loudspeaker at 2 kHz . The wavelengt at 2 kHz is about 17 cm . 1/4 of this is 4,25 cm . The tweeter must be very closed mounted to the bassdriver in this 2-way loudspeaker, If its gonna sound as only one driver.

They say that below the rooms schroeder frequency ( about 250 Hz ) the sound cant be spatially recognized anymore .
I find that this is true with sine-tones but not true when listening with music.
The first arriving sound from the speakers are the most important - attenuating later arriving sounds about -10 dB , also below the schroeder frequency. This cant be shown in measurements, but it happens in the listener brain in the listening position when listening to real music.

From this testing, I have drawn the following conlusion :

1. Stereo subwoofers are the best. The nearer the subs are from each front L/R speaker, the higher in frequency one can cross them.
Ofcourse I mean both LP and HP filtering. This is ( in my opinion ) also true with very steep crossovers ( 48 db/oct) .
Mono coupled subwoofers placed near each speaker dont sound as good as stereo coupled subwoofers.

2. If using only one subwoofer with music - one should follow the 1/4 wavelenght rule according the distance between the frontspeakers and the subwoofer . Crossing at 100 Hz with only one subwoofer gives you = 3,43 meter wavelengt/4 = 85 cm . The subwoofer should not be placed apart from any of the L or R speaker longer than 85 cm, to avoid worse sound.

And, If the crossover is set at 50 Hz , the distance between the single subwoofer and the front L or R can be up to 170 cm without sounding unnatural.
I find this very true when listening to music.

With stereo subwoofers, because of this, one can cross them much higher because they can be put much nearer each L and R front speaker. 100 Hz in this case can be done if each subwoofer are placed very near each frontspeaker.

Whats youre experience about this ? Are mono subwoofers good enough ? Can you cross a monosubwoofer at 100 Hz and not hearing that something is wrong with the music experience ? Does 4 subwoofers placed in corners far away from the main speakers sound good with music, or are the music experience much worse ?
 
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Tangband

Tangband

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We can’t hear subwoofers with a crossover of 100Hz 48 db/oct or 80Hz 24dB/oct

200Hz is a delusion that some members here entertain themselves with.
I can surely hear it down to 60 Hz with my SAM Genelecs ( 8340+7350:s ) If I use only one subwoofer. The SAM monitors cross with 48/dB oct . Crossing higher with only one subwoofer is making the music listening experience and the preceived pitch in bass tones worse.
Many other dsp subwoofers I have tested behave exactly the same .
 
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Tangband

Tangband

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I meant you can’t localise any subwoofer with one of the two previously mentioned crossovers.

Unless they’re creating high order harmonics.
The perceived pitch of the bassnotes with music will be less clear with a higher crossover frequency with only one subwoofer- if the distance is to big between the subwoofer and the frontspeakers. But with sine tones or sinesweeps, no differences can be seen on a measurement paper.
 
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Tangband

Tangband

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I meant you can’t localise any subwoofer with one of the two previously mentioned crossovers.

Unless they’re creating high order harmonics.
You can hear it in the way that the music dont sound really good with less defined pitch in the bass with only one subwoofer. But at 55 Hz 48dB/oct crossover , or crossing lower than that, I cant hear the pitch smearing any longer. This is my experience with many different dsp subwoofers ( DIY or SAM ) .
 
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SoundGuy

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I have done some experience with dsp subwoofers thru the years .
The latest has been done with Genelec SAM monitors and the 7350 subwoofer in an ordinary livingroom.
Before this I have tested one, two or four dsp subwoofer in mono and in stereo. With 4 subwoofers ( 2 in front of the listener and two behind listening position ) the measurements from listening position looks very good, but the sound is much worse than only two stereo subwoofers put in the front.

The theory is saying that one cant hear were the subwoofers are below 200 Hz . With music I find this to be not true . Even with a very steep dsp crossover at 200 Hz and using only one sub, I can easily hear that there is something wrong in the music with only one subwoofer.

In crossover design one often follows the rule of max 1/4 wavelenght distanse from the drivers regarding their crossover frequency If using a 4:th order Linkwitz Riley crossover.
One example is this: a crossover in a two way loudspeaker at 2 kHz . The wavelengt at 2 kHz is about 17 cm . 1/4 of this is 4,25 cm . The tweeter must be very closed mounted to the bassdriver in this 2-way loudspeaker.

They say that below the rooms schroeder frequency ( about 250 Hz ) the sound cant be spatially recognized anymore .
I find that this is true with sine-tones but not true when listening with music.
The first arriving sound from the speakers are the most important - attenuating later arriving sounds about -10 dB , also below the schroeder frequency. This cant be shown in measurements, but it happens in the listener brain in the listening position when listening to real music.

From this testing, I have drawn the following conlusion :

1. Stereo subwoofers are the best. The nearer the subs are from each front L/R speaker, the higher in frequency one can cross them.
Ofcourse I mean both LP and HP filtering. This is ( in my opinion ) also true with very steep crossovers ( 48 db/oct) .
Mono coupled subwoofers placed near each speaker dont sound as good as stereo coupled subwoofers.

2. If using only one subwoofer with music - one should follow the 1/4 wavelenght rule according the distance between the frontspeakers and the subwoofer . Crossing at 100 Hz with only one subwoofer gives you = 3,43 meter wavelengt/4 = 85 cm . The subwoofer should not be places apart from any of the L or R speaker than 85 cm, to avoid localisation.

And, If the crossover is set at 50 Hz , the distance between the single subwoofer and the front L or R can be up to 170 cm without sounding unnatural.
I find this very true when listening to music.

With stereo subwoofers, because of this, one can cross them much higher because they can be put much nearer each L and R front speaker. 100 Hz in this case can be done if each subwoofer are placed very near each frontspeaker.

Whats youre experience about this ? Are mono subwoofers good enough ? Can you cross a monosubwoofer at 100 Hz and not hearing that something is wrong with the music experience ? Does 4 subwoofers placed in corners far away from the main speakers sound good with music, or are the music experience much worse ?
My experience matches yours. I prefer a subwoofer close to the plane of the L & R speakers. I don’t understand it but whatever it is it is audible. I suspect early arrival of bass is messing up what you can hear at higher frequencies (masking). The audible effect is lack of coherence on transients. Placement of bass amps, like drums, is nearly always at the back of the stage - if it worked better in front then someone would have figured that out by now. Of course not all speakers or systems will highlight this as bass reproduction in most systems is often terrible to begin with.

Chasing smooth frequency response is just an example of how a pure focus on a specific measured aspect of sound reproduction can lead to poor results. This site makes the cardinal error of assuming that because you can measure something then it is the only thing that matters - this is not true - measurements do matter but they often don’t capture or characterize everything else that is important - this is where experience still has value…
 
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abdo123

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But with sine tones or sinesweeps, no differences can be seen on a measurement paper.

That's impossible though, if you're removing or adding speakers, changing crossovers, or moving speakers you will change the measurements.
 

Waxx

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The general rule is below 100Hz with at least a 12dB/octave crossover (2nd order or higher) to avoid that you hear it. It was also mentioned somewhere in Dr. Toole's book about the multiple small subs theory, with measurements and so (don't know the title and page by heart and I don't have the books near me). 200Hz is way to high like said before.

But i also prefer the subs under the main speakers. I don't know why, it may be just me fooling myself, but it sounds better to my ears.
 

gnarly

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I don't understand how/why the 1/4 WL rule for center-to-center driver spacing at xover frequency, would have anything to do with Schroeder.
I see 1/4 WL spacing being about good summation between two (or more) drivers, and minimizing lobing, by keeping drivers' relative phase close..
You know, the good ole phase wheel....
acoustic summation.JPG


With regards to audible localization of subs.......for grins I just ran some tests low passing full bandwidth pink noise to subs.
No low pass or xover in place on subs. So the signal itself becomes the source of the low pass, and for hearing frequency localization..
(This is a pretty convenient way to test frequency localization imo/ime......)

I could still localize the L vs R sub using the full-bandwidth pink noise low passed as follows:
with 100Hz 96dB/oct,
with 80Hz 48dB/oct,
and with 40Hz 24dB/oct !!!!!!!!! YIKES!

I could not localize 80Hz using a near brick wall low pass.


The moral of the story is clear to me.....xovers let more higher frequency content through than we think. Certainly so, for common LR 24's.

I guess that's why the multiple sub route has never appealed to me....overall sound just gets a bit muddier imo.
And even bass drops/transients fail to have the visceral impact that stereo subs have.
(or best yet for visceral impact, plain ole mono......)


edit: saw a post wondering if my subs might have high THD, causing the localization....(post was deleted i guess...)
Anyway, good question, one i think i can safely put to rest.
here's the subs' thd. This was taken at 2m, outdoors, and SPL was calibrated.
so +6dB to bring to 1m ...........SPL was over 125dB.
push push 2m distortion percent.JPG



Th localization tests i ran this morning were well under 100dB...so i have to rule THD out as an audible factor.
 
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Tangband

Tangband

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I don't understand how/why the 1/4 WL rule for center-to-center driver spacing at xover frequency, would have anything to do with Schroeder.
I see 1/4 WL spacing being about good summation between two (or more) drivers, and minimizing lobing, by keeping drivers' relative phase close..
You know, the good ole phase wheel....
View attachment 235134


With regards to audible localization of subs.......for grins I just ran some tests low passing full bandwidth pink noise to subs.
No low pass or xover in place on subs. So the signal itself becomes the source of the low pass, and for hearing frequency localization..
(This is a pretty convenient way to test frequency localization imo/ime......)

I could still localize the L vs R sub using the full-bandwidth pink noise low passed as follows:
with 100Hz 96dB/oct,
with 80Hz 48dB/oct,
and with 40Hz 24dB/oct !!!!!!!!! YIKES!

I could not localize 80Hz using a near brick wall low pass.


The moral of the story is clear to me.....xovers let more higher frequency content through than we think. Certainly so, for common LR 24's.

I guess that's why the multiple sub route has never appealed to me....overall sound just gets a bit muddier imo.
And even bass drops/transients fail to have the visceral impact that stereo subs have.
(or best yet for visceral impact, plain ole mono......)


edit: saw a post wondering if my subs might have high THD, causing the localization....(post was deleted i guess...)
Anyway, good question, one i think i can safely put to rest.
here's the subs' thd. This was taken at 2m, outdoors, and SPL was calibrated.
so +6dB to bring to 1m ...........SPL was over 125dB.
View attachment 235153


Th localization tests i ran this morning were well under 100dB...so i have to rule THD out as an audible factor.
Interesting.
In practise, only a few subwoofers with analog active crossovers have steeper slopes than 24 dB/oct , and very few dsp models have more than 48 dB/oct.
You could detect your subwoofer above 40 Hz with 24 dB/oct crossover - i believe you in this, because this is also my experience. At 55 Hz with only one subwoofer you will need an even more, steep crossover.

In practice - its much easier to use two stereo subwoofers where you can even use a simple 12 dB/oct crossover at 80 Hz HP/LP If each subwoofer is very close, or underneath each speaker.

Also - most AVR.s with mono sub out have crossovers ( 24/12 THX ) thats not enough steep for 80 Hz and for use with music.
 
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Tangband

Tangband

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The general rule is below 100Hz with at least a 12dB/octave crossover (2nd order or higher) to avoid that you hear it. It was also mentioned somewhere in Dr. Toole's book about the multiple small subs theory, with measurements and so (don't know the title and page by heart and I don't have the books near me). 200Hz is way to high like said before.

But i also prefer the subs under the main speakers. I don't know why, it may be just me fooling myself, but it sounds better to my ears.
It sounds better .:) There you have it.
I dont think its possible to avoid some blurring of the perceived pitch in the bass region if you use many multiple subwoofers thats crossed as high as 80 Hz . The measurements might get better , yes - but it gonna be harder to follow the bass tunes and to hear the bass articulation in a clear way - in my experience.
 

voodooless

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The 1/4 wavelength rule is not about localization. It about comb filtering effects. You’ll rarely find 1/4 wavelength distance though. It’s more 1/3 to 1/2 in practice.
 
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Tangband

Tangband

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The 1/4 wavelength rule is not about localization. It about comb filtering effects. You’ll rarely find 1/4 wavelength distance though. It’s more 1/3 to 1/2 in practice.
I might be wrong on this, but I have a suspicion that because of the precedence effect where all later arriving sounds attenuates with -10 dB in the brain , and the brain will therefore focus on the direct sound coming from the speakers , also will apply for frequencies somewhat below the schroeder frequency .

And - I also find the rule of thumb 1/4 wavelength a rather good one when positioning subwoofers and finding the correct crossover frequency between your L and R frontspeakers to the sub/subs. But it might be for other reasons than I think. I always set up loudspeakers for minimal bluring of the perceived pitch in the bass area.
 

Robin L

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My sub crosses over at 60 hz. I suspect my Infinity Primus 250 speaker's crossover is around the same frequency. No issues with deep bass being localized. The location of the sub is under one of the speakers, the other speaker on a wooden box of the same height.
 

ernestcarl

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The theory is saying that one cant hear were the subwoofers are below 200 Hz . With music I find this to be not true . Even with a very steep dsp crossover at 200 Hz and using only one sub, I can easily hear that there is something wrong in the music with only one subwoofer.

Who/what authority posited this theory?
 

ernestcarl

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Whats youre experience about this ? Are mono subwoofers good enough ?

Too bad, I can't really fully test this as I have only one subwoofer in my listening room. But, personally, I don't feel that my current listening experience is diminished because I only have one subwoofer in place. While it often can be difficult if not impossible sometimes to correlate what one sees and hears between our limited in-room measurements and actual hearing apparatuses (i.e. ears and brain), I would tend to agree strongly on the notion that both listening and measurements equally should have a place in our arsenal of tools when setting up audio systems.

Can you cross a monosubwoofer at 100 Hz and not hearing that something is wrong with the music experience ?

Below setup overlaps quite a bit:

FDW 15 cycles
1664911716258.png 1664911845875.png

Using a laser tool, the front mains are positioned about 2.5 m or more distance away from the sub along the front wall. A tiny little Fostex 6301 (center channel -- mostly serves now as a center "fill" on occasion -- isn't illustrated in the image) also sits atop my front desk's LED monitor and is closest to the sub.

I can show more measurements in detail (e.g. wavelet, decay, envelope, moving mic spatial curves, etc), but to be short, rest assured the final resulting summed responses all look fine. In the end, my own ears strongly agree with the measurements in that nothing sounds "wrong" in the way I have set up things here in this room. Could it be better by using stereo subs? Sure, possibly... but as it stands, there is nothing that I can hear that is broken or inadequate with what I currently have in place now.
 
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YSC

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It sounds better .:) There you have it.
I dont think its possible to avoid some blurring of the perceived pitch in the bass region if you use many multiple subwoofers thats crossed as high as 80 Hz . The measurements might get better , yes - but it gonna be harder to follow the bass tunes and to hear the bass articulation in a clear way - in my experience.
I have only one sub under the desk so difficult to compare, but I am guessing with multi sub the time domain delay would cause the un natural feel, like this same amplitude bass note in same frequency but comes to you a fraction of a second later, causing confusion from the brain
 

ernestcarl

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What I would like to to see are detailed measurements... why not upload mdat file comparison examples? Some of the timing induced anomalies should be visible (if examined closely) in the discrete and summed IRs. We're still missing some directional information with these omni mic measurements, but at least it's a start...
 

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"
They say that below the rooms schroeder frequency ( about 250 Hz ) the sound cant be spatially recognized anymore .
I find that this is true with sine-tones but not true when listening with music."

There is another explanation for your observation, that your ears and brain are getting the spatial information from the higher harmonics that are present in music but not, of course, in pure tones. I have a low-fi system in my kitchen that consists of ceiling speakers with a sub-woofer on the floor, and it it sounds like all of the music is coming from the ceiling speakers. I hear the lowest notes on string basses coming from their left-side location in the orchestra, for example, even though there is a single sub-woofer located on the floor way over on the right.
 

HarmonicTHD

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"
They say that below the rooms schroeder frequency ( about 250 Hz ) the sound cant be spatially recognized anymore .
I find that this is true with sine-tones but not true when listening with music."

There is another explanation for your observation, that your ears and brain are getting the spatial information from the higher harmonics that are present in music but not, of course, in pure tones. I have a low-fi system in my kitchen that consists of ceiling speakers with a sub-woofer on the floor, and it it sounds like all of the music is coming from the ceiling speakers. I hear the lowest notes on string basses coming from their left-side location in the orchestra, for example, even though there is a single sub-woofer located on the floor way over on the right.
That doesn’t mean it is good advice to crossover at ca 200Hz, because if you have 12 or 24dB/oct filters you still have audible fragments at 400Hz which certainly isn’t a sweet spot for subs either anymore.

I cross over as low as possible so the subs „fill“ the room mode induced nulls of the mains. In my case 80Hz.

Toole in his book has several interesting chapters on subs alignment, crossover and positioning.
 
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Capitol C

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That doesn’t mean it is good advice to crossover at ca 200Hz, because if you have 12 or 24dB/oct filters you still have audible fragments at 400Hz which certainly isn’t a sweet spot for subs either anymore.

I cross over as low as possible so the subs „fill“ the room mode induced nulls of the mains. In my case 80Hz.

Toole in his book as several interesting chapters on subs alignment, crossover and positioning.
Can't disagree with your choice of low crossover frequency. I'd have to check my inexpensive kitchen setup, but I think it is around 100 Hz.
 
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