# Sub localization problem



## schuberth (Jun 8, 2013)

I think I have a hearing problem - I can always tell on which side of the room I've got the sub currently placed. And I need some advice on how to mitigate this problem. 

It all started by me realizing I have some nasty room modes at my listening position (spike around 60Hz and null around 38Hz). So I started playing with the sub position and finally found a nice corner spot which mitigated most of the null problem I was having. But during the process I came to realize that the source of those lovely the low frequencies wouldn't stay put - I could always hear it moving around the room.

I have this problem more while listening to music than watching movies and also while testing the room modes with pure sine waves. 

Any advice?


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## schuberth (Jun 8, 2013)

I just realized I didn't post any details about the audio system:

It's a 7.1 setup made up of the following:

Harman AVR-360 (same as AVR-2600 in the US)
Revel Concerta 5.0 set (2xF12 fronts, 1xC12 center, 2xM12 surrounds)
Dali AXS 8000 back surrounds

Speaker crossover:
40Hz on F12 and AXS, 60Hz on M12 and 80Hz on C12

Room is EzSet/EQ calibrated, localization problem present with and without the EQ being used. Listening position is center-left of the room.

Room size: 5.76m width x 4.5m length x 3.18m height, which gives it almost perfect room ratio of 1 : 1.41 : 1.81.


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## tonyvdb (Sep 5, 2007)

Sometime room interaction will affect how you hear it, I had to move mine into the front centre position to have it blend nicely with everything and I could no longer "hear" it even though below 80Hz is not supposed to be able to hear where its coming from.


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## hjones4841 (Jan 21, 2009)

"Common knowledge" if there is such, says that crossing over at 80 should result in no bass localization. But, as with the OP, that did not work for me. I ended up putting the multiple subs on the front wall so that the LFE would blend with the mains.

In addition to room modes, if one sub has higher distortion, then the distortion will be heard since it is at a multiple of the original signal, resulting in localization.


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## tesseract (Aug 9, 2010)

Schuberth - Your hearing is probably hearing is fine. 

Speakers excite room modes. Your ears picked up on this. Moving the sub around is a good start to mitigating structure resonances (distortions). 

Center of the front stage like Tony suggests is a great place to start, or multiples like hjones4841 speaks of is another way to quash it.


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## Tom V. (Jul 12, 2012)

schuberth said:


> I just realized I didn't post any details about the audio system:
> 
> It's a 7.1 setup made up of the following:
> 
> ...



Which sub are you using?

You can try using the crossover on the subwoofer(if it has one) in addition to the subwoofer filtering already being done by the receiver. Cascading crossovers like this will attenuate the higher frequencies (from the sub) at a quicker rate. For example, the receiver may use a 12dB/octave lowpass filter for the subwoofer output. If the center frequency is 80hz, this means 160hz will only be attenuated 12dB. Activating the built in crossover on the subwoofer will cause 160hz to be attenuated 24dB or 36dB(depending on the slope used in the subwoofer crossover control.

Tom V.
Power Sound Audio


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## schuberth (Jun 8, 2013)

Tom V. said:


> Which sub are you using?


Sorry, missed that as well. SVS PB1000.



> You can try using the crossover on the subwoofer(if it has one) in addition to the subwoofer filtering already being done by the receiver. Cascading crossovers like this will attenuate the higher frequencies (from the sub) at a quicker rate. For example, the receiver may use a 12dB/octave lowpass filter for the subwoofer output. If the center frequency is 80hz, this means 160hz will only be attenuated 12dB. Activating the built in crossover on the subwoofer will cause 160hz to be attenuated 24dB or 36dB(depending on the slope used in the subwoofer crossover control.
> 
> Tom V.
> Power Sound Audio


A quick google for AVR-360 low pass slope showed up nothing relevant, so I have no idea if it's 12db or 24db/octave but I do know that sub output is cut off at 100Hz. But I would be hesitant to use the low pass on the sub itself, since LFE can contain info up to 120Hz. Maybe I'll try experimenting and see how it goes.


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## schuberth (Jun 8, 2013)

tonyvdb said:


> Sometime room interaction will affect how you hear it, I had to move mine into the front centre position to have it blend nicely with everything and I could no longer "hear" it even though below 80Hz is not supposed to be able to hear where its coming from.


Well, center is a bit difficult (using a TV on a stand), unless I sit on the sub. Which, in turn, might solve all my problems.


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## schuberth (Jun 8, 2013)

hjones4841 said:


> "Common knowledge" if there is such, says that crossing over at 80 should result in no bass localization. But, as with the OP, that did not work for me. I ended up putting the multiple subs on the front wall so that the LFE would blend with the mains.
> 
> In addition to room modes, if one sub has higher distortion, then the distortion will be heard since it is at a multiple of the original signal, resulting in localization.


The sub is a recent purchase (3 months old SVS PB1000) and I was already considering an upgrade to PB or PC-12 plus (with sub in it's current position I get usable response to about 25-26Hz and hear something to about 20Hz so I wanted more SPL at the low end) but maybe it would be a better idea to get another PB1000. 

That way I could have flanking subs on both fronts :devil:


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## orion (Sep 18, 2009)

Have you tried lowering the crossover on the sub to 80 and raise the others to 80? I thought that the lower the sub the less affect localization can have?


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## Tom V. (Jul 12, 2012)

schuberth said:


> Sorry, missed that as well. SVS PB1000.
> 
> 
> A quick google for AVR-360 low pass slope showed up nothing relevant, so I have no idea if it's 12db or 24db/octave but I do know that sub output is cut off at 100Hz. But I would be hesitant to use the low pass on the sub itself, since LFE can contain info up to 120Hz. Maybe I'll try experimenting and see how it goes.


 It is usually 12dB/octave. 

I wouldn't worry too much about setting the subwoofer crossover to say 100hz for a couple reasons.

1)this is only going to attenuate the 100-120hz portion of the LFE 2-5dB.

2)the upper portion of the LFE channel doesn't usually contain anything overly important that wouldn't also be covered by the rest of the channels to some degree. 

Some receivers even give you the option to LPF the LFE channel at 80/100/120hz now. 

I'd at least experiment and see what works best for you,

Tom V.
Power Sound Audio


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## schuberth (Jun 8, 2013)

orion said:


> Have you tried lowering the crossover on the sub to 80 and raise the others to 80? I thought that the lower the sub the less affect localization can have?





Tom V. said:


> It is usually 12dB/octave.
> 
> I wouldn't worry too much about setting the subwoofer crossover to say 100hz for a couple reasons.
> 
> ...


OK, I did some more listening tests while playing with the subs LPF (AVR doesn't have any).

Setup:
foobar2000 + Matrix Mixer plugin, redirecting front output to back surrounds (the bliss of quad towers
:bigsmile. HDMI output to the receiver, digital domain straight to the AVR's DACs. AVR audio mode set to auto 
and sensing 7 channel PCM, meaning no Dolby, no Logic 7, no DTS Neo etc.
AVR speaker crossover and bass redirection set to 40Hz (fronts + back surround). Couch is moved out of the way and I'm spinnig around with my eyes closed in the middle of 4 towers + sub trying to guess the sub's position.

Sound material:
Daft Punk - Random Access Memories album (has some mid to low bass info)
The Chemical Brothers - Setting Sun (nice song with a warbly mid bass line)
Shahmen - Mark low-bass (low-mid & low bass)
Bassotronics - Bass, I Love You (low bass)



1. sub is switched off, only towers playing: nice sound stage, highs, mids and lows are all centered.

2. sub switched on (sub LPF on on max = LPF bypassed): Highs, mids and upper bass stay centered, mid and low 
bass fly to the left where the sub is located 

3. sub with LPF set to 80Hz: similar to the previous case but while fiddling with the LPF I could feel the sub 
working less as I reached the 120Hz mark. I'm guessing the bass redirect of AVR-360 is maybe even 6db/octave? Sound stage is still skewed for the mid to low bass.

4. sub with LPF set to the minimum (according to SVS this should be 50Hz): mid bass is decimated, upper bass is slightly affected, low bass unaffected. Now things start to get interesting. With Bassotronics I get lower that 50% chance of guessing the sub position. With Shahmen I'm around 60%, The Chemical Brothers and Daft Punk have verly little output at the sub, hard to guess the position when there's no output to speak of. 

Summary:
Guess I'm sensitive to mid bass as much as upper bass, and less sensitive to low bass (below 50Hz). Need furhter testing for ultra-low bass (below 30Hz).

Solutions:
1. Get better fronts, acctually 2x2 fronts since I like my quad tower setup for music listening. Ouch, that would be expensive since I would probably need -1db at 40Hz or even better.
2. Get another sub for current setup, flank both front speakers.
3. You tell me?


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## Tom V. (Jul 12, 2012)

schuberth said:


> OK, I did some more listening tests while playing with the subs LPF (AVR doesn't have any).
> 
> Setup:
> foobar2000 + Matrix Mixer plugin, redirecting front output to back surrounds (the bliss of quad towers
> ...



#3 = your hearing mechanism could be influenced by your visual mechanism? 

Tom V.
Power Sound Audio


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## schuberth (Jun 8, 2013)

Tom V. said:


> #3 = your hearing mechanism could be influenced by your visual mechanism?
> 
> Tom V.
> Power Sound Audio


Possible but I was trying to guard against that. Let me quote myself:


> Couch is moved out of the way and I'm spinnig around with my eyes closed in the middle of 4 towers + sub trying to guess the sub's position.


Meaning I would spin around until I feel woozy, stop for a few moments and try to locate to sub's direction while keeping hands on my eyes as to prevent any light leaking and giving away the direction of windows. 

Granted this is not a real ABX or double blind test but it's much better than me standing upfront of the setup and guessing. 

Let me try and explain a bit what I feel while hunting for those low frequencies. It's not like I can exactly pinpoint the direction of the sub, as I could with higher frequency sounds, it is more a feeling pressure difference between the right and the left ear. My successful guess of the sub's direction means that I got it somewhere between 10-20 deg off my facial axis, not that I'm facing it head-on. 

Also listening to music at decent volumes for extended periods of time (1h+) is not pleasant for me. It's like my left ear (sub side) is tingling. And before I moved the sub, while it was on the right, it was the right ear that was tingling.


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## schuberth (Jun 8, 2013)

I've got a second PB-1000 for testing and was playing around with just the subs playing (fronts were disconnected from the AVR) and noticed that LFE out was pushing, in my opinion, way too much high frequency info into the LFE channel (bass management was active). Maybe the low pass on the LFE out is malfunctioning and that caused the localization problem to become severe. 

How could I test the LPF on the LFE out, any ideas on how to measure and not fry anything in the process?


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## Jason_Nolan (Jul 4, 2008)

While spinning around might be fun for a natural high as a kid, it's not going to be a way for you to forget where the sub is. You know what wall the front soundstage is on no matter what, which is where the sub is. Hearing is localized in these frequencies, therefore you'll know where the front is automatically and know your sub is there. Your mind is very capable of filling in gaps. 

Double blind and blind studies are more effective in doing this. Although nice attempt of trying to isolate though.

I had a problem with localization vs. frequency response nulls as well. I've had one or two subs all around my room. Good luck. I found I could never find perfect, ultimately you just have to choose what is the best placement and accept the downsides.


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## schuberth (Jun 8, 2013)

Jason_Nolan said:


> While spinning around might be fun for a natural high as a kid, it's not going to be a way for you to forget where the sub is. You know what wall the front soundstage is on no matter what, which is where the sub is. Hearing is localized in these frequencies, therefore you'll know where the front is automatically and know your sub is there. Your mind is very capable of filling in gaps.
> 
> Double blind and blind studies are more effective in doing this. Although nice attempt of trying to isolate though.
> 
> I had a problem with localization vs. frequency response nulls as well. I've had one or two subs all around my room. Good luck. I found I could never find perfect, ultimately you just have to choose what is the best placement and accept the downsides.


Agree on mind filling in the gaps. That's why I tested in quad tower setup with same stereo signal being fed to both front and the back stage. But yes, it was not a perfect test. :huh:

Right now I've got two PB-1000s flanking fronts and that might prove to be a more interesting testing environment.


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