# pressure waves in room



## Blaser (Aug 28, 2006)

As all of you know, deep bas is not directional. But there is a worst problem I am facing... bass sounds louder at my left ear than at my right one, which gives the impression that the sub is placed to my left. Initially I was sitting near the rear wall of my 2000 cu ft room and to the center, I then moved 2 feets to the left as I had a wide cancellation at 40-55 Hz. Problem solved, but sound is louder now at the left side. 

I don't know how to sit anymore to perceive an impeccable bass:bigsmile: 

I have 2 subs, and this phenomena is less accentuated when I place them both behind the TV. I like the "near the center and between fronts location" and have a good FR there, but this problem becomes much stronger.

Any suggestions?


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## Blaser (Aug 28, 2006)

Hey Wayne!

I know you are a specialist in solvig this kind of problems! Pls let me have your comment!


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## Wayne A. Pflughaupt (Apr 13, 2006)

Yes, I know what you’re talking about. Back when I had two subs on either side of my front speakers, I could indeed perceive the “equal pressure” thing. It was really obvious when I decided to co-locate both subs to the same right-side corner. Response and output improved tremendously, but I could definitely tell that only one ear was being “pressurized.”

There probably isn’t a magic bullet for this, as no two rooms are alike. As you’ve noted, relocating your seating position solved one bass problem you were having, but created another. It may well be the same situation moving the subs around instead of your body. In the end, you’ll probably just have to pick which you prefer: equal pressurization, or more uniform response.

If it’s any consolation, I noticed that once I was engrossed in a movie, I didn’t notice the unequal pressure any more because my mind was focused elsewhere. It was only with critical listening – testing with pink noise, sine waves etc. – that I really noticed. And with music too, but as it is with most things, after a while you get used to it.

And – along the lines of “no two rooms are alike:” We moved a couple of years ago, and I have the subs co-located in a front right corner here, too. In this living room, I don’t notice any unequal pressurization at all.

Sorry not to have anything definite for you. 

Regards,
Wayne


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## Blaser (Aug 28, 2006)

Thank you Wayne. I appreciate your reply a lot. Why didn't you try the opposite front corners? 

Pls have a look at my front stage (attached). Do you think moving the closet to have a perfectly right and left symetry may help? This would front allow corners loading.

An Info here: my subs have different FRs, one goes much deeper, do you think upgrading with the same subs would help?

Thanks!


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## Sir Terrence (Jun 8, 2006)

Deep bass in small rooms is probably the most unpredictable thing in hometheater and music listening. 

Wayne is right, you just get used to it.

I have two very large subs in each front corner behind and slightly to the side of my L/R mains. One sub fires down a long wall of 24ft. The other fires down a long wall of 17ft. Before doing equalization each one loaded the room in such different ways that I always heard the one on the 17ft a little louder than the other. After moving my listening seat forward just a bit, and some equalization to smooth the response, I no longer have this effect. I also found that when my mains are played (which are extended range speakers handling their own bass) the problem wasn't noticeable at all. 

In my last room no matter what I did(and I did everything one could think of) I could never get rid of this effect. I did get used to it though.


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## Blaser (Aug 28, 2006)

Yes, but what is weird is that my room is rectangular, and I don't have a longer wall than another. This is what is killing me!!


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## Blaser (Aug 28, 2006)

I am seriously thinking about having :bigsmile: "a diagonal room orientation now, with both subs behing TV.


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## Blaser (Aug 28, 2006)

I have thouroughly searched about this problem. I have made measurement laterally in my room (listening pos, 2 feet right, 2 feet left). I have noted that the difference is mainly in the 45-55 Hz range (which is of course related to the lateral mode in my small room.

Here is the solution I found the most suitable: I am sitting in the spot where the 45-55 Hz range is correct ... I have increased the lower frequencies to have a house curve. Indeed by as much as 8 db from 20-30 Hz. This has corrected 95% of the problem as deep bass is more felt and in this case more heard than the 45-55 Hz freq. Moreover this deep bass is always welcome.... but this increase inplied some bottoming out of my poor subs in Matrix. (But at low volumes, sound is cool, and the pressure problem is almost gone even with music). I have also found that there is nothing better in my room than colocating the 2 subs behind TV otherwise, I have phase problems (Tradeoffs, bass adds itself below 40Hz and substract it above, and vice versa).

Indeed, I think my real problem is that I need new subs to deliver real reference level in my room, and have strong Low extention down to 20 Hz, so that I don't have to raise 8 to 10 dbs SPL from my subs.

Thank you to all those who have participated to this discussion.

Blaser


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I have noted that the difference is mainly in the 45-55 Hz range (which is of course related to the lateral mode in my small room.


That sounds about right. With my subs separated, the one in the corner got response down to 25 Hz, while the other one practically brick-walled at 40 Hz. Yet, as far as the pressurization went, they sounded the same. I forgot to mention that earlier, but it looks like you figured it out for yourself.  Not sure it has anything to do with a small room though - mine was over 6000 cu. ft.

Regards,
Wayne


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## Blaser (Aug 28, 2006)

Do you think a bass trap can help? The couch sitting positions are for sure affected by the room lateral mode. Maybe a bass trap can reduce this effect? 

B Rgds
Blaser


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## Blaser (Aug 28, 2006)

Wayne A. Pflughaupt said:


> With my subs separated, the one in the corner got response down to 25 Hz, while the other one practically brick-walled at 40 Hz. Yet, as far as the pressurization went, they sounded the same. I forgot to mention that earlier, but it looks like you figured it out for yourself.
> 
> Regards,
> Wayne


Do you mean that different subs FR may be the problem or at least part of it?

Thanks!


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## Blaser (Aug 28, 2006)

Here are the graphs for different positions of the sub, at each ear locations. There are 4 graphs:


- the brown curve is unequalized (sub corner loaded, RS meter at left ear position)
- The blue curve is unequalized (sub corner loaded, RS meter at right ear position)

Ironically, you can see I have 6 db or more difference between the left and right ear fom 45-55 Hz, area which gives the impact and punch. It is not only distracting but annoying and makes me feel the sub is beside my left ear:hissyfit: . 

- The red curve is unequalized (sub placed 1/3 length of front wall), left and right ears have only 2 db difference which is more acceptable...... but see how much I lost in the 45-55 Hz (compared to the brown curve), and this is noticeable:rolleyesno: .

- Last the green curve is equalized (sub placed 1/3 length of front wall)), but I had to boost the 45-55 Hz area by 5 db. Sound is acceptable now at low volumes, readings between left and right ears are 2 db max, but the problem is that the sub produces a lot of distortion when I want to crank it loud. I have also reduced that huge peak at 35 Hz, and this reduces the headroom:dunno: .

I can Hit only about 106 db compressed/distorted at (45-55 Hz) whereas I would like to hit easily 120 db:raped: , "Am I experiencing cancellation at these frequencies?" What should I do.... I tried many locations around my room, but never had an acceptable FR.

For those who had many subs, "If I buy a new powerful sub, except better extention, is it possible to have different FR (better 45-55 Hz) in the same room, if the new one is still in the same position as the old sub? 

I am also afraid to invest much money in a capable sub, and still feel differences between right and left ear, or again have to sacrifice some frequncies SPL:scratch: .

What do you advise?:help: 

B Rgds
Blaser


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## JimP (May 18, 2006)

If you are in the experimenting mood, try this.

Take the sub that can go lower and locate it immediately behind the sofa with a cutoff of around 50hz. Be sure to lower the gain setting on it so that it matches your other sub. This should get you a flatter response at your primary listening position.

Take the other sub and move it out of the corner, probably about 1/3 the distance from the corner along the front wall. This should also be flatter.

Also be sure to vary the sub distance in your preamp/receiver to minimize any dips at the crossover frequency.

After doing all this, try to objectively tell if it really makes that much difference. I've found that sometimes getting the best frequency response on a graph doesn't always make for much difference in sound quality.


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## Blaser (Aug 28, 2006)

JimP said:


> If you are in the experimenting mood, try this.
> 
> Take the sub that can go lower and locate it immediately behind the sofa with a cutoff of around 50hz. Be sure to lower the gain setting on it so that it matches your other sub. This should get you a flatter response at your primary listening position.
> 
> ...


Thanks Jim for your kind input!! 

Indeed I have determined where exactly my problem is: The lateral room mode which boosts the 45-55Hz area... the closer you get to the side wall the higher the SPL difference between 5-6 inches (ears distance)... I had this confirmed by this program:www.rspu.ryazan.ru/~foboss/hi-fi/acoustic/room060d.xls, which I found to be very accurate according to REW sweeps.

I had tried to use dual subs to cancel this room effect (having only one, I used my car's), nevertheless this didn't help a lot as my mistake was that the subs have very different FRs.:innocent: 

Anyway, willing to upgrade since a while back, I had been very hesitating between brands.... and now I have decided (99.9% sure) to go with dual RL-p18, 600 L box, 10" port, tuned 16 (each in his own box), powered by dual 1800-2000W real Watts for my 1800 cu ft sealed HT room.

They will be placed along the backwall. According to room060d, everyone sitting on the couch will be equally happy:T ....

Being very busy this month and travelling a lot (working on oil platforms:duh: ), I have postponed ordering, but you can expect my impressions most probably next month:cunning: :boxer: 

Blaser


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## pgoko (Oct 25, 2006)

"my mistake was that the subs have very different FRs." 

Ok therein lies your problem - your two subs playing at two different SPLs. Of course the louder sub is going to pressurize the ear it is closer to. 

Solution:
Use your SPL meter and try to get the levels the same as much as you can from your listening position. I have multiple DIY subs and I have them at same levels just because of the same problem you are having.
NB: You never get a problem like this from stereo speakers because they play at the same levels i.e., balanced.


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## Blaser (Aug 28, 2006)

Right!

But this was only part of the problem, the lateral room mode was the strongest problem...After having my dual RL-P18s, this room mode is pretty inexistant now!!
:bigsmile:


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