[Housteau]

Fortunately my listening room is good due in no small part to my involvement over the years here at Audio Circle including this forum.  I am solid, but a friend of mine is having issues.  He has recently constructed a new room out of a renovated former garage space.  It is a beautiful room designed for both audio and video.  His previous room was open to the house and so the bass was very even and uniform.  Now with a dedicated room for the first time he has bass issues due to geometry and positioning of speakers and listening position.

I know the drill, having gone through and needing to resolve many issues myself.  However, I had begun correction using geometry and room treatments with the onset of designing and building my space.  So, I had a decent head start on mitigating the remaining issues.  What my friend is going through now is needing to do corrections after the fact.  I find this to be much harder and so I wanted to ask for opinions.

The room has deep broad nulls in the 80 to 100 Hz areas at the listening position, but no severe peaks.  This position is unfortunately not very flexible and needs to remain where it is.  I did some experimenting moving that position a bit forward, back and side to side anyway just to see the differences.  I was surprised not to see a great change at all, just minor ones.  Larger changes occurred with moves of several feet only.  The moving of the speakers also effected only minor changes.  In all cases the deep nulls varied slightly in width, center position and depth only in small amounts.  The room does not have any bass treatment built in, or added at this time.

I was looking for a few go-ahead plans for my friend from here on what may do the most good in mitigating what he has now?  Personally I don't think room treatments will do enough, because with the kind of room he has the volume needed is not allowed.  I was able to do complete corner treatments up to a foot thick.  That was enough to help.  I have also been able to use some digital correction to eliminate my peaks, which greatly helped to level things out.  But, he does not suffer peaks, just nulls and I have not known such correction to help with just nulls.  Am I wrong here?

What about multiple subs swarm style?  Do you think this may be a possibility?  I have only read about these systems and theory and do not have any experience working with them myself.

[John Casler]

What about multiple subs swarm style?  Do you think this may be a possibility?  I have only read about these systems and theory and do not have any experience working with them myself.

Hi Dave,

Hope you are well.

Swarm is certainly a path, although sometimes expensive.

Digital Equalization of course is also available, but likely not the best path.

Are you looking to get the best response at the listening area?  or evenly distributed?

My first suggestion would be to get a 2nd sub, place it in the room "opposing" the 1st, (for example the opposite corner, or sub 1 on the front wall, and sub 2 on the rear) and run the 2nd sub "out of phase" to create a push/pull.

You can also experiment with placement of the rear sub and PHASE.

Another option would be to have the main sub in the front, than place a 2nd sub RIGHT BEHIND the listening position, either out of phase firing at the listener, or in phase firing toward the rear wall.

The goal, is to get the "air" at the listening position to move optimally with the least interference from room nulls.

So that would be a good step, before going full MULTIPLE Subs (which in MUSIC has all kinds of phasing issues, but works well for HT)

[Housteau]

Hello John.  Yes, I am doing well.  The interest for my friend is to have the sound correct at the listening position.  Your suggestions experimenting with two subs are spot on and exactly what I was looking for.  I remember now that you had used a similar arrangement yourself.  I had been wondering about the phase issues regarding multiple swarm type arrangements.

Dave

[rollo]

Hi Dave,

Hope you are well.

Swarm is certainly a path, although sometimes expensive.

Digital Equalization of course is also available, but likely not the best path.

Are you looking to get the best response at the listening area?  or evenly distributed?

My first suggestion would be to get a 2nd sub, place it in the room "opposing" the 1st, (for example the opposite corner, or sub 1 on the front wall, and sub 2 on the rear) and run the 2nd sub "out of phase" to create a push/pull.

You can also experiment with placement of the rear sub and PHASE.

Another option would be to have the main sub in the front, than place a 2nd sub RIGHT BEHIND the listening position, either out of phase firing at the listener, or in phase firing toward the rear wall.

The goal, is to get the "air" at the listening position to move optimally with the least interference from room nulls.

So that would be a good step, before going full MULTIPLE Subs (which in MUSIC has all kinds of phasing issues, but works well for HT)

  Very good advice here.

charles

[Hipper]

An equaliser may help surprisingly.

I know the general principle is not to add dBs but just remove them (i.e. not to raise dips, just lower peaks) but I thought I'd try to EQ out a large dip and see what happens.

The dip was in the 50Hz region and has persisted before and after adding large amounts of room treatment (bass traps mostly) including trying different locations, and a range of speaker and chair movements. I have also moved my speakers and chair around but it changes little. This means the problem is either:

1.  The speakers.
2.  Some interaction between the speaker and floor or ceiling.

I played some test tones:

http://realtraps.com/test-cd.htm

I pushed my listening chair to one side. First I checked that the speakers actual reproduce these tones – they did from all the woofers. I then walked around the room to find the peaks as well is listening at the floor-wall corners and standing on a ladder to hear if it was at the ceiling. I found that where my seat was there was indeed a null but if I put my head on the floor at that point it was louder. At the front wall it was quite loud on the floor but got louder up to head height. On the back wall it was very quiet at head height but got louder down the wall to the floor.

I note that 50Hz has a wavelength of 680cm and a quarter wavelength of 120cm, and 60 Hz is 566cm and 142cm respectively. How that helps I’m not sure!



This is with no smoothing. Red is without any EQ, yellow is +5dB at 50Hz, green +10dB. The 42Hz peak is traffic noise.

[Housteau]

It is interesting and unusual that each 5 dB increase in gain equated to an actual 5 dB reduction of the dip.  In my experience, feeding a dip that is room generated is like pumping energy into a black hole where most of it becomes absorbed.

[Hipper]

I don't understand it at all.

I also took the equaliser out of the system to make sure it wasn't messing things up in some way but I still got the 50Hz dip.

I also tried to check the speakers themselves, or rather just the bass drivers (by putting the microphone really close to each driver), but there was nothing to indicate the problem.

Anyway, as I said, it might be worth your friend testing EQ to see if it does anything.

[JLM]

Can't give specific advice without knowing the particulars:

- room dimensions

- a list of the gear being used

- speaker/listening positions

- specifically what the dissatisfactions are

- budget