[*Scotty*]

Stupid question Jim, is one of subs located on floor in the center of the wall behind you or are they both in front of you.
Scotty

[jtwrace]

Jason:

I use two subs and have no complaints, especially after taking care of the eq. 

Jim

Please post your measurements as I'd like to see how good you got it.  Of course post before eq and after.

[medium jim]

Scotty:

Not at all a stupid question, I have both subs in front of me and on the outsides of the mains.  This was the location were they loaded the room the best and without smear.  My room treatments are modest, diffusion in the center of the front wall, absorption behind the subs and mains (dipole), and absorption at the first reflection points. The back wall has absorption via special curtains.

Jim

[medium jim]

Please post your measurements as I'd like to see how good you got it.  Of course post before eq and after.

If I can find them from when I did them, however, I only passively corrected the high pass as everything above 60hz was relatively flat (magnepan's).  Measurements were only taken from the listening position.

Thanks for your request,

Jim

PS. This is not about me, with that, I will not address any more questions about my system to keep it about the poll.

[JLM]

Scotty:

Not at all a stupid question, I have both subs in front of me and on the outsides of the mains.  This was the location were they loaded the room the best and without smear.  My room treatments are modest, diffusion in the center of the front wall, absorption behind the subs and mains (dipole), and absorption at the first reflection points. The back wall has absorption via special curtains.

Jim

Agreed that two subs are better than one, but unless your speakers are set up on the room's long wall, you have standing waves, period.  According to Floyd Toole, front and back walls should have absorption, side walls at first reflection points should have no treatment, and the rest of the side walls should have diffusion, but most normally furnished rooms need very little treatment.  Of course Toole doesn't like dipole either.  "Special curtain" absorption??  Like 10 inch thick high density fiberglass?  Again Toole points out that wide band absorption requires a minimum 6 inches of high density fiberglass.  Once again Toole recommends two to four subs located on opposite ends of the room.

[medium jim]

Agreed that two subs are better than one, but unless your speakers are set up on the room's long wall, you have standing waves, period.  According to Floyd Toole, front and back walls should have absorption, side walls at first reflection points should have no treatment, and the rest of the side walls should have diffusion, but most normally furnished rooms need very little treatment.  Of course Toole doesn't like dipole either.  "Special curtain" absorption??  Like 10 inch thick high density fiberglass?  Again Toole points out that wide band absorption requires a minimum 6 inches of high density fiberglass.  Once again Toole recommends two to four subs located on opposite ends of the room.

Do a google search for acoustic curtains....

Jim

[JLM]

Well Jim I did look around the net a bit.  Acoustic curtains are not advertized as being effective for bass frequencies (one site stated 9% noise reduction at 125 Hz, the lowest stated frequency and it was steadly dropping with frequency) while another admitted that a 1 or 2 inch thick panel would be better.  I'm sure that a whole wall would help some even at lower frequencies, but this is the "Bass Place" so I'm focusing on 20 - 80 Hz (where Toole states absorption is not practical).  Is your setup on the long wall?

[Tyson]

Problem with bass EQ - if you fix it for the sweet spot, it makes all the other spots worse.  One way to deal with this is via multiple subs, which will naturally smooth out the response, without EQ.  An alternate approach is to use an open baffle sub, which interacts with the room less and thus has fewer peaks and valleys.

[WGH]

Here is an example of what can be achieved with 4 subs on opposite walls although not many people will want to mount the subs off the floor in the middle of the walls as shown in the photo below:





If you are intrigued about this concept, follow the links:
http://www.audiocircle.com/index.php?topic=106838.msg1095060#msg1095060

[medium jim]

Well Jim I did look around the net a bit.  Acoustic curtains are not advertized as being effective for bass frequencies (one site stated 9% noise reduction at 125 Hz, the lowest stated frequency and it was steadly dropping with frequency) while another admitted that a 1 or 2 inch thick panel would be better.  I'm sure that a whole wall would help some even at lower frequencies, but this is the "Bass Place" so I'm focusing on 20 - 80 Hz (where Toole states absorption is not practical).  Is your setup on the long wall?

Again, this not about me or my system, but I appreciate the concern.  For the record, I'm rather pleased with how my system sounds.

I also apologize for noting what I done treatment/eq wise as it opened a door that shouldn't have been.

This thread is about sharing ideas on the subject or poll that is intended to help everyone who may be interested in the subject. Moreover, the question of treat/eq seems to evoke serious discourse, a good thing!

I have no problem if someone or more than one is willing to share what they have done to tweak their system, pictures welcome. 

Jim

[*Scotty*]

One of the single biggest problems that equalization fails to address is the presence of standing waves between the loudspeakers and listeners position. Why does this matter if the bass response at the listening position is flat?
Number one, the room is still resonating below the Schroeder frequency, which increases the rooms contribution to what you hear due long decay times in the bass region. Second, the potential for disturbing the neighbors, if there are any, is higher because the room is still behaving as though it is big bass bell. Third, and perhaps more importantly, is the negative impact that standing waves have on the imaging potential of the system.
 Improvements in imaging is one of the strongest arguments in favor of attacking the standing wave problems via the time domain and multiple subs. See link below for a complete explanation of this approach. 
http://vbn.aau.dk/files/12831869/AC-phd.pdf
Why be satisfied with less than the best that is possible when the tools for attaining this goal are within your grasp?
Scotty


 

[doug s.]

i checked "room treatment".  but, i agree that multiple subs should be considered a room treatment.  if you have a truly large room, you can do well with only a pair of subs and minimal other room treatments, ime.

and don't get me wrong - i am a huge fan of eq - i use a deqx in my system.  but...  the more accurate your system is before any eq is applied, the less eq that will be needed, and the least harm that will be imparted to the signal...

doug s.

[medium jim]

While sub bass is said to be omni-directional, is it?  Does swarming subs change the placement of sub bass in the soundstage?  Maybe I should reserve this for a different thread, but it seems appropriate in this one.  I like stereo bass, e.g., left channel and right channel subs.  To me it gives the best soundstage, especially for classical.

Jim

[doug s.]

While sub bass is said to be omni-directional, is it?  Does swarming subs change the placement of sub bass in the soundstage? 
Maybe I should reserve this for a different thread, but it seems appropriate in this one.  I like stereo bass, e.g., left channel and right channel subs.
To me it gives the best soundstage, especially for classical.

Jim

i have found stereo subs improve the soundstage, even when crossed over as low as 60hz, in spite of the supposed fact that it is omni-directional.  if/when i add another pair of subs, they will still be stereo, but behind me in the back of the room, and run out of phase to the pair in the front...

doug s.

[*Scotty*]

 Swarming subs operating in the same phase would tend to generate a more even distribution of pressure zones in the room and possibly a flatter bass response but trial and error regarding placement with be necessary to achieve the best results.
I don't think that they will cause a problem with where the bass appears to come from but it will depend on how steep the slope is on the cross over and how high the low pass frequency is set. The lower midrange is right there at 150Hz and you can tell where a tone at that frequency is located.
 In my case the low frequency capabilities of my front speakers cannot be separated from the rest of the musical spectrum. Running subs at other locations in my listening room hasn't caused any imaging problems whatsoever at any frequency.
However it should be noted that I operate the subs below 100Hz and at a level that is as much as 15dB or more lower than the front mains. I only have to cancel out the remaining energy of the bass wave after it has suffered absorption and transmission losses on its way towards the rear wall. You have to be standing right next to the sub in order to hear that it is even operating.
If you turn it off while listening to music you can hear the sound stage collapse towards the front of the room and the quality of the bass noticeably deteriorates.
It would be helpful if someone with direct experience the swarm approach would comment on any bass imaging problems they have encountered. Maybe Jim Romeyn will comment on his experiences with the swarm subs if he notices this thread.
Scotty

[JLM]

Another problem with EQ is that it can practically provide only about 6 dB of spl boost (a quadrupling of the corresponding wattage).   BTW to do this in the deep bass frequencies puts a major load on amps. 

Devices like the Behringer DEQ2496 (l own/use it too) only provides 1/3rd octave resolution which is way better than tone controls, but still only a rough approximation of what is really happening (sharp peaks/dips are missed).  Fortunately we can't hear those dips, but as Scotty mentions any frequency discrepancies have other deleterious effects.

EQ should be thought of as the tweak of the tweaks.  Absorption should be wide spectrum.  Diffusion should be varied (randomized).  But multiple subs (at the ends of the room) should be the first step.

[jtwrace]

I have no problem if someone or more than one is willing to share what they have done to tweak their system, pictures welcome. 

It's even better now....flat to 12Hz in room response. http://www.audiocircle.com/index.php?topic=86403.msg913119#msg913119

Again, multiple subs are very hard to beat so are room treatments.  Last, speaker design also has a lot to do with it.

[kevin360]

I voted for treatments first. My justification for that opinion is that I see the problem as being mechanical in nature - the physical boundaries. It seems logical to reduce the behavior of those boundaries with mechanical filters - tube traps. It's a bit painful to buy it all (passive bass 'management' currently matches my investment in subs) and I can see that WAF would preclude their use in anything but a dedicated room, but I am quite pleased with the result of adding the tube traps and sub traps.

I must, however, stress the fact that I don't see one correct answer to this question, aside from 'it depends'. As I see it, the only wrong answer is 'ah, don't worry about it - do nothing'. Of course, the only complete approach is a combination of passive and active methods - do both. I am aware that I have more work to do.

[medium jim]

I voted for treatments first. My justification for that opinion is that I see the problem as being mechanical in nature - the physical boundaries. It seems logical to reduce the behavior of those boundaries with mechanical filters - tube traps. It's a bit painful to buy it all (passive bass 'management' currently matches my investment in subs) and I can see that WAF would preclude their use in anything but a dedicated room, but I am quite pleased with the result of adding the tube traps and sub traps.

I must, however, stress the fact that I don't see one correct answer to this question, aside from 'it depends'. As I see it, the only wrong answer is 'ah, don't worry about it - do nothing'. Of course, the only complete approach is a combination of passive and active methods - do both. I am aware that I have more work to do.

Well said!

Jim

[Tyson]

I prefer OB bass myself, because it interacts less with the room - a physically based solution to a physical problem.  If I could not do OB, then a swarm of 4 or 5 box subs would be a good 2nd choice.