You need to first and foremost move out of the nulls as much as possible. From what I understand you have moved the speakers some, but not the listening position. Work on the latter and see if it gets better. Often sitting about 1/3 of the length of the room to the frontwall or backwall works well. I would do this while speakers are placed close to the corners or at least close to the sidewalls.
Addressing a Null
- Thread starter gshelley
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It's a balancing act because by eclipsing yourself from a null zone (moving away by re-positioning your main listening position) you might introduce another issue; a peak at another frequency, or even another null at a different frequency.
So many factors .... Listening position, loudspeakers' positioning, subwoofer's positioning, subwoofer's integration with your mains, some room treatments, and some judicious EQualization.
Main thing is this though (for simplification): Sit outside the main Null & Peak zones. ...And it is much easier to diminish a peak than filling a null.
I'm no expert* myself, but some members here are, and together they can help you tremendously to obtain a very high degree of satisfaction from your room's response with a very nice frequency target curve all across the full audio spectrum.
* ...Expert people like Amir, Bruce (Brown), Don (Herman), Roger (Dressler), Sean (Olive), Mark (Seaton), Gary (L Koh), Ethan, etc.
So many factors .... Listening position, loudspeakers' positioning, subwoofer's positioning, subwoofer's integration with your mains, some room treatments, and some judicious EQualization.
Main thing is this though (for simplification): Sit outside the main Null & Peak zones. ...And it is much easier to diminish a peak than filling a null.
I'm no expert* myself, but some members here are, and together they can help you tremendously to obtain a very high degree of satisfaction from your room's response with a very nice frequency target curve all across the full audio spectrum.
* ...Expert people like Amir, Bruce (Brown), Don (Herman), Roger (Dressler), Sean (Olive), Mark (Seaton), Gary (L Koh), Ethan, etc.
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As the null in the sub graph overlaps the null with the main speakers it is not helping at all to solve your null problem. My personal advice at this moment - put the sub on a platform with castors and move it along all the length, taking measurements each half meter. You will get a better understanding of your room.
Considering that the wavelength at 32 Hz is more than 10 meters, IMHO the sub should be far from the mains to help filling the mains null. I would consider putting it between the listener and the back wall, and then play with phase adjustment.
BTW, what are the materials on the walls?
Considering that the wavelength at 32 Hz is more than 10 meters, IMHO the sub should be far from the mains to help filling the mains null. I would consider putting it between the listener and the back wall, and then play with phase adjustment.
BTW, what are the materials on the walls?
The walls are double layer 5/8" Sheetrock with Green Glue. Wall framing is a staggered stud on 6" toe plate. About 75% of the exterior is brick faced. Wood flooring over a concrete foundation which itself is on limestone bedrock.
I do have a rather deep soffit around the ceilin. i currently have it faced with OC703 to tame some of the bass overhang. Still need more as I have some ringing in the lower frequencies. Perhaps a tuned bass trap can be placed in the soffit??
As I mentioned, have tried a few positions with the main speakers and can minimize the null with them pushed close to the front wall. Problem with that setup is I lose much of the soundstage and imaging.
Certainly need more acoustic treatments in the room. Tying to maintain focus on the bass and getting it right.
I do have a rather deep soffit around the ceilin. i currently have it faced with OC703 to tame some of the bass overhang. Still need more as I have some ringing in the lower frequencies. Perhaps a tuned bass trap can be placed in the soffit??
As I mentioned, have tried a few positions with the main speakers and can minimize the null with them pushed close to the front wall. Problem with that setup is I lose much of the soundstage and imaging.
Certainly need more acoustic treatments in the room. Tying to maintain focus on the bass and getting it right.
Then you should focus on your sub.
- Try various locations (available & possible to you).
- As mentioned before; a second sub is a big attribute (not to be underestimated). ...With two you can truly 'harmonize' the bass in your space.
- And, subs with DSP EQ (parametric).
- Try various locations (available & possible to you).
- As mentioned before; a second sub is a big attribute (not to be underestimated). ...With two you can truly 'harmonize' the bass in your space.
- And, subs with DSP EQ (parametric).
There is a technique to figure out where non-membrane absorption will work west, but it would require you to be able to (gently) excite the frequency of the dip, and then wander around with a figure-8 microphone, trying all 3 directions (frontback, updown, leftright) looking for peaks.
Any place that shows a peak will benefit from standard absorptive material. That's the good news. The bad news is it's likely going to be where your listening position is, or something of that sort, which is not so helpful when it's only in the middle of the room. If you do find a peak in the velocity field (that's what you measure with a figure 8 mike) at center back, or something of that sort, you can put a big chunk of absorption there and probably pull up that dip by quite a bit, as well as tame the room mode that creates it. The problem with moving speakers around is that it doesn't fix the real problem, which is room storage (the irony of a big dip in a room pressure response is that it means the room stores too much energy at that frequency). If you find a peak near any of the soffits, that would be a place to go after the problem, as well, of course, but it's unlikely to be in a corner, and only marginally likely to be along any wall, annoyingly enough.
Any place that shows a peak will benefit from standard absorptive material. That's the good news. The bad news is it's likely going to be where your listening position is, or something of that sort, which is not so helpful when it's only in the middle of the room. If you do find a peak in the velocity field (that's what you measure with a figure 8 mike) at center back, or something of that sort, you can put a big chunk of absorption there and probably pull up that dip by quite a bit, as well as tame the room mode that creates it. The problem with moving speakers around is that it doesn't fix the real problem, which is room storage (the irony of a big dip in a room pressure response is that it means the room stores too much energy at that frequency). If you find a peak near any of the soffits, that would be a place to go after the problem, as well, of course, but it's unlikely to be in a corner, and only marginally likely to be along any wall, annoyingly enough.
J_J,
Very interesting. However, considering that the dip is around 32 Hz, should not we expect that the maximum velocity should be around 2.5m from the walls, very close to the listener where we have a minimum in pressure? It why I would consider mainly membrane absorbers for this purpose. Also, as we will excite only very low frequencies, can we use a medium/large size non baffled loudspeaker unit as a velocity sensor?
It will be in the middle of the room as far as the direction that the mode is excited in. It may or may not be in the middle of the room against the walls that are parallel to the mode. That will depend on other modes, as well as wall impedence. Certainly membrane absorbers along the walls where the mode is coming from is a solution. A large loudspeaker with a low Fs would work, yeah.
I figure it's worth a try, if you can find a big velocity peak at center back or front, going left/right, for instance, you win.
If not, you can very nicely map where your pressure and velocity peaks are. Of course there will be pressure peaks at the walls, but they may be elsewhere as well.To me, it makes sense to treat the root cause of the problem to whatever extent possible. Root cause= low frequency reflections with long decay times. Symptom= uneven frequency response and long decay times. Perhaps, stating the obvious. Additionally, it makes sense to me to optimize speaker placement and listening position as other have suggested.
I am beginning to see this clearer now...
Is it possible to identify where to place treatments using REW?
It seems lo let me see the symptoms (uneven response, long decay times) but not sure how to use it to isolate where to place treatments in the room.
Will also do more homework this weekend with the sub position to see if I can get some improvements by relocating it.
I am beginning to see this clearer now...
Is it possible to identify where to place treatments using REW?
It seems lo let me see the symptoms (uneven response, long decay times) but not sure how to use it to isolate where to place treatments in the room.
Will also do more homework this weekend with the sub position to see if I can get some improvements by relocating it.
As suggested by Wayne yesterday, try positioning your sub near a corner (front).
...But make sure that the center of the driver (voice coil) is not the same distance from the floor, side wall, and front wall.
...Those three distances should be different. ...And not multiples of each other. ...I call this the full 3D impact.
+ One more thing: Choose the near front corner where the side wall is the longest (less obstructed).
...But make sure that the center of the driver (voice coil) is not the same distance from the floor, side wall, and front wall.
...Those three distances should be different. ...And not multiples of each other. ...I call this the full 3D impact.
+ One more thing: Choose the near front corner where the side wall is the longest (less obstructed).
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If one is sitting where there's a huge null, treatment alone isn't the answer. First thing is to move as much out of it as possible and find the best sitting position with the most even bass response. Treatment comes after that. If one is stuck at one position, a great result most likely isn't possible.
Was able to move the subwoofer and measure the effects. Tried ~1/2 the distance up the long wall (12 ft from front wall) with the woofer firing into the center of the room. No substantive change. Previously tried the sub in both front corners of the room. Again, no significant change.
As recommended here, moved the woofer to the back corner of the room. This had a big impact on the null- in a positive way. See the graphs below.
Lots of tuning and treatment left to do. Still, a nice improvement.
Not sure if I am hearing the location of the subwoofer. Sometimes I believe I can tell it's firing from one side of the room and that it is not symmetrical in its effect. Perhaps trying to sort out the psycho-acoustics from 'reality'. Need to do more listening. Oh, the burden.
Before:
After
As recommended here, moved the woofer to the back corner of the room. This had a big impact on the null- in a positive way. See the graphs below.
Lots of tuning and treatment left to do. Still, a nice improvement.
Not sure if I am hearing the location of the subwoofer. Sometimes I believe I can tell it's firing from one side of the room and that it is not symmetrical in its effect. Perhaps trying to sort out the psycho-acoustics from 'reality'. Need to do more listening. Oh, the burden.
Before:
After
Good progress. Given the results, it seems like the null was created due to interaction with the mains. In that case, changing the delay on it may have equiv. effect. Try adjusting that and see what happens.
Wow, quite a positive change! ...Each room's interaction with sub positioning is indeed quite different.
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Can’t say I’m surprised. You’d be surprised how often corner placement eliminates problems like you had. I’ve helped countless dozens of people deal with their subwoofer response issues over the past 15 years or so, and I can probably count on one hand the number of cases where corner placement resulted in an unusable response curve. All that’s needed now is to apply a little parametric equalization at 50, 65 and perhaps 23 Hz, and you’re done.
Regards,
Wayne A. Pflughaupt
Indeed it's a good change.
I don't think the OP has ability to delay the mains or sub...most two channel systems don't unless they are using a DEQX, Trinnov, computer with multichannel soundcard, etc. For optimal integration you REALLY need the ability to delay.
Still though there are some big swings in the bass. I like to aim for keeping the response at 1/12th within a 10dB window. It's pretty difficult but not impossible to achieve in the context of an audiophile two channel system. Normally SBIR is the thing that screws up reaching the target...
I don't think the OP has ability to delay the mains or sub...most two channel systems don't unless they are using a DEQX, Trinnov, computer with multichannel soundcard, etc. For optimal integration you REALLY need the ability to delay.
Still though there are some big swings in the bass. I like to aim for keeping the response at 1/12th within a 10dB window. It's pretty difficult but not impossible to achieve in the context of an audiophile two channel system. Normally SBIR is the thing that screws up reaching the target...
Yes, I've been saying that for years:
Subwoofer Placement
My single SVS sub is in a front corner, and I was able to get the LF response to within a 10 dB window. Though I do have a lot of bass traps!
--Ethan
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