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Discussion Starter · #1 ·
Looking for some suggestions/new ideas to overcome some bass response issues in my new HT room. I just got my 12x18 (x7.5) foot room 'mostly' completed and I've started tuning. I knew right away something wasn't right with my SVS PB-2000 (x2) as I had been using one of them in my family room while I was building this room. They sounded amazing but in this new room it was like listening to a soundbar sub at best.

I'm using a umik-1 with REW (Denon AVR, audyssey disabled, LFE crossover at 200hz and all speakers disconnected while testing). I've tested a single SVS at 11 different positions independently and measured at MLP. All 11 measurements are in the picture attached below. It appears my room hates 40-50hz :( While some positions are better than others, it appears that this outcome is shared at every possible location to some degree.

Note 1: In the sketch the red boxes are the possible locations where these SVS subs can live (and that I measured). The orange boxes are spots I measured with the SVS but that they won't actually fit in. I have plans to add more subs there in the future.

Note 2: I did put a bunch of vents along the back of the room into my riser which is loosely filled with insulation. I did tests with them open and closed, didn't seem to make a significant difference (maybe 2db better opened for some of the positions)

Note 3: Unfortunately the seating can't move, it's a limitation of a 18x12 room. Starting to think bass response will be another limitation of that.

Just wanted to get a fresh look at what I'm doing or something else to try.


11 positions.PNG HT sub positions.png room modes.PNG
 

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You can try subs in a corner. Looks like you avoided the corners.

Also measure different seating position to verify it is only a MLP problem.

This looks odd. Do you have any PEQ enabled on the sub you are using?
 

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Discussion Starter · #3 ·
You can try subs in a corner. Looks like you avoided the corners.
Didn't avoid on purpose, just not able to fit the SVS there to test. I would add the corners as additional future options (basically everything behind the AT screen). I'll post a picture below for reference (again, room isn't 100% complete).

Also measure different seating position to verify it is only a MLP problem.
Ya I can do this, but just listening in the seats to the left or right you can hear how poor the bass response is (basically across the entire front row). I haven't really done much testing in the back row, but I guess it would be good to see that data as well.

This looks odd. Do you have any PEQ enabled on the sub you are using?
Ya I double checked before doing the measurements but I have the SVS xover set all the way off (to LFE position). I have the gain at 50% and not that it matters for this but I also have the timing set to zero. I even went thru and did a factory reset on the Denon just to be sure before running these tests.



PXL_20210529_165119305.jpg
 

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Discussion Starter · #4 ·
Just did a quick test of MLP vs the back row, thou not as severe the dip still exists (sub center front).
MLP green Back Row Blue.PNG

To rule out the AVR I did a test going directly to my miniDSP and the result was identical (also removing the miniDSP from the chain has same result)

Also while testing all the above from the same locations I swapped one of the SVS for the other and they have identical results. So unless my sub cable can cause a huge dip, it's not the speakers/electronics.

A friend suggested testing with the sub off the ground, so going to see if I can figure out how to setup a rig to do that.
 

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Just did a quick test of MLP vs the back row, thou not as severe the dip still exists (sub center front).
View attachment 3142287

To rule out the AVR I did a test going directly to my miniDSP and the result was identical (also removing the miniDSP from the chain has same result)

Also while testing all the above from the same locations I swapped one of the SVS for the other and they have identical results. So unless my sub cable can cause a huge dip, it's not the speakers/electronics.

A friend suggested testing with the sub off the ground, so going to see if I can figure out how to setup a rig to do that.
Stack one SVS sub directly on top of the other if you want to try that just for measurements. Put the subs on a 4-wheel dolly either way to save your back and ease movement.

It clearly seems like you have your room dimensions working against you here.

I assume you have tried asymmetrical sub placement? In other words having one sub at the null on the left wall—let’s say1/4 into the room and then on the right wall—let’s say 1/2 way down the wall.

I strongly suggest watching this clip. Fast forward to the 31:00 mark and you might just find some help here. Watch through at least 38 minute mark.

Todd literally wrote the book with multi-sub placement. Might be worth a refresher you haven’t read in a while. Optimum Room Locations for Subwoofers An Analysis

if you can snag a pair of the SVS3000 micro and put next to your fronts so you have 4 subs that may be the ticket.
 

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I think you have confirmed it is your room and MLP. The fix may lay in the back of the room where your second row of seating is.
 

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put your 2 subs at the 1/4 points of the front wall (eliminates side-to-side null) and move your seating forward so that your ears are closer to 6'8" from the front wall (this will move you out of the front-to-back null)
This should fix your first row but not much can be done for the back row.
 

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Discussion Starter · #8 ·
Stack one SVS sub directly on top of the other if you want to try that just for measurements. Put the subs on a 4-wheel dolly either way to save your back and ease movement.

It clearly seems like you have your room dimensions working against you here.

I assume you have tried asymmetrical sub placement? In other words having one sub at the null on the left wall—let’s say1/4 into the room and then on the right wall—let’s say 1/2 way down the wall.

I strongly suggest watching this clip. Fast forward to the 31:00 mark and you might just find some help here. Watch through at least 38 minute mark.

Todd literally wrote the book with multi-sub placement. Might be worth a refresher you haven’t read in a while. Optimum Room Locations for Subwoofers An Analysis

if you can snag a pair of the SVS3000 micro and put next to your fronts so you have 4 subs that may be the ticket.
Thanks for the suggestions, I have watched all those videos Gene did with Anthony (they are excellent, I appreciate your videos with Gene as well!). I did spend some time last night trying the 1/4 x 1/4 & 1/4 x 3/4 placement technique across the front of the room, unfortunately didn't make a significant difference. I'll have to try the asymmetrical approach.

1623177839805.png

I think you have confirmed it is your room and MLP. The fix may lay in the back of the room where your second row of seating is.
The fix being that I need to have a sub behind MLP? This is what I am starting to fear.

put your 2 subs at the 1/4 points of the front wall (eliminates side-to-side null) and move your seating forward so that your ears are closer to 6'8" from the front wall (this will move you out of the front-to-back null)
This should fix your first row but not much can be done for the back row.
I certainly can try moving the MLP forward for testing, unfortunately that won't really be practical permanently because it will just be too close to the screen. Honestly I don't really care too much about the sound quality of the back row. Most of the people I would have over aren't nearly as picky about the sound as I am. :D
 

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The fix being that I need to have a sub behind MLP? This is what I am starting to fear.
Yes. If it is, you could just reduce 2nd row to 2 seats if that back corner works.
 

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😁 I don’t know if it’s going to work in your specific scenario but when Anthony starts talking about absorbers and membranes working on 50Hz nulls it reminded me of your issue. You’ve already tried all the proper steps and outside of adding another small pair of subs to make it 4x that may be the route to go.

I can’t tell exactly but it seems as though you may even have the ability to put some pretty thick absorption behind the speakers and screen at the front of the room and some options on the side. Food for thought.
 

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Discussion Starter · #11 ·
LOL trying to be positive...So tonight I did some measurements more on scenarios/positions that I don't know how to make work in the room, but did it for #science

I moved the mic all around the space in front of the MLP just to see what happens. Right and Left of MLP are even worse but the more forward you go, the "better" it gets (not really better)
MLP and forward.PNG front of MLP.jpg

Then I positioned the subs, one in front of MLP and one behind it (along the left wall). This did show a lot of improvement, still a narrow dip thou right at 45hz which I believe is a 1st mode on the width of the room (the blue line is the org position of subs in front, green is with one behind)

subs in front and behind.PNG subs front and behind MLP.jpg


There is no way I could put a 4th sub in the rear right corner because of the door. But it looks like I'm going to need to figure out how to at least stick something in the left rear, otherwise <I have nothing positive to say here> of the last year of blood, sweat and tears. Remind me to never play Russian roulette with the room mode gun again.

Thanks for all of the suggestions thus far.
 

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@INANE is there anything you can do to SHORTEN the room a foot at the front? Your dimensions of 12x18 are divisible by 2 and 3. If you shortened the room by a foot at the front to 17 feet (therefore a prime number) with a faux wall or absorption as Anthony mentions in his tutorial I wonder if this will help your room mode issue if you run some simulations.
 

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Discussion Starter · #13 ·
@INANE is there anything you can do to SHORTEN the room a foot at the front? Your dimensions of 12x18 are divisible by 2 and 3. If you shortened the room by a foot at the front to 17 feet (therefore a prime number) with a faux wall or absorption as Anthony mentions in his tutorial I wonder if this will help your room mode issue if you run some simulations.
Maybe if I ever replaced my front towers. The space behind the AT screen is basically exactly deep enough for them to fit. For now that's not an option, but it's an interesting idea for the future. From an experimentation perspective, I wonder if I could mock something up just to do testing. 🤔

RE: absorption, I was wondering what would happen if I created a bunch all around the towers (and center). It's just unused space right now. I was planning on iterating a bit in this room. As I mentioned I only just got it operational, I had planned to do acoustic treatments as future projects.
 
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