Is it time to go Helmholtz/pressure?

[NightHawkIX]

Hey guys,

I've been tweaking my system for mixed HT/music use, and sadly my wife makes me turn down the bass whenever she's in the room. Her complaint is that it's a bit boomy, and she feels a pressure build up in her ear/jaw. I'm less sensitive to the boom, but I do feel it a tad. If I use a shelf filter to turn down the bass though, I lose a lot of the "punch."

I took some measurements, and I see 2 regions that seem to be resonating: <35hz, and 65-75 hz. From what I've read, treating <35hz is an exercise in futility. But the 70~hz range might be doable with Helmholtz or limp mass/diaphragm traps. I've also played around with moving the SW and/or LP around. I'm a bit constricted by aesthetics and screen distance requirements, and the net result seems to be moving that problem frequency up or down a few hz.

My question is: is it worth it to go down that route? Will this solve the boom and allow me to turn the bass back up?

Thanks!


Front L/R: Klipsch RP-280FA
Subs: Klipsch R-112SW (x2)
Processing: Denon X3700H + MiniDSP HD
Source material: Tidal // streaming (vudu, appleTV)
Current treatments: 3" absorbers at reflection points. 2" absorbers with slatted plates on ceiling. GIK Corner Alpha 48" (one more 24" on order)

(only linking the L+SW waterfall, but the 70hz problem is in all speakers)

 

[TLS Guy]

Hey guys,

I've been tweaking my system for mixed HT/music use, and sadly my wife makes me turn down the bass whenever she's in the room. Her complaint is that it's a bit boomy, and she feels a pressure build up in her ear/jaw. I'm less sensitive to the boom, but I do feel it a tad. If I use a shelf filter to turn down the bass though, I lose a lot of the "punch."

I took some measurements, and I see 2 regions that seem to be resonating: <35hz, and 65-75 hz. From what I've read, treating <35hz is an exercise in futility. But the 70~hz range might be doable with Helmholtz or limp mass/diaphragm traps. I've also played around with moving the SW and/or LP around. I'm a bit constricted by aesthetics and screen distance requirements, and the net result seems to be moving that problem frequency up or down a few hz.

My question is: is it worth it to go down that route? Will this solve the boom and allow me to turn the bass back up?

Thanks!


Front L/R: Klipsch RP-280FA
Subs: Klipsch R-112SW (x2)
Processing: Denon X3700H + MiniDSP HD
Source material: Tidal // streaming (vudu, appleTV)
Current treatments: 3" absorbers at reflection points. 2" absorbers with slatted plates on ceiling. GIK Corner Alpha 48" (one more 24" on order)

(only linking the L+SW waterfall, but the 70hz problem is in all speakers)

Your sub is just too loud, like most. Listen to your wife. What you posted shows she is correct. Your sub needs to be turned down between 3 and 5 db. That will solve your problem. Those klipsch subs don't have a very tight bass either.

 

[highfigh]

Try moving the rear subwoofer a few feet back from its current position and see if it helps anything. The seating looks like it's at the midpoint between the two subs and if they are, constructive interference can make some frequencies too strong. The peak below 30Hz is in the range that makes people feel it in parts of their body that make the sensation uncomfortable. Also, and it may just be the effect from the camera's lens, the panels on the right seem to be thicker than the ones on the left and that can cause some odd sensations because of the difference in absorption. You don't have anything reducing the reflection from the ceiling in a place that would affect the outer seats- the bare area to the outside of the ceiling panel would make those two seats sound very different from the two in the middle- is she sitting in one of those?

 

[NightHawkIX]

I might be stuck with the sub placement given the wiring and such. I did try it on the far back wall once, almost opposite corners using a Klipsch wireless kit and IIRC it made the 50hz range very weak.

The L/R panels are all the same, 2'x4'x3". I was sitting in second seat from the left, and wife is 2nd from the right. I'm debating how I want to treat the ceiling over the far seats or if I want to put up some soffit type traps on the L and R wall.

 

[Trell]

I might be stuck with the sub placement given the wiring and such. I did try it on the far back wall once, almost opposite corners using a Klipsch wireless kit and IIRC it made the 50hz range very weak.

The L/R panels are all the same, 2'x4'x3". I was sitting in second seat from the left, and wife is 2nd from the right. I'm debating how I want to treat the ceiling over the far seats or if I want to put up some soffit type traps on the L and R wall.

Your front corner traps are made by GIK Acoustics so why not get some free advice from their acousticians? They would like to look at the measurements you've made as well.

 

[TLS Guy]

Your front corner traps are made by GIK Acoustics so why not get some free advice from their acousticians? They would like to look at the measurements you've made as well.

Turning the subs down is his cheapest solution. His room curve is not that bad. I would bet the 35 Hz problem is coming right out of the sub ports. I have actually heard Klipsch subs and what he describes is the way they are. Subs with a Q of 0.5 are to be much preferred, but they are not common and hard to design.

 

[Trell]

Turning the subs down is his cheapest solution. His room curve is not that bad. I would bet the 35 Hz problem is coming right out of the sub ports. I have actually heard Klipsch subs and what he describes is the way they are. Subs with a Q of 0.5 are to be much preferred, but they are not common and hard to design.

Agree, and I wish my living/HT room was as nice as yours and his, acoustically speaking.

 

[NightHawkIX]

If I had a do-over, I'd go with a Monolith or SVS. Unfortunately at the time, I was looking to match furniture styles to appease the wife, and they were on sale for $300/ea.

Maybe I'll get a 3rd SW like a Monolith 15"; make that responsible for 10-40hz range, and use the 2x Klipschs for 40-120.

 

[TLS Guy]

Agree, and I wish my living/HT room was as nice as yours and his, acoustically speaking.

The picture you posted of yours looked pretty nice to me!

 

[NightHawkIX]

I figured out a solution for some of my bass issues: better integration with the front L/R.

On my first setup, I got lazy with the sub and L/R integration. I solved any of the dips/cancellations by the phase differences by changing the freq response of the L/R below 80hz to be a super aggressive drop. I think that made the sw have to work a lot harder and louder.

I actually spent some time walking the SW distance on Audyssey until I got better alignment of the SW/LR and I think it sounds so much better now. Less boomy, and as a side benefit, much better sound stage.

 

[NightHawkIX]

So I ended up building a few tuned membrane traps to address the 70hz mode, and I'm very pleased with the measured difference!

 

[NightHawkIX]

I built 3, 4" deep each. Here some build pictures.

If there's interest, I can go into details on specs/build process. I think total cost for materials was around $150 for all 3.

 

[NightHawkIX]

Can confirm via the wife boom detector MKI, the measured differences are audible. Played some of the bassier/boomier mixes I have on my playlist for her and she can tolerate a full 5-7 dB louder than before! For me, I notice things feel punchier.

 

[NightHawkIX]

Tuned membrane (limp mass) absorber build guide:

The calculator for depth I used found here: http://www.mh-audio.nl/Acoustics/PResonator.html

The membrane I used was 1.5lb/sqft MLV, I got a total of 4.5'x4': https://www.amazon.com/gp/product/B08562XN48/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

The frame I used was 0.75" MDF

The sealant I used was just Alex Plus acrylic caulk

The absorber material was 3" Safe N Sound Rockwool


Steps:
Back of the chamber was a 24"x24" MDF sheet.
2x Side walls are 24"x5.5" sheets of MDF. I routed a 3/8" deep x 3/4" tall groove into one edge of this, so it would slot onto the chamber back.
2x of the side walls are 23 1/4" x 4.75", these are fitted in between the two slotted side walls. (Take measurements here to make sure the space between your 2 existing walls is in fact 23.25", and that the height to make the walls flush is 4.75"- there may be slop based on your routing/cuts).

Make marks along the interior of the walls 4" above the backing (for a 70hz resonator)

I then sealed all the seams with caulk.

Rockwool is then glued into the chamber

0.5" strips are cut from the MDF board and fitted so the top edge is 4" above the back of the board, using the previously made marks. Used glue and nails to hold them in place.

a sheet of MLV is cut out so it fits into the box. Take measurements here and cut accordingly to allow for slop in the box construction. The MLV is affixed using staples.

I then ran a heavy bead of caulk around the edge of the vinyl.

More 0.5" strips of MDF are used to frame the MLV. Pretty much you have 2 strips of 0.5" MDF sandwiching the MLV running along the entire perimeter of the box. Make sure when you put down the top MDF strip, you get an even spreading of the caulk.

Check if the chamber is airtight. You should be able to press on one section of the MLV and see another section bulge up. If not air tight, run more acrylic on the outside seams to see if it helps.

Wrap the thing in fabric.

Positioning/use notes:

Place your measurement microphone at your MLP. Play a 70hz test tone from your SW using REW (turn SW EQ off). Open your RTA window on REW and start recording. Move around the room with the membrane trap and watch for increases in the dB at 70hz.

There was one sweet spot for me where placing the trap there increased 70hz volume by 4 dB!

Rerun sub EQ. I have 2x SW and use MiniDSP- it was MUCH easier to get a flat response around 70hz with the traps in place.


Notes: Joints on the MDF need to be cut as square as possible. I'm no carpenter, but this build is a lot more complex and delicate than a DIY broadband absorber. If you don't have a table saw, and a good miter/router, this might be a difficult project to tackle.