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Going to try limp mass and absorption in corner traps

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A friend has built a new studio and heading down the treatment path.

We're planning the tried & tested floor to ceiling corner straddling absorption traps, but we're going to try limp mass also, done modular so we can measure independently.

The plan is to use standard 48kg batts across the diagonal, but in each of the 90 degree walls behind hang mass loaded vinyl (mlv) as close to each wall as possible, mounted to a pine frame.

That puts the absorption out from the wall for max air velocity & the mlv close to the wall for max pressure as a membrane.

Keep the 2 as separate structures so we can measure the effect.

Ideal outcome is the mlv will provide some effect below 100hz - who knows without a tuned sealed chamber behind. Prime Acoustic don't appear to seal behind their max bass trap.

Sealing afterwards would be trivial - just a layer of ply against each wall sealed against the mounting for the mlv.

Wait and see

Cheers

Mike

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If you want to play with membranes here are two to try (cheap too)

1. get some 3mil plastic (something like builders plastic or a drop sheet will do) hang it over the batts straddling the corners

2. Instead of plastic - pegboard

Have you got room or need for a riser?

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Cheers Ellil

Not sure of what a riser is in this context.

I also want to try a membrane in a high pressure zone, ie against the wall.

Is the builders plastic in your suggestion to bounce mid and hi freq off or to improve low freq trapping?

If to improve low freq trapping wouldn't you put the membrane at the back of the absorption closer to the high pressure region ?

Mike

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There was a BBC paper i read recently ( but can no longer find the link to) testing various modular loww bass control systems. They came out in favour of thick insulation with a perforated metal front.

I believe I got there through gearslutz.

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Not sure of what a riser is in this context.

Raised platform you sit on, typically for tiered seating in a home theater

Is the builders plastic in your suggestion to bounce mid and hi freq off or to improve low freq trapping?

Both - works nicely between layers of say 25mm each. Standard treatment for a front wall. Also what I used for my speaker baffles (wall mounted)

If to improve low freq trapping wouldn't you put the membrane at the back of the absorption closer to the high pressure region ?

Works best in between.

I've not got any measurements for pegboard across or in corners. I'd like to see someone do say a 600mm face at 45 degrees with pegboard and an L share in the corner. I suspect the results will be similar and much more pleasing to the eye

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Adding plastic to bass traps:

plastic.gif

Worth trying Mike - both the plastic and the two types of trap in one spot. Be sure to take measurements that isolate each change if you can, will be interesting to see.

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digging up an old thread, but just trying to do some research on bass trapping.

Question. If i have a significant null at say 50hz in main LP, do i then measure to find where the peaks of that frequency are?

Then add bass traps tuned to that frequency in those positions?

 

If yes, what I dont understand is, how does that raise the 50hz signal in the main LP?

Or do I got it all wrong?

 

Would some diy corner absorption traps help? or is 50hz too low?

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I would move the listening position as a preference. 

Failing that you could proceed as planned but you would need some very big traps to address 50hz. 

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On 12/2/2017 at 11:29 AM, Bilbo said:

I would move the listening position as a preference. 

 

agreed - or move the sub, so the null moves away from the LP.

Also try some EQ - at 50Hz it could be a "minimum phase" region of the room, and although boosting dips needs to be done with caution to avoid amp clipping and over extending drivers, I've had good success in my room.

Another sub can also fill in dips.

It's interesting to see old threads dug up, in this case highlighting my lack of progress trying "Limp Mass Absorbers" - I've still not tried any.

On 11/16/2017 at 12:51 PM, STAIN0 said:

digging up an old thread, but just trying to do some research on bass trapping.

Question. If i have a significant null at say 50hz in main LP, do i then measure to find where the peaks of that frequency are?

Then add bass traps tuned to that frequency in those positions?

 

If yes, what I dont understand is, how does that raise the 50hz signal in the main LP?

Or do I got it all wrong?

 

You have it right - if you have a 50Hz mode that has a deep null in a particular place in the room - by removing energy in the room with treatment effective at that frequency you reduce the height of the peaks and the depth of the nulls throughout the room.

On 11/16/2017 at 12:51 PM, STAIN0 said:

Would some diy corner absorption traps help? or is 50hz too low?

Treating 50Hz requires huge traps with absorption (broadband), and large traps with pressure traps (narrowband).

If you don't have any treatment in your room as yet, then I would be surprised if a null at 50Hz at the LP was your only issue - likely your room would benefit from some DIY corner straddling broadband absorption, but it won't do much for that 50Hz null, but provide great benefit in cleaning up mid bass above 120Hz or so.

 

Before trying EQ, try moving the LP forward or back 500mm - it makes a big difference.

If you use some EQ to fill in the dip, then expect that elsewhere in the room, the bass will be much louder - as long as amps aren't clipping, drivers aren't maxing out, and other's in the household aren't complaining, then this is fine/normal/expected - focus on the sound at the LP.

I only have a single sub, and have it tuned for bass at the LP - if I walk around the room, the bass has peaks and nulls - for fun I'll go stand in a corner for elevated bass (bass collects in corners).

 

If you did want to experiment with Limp Mass (pressure) traps to target that 50Hz null - keeping in mind that I've never built any - I'm happy to provide you my design ideas to build a corner trap combining absorption with limp mass - optimised so that the membrane is close to the boundary, and the absorption has gapping - a different approach to say the MaxTrap produced by PrimAcoustic.

 

cheers

Mike

 

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On 16/11/2017 at 12:51 PM, STAIN0 said:

digging up an old thread, but just trying to do some research on bass trapping.

Question. If i have a significant null at say 50hz in main LP, do i then measure to find where the peaks of that frequency are?

Then add bass traps tuned to that frequency in those positions?

 

If yes, what I dont understand is, how does that raise the 50hz signal in the main LP?

Or do I got it all wrong?

 

Would some diy corner absorption traps help? or is 50hz too low?

You can get significant absorption at 50 Hz and there is a question mark over what you consider to be HUGE! If you are hoping to use bass traps as a form of passive EQ, disappointment is likely. Bass traps tend to smooth the response, with a measurable improvement in decay. When you combine this with optimised listening position and sub positions, all well calibrated, what you get is bass that simply becomes part of the music. Compared to what you get just fiddling the dials in an untreated room, the difference is quite dramatic. It's not any one step in particular, but everything together. When it's all done correctly, it's a good example of synergy. 

 

It's impossible to say what is causing your 50 Hz null. It could be related to position - both the listening position and subs. It can also be phase related. Hence before working out a solution, you need to correctly diagnose that cause. Since writing the bass integration guide I've now been through the process over and over in many different rooms. Sometimes onsite, other times remotely. One of the key lessons is "never assume." 

 

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The 11.5m2 limp membrane bass trap that was installed with a tapered sealed area (300 to 600mm over 4m) behind

Trapping was evident in measurements down into the 20/40Hz region

Would believe in a light timber type build the actual wall that the membrane was attached to would act as a seal to the adjoining space, unlike a 300mm thick double leaf masonry wall which required the sealed space.

enjoy, it's worth the work and dosh, big time

 

post-149865-0-65168800-1468104647.jpg.a334e22b9dee345961f4426ff3d38308.jpg

3third dimension, filter, 10mm thick slat  boards spaced at 11mm

592a1a89befa6_mattwatterfall from Dave.png

Remember this is a plot in an almost completely concrete small room of 4 x 7m. Amazing results really, shows what some effort can actually achieve

in an area some would deem unsuitable for a hi end system, regardless of the treatments used

 

back of panel fixed MLV. 2 panels were made to cover rear wall of lounge

post-149865-0-59819600-1468048572.jpg

Edited by 125dBmonster

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On 18/09/2012 at 10:33 PM, sfdoddsy said:

There was a BBC paper i read recently ( but can no longer find the link to) testing various modular loww bass control systems. They came out in favour of thick insulation with a perforated metal front.

I believe I got there through gearslutz.

yep, that works as well :) the perf metal, current job, soaks up the bass

There are a few ways of dealing with difficult acoustic environments, all costs a lot of time and doe

IMG_4636.JPG

IMG_4576.JPG

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