The No.1 Website for Pro Audio
Tim's Limp Mass Bass Absorbers
Old 3rd September 2019
  #961
Here for the gear
Quote:
Originally Posted by diggo View Post
You left out the most useful method for very small rooms: pressure absorption, which is similar to limp mass 'membrane absorption' but not the same. It consumes significantly less space in the room.
Sorry my bad It was kinda late in the morning haha i still have vacation...
This whole new adventure sucked so deep into it, that i sometimes forget sum details haha

I was aware of it that a limp mass bass absorber is a pressure absorber also, same as helmholthz, but helmholtz is gonna be the last option for me, cuz imo they look quite difficult to built..
I haven't did a really deep search on them...

But are there also membrame absorbers which aren't pressure based?
Still learning tho

Quote:
Synthpark wrote:
Quote:
Originally Posted by diggo View Post
You left out the most useful method for very small rooms: pressure absorption, which is similar to limp mass 'membrane absorption' but not the same. It consumes significantly less space in the room.
Membrane and Helmholtz are both pressure absorbers.
Yes u are totally right about that also
Old 3rd September 2019
  #962
Here for the gear
Can someone tell me if this is possible to build such pressure device? which is actually works?

Imo it looks kinda interresting building 1 device that handles 2 narrow frequency bands which saves up space...
The only thing i'm worried about are the blue & green calculations due the Porous Absorbent after the maembrame which might not work because there must be sum space between them.
By adding a small air gap the whole calculations will change...
and in this calculator it ain't possible to add an extra gap..
I'm bad in math.. long live those calculators

Imo the red calculations have to best options to realize in a working build...

I'm hoping also if someone can tell me what's best the best thing to with superchunks and limp mass absorbers?
Should i place a limp mass in the corner & build super chunks on top of them, or build a superchunk from floor to ceiling & place the limp mass near them or somewhere else...
As far as i understand the real low frequency limp mass absorers have to be placed in the corners for the best results
Attached Thumbnails
Tim's Limp Mass Bass Absorbers-absorber-test.jpg  
Old 3rd September 2019
  #963
Lives for gear
 

There's a very long thread here which contains all you need to know regarding 'modex' plate-based pressure absorbers, which can give you the best low frequency bang for the buck when factoring in the loss of space in small rooms due to room treatment. That assumes the boundaries (walls, ceiling, floor) don't offer useful bass trap potential beyond the boundaries.
Old 3rd September 2019
  #964
Here for the gear
Quote:
Originally Posted by diggo View Post
There's a very long thread here which contains all you need to know regarding 'modex' plate-based pressure absorbers, which can give you the best low frequency bang for the buck when factoring in the loss of space in small rooms due to room treatment. That assumes the boundaries (walls, ceiling, floor) don't offer useful bass trap potential beyond the boundaries.
Your link didn't work cuz there was "http://" at the end...
But damn that looks like an veery interessting thread tho!

I allread build sum super chunk frames & have rockwool etc.
so it's better to leave those behind..

I only readed the first page of that thread...
Ahh maaaan this acoustic adventure is going to a brain cracking adventure..
So many options

Last edited by Davo013; 3rd September 2019 at 04:26 PM.. Reason: fault
Old 3rd September 2019
  #965
Lives for gear
 
akebrake's Avatar
 

Quote:
Originally Posted by diggo View Post
There's a very long thread here...
Hi Diggo

For some reson your link is broken, Try this one

My Experiment with a Metal Panel Absorber
Old 3rd September 2019
  #966
Here for the gear
Should i continue building super chunks? and go for a Metal Panel Absorber afterwords or just skip them chunks?
They act like broadband absorbers also, so that makes me doubt about it

Pfft i think i'm going to run short on space on my backwall if i want to put a diffusor on it lol with the chunks there's only 147cm width & 256 height space left for a pressure absorber & diffusor
It appears to be that those metal absorbers are quite big..
but i haven't read the whole thread.. Maybe i'm wrong about that..
Is so maybe limp mass would be a better option for me..
Old 9th September 2019
  #967
Here for the gear
 

It’s measured. Very small space and unusual construction - garden office SIP kit, although the room would have lower modes in the model, it doesn’t in reality due pretty much everything below 100hz just passing right through the walls. Mixed blessing as I need to be careful with volume when working, but have a flat bass response, apart from 164hz. It’s one of the main modes for the room size as well as measured. We’re talking rockwool for this? I put up some panels for my last from and they don’t help at this frequency.


Quote:
Originally Posted by nms View Post
Is this something you measured, or just calculated?
Any reason you're not treating this with porous absorption? 164hz is easy to deal with using broadband absorption. Tuned traps are meant to target the sub frequencies where porous absorption is less effective, in rooms which have massive boundaries (concrete or multi-layered drywall). It's the wrong direction to go for dealing with 164hz. Worse results, higher cost, and more work are the likely outcome there.
Old 10th September 2019
  #968
nms
Lives for gear
 
nms's Avatar
Quote:
Originally Posted by benferrari View Post
164hz. It’s one of the main modes for the room size as well as measured. We’re talking rockwool for this? I put up some panels for my last from and they don’t help at this frequency.
If they didn't help, the panels weren't designed well (too thin or wrong insulation type are common) or they weren't placed in the right location for the problem you are targeting. To put it one way, if you hang a curtain on your wall instead of in front of your window, it's not going to block the light. All around your room there are surfaces which cause acoustic interference of varying nature and severity. Even if you followed good advice in treating the usual spots, all it takes is one untreated reflection point in the right place to cause an issue that no amount of treatment in other areas will fix. Sometimes it's the desk and the only way is to replace with something which causes less acoustic interference.
Old 13th September 2019
  #969
Gear Head
 

I built 8 of these absorbers out of nice quality baltic birch plywood and the heavier MLV. They are in storage right now and I'd like for somebody who has use for them to take them if they like. I'm in the Seattle, WA area. If anybody is interested I can get exact dimensions. They were a lot of work so hoping this would save somebody some effort.
Old 23rd October 2019
  #970
Here for the gear
 

Hello everyone.

I've almost done basic velocity absorbers room treatment and now have only few nasty room modes: 37 Hz (axial) and 50 Hz (tangential 1:1:0).
While at 80+ Hz room is very dry (due to 30-35 cm of porous combined absorbers), aforementioned modes just can't be tamed by any sane amount of rockwool.
Spectrogram of subwoofer sweep in front corner (35 cm from both architectural walls) attached.

My main question is: where shall be located SLAM absorbers for tangential 1:1:0 and how it shall be oriented?
First obvious solution is a whole vertical corner stacked with triangle prisms, at least two (across room diagonals and pressure fronts). That can be done, but not easy to assemble and install.
Or if I just make flat boxes with same tuning and put these in corners it will be also equally (with same size) effective?

I'm not sure if this will be real problem, but my midfields going down to 35 Hz according to manual and it can make some troubles with positioning at least...
Attached Thumbnails
Tim's Limp Mass Bass Absorbers-flat-sub-fr-spectrogram.jpg  
Old 1st November 2019
  #971
Here for the gear
Quote:
Originally Posted by fedorM View Post
Hello everyone.

I've almost done basic velocity absorbers room treatment and now have only few nasty room modes: 37 Hz (axial) and 50 Hz (tangential 1:1:0).
While at 80+ Hz room is very dry (due to 30-35 cm of porous combined absorbers), aforementioned modes just can't be tamed by any sane amount of rockwool.
Spectrogram of subwoofer sweep in front corner (35 cm from both architectural walls) attached.

My main question is: where shall be located SLAM absorbers for tangential 1:1:0 and how it shall be oriented?
First obvious solution is a whole vertical corner stacked with triangle prisms, at least two (across room diagonals and pressure fronts). That can be done, but not easy to assemble and install.
Or if I just make flat boxes with same tuning and put these in corners it will be also equally (with same size) effective?

I'm not sure if this will be real problem, but my midfields going down to 35 Hz according to manual and it can make some troubles with positioning at least...
Well i should go first for going that 37hz mode it's quite huge, but what is the size of your room? it dusn't match with that nasty 31hz decay...
The length of ur room should be at least 5.5m long
But anyway most bass build up is in the corners... Place the boxes where the target freq is the loudest', use ur ears or an spl meter to locate 'm
Use for those low freq's thick & heavy rubber otherwise ur boxes gonna be deep lol 31hz 4kg is 93.7cm with 10kg it's 37.5cm deep
Old 1st November 2019
  #972
Here for the gear
Hi Folks!

I updated Tim Farrants Limp Mass Bass Absorber Sheet and made an addon & converted the formula to calculate the depth and added some tools & tips to support the DIY community!

Cheers!

Edit: zip file contains an xlsx file (2007)
Attached Files
File Type: xls limpmasscalc rev1.0.xls (32.5 KB, 24 views) File Type: zip limpmasscalc rev1.0.zip (14.5 KB, 8 views)

Last edited by Davo013; 3rd November 2019 at 04:06 PM.. Reason: Info about zip
Old 3rd November 2019
  #973
Here for the gear
 

Quote:
Originally Posted by Davo013 View Post
Well i should go first for going that 37hz mode it's quite huge, but what is the size of your room? it dusn't match with that nasty 31hz decay...
The length of ur room should be at least 5.5m long
Actually I really don't know how this can be.
At waterfall in empty room modes 37-40 Hz are clear.
Maybe it's just an artifact of improper measurements with my old subwoofer.

I really don't care much about 37 Hz and lower, because I'm just a consumer hifi user, and if down-tuned bass (like C F A# D#) will have even more weight, it's OK.

But little bit upper is a problem.
If I will be able to position speakers and listener point in such a manner like Room Sim attached, so i will not do anything more.
If not, I'll return to this thread ...
Attached Thumbnails
Tim's Limp Mass Bass Absorbers-room-scheme.jpg   Tim's Limp Mass Bass Absorbers-speakers-placement.jpg  
Old 3rd November 2019
  #974
Here for the gear
Well acoustics change when you treat a room with porous absorbers..
After that is good to re-arrange your speaker setup... there is a good sticky how to setup ur montiors.. i’s the cheapest option to get rid of the nulls.. speaker hight is also important! Same as symmetry is very important also! Replace everytime the speaker 5 cm & do a measurement.. after loads of measurements you see how your room reacts, so you can fine time everything.. it won’t cure your decay times, but the nulls 4 sure...
Try to place the speakers against the back wall to avoid sbir also

To get back sum live sound you can put slats over your absorbers, search for mls sequence

After you do all and still have problems with decay use a tuned device to tame the decay from the room modes

That 54hz 1:1:0 is a trouble maker if you going to cut the very low frequency’s.. they build up in the corners, with very large soffit traps they could be cured also..

https://www.hunecke.de/en/calculator...igenmodes.html

With this you can see where ur pressure points are located..

Good luck!
Old 2 days ago
  #975
Here for the gear
 

A little late to the party but I'm planning to build a few of Tims bass traps. I have a few questions about the membrane.

1. Would it work to have a pattern on the membrane or is it better if it's a flat surface? I'm thinking of using something like this. The flat side would face down so it becomes airtight. https://www.thomann.de/intl/stairvil...nmatte_10m.htm

2. Is there any downside in using a very heavy membrane? I've com across a 9,6kg/m2 rubber mat that would allow me to get very deep in frequency. Is this too heavy?

Thanks in advance!
Old 1 day ago
  #976
in my experience don´t go too heavy with the membrane, try and increase the depth of the absorber to reach your desired frequency.

I have used a PVC foil used to build ponds in domestic gardens: https://www.bauhaus.info/teichfolien...lie/p/20834465

it comes in .5mm and 1mm thickness and is comparably cheap.
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump