Acoustic Panels and Bass Trapping a new lounge

[playdough]

Took more than a day  to make,  so showing some progress as I got a little excited and wanted to tell someone. (no one else cares here) 

 

Design Brief, Treat the Lounge sounds like I'm in an echo chamber, that, just won't do.

 

Focus on broad band 100 Hz and up Trapping from 50Hz, Nah, full monty 18Hz (in the Rehm of pink unicorn myth Legend land)   however what the ceiling panels really do is an educated guess from making/measuring these for other rooms.

The frames are pine glue and nail, the outer shell material is felt backed upholstery. Lets light through if held up and looked through, not much though, so will absorb all frequencies in the target, more or less

 

They will go hard on the ceiling, one in each corner of the room and one in the middle. They will cover 2 thirds of the whole ceiling surface. The final third will probably have diffusion treatment.

 

The core is Polymax medium density at 40mm thick. A total of 14Kg of Polymax for all the panels (5) and would has at a guess total mass of these on the ceiling will be about 75 Kg

 

The Traps.

Not made yet but concept is to (in use)use Polymax rolls x 4 @ 12Kg each. They will end up about 550mm in diameter and 1200 long

They stack end to end to make floor to ceiling corner traps. Would like 8 but it's getting expensive !!

Similar upholstery material sewn into 550mm sausage bags sealed with velcro.

 

Wall treatments are only in concept at this stage of the job, any ideas ?

Lounge/Kitchen renovation included the removal of the center supporting wall, internal LVL Type beams were installed internally to the roof cavity. Double layer plaster (20mm) 57 x standard sheets ! Lots of other things done to seal and sound proof a little this lounge. Double Glazed all windows, Soft double layer blinds with built in pelmet.

 

The floor is done, a luxury really, wool carpet with cotton wadding underlay. Made a striking difference to the acoustic character of the room when added and to me in all practicality a minimum before the stereo is properly  interlegible.. Weighs  100Kg with the underlay. 

Room is a construction zone so the carpet needs a vaccy

 

If there is any interest I'll do a before and after set of measurements. Will make one more post on completion.

 

Back to work. Luckily I've still got the plaster panel lifter. Small mercy. 

Note, a frequency response curve was generated in REW and happy to say it measured at 10 Hz the same magnitude as 150Hz and tapered off 6dB at 16Khz. A hole at 50Hz, thanks room., Waterfall confirmed this. 

 

Edited August 12, 2023 by playdough
Job parameter change again, 2nd Rev.

[almikel]

3 hours ago, playdough said:

If there is any interest I'll do a before and after set of measurements.

definitely!

4 hours ago, playdough said:

Focus on broad band 100 Hz and up

3 hours ago, playdough said:

They will go hard on the ceiling

 

4 hours ago, playdough said:

so will absorb all frequencies in the target, more or less

I'm assuming you already realise your ceiling treatment won't absorb much under 2kHz or so?

Nothing wrong with that for ceiling treatment - just don't add too much absorption soaking up too much treble!

 

4 hours ago, playdough said:

The Traps.

Not made yet but concept is to (in use)use Polymax rolls x 4 @ 12Kg each. They will end up about 550mm in diameter and 1200 long

They stack end to end to make floor to ceiling corner traps. Would like 8 but it's getting expensive !!

Do you mean bass traps using absorption?

 

Unfortunately absorption traps that operate into bass frequencies need to be very large and very deep and air gapped (a common approach is to straddle corners).

A useful tool for modelling absorption is here: http://www.acousticmodelling.com/8layers/porous.php

It doesn't model corner straddling absorption, but shows how air gaps improve bass performance...

 

...an example is here: 200mm of fluffy absorption with 200mm of air gap

ie - you need large/deep absorption with a large air gap to operate at bass frequencies.

 

cheers,

Mike

[playdough]

Hi Mike, yes indeed the Porous Absorber graph is telling.

 

So far, the job has been more of a glue and screw everything job so nothing resonates, except the plates in the drawers. 

 

It's a light building in suspended oak floor, timber clad /plaster so was more intent on isolating the outside from in. Made the place a lot warmer because the old place had not a piece of sarking or insulation whatsoever. It does leak very low bass so in all practicality is a bass trap. Double plastering the walls and ceiling did work really well adding mass, to cut down road noise and lower the noise floor in the lounge.

 

After this renovation the area suffered an audible clap ringing echo. Installed the carpet that was nearly cured although could be better. 

I dragged all the insulation in to the area gave me an idea of what to expect, which went ok, music and speech sounded clearer and more detailed for a start, thankfully.

 

Should go find the mic and do some testing, it be in a box somewhere. will be back with measurements.

Complete re fit, while living in it has been, disruptive and don't know where most things are . 10 weeks more, covered in white powder, clean up is ongoing.

 

 

 

 

 

[playdough]

 

Found the mic,  downloaded a cal file. Graph 1 carpet and room internal insulation only Right Speaker.

 

Put up the panels is next, see what happens.

Edited July 31, 2023 by playdough

[playdough]

This is a fairly raw not much EQ sweep of the system in place, listening  position both speakers L and R

Should be better after Dirac is put into service. 

Sounds ok for now, seems to make bass from under 20Hz ok. Entire range is reasonable, for what it is, if not bass heavy.

I see an issue at 200Hz, maybe a transition/summation, with the 21's handing to the horns and a room suck out at 50Hz. A bit up and down around the 1Khz range, might smooth out with some fine EQ.

Edited July 31, 2023 by playdough

[playdough]

Couple more measurements showing more detail of what's going on.. In reality it is helping define a more detailed soundstage. 

Below 100 Hz there are some things happening that won't change much. Moving the LF speakers onto axis stands might make a difference. Coffee table sub, change strategy. 

Edited July 31, 2023 by playdough

[playdough]

The panels went in with the other bags of insulation and did some measurements. No EQ changes, tried to keep the same  sweep gain from the last set of readings. 

Put the bags in places there seemed to be summation of bass. Behind the speakers and in the opposite corner. 

The 50 Hz hole seems to be slightly relieved, Graphs show improvement of resonance times, higher frequencies. Clap echo has improved but not gone. It's still a lively space.

 

The REW measurement software can generate a lot of graphs,  and but I don't know how to explain them all that well  still learning. I put in the RT60 Graph for viewing.

 

Was a fun job  worth the time and it has improved the area enough for any speaker to sound better.

Still some more to do on the kitchen job so I can get the refrigerator out of the back wall of the listening area. 

 

 

 

[crtexcnndrm99]

Agreed on the annoyance of having a refrigerator within earshot.

 

Ceiling panels looking good there

[playdough]

3 hours ago, crtexcnndrm99 said:

refrigerator within earshot.

Indeed next to the listening position, once that goes I can attend to the walls.  Moving things around changes the graphs. measurements, makes reading them more complex than it should be..

I gave the HF Speakers 3dB of gain from 200Hz, was the only work on the system EQ. There is a Dirac capable mini DSP here I'll put into effect once the whole area is settled.

 

Job isn't over yet.

 

Thanks the panel job did go ok. pleased.

 

Edited August 1, 2023 by playdough

[playdough]

Re visiting all the graphs before and after.

The decay plots tell a better story and corelates with what is heard in that area.  Less reflections/interaction  from the ceiling and generally more details in the reproduction overall. Horn speakers can be fatiguing to listen to, for a number of reasons. Room treatment has a smoothing effect on what was sometimes a little edgy and peaky through the HF. No honking jokes pls.

 

Back to work on the kitchen hardware. Plumber tomorrow.

(Little bit surprised no one has asked for a nude photo of the speakers)

 

 

[playdough]

 

If anyone wanted to know what sub 20Hz at magnitude sounds like ? Yes it is present in some recordings, including classical. 

 

Well you don't hear it,  it's felt, it shakes the couch, the floor, it cracks joins in plaster, light fittings come loose. It finds things in cupboards. Gets into every corner of the house. Dust comes out from under the skirting boards.

It does this at quite low SPL, 70/80 dB will do.

Not for everyone.

 

I hope the nails stay in the floor boards.

 

This case it's unusual to use a speaker to handle sub 20 to 270Hz reasonably well and only be powered via 25w RMS per cab. Absolutely minimal. DSP convolution is used to do this. Yes the first crossover is 250Hz. 

They are pair of 8 ohm drivers  operated in parallel, high efficiency is the nature of the game at at least 97 dB + 1w at 1m, within the band of operation. 

 

System operates without  sub/s, so no transition issues/ additional hardware required.

 

Next 

The walls. Identified a few ways to go about this. 

Absorb  panels, minimal effect most likely as suggested above.

Constant directivity type speaker systems tend to not interact with the side walls so much so rear wall takes priority.

 

I've had some success in the past with heavy membrane trapping. A far more effective treatment for lower frequencies,  So off to CSR order a roll of lead lined vinyl. 

Concept is to make a 200mm thick heavily damped, 2400mm/ 1200mm rear wall  membrane trap, behind the main listening position.

 

Side walls TBA, one thing at a time.

 

 

 

 

 

 

[playdough]

6Kg per m2

5m x 1.35m Ordered. Might make 2 panels. close to 6m2. That'll do something. 

35 Kg plus the inner insulation and the outer shell.

@Sounding

[Sounding]

On 30/7/2023 at 8:37 PM, playdough said:

nothing resonates, except the plates in the drawers. 

And the fridge, but that’s temporary…

 

On 31/7/2023 at 1:35 PM, playdough said:

Found the mic

Beauty - looking forward to running side by side tests and see if these mics really are as good as each other (mine Dayton UMM6, yours UMIK1).

 

On 31/7/2023 at 2:56 PM, playdough said:

with the 21's

Let’s be a little more open here - with the FOUR monstrous 21 inch drivers, that look about as impressive as they sound!

 

On 1/8/2023 at 5:53 PM, playdough said:

It's still a lively space

Understatement! But you are doing so much there, it’s going to be awesome!

 

On 1/8/2023 at 8:16 PM, crtexcnndrm99 said:

Ceiling panels looking good there

Well said!

 

On 2/8/2023 at 10:02 AM, playdough said:

Little bit surprised no one has asked for a nude photo of the speakers

As Lil’ Nell says in Rocky Horror, 

“I’ve seen it!”

 

7 hours ago, playdough said:

5m x 1.35m Ordered

We’ll talk. Cheers.

 

Great work so far. I’m free Mon Tue Wed if you need a hand.

[playdough]

1 hour ago, Sounding said:

free Mon

Cheers Adam

Was a lot of fun having you over, we certainly "run in the space" with some good old fashioned 100dB solid ear flogging. took a day to wipe the smile off my face and my ears to stop ringing.

The system had only been set up in there for  a couple of weeks

mic comparison would be a good idea, mine has been out a fair amount and taken a beating. Gaffa is it's friend.

 

Going for a drive Monday have an appointment ( will give you a bell over the WE), I seem to have come across an Upholsterer that has a "lot of 4Kg, per m2 mineral loaded vinyl  with foam on one side"  as written off unsuitable for his use and heading for land fill. Delaminating or something

Have to check it out as a matter of urgency as I have found, it's not that easy or cheap to ship. Still have the first order coming.

Used the stuff in the past, it works particularly well. A whole wall in one lounge. No one would believe me if I said it worked into sub 100Hz, to subdue bass bloom out, but it does !! Measurement will sort  it out.

 

To acquire 15m or more, well let's suggest that's enough for a real man sized bass trap, or 3 is the plan.

 

Picture a bed sheet hanging on a clothes line, throw a basket ball at it. It hits the sheet, stopping. That's my theory !  Actually it Newtons fluid dynamic theory ....

 

Back in the educated guess realm again, what would life be without some risk of failure ?

 

I have a sneaky plan for low profile  design which will possibly involve 2 membranes per panel trap spaced apart, one behind the other 100mm spacing 200mm thick.  2.4 x 1.2m x 200mm x 3 provided I can get the materials. Some genius might model that for me .

 

Anyway if the vinyl stock is real, and its ok, the traps will be made next week/s, installed and measured in room.

 

I'll post a pic of the JBL's undressed just before they are taken out for the PSE144 Point Source Elliptical HF speakers literally kicking about here, keen to play with those again, although there is a certain Cinema magic that the huge JBL horns possess, undeniable.

 

Yea, the novelty never wears off the neodymium motor 21's, efficiency Kings of Bass they are.

 

 

 

 

[playdough]

Well, had a bit of luck and the loaded membrane is on site.

That little 10m roll weighs 80Kg and the vinyl is foam backed, so intuition says to me, single layer, polymax filled. Sealed against the double layer plaster.

 

The job will take a week or a little more starting now, to make 4 x low profile bass traps, 2400 x 1200 x 200mm

 

If there is any interest I can show construction, thinking how to go about that before buying the timber framing.

 

I may even be able to actually measure some performance attributes expected, of the constructed hardware. Thinking of how to that as the build goes ahead.

 

Beyond that a low Fz tone gen and localised spot SPL metering will help identify the best walls to mount them to for correct integration. 

 

Playdough.

[playdough]

http://www.acousticmodelling.com/multi.php

 

https://www.jochenschulz.me/en/blog/rockwool-glasswool-hemp-best-absorber-material

 

Going to have to science this a bit

 

After playing with the model link above, inputting 3 layer design, of limp membrane 4Kgm2 mass, air gap at 200mm and  3000 Pa * s / m2.  for the polymax damping at 40mm,  results around 60Hz,

It became fairly apparent this type of trap exhibits a narrow Q, and seemingly low sensitivity in the simulator

 

Logic suggests, 

Bigger it is the more sensitive it will be.

The deeper the  trap is the lower frequency target

Tapering the air gap, would widen the Q

 

Building the outer frame onto the wall and painting it in might help it blend in,

Like trying to hide an elephant behind  blade of grass. 

Big job.

 

 

 

 

 

 

 

 

 

 

Edited August 7, 2023 by playdough

[DVDHack]

Have you seen this?  There's also a calc spreadsheet but I don't know how to attach it.

 

I was wondering if you could decrease the Q (broaden the frequencies covered) by tapering the absorption inside the box resulting in variable depth.  Similarly you could slope the front of the box for variability.

 

limpmassbass1.pdf

 

 

Edited August 7, 2023 by DVDHack

[playdough]

1 minute ago, DVDHack said:

attach

Yea got it, having a read, thanks.

[playdough]

The simulator I'm using takes out some of the back of envelope maths, with a scientific calculator  not keen

 

After re visiting the measurements, treating from around 50 hz, can be achieved, so it (they) might work well.

 

I just have to decide weather or not to cut holes in the wall behind the trap to bring the building wall cavity into play.

 

Interesting, will build the outer frame onto the wall, first.

Then make the membrane frame and slide into the outer. From there re measure see what comes out of that.

Tapering the air gap might be a useful thing.

We will see. 

Better get to Bunnings !! With this plan pinging around the brain. 

Edited August 7, 2023 by playdough

[playdough]

The only thing I don't understand is

 Quote from the PDF.

 

The box L x W is not critical but should be kept small compared to the wave length of the resonant frequency. The limp mass bass absorber is not effective beyond 300Hz for this reason. Typical L x W would be 60 x 40 cm for frequencies below 100Hz, and 40 x 30 cm for frequencies above 100Hz.

 

ok, a bit more reading work out why 

 

[playdough]

50 Hz wave length is 6.8m in air so, traps will be smaller than that. 

You can use a 10" sub to make 50Hz, but a 21"  will be more sensitive, for the same power input. 

 

They are going to be bigger than the prescription, probably over kill, but so is 4 x 21" drivers in a lounge. 

 

Treatment Target can be 50 to 150Hz. 

 

Clear as mud.

 

[playdough]

Placement ?

 

Good question

 

I've done some hand held SPL Measurements with a tone gen at 50Hz (happens to be a suck out in the graph at 50Hz) and yea, the room has a resonance at 50Hz, 70Hz and 90Hz 

Pressure node, summation is prevalent behind the speakers and adjacent corners.

 

Geez, probably a good idea to straddle the corner, wall to wall  boundary.

Just get's bigger and harder

No gain without some pain they say.

 

I get the same gut feeling chopping up a grand in ply, making a simulated enclosure, praying the maths are ok, trust the model. 

 

 

Edited August 8, 2023 by playdough

[DVDHack]

I'm trying to make all my acoustic treatment a standard 1200x600mm so I can move them around into different positions.  I have standard absorption, absorption with BAD diffusion across the front and I'm making some 400mm deep absorption with BAD.  The only exception has been the skyline which is built for a specific position, first side reflection.  I don't want to attach them to the wall so everything has a big air gap and is self standing.  
 

If I build these for bass I'll also make them 1200x600 and have 3 chambers of different depths in each box.  These are pressure devices so I guess they can go hard against the walls in each corner, I'd make them with a hard back.

[playdough]

1 minute ago, DVDHack said:

hard back

Yea, the hemoltz resonator type trap. Heard good things about those. Complex thing. 

 

Looks like building onto the wall for me.

I've got a corner on the rear RHS of the listening position that is quite the hot spot if you need a back massage with LF, not ideal. Start there. Keen to cut up some pine, today.

 

This job is holding up the kitchen cabinet completion, kitchen is operating but, that's not ideal either........

 

 

 

[playdough]

Yea, the corner where the fridge is.  It's time that moved.

 

Building it (the corner trap) in suggests I can cut holes in the walls, if necessary, would get me from 200mm to 300mm depth of trap, or my target of 50Hz.