BroadBand Bass Trap's Build

**Prof.** · **05-25-09, 07:41 PM**

Quote:

cinema mad wrote:

Just picked up Floyd E. Tooles new book today: Sound Reproduction, Loudspeakers & Rooms, Looks like A good bit of usefull easy to understand info in it but its $80au ...

Also I was chatting to one of Australia's room acoustic experts and he seemed to favour the idea of the use of Helmholtz Resonator for treating the lower model region in certin applications hopefully my situation

, also pointed out A few ideas for bass traps that reach A little lower than the 6.0pcf fiberglass 6" broadband bass traps I built that are only realy good down to around 100Hz when corner mounted...

So I am going to modify my rear Broadband bass traps and see how it sound & performs after running R+D...
It cost's another $150au for the extra membrane but there is none in my state so its A 2 week wait... If it works well I will be sure to post the build....

Cheers...

Jason...Is this something that fits over an existing bass trap, or a completely new design?

**cinema mad** · **05-26-09, 12:15 AM**

Hi Prof, yes it is/can be intergrated into the existing Bass Trap....

I have the membrane on order but its A 2 week wait...

Cheers....

**Vaughan100** · **05-26-09, 12:00 PM**

Quote:

cinema mad wrote:

A few ideas for bass traps that reach A little lower than the 6.0pcf fiberglass 6" broadband bass traps I built that are only realy good down to around 100Hz when corner mounted...

I would have thought 6" thick fiberglass would be capable of reaching down quite a bit lower than 100 Hz (more like 80 Hz or slightly below that especially if using an air gap). But this guy is an acoustic expert so who am I to argue ?

Regards,

**cinema mad** · **05-27-09, 12:50 PM**

Hi Vaughan100 thanks for taking the time to post..

Yes I do have A big air gap especially for my front broadband bass traps and that is A must to get decent performance out of this type of absorber IE: 3x50mm 48Kq/m3 or 3cf fiberglass, But the reality remains while 6" may absorb A little down at 80hz the further up in frequency say 250Hz the more it will obsorb.. Even Broadband absorbers have an effective bandwidth (Q) that tapers off either side of that... Also the less the thickness the greater directional attenuation can accure, so I believe Ref (Floyed E Toole).....

So the thicker the fiberglass the lower it will absorb but also every time you add thickness say after 100mm & then double that to 200mm the less difference it makes compared from going from 50mm to 100mm in thickness...

Cheers....

**loupy31** · **06-15-09, 03:52 AM**

Hi All,
I have been watching this post for some time now, Most of the info has been very informative, I am currently working on my humble Home cinema room, I like many others am having a few problems with the acoustics, I am in the process of drawing up a floor plan of my room with the hope that you guys and gals can help out.

Regards Peter

**cinema mad** · **06-25-09, 12:26 PM**

Hi Peter,

I am sure that you will fined plenty of help on this forum mate, we are all hear to help each other where we can ..

I started this thread to show & share my ideas about building my own acoustic treatments in the hope that others would fined it useful and also share what they have come up with ...

Cheers....

**cinema mad** · **06-25-09, 12:30 PM**

I am still waiting on my membrane so no progress has been made with my rear bass traps

But hope I will have it next week at the latest...

Cheers....

**cinema mad** · **07-09-09, 02:03 AM**

Last week I finally recieved the Quietel 130kg M3 fiberglass boards From CSR Bradfords, By adding Quietel it will extend the low frequency absorption of the rear corner mounted Broadband bass traps..
Unfortunately the Quietel only comes in A max thickness of 25mm (1") 2400x1200 x2 per pack

as apposed to ultratel 48Kg M3 50mm 2400x1200 x3 per pack..

I just doubled up the Quietel to 50mm and added it to the rear of the existing 100mm 4" of Ultratel, so making A total of 150mm "6" thick bass traps for the rear wall corners...

Also I changed all my first reflection absorption panels (ultratel) from 50mm 2" to 100mm 4" thick
so as to obtain more "even" absorption for Mid & High frequencys, Floyd Toole's new book points out the importance of this..

I also re plastered the theatre's ceiling with one layer 10mm dry wall and only used 4 can lights this time as apposed to 8 and enclosed all 4 liqhts in MDF boxes sealed with Acoustic silicon placed in the roof cavity..

To further reduce my 4 Subwoofers decay time/ ringing I installed CSR Bradford sound screen plus 120mm thick in the ceiling cavity above the theatre wall to wall inc over the side wall cavitys paying attention that the acoustic batts were cut to insure A tight fit between the joists, also doubled it up 240mm thick directly above where the 4 corner mounted Broadband bass traps are..
The difference this made was immediate watching Bolt on blu-ray the bass was just so tight punchy and detailed...

At the moment I am fine tuning A helmholtz resinator placed in A high pressure zone to help smooth out the room modes,
Then the last thing I am doing with the room acoustics

is finishing my other 13 prime seed QRD abffusor for the rear wall

: So the back wall layout will have 7" deep QRD Diffusor/ 4" thick Absorbtion in the middel/ QRD Diffusor...

Cheers..
A couple pics..

**terry j** · **07-09-09, 05:16 AM**

go cinemamad! I'm rootin for ya.

will be going thru this thread again soon, picking your brains as it were.

Just finished my speaker build, and have begun experimenting with room treatments. Our local spotlight does not have anything really that looks like grill cloth (for any treatments), so will grab the details from the geelong store you mentioned, they should be able to get it in..fingers crossed.

I do think I will lean quite heavily towards diffusion rather than absorption. Strictly two channel here, you must be into HT with a name like that yeah!! ha ha

not to steal your thread, but this pic might be good for light entertainment!

Remember the old tip to just throw an unopened bag of f/glass in the corner and see? Well, I did that, and more! just hung the raw batts with string, quick and good for testing purposes.

Pretty heavily did the front of the room, very good results. But, I now get the feel of how easy it would be to overtrap, so will have lot's of diffusion.

, throwing a few raw batts on the wall is only a couple of hours work (even tho I have to use an extension ladder!), but it is not so easy to test diffusion and find out is it.

"let's see, just where are those diffusors I just happen to have laying around??"

anyway, thanks for your thread

**cinema mad** · **07-09-09, 05:48 AM**

Hi Terry J, Very nice speakers you have there mate, what Model/Brand are they ?? I love my 2 channel as well but more into HT now...

As far as the speaker grill cloth, Scott from spotlight Geelong will ship it to you no prob's, $10au to ship AU wide I think...

Cheers Terry
Hope to see more pictures & idea's of what you end up coming up with mate...

**terry j** · **07-09-09, 06:24 AM**

Quote:

cinema mad wrote:

Hi Terry J, Very nice speakers you have there mate, what Model/Brand are they ?? I love my 2 channel as well but more into HT now...

As far as the speaker grill cloth, Scott from spotlight Geelong will ship it to you no prob's, $10au to ship AU wide I think...

Cheers Terry
Hope to see more pictures & idea's of what you end up coming up with mate...

If the local cannot get it, then yeah for sure on to scott

diy speakers, bit of a write up here

http://www.hometheatershack.com/foru...howed-you.html

actually, you may be able to help.

there is a dutch site that had a project very heavily into diffusion, heaps of pics. used tons of mdf to do the build.

this looks very much like it could be it, but randomly pressing buttons I have not come across the thing I am thinking of

http://www.soundscapes.nu/home.html

have you any idea of what it is I am looking for from my vague description??

**cinema mad** · **07-09-09, 07:38 AM**

Actually I am familiar with that web site, there is A link to it in this thread..

To make there QRD flutter echo diffusors they use A Spindel Moulder Cutter, The cheapest one we sell is made by Jet for around $2000au.. It makes it A lot easier than using A router like I did.. When making my Flutter Echo diffusors I used Tasman Oak as it is A hard wood and A lot easier to work when using A router to make precise accurate Vain/well cuts in these type diffusors ...

Cheers...

**terry j** · **07-09-09, 09:15 AM**

Quote:

cinema mad wrote:

Actually I am familiar with that web site, there is A link to it in this thread..Cheers...

well blow me down! it is too.

Ha, this must have been where I got it from originally, how about that! I started a thread today on diy hoping people would know of it, and tonight we find it here.

Someone linked to the home page over on diy, it looked suspiciously like it could be the right site, but even with an hour clicking all the links there I still did not find it.

Why cannot my lotto picks be this serendipitous??

Just quickly glanced the thread looking for links, so not read it again properly yet. But I do recall you saying you found some good cheap plywood, do I remember right? Where did you source it from and is it exe?

**cinema mad** · **07-09-09, 10:25 AM**

One of the guys on that website went sick on the diffusor treatments lol, I think its safe to say he knows the importance of diffusion

I think it was The same guy that posted on An acoustic's forum that he loves & recommends abffusors, absorbtion Diffusion in the one panel...

I was able to get hold of 2400x1200 sheets of 2mm & 1.5mm ply through Belmont Timber from memory, also I think I bought some 2mm ply through my local bunnings store, I paid around $13au A sheet I think...

Cheers....

**Prof.** · **07-09-09, 08:43 PM**

Quote:

cinema mad wrote:

Last week I finally recieved the Quietel 130kg M3 fiberglass boards From CSR Bradfords, By adding Quietel it will extend the low frequency absorption of the rear corner mounted Broadband bass traps..
Unfortunately the Quietel only comes in A max thickness of 25mm (1") 2400x1200 x2 per pack

as apposed to ultratel 48Kg M3 50mm 2400x1200 x3 per pack..

I just doubled up the Quietel to 50mm and added it to the rear of the existing 100mm 4" of Ultratel, so making A total of 150mm "6" thick bass traps for the rear wall corners...

That's very interesting Jason..
What's the difference in density between the Quietel and the Ultratel?

I'm using 6" thick Supertel for the rear traps..
What improvement/changes did you notice in the low frequencies with the Ultratel added?

Quote:

Also I changed all my first reflection absorption panels (ultratel) from 50mm 2" to 100mm 4" thick
so as to obtain more "even" absorption for Mid & High frequencys, Floyd Toole's new book points out the importance of this..

Also interesting..What improvements did you notice with the 4" panels over the 2" ones?

**cinema mad** · **07-09-09, 10:30 PM**

Hi Prof, Supertel is 32Kg m3/ Ultratel is 48Kg m3 or 3pcf( Same as owens corning 703)/
& Quietel is 130Kg m3 (oc 705 is 90 or 6pcf...

Here is A link to CSR bradfords Glass wool specs
http://www.bradfordinsulation.com.au...ical/HVAC.aspx

Hope this helps
Cheers....

**cinema mad** · **07-09-09, 11:01 PM**

As far as going from 2" ultratel with 2" air gap to 4" of ultratel for my first reflections the absorbtion cf will be more balanced for Mid & High frequenceys as Apposed to 2"...

Cheers....

**Prof.** · **07-10-09, 08:10 PM**

Quote:

cinema mad wrote:

Hi Prof, Supertel is 32Kg m3/ Ultratel is 48Kg m3 or 3pcf( Same as owens corning 703)/
& Quietel is 130Kg m3 (oc 705 is 90 or 6pcf...

Here is A link to CSR bradfords Glass wool specs
http://www.bradfordinsulation.com.au...ical/HVAC.aspx

Hope this helps
Cheers....

Thanks Jason..

Hmm...It looks like the Quietel is significantly more dense than the Ultratel and a lot denser than the Supertel..
I think I might try and pick up some Quietel next time I go to Adelaide..

**cinema mad** · **07-10-09, 09:33 PM**

Hi Prof, I should point out that The density of Quietel is better suited to bass traps "NOT" first
reflections & Ultratel is best suited for first reflections..

Personaly I would go with Ultratel due to being very good for both applications..
I used the 2" of Quietel & placed it behined the 4" of ultratel rear bass traps to help absorb lower in frequ...

Hope this helps,
Cheers....

**Prof.** · **07-11-09, 08:22 PM**

Quote:

cinema mad wrote:

I used the 2" of Quietel & placed it behined the 4" of ultratel rear bass traps to help absorb lower in frequ..

.
That's what I'm planning on doing as well..if I can get hold of some of the Quietel..
I'll leave the reflection point panels as they are for the moment..

**ScruffyHT** · **08-03-09, 10:39 AM**

Hey Jason ... wonder if you could make some suggestions as you have clearly invested alot of time on this subject

Theatre is at rough-in stage but planning for acoustic treatments ... room size is ~ 14' X 23' ... 7.1 surround using Axiom M80 LR, EPIC 600 SUB, VP150 center and 4 X QS8 surrounds ( another sub to be added later on if needed )

I had planned to put OC703 corner wedge bass traps on screen wall, linacoustic on rest of screen wall and for the first 4' of the side/rear walls and empty space above that covered with a AT fabric like GOM or Dazian

my questions for you are:

- would you recommend using diffusors above the linacoustic on the side/rear walls ?

- if yes, then due to the linacoustic being 1" thick would it possible to use strips of hardwood to create the channels for the diffusor and glue to the drywall to save space ?

- if I build diffusors with a max depth of 1", would that be beneficial ? ( could go deeper on rear wall ... maybe 2" deep ) ... reason I ask is all your diffusors seem to be much deeper

- if all the above works out, I had planned to cover all the walls with a AT fabric, do you see any problem covering a diffusor with a AT fabric ?

I am very limited on the side walls due to the door location ( support post restricts entrance door location to be very close to side wall )

Thanks for any suggestions

**cinema mad** · **08-05-09, 12:29 PM**

Hi Steve,

Diffusors inc Flutter Echo Diffusors (around 25-30mm thick) will work fine on the rear sidwalls, you can place them over semi riged fiberglass or absorbtion substrait, but small cutouts in the deeper wells of the diffusors are needed as well as random spacing with an air gap behined the diffusors to allow for the lower frequencys to be absorbed below where there usfull diffusion stops...
Flutter Echo Diffusors can be mounted to small strips of wood that are attached to the drywall.. I have never cut varying depths of wood strips/vains based on QRD prime seed to form wells for diffusors, but they would need to be mounted to A hard backing such as wood and must be built very precisely to perform as designed....

The main thing to remember with QRD diffusors is the deeper the wells the lower they will diffuse
the larger QRD's I made are prime seed 13 & 7" deep but I chose to placed them on the back wall next to my rear bass traps...

I would'nt recommend covering diffusors with any thing due to affecting there ability to diffuse optimumly....

A good rule of thumb for the most important areas to cover when it comes to room treatments for A Home theatre is to first treat the 4 corners with bass traps either with super Chunk style or 6"thick floor to Ceiling if possable Also the first reflection points inc the Ceiling..
Then you can move on to treating the rear wall with absobtion directly behined the rear seats and diffusion on either side closer to the corners, Diffusion on the rear side walls also placing Accoustic insulation batts in the Ceiling cavity above the theatre can aid in low freq absorbtion...

It is important to not over treat the room with two much absorbtion as this will deaden the room to much, rather its A fine balance of Absorbtion reflection and Diffusion analizing the room with mic & Acoustic software then futher tweaking/refining untill you get A good balance & even decay time...

Hope this helps
Cheers Steve...

**ScruffyHT** · **08-05-09, 06:58 PM**

Hey Jason ... thanks for the response

Due to WAF and wanting to have the fabric theatre look where all walls are covered in fabric it looks like diffusors will be out for me then if they cant be covered with fabric

The ceiling will be R19 batt/rsic clips/hat channel/DD/GG ... walls staggered stud/R13/DD/GG

If you look at the drawing I can only fit corner bass traps in the front of the theatre room as the rear of the room has 2 doors to deal with ... I can probably put 2" or 4" insulation on the rear wall though ... maybe even 6" if that will help with bass trapping ??? - Should I just cover the entire rear wall then with absorbtion or just where the first reflection point software indicates ?

I had also planned to put a sub built into my riser ( 4 X 12" Shiva drivers firing to the back wall - drawing in my build thread http://www.hometheatershack.com/foru...struction.html )

Also I plan to build a coffered ceiling with Linacoustic in the areas of first reflection as my center channel will be mounted in the soffit

**cinema mad** · **08-06-09, 12:53 AM**

Hi Steve, This looks as though its going to be an Awesome HT mate, I could only wish for A room this size to Build A HT..

You could use Polycylindrical diffusers "Polys" on the rear side walls and paint them the same colour as your Acoustic fabric or put acoustic fabric over them, they can be fairly easy to make with thin Ply, also I think Bryan GIK sells polys...

you could put some form of absorbtion 6" thick semi rigid fiberglass on the back wall placed between the Ceiling and rear wall thus providing an air gap to boost the lower freq absorbton, or placed against the rear wall..

I found the more Subwoofers (I have 4) which in turn brings up the LF sound pressure the more bass traping I needed to try and tame the LF decay time/ringing..

Also the down side to: more rigid you make your side walls IE:adding 2/3 layers drywall) the less LF they absorb so the more important Acoustic treatment's become, same goes for concrete walls...

Cheers Steve,
RE: Jason...

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