Bass traps

[Ethan Winer]

tjschuhow wrote:

fiberglass insulation - even dense 705 FRK mentioned in Winer's article - is acoustically transparent below 100 Hz ... an even handier bass trap built by Paul White, Editor in Chief of SOS. This design is unique in that it's similar to a Helmholtz absorber, yet instead of pegboard, it uses a neoprene type material hung loosely over the rockwool (think, 'rigid insulation') barrier.

Just to clarify, rigid fiberglass is absolutely effective at frequencies much lower than 100 Hz. However, its absorption is improved by the addition of a membrane. I wouldn't charactertise Paul White's bass trap idea as a Helmholtz trap, but it might work better than plain rigid fiberglass.

You can see a comparison of three densities of rigid fiberglass, without and without the FRK facing, in this report:

www.ethanwiner.com/density/density.html

There you will see rigid fiberglass only three inches thick making a small, but very real, improvement even at the room's lowest 42 Hz mode.

--Ethan

[Fincave]

No progress as of yet, just more questions! Went and had a look at one store today and they have rigid rockwool panels that are 100cm X 60cm X 5cm, no mention of density on the packaging and no salesman in sight (no saleslady either). The panels are sold in packs of five though I may be able to get loose ones if I ask nicely. From the above package I would be able to get:

1) One trap with front being 78cm, sides being 50cm and 60cm and 100cm tall

2) Two traps, front of 60cm and both sides being 42cm and being 100cm tall, the second trap would have a face of 50cm with both sides being 35cm and 100cm tall

3)One trap (oblong) with sides being 60cm X 25cm and being 100cm tall

Of the above options what would be the best, options 1&2 are both triangular in shape and would fit nicely in the corner. Is option 3 being oblong a problem or not, appearance wise it would not bother me! While I was in the shop I happened to notice sacks of loose rockwool, roughly 100cm X 40cm X 30cm and weighing 20kg, these would be the cheapest, easiest and ugliest option though easy to cover in material.

I seem to be getting the hang of REW and will use it to take measurements before and after treatments, as soon as I decide on what traps to build.

Once again any and all input will be most appreciated. Thank you in advance.

[F1 fan]

bpape wrote:

Depends on how you do it. If you're going to use 4" straddling a corner then the 8lb would be a better option. If you're going thicker or even chunking it, no need to spend the extra money. As you increase thickness, you can slack on the density a bit and still get good performance.

For the same money, I'll take 8" of 4.5lb over 4" of 8lb any day.

Bryan

Thanks , I will use the RHT40 and shoot for a 8-12"thickness.

[bpape]

TJ.

Yes - those can work nicely - but they'll only work for maybe a couple of octaves. That may not be what is desired. And, I can assure you that if you use 6-8" of even 703, you'll get significant absorbtion well below 100Hz. Even 6" of 703/705 straddling a corner will be pretty effective down to the low 60's/high 50's.

Bryan

[tjschuhow]

Here's a link that will give you more things to think about for your project. As if that's going to help! http://www.sae.edu/startpage/support.php Maybe you've already checked SAE out, but go to the 'Free Reference Material' center panel and click on '1. Audio Studies.'

You'll find clear answers related to traps, absorbers, layout, design, materials, coefficients of absorption, acoustic transparency, etc. There's even a Helmholtz Resonator Calculator - my personal favorite.

If you get information overload, I won't fault you if you chuck all the data and stuff a couple bundles of old bluejeans in the corners of the room. It worked in the '60s, right?

Regards,
TJ

[Fincave]

Great, more reading! Seem to be spending more time reading than listening to music. Seriously, thank you for the link, will have a more in depth look soon. May well end up changing my plans yet again or even just throw bundles of jeans in the corner, quick and easy!

[Fincave]

Small progress report. Have purchased some rockwool panels and have cut them to size. Need to buy some wood for frames and then assemble them. Couple of bad pics included.

[basementjack]

Finclave -that looks like a lot of work!

What did you use to cut them?

[Fincave]

Cutting them did take some time. I would have wanted panels that were thicker but the thickest that were available were 50mm, there are 56 pieces in total. When I asked what would be the best way to cut the panels I was told that they have a special knife for the job that resembles a bread knife, being a chef with a good collection of knives I decided to use my oldest and worst bread knife, worked a charm though the knife is not quite the same anymore!

[Fincave]

Short progress report. Have two traps basically ready. Decided against making a wooden frame as the other half said it would be easy to just cover the traps in fabric. Purchased fabric and came to the conclusion that sewing triangular bags is not the easiest ting in the world. My girlfriend made the first one and then decided that maybe need to re-think the covering of the traps, me being stubborn decided sewing can not be that hard, can it? I gave it a go and well it is pretty difficult though I managed to not break the machine or sew my hand to the material or anything like that. Have now placed the cut panels into the two bags and they are having the final seam put in by hand. Should get the last two bags sewn up today or tomorrow morning and will then be able to first do a listening test to see if the boominess has been reduced, also have a look if thee are any changes in the subs response. Here are a couple of not very good pics.

[Sonnie]

Nice work Fincave...

[JCD]

Not bad! And yeah, I can see how sewing things up could be a huge pain.

Since I'm lazy and don't want to read through the thread again, where are you going to put the four traps you're making? Obviously in the corners, but one in each corner? Or stacking two in the front corners?

And I can't wait to see how they help your room.

JCD

[Fincave]

At first I plan on putting one trap in each corner, I have two traps that are 60 cm tall for the rear corners and two that are 80 cm for the front of the room. Depending on the listening results I may end up stacking them and make another two that would be 140 cm tall.

[brucek]

Depending on the listening results

You haven't touched on your testing methods in this thread too much.

Will you be using REW to do a before and after using response and waterfall?

What results are you hoping for?

brucek

[Fincave]

brucek wrote:

You haven't touched on your testing methods in this thread too much.

Will you be using REW to do a before and after using response and waterfall?

What results are you hoping for?

brucek

I will be relying mostly on my ears, not the most scientific method, I know! I will also use REW to have a look at the subs response before and after. I am using a BFD and have achieved a response that I am happy with, not perfect but good enough for my 'tin ear'. The main reason for builiding the traps was to get rid of some boominess I have when listening to certain music, Nick Cave and the Bad Seeds in particular, the boominess could well be in the mixing? Boomy bass may be a slight exaggeration as the problem is definitely is not severe by any means. Am not sure if the traps will make any difference, they may only make a difference that only I can 'hear', or may only serve as conversation pieces for visitors.

Probably won't use the waterfall as I do not really understand what I am looking at when looking at the results?

[brucek]

Probably won't use the waterfall as I do not really understand what I am looking at when looking at the results?

But isn't the waterfall plot the exact tool you want to use to evaluate the effectiveness of traps?

See this very interesting acticle on the subject of EQualization using a BFD versus using Traps, where they use waterfalls to test the results (with comments by member Ethan Winer). Perhaps he could comment further here.

Wayne P. also talks about waterfalls here.

With great respect to your ears, I think with all the nice work you're putting into this project, it would be a nice idea to do some REW testing, so we can all evaluate along with you.

brucek

[Fincave]

No need to respect my ears, they are not that great! Thanks for the links, had a look at both, must say that as it is a little late here Ethan Winer's stuff did not get the attention it deserved. Wayne P's post in the second link does make some kind of sense and probably will make more sense after the second reading. As soon as I get the next two traps ready I will take some measurements using REW, will also do some waterfall plots after doing some more reading. Using REW is still a bit intimidating but am getting the hang of it!

[brucek]

Here's another thread on waterfalls where I show my complete ignorance on the subject and where I learned a few things...... It seems quite important to set up the x and y axis and time. Waterfall is simply a response in slices of time after the main response to show how it decays....

brucek

Fincave

Hay mate that is a doodle thanks, I’ll check into the pricing for the materials, I doubt it will cost much and the glue as well to stick the separate pieces together.

If I didn’t see it written mate, how many slabs of rockwool was needed to create the triangular shapes?

[Fincave]

Brucek: Thanks for the link again, will look into it and post results as soon as I have some.

JBL-4645: I did not even glue the separate pieces together, just placed then into the triangular shaped bag of which the rear seam was left open, the final triangle had to be cut into two and then the seam is done by hand. The bag is cut pretty much to exact size and so it is quite a tight fit. I purchased one packet of panels as the store where I bought them will not sell loose panels, some stores will though. Panels were 120cm by 60cm, cut into half giving 60cm by 60cm, these were then cut into four triangles giving a size of 60cm by 42,5cm by 42,5cm. I used seven 50mm panels and got eight pieces from each panel for a total of 56 triangles, am using 16 triangles for each trap that I am placing in the front corners and 12 triangles for the rear traps, giving a height of 80cm and 60 cm respectively. It would have been handy if the rockwoll slabs were thicker as then the cutting would have been less, the ones I am using can be had as thick as 130mm but were not in stock and would have cost considerably ore as transport costs wuld have been added. Total price for panels was 45€ and about 14€ for the black sheet material, not expensive at all, especially if they work.

Fincave

Gotcha, thanks mate, did you spray paint them, not sure but from the look of the image it looks as if they where coloured, could have been the light on the camera?

Estimated cost for argument sakes?

PS. £45.00 UK pounds?

[Fincave]

Just covered in material, no spray paint. 60€ is about £40