I'm going to make some sound traps for my studio...

frobisher

I know there's a huge amount of info out there on t'net. Has anyone here built their own traps? Got any advice or knowledge on the various rockwool type products available in Ireland, both the common builder stuff and maybe the more audio specialised stuff too?

shayleon

Most of my traps are DIY. Rockwool from ATIL in Dublin. Think it was high density type. Don't forget to spray it lightly with PVA. I then used chicken wire to hold it in place.
cheers.
Shay.

PaulBrewer

I take it we're talking Bass Traps in a small(ish) room?

The problem with rockwool traps is in order for them to 'reach' down to a low frequency a huge amount is needed.

Huge equals using up room real estate - not an option in a smallish room.

The wavelength of 100 hz for example is 3.43 metres. 40hz is 8.58 m.

I believe a quarter wavelength is used to determine the depth necessary so for rockwool to work to 100hz , (which I'd consider the mid of the bass band) one would need .8575 meters deep.

If you wanted to reach 'actual' bass, which is around the low E string of a bass guitar and would cover a large percentage of the used frequency band (probably only a kick would reach down much further in a standard rock band) you'd need rockwool traps of at least 2.145 Metres thick to work.



Say one used a corner max depth of 30cm, about 1 foot it's effective average depth would be 15cm (deepest 30cm/shallowest 0 average =15cm)

If .15 metre is the quarter wave length then the full wavelength is .6 metres or about 572 Hz ..... no where near Bass.

If you take 2 feet deep off each corner of your room it's average is 1ft that still only leaves you at 286 Hz .... still no where near bass... and that's coming out along the wall 2.82842712 feet from each corner.


A practically useless route to take if the science is to be believed ?

Another downside is that having failed to treat your bass you've also introduced a lot of high mid absorption as rockwool is very good at that. So you've skewed your RT even more in favour of bass.

A superior solution in my opinion is a tuned dampened membrane absorber that can reach down to below 40hz and yet be only about 8 inches deep.

How they work is the 'membrane' part is mdf dampened with U5 barrier material with the length and cavity depth determining the frequency about which they work.

This can also be combined with foam to make a 'full range' absorber.
Melamine is the preferred choice as it's easy to work with, has a class A fire rating and does the job!

They're reasonably easy to build but know how and accuracy is necessary.


Old Engineering Wives Tales don't cut it if you're serious.

I should reiterate that I'm only going on recall regarding the 'quarter wavelength' and 'average depth' part of my post but I do know men with superior qualifications in the area to whom I'll send this post.

If they care to reply I'll post it here (once I don't come out of it lookin an eeejit!)

henessjon

can you advise if some is better than nothing ( for my 2x4 control room)


bearing in mind ****z in = ****z out :rolleyes:

ICN

PaulBrewer wrote: »

..What you said..

Hi Paul,

Hope you dont mind - Its something thats on my longest finger to do..

U5 - I'm wondering if thats the Spec of the Materials Absorbency? And what would be suitable to use for this?

And -

The Trap is tuned - Is that to the Room? or simply within itself?

I've seen some formulas out there, but my U factor is low LOL

So if thats correct - If One were to make a BT to absorb "X Freq" - then this would absorb this particular Freq in any room (but depending on size you would need a larger or smaller quantity of them?)


I had to pick something up from one of the corners of my room the other day (The Cleaner had a 1/2 Day). There was Music playing - not crazy loud by any means.. and when I put my head down, the whoomp of the bass was all I could hear.. Felt like I was being mugged! :pac:

studiorat

ICN wrote: »

Hi Paul,


The Trap is tuned - Is that to the Room? or simply within itself?

I've seen some formulas out there, but my U factor is low LOL

So if thats correct - If One were to make a BT to absorb "X Freq" - then this would absorb this particular Freq in any room (but depending on size you would need a larger or smaller quantity of them?)

If I may...
The trap is tuned within it's self to the particular frequency. If the trap is moved from the room it will still absorb that frequency ya see?

Be careful of the formulas online, there's a dodgy formula for Helmholtz resonators floating around the net. It was on the SAE site, basically it's a multiplies sign instead of a plus. This typo however has spread 'round the net like a dose of something because people don't check what they read online.

There's another problem you've brought up here too ICN is that it doesn't really work like that. Apparently, if you start to introduce more boxes into an array, they actually start to affect each other's absorbtion coefficent and the bandwidth of the absorbers.

frobisher

PaulBrewer wrote: »

I take it we're talking Bass Traps in a small(ish) room?

The problem with rockwool traps is in order for them to 'reach' down to a low frequency a huge amount is needed.

Huge equals using up room real estate - not an option in a smallish room.

The wavelength of 100 hz for example is 3.43 metres. 40hz is 8.58 m.

I believe a quarter wavelength is used to determine the depth necessary so for rockwool to work to 100hz , (which I'd consider the mid of the bass band) one would need .8575 meters deep.

If you wanted to reach 'actual' bass, which is around the low E string of a bass guitar and would cover a large percentage of the used frequency band (probably only a kick would reach down much further in a standard rock band) you'd need rockwool traps of at least 2.145 Metres thick to work.



Say one used a corner max depth of 30cm, about 1 foot it's effective average depth would be 15cm (deepest 30cm/shallowest 0 average =15cm)

If .15 metre is the quarter wave length then the full wavelength is .6 metres or about 572 Hz ..... no where near Bass.

If you take 2 feet deep off each corner of your room it's average is 1ft that still only leaves you at 286 Hz .... still no where near bass... and that's coming out along the wall 2.82842712 feet from each corner.


A practically useless route to take if the science is to be believed ?

Another downside is that having failed to treat your bass you've also introduced a lot of high mid absorption as rockwool is very good at that. So you've skewed your RT even more in favour of bass.

A superior solution in my opinion is a tuned dampened membrane absorber that can reach down to below 40hz and yet be only about 8 inches deep.

How they work is the 'membrane' part is mdf dampened with U5 barrier material with the length and cavity depth determining the frequency about which they work.

This can also be combined with foam to make a 'full range' absorber.
Melamine is the preferred choice as it's easy to work with, has a class A fire rating and does the job!

They're reasonably easy to build but know how and accuracy is necessary.


Old Engineering Wives Tales don't cut it if you're serious.

I should reiterate that I'm only going on recall regarding the 'quarter wavelength' and 'average depth' part of my post but I do know men with superior qualifications in the area to whom I'll send this post.

If they care to reply I'll post it here (once I don't come out of it lookin an eeejit!)

One day someone will post something that you will agree on in great detail Paul. I can't bleedin' wait :-)

It's not the bass I'm after. I'm not after an ultra tuned room, I just swapped rooms in the house for my studio and this one has da-ding in the high mid that the other one didn't. I want to get rid of it. So I'm going to make some traps. It's not a question of needing to either get it 100% right or not be bothered, it's about getting as much improvement as I can worth what I have. Knowarra mean?

artvandulet

I seem to remember there being a trick involving wavin pipe and sand.
You cut the pipe to a certain length to get rid of a particular frequency - based on a formula, fill it with sand -block the ends obviously - and hang it from your ceiling.
Someone else might tell you more

frobisher

artvandulet wrote: »

I seem to remember there being a trick involving wavin pipe and sand.
You cut the pipe to a certain length to get rid of a particular frequency - based on a formula, fill it with sand -block the ends obviously - and hang it from your ceiling.
Someone else might tell you more

Wow. Sounds interesting. Paul's right about one thing in this area, there can be a lot of snake oil about. I think it's a cross over from the whacky world of audiophiles that buy covers for the electrical plug sockets so the room sounds better. I kid you not.

I can only imagine some fairly low end as having enough energy in the to move sand inside a sealed Wavin piping. And at those levels I can't see whole lot of absorption. Got a link to any info on it?

PaulBrewer

frobisher wrote: »

it's about getting as much improvement as I can worth what I have. Knowarra mean?

That's the sort of attitude that has the country in the state it in! :eek:

PaulBrewer

ICN wrote: »

B]U5[/B] - I'm wondering if thats the Spec of the Materials Absorbency? And what would be suitable to use for this?

I think it's generic limp plastic like substance. In this instance, as I understand, if your tuned absorber is a bass drum the U5 works as a pillow against that bass drum.
So the Mdf sealed box is tuned to a specific frequency centre and the U5 dampens that i.e turns the energy into heat so the bass effectively goes into the box and instead of coming out again as a reflection it comes out as heat.

The Trap is tuned - Is that to the Room? or simply within itself?

Both I guess . It's tuned to itself insofar as it'd designed to focus on a particular band. The Bandwidth or Q is adjustable by design i.e you plan it to do a job.
That would be dependent on room measurement.

I've seen some formulas out there,

It seems to me from what I've seen working with proper dudes that the maths side ain't for the faint hearted - which may explain my experience of a lot of rooms being pants both here and the UK.

If One were to make a BT to absorb "X Freq" - then this would absorb this particular Freq in any room (but depending on size you would need a larger or smaller quantity of them?)

I believe that to be true - but I have no understanding (yet!) of how one decides how much shizit is needed. As the Rat says everything 'interferes' with everything else. It takes wise men to make it all work, in my experience.

I

had to pick something up from one of the corners of my room the other day (The Cleaner had a 1/2 Day). There was Music playing - not crazy loud by any means.. and when I put my head down, the whoomp of the bass was all I could hear.. Felt like I was being mugged! :pac:

I still don't understand why bass likes corners, but it does. That's why bass treatment gets put there - because it's there it's most effective.

PaulBrewer

artvandulet wrote: »

I seem to remember there being a trick involving wavin pipe and sand.
You cut the pipe to a certain length to get rid of a particular frequency - based on a formula, fill it with sand -block the ends obviously - and hang it from your ceiling.
Someone else might tell you more

How much is a wavin pipe filled with sand going to weigh? Then hang it from the ceiling ?

Let us know how you get on !!

PaulBrewer

frobisher wrote: »

One day someone will post something that you will agree on in great detail Paul. I can't bleedin' wait :-)

It's not the bass I'm after. I'm not after an ultra tuned room, I just swapped rooms in the house for my studio and this one has da-ding in the high mid that the other one didn't. I want to get rid of it. So I'm going to make some traps. It's not a question of needing to either get it 100% right or not be bothered, it's about getting as much improvement as I can worth what I have. Knowarra mean?

What you need is a bit of rock wool ..

ICN

studiorat wrote: »

If I may....

Excellent SR. The last thing you need is wrong info.. Very true!!

ICN

PaulBrewer wrote: »

I think it's generic limp plastic like substance. In this instance, as I understand, if your tuned absorber is a bass drum the U5 works as a pillow against that bass drum.
So the Mdf sealed box is tuned to a specific frequency centre and the U5 dampens that i.e turns the energy into heat so the bass effectively goes into the box and instead of coming out again as a reflection it comes out as heat....

Cheers Paul..


So is U5 is the actual Product/Brand?

frobisher

PaulBrewer wrote: »

What you need is a bit of rock wool ..

Exactly what I was thinking. Which is why I'm wondering if anyone here has experience with it to share with me on doing the same thing.

frobisher

PaulBrewer wrote: »

I still don't understand why bass likes corners, but it does. That's why bass treatment gets put there - because it's there it's most effective.

Maybe that's why so many studios have corner sofa units, like mine does :-) Great trap AND comfy!

PaulBrewer

frobisher wrote: »

Maybe that's why so many studios have corner sofa units, like mine does :-) Great trap AND comfy!

PaulBrewer

Just got a reply from Chris Walls Senior Acoustician with Andy Munro, acoustic designers office re my pontification ....
Chris has designed Mark Knopfler's British Grove Studio and U2's new Dublin recording room.

"Porous absorbers, like Rockwool, work on the velocity component of a sound wave* which is always zero at a room boundary and therefore a maximum a quarter wavelength from a boundary. The quarter wavelength relates to the thickness at which an absorber would be theoretically 100% efficient (i.e. absorb all incident sound).

100mm Rockwool will absorb sound energy below its quarter wavelength frequency (400Hz) but will not be terribly efficient, perhaps 30% at 100Hz. The problem, as you point out, is that it will absorb nearly 100% of incident energy at mid and high frequencies. Using this approach you generally end up with near anechoic mid & high end and a wildly uncontrolled low end. Most of the studios I've seen in Ireland exhibit these characteristics.

Using Helmholtz or limp mass membrane absorbers allows you to absorb low frequencies efficiently without taking up huge amounts of floor space and without killing the mids and highs. It's not complicated to do, it just requires a bit of know how. There's plenty of literature on the theory, and the BBC Guide to Acoustic Practice (free to download) gives some designs together with absorption data. Well worth a look.

* Limp mass membrane absorbers work on the pressure component of a sound wave, which is why they work at a room boundary. "

Here's the link -

http://downloads.bbc.co.uk/rd/pubs/archive/pdffiles/architectural-acoustics/bbc_guideacousticpractice.pdf

fitz

This is turning into quite an educational thread...

madtheory

frobisher, if you build the simple mid/ hi range traps (which is what you described in your OP), it's very easy to convert them for bass trapping, you just put a membrane on the front, i.e. use 1/4-inch plywood to absorb the deepest bass frequencies and 1/8-inch plywood and for the upper bass range. See here:
http://www.ethanwiner.com/basstrap.html

Paul- thanks for the BBC pdf! In return, here's Ethan Winer's brilliant guide:
http://www.ethanwiner.com/acoustics.html

It's actually pretty easy to achieve a 50% improvement in the room response, and it's cheap too. You'll never get it ruler flat, but it's amazing how much easier it is to mix with even a 50% improvement. You realise that your brain does a lot of compensation work! It's a lot less tiring to mix in a treated room.

Rooms that have stud partitions tend to act as bass traps. But you have to measure the room response. This is a great tool:
http://www.hometheatershack.com/roomeq/

So you have to keep measuring the room response, put in traps, measure, move them around, and keep tweaking until you get it as flat as humanly possible. It's cheap and edcuational

PaulBrewer

madtheory wrote: »

frobisher, if you build the simple mid/ hi range traps (which is what you described in your OP), it's very easy to convert them for bass trapping, you just put a membrane on the front, i.e. use 1/4-inch plywood to absorb the deepest bass frequencies and 1/8-inch plywood and for the upper bass range. See here:
http://www.ethanwiner.com/basstrap.html

Paul- thanks for the BBC pdf! In return, here's Ethan Winer's brilliant guide:
http://www.ethanwiner.com/acoustics.html

It's actually pretty easy to achieve a 50% improvement in the room response, and it's cheap too. You'll never get it ruler flat, but it's amazing how much easier it is to mix with even a 50% improvement. You realise that your brain does a lot of compensation work! It's a lot less tiring to mix in a treated room.

Rooms that have stud partitions tend to act as bass traps. But you have to measure the room response. This is a great tool:
http://www.hometheatershack.com/roomeq/

So you have to keep measuring the room response, put in traps, measure, move them around, and keep tweaking until you get it as flat as humanly possible. It's cheap and edcuational

I've had a run in with Mr.Winer on Gearslutz.

I could not get him to answer questions I asked, repeatedly. That didn't inspire my confidence.

Seziertisch

Where does asbestos fit in in the world of acoustic treatment?

PaulBrewer

Seziertisch wrote: »

Where does asbestos fit in in the world of acoustic treatment?

No where I'd imagine! Why do you ask?

madtheory

PaulBrewer wrote: »

I've had a run in with Mr.Winer on Gearslutz.

I could not get him to answer questions I asked, repeatedly. That didn't inspire my confidence.

Have you a link? Anyway, I think it's a very good article. It's a good one to start with because he's a very good writer, makes the F Alton Everest tomes easier to digest. They're not as well written, but are more accurate and in depth technically, and show that Winer's info is sound.

Seziertisch

PaulBrewer wrote: »

No where I'd imagine! Why do you ask?

If anyone was looking for some I could sort them out with a bit from an old cow shed. Easy to work with and 100% non-hazardous ...

PaulBrewer

madtheory wrote: »

Have you a link? Anyway, I think it's a very good article. It's a good one to start with because he's a very good writer, makes the F Alton Everest tomes easier to digest. They're not as well written, but are more accurate and in depth technically, and show that Winer's info is sound.

No was about 6 months ago.

Coincidentally it came from a discussion on bass trapping where it was said that 'one can't have too much bass trapping'

I questioned that and the answer was that in order for there to be the possibility of too much (of which there can be) there'd be no room in a small room.

This may well be the case using a porous bass trap as Mr Winer's company RealTraps make.

However when I asked about Limp Mass Membrane Absorbers all went quiet for a while, until I then got attacked by other people, presumably for questioning .....

Left a very bad taste in my mouth.

madtheory

Could be you were asking a question that comes up a lot...

ICN

PaulBrewer wrote: »

....However when I asked about Limp Mass Membrane Absorbers all went quiet for a while, until I then got attacked by other people, presumably for questioning ......

Sounds like a Trap to me... Groan! :D:D:D

PaulBrewer

madtheory wrote: »

Could be you were asking a question that comes up a lot...

Seemed to me I was asking a question that didn't suit ...:rolleyes:

PaulBrewer

madtheory wrote: »

frobisher, if you build the simple mid/ hi range traps (which is what you described in your OP), it's very easy to convert them for bass trapping, you just put a membrane on the front, i.e. use 1/4-inch plywood to absorb the deepest bass frequencies and 1/8-inch plywood and for the upper bass range. See here:
http://www.ethanwiner.com/basstrap.html

Munro say -

'You'd get a better result using a limp mass such as revac, or 1/8" ply bonded to a barrier mat or similar damping material (I think a lot of DIY studios use roofing felt). The problem with just using ply is that it creates an absorber with a very high Q so it will absorb very effiently but at quite specific frequencies. If you dampen the vibration you broaden the Q, unfortunately at the expense of efficiency, but it gives more usable results in my opinion. You can also get an audible ringing or 'booming' from just using ply as it re-radiates sound. Again the barrier mat dampens the vibration and eliminates this effect.'