Bass Traps

Right, I need some more so its off to the builders yard! They seem to just have a huge lot of bricks and blocks and so on. Is that the kind of place you were thinking of? I'll have to go ask them I suppose!

The tuning of the tubes wasn't that hard. I just started off with the neck 5cm too long (according to the calculator) and then shaved it down by 1 cm each time and took a measurement. I could see no difference at all until the neck got down to about 4cm long and it was working in the Reagan of 120hz. That's where I saw the change of 2db! Woohoo~~~

By the way, I do have my new monitors now - PMC AML1's

That's why I took a long time before I tried the tubes. They sound frigging amazing! Yes they are a bit harsh and bright but I am using them with my old NAD 3020 as a pre-amp. Soon my valve pre will arriv and I should be in business!!! These speakers have evil bass! I measure down to 28hz -6db.They only have a 6inch driver

Kewl anyhoo C ya!

 

Yay I have it all over my room!

It is in an ply wood and timber box that is sealed pretty-much air tight with caulk though. I am not too worried. If air can't get out then I doubt the rockwool can!

 

No Rockwool is safe it's an irritant but not a carcinogen, I wouldn't go round breathing it in for fun though. Health and safety data (MSDS link in product menu) can be found on the Rockwool site.

Rockwool RW3 (the grade sound studios use) should be available for about £30 for 8 120x60x5cm thick slabs from a builders merchant, depending on quantity and if you're trade. Your local stockist will be on the Rockwool or Knauf website. As Tenson says the rockwool is much cheaper and more effective than 'branded foam products' only more fiddly to install as it needs covering. I'd also agree from my experiments that the effect of Bass traps is easier to hear than measure

 

Oh, I thought you just had it covered in fabric..? If it's sealed in airtight boxes, how is it acting as an acoustic treatment? Or am I getting confused.......

Dunc

 

Well for mid and high absorption, you can just wrap it in a fabric to stop lose bits floating around. But like this i does not absorb much below 200hz (maybe down to 150hz?) If you want to absorb bass then you need to use it in the construction of a panel trap. Which you can see how to build/how it works from the link I gave before to Ethan's picture.

 

I just phoned the builders yard and they do not have Rockwool, but they do have ridged fibreglass. Which is what the plans were actually designed for with the panel traps. It is £27 for 20 sheets 120cm by 45cm !!! Wow that's cheaper! I am going to pop down there later on and take a proper look.

 

A panel absorber works thusly: The panel vibrates in sympathy with the sound pressure waves acting on it. Because the box is sealed, this creates pressure waves inside the box. To absorb the sound energy, one converts the pressure waves in the box to another form - heat. Rockwool works best as an absorber where the air velocity is maximised. This is mid-way between the front and back panels. The absorber works best at the resonance frequency of the panel but these devices have fairly low Q, so can cover two or more octaves. The resonance frequency of the panel will depend on the material (plywood, hardboard, roofing felt, metal), the thickness of the panel, and the depth of the box. Graphs and equations can be found by searching the net (or some of the links I provided earlier). Or just follow Ethan's plans.

BTW, these things work best built against a wall. If there is a back panel, it needs to be pretty solid - like 20mm MDF or something.

 

Sorry, but I didn't find anything about health hazards on that link...

 

Just for fun I'vebeen experimenting with surplus quilts/duvets (bedcovers). My SO has sets for winter and summer, so one set is always spare.

S=speaker
bbb= bookcase
|--|=sofa
O=rolled-up quilt

------------------------------------------
|.O............S.......................................|
|.....S........TV..........S..........................|
|.........................................................|
|.........................................................|
|.........................................................|
|.................................--------------------
|.................................|
|........|-----------|.......|
|.................................|
|.................................|
|.S...........................S.|
|Obbb.....................bbbO|
----------------------------

I tried to roll them loosely so that they approach a diameter of 20 inches, so as to absorb the problem-area in my bass (according to an ASC web-page.) They have done quite a lot to improve the bass that I no longer feel such a strong need to do it properly and I can relax and enjoy the music.

The one by the speakers is a rolled single duvet stuffed with hollofill fibre. The one to the back left is similar.
The back right is a double duvet stuffed with duck-feathers.

It's worth an experiment if you have a few duvets in the house. If you like the result, you could make a slip-cover in a thin material. The fibre stuff used can probably be bought by the meter from handiwork shops, and I would have thought almost certainly without health risks.

Side-benefit: the spouse doesn't have to find storage space for all those duvets

 

There should be a link to the Health and safety data sheet.
Does this direct link work? HSData PDF page 3 has the Toxicological info.

 

Hehe, I'm actually using a duvet as makeshift acoustic treatment (of the higher-frequency absorption kind). I have a largish double duvet folded once along the length and pinned to the front wall in between my speakers (making approximately 50m x 1.8m coverage). Seems to make a bit of improvement, though it's hard to tell for sure as I can't be bothered doing any A/B tests. It'll have to do until I can rustle up some funds for proper treatments (though this talk of rockwool may mean that this is cheaper than initially expected...)

Dunc

 

Taken from the PDF file on the ridged rockwool-

"Current HSE 'CHIP' Regulations and EU directive 97/69/EC
confirm the safety of Rockwool mineral wool; Rockwool
fibres are not classified as a possible human carcinogen."

So there you have it!

Proper fibreglass is however, so be careful with that one. I know most people suggest putting each slab into a black bin-bag to stop the fibres getting out. Then you can cover it in fabric to look nice. It will effect the acoustic properties at High frequency, but not much.

 

I've read of several people building corner bass traps by piling up those round bales of insulation you get in the DIY store. You don't even have to unpack it.

 

Hehe. I lined all the walls with duvets once, as an experiment. I nailed them in the corners to the top of each wall. They were convoluted when hung, as my main motivation for doing it was to reduce the echo in the room at the time as it was lacking in furnishings. Never had a problem with bass, as paper walls tend to dissipate whatever there is anyway.

They only stayed up for a day as it looked disturbingly akin to an insane asylum.

Also made a large 8ft absorption panel out of air conditioning treatments stuffed into a wooden frame, but i don't think his really achieved very much as the material wasn't appropriate.

Geeez, the things i used to do

 

The thing is, you will need a depth of about 2.8 feet to absorb even a 100hz wave when its just pure absorption. That's why panel traps are good, because they work on the pressure build-up not just being absorptive.

If you want to understand why take a look at this - Absorption Article Read about the bit with the peaks of the waveform having to fit into the absorptive material.

 

Asbestos used to be considered safe too...

Anyway, I am sure there is loads of the stuff around, but I will not put any more around me as long as I can avoid it... :crazy:

 

Chicken

 

Yup, 20 sheets 120cm by 45cm 2 Inch deep £20.61 !!!!

 

Nice - is there anywhere online that does 'em for that kind of price...?

Dunc

 

Dunno mate!

Buuuuut... I wont need all 20 sheets! By my estimate I will have around 8 left over if not more so anyone who wants it is welcome to it! Of course its only really worth it if you can collect from Gravesend, Kent.

Otherwise just find a builders supplier in the Yellow pages. Ask for ridged fibreglass. Its used to fill cavity walls.