Bass Traps

Okay, so I went down to Carpet Right today (that's right I know how enjoy boxing day ) I asked them if I could have a few of their Helmholtz resonators that the carpets come on and they said yes!

So I now have two 4 meter 10cm diameter strong cardboard tubes which I can play with.

I entered the numbers into that helmholtz calculator on the site technobear gave and it said that if I use 1 meter of the 10cm diameter tube with a 10cm length of 4cm diameter tubing for the neck then it will resonate at a frequency of 68hz. Which is just what I need! Woohoo!

It still needs to be put into practice but that should not take too long. I'll do it in the next few days when I have some time and let you all know what happens.

Oh, the 4cm diameter neck tube is just the standard size of plastic tubing used for plumbing sinks and so on. Very cheap and I had some in the shed.

One thing though, in order to make this a broadband absorber I have read that all you have to do it put a thin air filter between the body and the neck. Does that mean like.. just a layer of fabric starched over the hole or something? This is what the site says -

Is that really al there is too it? Because if having a broadband absorber like that means that it will smooth out dips and peaks then I might make a lot of different ones for all the frequency range! Remember that the higher the frequency the smaller they can be so... it sounds pretty good.

 

More DIY bass traps...

 

Now, this is SOMETHING... :yikes:

http://www.positive-feedback.com/Issue6/hallographs.htm

 

These DIY bass traps look aesthetically acceptable to me, but am I alone in thinking the quantity and placement shown below turns a nice looking lounge into a carpet showroom?




NB
If anyone has bought acoustic foam cheaply recently, or knows of a place where acoustic foam and related products are being sold particularly cheaply, would you mind putting a post up here?

I want to hang board/compressed paper/acoustic foam composites behind rugs in my living room.

Cheers !
Chris

 

NB

For a giggle Im making some of those bass traps aswell.

I'll be acoustically treating the floor, making panels for behind the speakers, and bass traps for the room corners.

WTF I thought, its only a few quid and it will be fun to make and try.

will keep you all posted if you want
Chris

 

Sounds good! How will you be treating your floor? Are the pannels for behind the speakers bass traps?

 

Did the floor last night.

Basically its a wooden floor (laminate) with a big rug.

I bought some acoustic panels from B&Q. They absorb up to 29db noise, 16db impact noise (18.99 I think)

Laid them under the rug so you cant see them.

early impressions - Sound is now a bit more natural in the room, perhaps less 'spikey'

Wall panels are going to be 4 parts. 1 part ply, 1 part acoustic boards (as above), 1 part acoustic foam, and a cloth covering. They are going to absorb sound behind the speakers, taming the room a little.

The bass traps are going to be identical to the ones lowrider poped up - Im copying the design.

1st day back at work, in exactly.....3 minutes !

 

I think you need a pair of Hollographs too... :JPS:

 

Ive just got a price on some 25mm thick acoustic foam = 21.07 for 1.5 sq/m sheet.


I'd need 2.85sq/m so thats 42.14 for 2 sheets

Sounds quite expensive to me, anyone know where I can get it more cheaply?

Chris

 

To be honest there is not too much point putting the wood/acoustic foam pannels behind the speakers. Only very deep bass goes behind the speakers and that wont do much to absorb it.

Use the bass traps behind the speakers and put the wood/acustic foam at the front, beside the speakers.

Thats what I reckon anyhoo..


Hwppy listening!

BTW, I have halted the build of my bass traps untill I change my speakers. No point tuneing them for some speakers that I wont have 2 weeks from now!

 

Bass traps are for tuning the room, not the speakers! Your room resonances won't change when you change the speakers. They are a property of the room itself.

 

Yeah but differents peakers excite room resonances in different ways. It would be a waste to spend hours building a bass trap to sort out a resonance that his current speakers are particularly prone to exacerbating when the new speakers may not have as much of a problem with it. This is especially true if your new speakers are a different fundamental design (i.e. infinite-baffle vs. bass reflex), have significantly larger or smaller cabinets, or have very different driver sizes/arrangements.

I'd say it's worth waiting till you get the new speakers.

Dunc

 

I know that the thread is a few days old now, but just a couple of points on Helmholtz resonators. Firstly, they are extremely frequency-specific (ie they have a very high Q, which is a function of operational bandwidth). This is fine if very narrow-band absorption is required, but be careful that some trial and error is built into the design - usually via the port, as Technobear suggests. Further, if the narrow-band route is selected i'd refine the formula posted by Technobear to account for port correction (ie the difference in actual and useable port length) - I have the calculation on the spreadsheet I use, so i'll dig it out and repost.

For wide-band (relatively speaking, the bandwidth in real terms is not much widened) operation you can add wadding to the cavity. A better solution is to slightly damp the operation of the port - by placing a gauze (etc) sheet across the inner end of the port.

 

Hi guys!

I just thought I would follow up on my build of the bass traps.

The helmholtzez made from tubes with a neck do fook all. I did four tests and there was maybe a slight smoothing of a spike and dip but only by about 2db and that was with 6 of them! So Technobear.. If it isn't too late - Don't bother!

I have also built some membrane (wood panel over a damped air cavity) and these work a charm! I followed this design by Ethan.

I changed the design a tad because I used 2ich rockwool rather than 1 inch ridged fibre glass. I did 2 5inch deep 120cm by 60cm (active area) traps and another 2 4 inch deep traps the same size. I also have 2 210cm by 60cm 2.5inch deep traps which follow the 'high-bass' trap design. The reason it is 2.5inches rather than 2 deep is because I only have 2inch rockwool and the ply needs room to vibrate.

I will be adding another huge 240cm by 120cm trap to my ceiling which slopes from 2inches deep to 4inches and then another nearer the back of my ceiling that is 240cm by 60cm and 4inches deep!

It sounds like a mad amount of them I know, but when they are on the wall in a corner (I did one one each wall of the corner not actually across) then painted the same colour was the wall they are pretty un-noticeable.

I will actually be writing all this up as an investigating for a college project over the next 2 weeks so I will post a copy of it here when I have finished it! It will show how to build them, the other methods I tried and a few frequency response measurements as evidence.

For you info, I got the rockwool from www.studiospares.co.uk you get 8 120cm by 60cm 2inch deep sheets for £52. The wood you can find for yourself!

 

Cool! Nice work Tenson. You say they work a charm... please elaborate.

Thanks,

Dunc

 

Well its hard to give a actual db measurement because I forgot to measure my room before I put the traps up on the wall! But it is so obvious when you just listen to the difference. The bass is far tighter, controlled and less boomy. It also clears up the rest of the spectrum, I guess because you can hear it better with less resonance in the room.

I will take a measurement of my room as it is now, and then compare it to when I have the extra traps on the ceiling though. This should give some idea of how it affects the sound.

I also bought some diffusers from Aualex and I cant hear a blasted difference with them, so I wouldn't recommend those either!

Although, if you had actual flutter echo between some of your walls and you placed these in the way I am sure it would help. It doesn't make the imaging any better or make the room boundaries sound further away as some people have said on other sites though! I got 1 T'Fusor and 5 Metrofusor's

Another thing I found out is that the Aualex 2Inch Foam Wedge's do work quite well, as do Acoustic Tiles But a sheet of 2Inch Rockwool wrapped in a fabric is even more effective and far cheaper!

I would have never known if I didn't try though!

 

Oh dear! Just as well I haven't had time to start these yet (still working on my kitchen )

So how did you go about tuning them. I imagine it's a fairly painful process of trial and measurement to get them tuned just right. They do have a high Q so they really need to be just right.

I would build large panel absorbers if I had space to put them. Not sure I want one bolted to the ceiling

You was robbed! You can get 120x60 cm Rockwool from any decent builders merchant.

 

Is rockwool one of those materials where if you don't cover it in fabric you die horribly in 10 years' time from some nasty lung infection?

& Technobear, how much cheaper you reckon it can be had for?

Dunc

 

It's not as nasty as loft insulation but it is best to keep it contained.

Damn, I knew someone would ask that. I can't remember :shame: I know it was a helluva lot cheaper than the likes of Custom Audio Designs. Don't be fooled by 'special' Acoustic Mineral Wool. It's just Rockwool. It said so on the pack - underneath the carefully applied 'Acoustic Mineral Wool' label

 

Rockwool is a big NO NO, started to be banned in some countries, it will sneak through even plaster board, and find its way into our lungs with permanent damage... :micro:

I use 2" of cork instead in my ceiling... :baby: