Bass Traps

[Jez]

Hi All,

I am happy with the way the higher frequencies are sounding in my room and I am just wanting to improve on the clarity of bass….at times you feel it could be a bit more defined and I know that’s to do with the room.

If I added Bass traps to my room, which should help with the bass, would it also make the room duller for the higher frequencies? At the end of the day it is thick foam….so would absorb a lot of sound? Which could mean that I may be able to improve the bass lines but may loose the top end as its sounding now?

Probably a stupid question but have to ask J

Help would be much appreciated.

Cheers

Jez

[ArthurDent]

Short answer is yes and the absorption ability of soft things like foam, fibreglass increases with frequency so an absorbing type bass trap will affect higher frequencies more than the lower bass ones you're installing them for. The usual way to correct this is to cover them with a reflective layer so the highs won't be absorbed. It does depend very much on how many you are installing and where. The minimum floor to ceiling at the front of room layout of bass traps isn't going to kill your highs that much.

And this is probably better off in the Room Acoustics and Tweaks thread.

[cheekyboy]

Hi Jez, there are others here that a far more into room treatments and bass traps than I am, but if the bass you're talking about is the room loading those nodes up and you place bass traps in the corners of the room, I don't think they are going to have much of an effect on your HF signal.

Cheers,

Keith

[Paul Spencer]

Jez, good question. Not all bass traps are created equal. The most common is probably the broadband porous type in the corners, but as the others have said, the area is not very large and if it makes the room too dead you can have a reflective layer. There are also membrane traps which are essentially a hollow thin walled box about 4" deep. These are pressure traps and in a corner would be placed so they form an L while the broadband velocity trap goes across the hypotenuse \ and often fills the whole area behind. An interesting idea is to combine both. The nice thing about pressure traps is that they take up less space, and you can put them at all corner junctions as well, including wall to ceiling. Real Traps showed a demo of a room treated with a mix of absorbers, diffusers and membrane bass traps. The diffusers were also working as bass traps. The result was extremely good as shown in measurements.

Bass trapping is on my to do list as well. Here is a measurement I took last night:

[ATTACH=CONFIG]26044[/ATTACH]

Black shows a gated measurement @ 1m. You can see it's smooth down to below 200 Hz which is the limit related to the gate. Bass not shown.

Red shows a room measurement at the listening position. It's actually smoother above 4k with some typical roll off - not a highly treated room. The bass is pretty smooth below 100 Hz after finding a good placement for the speakers/subs and just a little PEQ cut tames things a bit. What remains is some problems in the 100 - 300 Hz range. That's where bass traps are needed and where I hope to see an improvement when I get around to it. It often comes up that they don't work very well below 100 Hz. The good news is that it's needed most here in that range where they are quite effective.

You might want to think about getting a basic measurement setup so that you can see what is going on:

http://redspade-audio.blogspot.com/2010/08/basic-measurement-setup.html

The measurements will help show why things are booming. They will also help with choosing placement. Sometimes just a little placement and a little EQ will get you most of the way there. You can get broad sweeping improvements that way, but if you don't do that first, then treating the room may not go far enough. You also know what you are targeting. In my case I don't want bass traps to take any of the energy out of the room below 100 Hz, so I will be focusing higher.

[Guest Peter the Greek]

Be careful of foam - two reasons:

- its not normally dense enough to be effective for bass frequencies

- make sure its open cell not closed cell (the later wont work)

Even dense foams, fibreglass or polyester isn't great when just stacked in the corners, as Paul said the membrane type are more effective.

If you want to try a DIY solution get some dense insultion 32-48kg m^3 and put a 3mm or 6mm builders plastic over it.

There are other/better options, but making it look good in a room can be difficult.

One of the best things to do it to have a riser trap, along with a lot of insulation behind pegboard.....but then you need structure to cover all that/cant really be done in non-dedicated rooms

Got an ottoman? have one made and sutff it with dense(ish) polyester insulation - fiberous style traps work well away from room boundaries

[Nigel]

Hi Paul,

Your last comment about "traps taking energy out of the room", as I (mis)understand it all. Traps can increase the bass in a room that is being lost in cancellation. I presume you lose that boomy bass in the corners of the room but increase the bass out in the middle. I am probably wrong, but it seems that one does want to reduce the rebounding energies.

Also that dip at 280Hz, is that a problem? right in the vocal range. Might be a little low for Richie Benaud's broadcasts of course...

[cheekyboy]

If you want to try a DIY solution get some dense insultion 32-48kg m^3 and put a 3mm or 6mm builders plastic over it.

Hi Elill, that is extremely thick plastic [3mm or 6mm]. Just wondering how pliable it would be at that thickness and wouldn't that block the insulation completely?

Cheers,

Keith

[Guest Peter the Greek]

Thats the point - the bass frequencies drive through it and it reflects the mids/highs, which in this instance is what the OP wants

[Guest Peter the Greek]

Also - some people use thin MDF or ply as a membrane - flexible plastic most certainly works

[cheekyboy]

Thats the point - the bass frequencies drive through it and it reflects the mids/highs, which in this instance is what the OP wants

Also - some people use thin MDF or ply as a membrane - flexible plastic most certainly works

Fair enough Elill, I wasn't questioning the result, just the thickness of the plastic..........I wouldn't like to pick up a roll of it.

Cheers,

Keith

[Guest Peter the Greek]

No its heavy as......if I was doing this I'd get all the testing gear set up and start with the thin stuff like a thicker drop sheet and go from there.......or alternatively just hire someone to do it for you (this is what I'll do for our dedicated room......in our living room I'm hack a DIY job together - no measurements yet just add this there, add something else there and listen, if I get active left and rights I'll do measurements then)

Edit: our living room is complete crap to listen in though so I'm not too concerned about specifics.....the more soft stuff I can add the better (hardwood floors, high ceilings, back of it is open plan kitchen).....disaster mix for acoustics

Edited December 2, 2010 by Peter the Greek

[cheekyboy]

No its heavy as......if I was doing this I'd get all the testing gear set up and start with the thin stuff like a thicker drop sheet and go from there.......or alternatively just hire someone to do it for you (this is what I'll do for our dedicated room......in our living room I'm hack a DIY job together - no measurements yet just add this there, add something else there and listen, if I get active left and rights I'll do measurements then)

Heavy would be an understatement I reckon:D.............where do you buy 6mm thick plastic from and does it come in sheets Elill?

Cheers,

Keith

[cheekyboy]

Edit: our living room is complete crap to listen in though so I'm not too concerned about specifics.....the more soft stuff I can add the better (hardwood floors, high ceilings, back of it is open plan kitchen).....disaster mix for acoustics

Yeah Elill, it sounds like a shocker acoustically. I have two rooms set up and one soley dedicated to 2 channel music, but it is the other room that is more problematic, for one or two of the reasons you've mentioned and that's why I'm interested in the process you described. I'm just trying to get my head around 6mm thick plastic, as I'm in an industry that uses a lot of rolls of poly [plastic] that generally comes in 50mt or 100mt rolls, depending on the thickness of the poly. But these thicknesses are measured in microns and normally 100um - 200um thick.

Cheers,

Keith

[Guest Peter the Greek]

Good question - the previous supplier I had written down seems to no longer exist.....these guys do sheets though:

http://www.pacwestcorp.com.au/Plastic%20Sheets.html

Also a quick google (the last place I had was a cool room supply place - it was a good supplier of heavy duty ball bearing hinges as well for those wanting serious doors) - http://www.austcoldindustries.com.au/pvc-roll-specs.htm

[Paul Spencer]

Hi Paul,

Your last comment about "traps taking energy out of the room", as I (mis)understand it all. Traps can increase the bass in a room that is being lost in cancellation. I presume you lose that boomy bass in the corners of the room but increase the bass out in the middle. I am probably wrong, but it seems that one does want to reduce the rebounding energies.

Also that dip at 280Hz, is that a problem? right in the vocal range. Might be a little low for Richie Benaud's broadcasts of course...

Nigel,

You are right that they can increase bass by reducing nulls at the same time as reducing energy by reducing peaks. But in my case, if you look at the response below 100 Hz, where are the nulls? I only stand to lose. The PEQ cut that I use adds headroom - just one band in the midbass. Since I have a small room, there are really only two seats I'm concerned with and they measure the same. In fact, I have corrected in the past with EQ in my seat, and the other actually measured just slightly better. If you look at waterfall plots of bass trapped rooms, I've noticed that generally the decay doesn't change so much below 100 Hz. So I don't expect to gain an advantage below 100 Hz. In the 100 - 300 Hz range I can see some modal ringing and I suspect that can be fixed with some trapping that wouldn't be too obtrusive.

280 Hz dip? You see it with 1/12 octave smoothing, but let's see 1/3 octave smoothed:

[ATTACH=CONFIG]26045[/ATTACH]

That's more like what you hear. Being a dip it's not as bad as a peak. The eyes are more fussy than the ears. Sometimes I'm surprised by a measurement as it can look much worse than it sounds. Conversely, a measurement can look good but not sound good at all. Still, I hope to fix it with some treatment.

Sorry Jez, I don't mean to take over your thread. My main point was that some measurements will help with working out what you have to fix.

Some good info here:

http://www.realtraps.com/info.htm

Example of a small room treated

http://www.realtraps.com/video_hearing.htm

[Guest Drizzt]

... But in my case, if you look at the response below 100 Hz, where are the nulls? I only stand to lose...

*shakes fist* ... damn you and your lack of nulls My room on the other hand

[Jez]

woww not even close to being as simple as I thought which was to simply place traps in the top corners of the room.....now I am scared tempted to leave it as is....cuz i surely I dont want the energy sapped out of my system...

[Guest Peter the Greek]

....cuz i surely I dont want the energy sapped out of my system...

There in lies the reason I hate DIY - I've heard it do more damage then good. If its a massive issue give Ultrafonic or Acoustic Vision a call, get some advice an see how you go

or David Spargo? I think it is in Artamon (bit more local)

Edited December 2, 2010 by Peter the Greek

[Jez]

There in lies the reason I hate DIY - I've heard it do more damage then good. If its a massive issue give Ultrafonic or Acoustic Vision a call, get some advice an see how you go

or David Spargo? I think it is in Artamon (bit more local)

Could you please give me David Spargo's contact details? is he a consultant or only advises regarding his own products...

I am happy to pay fee to a pro to come out have a look and advise what needs to be done....

[emesbee]

Here is a different kind of bass trap.

http://www.lobstering.com/fish%20traps.html

[Paul Spencer]

Now I've done it! ... In truth you could do what you plan - traps in the front corners and see what it does. Chances are it will be an improvement. I'd be very surprised if it wasn't.

[Nigel]

Good luck, Jez, if you fancy the hifi hobby and think you will play for quite a long time to come, then it might be worth your while to learn how to take measurements. It is a little complicated but not all that expensive. Certainly cheaper than hiring pro's for every room you use in future. Lots of people here can advise and your friends will love you for improving their systems as well.

[Paul Spencer]

There in lies the reason I hate DIY - I've heard it do more damage then good. If its a massive issue give Ultrafonic or Acoustic Vision a call, get some advice an see how you go

In some areas you can certainly make backward steps. There are some things you can do to improve sound proofing and it can sometimes go the other way. But I think bass trapping is fairly safe.

[Guest Peter the Greek]

fairly safe yes - effective? perhaps not......lets not start that again

I dont see why people are so anti paying for advice, we spend so so so much money on gear, really....