Speakers s/h up to about £800 - recommendations please

yeah, it's a better approximation - at 20C it comes out at 343 Take a look here

 

Half wavelength - at the front and back boundaries.

Full wavelength - add the half way point.

Double wavelength - add the quarter way points.

When the room contains 1.5 wavelengths, cancellations will occur at the third way points giving rise to nulls.

Bass traps are just as effective at filling in nulls as they are at reducing peaks because to fill in a null you have to absorb the reflected sound which is causing the cancellation.

Room boom can be pretty well avoided by sitting at the third way point.

It's hard to completely avoid the nulls.

 

Yes, thank you for backing me up there technobear. BTW, the fact that temp does affect speed of sound accounts for amongst other things why sounds seem to carry better at night.

 

I thought as much. Your * should have been a +

 

The calculation I've seen a few times is 1130/2L if working in feet, I make that 169.5/L if working in meters:-

e.g. (my room)

2.83m wide = 59.9Hz, harmonic at 119.8Hz, etc.

5.2m long = 32.6Hz, harmonics at 65.2Hz, 97.8Hz, etc.

2.405m tall = 70.5Hz, harmonic at 141Hz, etc.

So it's the close standing waves at 59.9, 65.2 and 70.5 that look to be forming the peak I've measured.

I'm not too worried about 32Hz as IMHO there's apparently not a lot of musical sources down there, just low-frequency effects and a bit of underpinning.

BTW, the SVS 25-31 PCi sub goes relatively flat down to 18Hz in-room, with it's factory 22Hz tuned frequency!

regards,
Rob.

 

Hmmm! Not sure about that. The difference is not that significant. It has more to do with the level of background noise from traffic and industry being much lower at night. The brain also pays more attention to hearing at night to compensate for the reduction in visual data.

 

That surprises me.

I didn't think there was any traffic and industry in Somerset?

cheers,
Rob.

 

Yes, thanks for pointing out the typo. It should of course be a '+' as I had in my spreadsheet.

Yes, this really is reponsible for the night effect - see here I've had occasion to wonder about this as I live in a place where the ground is colder than the air in a winter night (inversion) and there is a railway accross the valley from me.

 

It's surprising how much traffic noise there is just from people driving to work or to the shops. And we have plenty of industries in Somerset. Not as concentrated as in other parts of the country though. Farming can generate a surprising amount of noise too and we have lots of that.

 

Aah I see where you're coming from now. I have a broadish peak in 70 to 90 region myself and I need to do one of you calculation-series too. I've had a heck of a job taming my Espeks. As I said, I'd be interested what material you find helps, and where you put it. I was thinking of getting a load of really thick foam (cheapskate) and hiding it behind bookcases, drawn curtains, etc., but I suspect it wouldn't be terribly efficient at its job so I haven't done it yet.

 

To use foam alone at low frequencies, it would need to be 1/4 wavelength thick. Not very practical.

Panel (or membrane) absorbers will work but as already said, they need to be very big.

Helmholtz absorbers (resonators) are tricky to tune but can be made in more domestically acceptable sizes for treating specific frequencies. You'd need quite a few though, ideally in each corner of the room at the very least.

 

Even so, many companies sell foam products and they do have some limited effect. After all, a big piece is thick in 2 of 3 dimensions In this case a thick 1.25m square piece is probably practical and foam is lossy. I'm trying to be helpful here.

The Auralex stuff looks interesting, fluffuser. I had a look at their website and it sure looks expensive. However there is a Swedish supplier that is handier for me. I might try a box of 6 panels of the VersTile that you mention, stacked as a corner reflector and in different arrangements, and work up from there.

Anyway, bye for now, time for home.

 

If anyone knows a good place to get really cheap polyurethane foam, let us know! I've been hunting and all I can find is fairly expensive stuff. Surprisingly, Auralex isn't that expensive - it's a bit more expensive than cheapie acoustic foam, but not much.

Dunc

 

Ive been reading myself all about acoustics (to the point of total boredom!) across the net.

Whats been said about the ineffectiveness of thin foam for low bass frequencies is dead right.

However, by using multiple layers of combinations of products the effects can be cumulative, and of course area of coverage plays a big part.

We all use carpet/rugs as absorbers in our living rooms.. by combining 3 relatively inexpensive acoustic materials Ive managed to get absorbancy roughly 70 times greater than carpet.

There is a point where you have to say ''this is the best I can do''.

I would also question whether neater, tidier, better looking and far more expensive pre-made absorbers are of greater effectiveness... especially when we look at the small sizes they tend to come in..

Chris

 

Some acoustics products links

Mike Hanson posted these on the Naim baord a while back. I haven't had chance to go into these yet:

http://www.soundproofing.org/index.html

http://www.acoustica.org.uk/

http://www.point-and-click.com/Campanella_Acoustics/faq/faq.htm

http://www.hunecke.de/default-english.htm

http://www.tubetrap.com/

http://www.asc-soundproof.com/

http://www.owenscorning.com/around/sound/acoustic.html

 

Thanks Steve. Most of those links were about acoustic insulation, not in-room absorption treatment.

Hi Bottleneck, having read Adam P. Sailsbury's Room treatment article (on the net), I thought I'd try and make use of the 60cm deep area behind my projection screen and speakers. I went to B&Q and bought two ready-made bass traps for £7.22 each. Actually one an a half foot thick 4ft long rolls of insulation fiber. My young daughter thought me balancing two of these on the trolly, with so little room I had to carry her too was very funny. I only went in for a light bulb

Still in their sealed packets, I've fixed one on the top corner of the front wall and the other is sitting on the front left speaker in the corner waiting fixing. This is definitely one for those with dedicated listening rooms, not the stylish minimalist living rooms at lot of you have, unless you can box around it vertically say with thin mdf or something. I'm probably going to simply put black cloth round these or paint them room-colour sometime, as the room is a fairly dark burgundy anyway (minimises reflections on and off the projection screen).

If you are thinking of taming low-bass resonances (70Hz and lower) in-room then these are THE things to try, placed in room corners, ideally to the ceiling apparently rather than floor. As you don't unwrap them, I'm sure you could return them if you can't hide the look or aren't taken by the sound improvement.

Me? I think they are staying. I still need some mid-bass/mid/treble treatment in there, but deep bass is much cleaner, both with only the Linn Keilidh's or high-passing the Keilidh's and running a big active subwoofer.

regards,
Rob.

 

Yes, it seems you're largely right, but in defence I'd point out the useful graph of tubetrap diameter vs. attenuation frequency. I think I'll get me some of that insulation. I can always bung it in the loft if it doesn't help. Digital Video Essentials has sweep frequencies with simultaneous frequency display, which should help me choose the right ballpark.

 

No defence needed Steve, it's all good information. I had missed the tube trap details.


I'm not sure how a hollow trap works v.s a filled one, but suspect the outer diameter (smallest dimention) controlling lowest frequency damped is the same.

From the Tube Trap 16-inch specs, it looks hopefull that that dimension is damping the standing waves around and above 60Hz, which is what's needed.

I agree for the price, the rolls can get dumped in the loft to save returning them whenever not needed.

I've yet to take the time to measure the room response again, but will soon.

regards,
Rob.

 

Wow! You must have dug deep to unearth this thread

 

yeah!!... and I disagree with my own posts!haha.

I'd visit Custom Audio Design's website (that's who I'm using), it shows the effectiveness of various products at different frequencies.

The Modex broadband panels for example provide amazing bass absorbancy in something really not that thick. They are £350 ish each though!