Bass Traps... the results

[WmAx]

Sploo, what are pots?

It is a potentiometer. A variable resistor, basicly. You will use it as a L-Pad, a.k.a., a voltage divider.

The process is straightforward/simple!

input[+] signal ---> leg 3 of pot

output[+] signal --->leg 2 of pot

[-] ground ---->leg 1 of pot

So, basicly, you feed the line input signal to one leg, and the ground to one leg, and the output leg is the 'adjusted' signal. Just rotate the switch to get the desired output level. As for values, use a 25 or 50Kohm potentiometer. These are common values that work well between standard output impedance, input impedance and typical cable capacitance values. Use a dual ganged potentiometer so that you can adjust Left and Right with a single switch, unless of course, you want a seperate control of each channel.

Here is more than you may have ever wanted to know about potentiometers:

http://sound.westhost.com/pots.htm

-Chris

 

[sploo]

I've finished! (until the next mod!)

Hi,

Well, after much 'fun' wrapping panels in fabric, I've finally got my side wall traps on stands and fixed the ceiling ones to, well... guess.

Having read (from numerous sources) that it's better to have a 'soft' ceiling and a hard floor than a hard ceiling and soft floor, I was surprised just how much better the results really are with the same panels moved from the floor to the celing.

For reference, these graphs are the last 'best' results, with the seating position at 38% from the front wall (where the speakers are placed), bass traps in corners, and HF panels on side walls and floor:

http://spikyfish.com/09 all traps, at 38percent - low range.gif
http://spikyfish.com/10 all traps, at 38percent - full range.gif
http://spikyfish.com/11 all traps, at 38percent - 3D.gif
http://spikyfish.com/12 all traps, at 38percent - impulse response.gif

These graphs show the same setup, with the four HF panels that were on the floor attached to the ceiling:

http://spikyfish.com/13 all traps HF on ceiling, at 38percent - low range.gif
http://spikyfish.com/14 all traps HF on ceiling, at 38percent - full range.gif
http://spikyfish.com/15 all traps HF on ceiling, at 38percent - 3D.gif
http://spikyfish.com/16 all traps HF on ceiling, at 38percent - impulse response.gif

The low range response is a little better, though I'm not sure that the ceiling panels would have had that much affect.

The full range response is arguably a little more even, though comb filtering is more evident. The real difference comes in the impulse response measurement - the ceiling was obviously creating fairly significant reflections, which have now been tamed (though, unsurprisingly, the floor reflection is back).

I then put a duvet (no rugs to hand) on the floor where the ceiling panels had been. The resulting measurements are the reason I started down the road of acoustic room treatment!

http://spikyfish.com/17 all traps HF on ceiling, duvet on floor, at 38percent - low range.gif
http://spikyfish.com/18 all traps HF on ceiling, duvet on floor, at 38percent - full range.gif
http://spikyfish.com/19 all traps HF on ceiling, duvet on floor, at 38percent - 3D.gif
http://spikyfish.com/20 all traps HF on ceiling, duvet on floor, at 38percent - impulse response.gif

Apart from a nasty null just under 4kHz, the full range response shows reasonably reduced comb filtering (within 10dB for most of the audible range), and a reasonably flat response. Compare this to the original measurement: http://spikyfish.com/02 no absorbers - full range.gif

The impulse response is much improved, though obviously only so much reduction in reflection can be expected from a duvet, so a small spike remains.

After every modification I'd run through a few CD tracks to see if I could detect any audible changes. Not very scientific, but after this last round of changes I ended up sitting through a couple of entire CDs, as I was enjoying what I was hearing! Can't give any better recommendation than that.

Huge thanks go out to Ethan, bpape, mrnomas, Chris (WmAx) and all the others that have assisted and inspired me in this quest. Hopefully I'll get some time to put the construction details together in a webpage so that others can have a go at making the panels (or just save yourself the time and buy better ones at www.realtraps.com )

Gordon.

 

[bpape]

When you moved them, did you notice that you also moved one of the impulse spikes? Got rid of a ceiling point and uncovered a floor point. Somewhere just less than 2' difference in paths.

Now if we could just ditch that null at around 40Hz, you'd be really good. The 4kHz null is puzzling given the rest of the graphs. Unless, there is just a suckout in the xover and tweeter response of your speakers which is entirely possible though I'd be surprised if that was all of it given it's intensity.

Overall congrats for sticking with it. You're 1000% better than most people out there who pay no attention at all to the room.

 

[sploo]

When you moved them, did you notice that you also moved one of the impulse spikes? Got rid of a ceiling point and uncovered a floor point. Somewhere just less than 2' difference in paths.

Yup. Hence the addition of a duvet on the floor. I'll have to look out for a nice thick rug to put down there permanently.

Now if we could just ditch that null at around 40Hz, you'd be really good.

Yea. The problem is that at that low frequency it's probably going to be an issue of not enough bass traps. There's isn't really any more practical room for big thick trapping.

The 4kHz null is puzzling given the rest of the graphs. Unless, there is just a suckout in the xover and tweeter response of your speakers which is entirely possible though I'd be surprised if that was all of it given it's intensity.

Interestingly, the bass unit on my mains runs out of steam at 4kHz (Scan-speak 21w/8554), though as the treble comes in at 2kHz (Scan-speak D2905/950000) I'd expect the crossover to be well before 4kHz.

My thickest HF absorbers are 2" of panel + just over 1" air gap (roughly 8cm). At 343m/s (speed of sound), I make 8cm just over 4kHz, so it might be due to the lack of absorption below that frequency. Unless my math (and acoustics understanding) is a bit dodgy.

Overall congrats for sticking with it. You're 1000% better than most people out there who pay no attention at all to the room.

Cheers. Despite taking quite a bit of time, the results have been worth it. It's also a lot cheaper than fancy new cables or a new CD player, and, from what I've seen, a lot more likely to succeed.

Gordon.

 

[WmAx]

My thickest HF absorbers are 2" of panel + just over 1" air gap (roughly 8cm). At 343m/s (speed of sound), I make 8cm just over 4kHz, so it might be due to the lack of absorption below that frequency. Unless my math (and acoustics understanding) is a bit dodgy.

A 2" rigid fiberglass panel with a 1" air gap would have an effectively high co-efficient somewhere between 200-300Hz . The co-efficient is not a direct 1:1 ratio relationship of thickness of material vs. wavelength in air.

-Chris

 

[Ethan Winer]

Gordon,

> these graphs are the last 'best' results <

Looking good. The long decay time around 40 Hz is still a problem, but you know the only solution for that.

--Ethan

 

[sploo]

A 2" rigid fiberglass panel with a 1" air gap would have an effectively high co-efficient somewhere between 200-300Hz . The co-efficient is not a direct 1:1 ratio relationship of thickness of material vs. wavelength in air.

-Chris

Interesting. Maybe that explains why the low frequency graphs do change a little when I move the HF panels around. I do try to keep the position of the SPL constant between measurements (within a couple of inches anyway).

 

[sploo]

Looking good. The long decay time around 40 Hz is still a problem, but you know the only solution for that.

Yep, go shopping at realtraps.com

I must admit I'd seriously consider some of the mondotraps. The problem is that I had to cut down the width of almost all the 2' wide boards to fit them in the room corners (window sills, curtain rails, projector screens in the way).

Those panels are also cut with a chamfered edge, so they don't actually 'stick out' from the wall.

Hence a full 2' wide trap that's several inches deep just wouldn't fit in my room. Shame really.

Still, I'm very much a convert to acoustic room treatment, and very grateful for your help!

 

[bpape]

Again, congrats. You've done what you can do within the limitations of your room and budget. You're a convert. After you get used to it, just for giggles if the treatments are removable, pull them all off and then listen again. Your reaction will likely be

Spread the word...

 

[sploo]

Again, congrats. You've done what you can do within the limitations of your room and budget. You're a convert. After you get used to it, just for giggles if the treatments are removable, pull them all off and then listen again. Your reaction will likely be

I can fairly easily remove the HF panels, and did try this (before I'd fixed a few to the ceiling).

Yes, the result was very (but that's only because this forum doesn't have a smiley vomiting wildly )

Spread the word...

Absolutely. I expect there are many people sitting in their rooms, being slightly dissatisfied with their kit, but not knowing why.

For many, I expect just two HF panels, one on each side wall, would have a hugely positive affect on their listening experience, and that's a whole load cheaper some of the voodoo trash being sold by some people.

Hmmm, that reminds me, I must start selling some magic beans on eBay... plenty of mugs around...

 

[sploo]

Treatment - the how-to!

All,

I've finally written up the results and construction details of my room treatment quest.

The intro and graphs (which you'll have seen if you've read my posts) are here:

http://spikyfish.com/acoustics/

Linked off the above, but included here so you can jump straight to it, is a page detailing the construction of the panels:

http://spikyfish.com/acoustics/panels.html

Hope that's useful to someone!

 

[chas_w]

Nice write-up sploo...thanks for documenting this.

 

[mtrycrafts]

All,

I've finally written up the results and construction details of my room treatment quest.

The intro and graphs (which you'll have seen if you've read my posts) are here:

http://spikyfish.com/acoustics/

Linked off the above, but included here so you can jump straight to it, is a page detailing the construction of the panels:

http://spikyfish.com/acoustics/panels.html

Hope that's useful to someone!

Thanks from here too. Great job. Nice planning before the fact, not remodeling during construction