Tracking my acoustic treatments...

I've recently undertaken the task of building some bass traps and broadband absorbers. So far, I've completed 1 of the 'studiotips superchunk' bass traps and was anxious to see what differences I would see. Well, it wasn't much. It tamed one dip, but not at a frequency I was expecting. I don't see anything going on below 80Hz where I was most hoping to see some improvement.

I still have 2 more of these to install in the corners, followed by some additional trapping in strategic spots. However, just wanted to get some opinions on what I'm seeing so far.

Here is the graph prior to the treatment:
http://picasaweb.google.com/jrames/R...67083608357154

Here is the graph with this first trap in place:
http://picasaweb.google.com/jrames/R...67079313389842

You can see a dip at about 110hz was tamed noticably, but nothing really happened at any lower frequencies. I can't seem to find the results I'd seen earlier, but I was certain these traps were effective at <100 frequencies.

I might just be jumping the gun - this is only the first very small portion of my treatment, but I was just surprised that the low end did not budge at all.

Thoughts?

I'll post some more graphs as I move forward. By the way - is there a way to show my before and after plot on the same graph? I couldn't find the option to do so..

Thanks,
Jeff

Yes you can overlay your plots. I know you can generate waterfalls, then overlay one onto the other. You may actually find that your bass trap has affected the decay times. Anyway you can reference the help file to find out more; look up the waterfall section.

-Steve

how do we hear the improvement of decay times? i mean in layman's terms ... what improves in SQ if the decay times improve?

Instead of "Powwwwwowwwwowww", you hear "Poww!". Individual sounds stop on time; they don't loiter and bounce around the room. They don't then have the opportunity to interfere with subsequent sounds. That yields more detail able to be perceived, and less sounds smearing together.


Tim

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He drove a black and white pirate ship at 190 mph.
- Dale in the #3 will never be forgotten. Thanks for the memories.

thanks Tim

powwwww huh!?

The "Measured" tab shows all of the measurements you have loaded on one graph. To have an effect at low frequencies you need a large treatment volume.

Tim is correct and for my setup, when I finished with all the treatment, the soundstage just filled the front of the room. It is difficult to describe but simply great to experience. Movies with good soundtracks are much more enjoyable to listen to, even when the movie itself may not be so great.

Bob

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"There is always hope, even if it is just a fool's hope."

I also tried a measurement during the building of my bass traps and it did not seem right. I didn't even save the result until I had at least filled the corners with Roxul. That gave me a large smooth bump from 20Hz up to my peak which was left unchanged in around the 50Hz area. If you are looking at reflections that are not in the corner use the impulse response window and set the Y axis to %FS. Then right click and hold control to measure from the largest peak (your starting point) to any other peaks that may be present.

Before I remembered to do this I knew I needed bass traps on my back wall but I couldn't seem to be able to measure anything indicating a problem in my front row. Then I found the peak at near 33ft indicating that my now largest concern is a reflection off of my back wall and my side wall combined.

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High Speed Cable/Dial Up User - Remodeling/Designing/Building

Any update on how the traps are helping?

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High Speed Cable/Dial Up User - Remodeling/Designing/Building

Not yet. I did look at the waterfall graph, but it wasn't showing anything significant either with the one trap.

On Saturday I should be finishing up the other 2 superchunk traps and installing them. I'll provide the before / after graphs on those sometime this weekend. I'm also going to put some broadband absorbers on the 1st reflection points on the walls, tho I won't be measuring those quite yet. Need to get a broadband mic

Will let ya know..

Thanks
Jeff

You only seem to measure sub response, but corner traps might have big effects on clarity of main speakers.

I recommend making all the measurements with one speaker at the time. One sweep for L, R and sub before installing traps and then another three measurements with traps in place. It's really hard, or impossible, to track the effects of traps when there is three speakers playing same frequencys. You might get deepers dips just because you dump echoes and sound from speakers happen to be in opposite phase.

That makes sense - I will try it. However, I did spend quite a bit of time testing the FR of the room with the sub phase control at a bunch of different positions. I settled on the smoothest curve, so I think I'm getting minimal phase issues.

I am going to have to redo my measurements. I didn't really get a great before / after because the mic was not in the exactly same position when I did my after measurements this weekend. I will go ahead and move the traps out of the way and try all of this again this week and post my results.

I'm not going to post the current before / afters (due to the test not being completely valid), but if it is valid I'm unimpressed. The curve looks almost identical from 15-150hz (my after measurements only went up that far). I need to redo it, but so far I'm a little worried my efforts were somewhat in vein, at least in the lower frequencies that I was trying to attack.

More on this later.
Jeff

Absorption is really only good to about 1/4 wavelength....

90Hz is about 12feet which means you need an absorber panel on the order of 3ft thick in order for it to be "effective".

45Hz would need to be 6ft, and 20Hz about 12ft (yikes).

Another thing to watch out for is HF reflections....even though it's an "absorbent material", most of the foam type solutions are actually reflective at the higher frequencies. It's probably no worse than a bare wall, but the acoustical properties vary quite a bit with different frequencies.

The most effective solution for really low frequency acoustical treatment is actually a helmholtz resonator. The tricky part is that the tolerances are quite small in order for it to be effective...which is where having the ability to measure results becomes extremely handy.

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-Mike Bentz

"It's territorial with the soundboard. So you're mixing and some dude comes by spewing opinions and trying to turn knobs. It's akin to going up to an artist and painting over his unfinished masterpiece. You just want to shove your paint brush up his nose and throw the soundboard out the window!"

I was in the same boat. Put in some tratments, measured, put in some more, measured... didn't measure much difference. Then I gave up, and just left the treatments for a month. Decided to do another run of tests, and removed all the treatments. It was like walking into a church! The room sounded completely different, even in the lower region. So the treatments are doing SOMETHING, even if measurements don't show it that clearly.

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My DIY build Status: Almost done.

My room thread

well if you really want to see the effect of treatments over the midband and high frequencies, then you really should be looking at the ETC curves...it should be readily apparent there.

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-Mike Bentz

"It's territorial with the soundboard. So you're mixing and some dude comes by spewing opinions and trying to turn knobs. It's akin to going up to an artist and painting over his unfinished masterpiece. You just want to shove your paint brush up his nose and throw the soundboard out the window!"

Mike is correct but even thinner panels have some effect and if you put in enough panels, the sum of the smaller effects add up even at the lower frequencies. If you go to Ethan Winer's web site and look at his room and his FR curves, you'll get a good idea of what it takes to tame a room. Ethan also has some great articles on acoustics that are well worth reading. This amount of treatment isn't to everyone's taste but even if you do a bit, it helps a lot.

Bob

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"There is always hope, even if it is just a fool's hope."

This is exactly what I was basing my expectations on. I know treatments encounter a point of diminishing returns, and that your initial treatment (done correctly) can yield significant results.

Obviously, I'm not quite done yet. However, I have covered my 3 visible wall-wall corners from floor to ceiling with solid OC3. The panels aren't as deep as drwho mentions of course, but the face of them is about 18" from the corner (rough guess). I plan to add some more panels in key positions, using Ethan's pinknoise MP3 and my SPL meter to locate them.

Although I did test the phase of the sub extensively, I suspect some of this could be due to phase cancellation with the fronts. The reason I think this is that the sound is noticeably better when watching movies. My crossover is set to 80hz in my receiver, but when testing with REW I will be seeing overlap starting at about 45hz. I am going to have to test completely separately, as someone mentioned earlier.

So, I will get those better measurements in the coming days here and hopefully we'll see something. I know its not going to be earth-shattering below 100hz, but I certainly expected some improvement.

Thanks guys,
Jeff

If you are using the Roxul bendable wool stuff, you might try compressing it by a good amount, try 2/3 of the height that you have now. Roxuls Rockboard, is much better below 100Hz, and is twice as dense, and breaks before it bends to far kind of stiffness. I bought 12 sheets of 2" thick and 2' x 4' for under $150 shipped. I am thinking about getting some more and cutting some up into triangles and going to about 5' high in my front corners. I would go all the way up, but I have my main electrical panel in the front right corner, and per my electrician (Uncle ), I can't cover the panel up even if its a removable object. I guess that makes sense, don't want a breaker getting stuck and spew sparks on my bass traps .

Ooops I see you are using 703, guess I had Roxul on the brain. Does 703 compress? I know 705 is twice the density of 703 and thus better at bass trapping. So I wonder if you could compress it a little and see if that helps?