My Room Measurement: Treatment Advice Wanted

Hey @Jimmy9 thanks for posting. You are right, the room decay is pretty average. Nothing to be too concerned with. The rise at low frequencies is normal but undesirable. More damping at low frequencies would smooth the LF response and improve decay some. The problem is that it is near impossible to do this. That doesn’t mean you shouldn’t try, but know that adding tons of LF damping can often have surprisingly little effect. If you want to try this I suggest buying some insulation and stacking it in some corners. Take measurements again and see how the results change. Be sure to measure before and after insulation. In fact, I usually measure without, with, without, with. This gives me series data with reversal so that I can be certain of the effect of insulation. Even adding what seems like a ton of insulation can sometimes have surprisingly little effect.

I usually advocate a multi-pronged approach to fixing bass. First is the use of multiple LF sources. This usually means subwoofers places around the room. Second is the addition of LF damping. This means adding bass traps. The third is equalization to flatten the response.

As for the issue with response flatness. High Q (narrow) peaks and dips aren’t very audible and often suggest a kind of error you don’t want to fix. So leave those alone. Low Q peaks and dips are fixable. The broad dip at around 70hz for instance could be addressed with EQ. However because there is such variation in the response between measurement positions I would want to take more measurements around the listening area to be sure of what you are eqing. I would also try some bass traps, and if you can swing it, multiple subs first.

Jimmy9 said:

Thanks for your considered reply!

I dont want to try and build 300mm thick LF dampening knowing the chance of big positive impact is not high. Should i focus on Bass Traps or Absorption panels at the reflection points?

I was thinking 150hz + absorption at first reflections, as first reflections need to be treated anyway...my ETC shows i have 4 key reflections to focus on.
Then maybe this will flatten the response and then if all that remains is the 70hz dip, i can make a limp membrane traps that are fairly well know to work at these freq? or focus on positioning until all dips are above 150hz?

What range do you usually say, well its cost effective to treat anymore? eg 10db variation, or 20db? 3db?
I still have some flexibility with positioning, so i will exhaust that first i think.
Next measurements i will following the dirac live model and take 6+ around my listening position and average them in REW?
I wont be adding subs. It's just a simple vintage 2ch system on a valve amp. (Yamaha NS1000xw and EL34 Tubes)

I am thinking about some products like http://www.megasorber.com/soundproofing-products/sound-absorbers/firesafe-lightweight-acoustic-panel that seem to get well in the 100hz range.

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The test data for the product you shows seems to show its effectiveness at 100hz is not great. It looks like similar absorption to typically 2” material. Appears to peak at 800hz and roll off below that? Am I looking at the wrong product maybe?

In general terms absorbing below 300hz is not so simple. You typically need materials that are about 2” to 4” thick and spaced from the wall. 4”-6” of total space is needed and that gets good absorption down to about 200-300hz. Getting it extended down to 100hz really needs higher density, 6” thickness, and maybe even the membrane approach that Gik uses.

You can try limp mass bass traps. I wouldn’t call it a simple proven method. A lot of people have had bad results with them. I have built them with mixed results. Some worked well and some did not. I pretty much always buy them from a place like Gik or ASC now instead. They are hard to test on your own and little errors can lead to missing the target frequency. They also need to be fairly large to be effective. Even though Giks are 24” cubes, you need like 4-6 of them to see real results.

A simpler method that seems to lead to better results is the use of a thin membrane. It won’t be as efficient but the absorption is broader. I suggest carpet protection film. Works well for me and is cheap.

If you do want to do the limo mass approach feel free to try it, but I would suggest building around 16-20 square feet worth to see good benefit. You might be ok with less but as I said, I’ve had mixed results.

Jimmy9 said:

I was reading it at NRC=.9 at 160hz and .6 at 125hz. I realise thats lab conditions, but thought that it or similar product might be effective in this range...but unlikely you think?

I am probably getting too specific too early.

I think i am asking.

Do i leave my speakers as they are and tackle the 75hz issue, or push them back and tackle the issues starting at 100hz.
Is that too big of a dip to tackle via eq and focus on absorption 200hz and up?

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While speaker placement is important for bass response, the reality is that the ideal speaker placement for bass tends to be the least ideal place for imaging. I would place the speakers where they image best. Then work on the bass with different approaches. If by chance (and some speakers work well like this) they image well against the wall, try that. If not, try pulling them even farther into the room. Sometimes a boundary interference effect goes away once a speaker gets far enough from a wall.

Since you are getting SPL readings, I assume you see that REW is reacting to sound. For example, if you turn the SPL meter in REW on and snap your fingers, the number goes up. if this is true, then when you run a sweep, does the speaker emit sound that sweeps from low to high frequencies? Is it loud?

Jimmy9 said:

thanks for the reply. Not sure if the second one is for me? i am definitely measuring with sound

Once thing i notice. all the guides suggest 75db, some 80db etc. This makes sense, you need some SPL to measure the room, esp when comparing to other rooms. But if you only every listen between 70-75db and you measure at 75db, you notice the issues you find at 75-80db dont exist to the same degree...

Do issues like the big dip i have 70 exist due partly to the room/sbir/lack of bass trapping but all partly to the SPL required to keep the bass jammed in the corners of the room, or does SPL have very little to do with this issue?

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Sorry about he out of place comment. It was posted to the wrong place somehow.

The 70hz dip is the result of boundary and room effects, nothing to do with volume. If turning it up somehow changes things drastically that would be odd (at the levels we are talking about here). Your idea has merit in a different way. You need sufficient duration of the sound energy to excite the modes properly so sometimes really short burst tests don’t reflect LF decay accurately. However the sweep tests are more than long enough. If your worried about it just do a 1M length test. It will dwell longer.

Sometimes the dips are also just phase related integration issues. Certainly exhaust all setup possibilities to be sure you have things optimized.

Oh I forgot to mention, the reason for the loud measurement volume is actually more about the signal to noise ratio of the measurement. You want to measure decay as much as 30dbs below the main signal.

Try measuring each speaker separately then both together and find what items are simply channel interactions. You might be surprised.