# Is bass trapping making much difference (graphs inside)? - HELP PLEASE?



## sparky5 (Sep 28, 2009)

Hi All,

I have become facinated with room acoustics, but I must say I am a complete novice. I am sure I will be posting many, many more graphs to help me learn from all the experts here over the coming weeks / months.

If you are interested in giving me a hand, please take a look at the graphs below. I am trying to acoustically treat a listening / mixing room at home (it is a study converted inot a makeshift studio space I can muck around in).

I am using a Radio Shack SPL for the level metering and a ECM8000 for the actual measurements. All measurements taken at 75db. I have purchased 3 bags of Sonobatt Silencer + acoustic batts (21 batts in total). I am awaiting 8 Bass Trap Bags from Ready Acoustics (should be here in a week or so. Between now and then I thought I would try just sticking an entire bag full of eight bats in each rear corner, and put up some pillows at the first refelcetion points just to see if it made a difference.

The first graph is of the untreated room:

View attachment 16641


I don't know much, but that looks pretty bad to me.

So the next graph is with the batts and pillows placed as detailed above. I am sure this will improve once I have the batts made properly and placed them in all four corners e.t.c but just wanted to get an idea:

View attachment 16642


Well, I am not sure much has improved at all! The top end seemed to smooth out a bit, but has much else really happened?

Here is the before waterfall:

View attachment 16643


And the after waterfall (something crazy happened with the attachments - see the green waterfall at the bottom for this one):

View attachment 16642


What has happened here? Everything below 30hz has just disppeared and the ringing has not gotten any better across the frequencies, just shifted frequencies a bit as far as I can tell.

Here is a combined graph with the before and after:

View attachment 16645


Is this really the only change I will get from $100 worth of batts? Now, I am going to be purchasing proper material for the first reflection points and back wall, and having the batts filling all four corners with the bags - but still, at this point I am not seeing much difference?


I am using ?Behringer Truth B2030A Monitors for the sound. The tweeters are a bit above ear height facing down, angled on Auralex Mopad pads. Would I need a sub to actually get enough bass for bass trapping to be worthwhile?

Thanks to anyone that can comment on this stuff.

cheers,

VidarAus


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## brucek (Apr 11, 2006)

Since you're smoothing all your graphs, it makes it impossible to observe any change in the reflections.



> Would I need a sub to actually get enough bass for bass trapping to be worthwhile?


Bass trapping isn't very effective at very low frequencies that a sub provides. For the low frequencies, position has the largest effect.

Positioning also has an effect on your main speakers (assuming that's what your graphs are representing?). Try different positions to get a smoother overall response in the 50-300Hz area. Then work on treatments to reduce the reflections.

This is generally a forum section dedicated to REW and its use. You'll get far more play and advice in our acoustics section for these types of questions. 

brucek


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## sparky5 (Sep 28, 2009)

brucek said:


> Since you're smoothing all your graphs, it makes it impossible to observe any change in the reflections.
> 
> 
> Bass trapping isn't very effective at very low frequencies that a sub provides. For the low frequencies, position has the largest effect.
> ...


I thought that smoothing all graphs was a posting requirement of these forums? I created the graphs as per the instructions in the thread sticky.

Thanks for the advice. Will look into it. And yes, the treated room is from the listening position.

Is there any way I can move this thread to the forum section you suggested?

cheers


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## brucek (Apr 11, 2006)

> I thought that smoothing all graphs was a posting requirement of these forums?


That's correct, we do prefer to see smooothing when we are attempting to see the underlying trend of a signal when people want to apply low Q filters. But, if you want to examine the effect of treatment to lower reflections, then smoothing masks the results.



> Is there any way I can move this thread to the forum section you suggested?


Done. 

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

As brucek noted, acoustics is not our field primary field of knowledge or purpose on this Forum. For instance, I have no idea what a Sonobat Silencer is or what acoustic batts are for. That said...




> I have purchased 3 bags of Sonobatt Silencer + acoustic batts (21 batts in total). I am awaiting 8 Bass Trap Bags from Ready Acoustics (should be here in a week or so. Between now and then I thought I would try just sticking an entire bag full of eight bats in each rear corner, and put up some pillows at the first refelcetion points just to see if it made a difference.
> 
> The first graph is of the untreated room:
> 
> ...


It’s a fairly typical reading, actually.




> So the next graph is with the batts and pillows placed as detailed above. I am sure this will improve once I have the batts made properly and placed them in all four corners e.t.c but just wanted to get an idea:
> 
> 
> 
> ...


The pillows at the reflection point are going to be absorptive and cut down on the amount of upper-frequency reflections. Excessive reflections can make a room sound “brighter.” So, it looks like the pillows at least were working.

Basically, treatments are intended to cut down on in-room reflections. A high level of reflections causes a lot of comb filtering, which would no doubt be visible had you posted the graphs with no smoothing.

Here’s what an unsmoothed graph from a fairly “live” room would look like. Note all the comb filtering in the mid-to-upper frequencies:


View attachment 16656​

And here’s what an unsmoothed graph from a better-dampened room would look like:


View attachment 16657​

If you see something more akin to the second graph after your treatments are in place, then you’re getting something from them, even if your smoothed response graph doesn’t look as good as you’d like it to.




> Here is the before waterfall:


Only bass traps will deliver an improved waterfall graph, and then only from perhaps 80 Hz and up. It would be best to make sure any “before” and “after” readings were calibrated to the same SPL level, using a broadband pink noise signal.

Regards,
Wayne


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## glaufman (Nov 25, 2007)

AS Bruce and Wayne have pointed out it's hard to say what's going on in the bass region with these graph limits and the smoothing, but...
there are acoustic effects other than modal ringing that can cause peaks and dips like you see... it's possible you've got one of these going on that's overshadowing anything your traps are doing for you... For instance, from your graphs in the other thread, it looks like some of your peaks/dips change frequency (slightly) as you move the mic around the room... I suppose this could be an effect of the smoothing/limits, BUT if they really are doing this, it could indicate they're not modes you're looking at... I think modes (or at least axial modes) are the frequency they are, regardless of where you're listening... their magnitude may change (from peak, to smaller peak, to dip, to flat) the frequency is set by the room...


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## weverb (Aug 15, 2008)

You can also look at Energy-Time plots to see what and where the reflections are that need to be reduced and how much they have been reduced by treatments.


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## sparky5 (Sep 28, 2009)

Thanks for all the information and insights guys. I really do appreciate your time and effort.

The shipment tracking for the Ready Bags I ordered from Ready Acoustics finally says they are getting close to my house. Hopefully will arrive this week and will be able to build the bass traps and get them up this weekend.

Once this is sorted I will post the before and after with proper treatment, including smoothed and unsmothed graphs. Then we can see what is what!

cheers,

VidarAus


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