# Bass traps not helping?



## elee532 (Aug 21, 2008)

Here's a reading I took after adding just one floor to ceiling corner superchunk bass trap in my room and then a second reading after adding two more floor to ceiling corner superchunks plus one front wall-ceiling superchunk the entire width of the room. I'm barely an amateur with this stuff, but it looks like I'm not seeing much of a difference. Can anyone comment on these two readings?

Thanks!


----------



## grn1969c10 (Sep 18, 2008)

You might want to redo the waterfalls with a longer time range, say 450 or 600ms to see how long the sound persist. I'm in the same boat, wondering if my traps were worth the time and expense.


----------



## thewire (Jun 28, 2007)

Is this a single subwoofer? What are the dimensions of your room and how much air goes in and out of the room or into a next room for example. It looks like it could be exciting some room modes but how close is the subwoofer to a wall? Is the subwoofer on the side wall between the front wall and the seating? Which subwoofer is this? I will try some searching to see what info I can find on your setup.


----------



## thewire (Jun 28, 2007)

The graphs look like they have a pretty even decay. Don't see many that good. Still would be nice to know more details. :bigsmile:


----------



## brucek (Apr 11, 2006)

> The graphs look like they have a pretty even decay. Don't see many that good


I don't see that as a good thing. The decay here is very, very slow in the low frequency region. Not good at all.

brucek


----------



## elee532 (Aug 21, 2008)

Thanks for the replies. I screwed up when generating the waterfalls. I had Time Range set at 300ms and Window set at 600ms when all my previous graphs had the two settings reversed. The two corrected versions are below. 

To the other questions... My room is about 10' x 16.5' with a small hallway of about 4' x 4' off to the front right side of the room. All the doors to other rooms are closed except for an opening of about 3' x 3' where I built an equipment rack into the closet of an adjacent room. I plan to seal this off. 

I currently have a single sub (HSU VTF 2 MK1 - though I am currently on the pre order list for Emotiva's new dual sub). The sub is in the front left corner currently. There are a few other locations that I can try. However, shouldn't the bass traps make some improvement regardless of the location of the sub?

Thanks!


----------



## brucek (Apr 11, 2006)

You should really consider equalizing with a BFD... You have some room modes that no amount of treatment will affect..



> shouldn't the bass traps make some improvement regardless of the location of the sub?


Can you tell us what your expectations are?

brucek


----------



## thewire (Jun 28, 2007)

elee532 said:


> Thanks for the replies. I screwed up when generating the waterfalls. I had Time Range set at 300ms and Window set at 600ms when all my previous graphs had the two settings reversed. The two corrected versions are below.
> 
> To the other questions... My room is about 10' x 16.5' with a small hallway of about 4' x 4' off to the front right side of the room. All the doors to other rooms are closed except for an opening of about 3' x 3' where I built an equipment rack into the closet of an adjacent room. I plan to seal this off.
> 
> ...


The modes in the room will be excited dependent on where the sub is located regardless of absorption. There just is no way to treat frequencies that low. I was thinking maybe the sub was closer to the listening position, but for a room that size, it looks better than your first graph. The ringing very low on the graph does seem to be lasting a very long time now looking at the longer decay which I agree with bruce on now seeing that. It would be a good idea to try new placements now with the traps installed and then you can try the locations with the new subs also. Since you are getting duals you will want to establish two locations.


----------



## elee532 (Aug 21, 2008)

brucek said:


> Can you tell us what your expectations are?
> brucek


Hmmm?? Good question... I kind of feel like it's all or nothing with the bass. It's either not there or it's overpowering everything and almost totally lacking in definition. This make any sense? Sorry for the amateur description. :dizzy:

While I'm thinking of it, what might a decent waterfall graph look like? Anyone have an example to share?

Here's one more graph. I took the reading about 4' closer to the front of the room.


----------



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

elee532 said:


> Here's a reading I took after adding just one floor to ceiling corner superchunk bass trap in my room and then a second reading after adding two more floor to ceiling corner superchunks plus one front wall-ceiling superchunk the entire width of the room. I'm barely an amateur with this stuff, but it looks like I'm not seeing much of a difference. Can anyone comment on these two readings?


It would have been best to do a no traps/all traps comparison, rather than one vs. three. 

It’s a bit difficult to compare the two because your second reading appears to be at a significantly higher SPL level than the first. Note in the blue graph that response in the 25-35 Hz range is a few dB below the 96 dB line, while in the green graph response in that range is peaking over 96 dB. This is going to make the second graph look worse in that range, whether it is or not. Consistent SPL levels from one reading to the next is mandatory for any kind of meaningful waterfall before/after evaluation.

That said, I do see some improvement in the second graph (looking at the first 300 ms pair). At 80 Hz, SPL levels in both graphs somehow look consistent despite (as mentioned) what’s happening below that point. Not sure, but that possibly could be a result of the traps. But notice in the green graph that decay is notably improved at 80 Hz compared to the blue (at least down to 45 dB, which is a bit high for many residential rooms). That’s most likely from the traps.

Also notice the far right of the graphs, in the range between about 150-200 Hz. Note that in the green graph the signal level is significantly higher, yet the decay time is about the same as the blue graph. All things being equal, the higher SPL level will show longer decay. So that definitely indicates an improvement in ringing. 

Personally, I prefer the linear scale for analyzing waterfalls. Above 40 Hz, the logarithmic graphs scrunch everything up like an accordion. The linear graphs spread things out, which makes them easier to analyze.

Aside from the graphs, how do things sound? The traps should make the bass sound tighter. They may also be working well above the 200 Hz cut-off point for these graphs, which certainly can’t be a bad thing.

I agree with brucek’s recommendation for equalizing. Traps mainly reduce signal decay times; they can only do so much for room modes, especially if you have only a few of them (traps, that is). Plus they are increasingly less effective the lower response goes.

Regards,
Wayne


----------



## DrWho (Sep 27, 2006)

Might I suggest measuring the frequency response in the corners where you've put the acoustic treatment? (without the treatments there).

Also, you'll want to make sure methods of absorption are at least 1/4 wavelength thick (that's like 3 feet at 90Hz, or 6 feet at 45 Hz....not exactly practical at the lower frequencies).


----------



## thewire (Jun 28, 2007)

elee532 said:


> While I'm thinking of it, what might a decent waterfall graph look like? Anyone have an example to share?


I was told mine was good but I have also been told the reflected sound is under 30dB lower which is to far meaning I have to much absorption. I am getting more room treatments soon. This is my unequalized response with a pretty high target. My room is considered to be a little more challenging than many other dedicated rooms. Your looking at your waterfalls with a high target, and it is more common to look at the 75dB target. I prefer about -5dB or -12dB lower listening level. I have a semi impressive amount of bass trapping.


----------



## elee532 (Aug 21, 2008)

Thanks for all of the additional responses. Some additional info...

I accidentally forgot to save the reading the reading that I took before I added any traps. Thus the comparison between 1 trap and 4 traps. To further complicate matters, when I opened my MDAT file today, ALL of the readings were gone except for the last one taken the other day. What the happened?

The SPL difference between readings... glad you brought that up. I am almost sure I was using the exact same Windows volume, REW, and pre-pro volume settings for both readings. I don't understand why the difference. Anyway, I adjusted the volume on my pre-pro to get a reading with peak SPL closer to the initial reading. I hope this is the right way to approach this. 

Also, one other error I noticed between my 1 trap reading and my 4 trap reading... the open port on my sub was pointed away from the wall on the former and toward the wall on the later. I did some readings each way, and this definitely seems to make a difference. The new reading below reflects the port pointed away from the wall again. 

One more thing about the reading below... I added one more 34" superchunk bass in the middle of the back wall-ceiling corner. 

Another question... I tried switching my waterfall from logarithmic to linear. However, it comes out all scrunched up with I do linear (see below). What am I doing wrong here?

In general, I still don't feel as though I hear the tightness I would hope for. If it makes any sense, I kind of feel like it's all or nothing with the bass. It's either not there or it's overpowering everything and lacking in definition.

It sounds like it might be another six months before I get my new dual subs (which will also include EQ options). :-( Until then, I can tinker around with seating and sub location. 

I just want to know that the countless hours and money that I sunk into building these bass traps is at least having some positive impact. 

Also, DrWho, can you explain how I would measure the frequency response in the corners where I put the acoustic treatment? Do I simply remove the treatment, place the SPL meter in the corner on my tripod, and take a reading?

Thanks again!!


----------



## grn1969c10 (Sep 18, 2008)

I'm having the same problem with the waterfall not matching the x-axis scale when switching from logarithmic to linear. The only fix I know of, is to redo the actual test with the graph set to linear and generate the waterfall again. Hopefully someone can suggest an easier way to do it.


----------

