# Why would treating my room make the frequency response worse?? [graphs]



## Kiddcabbage (Sep 25, 2012)

Hey, I recently came into a LOT of OC703, and so I used it to treat my room pretty completely. But the problem is that after comparing my before/after tests, it looks like the frequency response got worse! Though things like the RT60 and Decay look better. Why might this be?

Here are the comparisons, all in 1/6 smoothing.

Left speaker: green is before treatment, red is after.
http://i123.photobucket.com/albums/o285/IBBIAZ/Speakers L_zpshaq73nel.jpg

Right speaker: Purple is before treatment, green is after.
http://i123.photobucket.com/albums/o285/IBBIAZ/Speakers R_zpsvuiekcsp.jpg

Average: Pink is before treatment, blue is after.
http://i123.photobucket.com/albums/o285/IBBIAZ/Speakers Avg_zpsah1e8rdo.jpg


----------



## tonyvdb (Sep 5, 2007)

You wont be able to post pictures till you have at least 5 posts however I can try to answer your question.
It is very possible to over treat a room as well as depending on what material used and how thick you can easily affect only certain frequency ranges.


----------



## Talley (Dec 8, 2010)

The worst thing you can do is go overboard with absorption. General rule would be about 15-20% of the wall/ceiling square footages to be covered in absorption and around 25% diffusion and the remaining 55-60% just leave space. 

Too much absorption sounds bad. It doesn't take much.


----------



## Talley (Dec 8, 2010)

Kiddcabbage said:


> Hey, I recently came into a *LOT* of OC703, and so I used it to treat my room *pretty completely*.


Define this... did you line all the walls/ceiling with this stuff? your room is going to sound horrible.


----------



## Kiddcabbage (Sep 25, 2012)

As for the pictures, I included links as well as attachments. Otherwise, I've hit 5 posts now so I'll reattach them to this post.

As for the amount of treatment, this is for my unfinished basement (concrete walls) which is the only space I have to try to mix music in. Considering the concrete walls and strange dimensions of the room, I guess I just assume that more absorption is going to be better.

Here are links to pictures of how it's set up currently (Not attached due to size):
https://www.dropbox.com/s/rc5nsue6zsymuuh/treatment1.JPG?dl=0
https://www.dropbox.com/s/3dug3ufzzxqvli8/treatment2.JPG?dl=0

Basically, 8 large squares set up as a shell around the mixing area, with about 18" of clearance above and below and about 10" of space between the paneling and the walls. All of the paneling is 2" thick, aside from the right wall which I doubled to 4" thick.

Is this too much? If so how do I know what is going to work and what won't regarding this?

If it helps, here is the REW data from the tests:
https://www.dropbox.com/s/lqvwuxu9y5ygnl9/Basement room data.mdat?dl=0

The measurements in question are the ones labeled 6ft from the back wall, and 6ft post-treatment.



I mean, clearly concrete walls are going to be bad for anything audio, and the absorption has really helped the RT60 of the room, but what can I do to get the best sound out of this space that I can?


Attachment key, again:
Left speaker: green is before treatment, red is after.
Right speaker: Purple is before treatment, green is after.
Average: Pink is before treatment, blue is after.


----------



## Talley (Dec 8, 2010)

crank it up... run the tests at 85db is my preference.

your panels are hanging which has alot of space between the walls and the panels. this can absorb way more at whatever the distance to frequency relation is at but this is me guessing too.


----------



## Kiddcabbage (Sep 25, 2012)

Yeah I left the space between the panels and the wall to get more absorption out of them. How would that alter my frequency response negatively though? Also, running the measurements at higher DB wouldn't alter the frequency response, would it?


----------



## Talley (Dec 8, 2010)

Kiddcabbage said:


> Yeah I left the space between the panels and the wall to get more absorption out of them. How would that alter my frequency response negatively though? Also, running the measurements at higher DB wouldn't alter the frequency response, would it?


yes...

higher db can affect response... due to room gain and speaker response can change slightly based on how far they are driven.


----------



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

Kiddcabbage said:


> Hey, I recently came into a LOT of OC703, and so I used it to treat my room pretty completely. But the problem is that after comparing my before/after tests, it looks like the frequency response got worse! Though things like the RT60 and Decay look better. Why might this be?


It’s because the main benefit of treatments is to improve acoustics, not frequency response (with the exception of low freq treatments like bass traps). If decay measurements look better, then the treatments have been effective.

Practically speaking, there isn’t enough change in the “before and after” graphs to make an audible difference. And actually, if the room is concrete (as alluded to in your post), it’s possible that reflections were so severe that it affected the results of the “before” measurement. So it’s quite possibly that the “after” graph the more accurate of the two.

Another thing to consider is the amount of time that might have passed between the before and after measurements. A measurement taken in a few months or even weeks will virtually never be identical to one generated today. Things like temperature and humidity effect transducers on both ends of the equation (e.g. speakers as well as measurement mic). This will result in visibly different graphs, even if the “change” isn’t audible.

Bottom line, don’t sweat it – both measurements are excellent. I’ll bet those are some awesome-sounding speakers. :T




Kiddcabbage said:


> Also, running the measurements at higher DB wouldn't alter the frequency response, would it?


As long as you’re above the room’s noise floor you’re good. 75 dB is perfectly fine. In the nine years this Forum has been active, we’ve never seen anyone present graphs showing different response at different sound pressure levels. Not that it would matter; the difference (if one existed) wouldn’t be enough to be audible.

Regards, 
Wayne


----------



## JohnM (Apr 11, 2006)

Measurement level shouldn't affect response unless it is very high (causing heavy distortion and compression in the speakers) or very low (meaning background noise has a greater influence).

The response can become a little more uneven with absorption as the reflections that were (for example) filling in some dips in the response get absorbed, but the arrangement you have of those thin panels isn't likely to do much at the low end, which is reflected in your measurements as the main resonances around 50 Hz and 75 Hz are hardly affected. You may get better results stacking the panels to get something much deeper.


----------



## Kiddcabbage (Sep 25, 2012)

Thanks Wayne, I built the speakers myself!

Question - would sacrificing panels from parts of the wall that are not giving me direct reflections in order to double up on direct reflection points in order to absorb more bass result in a longer RT60 again? Is this trade-off going to be worth it? Or should I be prioritizing corners more than direct reflection points? Should I just test it all and post the results to see what happens?


----------



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

Sorry, I don’t know enough about the material you’re using to give a definitive answer. I’d suggest taking your question to our Acoustics Forum; lots of folks there knowledgeable on the subject. :T

Regards, 
Wayne


----------



## Tonto (Jun 30, 2007)

I'm wondering about the high end roll off, seems to be pretty drastic. Makes me think something in the REW set up is not correct. Those tweeters should play up to 20K pretty flat.


----------



## Kiddcabbage (Sep 25, 2012)

Yeah, you're right. Anything in particular in the settings that night do that?


----------



## JohnM (Apr 11, 2006)

What are you measuring with and is it pointed directly at the speaker being measured? No mic cal file loaded, so there is no correction for the response of whatever you are using to measure.


----------



## phazewolf (Feb 5, 2012)

Here try this. Place the mic and measure and then without going near the mic remove the panel's and run the test again and post those results. Moving the mic even a 1/2 of a inch can cause what you had measured to get all messed up.


----------



## Kiddcabbage (Sep 25, 2012)

I'm measuring with an MXL 2001 condenser mic pointed directly cenetered in the position that my head is at my desk.

I'll try that again. I've also picked up some more insulation (Lowes had some Roxul 6" R-15 on clearance because the bag was torn up), which I'll just plop in the closest corners.


----------



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

Kiddcabbage said:


> I'm measuring with an MXL 2001 condenser mic...


That would explain the apparent high end loss in the measurement. Due to limitations caused by their physical characteristics, large diaphragm mics aren’t able to handle very high frequencies. A hard drop above 10 kHz is common.

Regards, 
Wayne


----------



## Kiddcabbage (Sep 25, 2012)

Oh, good to know. I'll use my Rode NT-4 for my next measurements. Unless the fact that it's an X-Y stereo mic will change things. Unfortunately I don't have any omnidirectional small diaphragm condensers to test with.


----------

