# Home Studio Control Room



## blackcloud77 (Jan 18, 2013)

Hi all. 

I had posted a couple weeks ago looking for a solution to a lacking bass issue. I'm holding judgement on that issue until I get my acoustics straightened out as best I can. After building quite a number of broadband panels, I think I know where to put them but I'd like some feedback and ideas. I had a Sketchup drawing on my other post, but that file is residing on another computer so I did a quickie sketch in Paint of the existing conditions. I'll try to highlight questions I have along the way. 

I've built 8 bass traps out of 6lb fiberglass, 2'x4' at 4" thick, on a 3/4" thick wood frame. Pretty sure the best use of the first four is across the front wall corners, floor to ceiling. I've put 2 in the available rear corner, floor to ceiling. The remaining two I've put on the floor-wall corner near the front of the room. None are mounted so any could move anywhere. I've also built 6 similar panels, 2" thick instead; 2 of them along the front wall, one at each right and left reflection point and intend to put one or two in the cloud above the mix position (not in play yet). I should also note that I placed 1'x1' foam panels on the desk at reflection points.

I've attached the frequency response, smoothed to 1/24 octave. While the dip around 110Hz was much steeper before treatment and is much smoother now, it still looks like a wide cavernous null. Trying to get this curve into perspective, I haven't figured out exactly from where to measure the 'depth' of the null (in REW) but eyeballing an average of 90dB, I guess this null is about -8dB? I suppose that could be much worse. I also wonder if this wide null could be the source of my want for more bass out of my sub...

The next null at 207Hz I thought of trying to treat by spacing the 2" panels off the wall, but I'm not sure that would be effective given the allowable space and wavelength at this frequency. 

Next null at 1kHz could possibly be treated with spacing the panels off the wall, but I've done much less research on how to tame these mid frequencies. Do you think it's advisable to try and tame this frequency with that method, or should I just stick with the spacing equal to panel thickness rule? I know 1k is a frequency that the ear is very sensitive to, so I definitely want to get that one sorted out.

For my next step, I was planning to pick up a Radio Shack SPL meter and use Ethan's filtered LF Pink Noise to locate the loudest corners; as a method to find the best placement for the 4 traps not in the front of the room. 

I guess my main reason for posting is that I'd like some input on what you might do if you had this room, 8 4" (OC 705 equivalent) bass traps and 6 2" panels (same OC 705 equivalent). Again, none of my panels are mounted so any changes are possible. 


I'm pretty new to all this (within the past 3 weeks or so), and I think I'm off to a good start (MANY thanks to Ethan for all his articles!) but I sure would like some input to make sure I'm off in the right direction.

Thanks so much!


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## AudiocRaver (Jun 6, 2012)

If anyone wants to call me crazy, feel free, I am just going to throw this out there as a possibility.

I think you should look at your REW impulse diagrams for early reflections at 0.5 ms and at 2.5 ms. A soft reflection at 2.5 ms would be the result of a 2.8 foot reflected signal path delay, and would account for partial phase cancellation at 200 Hz, 600 Hz, 1 kHz (something else is going on there, too, though), 1.4 kHz, and the effect disappears above there because it is a softer reflection. A sharper reflection at 0.5 ms would be the result of a 0.56 foot reflected signal path delay, and would result in phase cancellations at 1 kHz, 3 kHz, 5 kHz, 7 kHz, and you can see some combing effect even above that - all rough numbers, of course. A few of those frequencies don't show up, could easily be being washed out by some other effect, but enough of them do show up to look suspicious.

Like I say, I could be totally off, but it is easy to check on your impulse diagrams if you zoom way in. If I was a betting man, I would wager a shiny new nickel that the 0.5 ms reflection is the delayed signal off your desk top. That would be a fairly sharp reflection, and the delayed path length is about right. If there is a 2.5 ms reflection, the 2.8 foot delayed signal path is a little harder to figure. If, for instance, the listening position (LP) is 6 feet from the speakers, that would mean an 8.8 foot path for the delayed signal from speaker to reflection point to the LP. You can use a tape measure or cut a string to that length and see if the location of any potential reflection surface fits that path length. If it is a softer reflection, broader and not as high on your impulse diagram, then it might be a surface with some dissipation, or a somewhat slanted reflection angle.

If you find that the desk top is indeed a cause of an early reflection, good luck solving it, but at least you are in good company. Every recording studio has to deal with something like it. Usually the angle of the recording console is designed to help minimize it, sometimes other treatments are called for. It is worth doing something about, as you suggested, because that kind of early reflection affects clarity and imaging. Same with the 2.5 ms reflection, if that is what it is.

I certainly do not mean to lead you astray, but these are quick, easy things to check, and if I am wrong, you will know it in a fraction of the time that it took me to write this up, so the laugh will be on me, which is fine.:rofl:

That is my only suggestion, I am sure that others will soon jump in with excellent advice.

Best of luck!


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## blackcloud77 (Jan 18, 2013)

Thanks so much, that's just the kind of insight I'm looking for; things I never would have thought of! Surely it comes with much experience interpreting and recognizing patterns in the charts. 

Although I've read through most of the guidelines on posting graphs, I don't know if I recall seeing anything about impulse diagrams, so the best I can do is zoom in on anything interesting happening there. I don't know if it's enough zoom to address your suspicion or not. In a nutshell, what exactly are we looking at in an impulse diagram and is there an easy way to explain how to interpret it? 

Since there's lots of talk about waterfall plots, I've included that too. Hope I set them up right. Looks like I've got some fair hang times on a few lower frequencies.


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## bpape (Sep 14, 2006)

The 205 looks like a single problem. The other one is wider - from 80-105 or so and indicates that it is multiple problems. I'd be a buck that part of it is a cancellation off the wall behind you.

For the other items, I would recommend using 4" absorbers - including the ceiling.

Also, remember that when looking at impulse response, it's important to only run 1 channel at a time.

Bryan


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## AudiocRaver (Jun 6, 2012)

blackcloud77 said:


> Although I've read through most of the guidelines on posting graphs, I don't know if I recall seeing anything about impulse diagrams...


To look for early reflections on the impulse, switch the vertical axis from "dB FS" to "%FS" and zoom in the horizontal (time) axis so it covers from -1 mS to 10 mS.


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## blackcloud77 (Jan 18, 2013)

OK so I had a few things going on and unfortunately probably won't get to the studio this weekend to get anything sorted out or accomplished. I did pick up a SPL meter from Radio Shack to try and place some of the traps, but I don't think it's the same quality as the older ones.

I've readjusted and focused the impulse diagram as suggested, I'm still unsure of how to use it in detecting early reflections. 

I think I have 7 extra 2" insulation panels, does anyone think it would be worthwhile to convert any of the 2" to 4"? Or 4" to 6"? With the 6 of the 7 pieces, I could also just make 2 additional traps at 6". If I were to do any of these, where would be the most effective place to put a thicker panel? 

What does anyone think about using a single panel in each corner (instead of floor to ceiling), and covering more corners instead? Ethan says on his site that his MiniTraps are much more efficient with space above and below, but he's probably implying as opposed to setting a single trap on the floor and not mounting it. I don't know how it would compare to 2 traps stacked floor to ceiling.


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## AudiocRaver (Jun 6, 2012)

Your last posted impulse diagram is perfect for looking for early reflections. The sharp peaks between .3 ms and .8 ms indicate the *possibility* of early reflections corresponding to a delayed path length of between 12 cm and 27 cm. The affected frequency range were cancellations and notches would occur is between 600 Hz and 1400 Hz, where there are clearly some issues. Your desk top is a likely cause, and you can easily find out by throwing a quilt or heavy blanket over it and re-running the plot. You should see the sharp peaks disappear from the impulse, and the notches soften or disappear from the frequency response plot. If the desk is to blame, about the only way to treat it is by changing its angle or covering it with a sound absorbing layer. Neither solution is very convenient for a desk top surface, but those disturbances are worth getting rid of.

As I said before, I could be wrong about all this, but the disturbances in that portion of the impulse diagram appear to confirm my earlier suspicions, at least in part, and it is easy to test a solution.

Of course you are getting loads of expert advice from the regulars in this forum, and this little interjection should only cause a brief minor distraction.


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## blackcloud77 (Jan 18, 2013)

Alright, I'll certainly look into what's causing that. It is a little surprising because I actually had some absorbtion on the desk. I have a bunch of 1x1 foam tiles that are getting replaced by the 2x4 panels so I had put a couple on the desk at the reflection points. I thought a single 1x1 tile on each side would be sufficient, maybe I need more or they might need moved around. I could possibly tilt the back of the desk up as well, similar to a large console.

Thanks for all the help, any ideas on my other questions? Thanks!


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