150hz peak - HH vs. Panel vs. Perforated Panel

[kosborne]

Hey all -

Just wanted to say thanks everyone for all of your help over the past 10 years - I have gotten my studio[s] sounding pretty #@$%!@#)%(@U great thanks to all of the wonderful and generous contributors here!

In my current live room, I've got this issue at around 140-160hz. I've taken dozens of measurements from all over the room and even though the response various drastically from different speaker and mic spots, the 140-160hz issue remains. I really notice it in my recordings as well. I'm very happy with my decay times and response overall, but it's just this tiny issue! I can live with everything else in the room but this! I've walked around the room with an SPL meter and noted some spots where various frequencies in this region are at a hotspot - and the good news is, there are definitely spaces available for me to treat. I've tried fiber, 4" and 6" spaced 2" off the wall, and it helps, but not quite as much as I had hoped. Plus, I don't want to start popping more fiber traps all over the room and start killing my top end.

SO I'm considering building some tuned traps -- This 100-200hz region is difficult because it seems to be at the lower end of fiber and slot traps, but at the higher end of panel traps. What do you guys usually use to treat this region in a targeted manner?

I know slots are out - there's just no way to make the numbers work for my situation. Panels are likely out because I don't really have enough surface area worth sacrificing, so I'm curious what you guys think on a true helmholtz design (individual sealed cavities) vs. a perforated panel. I've done the numbers and both are feasible, but I'm just curious how you guys would handle this frequency region with tuned traps? I've built some helmholtz traps in the past with good results, so I'm leaning towards that. I'm good in the woodworking department so I'm not afraid to do whatever will work best.


Thanks again

[Soundman2020]

We'd need to know a lot more about the room to be able to help. It's a strange problem if it occurs at that specific frequency everywhere in the room. It can't be modal, since modes manifest at very different intensities as you move around the room, from nothing at all to extreme, depending on which part of the standing wave you are in. They also ring, but you made no mention of that. So modal is probably out. It can't be SBIR either, since that would occur at different frequencies as you move around the room, although it might be at the same intensity. But you mentioned only one frequency.

You also didn't mention how it behaves in the time domain (except to say you like the decay time), or if there are any phase clues. You really should post your actual REW test data (MDAT file) so we can download it and analyze it properly. There's way too little to go on in your explanation.

Also, an accurate diagram of the dimensions of the room, description of existing treatment, room geometry (speakers, listening position), speaker make and model, measurement mic, your REW test procedure, and all other pertinent details. Photos of the room would help too.

Without those details, this is like going to the doctor and saying "Doc, my body is hurting, and I don't like it. What pill should I take to fix it?". If you don't tell the doc everything there is to know about your pain, in detail. he can't help you. And any pill you decide to take on your own is likely to do more harm than good...



- Stuart -

[kosborne]

Hey Stuart -

More than happy to provide more info. I should clarify, there ARE places in the room where this region is not prominent, but when I took AVERAGES, it seems to be large in the majority of measurement places in the room. It definitely exhibits different intensities at different locations, but overall it seems quite strong, again, on average.

Hopefully this will help things along:

1. Room is 18x20 roughly, two angled walls (West and north), roughly 5 - 8 degrees each. Ceiling is cathedral, 10' at the sides and 13' at the apex. Double wall construction, 6" exterior wall, 4" interior wall, 1.5" air space between, double drywall, etc. Laminate over concrete floor.

2. Speaker used for live room tests was a Yamaha HS80. I know it's not the flattest, but for live room testing and comparisons it was loud and worked fine. Mic is a calibrated Dayton EMM6.

3. Decay time is decently low in this area as compared to the rest of the spectrum, but amplitude is still quite high.

4. REW test procedure was as follows: a) calibrate microphone using Subwoofer cal and SPL meter. I used 90dB as my reference. b) placed the speaker at various locations around the room. Since it's my live room, I placed the speaker in locations where sources might go, drums, guitars, amps, vocalists, etc., at different heights - flat on the floor, 2' up, 4' up, 6' up, etc. I also placed the speaker in the bottom corners of the room. c) Microphone was moved 10 - 20' away at any given location. For the most part it was placed 3 - 8' off the floor, which is normally where I would put a mic for recording. Wanted to try to get a good average representation of the room's frequency response and decay times. Over the course of 3 days, there were 90+ measurements. d) Since the decay time in this region wasn't as prominent as the mids and highs, I started taking averages of the frequency response measurements, and from all of these measurements, I found that 140-160hz was clearly boosted. It's boosted back by the drum area, it's boosted by the guitars, it's boosted in the corners, it's boosted in the middle of the room...it seems to be hot in almost every place I measured. There were definitely measurements where it was reduced, but for the most part, there was a large boost somewhere in this region. From walking around the room and playing tones in the 120 - 200hz region, there were only a few spots where I actually heard deep nulls in this area.

5. In the room I currently have GIK Monster Traps in two of the corners, 8' high, GIK Tri Traps in one corner, 8' high, and GIK Soffit traps in the opposite corner, 8' high. I have 4x Diffusers that I built, they are QRDs centered around 700hz, 7 root, I believe 5.5" deep. They are two periods of 7 each, with an end cap so it's symmetrical - purely for looks, really. In between the diffusers I have 4" and 6" panels flat on the wall - which I have been experimenting with a LOT lately, spacing them, using 6" vs 4", spacing 2", spacing 4", spacing 6", etc. All of the panels are on clips that I can remove and adjust as needed. Below the diffusers, I have GIK Range Limiter traps, 4" (with built in air gap) down along the walls. This is the most recent picture I have taken in the room.



I'm taking this photo from the SE corner. The drums are in the NW, and so on. On the East wall and south wall, I have 4x4 panel traps that I built recently as an experiment - according to my tests before and after, they are working in the 180-280hz region which is nice - I used to have a big boost at 180hz and one at 210hz, and those have been taken care of by the panel traps, but it hardly touched 150! I was hoping they would but I got maybe -1dB at 150hz when I installed the panel traps. A result, but not quite as much as I had hoped. On the North wall, you can see one of the panels covered by a 2x4' sheet of plywood - I had plywood sheets across 5 2x4x4" absorption panels in the room, but only on the side opposite of the drums - this was also an experiment. Sort of a "live end dead end" test - I didn't really like what it did, so I ended up not keeping them up.

The ceiling has very little treatment - I have a 2x6x4" panel straddling the apex of the cathedral ceiling, and that's it. Honestly I haven't experimented much with treatment on the ceiling because I don't have the ability to test it myself as I don't have a scaffold or even a 10' ladder. I don't feel comfortable attaching large acoustic panels on an 8' ladder by myself. Maybe I'm more afraid of heights than I lead on.....haha

As I said, I'm very happy with the way the room sounds overall, but It just seems odd how strong this frequency region is! It's easily +8 to +15dB hotter on average compared to the rest of the lows, mids, and highs.

[Soundman2020]

Great! Much better! But I still need the MDAT files from a couple of key locations. If they are too big to upload to the forum, put them on a file sharing service and post the link. If you don't have them, then do one test with the speaker down on the floor in one corner of the room, and the mic up in the diagonally opposite corner, and another test with the speaker up on a stool a bit off center from the room (1/3 distance front/back, one third distance left/right) and the mic at standing ear height in a similar position on the opposite side of the room (also 1/3, 1/3, but the other way).

I'll be out of the office for a few days over the Easter weekend, so probably no contact until Monday. If you don't hear form me before then, then it's nothing personal!

Nice looking room, by the way!

- Stuart -

[kosborne]

Stuart -

Great! I'll do those tests you suggested this week and upload them. I'll also try to upload some other tests I've done recently - I won't bother uploading my 90+ test extravaganza (nearly 4 REW files worth!), but I'll upload some that I feel are important and representative of what I'm talking about. haha.

[kosborne]

Here are the tests you requested:


Speaker and mic in opposite corners:

https://dl.dropboxusercontent.com/u/129 ... rners.mdat



Speaker / Mic at roughly 1/3rd X and 1/3 Y on opposite sides of the room. First test is mic at 1/3 and the others are with the mic moving around to different spots:

https://dl.dropboxusercontent.com/u/129 ... round.mdat

[Soundman2020]

Sorry about the long delay in getting back to you! Hectic times. Lots of work with paying customers, and very little time for the forum.

Anyway, there's a lot of stuff going on in that room, especially in the low end... it looks pretty baaaad in places. And there is also stuff going on around the region you mentioned.

Most of your axial modes are present and prominent: 29 Hz (0,1,0), 52 Hz (0.0.1), 57 Hz (0,2,0), 85 Hz (0,3,0), 94, (3,0,0), 102 Hz (0,0,2), ... Notice something? You have (0,1,0) then (0,2,0) then (0,3,0) there's a big hole at (0,4,0) and guess where (0,5,0) occurs? (drum roll, please... ) 141 Hz! Tah-dah!

Notice something else? You have (0,0,1) and (0,0,2), and guess what happens at (0,0,3)? That would be 154 Hz!

And both of those (141 Hz and 154 Hz) are ringing quite nicely almost everywhere...

So basically you have a modal issue. Hit the fundamentals, and your higher order problems will go away too. The reason you are not getting any success from targeting those frequencies directly is because that's not where the underlying problem is. Hitting only the (0,0,3) mode won't do much to kill it, since the REAL problem is at 0,0,1, and 0,0,3 happens to be the third harmonic.

So what you need is bass trapping. Lots of it. Biiiiiig. Deeeeep. Bass trapping.

I would suggest large superchunk style traps in your wall-ceiling corners on the width axis of the room, since those are the biggest problems, but I would also do them on the length axis. However, to prevent them from sucking out your mids and highs as well, you'll need to cover the front faces with thick plastic, NOT stretched taught, and with some holes cut in it, to prevent it from acting as a membrane trap. I would try with 6mil plastic (the type often used under building slabs) to see how that goes. Use insulation that isn't too dense as well, so it concentrates on the lows, not the highs. Maybe something around 7000 mks rayls, give or take a couple of thousand. You could also put broad wood slats across the front of the traps, with wide gaps between them, to keep even more highs in the room (and also to look good).

But make the traps big. No, bigger. Nope, you still aren't thinking big enough! I mean BIG!

If the wall-ceiling corners aren't enough, then do some in your wall-wall corners as well (replace one of the ones you have there already).

Your ceiling also needs a bit of treatment: You have a huge broad "hole" around 120-130 Hz, which I suspect is related to the ceiling, as it matches the height dimensions and is broad (varying height). So I would consider building some hard-backed clouds, hung at random angles and locations around your ceiling. Put insulation (with thinner plastic) below the hard back, and thicker insulation (without plastic) above it. Make the hard back from substantial MDF or plywood: at least 5/8", preferably 3/4". Hang on hefty chains, at angles around 5° to 15° from level, some angled left, some right, some front, some back.

You might also want to consider a couple of wide poly's on your side walls, tuned to the lowest problematic frequencies.

Do all that, then repeat your REW tests. Try to get the speaker and mic in about the same locations as you used for the first tests.

With a bit of luck, that should take care of several of your problems at once, including the stubborn 140-150 Hz ring, and the 125 hz, null, and the low end stuff- Right now, your room must be roaring like an angry wounded buffalo in the low end, with no clarity on the kick, toms and and bass! The above should help fix that too, and tighten up your low end. The trick is to do that without killing your mids and highs...


- Stuart -

[kosborne]

Hey Stuart -

Thanks for your response and great treatment ideas.

What's weird is - the room isn't crazy boomy or muddy to me, and I've been doing this a while, I'd be able to tell you if it that's how it sounded. Keep in mind, too, I had to remove two huge corner traps to do the tests - the other two corners have more permanently installed traps, so I couldn't remove those. Those corner traps that I removed are helping a lot < 300hz.

To be fair ... Notice my boost between 55-60hz - it may just be convenient / coincidental that I like my Kick drum centered around 60hz and it sounds awesome to me LOL.

Since I made this post originally, I swapped out a couple of traps for some deeper traps, particularly the GIK Monster w/ Range Limiter. These have been testing MUCH better - easily got 2-6dB improvements below 300hz.

I also removed the thick-ish rug pad I had underneath the rug. This was more of a function of getting more decay time, but it seems that my midrange say 500-2khz has been brought up by an average of about 2dB. By contrast, this makes the low end less prominent to the ear as well. I know it's not a solution to the bass problems, but hey, kill two birds - more decay time in the room and less noticeable bass issues.

Swapped out some of my 4" traps on the wall for 6" traps. A small improvement, but an improvement no less.

You mentioned:

I would suggest large superchunk style traps in your wall-ceiling corners on the width axis of the room, since those are the biggest problems, but I would also do them on the length axis.

Just to clarify, do you mean "width" as in the shorter dimension and length as the longer dimension? I know that sounds like a stupid question, but hey, people 'round the world speak differently! haha. Looking from my control room window, the longer dimension is the "width"...but you know what I mean.

I greatly appreciate the responses! Makes complete sense. I'm happy to have had the small successes since we spoke last, but now I'm eager to try some of these solutions.

[Soundman2020]

Keep in mind, too, I had to remove two huge corner traps to do the tests - ... I swapped out a couple of traps for some deeper traps, ... I also removed the thick-ish rug pad I had underneath the rug. ... Swapped out some of my 4" traps on the wall for 6" traps.

Ummm.... WHY? So you are saying that in order to show how the room is behaving when you play in it normally, you took out the most important part of the treatment to do the tests???? Sorry, but I'm not following your logic at all there, Why would you take out the very things that the tests are supposed to tests? Why would you change the room to be something very different acoustically to test it, when the entire point of the test is to see how it behaves normally?

Put all of the treatment back in again, and repeat the tests with the room set up exactly the way you normally have it when rehearsing.

Just to clarify, do you mean "width" as in the shorter dimension and length as the longer dimension?

Correct. And it's not a silly question at all! The only silly question, is the one you don't ask....


- Stuart -