Serious low end issues in stone control room... any advice?

[The Beatsmith]

Hi guys

I'm trying to treat my new mix and production spot, for a pretty area accurate mixing area. I did some room analysis using a Peluso 2247LE in omni, with FuzzMeasure Pro. I used a 10sec sine wave sweep, and used Adam S3A's. I followed a primer on Gearslutz and turned the mic to face the speaker.

I've taken some pictures of the room to show the basic (starting) treatment, along with frequency & waterfall plots. I've done a room mode calc and am not exactly sure how to interpret the results, but the curve generated at the bottom of bob's page looked very close to the 'good' example. I've also attached the barefoot wallbounce calc results.

The room dimensions are: L: 7.15m x W: 5.3m x H: 2.2m. Nothing i have done, in terms of moving panels around, or moving the speakers around, has done anything to budge a 64Hz-ish peak, caused by the main width mode.

I've played a 64hz sine wave (out of both speakers) and walked around the room observing the changes, which are similar to the those displayed on the hunecke eigenmode calculator. In the past few days i've tried having 12inches of RW5/RS100 on the sides (with 4 inches of that floor to ceiling), having 8 inch corner traps at the front as well as this, just piling tonnes of traps/rockwool on the sides. And also scattering traps around the room as well as this. Clearly my broadband absorbers are not working at these types of thicknesses...

I have been measuring one speaker at a time, moving the mic roughly around mix position, and getting pretty similar results. Can you suggest a different type of trap/solution to this? The place is rented and i can't destroy anything/build a room in a room, etc. I am happy to build panels/am open to suggestions.

While this 64hz problem is rather immovable, moving front and back wall panels makes quite a bit of difference to the nulls. Small changes in the listening position seems to create different/new nulls.

Some notes:

- Front corners are floor to ceiling 4" traps, filled with RS100 (everything's RS100 other than the small, thin, square panels which are Wickes high density insulation). The four, 7' uncovered panels at the back are intended to become two hinged partitions for vocal recording, and also double up as some back wall bass trapping.
- Past these large vocal traps on the back wall the large open plan room wraps round to the kitchen area. There's no partition.
- The stairs section obviously goes up very high, giving some flutter echo.
- The 'bin-bag wall' helps to stop quite a lot of sound from leaking outside as the 4" RW5 in there really does a decent job of heat and sound insulation. This will be covered in fabric.
- The walls are all thick stone. The one to the left of the mix position has plasterboard with some insulation on it. Front and rear of mix position is merely plaster on top of the stone/brick.
- The floor is wooden laminate on concrete
- The plasterboard ceiling is quite thin as you can hear everything that happens downstairs quite clearly. I intend to make a cloud with two, two inch, 2' x 4' panels above mix position.
- The wooden stairs section is all hollow. It's just got empty gear boxes in it and the wood is quite thin. I plan to hang some thin panels on the underside of the slanted bit, behind where the big cream 4" panel currently is.
- I planned to build a plasterboard plug with handles for the window to the left of the mix position. The gap in the wall on the right, is filled with rockwool too, and i'll put some fabric or something over it.
- The 2'x'4 panels will be raised 30-50cm off the ground, as soon as i figure out how to make some stands for them. Some of the thinner panels will be hung on the walls, obviously things aren't quite finalised yet.

I understand there's a huge amount of information here, but i'd really appreciate some advice on how to tame that 64-ish-Hz bump. I'd be more than happy to try out any suggestions you might have, or answer any questions. I hope i didn't forget anything!

Thanks for any advice you can give!

Eddie

(Edit: viewing the pictures in reverse order makes more sense).

[The Beatsmith]

Here are some more enlightening result measurements (removed the original waterfall), although i am still experimenting. As you can see there are variations with other peaks/nulls between the right/left speaker, however the 64hz stays strong on both speaker, and also regardless of any panel placement. The left/right speaker are perhaps more similar than these graphs show, however. I've run so many tests i've started to lose track of things.

I've also noticed, for what it's worth, that when playing a 64hz sine wave, the window bay to the left of the mix position has an incredible build up of energy there.

Any advice would be greatly appreciated. Regards,

Eddie

[The Beatsmith]

Hi, as an update, i'm currently researching how to build perforated panel traps, tuned to 60-75hz. I have the C. Whealy calculator, seems to be quite helpful (see attached , as does this tutorial: http://www.stereo.net.au/forums/showthr ... -absorber-(bass-trap

If anyone has any advice on these or the materials that i should use, i'd certainly appreciate it. I need the panels to be freestanding, and so i'm not sure what kind of 'backing' i should use, and what thickness? And what kind of size would be required to really tame the problem peak by the 15db or so required?

I assume i would need to build two and place them at the side walls, roughly near the first reflection points (next to the wall), with my usual 4" broadband panels in front of them to act as first reflection absorption.

I'm also interested in putting some more insulation behind the 4" straddled, floor to ceiling corner traps i have, but am not sure what type of insulation i should use.

Please see attached a possible set of properties for a perforated panel

Many thanks

Eddie

[gullfo]

for your traps to work effectively, you want them positioned on the walls where they will do the most good. matching them up with the mode locations will be important. size matters, larger is better. you may need several on each wall to fully address the problem.

you can build them out of 3/4" (19mm) MDF and the face can be also be the MDF or plywood, or other wood like 1x lumber or 2x lumber if needed. you might build them as 2 half-height units for easier movement. while you're at it, you could consider making them angled as well which may help with your reflections. if you haven't already downloaded John Sayers' components.skp which has a number of devices which may prove useful.

[The Beatsmith]

Hi Glenn, thanks for your reply.

How big do you think they need to be, roughly? I don't mean in terms of depth, but in terms of height and width?

I was just thinking of making two boxes, 2'x4' each, and place them at the side reflection points (with some experimentation). Would this be entirely too small?

I also would like to put my broadband absorber in front of it in order to tame mid and HF early reflections, but am not sure how close to the holes i can get without ruining the function of the box...

Many thanks!

Eddie

[The Beatsmith]

Also, given that these are targeted at a specific and narrow frequency range, if i moved to a different space in a month, 6 months, or in two years, are these boxes essentially going to be useless?

At the moment i have the luxury of a bit of space, but i might not always have that luxury. Regardless, I was just wondering if these perf. boxes would be transferable or if they are 'tuned' to this room and basically i need to scrap them when i move.

That would change things on how good i make them look, aesthetically

[gullfo]

you could always find a new room with the same problems and then they're perfectly re-usable...

the units should be minimum 3x5 or better 4x8 (basically covering most of the floor to ceiling height) and wide enough to be acted upon and to do the absorption needed. depending on how you build the unit, the perforations (slats/slots/etc) could be replaceable meaning you could either rearrange them or if you use a panel approach, cut a new panel with the appropriate values.

[The Beatsmith]

I was hoping they wouldn't have to be so big. However, if that's how big it needs to be then i don't have much choice.

The room only has a 220cm/just over 7 foot ceiling, so 8' is out anyway.

Perhaps two 5'x3' ones will suffice. I hope so.

At least it currently appears to be just a load of mdf at the moment. It will be ugly, but at least it won't be too expensive (i hope). If/when i move, i can just trash the mdf and keep the rockwool.

Many thanks, i'll report back soon.

[gullfo]

you can paint it or silk screen it

[The Beatsmith]

Hey, thanks man.

I'm really unsure about the size of these things. I hate that these things are going to take up so much space just to tame ONE frequency that is going to make the room look very uninviting, and ruin my side reflection trapping.

How close can i put a broadband absorber in front of it, so that i can have side reflection points under control?

I'm worried that it might (might!) fix my 64hz issue, and throw up a whole bunch of new issues, if i have these huge boxes either side of me. Then again, i am very tired.

I'm currently thinking 1220mm wide (that's the width that MDF panels seems to come in), and i'm not sure about the height yet. I guess at least 170cm, or should i just go all the way up to around 210cm? I was hoping it didn't have to be as wide and tall. Perhaps 100cm wide and 200cm tall?

Pretty disheartening stuff..

Thank you for your ongoing advice

Eddie

[gullfo]

your absorbers can sit in front of them - just not touching. the proximity will have some damping effect but there is also exposure wall around (150mm or so) on a 600x1200 absorber so it should function well.

[The Beatsmith]

Thanks for that Glenn! Great diagram also

Also to finally answer your question on Gearslutz about the first mode - 32.5hz frequency - i am actually sitting in a huge null for 32.5hz. I just heard a track that has a large amount of very low sub on a software synth, and i was sure it was the wrong patch. If someone weren't sitting on the couch along the side wall to tell me that it sounded fine to them, i would have been here for days.

So it's definitely a 32.5hz null i'm sitting in the middle of. Although on the graphs at least, the issue doesn't seem nearly as bad as the huge 65hz peak. However, should i be treating this 'null' instead of the 65hz peak? Will the side wall 65hz panel traps improve things at 65hz as the frequencies are 'related'?

I just need to find out some more about flow resistivity of some insulation in the UK, and i can get back to 'my guy' about needed specs of the panel trap.

Cheers, and happy new year!

Eddie

[gullfo]

then you might be building a panel for the 32hz as well (or instead)... see the adjacent thread on the 36hz issue...

[The Beatsmith]

The thing is, that my graphs do not show such a serious problem at 32.5hz. It's the first width mode of a room this width.

If you have a problem at a 2nd or 3rd mode, do you chase the first one as the root, or treat the problem as it stands? Anyone?

I'll definitely check out the other thread on the 36Hz issue.

The idea of making more/different traps/changing plan, is a nightmare at this point...

[gullfo]

i agree it's not showing on your graphs but as i pointed out on GS i had a similar issue with the same speakers and we fixed the 32hz (actually 33 or so) and the remaining problems were also dealt with. we solved it though with a lot of extra rigid insulation which may not be what you need - but if you are not able to work with the 32hz as-is, you might consider fixing it. otherwise just target the 65hz and see if that meets your needs.