Garage Studio Conversion - Low Frequency Problems.. Help!

Hi all, This is my first post here & must say after months of browsing this forum I have been educated & staggered by the wealth of knowledge circulating this site. I must turn to the experts for help. I have been in the process of turning my garage into a home recording studio for the last couple of years, I have managed to achieve isolation to the point where I have not received any complaints and generally only loud drums and a cranked up bass amp can be heard within 25 feet of the building from outside. (so for me that is pretty successful.) The Room is 21 feet long, 12 feet wide and 8 feet high at one half of the room and 10 feet at the other half (however the garage itself is 28 feet long, including the entrance area/toilet area. 14 feet wide including walls and the roof is a triangular garage roof with two half faces sloping from 11 feet high to 14 feet to the middle. Hope that makes sense..) Here's a plan Diagram and a couple of photos of the room: note that the diagram does not show that the back wall is a drywall inner leaf attached to a 4" stud wall with RC, stuffed with 4" RS45 (45kg/m3) rockwool, with a 2" airspace filled with fluffly fiberglass and more rockwool. This is in front of the original garage door which 4" celotex boards have been placed on. Another 2 layers of drywall on the outside opening of the garage door were also constructed, effectively sealing the garage door. I am looking to further improve the bass response of my room. So far I have managed to install:- 8 x superchunk bass traps (the room unfortunately came with two concrete pillars that my dad insists are piles there for structural support.. maybe someone could shed light on this? :wink: ) 2 x 4” thick absorbers in ceiling corners of back half of room 4 x 6" absorbers to the rear wall (with a 2" air gap), 2 x 4" absorbers to the front wall (with 2" air gap.) 2 x 6" 6ft 6" tall absorbers spaced 4" from the side walls at the mixing position 4 x 4" absorbers on the side walls behind the mixing position (currently not mounted..) I have also added a cloud along the whole ceiling (well.. added 4" insulation between rafters of false ceiling - made up of 1 layer of 15mm drywall) I definitely noticed a big improvement to the recordings and the clarity of my monitors after these additions. but after testing the rooms’ low frequency response with a SPL meter some discrepancies have come to light that need addressing. I've attached a couple of word documents with the readings: (unfortunately I had no luck getting REW to work, couldn't get past the calibration part.) The first set of measurements were taken with my Adam A7s placed 4ft apart, 2ft from the front wall and 4ft from each side wall. The SPL meter was placed 7ft from the front wall , in the center of the room from the side walls and 45" from the floor and forming an equilateral triangle with the speakers. note - the SPL meter was placed where the chair in this photo is placed. The second set of measurements were taken with my Adam A7s placed 6ft 8" apart, 4" from the front wall and 30" from each side wall. The SPL meter was placed 7ft from the front wall, in the center of the room from the side walls and 45" from the floor - forming an equilateral triangle with the speakers. a few other details to mention: the walls (except the back wall) are generally two layers of brick wall with approx a 2" air gap (no insulation), however at the listening position the inner right side wall is made of what is called Breeze block in the UK (and has a considerably lower density than brick.) This is also the case for the same inner wall at the back half of the room. Now my questions are:- 1.) Will the lower density walls affect the room's frequency response and to what degree? 2.) The door into the room is almost directly behind the right speaker, will this affect the room's frequency response and to what degree? 3.) Would the outside of the back wall benefit from being made up of brick too? 4.) I also made up another diagram of a potential future room setup, does this seem along the right lines? the plan is to soffit mount the speakers as I like to hear more bass when mixing, add slat walls, acoustic hangers and possibly two angled, hard-backed clouds above the mixing position. (but one thing at a time :? ) I have more questions, but this post is already starting to feel too long.. so I'll leave it there for now. Any help would be much appreciated! Thank you. Aaron.

46 views and no replies.. Cmon guys, surely someone can help me? :wink:

Hi Aaron, and welcome to the forum! :) And a big apology for the loooong delay in getting a response :oops: . For some reason, I only just noticed your posts now. Well, better late than never, I guess... Anyway,

unfortunately I had no luck getting REW to work, couldn't get past the calibration part.

You can skip the calibration stage, if you are having trouble with that. All that it does really is to compensate for the response curve of your system itself. Without calibration the absolute values will not be accurate, but the relative values will be fine. In other words, you can use it to compare different treatments with no problem, as the same deficiencies will be present identically in all readings. So the curves won't show the actual frequency response of the room, but the will still be good for comparing, and time-domain response graphs will still be useful too. So go ahead and run the test without calibrating, save the session, and post the data file.

1.) Will the lower density walls affect the room's frequency response and to what degree?

They might affect the isolation of the room, but should not have much effect on the acoustics inside the room.

2.) The door into the room is almost directly behind the right speaker, will this affect the room's frequency response and to what degree?

It could, yes. In any of several ways. It would probably act as some type of panel trap (membrane trap) tuned to one or more frequencies, in which case it would be removing some energy from the room, in that corner. It all depends on how that door is built: (eg. solid core / foam core / hollow core. Thickness of materials. Density of materials. Depth of internal cavity if hollow. etc.

3.) Would the outside of the back wall benefit from being made up of brick too?

Probably not. You are talking about the outer leaf, not the inner leaf, right? That will have an effect on the isolation, yes, but not so much on the room acoustics.

4.) I also made up another diagram of a potential future room setup, does this seem along the right lines?

I think the overall plan looks better than what you have currently, but I'm not so sure that putting hangers behind a slot wall is going to be effective. Slot walls are tuned systems, so the hangers will only ever "see" the frequencies that the wall is tuned to. but slot walls are normally tuned to low mids or mids, and hangers appear to do a good job treating deep lows, so I suspect the hangers would never see the frequencies that they treat best. The soffit mounts for the speakers will be a great improvement for overall room acoustics, and is well worth doing. It's a pity about those support columns, though. The really do mess up the side walls.

the plan is to soffit mount the speakers as I like to hear more bass when mixing,

The purpose of soffit mounting is not really to increase the base, but to fix many of the issues caused by having a speaker close to walls. It fixes the power imbalance, deals with SBIR issues, front wall reflections, etc. It will greatly improve imaging, tighten bass response, etc. Yes, you will get a bass boost of up to 6 dB, but that's not the point, and in fact you need to compensate for that by setting the bass roll-off controls on the back of your speakers, in order to return to flat response (or rather, as flat as possible). A correctly designed room with a correctly calibrated system should give you practically flat response in the frequency domain across the entire spectrum that your speakers can produce (within +/- 6 dB, ideally), as well as a good response in the time domain, according to ITU and EBU recommendations, or at least as close as the room itself will permit. So installing soffits just to get a bass boost is not really the right reason. Installing soffits to solve all the speaker-boundary issues and improve overall acoustics is the right reason. If all you want is more bass, then just turn up the bass! :) I looked at your two documents, but it's really hard to get an idea of what the room is doing just from a list of numbers, and only in the frequency domain. Maybe if you put those into a graph in Excel, it would be easier to get some idea of what is going on, but even then it would still only be frequency domain, while your real issues are only going to be revealed in the time domain analysis. Also, your files only show single values, and you don't say which speaker you did the test with (left or right), so it's not even possible to compare tests and see if the door is an issue or not. Finally, you don't way how the meter was set up (weighting, response), so once again the numbers in your tables aren't much use at all, since the cannot be correlated to actual sound pressure levels or time spans. It would be much better to try again with REW, as it gives a comprehensive view of what the room is really doing. Like I said before, even if you can't get it calibrated right, it will still give much more useful information about your room than a set of numbers in a table. - Stuart -