Cntrl/Live Rm Acoustic Measurements - is my method correct?

Hi Everyone, Been a long time since i've used/posted the site but have now got to the stage where i definitely could do with some guidance from all of you lovely people. I have read absolutely everything i can with regards to my situation on the site but i still have a few doubts/queries as to a few things. The story so far: I am in the process of moving into a new studio. My previous premises was waaaaay out of town and much as i loved it, it was becoming a problem. I was also sharing the space with another business which limited the hours in which i could work plus there was no room for expansion etc so when i was offered a chance to take over the recording side of a busy rehearsal studio right in the middle of Glasgow it seemed like a great opportunity. The studio has turned out to have quite a few more problems than i intially thought - i.e terrible leakage from the adjacent rehearsal rooms, doors not fitting/sealing properly, wobbly floors etc. I have managed to minimize the majority of the problems structurally & aesthetically so now i am at the point where i am attempting to analyze and treat the Control & Live rooms to get the best from them. My new space consists of a: Control Room L=4.72m x W=3.28m x H=2.29m and a Live Room L=4.63m x W=3.23m x H=2.24m The Control room is carpeted and the Live room has laminate flooring. I am completely new to the whole acoustic measurement process, i literally installed REW for the first time 5 days ago and since then have been furiously reading every scrap of info i can find to point me in the right direction to gain accurate measurements of my two rooms. Any help you could give me would be fantastic - here's what i've done so far. (As the two rooms are almost identical in size i've basically carried out the same process in both rooms - to simplify my description here i'll only deal with one room) For my measurements i used an Audix TR40 measurement microphone and calibrated my system to 94dBSPL using an acoustic Calibrator. The speaker was not ideal however, but it was the only full range speaker i had available to me at the time - i will use the same speaker for all of my subsequent measurements so that later results can be compared to my initial findings. I understand the basic theory of how a sound works within a space - modes, standing waves, flutter echo etc but am not sure if my measurement technique is correct. In my brain it appeared the right thing to do to divide my measurement process into two elements: 1. Measuring the overall frequency response of the room from approx 500Hz upwards to discern RT60 times, flutter echos etc 2. Measuring the low end frequency response & modal 'ringing' from approx 500Hz downwards. It also seemed to make sense to me that if the second measurement was concerned with the sub 500Hz range, modal ringing and such then the first should be focussed on the upper frequency range and basically 'everything else' that isn't Low end. By the same token, if my speaker & mic placement for the LF measurement is orientated towards illustrating the low end problems in the room i.e placing the speaker in the worst place (on the floor, in the corner) and the mic in the mirror position of the speaker - the 'best' place to capture these 'worst case' LF readings (the opposite corner, near the ceiling), then the same (but opposite) should hold true for the first measurement - Placing the speaker & mic away from all surfaces and in positions which are not related to the dimensions of the room i.e - 1/4, 1/2, 3/4 of the L/W/H of the room. Here is a drawing of the room with accurate mic & speaker positions. 1. For the first set of measurements i created an imaginary 3D box in the centre of the room (the shaded area) with the boundaries of the box 1 metre away from every surface. I placed the speaker on a stand within the box (Pos 1) and proceeded to measure in 6 semi random positions within the box. To try and avoid the modes of the room, using prime numbers i placed the mic in positions not related to the multiples of the room dimensions or multiples of the positional measurement values themselves in all three axis. I then averaged the results to give me a overall frequency response of the room. Below are my results: Average of 6 measurements with 24th octave smoothing applied. 2. For the second measurement i placed the speaker in the corner (LF Pos in the first image). I would've liked to place the speaker closer to the corner but i deliberately left space so that once acoustic treatment has been applied (i.e bass traps etc) i am able to repeat my measurements and compare the results. I then placed the microphone in the mirror position in the opposite corner. The distance from the walls to the speaker in one corner is identical to the distance to the microphone in the other. Here is the freq resp. result with 24th octave smoothing applied. Here are two versions of the same waterfall graph from the LF measurement: And here is the RT60 response: Ok, so after all of that i guess my first question is: 1. Is my measurement technique correct and are my results a valid and accurate representation of what is happening in my room? 2. If the answer is 'yes' and they are, then i guess my next question is how do i interpret them? I understand what the RT60 is in theory (good ole SAE! :D )and how it applies to rooms and recording etc but what i don't understand are the results on my graph. If i'm looking at the RT60 and the waterfall side-by-side and the waterfall is showing that the room is ringing between approx 110Hz and 170Hz then why does the RT60 graph show me that the longest RT60 time is at approx 250Hz? On the waterfall graph the 250Hz reigon has already dropped significantly after only 150ms whereas the 110Hz and 170Hz region still has plenty of energy - surely the frequency bands being exacerbated by the room will continue to ring the longest producing the highest RT60 reading? Does the ringing of the room not contribute to the RT60? or does it only concern the length of the reverberant field once the discrete early and late reflections have subsided? - if that's the case how does it differentiate between modal ringing and the reverberant field? I think i've got how the waterfall results apply to my room, my next question however would be: 3. Is this a good or bad room? - i can see the build up of energy between approx 50Hz and 170Hz and the peaks of the frequencies are quite tightly packed, would this be quite quite easy to treat? Based on my results (assuming they are correct?! :D ) and after reading pretty much all of the Real Taps website (thanks Ethan!), i was planning to put as much broadband bass trapping in my studio as is humanly possible. I notice on the waterfall graph that there is also a large resonance at around 38Hz, is this something i should be worried about? - i know that trying to treat frequencies this low can be a real problem and very expensive (i have a budget of almost nothing too! 8) ). I usually mix at a low level (83dBSPL) one, to protect my hearing and two, to try and minimize the effects of just such a problem - i do use a sub woofer to check the bottom end of my mixes though. I was thinking that i could build two superchunks from floor to ceiling packed with 75mm Rockwool in the front wall corners, i also own quite a bit of Auralex stuff - a huge Venus Trap, again, for the front wall and quite a few Bass Traps which could be put in the wall/ceiling join all the way around the room. I also have quite a few 50mm and 75mm acoustic tiles which could be used for the first reflection points. Based on my results above does anyone (with more experience) have any tips/advice as to what i should look at in terms of treatment? - do my ideas above seem appropriate for the problems this room is exhibiting? Any help that you guys could give me would be enormously appreciated. Here are the REW files for my Control room and my Live room if anyone would like to see them in more detail. (ZIP file 11.6MB) Thanks for a great site by the way, the wealth of information here is staggering and the generosity of effort and time you all put in is quite humbling. Thanks. Roddy.

Is the reverbationtime graph bulid from the same measurement like the waterfall graph?? For my eyes it mus be a different measurement! You have a incredible reverbationtime in the low end for a room like this :shock: Is it a completely empty room? cheers Mika

Hi Mika, Yes they are definitely from the same measurement. The room is completely empty at the moment too. Here's a pic: Cheers. Rod

Hey Roddy, welcome aboard! I know it has nothing to do with your measurement questions, but I'm curious about the diagram you posted: it clearly shows a three-leaf wall between your CR and LR, and another one between your CR and the rehearsal room. Is that an error on the diagram, or are your rooms really built that way? If so, any particular reason for it, and how does it work out in practice? It would be interesting to get some real readings of transmission through those walls at low frequencies. Anyway, that was my curiosity. I can't really comment on your measurement issues, because I'm not too clued up in that area anyway. Except to say that I did notice that mic position 4 seems to be roughly half way along the room, so I assume that one gave you the strangest readings since it is right in the 50% null? - Stuart -

its as expected and i would say not bad at all... adding basstraps should do the trick... but i wouldnt worry about overal room response for now, for now you should try to find best place for your speakers and mix position.

Hi Guys,

I know it has nothing to do with your measurement questions, but I'm curious about the diagram you posted: it clearly shows a three-leaf wall between your CR and LR, and another one between your CR and the rehearsal room. Is that an error on the diagram, or are your rooms really built that way? If so, any particular reason for it, and how does it work out in practice? It would be interesting to get some real readings of transmission through those walls at low frequencies.

The diagram is correct - the studio was already constructed before i arrived so unfortunately i haven't had much choice in the matter! :roll: There is some transmission through the structure from the rehearsal room to the control room. This usually only happens at high volumes (unfortunately most bands practice at ridiculous volumes!!), mainly the bass guitar and sometimes the kick drum as would be expected. The thing that the diagram doesn't show however is the fact that the control room is not properly isolated i.e 'floating' i think this accounts for the transmission more than anything else, but despite this it's actually not too bad. Once i have the studio is finished i am planning to do some work in the rehearsal room to reduce the transmission problems. I'm going to build a isolation platform for the drums and the guitar/bass amps, i figure if i can reduce the amount of energy getting into the structure (floor) it will help greatly with the level of transmission into the control room. I will definitely do some testing of the before and after transmission levels into the control room etc so i will post them up if i get a chance.

Except to say that I did notice that mic position 4 seems to be roughly half way along the room, so I assume that one gave you the strangest readings since it is right in the 50% null?

It wasn't too bad actually. As i mentioned in my first post, i deliberately chose positions that were not related to the multiples of the room dimensions specifically to avoid the peaks and nulls if possible. I took as many of these measurements as i could (REW will only let you take so many) and then averaged them - again with the thinking that it would smooth out the readings so that i could get a more accurate frequency response reading. If you've got REW you could download my files here for a closer look if you'd like. Cheers. Roddy.