| Home recording and general music post from the archived Yabb Recording Website Message Board. Some of the info here may be outdated but many of the audio recording and home studio tips are still good. Note: The only tags I made and attempt to convert are italics, bold, center and underline. So if you see some gibberish surrounded by brackets, just ignore it.
Recording Website Archived Yabb board Post
Febuary 2001 Yabb Message Board Archive
Subject: For Maury and others regarding room resonance
by Tim_Z | 03/29/01 at 15:54:00
Maury, awhile back you asked me how I knew what the resonant frequencies were in my tracking room. At that time we were going only by our ears. While we knew there was a resonant frequency that was a bit of a problem, we were only guessing at its frequency. So the other day a good friend of mine (and keyboard player on Freefall 2) who is also a brilliant electronics tech, brought over a bunch of gear and "swept" my room by running frequencies through one of my Event 20/20bas monitors. He measured the results and deduced that the major problem centres around 110Hz. He then did some more research and found info suggesting that standard 2 litre platsic pop bottles are perfect for trapping 110Hz. So, since it is very cheap to experiment with these bottles, we are getting a bunch of 2L bottles and will be hanging them from the ceiling and sticking them on the walls. This will hopefully trap the resonant frequency, but will also (again hopefully) do a decent job as defusers.
I was extremely amazed at how there were null spots in my room when we were sweeping it. It is only a 12x12x10 room, and yet there were spots where I could barely hear the tone coming from the monitor, and other spots where it was REALLY loud.
I still know very little about room treatment, but it was very enlightening.
Cheers
Tim
Subject: Re: For Maury and others regarding room resonance
by Maury | 03/30/01 at 14:41:09
Thanks Tim! I really appreciate you sharing such a cool experience with us. How can "I" do that? I saw that in Soundforge & CEP they have test tones you can play. If I sat in the mixing position and cranked them thru my monitors, would I be correct in trying to "tame" any freqency that jumps out at me? Sorry if I'm already assuming your an expert at this ;D, I just wonder if I'm getting the "big picture". Best of luck in your experiment & let us know how it goes. (and good luck drinkin' all that soda!)
Maury
Subject: Re: For Maury and others regarding room resonance
by Tim_Z | 03/30/01 at 14:51:26
Soda?? No way man, I'm frantically looking for 2 Litre Bottles of Guinness 8).
If SF will allow you to select frequencies incrementally, and play them through a reasonably flat but accurate monitor, then yes it should work. Just make sure that you listen from various positions in the room and carefully listen for any frequencies that jump out at you, or sound louder than the others. After that the hard part is determining what to use to trap, or calm, those frequencies. I'm sure there must be websites that identify what size of Helmholtz resonators to make to calm particular frequencies. I'll post back after we place the bottles to see how well they work. I may have to replace them with something that costs more if they don't work, but I'm keeping my fingers crossed.
Cheers
Tim Z
Subject: Re: For Maury and others regarding room resonance
by Maury | 03/30/01 at 15:26:54
Ahhh - now that's a better idea! Maybe I'll just spend the weekend making corner bass traps out of empty Sam Adams barrels! I'll give your idea a whirl... I have a pair of Event 20/20p's that I'll have to make do with- not ruler flat I'm sure, but I can refer to their documented freq response specs and expect certain things in certain places, just from their design and know it's not my room. Good luck & thanks again-
Maury
Subject: Re: For Maury and others regarding room resonance
by chaz | 05/02/01 at 03:08:27
I found a little info on acoustical room resonance that may be of interest to you guys. Rather than guessing and experimenting, there is a formula that can be used to calculate and isolate resonant frequencies. It goes like this: The Fundamental resonant frequency between 2 surfaces, F, = V (sound velocity, 1130 ft./sec.) divided by D (the distance between the opposing paralell surfaces) x 2. For example, For a room 28 ft. long, the calculation would be,...F = 1130/28 x 2. That calculation squares out at 20Hz. However, you must consider that not only is 20Hz the base resonant frequency, but all mulitples of 20Hz above it up to around 300Hz, where they begin to diminish due to dissipation by the relative roughness of the wall surfaces and attenuation in the air. Therefore, you have to be concerned about 40Hz, 60Hz, 80Hz, and so on up to 300Hz. Now consider this,.......typically, rooms have 3 pairs of paralell surfaces and this calculation must be carried out for the other 2 pairs as well! Based on this fundamental, it becomes clear that the absolute worst scenerio would be a room that is completely cubed in shape. Remember, that since we are dealing with low frequency resonances, that using flimsy material to absorb the offending frequencies is not substantially effective due to the nature of low frequencies and thier propensity to "pass through" flimsy materials and seek more "solid" structure to reflect off of. In short, use oblique surfaces to attenuate resonances whenever possible. I hope this helps you guys! ROCK ON!!!!!!
Subject: Re: For Maury and others regarding room resonance
by DanS | 05/02/01 at 07:47:34
Interesting info gents.
However, I'm with Tim on the 2L Guinness bottles. You can make wind chimes with the plastic balls inside. ::)
Subject: Re: For Maury and others regarding room resonance
by Jon_B | 05/03/01 at 21:43:22
If your walls are parellel, I remember something about verticle strips on the walls being effective at breaking up standing waves. If that does't work, have some more beer. Not only will your recordings sound better, the wimmin will look better at the end of the night. ;)
Subject: Re: For Maury and others regarding room resonance
by Carbo | 05/03/01 at 22:05:24
Yes indeed that is interesting info. The math threw me for a bit (I literally had to fight the overwhelming tendency to glaze over during the all the F=thedividedratioofthesquarerootofmyauntmary'sfigpie), but are you sure about using every MULTIPLE of the fundamental frequency? It seems that it ought to be the octaves of the fundamental frequency (as well as the strongest overtones) that would be the problem frequencies. So instead of 20, 40, 60 etc, it would be 20, 40, 80, 160.
And so, either way, once you know the F of two walls, then you have to do the other two, and then the ceiling/floor. And then you'd simply compare your 3 lists of problem frequencies and find the ones where the same frequency shows up in two (or all) of the lists?
And does this mean that non-parallel walls will almost certainly eliminate resonant frequencies in a room?