Altering the Acoustics of a semi-anechoic chamber

Here is a question for you. I am building an isolation booth in my flat in a room that is too small to generate good acoustics (no choice in terms of room I am afraid as my budget and the present rental market is not in my favor at present). As I can not build an isolation booth that is live (because the room is too small), I have only two choices, 1. make no isolation booth and give up. :-( Or 2. Build an isolation booth with the max absorpsion possible for the space given. As I do not want to give up, I am going to attempt to create an isolation booth with the max absorpsion possible. However, I am worried that if I am able to achieve my goal of building an isolation booth that has a high level of absorpsion over the audible frequency range (semi-anechoic) then the isolation booth's lack of reverb will result in life less recordings. This would be a problem, as i wish to use the booth to record vocals and acoustic instruments (such as acoustic guitar and maybe percussion), and maybe even the occasional electric guitar via small combo amp. (for pro demo's). So, I was wondering if anybody knew of anyone who had attempted to adapt a small semi-anecholic chamber in order to make it a more reverberant acoustic space. As, although I understand that the size and shape of the room has a great deal to do with creating a natural reverbarent environment. I was wondering if any one had ever been successful at creating a good recording environment for vocals and acoustic instruments by adding materials that exhibited a specific reflective acoustic quality in specific areas in the small semi-anecholic chamber with the specific intention of creating a chosen type of reverberant response, and if so, what materials were used, what shape and size were the materials, what placement in the chamber and what effect did they cause? I was thinking of materials that exhibited reflective qualities that would reflect a specified range of a chosen instrument. And I also considered experimenting in the quantity of surface coverage and position (3d) within the chamber. I also thought that it may be possible to construct an object that reflected frequencies over a given range that was also directional, (as microphones are). And perhaps if you spend time experimenting, perhaps you could engineer the material used as a reflector to be only reflective to your required amount (perhaps this can be done by using a specific material or combination of materials in a specific thickness/size?). I thought that perhaps it would be possible to engineer the reflector material to a high enough level, to make it reflect a range of frequency content only to a degree, in order to reflect or bounce the frequencies within a givin range only a limited distance that was not so great that it allowed standing waves. The design could also allow the surplus frequencies to be absorbed due to energy disipation caused by the friction when coming into contact with the absorbing material converting the 'sound' energy into heat. In the strange world in my head this kind of made sense, as if this was possible (although, not sure if it is) then perhaps it is possible to arrange reflectors much in the same way that you would arrange a microphone, in order to cause a controlled reaction in your recording environment, ie. in this case, a specific reverberant response. Perhaps, I am just grasping at straws here and do not understand the complexity of the nature of modes yet. If so, I apoligise to all those reading for wasting their time. However, if any thing I have said is valid on this thread, please let me know. Otherwise, thanks for reading. Cheers Pootle

"So, I was wondering if anybody knew of anyone who had attempted to adapt a small semi-anecholic chamber in order to make it a more reverberant acoustic space." I am fairly certain that the "inside out" wall found at this site does pretty much what your mind is trying to point you to do in this situation ;)

Thanks very much for the reply, and i will search this great informative site to see if i can find the inside out wall you described. However, I am not sure if you understand what I was getting at. I am first going to try and make a semi-anechoic chamber, which, i imagine that the inside out wall you mentioned will help me achieve. However, i do not really want to stop there, as, I wish to attempt to make an impossibly small chamber / isolation booth (2 m cubed on the inside) into a reverberant space that will be suitable for not only vocal recordings but also acoustic guitar and other acoustic instruments (plus the occasional electric guitar). (no drums needed as can use high qual multi-tracks). compromises! I thought that if I first made a semi-anechoic chamber, which absorped most of the frequency content from any sound source in the chamber, I could then create different reverb effects by placing different materials of various sizes/shapes into the chamber for different results. I was wondering if anyone had success in this area of research for an isolation booth which has very limited interior space of say 2 meters cubed (as anecholic, the shape is less important). From my understanding, some materials such as drylining board and ceramic tiles are very reflective across the mid to high range. I was wondering if perhaps it would be possible to create a usable reverbarent recording space for the tasks mentioned above, if I strategically placed several objects chosen specifically for their reflective properties in the interior of my semi-anechoic chamber, in a way that did not create complex mode problems* (lots of math and guessing i guess). From what I understand, if you place a reflective/absorbing material that offers only a limited amount of reflection in an anechoic chamber, then, if a sound is made, the energy of the sound will travel through the air until it makes contact with a material of different density. Once after making contact, the energy of the sound will either: 1> pass through the material and then be absorbed by the semi-anechoic chamber. or. 2> be absorbed by the material. or. 3> the energy will be reflected to what ever surface that is within its angle of trajectories. or 4> The energy will disipate and transformed into heat due to friction acording to the wavelength of the frequency content. I also thought that maybe it was possible to even make a thin reflective inner shell that could be fitted inside the semi-anechoic chamber in order to cause a reverbarant effect to any sound source within it. This, I thought may be an interesting idea as I would imagine that there would be less low frequency problems usually associate with small rooms due to the qualities of the semi-anechoic chamber. I also thought it may be possible to engineer a material that is able to reflect a chosen freq range of a specified spl for a chosen distance (disipating wavelength). (could a thin reflective material/s work in a small semi-anechoic chamber without causing mode problems? Surely the theory for small rooms is the same as big rooms, you just use thinner and less reflective materials? And if the mode problems are due to low freq, then what about using materials that only reflect high/mids within an anechoic chamber? is it possible to create only weak reflections that disipated quickly and if so. would these be inaudible? or would you hear them as they passed the mic? Limited reflections?) If this was possible, then surely it would be possible to engineer an environment that would be ideal for recording instruments of a specific freq range at a specific spl even in a small room (within a semi-anechoic chamber). If this concept was successful, then perhaps a frame design could be developed that the inner shell could be secured to, in order to allow for the inner shells to be interchangable in order to create different acoustic environments in the same anechoic chamber. If this inner shell concept worked in practice, then, perhaps it would be possible to use a variety of shells in order to tailor a recording's freq range / content. (match material for instrument freq range and desired effect). I guess, if you were very scientific with this approach, it may be possible to engineer the recordings so that each instrument's recording would be within a specified range. In the same way a mix engineer applies eq to each element of a composition, in order to create subtle seperation. In this way, the room would in fact become an eq. Anyway, just wondering. As if this was possible, It would mean that I may be able to change the reverb qualities of even a very small room, which would mean that i may actually get a variety of half decent vibrant recordings out of the small isolation chamber (of death) Also, if this theory worked in practical, the room would in fact be an illusion as it would simulate a room that would be percieved as bigger. A tardis live room so to speak. If it didn't work, I guess it would just be more of a turdis than a tardis..... I think this is worth experimenting just in case. If this is impossible, i guess i will just have to make do with lesser quality recordings and hope that my recordings will be good enough to show potential publishers / record companies that the music recorded has potential even if it was poorly recorded due to the limitations of the recording space (and would be commercially lucrative if rerecorded). I thought that i could also use the anechoic chamber to write music in using computer/daw/synths/samplers/virtuals instruments and to do a 1st mix in, before taking the mix to a higher quality larger roomed facility specially designed for mixing in. Anyway, thanks for any help or reading. Any more suggestions are welcome. ( I hope the language that I use is not too confusing. I am afraid I am dyslexic, which means that I find it extremely difficult to explain in words what is inside my head, especially where the subject matter is complex. However, if I struggle and perservere, I am sometimes able to untangle the mess into a something that is precise and comprehendible).

I also figured that if you had the space / budget, that it would be possible to make a room that is adjustable in size and shape. Either by using different frames fitted with acoustic reflector planels (with resilient fixings in order to stop rattles or other unwanted noise problems). Or, by fitting a comprehensive adjustable animatronics mechanical frame that would allow the user to adjust the size of the room to fit the desired reverbarent result. Perhaps someone has made such a room at some point in the history of recording studio buildings.

Its probably cheaper to build separate rooms for different acoustic performances, shouldnt it?

Pootle - what you are suggesting is a guitar that can play bass, lead, and mandolin and violin. Take a recording space that is relatively small - say 14' x 12' and treat it with angular timber, tile floor, glass walls, every surface reflective etc and end up with a room with a live 0.9 msec reverb. Cool - I could use that. Or you can treat the same space with hangers and slots etc and end up with a room with a .2msec reverb - I could use that also. It depends what you want it for.