Tuning the modes to amplify harmonics in a new design?

Hi all, as I have just joined the forum I would like to say thank you to anyone who takes the time to respond to my post. I am currently in the research stage of a very small studio for recording in a portion of a single garage. Unfortunately its all I have to work with as the rest of the garage is used for other things. I realize bigger rooms are ideal but one has to make the best of what one has. I wanted to ask a question regarding room modes. The room would just be used for quiet acoustic sources; guitar(nylon string plucked), kora and mbira. Mbira music uses tuned overtones within the bass notes to interlock with the high notes so it’s an important facet of the music which would be nice to bring out. I was wondering how you would approach amplifying the overtones within the room across the whole heptatonic spectrum i.e tuning the room to the scale. My idea was to use the proportions of the room to target all the overtones. The length of the room is the lowest fundament at F# and the sides in ratios which are a fifth and a fourth. Specifically the dimensions would be L=3.81m, W=1.43m, H=2.56m. I don’t have much width to play with. Length is at its maximum and I am already slightly above the rafters (no ceiling) in height but could perhaps go more, although this makes construction more complicated. I would treat afterwards with bass traps etc Is this a wise idea or is it better to just try evenly distribute the modes? Would the quiet acoustic sources drive the room hard enough to cause issues with a design like this? Warrick

Hi Warrick, and Welcome! :) On tuning room modes deliberately you might want to look into the work Wes Lachot has done on this, and the way he uses room ratios and musical scales. Personally, I'm not a big fan of doing that for the control room, since my philosophy is that the control room should be as neutral and flat as possible, but for the live room (tracking room) there is certainly a case to be made for that. However, it's not just a simple matter of setting your room length, width and height to match the first three tones that you want, so you get the axial modes correct: There's also the issue of tangential modes and oblique modes. While they are less energetic than the axial modes, they are still there, and still an issue, so you do need to take into account that there will be additional modes that you might not have considered, but that might happen to pop up unexpectedly. One of the issues with modes is that it's hard to predict which ones will actually be triggered by the music you play in the room, since it all depends where the instrument is located in relation to the positions of the modal peaks an nulls inside the room. For example, if you happen to set up an instrument in a room that has a major axial mode at F1#, but the location of the instrument is at a modal null for F1# and the mic is at another modal null for the same tone, then obviously it will not sound the same as if you had placed both the instrument and the mic at the locations of modal peaks for F1#. The obvious solution is to only ever play your instruments in one of the tri-corners of the room, with the mic located in another tri-corner, but that does present some interesting practical issue! The other issue is what happens when you want to record a different instrument in there, in a different key? The modal response might or might not bear a good musical relationship to that specific key, and there is always the possibility that a mode can be triggered by a note that is very close on the scale... So there are pros and cons to going down this route of deliberately tuning the modal response of a room to a particular scale, and to my way of thinking, the cons outweigh the pros. Having said all that, if you plug in your numbers to a good room mode calculator, you do get interesting results. At least for the Octave #1. You hit F1, C2, E2, F2, and A2 fairly close (but far from perfectly). However, above that first octave, things start getting a little strange. For example, let's say you play a fundamental F3 (175Hz): Well, the room does not support ANY modes for an F3. However, there are four room modes very close by, at 179.8Hz, 180.1 Hz, 185.3 Hz, and 190.2 Hz. But of those are actually F3#, so your plain F3 stands a really good chance of triggering one or more of those, which is probably something you did not want! :) It's not nice if you play an F bu the room response by playing an F#... Try it for yourself here: http://www.bobgolds.com/Mode/RoomModes.htm However, thi biggest question here is this: do any of the instruments you mentioned go that low, to be able to benefit from the modal resonance? I doubt it. I'm not familiar with the kora or mbira, but there aren't many instruments that can produce fundamental tones at 43 Hz, 65 Hz and 83 Hz. That's the territory of bass guitars and pipe organs, or the very low end of some keyboards. Is that the part of the scale that you normally record in with those instruments? If their fundamentals are higher up the scale, then the entire thing is a moot point, because 2 or 3 octaves up from the region where you can tune the axial modes of your room, the modes are so closely spaced and evenly spread that you don't get any modal boost at all. In any event, Wes Lachot is the big promoter of tuning rooms to musical scales, so your best bet is probably to look at some of the things he has written, to see if you can use that in tuning your room. Here's something about the concept that he wrote a few years back: http://www.weslachot.com/articles_scales.html He has built some pretty good rooms, so there might be something to what he says. On the other hand, other designers (like John Sayers, for example... :) ) have built pretty darn good rooms that don't follow musical scale ratios... - Stuart -

An interesting thing to note is that Wes Lachot is recommending room ratios where all 12 notes are represented rather than choosing a particular scale. I think that it is a good idea to aim for evenly distributed eigentones (room modes) either based on the musical scale (Lachot) or more mathematical principles (Louden etc.). I agree with Stuart that in control rooms these should be damped for even response. The main issue I have with using 'musically tuned rooms' is what happens when you switch to just tuning or switch to A=432Hz. Would the room cause the players to go sharp because it resonated better at 440Hz?

what happens when you switch to just tuning or switch to A=432Hz. Would the room cause the players to go sharp because it resonated better at 440Hz?

Good question. And what happens if you need to use the room to record some types of Eastern music, which are based on different scales, or rich semi-tones are the prominent feature? One more point that should be made is that in order to hit these notes spot on, you need to be quite accurate with dimensions in the design and actual construction: differences of less than an inch can put you off the exact note by several cents, especially once you start getting up the scale a bit. - Stuart -