--- Jamie Guinan <guinan@xxxxxxxxxxxxxx> wrote: > On 22 Jul 2004, Fernando Pablo Lopez-Lezcano wrote: > > > I have four 824's at home and they are fine, very > good the the price (a > > little too much bass) <snip> > > Funny, I just got a pair of 824's a few weeks ago, > and I found that the > bass was really weak in my intended "sweet spot" > position (speakers are > a few feet apart on a shelf, against the wall, at > ear level). > > Turns out I have some serious acoustic issues. The > bass all but > disappears around the point between the front and > back walls (standing > wave?), but I discovered that there's a lot of bass > "hiding" in the > corner, very loud and boomy there. Your room probably needs some accoustical design work. To build a standing bass wave a minimum amount of square footage needs to exist, (I forget the amount). Otherwise, you won't hear the bass and you will artificially boost it in your mixes. Then when you play it back in a car or wherever and the mixes will be very bass heavy. I think one other issue is wave cancelation but I'm not so sure about this. Assume a 12 foot long room with source against one wall. Cancelation will occur where the waves meet which is at six feet. So, you don't want to locate the mixing chair in the cancelation zone. DISCLAIMER: I haven't thought about accoustical design for awhile so what follows is just a primer and probably a bit inaccurate. It should be enough to give you a sense of the challange. Everytime I design a room, I have to relearn this stuff. :) Ideally you meet the requirement for square footage. Then you decide what the appropriate room reverberation is. At this point, you're concerned with total square footage and sabin values for existing materials. Then begins the math for which we use formulas in a spreedsheet that someone helped us put together. The first thing you find is the current room condition; equalization and reverberation responses. Then you introduce X amount of square footage of absorption to adjust the responses within about six frequency bands beginning at 20Hz and going to about 5kHz. So, for example, you target sabin values per band and by introducing 80 square feet of four inch thick Ownes Corning Accoustical Insulation (forget the product number) you become acceptably close to the target value. Of course that adjustment could negatively affect one of the other frequency bands. Basically you experiment with balancing the amounts of materials and absorption to get the close as possible to the target values. Perhaps the higher bands need to be tamed so you introduce 80 square feet of four inch ownens corning but you cover it with peg board so that only the high band frequencies penetrate into the absorption material. This module is likely to be on the ceiling. The question is, how does buying anyone's prebuilt bass traps figure into this. The traps obviously treat frequencies but you've got to know what your room requires. It's definitely not arbitrary. So, unless someone selling traps knows the values of your room and what you're going to use the room for they aren't providing you with anything that you can't design yourself. You can design a room through experimentation but that takes time and you're always a bit unsure of what's happening in the mixes. That's not a killer until you do work for hire and someone comes back and says, "the mix sounds like ass." Speaking from experience, that really sucks. If you don't want to do the math, I'd suggest calling around until you find the Owens Corning product and then build your own modules. Design them in four x foor foot profiles and so they can be installed in different rooms. That way you can take them with when you move. Removable modules also enable you to change the accoustics of a room; imagine, a dead room vocal both becoming a live percussion room. A great feature for limited spaces. Somewhere in my empire of junk, I've got photographs from the last studio that my partner and I designed and built. They show construction strategies for sound containment. There's room drawings and the accoustical design spreedsheets. The variables are only for basic cube shapes because we weren't dealing with angels and diffusion. If anyone actually needs this stuff, I'll put forth the effort to find it. ron > I found this interesting/informative (disclaimer: > the author sells bass > traps), > > http://www.realtraps.com/art_vibes.htm > > Looks like I have some work to do... > > -Jamie > > > > > -- Fernando > > > > > > > > __________________________________ Do you Yahoo!? New and Improved Yahoo! Mail - 100MB free storage! http://promotions.yahoo.com/new_mail
