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Emmett Location: USA Posts: 59	Posted - Thu Aug 07, 2003 6:40 am  This may best be posed to SteveG. I recently moved and was very very excited to finally have a dedicated room for my production studio. I am not at all worried about the EQ of the room, being that I am only making commercials for radio airplay. My problem is, I think, standing waves. I have the mic in the room with the monitoring system. If I record my voice and listen through my AKG 240 headphones, it sounds fine...when I listen through my Fostex monitors, there is a ringing sound. I don't notice it if the voice was recorded in another envornment...It's only voice that is recorded and played back in the same room. I thought lining the walls with rugs and heavy fabric would work...it seems to have helped a little, but the ringing is still almost unbearable. The room measures 12 feet by 9 feet 8 inches. What can I do that's inexpensive? Thanks in advance. _________________ Emmett KPNT, St. Louis, MO
VoodooRadio Location: USA Posts: 3971	Posted - Thu Aug 07, 2003 11:43 am  Sounds like your creating a "feedback loop" with the monitors and the "open" mic. BTW, what exactly is your monitoring setup? I mean, are you sending the signal straight from the soundcard outputs to powered monitors? Are you using a board? _________________ I said Good Day! Voodoo
SteveG Location: United Kingdom Posts: 6695	Posted - Thu Aug 07, 2003 4:35 pm  Quote: If I record my voice and listen through my AKG 240 headphones, it sounds fine...when I listen through my Fostex monitors, there is a ringing sound. I don't notice it if the voice was recorded in another envornment...It's only voice that is recorded and played back in the same room. Okay, one scenario: It's possible that the last sentence contains a big clue. If you have a room that's not particularly flat, and record your voice in it, that's fine - even though you will have a recording that has excited a few room modes. But if you play this back into the same space, you are going to excite those modes over again, and with a signal that's already got more output than perhaps it should have at these frequencies. And you are going to re-excite those same modes again... (you can probably work the rest out yourself!) But whilst this is possible, it wouldn't neccessarily result in ringing - usually it's the primary axial modes (the most powerful, low frequency ones) that get excited, and they tend to boom rather than ring. So like Voodoo says, a little more info about the monitoring would help. Also, to work out quickly where the LF modes are in your room, I'd need the height info as well as the width and depth. At that point, it's pretty easy. But I must say that it doesn't sound exactly as though it's the room that's causing the problem, because if it was that bad, you'd hear it on the phones playback. But regardless of what's actually causing this: With any sort of drapes, they become far more effective if you leave a six-inch gap between them and the walls. Also, make sure that if you have a window in the room and you can't curtain it off, that there is a heavyish drape on the wall opposite it. And keep a carpet on the floor. You should beware of covering too much of the walls with anything absorptive - it's quite easy to over-damp a room, and then you won't like working in it at all. Anyway, there's a starting point... _________________
Emmett Location: USA Posts: 59	Posted - Fri Aug 08, 2003 5:16 am  VoodooRadio wrote: Sounds like your creating a "feedback loop" with the monitors and the "open" mic. BTW, what exactly is your monitoring setup? I mean, are you sending the signal straight from the soundcard outputs to powered monitors? Are you using a board? Voodoo, It's funny you say that because that's exactly what it sounds like, but it's not. I am using a board...a small Deadringer (I know, I know:S) My monitors are Fostex PS3.1 (the little ones)...connected to the board. It has a sub and my first thought was that it was causing the problem, so I disconneted it. My second thought was that it might be resonating through the desk itself, so I panned the signal tot he left and held that monitor up off the desk...Also made no difference. I had the same setup before, but never had this problem until I made it into this new room...It use to share the space with a spare bedroom. --------------------- Steve, the room doesn't really have a boom...the bass doesn't sound great, but it is certainly tolerable. The ring is absolutely horrid. I decided to try an experiment...I hummed the tone that rings, and then some other pitches. If I hum that ringing tone (with the mic off) you would swear it was amplified. The room almost rumbles, but if I hum up or down a step, it's fine. Unfortunately, it's a tone that is a large part of my speech pattern. It seems to be okay if I get up and walk to another part of the room. Right now, my setup is in the center of the room and I'm wondering if perhaps I back it up to a wall, maybe that will help the problem. The room sits right above an unfinished, open room...I wonder if it's possible that it's resonating through the floor, throughout that room and back through the floor into my studio room. I have been working about 12 hours (on the air right now) a day and haven't had a chance to try moving the entire setup. If you have any new suggestions, let me know and I will try anything you have. I will also try moving the setup and see if that fixes it. If the problem is still apparent after this weekend, I will get you the full measurements of the room. Unfortunately, EVERYTHING is parallel, which is the first problem. The room has carpet and I think I have over dampened the room. When I couldn't eliminate the ring, I kept adding drapes, carpet, anything I could find. Now, if you clap in the room, it just kind of makes a thud. If I can get the ring taken care of, I will pull some down. My plan was to cover one of each parallel wall, and hang drapes diagonally in each corner. Right now, nearly everything is covered. This is so frustrating >:K! Thank you for all your help. _________________ Emmett KPNT, St. Louis, MO
SteveG Location: United Kingdom Posts: 6695	Posted - Fri Aug 08, 2003 6:36 am  Okay, it's the room - first scenario is the one. A couple of things: You really should get away from the centre of the room - this really is the best place for anything like this to happen. And yes, it's quite possible to have a massive resonance in a bit of the flanking construction. And if this is what's causing the effect, then it's unlikely that any hanging acoustic room treatment as it stands is going to fix it - they are not really any use for resonance control at all. This is the point at which the physical construction of the room itself becomes significant. If you have something relatively high pitch that's resonating, then there is a good possibility that you've got something like an undamped cavity resonance. The good news is that you already have the tools to possibly find out what's causing this. What you have to do is to use the CEP tone generator to generate the offending frequency, and whilst it's being reproduced by your monitors, move around the room listening closely to the walls, ceiling and floor to see if you can isolate the sympathetic resonance. If you find, for instance that parts of a wall are vibrating at this frequency, then you have to fix the problem with the wall! But anyway, there's a pretty good chance that you'll find something this way. You may well find that this is confusing to do, because the effect is bound to vary as you move around the room. If you find more than one thing resonating at this particular frequency, then you know you've got a problem! Whilst you are about it, get the tone gen to do a s-l-o-w frequency sweep from as low as your speakers will go up to about 3KHz and listen to what happens anyway - you are bound to get a series of peaks and dips, but it will be worth noting if any other ones apart from the one that is causing the ringing stand out particularly - especially in the region from about 150Hz on up. This should occupy you for a little while! When you report back, can you say what frequency the ringing is at, and provide the room dimensions anyway? This would actually make it a lot easier to find out if the room dimensions themselves are aiding the problem, which they might well be. _________________
Emmett Location: USA Posts: 59	Posted - Fri Aug 08, 2003 5:17 pm  Alright...I still havent had a chance to experiment with everything I want to, but I did take about a half hour out of my day to find the frequency and get the room specs. Let me be as specific as possible, so you have plenty to go on. The directions listed are not the actual directions, but I thought using a Cardinal scale would best allow you to visualize the room. As I mentioned, my setup is centered in the room. When I sit in my chair, I am facing the North wall, which means the monitors are firing into the south wall. They are set to a slight inward angle, roughly 3.5' from the ground. And 3-4 feet apart. The North and South walls are 12 feet, the East and West walls are 9' 8"...the height is 7' 8". In the Southwest corner, on the South wall, there is a small closet, with closed sliding doors. In the Southeast corner, on the South wall, is the entrance to the room. In the center of the north wall, there is a window, which measures roughly 4' across. There are no permenant obstructions on either the East or West walls. Now that you have an idea of what the room looks like, we'll move on to what else I discovered. The problem frequency falls within 5Hz of 150Hz. I would say more than likely to the flat side, between 145 and 150. I did not have a chance to see if the octaves or any other frequency creates a problem. I may get a chance to do some more experiments this weekend, but for now, that's what I can offer. I hope that helps. Thanks a lot. _________________ Emmett KPNT, St. Louis, MO
SteveG Location: United Kingdom Posts: 6695	Posted - Sat Aug 09, 2003 7:34 am  Allowing for very slight inaccuracies (which won't make that much difference) there certainly are two axial modes at 141 and 147Hz, and a tangential one at 150Hz (not as predominant as the axial ones) and of all of the frequencies that you might want to trap, a trap centred around 146Hz or so would be the one I'd actually go for initially, but I should warn you that you may want to consider what happens at 175-188Hz as well, because there is a similar piling effect (although not as great). I would have thought that this lot combined would definitely need trapping in some way - in a relatively untreated room, these modes would be noticeable. And it's not surprising that hanging drapes, etc did nothing for this problem - they are acoustically transparent at frequencies this low. Whilst there are certainly places that you could buy traps, it's not impossible to make them for yourself - there are designs around on the web that anybody who's basically competent to make a wooden box could probably manage - a membrane absorber isn't too difficult to build if you are careful about measuring the dimensions correctly. And at 150+ Hz, it's not going to be anything like as huge as a 50Hz one! You will probably have to mount it on the wall, and you may well find that you need more than one - it rather depends on the room. Or you could buy a ready-made solution - just make sure that you're sitting down when they quote you... _________________
Emmett Location: USA Posts: 59	Posted - Sat Aug 09, 2003 6:37 pm  Well, first off, I would like to thank you for all the free help that you're providing. I think it's really cool that you don't have to, but you choose to. It is much appreciated. That being said, I have a few more questions.:) I had always thought of bass traps as a luxury item for me, but now that I NEED them, I want to eliminate the problem as cost efficienty as possible. I found a few designs online. The first design I found is a panel design...it looked time consuming, but still possible for me to build. If that's what I need to do, that's what I will do. However, I also found a much less expensive option that also looks considerably easier. But before I start any project, I would like your opinion. It is a cylindrical design, with the primary part being a fiberglass tube used for plumbing insulation, with drywall discs for ends and covered with fabric. Do you think that this would work? The person who wrote it claims a 10" tube would be effective as low as 70Hz and a 20" tube as low as 40Hz. My other question is about how to determine the center frequency. If this design would work, what size would I want to best kill that 147Hz tone. Again, many thanks. _________________ Emmett KPNT, St. Louis, MO
SteveG Location: United Kingdom Posts: 6695	Posted - Sun Aug 10, 2003 1:16 am  Quote: However, I also found a much less expensive option that also looks considerably easier. But before I start any project, I would like your opinion. It is a cylindrical design, with the primary part being a fiberglass tube used for plumbing insulation, with drywall discs for ends and covered with fabric. Do you think that this would work? The person who wrote it claims a 10" tube would be effective as low as 70Hz and a 20" tube as low as 40Hz. My other question is about how to determine the center frequency. If this design would work, what size would I want to best kill that 147Hz tone. The problem with cylindrical traps isn't that they don't work - obviously they do! - but that they have a very high Q factor compared to a panel trap. This means that whilst they will absorb the frequency that they're tuned to very well, they won't catch anything else, even if it's really close in frequency. This is because they are effectively like an organ pipe working in reverse, if you like - they only 'suck in' one note! (please note that this isn't a totally accurate analogy, but it's close enough). OTOH, panel absorbers have a lower Q value, so they don't absorb so much at the centre frequency, but they do absorb a significant amount at frequencies close to the centre frequency as well. In general, in an otherwise LF untreated space of not quite ideal dimensional ratios (this is your room!) panel absorbers are a much better bet than cylindrical absorbers, because the troublesome frequencies don't ever quite coincide. And when you have three within a few Hz of each other and there's stuff in the room to diffuse the modal effect somewhat, the chances of being able to tune a cylindrical (resonant) absorber accurately enough without a lot of effort are quite slim. And the positioning of them is somewhat more critical than panel absorber positioning too. Obviously it's up to you, but I know which type I'd go for in this situation! It's interesting to note that in the London Royal Festival Hall, they used an amplified version of the tuned traps (Helmholtz resonators) with individual microphones and loudspeakers to control the LF reverberation in the hall. And they had to use well over a hundred of them to get it to work properly across the spectrum! _________________
Emmett Location: USA Posts: 59	Posted - Sun Aug 10, 2003 11:40 am  I think I will use a little of both. Those tuned traps seem so simple to make that it should take only a few minutes to build two of them. Perhaps if I can find out what diameter they need to be to kill 147Hz, I could make two of those and then several of the panels... Or would that be too much? I also read that cardboard boxes filled with news paper. Don't know if that holds any water or not, but since I just moved, I have boxes and newspaper everywhere. It's worth a shot as a temporary fix, until I have time to do better. _________________ Emmett KPNT, St. Louis, MO
Emmett Location: USA Posts: 59	Posted - Mon Aug 11, 2003 8:13 pm  Wow! I moved everything from the center of the room to a corner. The difference is amazing. It's far from perfect, but it's a lot closer to good than it was. I still need to build some bass traps, but it's at least tolerable in the mean time. Thanks for all the great advice. _________________ Emmett KPNT, St. Louis, MO
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