Any acoustic engineers out there in TT Land?
I'm looking for a little advice from anyone who has experience with sound dampening/absorption for purpose built music rooms.
I won't bore you all with the details unless someone out there can offer some advice.
many thanks in advance
(Sorry - I should mention - I'm talking about fairly major renovations or building a structure from scratch, not just 'foaming a room' level stuff.)
Depends if you're making a Josef Fritzl type bunker where you want to prevent sound getting out or a studio for production where you want it to be a reliable space for accurate referencing.
Hi Bobby - thanks for replying.
I work (main job) as a teacher of Japanese taiko drumming. Wife and I are currently looking to either buy or build a house with an attached dojo.
I live in semi rural germany, so possible renovations would be for old houses with attached barns/stables. Most of these places have thick walls but we'd still build a room within a room and try and insulate further. Unfortunately, when you're talking of renovating a house older than 200 or 300 years, there can be a lot of hidden and unexpected costs, so predicting a budget is tough.
a newly built house gives you a pretty good estimate of costs upfront. The main concern is keeping the noise in and not bothering the neighbours. I teach in groups of 7-9 drummers. If you've ever heard/seen taiko, you know that's fairly loud. We'd be planning for around 50-60 sq meters. Muffling the noise inside the space is a secondary concern for now. If the neighbours complain, I lose income (and waste building costs).
I've been offered a couple of construction options here by builders, but I'd like to run them past someone with specific acoustics experience. They sound ok, but like I said, they're coming from builders who may not have the experience I'm looking for.
Is your background in this area mate, or have you done something similar yourself?
So you've got a two-fold set of requirements: You want to keep sound in as well as making it suitable for those inside drumming.
On the sound treatment for recording/teaching purposes I'd suggest investigating a way to make the drums quieter. I know some other type of drums can be deadened somewhat without ruining the sound too much. Taiki drums - which I've heard many times - are very loud and have a low register for drums (because of their size). That low register is something the sound-proofing would need to consider from the outset.
Typically solid brick/stone/concrete is the only practical way to block low-end sounds. It works better than foam type insulation. In your case you would probably still need a combination of both - to keep the sound in but not make the room unbearable for those drumming. It would need some deadening in the mid and highs and perhaps even a bass trap (google it) in the corner to help keep the sound natural.
Germany has a massive recording industry - one of the biggest in the world thanks to the popularity of electronic music there. I'm certain you could track down someone who could offer advice. I suggest seeking out a sound treatment/insulation products company and ask them. They likely offer some good advice to help potential customers buy the right stuff.
Thanks mate. Yes - I plan to engage a professional and just pay for advice upfront, but not many people know taiko in this part of the world. Bass traps already planned. we already practice with earplugs and I'll do my best to make it comfortable for the students, but the real worry is investing the money and then getting shut down because of external noise.
A builder has shown me a hollow wooden wall filled with pebbles (about 10" thick). Another guy has shown me a similar sandwich type construction with a third zigzagged wall in the middle and the spaces between the angles filled with a hemp like insulator. Unfortunately for them, it's all guesswork.
I'll keep looking and talking to people but I appreciate your replying - thank you.
Once the sound is kept in, then you will also need to adjust the sound properties INSIDE the room. The massive walls, floors and such will often cause echoes within the room that will require some amount of sound deadening. (I think I'd hate to be in there with 9 taiko drummers! I'm already about half deaf.)
One of the bands I played in built a room inside a garage for practice. We built walls of multi-layered sheetrock with the bottom sill resting on rubber hose to prevent any sound leakage from under the wall, a solid ceiling with an addition drop down ceiling with acoustic tiles to kill the sound going upward, carpet on the floors and walls to deaden the sound inside. Outside the garage, you could barely hear anything from inside.
The big drawback was the air inside. It was hot in there. We put a small airconditioner through the wall to help cool and give us fresh air to breathe (that's where some of the sound leaked). MAybe a split-system ductless system would work better? <shrug>
Lemme pitch in as a sound engineer who has done several acoustic work in the past. English is not my first language so forgive any grammar/vocabulary issues.
Three things that you should pay special attention if you need to treat a room. If you're able to BUILD the room, that's better.
Absortion, Isolation and diffusion. Absortion and diffusion is what you need inside the room. Isolation is what you need to avoid noise getting out of the room or getting in.
As an orchestral arranger, I'm very familiar with Timpani, and in frequency and loudness terms, taiko drums are not that far off.
Bobby and cholly both have very good points, although other measurements must be considered.
First, Taiko has a very strong low end component. Low end is the trickiest freq. band to control, as the wavelenghts of each hit could very well be 2-3 meters long.
To make things worse, low end is the most common enemy of any room, as any standing wave you may have will most likely be below 200 hz. Standing waves in a room with 7 taiko drummers would be pretty much my definition of hell.
(I'll continue in my next post)
If you have the chance to actually build the room, try to avoid symetrical walls. A room with 5 walls is, acoustically, miles better than 4 room. For early reflections, the most walls, the better. In fact, having a fairly square room can be improved by adding diagonal "walls" to cut the corners. An octagon.
If there's the chance, the ceiling shouldn't be paralel to the ground. Even a 5º angle is better.
Now, for the construction itself:
Low end needs MASS to be stopped. Mass + Absorptive material for low end absorption. Really dense wood is pretty good, but nothing beats glass wool and fiberglass insolation.
(I'll continue in my next post. Need to check some numbers)
Ok. Typical foam won't work for low end, since even the deepest Fonac (75 mm) only absorbs 17% of the incoming energy at 125 hz. In comparison, a 50 mm fiberglass panel will absorb 30% at 125 hz, 75% at 250 hz and close to 95-100% at 500 hz and beyond.
Not only you need MASS, you also need DENSITY. A 20 cm concrete wall is great, but 20 cm of wood agglomerate would work tremendously well in low frequencies.
Let's break this down into numbers:
A panel of wood agglomerate has an α (absorption coefficient) of 47 (base 100, 0 means 0% absorption, 100 means full absorption) at 125 hz and 52 at 250 hz. In terms of absorption, nothing beats that except (guess what?), PEOPLE. People are incredibly dense.
Fiberglass insolation or glass wool (50 mm) has an α of 30 at 125 hz and 75 at 250 hz.
Typical fonac or sonex foam (75 mm) has an α of 7-13 at 125 hz. Is pretty much useless for low end.
So, this is what a good construction combination would be:
(TL means transmission loss, and it represents, on a base of 100, how good insolation provides at different frequencies)
STC (sound transmission class) is an overal average at all frequencies:
Concrete wall (290 mm): PT of 33 at 125 hz, 41 at 250 hz and an overall STC of 50. It's pretty good, but makes up its STC by being good on high frequencies, not really at low frequencies.
Drywall (2 x 12 mm): PT of 19 at 125 hz, 26 at 250 hz and overall STC of 31.
And now the best buys:
Concrete (90 mm) + AIR (yes, air) (25 mm) + Fiberglass/Glass wool (65 mm) + Concrete (90 mm) + Drywall (16 mm): 49 at 125 hz, 54 at 250, and an overall STC of 62.
Drywall (2 x 12 mm) + 40 mm of air + 50 mm of fiberglass + 2x12mm of Drywall: 34 at 125 hz, 47 at 250 hz and overall STC of 55. Less functional than the concrete combo, but as you may see, a lot, lot cheaper.
If you can build the walls, ideally, you'd need concrete + air + insolation + concrete + drywall. And that only covers what goes in and out of the room.
Covered the structural issues (which are no true issues at all, just a matter of the right materials), let's check the proper treatment inside the room:
I just HATE going to a rehearsal room and find it covered by absorptive foam which deadens everything except the bass and the kickdrum, making it a low end echo chamber. AVOID THAT at all cost.
First and most important thing: Bass traps. I even build mines myself. But since you'll have taiko drums, you'll need plenty.
Ideally, you'll need at least two to three basstraps for each corner (floor to wall corner, wall corner and wall to ceiling corner). Basstraps will make a day-to-night difference in the overall acoustics of the room.
Good thing is, basstraps can also absorb high frequency energy, so everything will be balanced without spending hundreds and thousand of dollars in foam.
Basic basstraps pannels for dummies: 120 cm tall, 60 cm wide and 10 to 20 cm deep rockwool or fiberglass, covered in some soft fabric. You can even do a nice wood frame for it. And remember not to lay it ON the wall nor the corner, but a good 20 cm of the corner for better absorption.
You can build your own traps for.... $10 or $15 each.
Now, basstraps are covered, and if laid on the corners, standing waves should be covered too.
Instead of adding absorptive material for high end, try using DIFFUSERS. Plywood is a really good and cheap diffuser material. There are several designs for more complicated diffuser, but the easiest and cheapest ones are CURVED PLYWOOD PANELS. You can lay several of them in different acoustic sweetspots across the room and having an uniform response everywhere.
Now, some extra money-saving tips:
* Soundwaves don't bounce on paralel walls pretty much... never. If you plan on treating one wall with absorption, the wall right in front of it doesn't need it so much. Same goes with ceiling vs. floor. If you plan on laying carpet on the floor, the ceiling can be untreated.
* Diffusion works like a charm, and makes it feel like you're swimming in sound. Try using absorption only to correct acoustic disbalances and use small diffusors in different points of the room.
* Basstraps are a must. High spectrum basstraps like the one I said earlier work better than foam for every frequency band.
Ok, I'm off to lunch. I'll be back later. Feel free to email me at firstname.lastname@example.org for further inquiries. I check my emails 10 times a day, so it's no big deal ;)
Cholly, Andres - thank you indeed.
Andres - I'll send you an email later today. Much appreciated.
No worries. I'll be here ;)
Got your email galain. Replied to it yesterday ;)
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