Practice Studio--Attenuation that's "Good Enough"?

[Kotedjuga]

Reposted from Newbie Forum:
Isolation Questions for a Practice Studio

At the risk of being yet another newbie asking for the impossible, I'd really like a second (and third...) opinion on the approach suggested by an acoustician. I've read the forums (this, GS, Tweak's), ordered and read the books (Brandt and Gervais), and hired an acoustician. I'm just looking for other ideas/suggestions/confirmations before taking the plunge.

Objective: Provide enough sound isolation so I can practice my djembe hand drum without driving the rest of the house nuts, and keep the outside level below ambient (~50dB) to keep the neighbors happy. I'm targeting enough isolation to get the sound level to 50dB in the family room and at the property line.

Background: I have a bedroom over the garage that I will turn into a practice studio. The house is 5 years old and well insulated/air tight. Inside the untreated room the sound pressure measured 95.5dB. Downstairs (and in the opposite corner of the house) in the family room, it is 58dB. My closest neighbors are 12' away and the SPL at the property line was measured at 55.4dB. Most of the djembe's sound is mid-frequency, so I don't have a huge amount of bass to attenuate (RTA spectrum attached).

The interior walls are 2x4 with 1/2" gyp rock and no insulation (measured at about 31dB attenuation--sketch attached). The door is a hollow core with 1/2" gap at the bottom (measured at 9dB attenuatiion). The exterior walls are 2x6 with the same gyp rock and Tyvek and Hardi plank. Windows are vinyl thermopane. Room is above garage with fairly well insulated floor. Ceiling goes to attic with a boatload of insulation (~24"?) in the attic. There's one duct and it's flexible fiberglass not sheet metal.

Approach: 1) solid door with Zero gaskets/seals (41 STC), 2) cellulose blown-in insulation for all interior walls, 3) Window plugs, 4) Acoustic treatment (I may do some recording as well, but that's a secondary requirement)

Questions: 1) Will the above get me close to what I'm looking to achieve, or will I end up ripping out walls and putting in rock wool with resilient channel and double sheetrock or a room-in-room anyway (and is <50 dB low enough to be tolerable in doors)? 2) Will the floor be a problem even if I upgraded the interior walls with resilient channels, etc.? 3) What about the duct--do I need a soffit or something to keep sound from traveling to the rest of the house? 4) Anything else I should be doing?

Thanks in advance!

 

[c7sus]

You're talking about an un-amplified drum, right?

I wouldn't do anything.

The background noise floor in my room is about -55dBFS on a good day.

Check your local sound ordinance, but in most places you can go to 80dB at the street.

 

[Kotedjuga]

Yes, the drum is unamplified.

Again the primary concern is the noise in the family room downstairs and on the opposite side of the house from the studio. Currently the sound in the family room is too high at 58 dB when I drum in the untreated studio.

The SPLs at the property line are well within legal limits, although not necessarily below annoyance levels, particularly when the 2 year old's room is directly opposite the studio 12 feet away. I haven't had any complaints from the neighbors, and don't want to. My daughter has remarked that the drum can be heard outside, but it's just audible. About the only thing I'm considering to treat the sound outdoors is the window plugs, which should be good for another 6 dB and get things below 50 dB outside.

It's good to know that if I get the levels down to 50 dB inside and out that it should be below the annoyance level.

Thanks!

 

[jhbrandt]

Kotedjuga,

installing a solid core door with good seals will get you most of the way there. Next would be the ducting. A baffle box connected to the I/O ducts in the music room should provide enough attenuation through the ducts for you. Following that, you may want to install some impact resistant flooring ( not carpet ).
So my recommendation would be to first install the new door and seals & then test again.
Cheers,
John

 

[Jeff_D]

IMO the door is definitely the weak link... and I'll concur with John- fix the door and go from there. The other weak link is likely to be the window. Maybe you could build like a pair of swinging shutters to close over the window. You could even put some acoustic treatment on one side so when the shutters are covering the window the ac treatment will be exposed.

 

[Kotedjuga]

John, Jeff,
Thanks for weighing in on this.

The door is definitely the main thing, but I've been looking at a $1500 - $1800 door with frame, so I wanted to make sure I have the walls figured out so I ordered the right depth (if I mess with the drywall I'll want to go with a deeper frame). I'm now thinking I will keep the existing frame, move to a solid-core door and add weather stripping and a sweep, which should get me well above 20 dB attenuation. (The other thing that happened in the past 24 hours was a reprieve on the SPL levels in the family room--it turns out my drumming isn't as annoying as I'd initially assumed. Basically anything I can do to make things a "little quieter" would be greatly appreciated--so getting down even to 53-55 dB in the family room is probably fine, which means I really only need to get the door up to 15 dB or so).

I'm pretty sure I already know the answer to this question, but I have to ask anyway--would continuous rigid fiberglass/Guillford panels covering the east wall do anything for abatement? I'm thinking of doing it for acoustics anyway, and thought it might help a little to damp transients.

Jeff, I was thinking of something similar to what you suggested for the windows, only with removable sealed plugs instead of shutters. The house has wood blinds in the windows, and in order to keep the look the same from outside I was planning on MDF plugs with gaskets that fit tightly in the frame on the inside of the blinds (so they wouldn't be visible from outside). On the interior face of the plugs, I was thinking of some sort of diffuser or absorber. If I do the east wall in rigid fiberglass, I'll definitely do diffusers on the windows and probably slats over a bass trap in the NW corner to keep things from getting too dead.

Thanks again! This really helps.

 

[Jeff_D]

There lots of different type of door seals out there. The stuff you find at the home centers will leave quite a bit to be desired... You'll want to shop the internet or find a local commercial door supplier. Here a few links to seals and drop bottoms...

http://www.ngpinc.com/pdf/catalog/2010 gasketing G29.pdf
http://www.ngpinc.com/product_view.cfm?nProduct_ID=596

http://www.ngpinc.com/product_view.cfm?nProduct_ID=757
http://www.ngpinc.com/pdf/catalog/2010 gasketing G31.pdf
Thats a little different than a regular door sweep. There is a little "button" on the hinge-side jamb- when the door closes, the sweep drops and makes a tight seal to the floor.

 

[Kotedjuga]

Jeff,
Thanks. The door the acoustician spec'd out had Zero hardware, which appears to be about the best out there (albeit spendy). I'd hoped to just use home center exterior weatherstripping and door sweep, but I'll stick with the Zero hardware, which when combined with a decent solid door should get me where I want to go.

 

[Kotedjuga]

John,
One other question: I didn't mention it, but maybe you assumed correctly that the room is carpeted. By "impact resistant flooring", do you mean pulling up the carpet and replacing it with a hard surface (Pergo or hardwood) over a pad? If so, I'm considering that, but thought I'd wait to see how the room sounds first.

Thanks again in advance.

 

[Jeff_D]

Jeff,
The door the acoustician spec'd out had Zero hardware

I missed that. Looks like the same ballpark as the NGP stuff I linked. The important thing IMO is to get an automatic drop bottom, not just a sweep thats gonna wear out, fall off, ect. Let us know how it goes!

 

[Kotedjuga]

Jeff,
I'll keep you posted.

Thanks again.

 

[Kotedjuga]

Thoughts on the 1" rigid fiberglass reducing SPLs?

What about the drum platforms? Do they work? If they do, can someone explain how? It makes sense that decoupling drums from the floor would reduce the floor amplification, but other than that?

 

[jhbrandt]

...What about the drum platforms? Do they work? If they do, can someone explain how? It makes sense that decoupling drums from the floor would reduce the floor amplification, but other than that?

compare the sound of a light, cheap home stereo speaker to even a small set of JBLs. The cheap speakers' cabinets resonate and make their own tones while the 'better', heavier speakers don't add anything of their own. Drum platforms (properly constructed) offer a similar difference in sound.

Cheers,
John

 

[Kotedjuga]

So in the case of a drum platform, adding mass and isolation to just part of the floor reduces the sympathetic vibrations of the entire floor? If that's the case, it may make my drum sound "better" (fewer colorations from the floor vibrations), and might reduce transmission to the garage below, but won't do much to reduce sound escaping through the walls and outside or to the family room. That makes sense. I was just having a hard time figuring out how putting drums on a platform would reduce SPL where I'm most concerned.

What about the rigid fiberglass on the wall? Just mid/high absorption, or will it help reduce transmission at all?

 

[Kotedjuga]

Ok so this is a $250 experiment in minimalist sound isolation. I've ordered a solid-core door with a Pemco automatic door bottom already installed. There will be tear drop gasketing in the corner of the jam, and hollow neoprene gasketing against the face. Using the existing well-sealed frame and hardware. Targeting >20 dB of attenuation. If I don't quit make it, the plan is to add mass to the inside of the door. If it still doesn't cut it, back to plan A and a steel-framed pre-hung sound door.

I'll post results when I get them.