Worst drum room ever?

[JasonMorris]

Hey guys.
This project has not died yet!
I have actually gotten to a place where the room is pretty much sealed up. Doors are on and I can start testing to see how well I have done in the isolation dept.

I am already a little worried about the amount of low-frequency rumble I am hearing out of the silencer box I have built.
When the HVAC is running I can just barely hear very low rumble, and after hunting around with my SPL meter, it does seem to be coming from my silencer.

I built two silencers, one for the inner and one for the outer leaf. They are connected with what I think is 3/4" thick sorbothane rubber.
They each have 4 or 5 baffles in them, and the boxes themselves are built out of 2 layers of 5/8 MDF, and lined with 1" John Manville duct liner.

I have uploaded a couple of images of one of the silencers as it was being built. The second layer of MDF is not applied in the photo.
Also is a photo of how that silencer was mounted. Not sure if those will help or not.

I DID upload a video. I know you guys like files to be directly uploaded to the thread, but it was just too large, and sometimes its easier to explain what one is dealing with via video.

https://www.youtube.com/watch?v=V7nmlNk5H7k

Any advice would be appreciated!


edit: after uploading the photos I realized that the silencer being built is the one on the OUTER leaf, while the one mounted is the INNER leaf silencer.
THey were both built in the same way, and just had their Ins/Outs in different places.

[Waka]

HI Jason,

I don't think I've spoken to you before. So "Hi!".

It's very difficult to see what's going on in the video I'm afraid. I think I kind of understand how you've built them, but I'm not certain.

The silencers: what dimensions did you make the cross sectional path in your silencers? They look quite narrow and a bit shallow also, although that could be the angle of the picture.
Silencers generally want to add a change of cross sectional area of at least twice the duct cross section, and ideally make this change twice (or more). This is usually achieved by increasing the cross section in the box, then decreasing (or increasing again) between the inner and outer leaf silencer, before returning to the double cross section within the other silencer and adding a large diffuser/grille on the inside of the room.

It could be that the velocity is too high in the silencers.

You mention that they are attached with sorbothane. How does that work with the one mounted vertically on a wall? If you screwed through the sorbothane then you create a flanking path directly to the stud work and this will probably produce more vibration then just screwing nice and securely into the studs. Also did you compress the sorbothane the recommended 20%? If it's under compressed it will often actually make vibration worse. Putting too much sorbothane is a common way of undercompressing it (the sorbothane has too little pressure on it per inch and the box just sits on top of it with almost no compression.)

Also, how are the silencer's ducted together? Is there a flexible duct that joins the two, or is there rigid ducting? If you used rigid ducting how did you decouple the two silencers?

Dan

[JasonMorris]

Hey Dan, thanks for taking the time to comment! I appreciate it!

The silencers: what dimensions did you make the cross sectional path in your silencers?

Honestly, I don't recall. :/ I know that the cross section started out larger than the cross section of the flex duct feeding it, and each baffle was placed a little further apart, so that the cross section expanded.

It could be that the velocity is too high in the silencers.

I don't even have the silencers pushing any airflow yet. The rumbling I am hearing is not from the Fantech ventilation unit I have.. The rumbling is from the AC/Blower that is conditioning the REST of the house. That low frequency noise seems to be transferring into the my drum room.

When the AC is running in the house, the ambient noise in my drum room is between 56 and 58db. (spl meter is set to c weighted, slow) I can just BARELY hear a low rumbling noise, and sticking my ear to the silencer box vent, it does seem to be emanating from there. Of course this is such a low frequency and it is so quiet that maybe im imagining things.

You mention that they are attached with sorbothane

I meant that the silencers were connected to one another with sorbothane. It's acting as a duct between the two silencers, passing between the leaves.

The wall mounted silencer is actually screwed to the concrete basement wall and is not actually touching the inner leaf.
That OTHER silencer.. The one on the "outter leaf".. well. That one is just sitting on top of the joists, and I fear is picking up vibrations they are rumbling thru into my room.

Also did you compress the sorbothane the recommended 20%

This comment has me a little worried as well. I am wondering if I was sent the wrong stuff. .. just checked my order history.
YEP! I bought Neoprene, not Sorbothane.
This is what I used to connect the silencers:

https://www.amazon.com/gp/product/B01CT ... UTF8&psc=1

[Waka]

The rumbling is from the AC/Blower that is conditioning the REST of the house. That low frequency noise seems to be transferring into the my drum room.

This is disconcerting. It seems your silencers are not really silencing! Have a measure with your sound level meter in other areas of the house when it is quiet, with the AC on. Is it as loud?

When the AC is running in the house, the ambient noise in my drum room is between 56 and 58db. (spl meter is set to c weighted, slow) I can just BARELY hear a low rumbling noise, and sticking my ear to the silencer box vent, it does seem to be emanating from there

You seem to have reaaally loud AC what do you measure in the rest of the house when it is quiet but with the AC Blower on?

If it's less than in the isolated room, then the only thing I can think of is vibration. Both sleeves need to be either very securely mounted, or resting on an absorbant material (eg. neoprene/sorbothane)

one on the "outter leaf".. well. That one is just sitting on top of the joists, and I fear is picking up vibrations they are rumbling thru into my room.

This could possibly be the issue. You could screw some angle brackets to the outside of your silencer and screw them securely into the joists, then see if the situation improves.

Is it just your AC you hear, at that specific frequency? Or does loud music being played in the studio also pass through your silencers without hindrance?

I meant that the silencers were connected to one another with sorbothane. It's acting as a duct between the two silencers, passing between the leaves.

I'm struggling to picture this, can you do a quick sketch or something to describe what you mean. Do you mean that each silencer has a rigid sleeve padding through the appropriate leaf, and within the cavity the two sleeves/boxes nearly meet, and there is some neoprene between the boxes?

Dan

[JasonMorris]

It seems your silencers are not really silencing!

After poking around in there for a while, I . have changed my mind..
I don't think it is the silencer per say. I stuffed the vent of the silencer with mineral wool and placed a 3/4" piece of MDF over it and there was NO difference in the level of low end rumble heard in the room.

I'm wondering if its just coming from the HVAC ducts running thru the floor joists.
Its such low end it seems to be coming from everywhere. its really hard to pinpoint the source.

You seem to have reaaally loud AC what do you measure in the rest of the house when it is quiet but with the AC Blower on?

Yeah I am wondering if am doing something wrong with my measurements or if my SPL meter is not functioning correctly.
I should have the SPL meter set to C weighting, SLOW, right? A weighting certanly LOOKS better, but I think thats because its not really looking at frequencies below 250hz?

what do you measure in the rest of the house when it is quiet but with the AC Blower on?

I will take measurements from around the house and try to be a bit more methodical in my testing methods and I will post back here after I have better numbers.

If it's less than in the isolated room, then the only thing I can think of is vibration.

I know its not LESS than in the isolated room, but the isolated room is only a few DB less. But my isolation must only be really poor in the really low end of the frequency spectrum becuase my family has said that the drums are dramatically quieter played in there. Quiet enough that they could watch TV or sleep while I drum.
In the end, thats what I wanted, but my quest was for good low end isolation, and that stupid SPL meter is saying I didnt do it well enough!

You could screw some angle brackets to the outside of your silencer and screw them securely into the joists

I will have to double check with the guy that helped me build and install these things but I think we DID use angle brackets to secure them to the joists.
I wonder if packing some insulation around the outside of the silencer would help?

Is it just your AC you hear, at that specific frequency?

There is just a low-end rumble heard throughout the room. Otherwise, the room is dead silent. When the AC kicks off, Im pretty sure I can hear my hair growing.

Or does loud music being played in the studio also pass through your silencers without hindrance?

When I play loud music in the other room (like 95db) and I check the SPL in my drum room, it looks like I am getting about 35DB of isolation.
The music is barely audible, and only the low end of the music is heard thru the doors. I don't hear the music thru the silencer.

Do you mean that each silencer has a rigid sleeve padding through the appropriate leaf, and within the cavity the two sleeves/boxes nearly meet, and there is some neoprene between the boxes?

I think so. I basically stole Bigby's design. (http://johnlsayers.com/phpBB2/viewtopic.php?f=2&t=15430)

Attached are photos of the couplers HE built to pass thru the wall, joining the two silencers.
I did the same thing (but wasnt smart enough to take pictures, becuase what could possibly go wrong?)

[JasonMorris]

So it looks like my AC unit (which is old as dirt) IS pretty ridiculously loud.
attached is a pic of what I am seeing from the SPL meter at the AC unit.. spoiler alert its 106db

also attached is a screenshot of AudioTools RTA app and what it is seeing inside the studio.. Im sure its not super accurate considering its going thru the iPhone mic.
but maybe still helpful?

[Waka]

That is unfortunately loud! You might be getting fine isolation in general, it's just so loud. Have a measure of ambient levels without the AC, inside the drum room and outside, and various locations around the house, then turn on the AC unit and take those measurements again. Subtract AC off from AC on measurements, this will tell you how much noise it produces in the house and how much isolation you're actually getting at the AC frequencies in your room.

There might not be alot you can do about it though, aside from replacing the AC for a quieter unit.

It's probably worth measuring your isolation in the room in general to though. Play loud music in the room, measure in the room and then outside the room with the doors closed. Subtract outside from inside measurements. That will give you the isolation values.

Dan

[JasonMorris]

Hey Dan,

Yeah, I never realized just how loud that unit is! It is slated for replacement next summer, so I may just have to live with it till then.
If you put your hand on the outside wall of our walk-out basement you can feel it vibrating. Im guessing that line coming into the mechanical room is vibrating a ton.

I did a quick test by putting a monitor in the drum room and running some sine waves thru it at various frequencies and checking the isolation from 3 feet back from the door.
I tried to hit about 100db IN the drum room, and I was getting 53-56 away from the door, which is actually the noise floor in the house when that AC unit is running!

These numbers persisted until I got down to about 30HZ. Then I was at about 90 or so in the drum room and a little over 70 just outside the door.

I'm not sure what I should expect to get at frequencies that low? In the end, the wife is happy, and I think I will be happy once I replace that loud AC unit.

[JasonMorris]

OK, new question.
I currently have the silencers for the exhaust side installed, with one silencer for each "leaf".
I am getting ready to cut a hole in my wall to install the silencers for the supply side to bring in fresh air (im using a Fantech ERV)
I have easy access to both leaves, and I am planning to have each silencer on the "outside" of each leaf rather than between the leaves.

My question is concerning the silencer mounted on the INSIDE of the room when the walls were built "inside-out"
I cant put the silencer flush against the sheathing, as the studs are in the way.
Can I just secure the silencer to the studs of the inside-out wall and have a longer "duct" penetrate the sheathing to connect to the silencer on the other side?
And when I say duct in this case I mean a duct built out of multiple layers of plywood or 2x material connected with neoprene. Im not talking about flex duct.

Thanks!

Jason

[JasonMorris]

OK, so my last question was kinda dumb.
There isn't really anywhere to attach the silencer to other than the 2x framing of the inside out wall, so that's obviously what I am going to do.

As I start zeroing in on the end of this build, I am kinda jumping around from one task to the next, trying to busy myself with the things I can do on my own while I wait for my buddy to have time to help me out with some of the things that I need assistance with.

One of the things I have been working on is acoustical treatment. I have taken a LOT of inspiration from Bigby's live room build, and also I have picked up a lot from reading Stuart's posts on treating small rooms.

right now I have lined darn near every surface except the floor with Owens Corning Fire and Sound.. it has pretty much the same specs as Safe N Sound.
I have also built bass traps in every corner, vertically and horizontally.

As one would expect, the decay time of the high end is pretty much nil.

Stuart mentioned 6 mil plastic stapled across the walls and bass traps to reflect frequencies above 1K.

What I am uncertain of is how MUCH of these absorbent surfaces should be covered in plastic.
I know my longest wall, which will be in FRONT of the drum kit is going to be a slat wall, so no plastic there.
Do I cover the ceiling in plastic if my ceiling height is just over 8 ft? OR will that just create nasty reflections between the floor and ceiling?
Should I cover three walls to the left, right, and behind the kit with plastic? Some of them? None of them?
I'm feeling like I can get away with covering all of the corner bass traps in plastic?

[JasonMorris]

I dont know if anyone is interested, or if this is even useful...
But here is a REW file from a measurement taken as of today (jul 31).
This is after all of the corner traps are installed, but BEFORE the slats are placed on the walls.

If I am reading it right (which is doubtful) it looks decent, but the waterfall bears out what my ears are hearing which is that this room is certifiably undeniably DEAD DEAD DEAD.


I think tomorrow I will just start stapling 6mil plastic up over the traps and see if it brings any life back into the room.,.

[Soundman2020]

I haven't lost interest in your room, Jason! Still following your thread. But I'm just recovering from some minor surgery, and not really up to much analyzing and suggesting, for the next couple of days.

- Stuart -

[JasonMorris]

No worries at all Stuart! Life will be busy for me for a week or so with a vacation anyway!
I hope your surgery was nothing serious and I hope you mend quickly!

[JasonMorris]

Hey Stuart! Hope you are healed up nicely after your surgery.
I am back from vacation, and bumping my thread as I am anxious to start working on it again.

I have my small drum room (booth) built and some basic acoustic treatment in place.
I have Rockwool in the bays of all my inside-out walls & ceiling, and corner traps in the vertical and horizontal corners.

I posted a REW file a couple posts back, and things should not have changed much since then. Since that time all I did was put down some luxury vinyl on the floor.

I have taken a lot of inspiration from Bigby's garage studio, as our room size was similar.

I referred to this a lot during my build: http://johnlsayers.com/phpBB2/viewtopic.php?f=2&t=15430

I framed the longest wall, which is at the far side of the room to be angled, and the depth provides for about 8" to 3 1/2" of mineral wool.

I THINK my plan for that wall is to do 1x10 slats spaced 1/6th of an inch apart.
If I understand that hemoltz calculators correctly (which is unlikely!) that should give me between 67hz and 109hz traps?

I am not planning to put slats up on the other three walls. Just Mineral wool covered by fabric with a little bit of wood as trim at the bottom, around the electrical outlets and maybe a strip here or there to protect the cloth.

One question I have is: I have read differing opinions regarding whether it’s a good idea to put plastic up over the mineral wool in a room this small.

The room is roughly 10’ 4” x 13 x 8’2“ before the treatment.

I read that I can put 6mil plastic over my mineral wool to reflect back frequencies above 1K to improve the decay time of the high end, and help alleviate some of the “deadness”

But I also read it might not be a great idea to have high frequencies reflecting back into my mics.

I know it’s a small room, and I cant get the universe to rewrite the laws of physics for me. But I would like to do what I can within the bounds of those physics to makes things “less dead”.
But maybe “dead” is best in my situation. Just looking for some consensus, I guess.

Anyway, thanks in advance for any advice you (or anyone else reading this) can offer.

Jason

[Gregwor]

You could use polys to bring life back into the room and avoid the crazy reflections that come from flat surfaces on your walls.

Greg