Floor Bracing

[admin]

There was some conversation about the effect of floor bracing for listening rooms and I thought I would make a dedicated post about here to continue the discussion.

I have a relatively large (approximately 550 sq ft) listening room that I built over an open two-car garage. There was a lot of vibration of the floor especially when people were walking in the room. I wanted to brace the floor to cut down on this vibration which I am sure also had an effect on the acoustics of the room. I built a support beam crossing the middle of the garage and secured it with a metal pole secured into the cement floor of the garage. Technically, it's a 3 vertical beam support as there is another beam on the left wall and then a near end beam on the right (as viewed in the picture below). It's hard to see in the picture as the garage doors are blocking the view at the cieling attachment but basically it's constructed of a 2x6 running along the cieling with three 2x10's sandwhiched together on their long end and supported by the vertical beams. You can see this a bit on the extreme left side of the picture. It's rather massive and adds to the dampening effect.

It has cut down on the vibration of the flooring and feels much more solid when you simply walk into the room.

20200926_093020r.jpg (264.63 KiB) Viewed 7838 times

[AnotherJohnson]

It looks like a great solution for your vibration problem. You are correct In assuming that this impacts the low frequency acoustics in the room too.

The two car garage at the house where I had my problem is not wide enough to implement this solution.

I am thinking steel I beam supported at each end. I may go and measure the span today.

[admin]

If you go with a steel horizontal beam, the possibilities are endless. The downside is that it's a lot more expensive and the install gets more difficult.

If you decide to do this yourself, it's definitely more than a 1 man project. The most important thing to do is to make sure you stress the cross beam against the ceiling so that it's giving some counter pressure. You don't want the cross beam to not put any pressure against the ceiling as that will allow the above floor to continue to move. You want to jack up the beam really tight against the ceiling prior to putting in the final vertical beams. You need something called a "jack post". It will allow you to really get it nice and tight.

[AnotherJohnson]

An L would be lighter than an I.

It is definitely more than a one man job.

The usual method is to let a person in the room above monitor the movement of the floor. The goal, of course, is to take up the sag and change the boundary conditions.

I’m going to take a look later today.

[admin]

Very good. Let us know what you decide. I have to say that it was definitely one of the bigger "accoustic treatments" that I did to the listening room in terms of noticable outcomes.

[AnotherJohnson]

The span in the garage is 19’ 2”. The bedroom I’d mentioned is not over the garage, but behind it.

I think maybe a center support might be possible.

With a center support, I could make a suitable beam from a pair of 2 or 3 bundled 10’ long 2x10s.

Then, with addition of an HVAC zone, I could seriously consider moving the main system to this house as was the original plan.

I probably would not have thought of the addition of a support without admin’s encouragement, so ... thanks!

[admin]

If you use 2x10's then it makes the job a lot easier. You still need 2 people but you don't have to hire professionals. You also need two ladders. One person can do all lifting and the other just kindsof holds things so they don't fall over. This is how I did it. Very doable with two amatuers and regular hardware store equipment.

[AnotherJohnson]

I ended up selling a house in Nashville, buying another house near the house with the room over the garage, and moving my older son into that house.

We’ve moved to the new one, all on one level.

Thursday we break ground on an addition for the one story.

The addition will include a 16’x34’, 10’ ceiling, room where I will be setting up a single main system. That room will be on a slab. The total addition includes a new Master Suite on a crawl space matched to the rest of the house, with large storage area, and garage on the slab.

I would have liked 20’x34’ for the listening room, but this will work ... I needed to compromise to accommodate the Master and garage.

I’m going with 2x6 R19 for both interior and outside walls for noise reduction. R38 for overhead of all.

The back third of the listening room will be set up for lutherie, gunsmithing, photo and video editing, and other clean work.

Cant wait to get done ... probably 90 days. More as it unfolds.

[admin]

How exciting! Sounds like it will make for a great listening room/shared space. That is about the same overall size as my listening room, although mine is more squarish vs rectangle. There are always limitations in one form or another but I think most people would feel that +500 sq ft for a listening room is generous.

If you are looking for maximum sound insulation between the room and the outside, the best thing you can do is double frame so that the sheet rock of the listening room is not directly fixed to the same wood frame of the other side's sheetrock. Exterior walls don't matter but if you are worried about disturbing others in the house while listening to music (or vice versa), then that is the best approach. Breaking a direct connection for sound conduction will be superior than insulation materials.

You should take some pictures so we can see how the progress is going. I did that somewhat with my listening room build but I wish I had taken a lot more shots during the build process. I kind of have before and after, but not so much the middle work phase. Keep us updated on the progress.

[AnotherJohnson]

Yes, staggered stud construction provides the least transmission through the structure. Heavier drywall sheets are also a good idea. Most transmission here will probably be through the common new HVAC system, so I’m working on that. Adding the master suite to upgrade from the existing master suite on the other end of the house did force some compromises. I would make the whole thing larger were it not for the footprint issues with setbacks and the need to avoid encroaching on the septic field.

[AnotherJohnson]

2x6 R19 will provide a lot better isolation from outside noise too, so that is why I’m going with 2x6 for all walls. It should be quite solid, and decently quiet.

In my present main system in another city, I’ve got ambient noise levels in the neighborhood of 30 dB. I’d like to try to get close to that for the new space.

[admin]

I also recommend the 2x6 being far superior to 2x4. My home is built 2x6 and I think it makes a big difference in cutting external noise, better insulation, and just general stability to the structure. I'm sure it will be great when it's all finished.

What are you planning to do with the flooring? I find that has a pretty significant influence on the overall sound.

[AnotherJohnson]

Haven’t decided. Probably one of the modern LVP products with appropriately placed area rugs. It has worked well in other rooms I’ve set up. I am not a fan of wall to wall carpet ... and hard surfaces without good rugs can be too reverberant.

I think this room will be too small for CLX Arts.

My goal is always to try to control the reverberant field while enhancing the direct field. My speakers will be 4’ from side walls and 5’ to 6’ from the front wall.

I’ll experiment, but I’ve used these dimensions before with success.

[admin]

Haven’t decided. Probably one of the modern LVP products with appropriately placed area rugs. It has worked well in other rooms I’ve set up. I am not a fan of wall to wall carpet ... and hard surfaces without good rugs can be too reverberant.

I think whatever you go with will be fine. With the use of carpets (and acoustic treatments) placed in the proper positions, I have never found a situation where reverberations and echoes couldn't be well controlled.

I think this room will be too small for CLX Arts.

Don't let Roberto see that you wrote that! I believe he has them in a much smaller room and reports really good outcomes.

My goal is always to try to control the reverberant field while enhancing the direct field. My speakers will be 4’ from side walls and 5’ to 6’ from the front wall.

If you do decide to go with planar speakers, I think they are a little more easy to control reverberations as the sound wave is more more narrow field compared to traditional cone and woofer speakers. You can then put acoustic dampening right behind the panel and that will dampen down 50% of the sound wave dramatically. Likewise, there is considerably less sound wave hitting the walls on those first reflection points on the front end as well.

[AnotherJohnson]

If you do that, you may like it. But I do not. One of the huge advantages of the dipole design is that you get the reflection off the back wall just slightly out of phase, and it leads to a greater sense of realism and presence.

[admin]

Well, it can certainly be over done. I'm not suggesting using so much dampening to eliminate the backwave completely. I was referring to the problem of having too much reverberation or echo in the room. You may not need any acoustic treatment. Especially because your room is large. I was just saying that if you do find the room producing echoes, dampening the front wall would probably be my first course of action. I would start with zero acoustic treatments and then only work up from there if you need to.

[AnotherJohnson]

Yes, speaker placement and room treatment are arts.

I remember in 1973 when I first discovered Egan’s work in architectural acoustics. And then Sabines.

I studied with Allan D.Pierce, later to write the now classic text

https://www.amazon.com/Acoustics-Introd ... 0883186128

I did my MS under Pierce and then returned to industry working as engineering specialist for noise control and vibrations at Kodak (now long gone).

As a professor, I had laboratories and budgets that allowed a lot of fun. I had one of the first FFT machines (from B&K) in the US. Early in my career, 40+ years ago, I schlepped microphones, data recorders, tape recorders, filter sets SLMs, etc, all over the country. It was worse than being a photographer.

This room will evolve. I am always going for a sense of realism. I can tell good from bad fairly quickly as a rule.

I am a sucker for gadgets, like anthem room correction. But in the end, I usually cut them off and follow my own ears and instinct.

I’ve had producers, recording, and mastering engineers relax with systems I’ve set up... and the comment “it’s like the master tape” has been shared. Harry Pearson and Harry Weisfeld always shot for this too.

I’m always a bit suspicious since I’ve been in studios and watched mastering. Live is different than master. But it doesn’t matter.

I do believe that what sounds good for you - is good for you.

But as you observed first hand when I goaded you into the Arts, things can nearly always get better.

[AnotherJohnson]

Cant wait to get done ... probably 90 days. More as it unfolds.

Anyone involved in construction this year will recognize the folly of this hope last January.

On the bright side, contrary to many projects, ours has moved forward at a tolerable speed. Just the trusses alone were late by a month. Materials costs have been a constant variable. Scheduling the trades has been a challenge.

We are now waiting for the Inspector to sign off on the plumbing rough in before we can drywall, insulate, and drywall.

The HVAC noise issue was dealt with by going with two distinct systems with no common duct work.

We will use the old standard rock wool for the insulation between the workshop/listening room and the master.

I think that we could still be 90 days away from finishing … this has been a crazy year for construction.

[admin]

Hang in there. As you mentioned, construction has been very difficult this past year. Wood prices have gone crazy and it's still difficult to find the materials in ample supply. At least you are getting close and can see the light at the end of the tunnel!

[AnotherJohnson]

Hang in there. As you mentioned, construction has been very difficult this past year. Wood prices have gone crazy and it's still difficult to find the materials in ample supply. At least you are getting close and can see the light at the end of the tunnel!

A tale from my lumber yards:

My contractor got into some cash flow issues due to crazy material prices and delays that set back draws.

So to keep things moving, I bought lumber directly from two yards myself. There’s nearly 2000 ft2 of floor space, framed in 2x6 in this addition, with 10 ft ceilings. So although it’s not as much as a big house, it is “house” sized.

The total bill for the lumber was about $7500. Add about 120 sheets of OSB, and that was another $3600. Add 22 46’ long trusses, and that’s another $11,000 including labor and delivery, so probably really only another $3000 of wood, maybe less. So … probably less than $15k for wood products.

I keep reading about lumber creating $30k increases in material cost to average houses.

It makes no sense. A lot of it is flat out gouging by contractors. OSB has been reported to be $60/sheet, but a little shopping found it for $30/sheet in bundles.

Assorted lengths of 2x6s were all priced maybe 20% higher than I remembered, but none were shockers. 16’ 2x12s we’re high, but we only needed about 20 of them because only the master suite is over a crawl space. The rest is on a monolithic slab.

All in all, my sense is that builders are taking advantage of panic and the fear of hyperinflation.

On a different project at the same house, I was having a heavy glass sliding shower door installed. I got a bid and sat on it for a month. When I said I was ready, they wanted to jack up the bid. I said no. A week later they agreed to do it for the original bid … so a bit of pushback might be useful.