Adjusting HT room dimensions

[Seismo]

Hi all,

My HT room has been semi completed for a long time, I mean one side wall is open while the other walls are finished. I decided that it was time that I complete this project. The room is in the basement and the size now is W= Open to one side, L = 18.3 ft and H = 94 inches to the floor joists ( 103 inches to the floor).The ceiling will be a drop ceiling (tiles). I will put sound proofing (Roxul) between the floor joists.

Now, if I want to adjust the dimensions for a ratio of 1.6 for the width and 2.33 for the length for example, I need to know exactly the height of the room. I am aiming at something like W= 12 ft, L= 17.5 ft and H= 7.5 ft. At the moment, the length is adjustable by about a foot and the width is fully adjustable.

Here is my question....in order to define the proper dimensions, the height is the key factor, so what height should be used here. Should I use the joist or the floor height?

Thanks for your response

 

[Ethan Winer]

Seismo,

> the size now is W= Open to one side, L = 18.3 ft and H = 94 inches to the floor joists ( 103 inches to the floor). <

The modal height is to the bottom of the floor above because that's the rigid boundary. So a width of 13 feet will be pretty good for those other fixed dimensions.

--Ethan

 

[mtrycrafts]

Seismo,

> the size now is W= Open to one side, L = 18.3 ft and H = 94 inches to the floor joists ( 103 inches to the floor). <

The modal height is to the bottom of the floor above because that's the rigid boundary. So a width of 13 feet will be pretty good for those other fixed dimensions.

--Ethan

I think he want to finish the ceiling as well with a dropped ceiling and is looking for that height?

 

[Seismo]

[QUOTE=mtrycrafts]I think he want to finish the ceiling as well with a dropped ceiling and is looking for that height? [/QUOTE]

That is correct.

The ceiling will be finish with a dropped ceiling and roxul between the joists.

The modal height is to the bottom of the floor above because that's the rigid boundary. So a width of 13 feet will be pretty good for those other fixed dimensions.

Just to be clear now, even with a dropped ceiling and roxul in the ceiling, the heigtht from the bottom of the top floor still prevails?

Thank you both

 

[mtrycrafts]

Just to be clear now, even with a dropped ceiling and roxul in the ceiling, the heigtht from the bottom of the top floor still prevails?

Thank you both

No. Now you have the dropped ceiling as your rigid boundary and you measure to it.

 

[Ethan Winer]

Seismo,

> Just to be clear now, even with a dropped ceiling and roxul in the ceiling, the heigtht from the bottom of the top floor still prevails? <

Yes. Assuming by "dropped ceiling" you mean a standard grid with ceiling tiles. Ceiling tiles are transparent to bass frequencies so they're irrelevant for mode calculations. Now, if you attach sheet rock (or plywood or MDF) under the joists, that would lower the modal height. But not ceiling tiles.

--Ethan

 

[Seismo]

I need more expert advice please,

I will be getting my Roxul sound proofing material this weekend and start the installation between the ceilling joists (6 inches thick). Now, a few questions come up to my mind. As I explained earlier I plan tu use a drop ceiling (white tiles painted black) and I understand that lower frequencies will tend to go through the sound proofing material, but what will be the effect at higher frequencies? Will the sound proofing material act as an absorber at higher frequencies? If so, would it be to much absortion? Should I install a drywall ceiling instead of a drop ceiling and then treat the first reflexion point with something like the OC 703?

Thanks for your help.

 

[Ethan Winer]

Seismo,

> white tiles painted black <

Be careful painting tiles because that blocks their pores and reduces absorption at mid and high frequencies. Acoustically, the best thing you can do is stuff the joist cavities with fiberglass as thick as possible. (Can you fit fiberglass one foot thick?) Then stretch porous fabric and staple it to the joist bottoms, and cover the staples with thin wood trim strips. This will give you bass trapping, and also mid/high frequency absorption that's better than any ceiling tiles.

--Ethan

 

[Seismo]

Seismo,

> white tiles painted black <

Be careful painting tiles because that blocks their pores and reduces absorption at mid and high frequencies. Acoustically, the best thing you can do is stuff the joist cavities with fiberglass as thick as possible. (Can you fit fiberglass one foot thick?) Then stretch porous fabric and staple it to the joist bottoms, and cover the staples with thin wood trim strips. This will give you bass trapping, and also mid/high frequency absorption that's better than any ceiling tiles.

--Ethan

Thank you Ethan,

Maybe I am on the wrong track here (please let me know). The Roxul Safe&Sound material that I want to use was in my mind only for soudproofing purposes. I realise that the sound proofing material absorbs mid and hi frequencies. That is why I was asking if drywall would be a better choice in order to control the room acoustic.
My original plan was to sound proof the ceiling plus one side wall (open side to the room at the moment) and the front wall (2x6 studs) where the speakers will be (laundry room on the other side of the original wall). Then use OC 703 fiberglass to build 24 inch wide bass traps in corners (using 2x6) and treat first reflexion points on side walls and ceiling using OC 703.

Thanks for any comments

 

[Ethan Winer]

Seismo,

> I realise that the sound proofing material absorbs mid and hi frequencies. That is why I was asking if drywall would be a better choice in order to control the room acoustic. <

I think you still have the wrong terminology. Sound proofing means preventing sound from getting in or out of a room. This is typically done with sheet rock, which does not absorb mids and highs very well. But it blocks well. Soft materials like fiberglass and mineral wool do a poor job of blocking sound, but they absorb well. The two goals - room treatment and sound isolation - are more or less mutually exclusive. What helps one hurts the other. So which do you want more? Of course you can have both, but it will make the ceiling lower.

--Ethan

 

[Seismo]

I think you still have the wrong terminology.
--Ethan[/QUOTE]
Sorry about that, now I realise my text was confusing because I overlooked to state a few elements, like stating that yes I want to do bo the sound proofing and acoustic treatment.

If you bare with me , I will get this right.

So now as you said, doing both soundproofing and acoustic treatment will lower the ceiling height (back to original thread question).

For sound proofing purposes only (kitchen is above the HT room), I am wondering if painted ceiling tiles would have the same characteristics as drywalls for blocking mid and high frequencies? What would you recommend, please.

Being a newbie with this stuff, I appreciate your patience.

 

[Ethan Winer]

Seismo,

> So now as you said, doing both soundproofing and acoustic treatment will lower the ceiling height <

Treatment doesn't have to lower the ceiling, if you put it between the joists.

> I am wondering if painted ceiling tiles would have the same characteristics as drywalls <

Probably not, even for mid and high frequencies. Sheet rock has the advantage of mass. But if you're willing to accept bass leaking through, and you don't want to lower the ceiling, then fiberglass between the joists, and no sheet rock, is probably a good way to go. With or without ceiling tiles.

--Ethan