Sub placement driving me crazy!

[kermyb123]

Attached is a VERY rude drawing of my room. The dimensions are: 14'6" X 11'2" X 7'. My surround speakers are at 90" from the front wall about 42" from the floor. Front speakers are on the wall where the screen is (Object in yellow).

Blue= Speaker
Yellow= Screen
White=Door
Red=Where I have tried to place sub
Dark area=Dramatic drop in LF sound

I think its just a poor design room LxWxH, however there is not much I can do about it at this point. The room is 5/8 drywall all around insulated floor is concrete with carpet. I have not run REW yet, I need to purchase a Mic/spl meter.

I can't move my seating area much since the speakers I'm using are Yamaha flush wall mounted speakers (t conserve room). I would have to move my surrounds which would be HARD to do - to say the least.

My first question is: could placing the sub higher (since I have plans to make a box built into a wall at 20cuft) produce any promising help?

Bass Traps? - Is this issue caused by standing waves? - I would say it is STRONGLY affecting fq from 80hz down to 20.

Any ideas would be great.

[brucek]

I have not run REW yet, I need to purchase a Mic/spl meter.

Fairly difficult to do anything until you accomplish this first....

My first question is: could placing the sub higher (since I have plans to make a box built into a wall at 20cuft) produce any promising help?

No, your dead zone would likely be caused by a length axial mode, and not from floor to ceiling (given the 7' distance). Want to prove it - stand up in the dead zone and listen - likely no appreciable change.

Traps don't affect that low as you suggest...

You simply need to move that listening position out of the dead center of the room....



brucek

[kermyb123]

Not my favorite answer... I was expecting it. Just to note I can hear slight differences based on seating height.

Would having two subs help or am i compounding the issue?

Thank you for your reply.

[Wayne A. Pflughaupt]

kermyb123 wrote:

Dark area=Dramatic drop in LF sound

I think its just a poor design room LxWxH, however there is not much I can do about it at this point.

It's not uncommon for "shoebox" rooms to exhibit this problem: Dead-center is a bass "dead zone" where the SPL level is noticibly reduced, and bass SPL increases the closer you move from that point to any boundary. You will be able to check it for yourself once you get your SPL meter, using a pink noise source. Not to mention, REW will be able to tell you where (physically) it's worse, and what frequencies are affected at what positions in the "dead zone."

Not sure what you can do about it. Seperated placement of a second might make a difference. At the very least, co-locating both subs, if they're substantial enough, should get you enough "woofage" to where bass sounds acceptable in the "dead zone" (assuming you're not happy with what your getting from the one sub).

Regards,
Wayne

[kermyb123]

Thank you Wayne,
I have been down in my room for the past hour or so playing with ideas and measuring. I have a relatively "good ear" for sound, obviously I can't tell a 2db difference between 36 and 38hz however it's quite amazing how much of my lower end is just gone - I won’t stretch to say in DB amounts but easily 85-90%.
The one thing that strikes me is at a "loud" volume bass notes (I'm using test tones at this point) are in magnitude outside of my room. I can truly hear the points where I can only assume the waves are peaking. This brings me to an idea: How well would a 4th order or even a ported box channeled into the room work. I believe I'm only about 1-2' off from being able to make things work. I have a staircase on the back of the rear wall that I could use the dead space under to create an enclosure. Is this heard of?
I would hate to move my sitting area since to make things work I would be just 5’ from the front wall! Moving back would place my surrounds at about 75-80 degrees, also unacceptable. All in all I would like to make this all work and in the same notion keep more of the bass in the room rather than having it reverb the walls and mirrors four feet across a hallway in another room.
Where can a person find a reasonable mic for REW? I already have a media center PC in the room to run the soft ware from with digital outs and ins…

[brucek]

Is this heard of?

Absolutely, you may join the SLLT (Structural Large Low Tuned) club. The requirement is that you have to be able to sit inside your sub.....

Where can a person find a reasonable mic for REW?

Read here for everything you'll require to set up REW and where to get it...

brucek

[kermyb123]

Ok I posted on that thread for further review... sounds like what I want/need - however still places the sound in the same location as it currently is - i was thinking I would be able to "fake" the waves into thinking the room was bigger almost "horning" the bass into the room.

PS whats the deal will 50% hate on RS spl meter and 50% like???

[brucek]

i was thinking I would be able to "fake" the waves into thinking the room was bigger almost "horning" the bass into the room.

No.............. you need to move the listening position.

whats the deal will 50% hate on RS spl meter and 50% like???

I don't really understand the question, but the Radio Shack meters are unreliable at higher frequencies and not to be used above about 3KHz due to variances in the response. They are fine for sub measurements though.

brucek

[kermyb123]

I think I have pandora's room of sound...

[kermyb123]

Folded horn?

[mrsollars]

if it makes you feel better...

when i posted my room diagram mock up....asking about speaker placement.......the first response was:

''are there any other rooms available?...in the basement?''

here's to having crummy rooms

[publius]

your room dimensions are almost exactly 1.0 : 1.5 : 2.0

having this multiple is so bad it was actually identified by toole in one of the harman papers as a "case study" of a room that is going to have problems.

you, then iced the cake by putting the seats right in the middle of the room. this is the worst possible place.

so, when you report that you have problems, it is no surprise.

your only option is to "get out the hammers and the saws" and fix the room. DIAPHRAGMATIC ABSORPTION. you will need to "soften up" the walls by adding one layer of acoustic barrier and then another layer or two of drywall. this will create walls that "vibrate" which will dramatically reduce nulls that you have at 50, 67, and 80hz (which is, of course, the critical range for bass!) good luck.


from toole's "loudspeakers and rooms working together":

2.3.2 DIAPHRAGMATIC or MEMBRANE ABSORPTION
The most common membrane absorbers we encounter are the walls, floors and ceilings in rooms. The proof that they are absorbers is that they vibrate in response to bass sounds; acoustical energy is converted into mechanical energy. As luck would have it, conventional home construction, gypsum board on 2” x 4” studs, is an effective low-frequency absorber - play some loud music and feel
the walls. Double-glazed windows are quite similar in their absorption properties, so we are off to a good start. The worst possible rooms are those built in basements, with concrete floor and walls. Such rooms need to have false walls built inside them. To improve on normal construction, I suggest two layers of gypsum board on some (not necessarily all) surfaces, possibly with a layer of 1/2-inch
“sound board” between (glue the three layers together, using nails or screws only to hold while the adhesive sets).
Concrete floors are a problem for two reasons. First, they don’t absorb sound. Second, because they don’t absorb sound, they don’t vibrate and supply the tactile sensation of bass through the soles of the feet. In these cases, a false floor is a useful addition. Oh yes, leather upholstered furniture is also a membrane absorber, and also provides vibratory sensations to stimulate the audience. H-m-mm.
Obviously, it is possible to construct customized absorbers to address problems at specific frequencies. Reference 16 has design aids for diaphragmatic absorbers (p.172). Remember to place them at high-pressure points for the mode that is being damped.

[kermyb123]

[kermyb123]

What would happen if a half wall was placed into the room 8' wide and 4' tall? Also will it help if there is more mass in the room - furniture ect? Carpet on the walls 3'?

[brucek]

kermyb123,

I'm moving this thread to the Acoustics sections where I think you'll get the benefit of more advice about the room. The REW section is more about the use of REW.

Hopefully the experts in Acoustics can help out..

brucek

[salvasol]

kermyb123 wrote:

I can't move my seating area much since the speakers I'm using are Yamaha flush wall mounted speakers (t conserve room). I would have to move my surrounds which would be HARD to do - to say the least.

Yes you can move your seats

I'm assuming that you have a 5.1, Right??? ... Is your receiver a 5.1 or 7.1???

If you have a 7.1 you can add a pair of back surround speakers, and seat between surrounds and back surrounds (not ideally, but you can try ).

If your receiver is a 5.1 ... maybe another pair of speaker in parallel??? ... Just my ideas

[kermyb123]

7.1 running as 5.1 right now - and thats not too bad of an idea - throws the whole 110degree thing off but not a bad idea...

[Blaser]

brucek wrote:

Absolutely, you may join the SLLT (Structural Large Low Tuned) club. The requirement is that you have to be able to sit inside your sub.....
brucek

[Blaser]

If your receiver is a 5.1 ... maybe another pair of speaker in parallel??? ... Just my ideas

Hi David,

What's the point in doing that?

[Blaser]

kermyb123 wrote:

What would happen if a half wall was placed into the room 8' wide and 4' tall? Also will it help if there is more mass in the room - furniture ect? Carpet on the walls 3'?

Hello,

I don't believe you have to do that to get some good bass. Assuming you have the necessary woofage, you should sit somwhere in the 2/3 back of the room, make some room treatment and use a BFD

[Blaser]

KB,

What sub do you have to begin with?

[kermyb123]

Ahmed - The RE 18 XXX going in to a VERY large ported box. SLLT of sorts internals will be about 23.5cuft after sub and port. Didn't you help run the numbers!?

[Blaser]

Oh yes I remember...But I mean did you already build it? Do you have it now firing in your room?

[kermyb123]

No im about 40% built... Im currently using a retail polk Pro600 to see where best to place my sub. Right now it seems like the back wall almost center will work best. As for seating I agree its either four feet from the screen or about 10 = the six in between are amazingly quiet. No kids yet but when our first comes that six feet may be the most quiet place in the house.

I have a Behringer EP2500 showing up tomorrow, fan for it the next day.

Half wall wont help???

[kermyb123]

PS... I like the idea of sitting in a sub!