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In Reply to: RE: Building a room for my Magnepans posted by TwoTurntables on February 08, 2015 at 17:05:14
Lots of useful comments here. I have a dedicated basement room so have some practical experience with this. Here are some observations for your room. But let's start with what Floyd E. Toole says, 'There is no uniquely good set of room dimensions'. I think your room is fine so far; set-up will be the key.
- Room Modes & Dimensions: The room width of 13.1 is only problematic if you want to use subwoofers (they'd best be placed to the outside of the Maggies unless you're going to use DSP room EQ). The other dimensions are ok - remember, when we're talking about room dimensions, we're talking about bass. You don't mention any openings in the wall, but hopefully they're not near either of the speakers and the room is symmetrical. Your room modes are reasonably spread out so good e.g.:
Long wall: 25, 50, 76Hz
Sides wall: 43, 86 7 130Hz
Floor/Ceiling: 63, 126, 188 Hz
Dipoles excite a strong longitudinal mode between front and rear walls but side-to-side and floor-to-ceiling modes only weakly. You should not have any major problems with room modes if the speakers are placed correctly.
- Speaker Placement: Absolutely DON'T use the long wall! Your room's not wide enough. The speakers need to be a minimum of 68" from the front wall for a minimum delay of 10ms for the back wave following the front. Less than that distance and you'll loose both soundstage depth and articulation. Best place starting point for non-resonant for bass playback could be about one-quarter each of the room dimensions, e.g. one-quarter the room length off the front or back wall.
- Diffraction /Diffusion: Untreated cinderblock basement walls result in significant slap echo; however, with treatment of first reflections and modest treatment of the front wall, you could save yourself needing any drywall. A lot of the choice of absorption vs. diffusion is personal preference. Most people prefer a mix. I like diffusion and minimal absorption on the front wall and absorption on sides and thick panels in corners and the back wall. That doesn't mean you will. Absorption directly behind the listener seat is mandatory.
Seating location: Due to room modes, optimal dipole location may be where the speaker distance to front wall equals the listened distance to back wall. Your seating position is going to be several feet of the back wall given the size of your room. I can't tell where exactly as it'll be what sounds best to you and you may prefer a more near-field or reverberant sound than I do.
- Carpeting: Carpeting is ok but be very careful of padding underlayment. I wouldn't use any as it may overdamp the room. I had to rip mine up and reinstall the carpet. Dipoles have limited floor ceiling bounce. I don't need to treat the ceiling at all.
Buy a laser distance measurement meter for exact set up. Makes a big difference and cost effective. I'd also get REW software (free) or something similar for room measurements.
Great sources for set-up are:
http://www.linkwitzlab.com/rooms.htm
http://www.asc-home-theater.com/ht-acoustics-vol3.pdf (more useful for subs)
http://www.genesisloudspeakers.com/ownersmanuals/G2.2_Owners_Manual_v2.pdf
Jim Smith Get Better Sound is useful for set-up. If you want to really understand everything about room acoustics, buy the Bible, Floyd E. Toole's "Sound Reproduction". Of course some people would rather listen to music ;)....
Have fun and post some pics when you're done! Barry
Follow Ups:
concise and right!Diffusion is your friend - added Dynamics - even frequency response.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
Edits: 02/12/15
I hate it when someone who knows what they are talking about adds a post as to my unenlightened dribblings :). Listen to Barry!!
She's pretty convinced I don't know much of anything!
I got the "Sound Reproduction" Floyd E. Toole book for Christmas. 535 pages with some really fascinating stuff and lots of pictures. It's also great for dampening unwanted vibrations from audio equipment if you can't get around to reading it.
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