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Room Acoustics Forum by Rives Audio Welcome! Need support, you got it. Or share you ideas and experiences. |
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Room Acoustics Forum by Rives Audio Welcome! Need support, you got it. Or share you ideas and experiences. |
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In Reply to: I decided to build... posted by LimLim on September 9, 2003 at 02:36:20:
Thanks for your opinion. I decided to build listening room with 10.71' H x 15' W x 20.36' L dimension. I have Excel file that calculate listening position peaks and nulls, but I can't interprete it. Where is my optimal speaker placement (ProAc Response 3.8) and optimal listening position that minimize peaks and nulls? One more question, which do you think better for listening room, carpeted floor or solid wood floor with area rug? Thanks for your help.
RG:
I prefer flexible floors with thick carpet and padding so naturally
I have a concrete slab floor. With subwoofers flexible floors are prone to buzzing. While a concrete slab may set up a strong
floor-to-ceiling room mode, it won't makes any buzzing noises.Axial room mode analysis (me + $2 calculator & hopefully no mistakes)
565/20.36 ====== 27.75Hz.
565/15 ========= 37.66Hz
565/10.71 ====== 52.75Hz.
565/20.36 x 2 == 55.5Hz.
565/15 x 2 ===== 75.3Hz.
565/20.36 x 3 == 83.25Hz.All of these axial room mode center frequency estimates are
+/- a few dB's -- I only show them to two decimal points
so people think I know what I'm talking about!The only room modes that matter are the ones you hear.
Bass peaks are more annoying than nulls.
Partly because it's easier to overlook frequencies that are missing (nulls) versus frequencies that are too loud (peaks)
... and partly because peaks are broad and cover large
portion of the room, so it's almost impossible to move
your seat away from all of them.If you happen to be sitting in or near a null,
just moving your seat one or two feet will make a
big difference -- nulls are very narrow.Your room will have six axial room modes from about 28Hz. to 83Hz.
The first order side wall to side wall mode (37.66Hz.) is not likely to be excited (see below), as is typical with stereo speakers.That leaves three modes between 28Hz. and 83Hz.
It would be best if these remaining modes were evenly distributed between 28 and 83Hz.. Doing that would give your ears the best posssible starting point to apply their one-third octave smoothing effect. That effect helps make the bass peaks and troughs blend together somewhat, so hopefully no particular bass peak will stand out. The effect works well above 200Hz. where room modes are quite dense in almost all rooms ... but usually not so well under 100Hz.
in most rooms (except for very large rooms where there are more than 5 or 6 axial room modes between 30 and 80Hz.)Room mode center frequencies that are 10-15Hz. apart are a good target. If under 10Hz. apart, the two modes may combine to sound like one broad bass boom ... over 20Hz. apart and our ear's one-third octave mechanism can't smooth the bass frequency response well, so a bass frequency peak tends to stick out like a sore thumb.
Worst case would be two bass peaks at the same frequency (aka "stacked room modes").
Almost as bad are two bass peaks with center frequencies close together (aka "adjacent room modes") that combine to sound like one broad bass peak.
- Your 27.75Hz. room mode will be heard but may not be a problem:
The 27.75 room mode will cause a bass peak unless you sit at or near half way between the front and back walls (or place speakers there) which is a null for that mode. Fortunately a boost at 27.75 Hz, will rarely be excited by the music content, and even if excited, your speakers may be weak at 27.75 Hz. and need a boost!- Your 37.66Hz. room mode will not be excited by stereo L-R speakers:
Assuming you use left-right speakers and sit half way between the side walls: The 37.66Hz. room mode will not cause a bass peak because the two speakers will be out of polarity for that mode, so can't excite it. In addition, you would have your ears at or near a null for that mode, so you wouldn't hear a bass peak even if it was excited.- Your 52.75Hz. room mode will be excited -- here a flexible floor would be useful (to absorb more energy than a stiff floor):
The null for this floor-to-ceiling mode would be at 5.35 feet off the floor which will be well above your ears and your bass driver ... unless you are really tall or stand up when listening -- so you will hear some bass peak from this mode. It would be nice if your ceiling was higher and the center frequency of this mode was less than 20Hz. higher than your 27.75Hz. room mode.- Your 55.5Hz. room mode must be controlled by speaker/listener position because it's so close to the 52.75Hz. floor-to-ceiling mode:
This room mode has nulls at the 1/4 and 3/4 points between the front and back walls. Since the center frequency is so close to the
52.75Hz. floor to ceiling mode, if both room modes are excited you will have a loud boom from about 48 to 60Hz. ...
(welcome to my listening room before parametric EQ is applied to my subwoofer!).
If you can place your speakers about 5 feet from the front wall,
and sit about 5 feet from the back wall, this mode can be silenced.- Your 75.3Hz. room mode can be controlled by speaker placement:
The nulls for this mode are 1/4 and 3/4 of the way between the side walls. But 1/2 way between the side walls, where you are likely to sit, is a peak for this mode. So place your speakers about 3.75 feet from the side walls in or near the nulls to avoid exciting
these room modes.- Your 83.25Hz. room mode will be a problem:
Nulls will be at 1/8, 3/8, 5/8 and 7/8 of the distance between the front and back walls.
Peaks will be at 1/4, 1/2 and 3/4 of the distance between the front and back walls.Oh oh.
The 1/4 and 3/4 peaks for this 83.25Hz. third-order
front-to-back-wall room mode ... were nulls for the
55.5Hz. second-order front-to-back-wall room mode.
So now you have to give up and buy a parametric EQ.
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Not so fast your 10.71' height and 20.36' length are too close to being multiples - Richard BassNut Greene 12:44:48 09/09/03 (4)
- So..., what is the better Length and Height? - LimLim 19:31:57 09/09/03 (3)
- Sorry, I think 16 feet Width - LimLim 19:41:28 09/09/03 (2)
- Golden ratio of 1.62 x 1.0 x 0.62 ... = 26' by 16' by 10' - Richard BassNut Greene 13:58:50 09/10/03 (1)
- The space not allow 26', too long. - LimLim 04:32:57 09/11/03 (0)
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