I hope you don't mind me writing directly to you. I've been posting on Romy the
Cat's audio board about the pros and cons of a bass horn in my new Barn
Conversion. I'm probably not going to go ahead with it for various reasons. But
I was thinking of installing Bass Line arrays below 40hz against the short wall
of a 10m by 7m double height room with vaulted cieling. Probably 6 or 8
15" drivers in a sealed box per side. But - at this is the question, Romy
seems sure that Line arrays will only work properly when used on the long
dimension of the room. Is this correct? Intuitively I can't see why...
Your thoughts on this would be most welcome
they do work and can work extremely well. Probably the best authority on
the planet when it comes to bass, period, is Tom Danley. His first
commercial success was a product that had to fit in a Land Rover and call
elephants when it was first discovered that the communicated over great
distances in the 20 Hz region. It was the Packiderm 6 and was the
predecessor to the Intersonics ServoDrive subwoofers that came out in the late
70's. ( www.servodrive.com) Since then, he created the acoustic suspension
chamber that created perfect crystals on the space shuttle. It requires
175 dB SPL. He has been involved with two sound companies since
ServoDrive, Sound Physics Laboratories (SPL) and he currently designs product
for Danley Sound Labs (www.danleysoundlabs.com).
At Danley, his mid-high products are the best passive speakers in the
professional sound reinforcement industry, in my opinion. Let alone that
he makes the best subs in the industry. This link will give you an idea
of Tom's world:
Google-search Tom Danley and lab horn and see if you can dig
up the article where somebody built-in Tom's lab horn in a rather
large-scale (multiple drivers) application in a large room. It would be 2
-5 years old by now. It would be very similar to your application.
important than what wall they go on is what is the ratio of the room
dimensions. Regular room dimensions, like 10 X 20 X 40 aggravate isolated
room modes where the room literally rings at low frequencies (think
cathedrals). There are ratios recommended by acoustical consultants that
distribute modes to prevent this. However, if you are stuck with your
dimensions, then narrow-band notch filters can prevent your system from
exciting them. The trick is finding someone that can discern room ring
modes from localized standing waves (In England, my friend Peter Mapp comes to
mind). They are not the same and you must look at time vs.. frequency,
not frequency vs. dB to find them. >>
first mistake most make when doing a bass line array is stacking them
together. In order to act as a line source there are two requirements:>>
The array must be sufficiently long to provide the -3 dB/doubling of distance
for more level from less cabinets at a given distance.>>To
do this in your barn, I would suggest going from wall-to-wall across the short
wall. The reason for the short wall is two-fold: a) They will be aligned
with the mid-highs on the same wall without the need for a digital delay
to align them. b) If you go wall-to-wall, then the side walls, if massive
enough, will act as extended virtual sources, making the line array virtually
infinite. The more massive the side walls and the one behind the
speakers, the better. >>
The array elements must be within 1/2 wavelength of the highest frequency they
you are using 15" woofers, I would crossover into your mid-highs at
about 90 - 125 Hz. At 100 Hz, 1/2 wavelength is 1128/100 =
11.28 11.28/2 = 5.64 ft. = 1.7 meters So, at 7m, you could
put 5 cabinets across the front wall on the floor (a 1/4-space loading for 12
dB more output than in free space) with the first and last in opposite
corners. This is a proper line source at long wavelengths. If
you want more level, use pairs instead of single cabinets.
it were me, I wouldn't bother designing my own cabinets and selecting a driver
with the right parameters. Leave that to the home theater tweaks that
convince themselves that expensive AC cords make a difference. I'd use
something like Danley TH-115's for level or TH-112's or DTS-20's for extreme
His old company SPL also has a couple of models I'd consider, like the B-Deap32
for level or the Contra Bass for extreme lows (www.servodrive.com/products.html).
Sound Labs mid-highs array together very well too. But, in my opinion,
the best sounding non-arraying high-output mid-high sound-reinforcement
speakers in the industry are from a new company called KV2. They will
absolutely smoke products like JBL, EAW, and Meyer at half the price.
They are powered and they are as clean as studio monitors. I handle
them so I've heard them against all comers. I call them loud
Genelec's on a stick. They are as low in distortion as many good studio
monitors are and get stupid loud. KV2 has a distributor in elace>ngland. lace>See if you can
get a listen to them. For very loud boxes, you will love them. www.kv2audio.com/Products/index.php>>
John A. Murray
Your email is fascinating and hugely interesting. Thanks for
being so free with your expertise.
And thanks too for introducing me to Danly. The DTS-20 looks quite incredible.
Just might solve the problem at a stroke.
I just have one more question. If, as you suggest, I use the short wall in a
horizontal array (my side walls are 30 inches thick stone!) How do I deal with
stereo? One channel on top of the other? or mono in the middle and 2 either
side as stereo in a single array?
Also it seems to me that if I use both corners and the roof 'corner' (the barn
will be open to the rafters) below 40hz then that would constitute an array
too? And maybe load the room every well? Ok, I'm sorry that's 4 questions.
is no stereo for subwoofers because we cannot perceive stereo at extremely long
wavelengths. Our ears are 5 - 6 inches apart. Even from the side
the longest wavelength that will have even a 90-degree
phase difference (1/4 wavelength) relative to each ear is that
of a 564-Hz signal (6 inches = 1/2 ft. 1/2 ft. X 4 = 2 ft. 1128 ft./2 ft.
= 564 Hz). If the phase difference is less that 90 degrees, it becomes
more difficult to discern the directional location of the source. You
will say, "But I can localize where my subwoofer is when it's
playing, even with my eyes closed." Not without the short
wavelength components of harmonic distortion, you can't. Try playing a
very low distortion sub at a relatively low volume. Blindfold someone,
spin them and see if they can tell where the sub is....
answer to a short question, mono-sum your subs. That's why there's a 1 in
including the barn's "roof corner," as an array component, I
think you've missed something here. First, depending on your sub type,
use them up to 80 or 125 Hz as the manufacturer recommends. They are the
best component for that frequency range. Your mid-high box's LF speaker
will not do that range better than the subs, especially if it's at a high
volume. Second, a bass line source array would be a straight line of
sources on 1.7m centers. Sticking a sub in the roof would not be part of a
line array across the front wall at floor level. Since it is up high and
farther from most listeners, it would also begin to smear the bass in
time. However, you could put subs all over the place to even out
ringing room modes, but the bass would loose definition, tightness,
impact. This is a time smearing, distorted impulse response issue.
Just put them across the front wall and, if needed, have a good tech measure
and notch out any bothersome room ring modes with 1/6th- to 1/10th-octave
don't listen to any smoke-and-mirrors shaman that tells you rubbish
about narrow-band filters causing phase distortion. If the signal in the
room has a narrow (2-3 Hz wide) ring mode, it has a nasty phase shift that
mother nature packs along with it. The filter dampen the amplitude of the
ringing and improve the phase.
is what proper equalization does as well. If a speaker has a peaking
resonance, equalization removes the amplitude problem and cancels the peak's
phase shift with the opposite shift in phase. All IIR filters, be
they transducers or electronic filters, have a minimum-phase
component that is the amplitude's partner. All good speakers are
equalized because no transducer, as a fixed-diameter moving piston, has a flat
frequency response. Mother nature says no, despite what any company's marketing
department may want you to believe. In the home high-fi world, they just
put the EQ filtering components inside the speaker cabinet on the
crossover network board. That way "he who abhors EQ and all its
nasty phase shift" is blissfully ignorant.
for putting what I'm saying on that message board, go ahead. I haven't
had any hate mail for a while now.......
John A. Murray
everybody used to call me James in my past other-worldly life.