Speaker Design
and DJ's Part III of III
by
Larry Mundy
May 2004
The following
article by Larry Mundy will appear in a forthcoming book on the
design and construction of pro-audio cabinets. Larry Mundy retains
ownership of this article and it is republished here with his
permission.
[Editor's Note:
At one time or another, "distortion," "clipping,"
and "blown speaker" are words you will hear in almost
every DJ booth. A fundamental understanding of speaker design
may improve the quality of your sound and ability to move a crowd,
while avoiding system problems. This month's tip is the final
of three parts on speaker design by Larry Mundy.]
Better Sound
From Your Speakers
The March tip on this site dealt
with replacing speaker drivers in your existing cabinets. This
is a follow-up note on some other things you can do while your
cabinets are partially disassembled.
A lot of speaker
manufacturers catering to the DJ market take advantage of consumers'
unfamiliarity with what goes into a good-performing speaker cabinet.
They assume you will make a purchase decision based on the size
and number of drivers in the cabinet, the (often inflated) power
rating, and various external appearance features that have little
to do with the actual sound a speaker produces. And, the manufacturer
has several advantages over the consumer. It knows that there
are enough different power-handling rating systems that it can
"fudge" the specs in a variety of perfectly legal ways.
But more critically, it knows that even in a dealer's sound room,
you can't see what's inside the box or where corners may have
been cut. A great deal of the cost of a DJ speaker system lies
in the shipment and storage of a finished unit, because it is
a large and heavy item that is sold in relatively low volume.
At the same time, with so many manufacturers, competition is
fierce and the manufacturer knows that a few dollars' lower price
may well tilt your decision in favor of its products.
If you bought
your speakers based on affordability, and aren't completely satisfied,
there are several steps you can take short of trading or selling
them and getting new ones. If the cabinets are solid and look
good, a little tinkering with the "guts" may improve
your sound remarkably.
The biggest improvement
you can make in an existing speaker cabinet is to upgrade its
drivers, as discussed in the March "tip" on this site.
Unfortunately, this is also the most expensive improvement as
well. If you're not ready to spend a lot of money upgrading your
sound, but willing to get your hands a little dirty, here are
some other, more inexpensive things you can do to improve your
existing speakers. All of them require disassembling your cabinets,
but the components and wiring in them are not all that complex,
so these tips will be more time-consuming than brain-taxing.
Usually, speaker cabinets have either a removable back, or their
interiors are accessible from the front when the driver(s) are
removed, or both. If you remove a back or driver, here are some
things to check.
What's the
cabinet made of?
You can't change it, of course, but you should know that "composite
woods" such as particle board are both heavier and less
rugged than alternatives such as plywood or thermoformed plastic
and cheaper too, so many less-expensive speakers are made
with particle board. Its biggest disadvantage is that with time,
humidity and moisture can weaken the adhesive that holds it together
particle board is basically glued-together sawdust. Anything
you can do to protect its outside surfaces from moisture will
extend its life. The exterior of the cabinet is probably covered
with vinyl or carpeting, and thus inaccessible. However, if the
interior of the cabinet is not covered with sound-absorptive
material such as fiberglass or foam, you may see raw particle-board
surfaces. Paint them with any sort of latex-based sealant
paint, sealer, even diluted Elmer's glue and let them dry
thoroughly, and your cabinet will be far more moisture resistant.
And be careful transporting them when it's raining outside!
Sound absorption if the interior
of your cabinet was lined with fiberglass or foam, great. If
it was not, do so now. Your drivers put out just as much sound
pressure "backward" (that is, into the cabinet) as
they do "forward." The cabinet's principal purpose
is to trap those back-pressure waves; in a ported design it may
even send some of them out the front. But every surface in every
cabinet has a "resonant frequency," a frequency at
which is likes to "sing along" with the sound from
the drivers, based on its panel size and thickness. And, every
hard surface inside a cabinet reflects or "bounces"
internal sound waves off to another interior panel somewhere,
or even worse, to the back of your driver cone, until the sound
wave runs out of energy and dies down. At best, this can make
your cabinet seem to emphasize certain midrange frequencies and
give it a "honky" sound. At worst, it can make the
cabinet resonate or "buzz" and interfere with that
the driver cone is supposed to do, resulting in increased distortion.
So if the inside
of your cabinet is bare, hard wood, attach foam or fiberglass
batting to all side and rear surfaces with glue and/or a heavy
stapler. Compared to the hard-surfaced wood, when you shout into
an empty driver hole, the interior of the cabinet should sound
"dead." Then you know it's not contributing anything
weird to the sound you're asking your speakers to make.
Wiring the cables from
your amp to your speakers are a certain wire size or "gauge,"
and you've probably heard or learned that the larger or heavier-gauge
these wires are, the better they carry high-powered signals because
larger wire has less resistance. Makes sense, right? What doesn't
make sense is having small wires inside your cabinet from the
input jack to the drivers, for the same reason. If the wiring
inside your cabinet is really small, try running a second wire
in parallel to the factory wire, from each point to every other
point. Twist one around the other to keep things straight, and
connect them securely at both ends. Two small wires equals one
larger wire, and you haven't done anything to disturb the original
connections.
Jacks and
Plugs
if you are sending powerful bass signals to your cabinets,
but hooking them up with standard 14" plugs and jacks, all
that power is trying to go through the very tiny contact point
the jack makes with the plug tip. Consider upgrading your connectors
to Speakons (as described in Shavano) and while you're doing
that, make sure your connection cables are at least 16-gauge
wire, or even better, 14 or 12 (lower numbers mean larger-diameter
wire).
Improve Driver
Mounting
if your bass drivers are mounted into a wooden cabinet
with wood- or drywall-type screws, and the holes in the wood
are stripped or loose, consider replacing them with bolts and
"T-nuts" to hold the drivers more securely. Consider
the same treatment for any casters, polemount sockets or handles.
This is especially important if your cabinets are made of particle
board, which tends to crumble under pressure from wood-type screws.
Make Sure
Everything is Secure there is no reason for anything inside the
cabinet to be loose, and if it is, it will vibrate and buzz along
with the music. Fix any loose interior parts. Then consider whether
the wires to your driver(s) are too long, or placed where they
fall against an interior panel and buzz when the driver is installed.
Sometimes a small wiring clamp or even a bit of duct tape can
stop this.
Keep it Clean carpet covering
gathers dirt, cat hair, and who-knows-what over time. Keep carpeted
cabinets looking good with a sticky lint roller, or in really
extreme cases, an upholstery shampooer. For vinyl covering, use
ordinary spray cleaner and follow up with a light coating of
Armor All. Glue down rips or tears with contact cement. Replace
broken or missing corners, handles, and grilles. Rusting metal
parts can be revived with spray epoxy paint intended for appliances.
If you can see bright-colored fiberglass batting through a front
port hole, give it a light dusting of black spray paint right
behind the port. These things won't change the sound of your
speakers, but will help the audience view you as a serious professional.
Contact Larry
Mundy at larry.mundy@comcast.net
Related Links
Shavano Music Online
Speakerbuilding.com Interview with Joachim
Gerhard
AudioVideo 101
World Studio Group (WSG) Directory of
Related Sites
NAMM
Syn-Aud-Con
Audio
Engineering Society
Mackie
JBL
Pro
US
Speaker
Parts
Express
Industry
News
* The Mobile
Beat DJ Show
will take place in Orlando, Florida from June 28 through June
30, 2004. All events - which includes seminars, exhibits, parties,
and gear giveaways - are located at the Radisson Universal Hotel
Orlando (1-800-327-2110). For additional information, call 585-385-9920.
* David Bowie
has invited the world's bedroom DJ's to remix his music. "Please
remix my songs"
states Bowie, whose contest ends on May 17. See AcidPlanet.com for additional information.
* Guitar
Center's Spin-Off '04 begins Tuesday, May 11, 2004. There is no fee
to enter. Prizes range from shirts, slipmats, DJ gear, Nike footwear,
magazine subscriptions, etc., to recording and producing with
the Warner Music Group, as well as a 2005 Scion xB (Toyota Motor's new
"remix" vehicle).
* A new "hip
hop violinist" is "juicing the hook" of major
artists. Helping to bridge the gap between hip hop and classical
music, Tel-Aviv based violinist Miri Ben-Ari can be heard on
songs by Janet Jackson, Twista and Kanye West. See CNN.com
* An article
appearing in New
Scientist
reveals that particle physicists are working to rescue rare vinyl
recordings. An optical analysis of the vinyl grooves appears
to eliminate background noise and scratches. The article - as
well as before and after sound samples - can
be found at http://www.newscientist.com/news/news.jsp?id=ns99994899
Tip of the Month