By Eddie Runner
boxes can be made of anything rigid enough to not vibrate and cause losses or
distortion; the most common materials are Plywood, Particleboard, and MDF
(medium density fiberboard).
Plywood is more impervious to water and probably the strongest and lightest, but
Particle board and MDF being much denser have (possibly) better sonic
properties, and MDF makes the nicest looking boxes and is easy to work with…
The box material should be considered for the application by the system designer
and chosen for the individual application.
folks seem to think MDF is the best and anything else will blow apart when you
fire up your sound system, that's totally incorrect. All of these woods have places of
honor in the car audio field.
for car audio, custom boxes are usually made from MDF and are glued together
with wood glue, the box builders usually tap these boxes together with a brad
nailer or screw it together. The brads, screws or nails are basically to hold
the box together till the glue dries, the glue is the real strength, but we don't
want to waste time clamping it together and waiting all day for the glue to dry.
The screws, brads or nails allow the box to be completely assembled. upholstered
and installed while the wood glue is drying.
Also, most installers will seal the inside seams of the box with some kinda goop
or caulk, I have used clear or black silicone for decades and I like it the
some folks have been claiming the fumes from silicone is bad for loudspeaker
surrounds.. I say bull !!! I have not only been using silicone since the 1970s
with no bad effects on the speaker boxes I have also used silicone to repair
small tears in speaker cones or torn surrounds 100s of times, whoever is telling
these lies must have some playdoe fetish or something???
the woofer moves in and out while in the speaker box a fair amount of internal
air pressure is present when the speaker moves in and a negative air pressure
occurs in the box when the speaker moves out, plus a whole lot of vibrations
occur from the speaker moving and these pressure changes…
The wood the box is made out of can vibrate also, using a thicker wood or
denser wood will minimize these vibrations..
If the box panels are large (or thin), they can resonate enough to cause
hearable distortions. Bracing the box can help minimize these distortions.
In a box with two woofers a center divider can also act as a brace…
Making internal bracing (or external) is pretty easy and makes the box a lot
more sturdy… One trick I seldom
see anymore is using the circle you cut out from the woofer hole as a brace
elsewhere in the box, it can be cut in quarters and used as brace material or
used to thicken the center of your largest panels which could vibrate.
box is a seriously braced box! Folks rarely go to these extremes to
brace a box used in car audio, but some go so far as to use double
panels and fill between them with sand or concrete! Its up to you.
sealed enclosure is designed to (a) keep the back wave of the speaker from
coming in contact with the front wave of the speaker. (b) allow the air pressure
in the box to add a suspension component to the speaker (in other words the air
pressure of the box keeps the speaker from moving too far as it plays)….
folks seem to think the box should be absolutely airtight! Some folks go so far
as to seal the inside of the woofer box with fiberglass to ensure an absolute
airtight seal! Some folks seem to be worried about the way some wood allows air
to seep through it! I got news for
those guys, most woofers are much more porous to air pressure than any wood we
will be using!
it wont hurt anything to be airtight, but I get the impression from a lot of
folks that they put way too much effort into trying to achieve air tightness…
To be honest though, the main problem with air leaks is high frequency
sounds caused by air rushing though any small holes.. The air pressure changes
inside the box can force air in and out of any small leaks and cause whistling
sounds! DISTORTION! The distortion
is what were trying to avoid… Generally, a few small air leaks wont change the
performance of the woofer like folks seem to think, in fact an air leak would
have to be huge to greatly affect (a) and (b) above…
The main thing we want to do is avoid air leaks because of whistles!
seems to be some confusion about using a divider in a woofer box with two
woofers… Many installers seem to be telling their customers that by having no
divider the box will make more bass! I
think those installers either don’t know anything about speaker boxes or are
making excuses because they are too lazy to build the box correctly…!!!
both woofers are exactly the same, the box will sound the same with and without
a divider! There is no increase at all by not using a divider…
there are some good reasons for having the divider!
It braces the box!
And most importantly (to me anyway)
prevents the speakers from interacting inside the box…
Let me explain, we know that if the woofers are putting out the EXACT
same sound and level then having no divider wont matter, but what happens if one
speaker is playing LESS than the other speaker???
Lets say one speaker is working fine and the other speaker is not playing
at all, the working speaker will push the non working speaker (through the box)
allowing out of phase air pressure to come out of the box through the non
working speaker, causing the good speaker to sound really bad! If there was a
divider, this wouldn’t happen, if there was a divider the good speaker would
still be pumping nice clean sound to your ears, while the non working speaker
just sits there… Even if the speakers are both playing but one is playing less
loud, the sound from the loud speaker averages DOWN with no divider, but having
a divider will leave the loudest speaker still playing loud, and even the less
loud speaker will reinforce it somewhat making it even loader….
basically, with no divider even a small problem with one speaker will make the
whole box sound bad, but with a divider it is common for one speaker to
completely go silent and the working one still sounds great!
conclusion, my advice is to use a divider!
Unless your too damn lazy…
GOTO Speaker parts pageBack to the tech section