I've got a Raspberry Pi 3 and the official Raspberry Pi Touchscreen that
I'm working on building a case for. I've come across a design decision I'd
like a little input on.
I have an amplifier and speaker arrangement to give me basic sound. I'm
using 2 small speakers, about 1" by 2". The speakers are in their own
plastic enclosure with a provision to mount the speaker using a
sufficiently small screw, probably 2-56 maybe 1-72. FWIW, the case will
probably be pine.
It makes sense to make some form of grill or hole in the wood to make sure
the sound can pass unobstructed. I could possibly cut 1/8" wide slots with
an endmill or drill a series of holes. Which would be better, or does it
Also, I'd like to keep little bits of debris from sticking to the speaker
cone. Would a piece of cotton cloth or something similar work as "speaker
fabric" without affecting the sound too much?
Simplest might be to just bore a hole a little smaller than the diameter of
the speaker cone, and glue a very light piece of cloth across the opening
between the wood and the speaker. Shouldn't have much of an effect on the
sound, if any. Maybe your wife or girlfriend has a pair of black nylons
she's about ready to throw away ;-)
For that application (all things considered) he could probably glue a
piece of cheese cloth over the opening and never know the difference
other than a VERY slight degradation in volume. In short, most anything
would work. Nylons would work but I'd have some concerns about longevity.
On Mon, 28 Mar 2016 18:32:45 -0500, Unquestionably Confused
Cheesecloth is too pores (SP) too soft/stretchy. Nylon's would be
better and have a sexy sound. (g) but the best would be a stiffer
If the speaker is going in a box the harder the wood the more it
reflects sound. Also drill a small hole for the back side of the
speaker to allow the diaphragm to fluctuate freely, you can tune the
speaker by the size of the hole.
All valid points but in this instance he refers to 1/8" slots covering
the speaker opening. I wouldn't be worried too much about the
"stretchiness" of the cloth nor, for that matter, the porosity (read:
Acoustic Transparency) of that material. Likewise, if we go away from
1/8" slots, we may find that SWMBO's used panty hose will not be
sufficiently strong to withstand repeated finger pokes after x number of
months of exposure to UV light, etc.
I'm thinking about just gluing the fabric to the backside of the speaker
grill, which should take care of things nicely. I'm not worried about
fingers or stuff like that getting in, just the annoying little bits of
debris that these things tend to collect and can sometimes be a pain to
The speaker has its own enclosure, and the enclosure will be mounted to the
This sort of depends on how concerned you are with the sound
quality. A soft, porous cloth will attenuate the sound, and
affect the tone. If you want good acoustics, use a stiff cloth.
If you just want to keep debris out, use whatever's handy.
This is important - not the tuning, but having some sort of
vent on the backside of the speaker. A speaker makes sound
by pushing air forwards and back, and if there's no way for
air to move behind the speaker, it's not going to move much
air in front either. Result - not much sound. (this is
assuming the box is smallish - a big box with small speakers
has enough volume inside it won't need a vent).
Also, since you have two speakers, make sure they are phased
correctly. If you connect them out of phase, they will cancel
each other, and again you get not much sound. This is more
of a problem with big bass speakers, but even with small ones
it's worth checking the plug is right way round.
FWIW I have not ever witnessed this. Maybe a little if the cloth is
denser/thicker than the length of the sound waves and that is more if a
concern for higher notes where the sound is more directional. But I
used drapery material in from of my L?R and center speakers and you can
not tell if the material/door is open or closed.
That is not true either. Long ago many speakers were built to be air
tight. Case in point many subwolfers use a driver speaker and a slave
speaker inside the same enclosure. The whole speaker assembly is
dependent on being air tight for the slave speaker to function and
And the speakers do not move enough to be hampered by air that easily
compressed or expands from the movement of the speaker. I have a
totally enclosed 12" subwolfer with no issues.
Swingman would be the one to consult here, he has built, owned and
operated recording studios. He told me that the material would not
matter when covering my entertainment center doors with drapery
material, and you cannot tell the difference. My only concern was that
the weave was not so dense that IR light would not pass through. I
simply held the material up to a light to see if the light penetrated.
What would the slave speaker tend to look like? Basically like a speaker
without a magnet? I picked up a speaker from Walmart that had one real
speaker and one that kinda looked like a decoy or fake speaker.
*snip & trim*
Puckdropper <puckdropper(at)yahoo(dot)com> wrote in
>> That is not true either. Long ago many speakers were built to be air
Slave speaker is a special case - in that case the slave is
moving outward when the driven speaker is moving inward, and
vice-versa, so the volume of air inside the enclosure doesn't
With two driven speakers, if the enclosure is airtight you're
compressing (or decompressing) the air in the enclosure, which
is generating a force opposing the way the speaker is being
driven. How much force depends on how big the speaker is, and
how much volume is in the enclosure. If your enclosure is
small, it can have an appreciable effect.
The air volume does not change in a sealed speaker either. The pressure
does change but not the volume.
Not so if the speakers are air tight in their own compartments inside
the speaker housing, which apparently is how my center speaker with 2,
5" speakers is set up.
How much force depends on how big the speaker is, and
Yet if there is no vent the volume of air does not change, only the
pressure changes. So the sound is dampened in that the speaker is not
free to fully travel, unless it is a metal coned speaker. I believe
that is what Leon was referring to.
Eh? You guys are trying to re-write the laws of physics here.
Boyle's gas law applies, p1v1 = p2v2, just as krw said.
This is not complicated - assume there is a speaker in a
sealed box. The speaker cone moves as it's being driven with
the audio signal. As the cone moves outward, the volume
inside the box increases, and the pressure decreases. As
it moves inwards, the volume in the box decreases and the
As noted (several times) whether these changes are significant
depends on the size of the box relative to the speaker.
Nope, in a sealed speaker the same amount of air is in the enclosure
regardless if the speaker cone is moving in or out. What you are
confusing is displacement. The measurable area, not air volume, inside
the speaker changes but not the volume of air. Air easily compressed
and decompresses, that does not decrease the volume of air.
Regardless, boules law has nothing to do with a speaker working correctly
whether it is ported or whether it is an air suspension/acoustical style
Your earlier comments indicated that speakers had to be ported to equalize
air pressure on both sides of the speaker unless the enclosure was large
and the speakers were small. That simply is not true.
What I actually said (regardless of what you think I
"indicated") was that you won't get as much sound if the
case isn't vented. Which is simply true and always will
be (except, as krw pointed out, in the special case of
air suspension speakers).
Actually, there is another special case - if the enclosure
is thin enough to flex. In that case the enclosure itself
will act like a slave speaker. This tends to sound really
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