Subwoofer grill

[Pete]

I just bought an S2000 and it has a 10" sub in an enclosure built into the floor of the trunk. The
previous owner banged up the steel grill that went over the sub, so it's pretty much useless now.
Since I've got an exposed sub lying face up in my trunk, I have to avoid actually _using_ my trunk
most things, lest I puncture or tear the sub.

Seeing this as an opportunity, I purchased a piece of 3/16"-thick acrylic. Using a quickie program
I wrote, I designed a hole pattern that I think I can get the guys up in the Mechanical Engineering
school at Georgia Tech to punch into it for me with their CAD-controlled drill press. The holes
will spell out S2000 accross the center and will be evenly spaced in concentric circles surrounding
that.

My question is this: What's a good guideline for the minimum total amount of airflow I need to
allow through the holes? Given equivalent total area, is one size of hole better than another? The
total diameter of the sub is actually 10 7/8", including the rubber long-throw surround around the
cone. So the airspace above the speaker is approximately 92.9 square inches. The hole patterns
I've come up with are comprised of about 1,000 - 3,000 1/8" and/or 1/4" holes. Adding up the area
of each hole, the total area left uncovered by this new "grill" will be at most about 40 square
inches (~ 40%), and my favorite design only leaves a total of about 11.1 square inches (~ 12%)
uncovered.

The original steel grill has 2mm holes spaced 1mm apart. According to my calculations, this
configuration yields about 40.3% air space, or about 37.4 square inches in this case. This gives me
a little hope that maybe my configurations aren't too restrictive. The main things I'm concerned
about are (1) decreased volume, (2) extra strain on the voice coil, and (3) change in resonant
pitch.

Of course, I'm assuming that once I've got this thing fastened down that the speaker won't vibrate
up against it. If that proves untrue, I'll have to put some spacers underneath it. If so, I guess
that'll probably take care of my airflow, right?

[KU40]

Interesting question, not one that I've ever seen asked or addressed.

My logic refers me to a downfiring home audio sub. The floor is
obviously 0% air movement through, but the sub is up off the ground by
a couple inches, and that works just fine. So I would say that if you
can raise the grill above your sub by 2" you can put any design you
want in it. If you don't want to have it raised that much, then I'd
say size of the holes in the grill will be more important, with it
needing more hole surface area as the grill gets lowered closer to the
sub.

so if you can raise the grill off of the sub by 2, maybe even 3", you
wouldn't have a decrease in volume, no extra strain on the voice coil,
and no change in resonant frequency.


--
KU40

[GregS]

In article >, KU40 > wrote:
>
>Interesting question, not one that I've ever seen asked or addressed.

What question?


>My logic refers me to a downfiring home audio sub. The floor is
>obviously 0% air movement through, but the sub is up off the ground by
>a couple inches, and that works just fine. So I would say that if you
>can raise the grill above your sub by 2" you can put any design you
>want in it. If you don't want to have it raised that much, then I'd
>say size of the holes in the grill will be more important, with it
>needing more hole surface area as the grill gets lowered closer to the
>sub.
>
>so if you can raise the grill off of the sub by 2, maybe even 3", you
>wouldn't have a decrease in volume, no extra strain on the voice coil,
>and no change in resonant frequency.
>
>

[Mister.Lull]

KU40,

I don't know if that would work in this situation. If he's using
spacers to raise a grill up off of a subwoofer, there's no airspace for
the pressure/air/sound to go to off to the sides like in your home sub
analogy... Though, your theory is completely sound other than that.
My suggestion is to go with the design that leaves the most open space
(your favorite). If your math is correct, then you have nothing to
worry about.
~Mister.Lull
KU40 wrote:
> Interesting question, not one that I've ever seen asked or addressed.
>
> My logic refers me to a downfiring home audio sub. The floor is
> obviously 0% air movement through, but the sub is up off the ground by
> a couple inches, and that works just fine. So I would say that if you
> can raise the grill above your sub by 2" you can put any design you
> want in it. If you don't want to have it raised that much, then I'd
> say size of the holes in the grill will be more important, with it
> needing more hole surface area as the grill gets lowered closer to the
> sub.
>
> so if you can raise the grill off of the sub by 2, maybe even 3", you
> wouldn't have a decrease in volume, no extra strain on the voice coil,
> and no change in resonant frequency.
>
>
> --
> KU40

[Matt Ion]

GregS wrote:
> In article >, KU40 > wrote:
>
>>Interesting question, not one that I've ever seen asked or addressed.
>
>
> What question?

The part following "My question is this:"

[KU40]

Mister.Lull Wrote:
> KU40,
>
> I don't know if that would work in this situation. If he's using
> spacers to raise a grill up off of a subwoofer, there's no airspace
> for
> the pressure/air/sound to go to off to the sides like in your home sub
> analogy... Though, your theory is completely sound other than that.
> My suggestion is to go with the design that leaves the most open space
> (your favorite). If your math is correct, then you have nothing to
> worry about.
> ~Mister.Lull

why not? they aren't solid spacers all the way around the sub. all
he'd need are 3-4 little pegs to stand the grill on, very similar to
the pegs/feet that a downfiring home sub sits on. there would
certainly be room, it's just like a home setup.


--
KU40

[MOSFET]

> why not? they aren't solid spacers all the way around the sub. all
> he'd need are 3-4 little pegs to stand the grill on, very similar to
> the pegs/feet that a downfiring home sub sits on. there would
> certainly be room, it's just like a home setup.
>

I agree. Good logic.
MOSFET

[Pete]

Thanks for the suggestions. I was hoping, though, that if I have to raise it, that it would be not
much more than about a half an inch or so. Since the idea is to make my trunk more usable, I don't
want to have this acrylic sticking up several inches off the floor. Also, the higher I raise it,
the more stuff is going to find its way underneath it.

Mr.Lull, my favorite design was actually the one that left the _least_ open space.

I could maybe link to some images of my candidate designs if people are interesting in seeing them.

"I. Care" > wrote in message
.net...
> In article >,
> says...
>> > why not? they aren't solid spacers all the way around the sub. all
>> > he'd need are 3-4 little pegs to stand the grill on, very similar to
>> > the pegs/feet that a downfiring home sub sits on. there would
>> > certainly be room, it's just like a home setup.
>> >
>>
>> I agree. Good logic.
>> MOSFET
>>
>>
>>
> I don't know that I am following this thread correctly, but, my pair of
> 8" subs for my competition (was) car are down firing and has only about
> 1" space underneath with no grill. It wasn't set up for SPL but worked
> OK for SQ.
> --
> I. Care
> Address fake until the SPAM goes away ;-}

[Matt Ion]

Pete wrote:
> Thanks for the suggestions. I was hoping, though, that if I have to raise it, that it would be not
> much more than about a half an inch or so. Since the idea is to make my trunk more usable, I don't
> want to have this acrylic sticking up several inches off the floor. Also, the higher I raise it,
> the more stuff is going to find its way underneath it.
>
> Mr.Lull, my favorite design was actually the one that left the _least_ open space.

In reality, most of the bass is going to go straight through the acrylic, holes
or not. Low frequencies tend to do that. The only clearance you really NEED to
have is enough so the cone doesn't hit the acrylic. You can determine how far
that is by gently pushing the cone up (pushing evenly on at least two sides, so
it stays straight), or by simply looking up the X-max spec.

> I could maybe link to some images of my candidate designs if people are interesting in seeing them.

That would be cool!

[Tony F]

It sounds to me your math is very well thought out and I for one tend to
believe your plan will work just fine. If you really want test it before
hand, just use the sub in an enclosure with the original steel grill, and
cover up some of the appropriate number of holes to simulate your design.
That's what I would do. Otherwise, I'd just make it, put it together, and
see if it works!

Tony


--
2001 Nissan Maxima SE Anniversary Edition
Clarion DRZ9255 Head Unit, Phoenix Gold ZX475ti, ZX450 and Xenon X1200.1
Amplifiers, Dynaudio System 360 Tri-Amped In Front and Focal 130HCs For Rear
Fill, Image Dynamics IDMAX10 D4 v.3 Sub

2001 Chevy S10 ZR2
Pioneer DEH-P9600MP Head Unit, Phoenix Gold Ti500.4 Amp, Focal 165HC
Speakers & Image Dynamics ID8 D4 v.3 Sub

2006 Mustang GT Coupe
Alpine IVA-D310 DVD Head Unit, Alpine MRA-550 Digital 5.1 Amp, Boston
Acoustics Z-Series Speakers, Alpine SBS-05DC Center Channel Speaker,
Amplified MTX Thunderform Sub

[Mister.Lull]

Oops, I thought spacers were solid all the way around... My bad.

Damn, I'm 0 for 2 on this post, I thought the favorite design had the
most amount of breath-ability..........

Okay, here's another suggestion (and I know this isn't what you want to
hear): have the plexiglass cut in the shape of a normal subwoofer
grill... It's a lame suggestion, I know, but at least then you wouln't
have to worry about the airflow.

~Mister.Lull
KU40 wrote:
> Mister.Lull Wrote:
> > KU40,
> >
> > I don't know if that would work in this situation. If he's using
> > spacers to raise a grill up off of a subwoofer, there's no airspace
> > for
> > the pressure/air/sound to go to off to the sides like in your home sub
> > analogy... Though, your theory is completely sound other than that.
> > My suggestion is to go with the design that leaves the most open space
> > (your favorite). If your math is correct, then you have nothing to
> > worry about.
> > ~Mister.Lull
>
> why not? they aren't solid spacers all the way around the sub. all
> he'd need are 3-4 little pegs to stand the grill on, very similar to
> the pegs/feet that a downfiring home sub sits on. there would
> certainly be room, it's just like a home setup.
>
>
> --
> KU40

[keith]

Hi Pete,

What you're trying to avoid here is effectively slot loading your sub...
this will change the frequency response of your sub, and likely throw
off your cross over points unless you compensate elsewhere...

It looks like you have your bases covered though. Basic rule of thumb
is that free-air clearance of anything less than 2 times the cone area
of your sub will create a slot loading situation. That's not
necessarily undue stress on your VC, but it is in fact considered
beneficial in certain circumstances (ie. tuning an overly small
enclosure to a particular frequency).

therefore, calculate the area (not volume) around the edge of the grill,
and add it to the sum area of the holes. Compare it, and as long as it
is 2x the cone area, you're cool.

That said, with a CAD press, your possibilities are endless. Have Fun!!

KeithS


Pete wrote:

> I just bought an S2000 and it has a 10" sub in an enclosure built into the floor of the trunk. The
> previous owner banged up the steel grill that went over the sub, so it's pretty much useless now.
> Since I've got an exposed sub lying face up in my trunk, I have to avoid actually _using_ my trunk
> most things, lest I puncture or tear the sub.
>
> Seeing this as an opportunity, I purchased a piece of 3/16"-thick acrylic. Using a quickie program
> I wrote, I designed a hole pattern that I think I can get the guys up in the Mechanical Engineering
> school at Georgia Tech to punch into it for me with their CAD-controlled drill press. The holes
> will spell out S2000 accross the center and will be evenly spaced in concentric circles surrounding
> that.
>
> My question is this: What's a good guideline for the minimum total amount of airflow I need to
> allow through the holes? Given equivalent total area, is one size of hole better than another? The
> total diameter of the sub is actually 10 7/8", including the rubber long-throw surround around the
> cone. So the airspace above the speaker is approximately 92.9 square inches. The hole patterns
> I've come up with are comprised of about 1,000 - 3,000 1/8" and/or 1/4" holes. Adding up the area
> of each hole, the total area left uncovered by this new "grill" will be at most about 40 square
> inches (~ 40%), and my favorite design only leaves a total of about 11.1 square inches (~ 12%)
> uncovered.
>
> The original steel grill has 2mm holes spaced 1mm apart. According to my calculations, this
> configuration yields about 40.3% air space, or about 37.4 square inches in this case. This gives me
> a little hope that maybe my configurations aren't too restrictive. The main things I'm concerned
> about are (1) decreased volume, (2) extra strain on the voice coil, and (3) change in resonant
> pitch.
>
> Of course, I'm assuming that once I've got this thing fastened down that the speaker won't vibrate
> up against it. If that proves untrue, I'll have to put some spacers underneath it. If so, I guess
> that'll probably take care of my airflow, right?
>
>