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#1
Posted to rec.audio.car
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Subwoofer grill
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? |
#2
Posted to rec.audio.car
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Subwoofer grill
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 |
#3
Posted to rec.audio.car
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Subwoofer grill
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. |
#4
Posted to rec.audio.car
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Subwoofer grill
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 |
#5
Posted to rec.audio.car
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Subwoofer grill
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:" |
#6
Posted to rec.audio.car
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Subwoofer grill
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 |
#7
Posted to rec.audio.car
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Subwoofer grill
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 |
#8
Posted to rec.audio.car
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Subwoofer grill
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 ;-} |
#9
Posted to rec.audio.car
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Subwoofer grill
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! |
#10
Posted to rec.audio.car
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Subwoofer grill
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 |
#11
Posted to rec.audio.car
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Subwoofer grill
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 |
#12
Posted to rec.audio.car
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Subwoofer grill
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? |
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