Hey there guys,
First off id like to say I'm new so I'm sorry if this is an inappropriate post on your forums, I'm just looking for some help/advice as its my first time designing a subwoofer box and I want to do it right.
I've picked out a sub I like, JBL GTO804 8", not exactly high end but perfect for what I need. I'm making a small, 9" high subwoofer box to go under my bed. I would like it to be one box with 2 subs but with 2 separate chambers (one for each sub) Also I would like it to be tuned to 30hz if possible.
Now I've done a little reading up myself but I can't quite get me head around it all. I get I need to have a certain volume (sized box) for my sub, and a certain port length/diameter but from the info I've got about my sub, I can't work it out. Here is the PDF manual for the sub I have selected: JBL GTO 804 8" SPECIFICATION SHEET Pdf Download. There is an example of a ported enclosure on there but there's no dimensions, only that it need to be 0.6ft³ (16.99 litres) That's where I'm stuck.
If anyone could just give me some dimensions of the box I might be able to work it out from there. I need it to be 9 inches high max (as its for under my bed) Even if you can give me dimensions for just one speaker, I'd be able to work out how to make it a double. I could also work out the port size myself as well (I think).
Id be truly grateful if anyone could help me out here! you don't know how frustrated I've been trying to work this out
I would even pay a little money for you trouble.
I will reply to anyone as fast as possible.
Thanks again,
Tom.
P.S If a mod wants to remove this thread, please contact me as I would like to copy it to post it else where.
First off id like to say I'm new so I'm sorry if this is an inappropriate post on your forums, I'm just looking for some help/advice as its my first time designing a subwoofer box and I want to do it right.
I've picked out a sub I like, JBL GTO804 8", not exactly high end but perfect for what I need. I'm making a small, 9" high subwoofer box to go under my bed. I would like it to be one box with 2 subs but with 2 separate chambers (one for each sub) Also I would like it to be tuned to 30hz if possible.
Now I've done a little reading up myself but I can't quite get me head around it all. I get I need to have a certain volume (sized box) for my sub, and a certain port length/diameter but from the info I've got about my sub, I can't work it out. Here is the PDF manual for the sub I have selected: JBL GTO 804 8" SPECIFICATION SHEET Pdf Download. There is an example of a ported enclosure on there but there's no dimensions, only that it need to be 0.6ft³ (16.99 litres) That's where I'm stuck.
If anyone could just give me some dimensions of the box I might be able to work it out from there. I need it to be 9 inches high max (as its for under my bed) Even if you can give me dimensions for just one speaker, I'd be able to work out how to make it a double. I could also work out the port size myself as well (I think).
Id be truly grateful if anyone could help me out here! you don't know how frustrated I've been trying to work this out
I would even pay a little money for you trouble.I will reply to anyone as fast as possible.
Thanks again,
Tom.
P.S If a mod wants to remove this thread, please contact me as I would like to copy it to post it else where.
That woofer is intended for use in a sealed box. Vas is very small and Equivalent Bandwidth Product (Fs/Qes) is 66, indicating suitability for sealed cabinet more than vented.
To design the box, you can use a woofer box simulator like (free) WinISD beta, to simulate the behavior of the driver in any box you care to simulate. The software will automatically calculate the internal "closed box" volume that gives you Qtc .7. That will work fine for your application.
A sealed box is a good place to start your speaker building hobby, they are much easier to design and build than reflex vented "tuned" box. Volume is the only significant box parameter in sealed design, and if you get it wrong (within reason) the speaker will still sound good. Reflex design is a black art and takes time and mistakes to figure how to achieve your desired sound. Simulator reflex formulas are OK for home theater boomers, but for clean music a reflex box is an artistic process.
Once you know the desired internal volume of the sealed box which will net the Qtc that you want (.7) then you can just use your basic "volume of a rectangle" formula (LxWxH) to determine the width and length. You must factor in the desired external height constant of 9", plus the thickness of the boxwalls, and provide additional internal volume to compensate for the volume of the driver's protrusion into the box, the internal vibration reducing bracing of the box.
So if you use 3/4" (18mm) thick plywood, you would subtract 1.5" from your 9" max height, that gives you 7.5" max internal height. Add 15% to the desired box volume (Vb) to compensate for driver and bracing volume, and use that to determine what your internal dimensions will be. Then add 1.5 inches to each dimension to determine the outer overall dimensions. Use CAD or paper drawing to determine parts sizes and assembly. If it plays under 80Hz you don't really need bracing, but it will make it sound a bit tighter. Under the bed, it probably doesn't matter.
A nice tool for designing boxes is CADstd, a free, easy to use CAD program
CadStd - Cad Standard Lite freeware and inexpensive Pro software.
In WinISD, you can set the wall thickness and it will spit out external box dimensions, but I think you can't constrain one dimension, like your max height. LinearTeam
If you want to do a vented speaker for the challenge, or the fun of it (masochist,) consider picking a driver that is more suitable for a reflex box. Read about EPB. Parts express makes some inexpensive subwoofer drivers that are good for vented. WinISD can help design a vented box. It will give you the vent dimensions and box volume.
If you use a sealed box, you may need some kind of EQ on your sub to make it play low enough to fulfill your intended performance. The JBL specsheet says it will play flat to 30Hz without EQ, so if that's really true then maybe EQ is not necessary, but it is always nice to have.
PM me if you want help making a mechanical drawing for your box, no charge. Welcome to diyaudio.com!
Rich
To design the box, you can use a woofer box simulator like (free) WinISD beta, to simulate the behavior of the driver in any box you care to simulate. The software will automatically calculate the internal "closed box" volume that gives you Qtc .7. That will work fine for your application.
A sealed box is a good place to start your speaker building hobby, they are much easier to design and build than reflex vented "tuned" box. Volume is the only significant box parameter in sealed design, and if you get it wrong (within reason) the speaker will still sound good. Reflex design is a black art and takes time and mistakes to figure how to achieve your desired sound. Simulator reflex formulas are OK for home theater boomers, but for clean music a reflex box is an artistic process.
Once you know the desired internal volume of the sealed box which will net the Qtc that you want (.7) then you can just use your basic "volume of a rectangle" formula (LxWxH) to determine the width and length. You must factor in the desired external height constant of 9", plus the thickness of the boxwalls, and provide additional internal volume to compensate for the volume of the driver's protrusion into the box, the internal vibration reducing bracing of the box.
So if you use 3/4" (18mm) thick plywood, you would subtract 1.5" from your 9" max height, that gives you 7.5" max internal height. Add 15% to the desired box volume (Vb) to compensate for driver and bracing volume, and use that to determine what your internal dimensions will be. Then add 1.5 inches to each dimension to determine the outer overall dimensions. Use CAD or paper drawing to determine parts sizes and assembly. If it plays under 80Hz you don't really need bracing, but it will make it sound a bit tighter. Under the bed, it probably doesn't matter.
A nice tool for designing boxes is CADstd, a free, easy to use CAD program
CadStd - Cad Standard Lite freeware and inexpensive Pro software.
In WinISD, you can set the wall thickness and it will spit out external box dimensions, but I think you can't constrain one dimension, like your max height. LinearTeam
If you want to do a vented speaker for the challenge, or the fun of it (masochist,) consider picking a driver that is more suitable for a reflex box. Read about EPB. Parts express makes some inexpensive subwoofer drivers that are good for vented. WinISD can help design a vented box. It will give you the vent dimensions and box volume.
If you use a sealed box, you may need some kind of EQ on your sub to make it play low enough to fulfill your intended performance. The JBL specsheet says it will play flat to 30Hz without EQ, so if that's really true then maybe EQ is not necessary, but it is always nice to have.
PM me if you want help making a mechanical drawing for your box, no charge. Welcome to diyaudio.com!
Rich
I just saw the 2nd page with vented design. This will work fine. You would design the box using the method I outlined above, but in addition to allowing additional volume for the driver protrusion into the box, and for internal vibration bracing, you would also want to add the external volume of the port to your compensation, because the .6 ft^3 volume does NOT include the volume of the port protruding into the box. The specified volume is the resonant volume of the space inside the box which will resonate through the port. The air in the box is a spring, so the volume is critical to the proper tuning of the system.
The port length is the internal length of the port tube, the length the air sees. If the port is glued to the inside surface of the box, then the port tube should be shortened by 3/4" so the total internal length of the tube is per plan, including box thickness.
The port diameter is the diameter that the air sees, not the outside diameter of the tube. The nominal dimension of the tube is probably the internal diameter, so a 2.5" PVC pipe should have 2.5" inside diameter.
Make sure the port is no closer than 3" to any wall, either sides or back. Give it room to breath. Keep a clean path from woofer to port, free of stuffing.
Don't over drive a reflex speaker. Playing frequencies lower than the tuning frequency at high volume can damage the woofer. Tuning is 40Hz, so ELF effects (20Hz stuff) like space explosions and dinosaur footsteps should not be cranked to the max.
Make sure there is a path for sound from the driver to get out from under the bed. If it fires into the bottom of the bed, might make nice massage effect, but it will reduce SPL in the room. Also don't fire the vent into the ground or bed. It needs a long unobstructed space in front of it for the column of air it squirts to be undisturbed, in theory anyway... Do what works best for you.
The port length is the internal length of the port tube, the length the air sees. If the port is glued to the inside surface of the box, then the port tube should be shortened by 3/4" so the total internal length of the tube is per plan, including box thickness.
The port diameter is the diameter that the air sees, not the outside diameter of the tube. The nominal dimension of the tube is probably the internal diameter, so a 2.5" PVC pipe should have 2.5" inside diameter.
Make sure the port is no closer than 3" to any wall, either sides or back. Give it room to breath. Keep a clean path from woofer to port, free of stuffing.
Don't over drive a reflex speaker. Playing frequencies lower than the tuning frequency at high volume can damage the woofer. Tuning is 40Hz, so ELF effects (20Hz stuff) like space explosions and dinosaur footsteps should not be cranked to the max.
Make sure there is a path for sound from the driver to get out from under the bed. If it fires into the bottom of the bed, might make nice massage effect, but it will reduce SPL in the room. Also don't fire the vent into the ground or bed. It needs a long unobstructed space in front of it for the column of air it squirts to be undisturbed, in theory anyway... Do what works best for you.
Greets!
No, you’re on the right forum………..
Since you’re using two in a common cab, then normally they will be at opposite ends, so that they will ~cancel out their rocking motion.
WRT cab size and tuning, the one JBL lists is for mobile apps, so not appropriate for a home sub as it will be tailored to blend with the high cabin gain of a car’s very small ‘room’, i.e. it won’t have much bass in your room.
Anyway, at a glance a typical dual driver alignment would be ~37.511 L/28.6 Hz Fb and if you need them to handle up to 800 W/driver, then a large, long vent will be required to keep vent power compression low; ideally ~11.68 cm diameter x ~93.98 cm long assuming you will be playing music/movie LFE at high SPL this low.
So, how much power is available and what will you be mostly using the sub for?
If you decide to pay for whatever reason, then please donate here: diyAudio - Donations
GM
No, you’re on the right forum………..
Since you’re using two in a common cab, then normally they will be at opposite ends, so that they will ~cancel out their rocking motion.
WRT cab size and tuning, the one JBL lists is for mobile apps, so not appropriate for a home sub as it will be tailored to blend with the high cabin gain of a car’s very small ‘room’, i.e. it won’t have much bass in your room.
Anyway, at a glance a typical dual driver alignment would be ~37.511 L/28.6 Hz Fb and if you need them to handle up to 800 W/driver, then a large, long vent will be required to keep vent power compression low; ideally ~11.68 cm diameter x ~93.98 cm long assuming you will be playing music/movie LFE at high SPL this low.
So, how much power is available and what will you be mostly using the sub for?
If you decide to pay for whatever reason, then please donate here: diyAudio - Donations
GM
Thank you you have been a lot of help. I'm downloading the WinISD program as we speak. Ill have a play and get back to you.
I'm using a crossover to separate the lows and the highs (signal not amplified) so 30Hz shouldn't be a problem, also I am considering getting an EQ for fine tuning.
Oh and I've got CAD, done an engineering course at college so I'm pretty familiar with it.
Thanks for the reply, and ill get back to you soon!
Tom.
EDIT: The sub I've selected isn't listed in the WinISD Program 🙁
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I've got a 200w RMS amp lined up (670w in total) and it will mostly be used for listening to bassy music (up quite loud as well) I haven't ordered the speakers as of yet so if you have any other suggestions, feel free. But they must be 8" as I've only got just under 10" clearance.
I will admit i am a complete nooby when it comes to making a box. Messed around with sound systems all my life but never properly designed something, or at least to a professional quality. All the math will probably be the mind boggler for me
Thanks for the prompt reply from both posters! Much appreciated
Hi, that box design isn't very good IMO ! See why in screenie 1. Unless of course you would be happy with that ?
The same box tuned to 30Hz is in screenie 2. A lot more linear, BUT the port is too long to fit in the box as a straight tube ! You could though, make a rectangular port down one dimension & have a 90 degree bend which then goes along another & exits. You would need to calculate the extra room taken up by the increased port size, & add this to the internal box dimensions.
All the above is for ONE internal 16.99 L sized box. If you could allow a larger sized box, but still no higher than 9", then there are more options.
Those designs i made using WinISD & you might find this thread i did useful http://www.diyaudio.com/forums/subwoofers/148729-how-correctly-use-winisd.html Here's the link for the latest version http://www.linearteam.org/download/winisd-07x.exe
The same box tuned to 30Hz is in screenie 2. A lot more linear, BUT the port is too long to fit in the box as a straight tube ! You could though, make a rectangular port down one dimension & have a 90 degree bend which then goes along another & exits. You would need to calculate the extra room taken up by the increased port size, & add this to the internal box dimensions.
All the above is for ONE internal 16.99 L sized box. If you could allow a larger sized box, but still no higher than 9", then there are more options.
Those designs i made using WinISD & you might find this thread i did useful http://www.diyaudio.com/forums/subwoofers/148729-how-correctly-use-winisd.html Here's the link for the latest version http://www.linearteam.org/download/winisd-07x.exe
Attachments
Nice one fella thanks! I'm looking to produce the lowest frequency possible from an 8" woofer, I listen to very bassy music - my neighbours hate me 🙂
Does anyone think this sub would be more suited? http://uk.infinitysystems.com/tl_files/catalog//Infinity/Infinity-Car/Specsheets/Reference/Reference/860w/860W_PI_EN.pdf
Little more power, I like 😉
Little more power, I like 😉
both have 2"coils, both seem to want 16-17L tuned to 30hz, same sensitivity. Only diff I see is 2mm more xmax on the infinity, but they could be exaggerating also.
I don't think you can get a big enough port in a box, but a 4" one will help the excursion a bit.
I don't think you can get a big enough port in a box, but a 4" one will help the excursion a bit.
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2 mm is an inaudible difference at woofer frequencies, though combined with corner loading it might be barely audible.
GM
GM
OK, 200 W is all these can safely handle in your app, so should be good to go.
I’ve no clue what you mean by ‘bassy’ music WRT frequency response, so please elaborate.
I mean that ‘bassy’ to me will include pipe organ symphony CDs that can have house shaking 16 Hz pipe fundamentals with 32 Hz pipes being loud enough to hear clearly and 64, 128 Hz pipes that can pressurize your chest, inhibit free breathing like one can experience at a live rock concert, all assuming you have the system capability to take advantage of them of course, which you won’t.
WRT driver size, have you considered larger drivers on angled baffles to reduce their effective height?
GM
I’ve no clue what you mean by ‘bassy’ music WRT frequency response, so please elaborate.
I mean that ‘bassy’ to me will include pipe organ symphony CDs that can have house shaking 16 Hz pipe fundamentals with 32 Hz pipes being loud enough to hear clearly and 64, 128 Hz pipes that can pressurize your chest, inhibit free breathing like one can experience at a live rock concert, all assuming you have the system capability to take advantage of them of course, which you won’t.
WRT driver size, have you considered larger drivers on angled baffles to reduce their effective height?
GM
Correct for a single driver, but I was addressing the pertinent issue of comparing excursions of same area radiators, though in retrospect, 'haste makes waste', I should have posted '2x acoustical power'.
GM
GM
and.............
200 watts vs 100 watts, you usually don't pick up 3db (losses from the voice coil heating). And 200 watts to 400watts, you probably pick up less than 2more db............
I usually plan on +20db from a single driver (100 watts).
If I need more db, I add more drivers.
Norman
200 watts vs 100 watts, you usually don't pick up 3db (losses from the voice coil heating). And 200 watts to 400watts, you probably pick up less than 2more db............
I usually plan on +20db from a single driver (100 watts).
If I need more db, I add more drivers.
Norman
Some offbeat ideas...
First, be aware that I am the resident jackass here
Pity his driver is not suitable; he might be able to try a tapped horn otherwise (what do we know about his wood working skills?) I mean, I get 30 Hz with a single Bose 901 driver (modeled at least). Would a small real TH be much harder?
Is the bedroom floor wood? Can he just saw a hole in the floor under the bed? Quick and easy, infinite baffle, and if the neighbor downstairs likes bass, a win-win situation!
First, be aware that I am the resident jackass here
Pity his driver is not suitable; he might be able to try a tapped horn otherwise (what do we know about his wood working skills?) I mean, I get 30 Hz with a single Bose 901 driver (modeled at least). Would a small real TH be much harder?
Is the bedroom floor wood? Can he just saw a hole in the floor under the bed? Quick and easy, infinite baffle, and if the neighbor downstairs likes bass, a win-win situation!
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