Hi. I'm a newbie, just starting to put together ideas for a home theater / music system, starting out cheap. However, I have a very large room, open at the ceiling to the entire second floor of the house. See these photos:
www.3Prong.com/homex/images/lrm02.jpg
www.3Prong.com/homex/images/view02.jpg
Ignore the old gear that's visible now. But see that red and black "coffee table" in front of the red and black sofa? It's going to be my new subwoofer. It's got a hinged lid and sides of 1" plywood, covered with upholstery foam and Kilim carpet. The bottom has 4 solid maple feet, discs about 5-6 inches in diameter, and 3 inches high. The entire inside is lined with a black fabric over a thin layer of upholstery foam. The bottom is weak and resonant, probably 3/8" plywood with a fabric cover.
My idea is to fit a piece of cement backer board in to cover the entire bottom, and cut a hole through both for a down-firing driver, either 12" or 15". The internal dimensions will be 28" x 36" x 8" deep, = 4.67 cubic feet or 132.5 Liters.
I'll put a 2x2 brace across the bottom of the lid to increase the frequency of any resonance there, and add some fiberfill. If it's going to be a sealed enclosure, I can then put some kind of gasketing material around the bottom of the lid (though it's already pretty tight, you can't slide a piece of paper in there). Or it could be a ported system, or whatever.
I don't think I'll need a crossover as I'll get a mid-range home theater receiver with a subwoofer output. Perhaps I'll recycle an old 50w/channel stereo amp, rewired for bridging to produce up to 200w, to feed the sub, with speaker-level cable under the carpet, rather than feeding AC power and line level audio to an in-built amp.
For the other speakers, I'm thinking of starting with the Fluance SX-HTB home theater system.
Maybe I'll build the subwoofer equalizer kit from
http://sound.westhost.com/project84.htm
get a mic, and tune the room using the 1/3 octave Real Time Analyzer software from
http://www.trueaudio.com/rta_abt1.htm
but with the room this open, I don't think there will be so many standing waves.
Can you folks who are up on the math suggest a particular driver and design suited to this enclosure? I am hoping to get some nice dry extended bass out of this while keeping the sub costs under $200.
If I get dual voice coils on the driver, maybe I don't have to do the bridging mod to the amp? http://sound.westhost.com/project20.htm
Any other ideas or caveats?
I'm in Canada (the Toronto area), so I'll be ordering from one of these dealers, who seem to have quite a good selection:
http://www.creativesound.ca/
http://www.solen.ca/salesol.htm
http://www.q-components.com/
TIA,
Andre Brunger
www.3Prong.com/homex/images/lrm02.jpg
www.3Prong.com/homex/images/view02.jpg
Ignore the old gear that's visible now. But see that red and black "coffee table" in front of the red and black sofa? It's going to be my new subwoofer. It's got a hinged lid and sides of 1" plywood, covered with upholstery foam and Kilim carpet. The bottom has 4 solid maple feet, discs about 5-6 inches in diameter, and 3 inches high. The entire inside is lined with a black fabric over a thin layer of upholstery foam. The bottom is weak and resonant, probably 3/8" plywood with a fabric cover.
My idea is to fit a piece of cement backer board in to cover the entire bottom, and cut a hole through both for a down-firing driver, either 12" or 15". The internal dimensions will be 28" x 36" x 8" deep, = 4.67 cubic feet or 132.5 Liters.
I'll put a 2x2 brace across the bottom of the lid to increase the frequency of any resonance there, and add some fiberfill. If it's going to be a sealed enclosure, I can then put some kind of gasketing material around the bottom of the lid (though it's already pretty tight, you can't slide a piece of paper in there). Or it could be a ported system, or whatever.
I don't think I'll need a crossover as I'll get a mid-range home theater receiver with a subwoofer output. Perhaps I'll recycle an old 50w/channel stereo amp, rewired for bridging to produce up to 200w, to feed the sub, with speaker-level cable under the carpet, rather than feeding AC power and line level audio to an in-built amp.
For the other speakers, I'm thinking of starting with the Fluance SX-HTB home theater system.
Maybe I'll build the subwoofer equalizer kit from
http://sound.westhost.com/project84.htm
get a mic, and tune the room using the 1/3 octave Real Time Analyzer software from
http://www.trueaudio.com/rta_abt1.htm
but with the room this open, I don't think there will be so many standing waves.
Can you folks who are up on the math suggest a particular driver and design suited to this enclosure? I am hoping to get some nice dry extended bass out of this while keeping the sub costs under $200.
If I get dual voice coils on the driver, maybe I don't have to do the bridging mod to the amp? http://sound.westhost.com/project20.htm
Any other ideas or caveats?
I'm in Canada (the Toronto area), so I'll be ordering from one of these dealers, who seem to have quite a good selection:
http://www.creativesound.ca/
http://www.solen.ca/salesol.htm
http://www.q-components.com/
TIA,
Andre Brunger
Thanks! It looks like Shiva will fill the bill for price and performance.
I guess you mean a 3" diameter port. The spreadsheet at http://www.diysubwoofers.org/prt/ported.zip and the java version of ISD at http://www.linearteam.dk/default.aspx?pageid=ventcalculator roughly agree that when tuning to 22 Hz with a port diameter of 3", the length should be about 6", which would leave 3" clearance to the bottom of the lid.
Where they don't agree is whether the port size is large enough for whistling to be inaudible. The spreadsheet asks for an impossibly large port of ~10.5" x ~95". The ISD calculator indicates a Mach below 0.16 is acceptable, and I will be at Mach .05. However, Ron E on this board has been saying that a Mach of 5% is a maximum. So I will try it and hope for the best.
Or would I be better off with a 4" x 12" flared port with an elbow?
Andre Brunger
I guess you mean a 3" diameter port. The spreadsheet at http://www.diysubwoofers.org/prt/ported.zip and the java version of ISD at http://www.linearteam.dk/default.aspx?pageid=ventcalculator roughly agree that when tuning to 22 Hz with a port diameter of 3", the length should be about 6", which would leave 3" clearance to the bottom of the lid.
Where they don't agree is whether the port size is large enough for whistling to be inaudible. The spreadsheet asks for an impossibly large port of ~10.5" x ~95". The ISD calculator indicates a Mach below 0.16 is acceptable, and I will be at Mach .05. However, Ron E on this board has been saying that a Mach of 5% is a maximum. So I will try it and hope for the best.
Or would I be better off with a 4" x 12" flared port with an elbow?
Andre Brunger
Well, now, I'm kind of looking forward to the added efficiency of the ported design. Since the listening space is so huge. I'd be tempted towards the Tempest ported designs but they seem to want a much bigger box.
BTW, when I said:
The spreadsheet asks for an impossibly large port of ~10.5" x ~95".
...I meant, for a minimum diameter.
When I said:
The ISD calculator indicates a Mach below 0.16 is acceptable, and I will be at Mach .05.
...I meant, with the 3" x 6".
I suppose I can tune the box by the method of measuring the AC current flow through the driver at various frequencies, looking for the impedance bump, and sawing off a little more of the extension tube as needed.
Andre Brunger
BTW, when I said:
The spreadsheet asks for an impossibly large port of ~10.5" x ~95".
...I meant, for a minimum diameter.
When I said:
The ISD calculator indicates a Mach below 0.16 is acceptable, and I will be at Mach .05.
...I meant, with the 3" x 6".
I suppose I can tune the box by the method of measuring the AC current flow through the driver at various frequencies, looking for the impedance bump, and sawing off a little more of the extension tube as needed.
Andre Brunger
At those low frequencies the sub will definitely benefit from room gain and the extra 3 db you're looking might not really be necessary.
I had just finished modelling a system for a friend and discovered that the Tempest is a nice system to use for a "convertible" sub.
For music, you seal the complete system to give you the transient response you want and in the system it yielded a Qtc of around .6. When we took the same enclosure and slot ported it, the peaking was only around 1.5 to 2 db. The excursion matched the sealed system until very low frequencies where the ported system went down. From this we determined that at very low frequencies, sound effects would probably tolerate a less than perfect transient response but would benefit from the extension and would be well suited to the port.
the 3" port is really too small for a high excursion subwoofer and you will definitely suffer from compressive effects and a noisy port.
In this size range, I prefer building a slotted port/tunnel rather than a round pipe as it integrates into the enslosure much easier.
I had just finished modelling a system for a friend and discovered that the Tempest is a nice system to use for a "convertible" sub.
For music, you seal the complete system to give you the transient response you want and in the system it yielded a Qtc of around .6. When we took the same enclosure and slot ported it, the peaking was only around 1.5 to 2 db. The excursion matched the sealed system until very low frequencies where the ported system went down. From this we determined that at very low frequencies, sound effects would probably tolerate a less than perfect transient response but would benefit from the extension and would be well suited to the port.
the 3" port is really too small for a high excursion subwoofer and you will definitely suffer from compressive effects and a noisy port.
In this size range, I prefer building a slotted port/tunnel rather than a round pipe as it integrates into the enslosure much easier.
I don't think you need to be too concerned about the size of your room. I assume you'll be sitting on the sofa, right next to the sub, so you'll want to balance the SPL with the other speakers for that position. Any reasonable driver should be able to play plenty loud because you are so close to it.
About the bottom of the box, I'd glue in a thick piece of MDF or plywood. Cement backer board isn't very stiff or strong. I'd add quite a bit of internal bracing as well. Those panels are big enough to resonate. A brace every foot or so is good.
If you are going with an Adire Shiva or Tempest, you can download plans for various designs from the Adire site. The shape of the box doesn't matter as long as you keep the same internal volume. You can also look at their plans to get an idea of how to do the bracing.
http://www.adireaudio.com/
Click: Technical - App Notes
Edit: another thing, don't forget to subtract the volume of the driver and the bracing when figuring your internal volume.
About the bottom of the box, I'd glue in a thick piece of MDF or plywood. Cement backer board isn't very stiff or strong. I'd add quite a bit of internal bracing as well. Those panels are big enough to resonate. A brace every foot or so is good.
If you are going with an Adire Shiva or Tempest, you can download plans for various designs from the Adire site. The shape of the box doesn't matter as long as you keep the same internal volume. You can also look at their plans to get an idea of how to do the bracing.
http://www.adireaudio.com/
Click: Technical - App Notes
Edit: another thing, don't forget to subtract the volume of the driver and the bracing when figuring your internal volume.
A 3" port is far too small for a Shiva in the suggested enclosure, unless you get a flared port and don't feed the shiva more than 60 watts.
A 4" port is just good enough, but be sure to flare the ends somehow. Dual 3" ports, each 16" long would be even better.
A sealed Tempest could give you close to output of the ported Shiva, and porting the Tempest could get you even more. If this were me, I would just use a sealed Tempest.
Dan
A 4" port is just good enough, but be sure to flare the ends somehow. Dual 3" ports, each 16" long would be even better.
A sealed Tempest could give you close to output of the ported Shiva, and porting the Tempest could get you even more. If this were me, I would just use a sealed Tempest.
Dan
Another vote for the Tempest! Okay, you've all talked me into it. Only a few dollars more than the Shiva. I save a bit by not buying a flared port, and I save a lot of trouble. If I need to, I'll add a port later.
Remember, I wasn't planning on getting and installing a proper subwoofer amp. In addition to the expense, the plate amps have no back, so they need to be in the enclosure itself, and I don't want to run AC power under the carpet. I intended on using an old stereo receiver, one channel to each voice coil, giving 2x50=100W. Now it's going to be pushing a 15" driver! Am I dreaming?
So for a sealed system, no tweaks, all I need to do is line the interior with some stuffing, to taste?
And I need some gasket material around the lid. I see closed cell foam tape recommended. The lid is quite heavy so it should compress the tape to form a reasonable seal. Don't want to put screws down through the top of the upholstered surface!
catapult, the bottom is actually 3/4" plywood, not 3/8"; I was going to lay the concrete panel on that, and cover all but the driver with stuffing. To stop any rattling, I could sandwhich some stuffing or stripes of caulk in between the cement board and the plywood.
OTOH, if I use a 3/4" MDF panel, I can just screw it to the plywood, and the difference in resonances and a brace or two would probably be enough. Might be easier than cutting a precision 15" hole in the cement board. I thought that cement board would be nice and dead, but it might be too hard to work with.
Andre
Remember, I wasn't planning on getting and installing a proper subwoofer amp. In addition to the expense, the plate amps have no back, so they need to be in the enclosure itself, and I don't want to run AC power under the carpet. I intended on using an old stereo receiver, one channel to each voice coil, giving 2x50=100W. Now it's going to be pushing a 15" driver! Am I dreaming?
So for a sealed system, no tweaks, all I need to do is line the interior with some stuffing, to taste?
And I need some gasket material around the lid. I see closed cell foam tape recommended. The lid is quite heavy so it should compress the tape to form a reasonable seal. Don't want to put screws down through the top of the upholstered surface!
catapult, the bottom is actually 3/4" plywood, not 3/8"; I was going to lay the concrete panel on that, and cover all but the driver with stuffing. To stop any rattling, I could sandwhich some stuffing or stripes of caulk in between the cement board and the plywood.
OTOH, if I use a 3/4" MDF panel, I can just screw it to the plywood, and the difference in resonances and a brace or two would probably be enough. Might be easier than cutting a precision 15" hole in the cement board. I thought that cement board would be nice and dead, but it might be too hard to work with.
Andre
I do have another option. The wall behind the TV is cinder block, covered with drywall. Behind it is a furnace room, about 12' x 15' x 7.5', half full of normal stored stuff. There is an old doorway opening in the cinder block, right behind the TV. Can you guess what I'm thinking?
Can you point me to a thread on using an adjoining room as a subwoofer enclosure? If I recall from my youth, this is called an infinite baffle. I'm curious how well that might work.
Andre
Can you point me to a thread on using an adjoining room as a subwoofer enclosure? If I recall from my youth, this is called an infinite baffle. I'm curious how well that might work.
Andre
Regarding your sealed setup, you might want to reconsider how you build this thing. I would not trust the weight of the lid to keep a seal. Even if it did, a good sealed enclosure needs to absorb the back wave of the driver. You could have no air leakes, but if the enclosure is radiating sound that is out of phase with the front of your driver, there will be cancellation.
You have to make it stiff, it should not flex. Accomodating the flexing with gasket material only fixes the rattling.
Dan
You have to make it stiff, it should not flex. Accomodating the flexing with gasket material only fixes the rattling.
Dan
The lid was built years ago, and from 1" plywood. It does not flex perceptably. I will make sure that it does not resonate too much by adding interior bracing as needed. The gasket material is to complete a seal because of the coarse and inexact nature of the carpet upholstery. If the compression on the seal is not adequate, I suppose I will have to add a latching mechanism that is not obtrusive from the outside.
Thanks, point taken.
It wouldn't be quite hermetically sealed, but I would say, for example, if it were immersed in water, ignoring buoyancy issues, it would take at least tens of minutes to flood. Similar to a Canadian submarine. ;^/
Is that good enough to give it a try?
The other concern is what happens if someone opens the lid and then drops it closed. The pressure wave might damage the woofer.
These issues would not be a problem on a vented system.
Andre
It wouldn't be quite hermetically sealed, but I would say, for example, if it were immersed in water, ignoring buoyancy issues, it would take at least tens of minutes to flood. Similar to a Canadian submarine. ;^/
Is that good enough to give it a try?
The other concern is what happens if someone opens the lid and then drops it closed. The pressure wave might damage the woofer.
These issues would not be a problem on a vented system.
Andre
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