Coffee table sub (1 Viewer)

[Dennis_H]

Due to circumstances way out of my control (wife changed her mind), I don't think I'll get to fill in the area around my fireplace and go with the dual Tempest IB project I had been longing for. But, I'm still going to make a new sub in the next couple of months. I'm toying with the idea of a noisy coffee table. I should be able to go 8 ft3 or so I would think. Has anyone done this, and do you have pictures? I think a single ported Tempest design would be good. Maybe a bottom firing driver with ports on each end? What do the experts think?

 

[Philip Hamm]

Sub "furniture" is a really bad idea. Subs tend to vibrate a lot. Anything on the Sub "Furniture" tends to vibrate off. I've seen implementations and they never work as a usable table unless the volume is low.
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Philip Hamm
AIM: PhilBiker

 

[Jack Gilvey]

Here's one:
http://www.geocities.com/manurescape...l?981609316640
If possible, though, I'd prefer to mount two drivers opposite one other, one on each end, to largely cancel the vibrations that Phil mentioned. In your case, to keep the size manageable, I might go with two Shivas.

 

[Dennis_H]

I'm wondering, if I kept a small airgap or other deadening material between the sub box and the finish laminate, would that would decrease vibrations enough. With 4 kids, I would like to keep it bottom firing. Maybe the dual Shiva design would be do-able, but the recommendation is to keep them on opposite ends instead of 2 on the bottom, right? I guess I could put a steel grill over the drivers, then cover the ends with speaker cloth. A water heater design is pretty much out for now.
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[Mark Seaton]

Dennis,
I agree about the only way to do this right would be with opposing driver mounting to have a "balanced force" design. That said, take another look at some of the IB projects out there, particularly Rich Krauss's. You will see that the drivers fire into a front chamber which ducts to the room. There is no reason you couldn't do the same inside of a large box. I would then have the duct open to one side of the table, where you can then cover the opening with a grill. You could do what I'm going to do for a friend's IB, and place the amplifier at the back of the duct to conceal it, while still making it acessable. The only downside of puting the amplifier in the duct is that it requires a wider duct, as most of the amps are at least 10-11" wide. A pair of Shivas could do well and would probably only need a duct 14" x ~6" x 14". Ports could be placed most anywhere on the box, but I would hesitate to place them in the duct unless the duct is rather large, particularly in width.
Mark Seaton

 

[Dennis_H]

Unfortunately, that's not feasable for me in this location. I don't have a large area for a IB configuration. The one place I was going to have has now been changed. I'm stuck with a box (or tube) of some type. There isn't a lot of floor space in the room, so I wanted to double duty a coffee table. Possibly I could do something like the James' Sonosub Table, but box around it. That should keep vibrations down too. Maybe a horiontal tube with a Shiva and port on each end? The drivers wouldn't be facing me. That shouldn't be a problem though.
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[Jack Gilvey]

Mark's not referring to an IB, he's describing a way to have the drivers oppose each other in a box sub while keeping them concealed. Rather excellent idea.

 

[Dennis_H]

You're right... I misread it the first time. So how's this for a design?
Link Removed
The thick dashed lines are internal braces. I tried to hide the drivers a little more by putting the box in the bottom. I haven't done any real size calculations or tuning lengths, this is just a rough sketch. Comments?
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[Jack Gilvey]

I can't get a really clear picture of what's going on, but I think you might be able to have the ports outlet on the bottom also, hiding everything.

 

[Mark Seaton]

Hi Dennis,
It looks like you got the idea I was trying to convey there. One thing to remember about down-firing ports is the required clearance needed to the floor. I would probably just put the ports on the sides like you have shown and be done with it. Another idea would be to enlarge the grill which will cover the woofer duct, and place the ports to one or both sides of the opening, where they would lie underneath the woofers (closer to the floor). This way a larger grill would cover everything.
My last question for you is whether you plan to place the amplifier inside of the duct as I had mentioned, or use an external amplifier? If you aren't placing the amp in the duct, I would consider making the driver to driver spacing smaller, down to at least 8" to gain some more volume in the box. I'm also guessing you will want a little more bracing than you have shown at the moment to get the most peformance and the least vibration on the top of the table.
Please keep us and me posted as to your progress if you do decide to go this route. I had this idea a while back while working on an IB subwoofer, but never had the occasion to build one. Personally I'm not much a fan of down-firing drivers, and I'm a huge fan of a balanced force configuration of bass drivers, so this design fit the bill quite nicely. Co-incedentally, as long as you don't put the amp in the duct, there is no reason the duct couldn't exit the bottom of the enclosure if it was spaced from the floor a few inches, thereby hiding most everything, but I personally think a grill will break up the large scale of the box visually.
Mark Seaton

 

[Dennis_H]

Thanks Mark. I'm still toying with the idea of the large vent with the Shivas on one side and the port(s) on the other. This allows me to gain a little in height by not having to put legs on it. Really the reason I had the drivers 12" away from each other was for ease of mounting. I don't know the exact depth of the drivers and I want to give it enough room to get in there and to get a screwdriver in there afterward. This way I can make the ends like I did my last box. If you are looking from the end of the box, the sides extend an inch past the end. I'll make a 1" frame and put grill cloth over it and put it in there. Works well and looks pretty good. With my last sub, the frame and cloth have a nice tight fit and it hasn't fallen out. I'll probably put in a few small pieces of velcro if I go this route.
OK, I have the PE 250W amp that was on sale last week. The box size is going to be somewhere around 8 ft3 when done. If I get a couple Shivas, where do you experts think I should set the tuning frequency? What about wiring it? They are 8ohm per VC, so do I parallel each VC on a driver and wire the drivers in series for an 8 ohm load? Seems like I want to get it to a 4 ohm load, but I can't afford 4 drivers or the room for them.

 

[Jack Gilvey]

I think the only option is to wire the Shivas for an 8-ohm load with that amp, 2 ohms would be a little much. Also, I believe the bass-boost is already defeated on the 300-794's currently shipping, and definitely is on the 300-793 (with the remote control), so you won't have to do that.
With 8 ft.^3 net (lined)to play with, tuning to 18Hz looks nice with two 4" flared ports at 17" each. Should be good for over 110db @ 20Hz in-room while running easy on the amp and staying well below Xmax on the drivers. Port airspeed is very low, also.

 

[Dennis_H]

I think we have a winner... I picked up the 300-793 because the bass boost was disabled. Didn't know the 794 was disabled now from PE. When you say 8 ft^3 lined, you mean using polyfill at 1 lb per ft^3? 110dB @ 20hz is louder than I'll probably ever get it, but it's nice to know it's there. I'm putting the amp in a different box kind of hidden out of the way so I can change it later if I want, but I don't see needing any more volume than that for quite a while. And having it only a couple feet from the listening position, it should be great. Now I just need to decide on the internal design and finish. What did you think of having a layer of 'whisperwalk' or similiar under the veneer to lower vibrations?

 

[MarkRS]

Dennis - I just finished a Shiva ported box. I ordered some t-nuts from Adire included in the sub V kit that includes port, input cup etc. and the t-nuts screws were tightened with an allen wrench, not a screw driver. This would allow you to greatly cut down on the space needed between the driver. Actually down to just less than the depth of the driver.
Just a thought.
Mark
[Edited last by MarkRS on August 16, 2001 at 02:43 PM]

 

[Jack Gilvey]

Yeah, Dennis, I just mean a 50% fill or so, as you'd get with lining the sides with 3" of fiberglass (or anyway you want to do it) just to get a little more usable Vb.
Do you have Adire's LspCAD? I could e-mail you my .box file (although I already told you what it consists of).
[Edited last by Jack Gilvey on August 16, 2001 at 03:29 PM]

 

[Greg_R]

Sub "furniture" is a really bad idea. Subs tend to vibrate a lot. Anything on the Sub "Furniture" tends to vibrate off. I've seen implementations and they never work as a usable table unless the volume is low.

My DIY sub as well as my Servo-15 don't exhibit any vibration, even when they're playing at high SPLs. Both have spikes anchoring the enclosures to the floor. The enclosures are thick and heavily braced. I've placed a small sheet over the DIY sub and used it as an end table w/o any problems.
Greg

 

[Deane Johnson]

What if the coffee table's location is not a good location for the sub's response in the room? What if your sweet spot ends up in a null spot with the sub in the coffee table location?
Mixing furniture and subs is not a good idea.
Deane

 

[Dennis_H]

What if the coffee table's location is not a good location for the sub's response in the room? What if your sweet spot ends up in a null spot with the sub in the coffee table location?

That is probably the best argument against it. I think I can deal with vibration issues, size issues, etc. In my current room, I did have a bad null at the listening position till I moved the sub. This room is different though. The vaulted ceiling slants from 8' to 18' and there really is only 2 walls. The rest is open. Having it close may be whats needed at the listening position to get the volume instead of adding massive amounts of power. I guess depending on how we lay out the room, I may be able to go the sonotube route or make a nice box, but I won't know for sure till we get rid of the current furniture and put in the new. (Anyone want to buy a like new white couch and love seat in the DFW area???)

 

[GeorgeHolland]

I agree a sub coffee table can present challenges due to placement limitations, but a down firing end table is working well for me. The design allows me to place the sub in a corner next to my couch. The sub is certainly furniture quality, rock solid with minimal vibrations and most importantly, excellent sound.
Long URL recoded by Admin - and what a beautiful end table sub it is!
[Edited last by Philip Hamm on August 17, 2001 at 02:04 PM]

 

[Jack Gilvey]

Dr. Hsu, of Hsu Research, is a proponent of having the sub as close as possible to the listening position. Something about the sub exciting the listener before the room, I think.