How To "Bridge" A Stereo Amp to Just One Channel

[Super]

In my opinion, an enclosure is one thing you'd be better off making yourself. Personally, I'm not too fond of particle board for use as a sub enclosure, which is all too often the case with older cabinets. At my local home depot, 2 4x8 sheets of MDF can be purchased for 20 bucks, with plenty of scrap left over for internal bracing. A little wood glue, a table saw, some screws, and a port or piece of pvc pipe and voila. You have a much sturdier enclosure with less resonance. Its up to you how much money you want to save, but in my opinion, the enclosure for a subwoofer is too important to cut corners with.

(Oh yea, if you go with the Shiva, don't rule out the possibility of a sonotube enclosure. Mine is almost completed and is looking pretty good. But if you use the Titanic or Peerless drivers, dont try a downfiring design. They werent designed for this configuration, and gravity will cause the driver to sag.)

[Edited by Super on 09-18-2001 at 10:30 PM]

[GRollins]

Wear out the channel?
Man, I hate when that happens!
(Ahem...)
Even with the Titanic/Shiva/whatever, you're not going to get to 16 Hz without some electronic help (bumping up the bottom end by one method or another). Those drivers are good for -3 dB in the 25-28 Hz range. -10 dB is pretty much useless. It's something the marketing people came up with so companies could claim ludicrous frequency specs. -3 dB is already half as loud. -10 dB...fergitit.
Corner placement does not give flat response. You're trapped between 1/8th space radiation patterns and a crude horn. Ugh.
In my mind's eye, I'm looking at an old (large) Advent. I'm thinking it's about half the volume you'd need to get one of those drivers down to the upper 20 Hz range. With a smaller box, you're going to roll off early, with a horrendous bump right before rolloff. Those boxes weren't so well constructed that I'd go all rubbery in the knees wanting to gut one to use for a subwoofer. Bear in mind that 3/4" MDF goes for less than $20 a sheet. You could build your own enclosure, at the proper volume, probably with one sheet.
If you're thinking of a 10" driver, you might--maybe--be able to get a box that's within shouting distance of a properly sized enclose, but either way, you're going to wreck havoc on the Thiele-Small response.
(And, in passing, you hit the nail on the head when you said rotted drivers in those old speakers. Why? Foam surrounds! Like I said...beware.)
You're likely to have trouble mating a passive radiator to one of those drivers.

Grey

[Super]

I'm not sure if you noticed, but the Adire Audio website also gives examples of buyer's projects, and some reccommended designs of their own. They can be rather helpful when designing the enclosure, considering some of the designs have already been tested and tweaked themselves.

[kelticwizard]

Grey:

"Corner placement does not give flat response. You're trapped between 1/8th space radiation patterns and a crude horn. Ugh."

My understanding is that corner placement is no good for midrange and highs, but recommended for bass. How bad are these corner irregularities, and are they markedly improved by movng them to another spot along the wall, (I assume you don't put the subwoofer in the middle of the floor)?

[kelticwizard]

Super:

Did a search for sonotube. Do you mean the round cardboard tubes used for puring cement? I have a pair I was going to use for another purpose, but didn't.

I thought of them as loudpeaker enclosures, but it seems to me the that although the cylinder shape gives added strenth, they would need re-inforcing. It is easy enough to slice another tube lengthwise with a knife, and fit the second one around the first. But I woonder how many layers are necessary?

It also seems to me that you can cut a 45 degree angle near one end, turn it around and have a 90 degree angle at the bottom, where you can fit the speaker. This avoids up or down firing woofers. Then construct a tiny stand to hold the thing upright.

Just spitballing a few ideas here.

Where can I read more about your sonotube project? Do you have a link I can click on?

[kelticwizard]

Thoth:

Re-checked out the circuit you gave on that link, thanks.

Have you ever heard of anyone improving the performance of a mid-fi amp or reciever by adding larger capacitors to the power supply? Often wondered about that. It would seem easy enough to do.

[Super]

Yes, sonotube is the forms used for casting concrete pillars. Sorry, but I haven't published the sub online. Actually, no additional bracing is required, because of the tubes shape. You can push in on one of the sides, but when internal forces from the driver push out on all areas inside the tube evenly, the tube wont flex, making it a very ideal enclosure. What some people do is add a circular insert inside of the tube, although it isnt necessary. I would suggest doubling and tripling up the endcaps in order to provide extra weight to keep the sub/speaker from vibrating on the floor. You will need to line the inside of the tube with foam however. If you don't, it can resonate and give off a ring, similar to a tapping the side of a bell or wine glass.

Your idea would work, but it would be even easier to just glue a face or gasket onto the area where you made the 45 degree angle cut, and let the speaker stand on the 90 degree angle. This site has links to SEVERAL sonotube projects which I found extremely useful: http://terryctheater.tripod.com/shiv...um/page12.html

If you have any more questions, feel free to ask.

[GRollins]

Yes, sonotube is the paper tube stuff, available in a number of diameters and thicknesses. Obviously, for speaker use you want it as thick as possible. Another similar possibility is PVC pipe. Some people use "T" joints with PVC to mount the drivers. For a 10 or 12" driver, you'll need to go to the larger PVC they use for sewer and such. I've got the stub of a 24" pipe that has 1" thick walls. Pretty stern stuff.
Yes, out in the room is the preferred placement for subs. People frequently speak of room reinforcement and corner placement as though they are magic wands. They aren't. There ain't no such thing as a free lunch. If--and I'm assuming, here--your goal is something like high fidelity and flat response, you'll be better off placing all speakers away from walls. Yes, subs are largish cabinets and don't always fit into peoples' decor, etc. Sometimes compromises must be made. But corner placement is to be avoided for nearly all speakers (and the speakers that are designed to be placed in corners are generally best avoided)--two walls at a 90 degree angle do not a horn make.
The best rule of thumb I've seen for speaker placement is one third of the length of the room from the front wall, and one third from each side wall. That's for starters; fine tune a bit, as necessary. My current speakers are one third down the room, but are spaced somewhat further apart. They're able to sustain an image across that width. The setup I was using before could not.

Grey