Quad Drivers (ooooh =p )

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
(big puff of dense smoke...genie appears...)
(smoke cloud draws in on itself and disappears...genie gone...)
I take no responsibility for what transpires after you visit this site. Just remember that in a lot of stories, wishes granted often have unpleasant side effects.
Space? That's what front yards are for--to store unused furniture, and other sundry objects (parents who object, for example) that aren't needed at the moment.
Money? Whaddya think Wells Fargo trucks & banks are for? Knock over little old ladies and take their lunch money.
Self control? We don't need no stinkin' self control!
Been nice knowin' ya, fella!

I'm trying to avoid simply plugging it into the '+ -' jacks of a reciever, besides, I lack a serious reciever that would power the enclosure (I have a Philips Magnavox MiniHifi and an old Harman Kardon reciever that I wouldn't trust too far)..my parents aren't trusting me to plug it into their legitimately good stereo equipment..ah well. Anywho, plans for a powered sub enclosure.

BTW - is there something wrong with a 4th order bandpass, you didn't sound too hot on the idea, Keltic - you're definitily more experienced in this field than I, so maybe there's something I should watch out for?

You're right, there is lots of space on the front lawn, which if these projects continue, I'll likely be spending a lot of my time... in a tent...

Lloyd: Depending on how sturdy the particle board is, screws might not hold up too well. Drywall screws with the bigger, coarser threads work nicely in most cases though, but you might try putting the edges together using biscuits or dado joints. Personally, I use biscuits.

Also, stop by a local cabinet/woodworking shop and see if they have any "rue glue". I've seen MDF rip apart before this glue gave way...
Ordinary aliphatic resin woodworking glue will do the job quite nicely. Been using it for years. Stands up to bass drums, bass guitar, pipe organs, and exploding planets. Cheap, cleans up with water. In case, like Bryan, you'll end up listening in the rain out in the front yard, it's also available in a water resistant formula. Don't know how to keep the MDF going in the wet, though...


I dont know if its my just being tired, but I can't find the forementioned sub on the Wisdom site...

And on the subject of cabinet construction, I figure why not throw out a few more tips while I'm at it:

1) <i>Sand</i>. Can be a sub's best friend. By adding sand to an enclosure, you a) add mass and better the system's coupling b) help dissipate those nasty vibrations and resonances as heat. Negative side: Makes your enclosure bigger, functionality is inversely proportional to SAF.

2) Wire ties/silicon. Quite often, people forget to secure the internal wiring to the driver frame or bracing of the cabinet. If you forget to do so, finding that rattle is going to drive you nuts. A little dab of silicon or a few wire tires along the bracing can go a long way. (I used adhesive-backed phone wire clips from Radio Shack. They worked nicely on the driver frame.)

3) Spike it. Another thing often overlooked is how the sub will be coupled to the floor. If you're worried about marring your floors, threaded bolts and cap nuts can create dome-shaped "spikes" to sit on. Practice point arrowheads work well also. There are also a number of commercial offerings, which are easy enough to find if you look around online. Oh, and just remember, three spikes are easier to level than four.
(dense cloud of dense smoke...genie appears...)
(...something to do with being at the business end of a flame thrower)
Stupid genie. I fired him. You just can't get good help any more.
It's not you that's tired; it's me. It frequently happens when I'm short on sleep. Try:
Maybe I'll get it right this time.
(No, they're not real big on information or sexy pictures, but at least somebody out there is doing big subs in cans.)

hifi said:
ok..i se your point audiofreak i was more worried about in room respons and so on than high spl =)


I was worried about response more so than SPL also and acoustic coupling has a lot to do with it.

If you use a line array as you described @ certain frequencies the top driver will not be well coupled to the bottom driver and the 2 will act (at least in part) as seperate point sources causing peaks and toughs in the response @ different points in the room.... in the 2x2 square config all the drivers are well coupled to each other because they are all physically very close to each other making response more even across the room.
Consider the top driver in a line array:
An impulse begins (say, a drum). Pressure mounts in front of the cone as it travels forward. The impulse will not travel down the front of the cabinet because as it leaves the cone, it is met by an equal intensity pressure wave coming from the cone beneath it. Elementary thermodynamics: for energy to flow, it has to flow from a place of higher energy to a place of lower energy. It will not flow between points of equal energy. (Think of it in terms of voltage or current if it helps.)
The wavefront cannot travel down the length of the line in order to be out of phase with the bottom driver; it leaves the cabinet as a cylinder (assuming close proximity between the individual drivers, not likely to be a problem here due to the wavelengths involved).
Basic line source theory.
The four-square array you're describing:
is going to be a good approximation of a point source at low frequencies. If you wish to debate point source vs. line source, that's cool--both have advantages, both have disadvantages--but don't misrepresent the action of a line source.

diyAudio Moderator Emeritus
Joined 2001

I am neither for nor against your bandpass enclosure, since I have never built one. I read an article by Laurie (man's name in England) Fincham of KEF and it seemed to show some nice bandpass setups-one has a 3 dB improvement over the ported box. When I try to model using a program, though, I find very little improvement, at best, over the ported box.

Some people on this board have said bandpass enclosures have a habit of not turning out the way the program shows, either.

But if you have faith in your modeling program, or have read an article with a specific setup that works, go to it.

The wiring setup I gave you would apply to any enclosure-sealed, ported, or bandpass. If you run off two channels, make sure what your amp puts out most power to-4 ohms or 8 ohms. That will have a lot to do if you should hook your speakers up in series, (twice the single-speaker impedance) or parallel (half the single-speaker impedance).

Hooking all four up to one channel yields the same impedance as a single speaker, and is recommended. You might be better off bridging a two channel amp to get that single-speaker impedance if it is convenient.
Since I'd mentioned spiking the sub in my previous post, I just thought I'd mention that www.partsexpress.com has their chromed Dayton spikes on special until December 31st, for a bit over $12, from their normal $20. These are heavy duty and of very high quality. I've only heard good things about them.

And since we're on the whole line array thing... has anybody seen or had experience with line array subs with a cylindrical backing? I'm thinking that a half a sonotube with an MDF baffle would be nice... I've got 2, 4 foot sections of sonotube left downstairs , cut in half, thats enough to do 4 more subs! Who am I kidding, the Firebird's new engine isn't going to pay for itself...
Bear with me here because I'm thinking out loud (in a manner of speaking--if you can't hear me, then lean closer to your monitor...).
I've always thought that there should be a clever way to use a hemispherical cabinet backing. It goes like this:
Launch a wavefront into the cabinet. It reflects. By basic laws governing optics and any other wave-related phenomena, this reflected wave front will return to the center (the radius of curvature) of the cabinet, thus focussing the wavefront.
Okay, so what?
What if you were to slot load the cabinet <i>right there</i> where the pressure wave focusses? Is there any benefit to doing that?
Remember the wave/partical duality of light. Your first impulse will be to think of this in particle terms, i.e. air molecules rushing back and forth. Don't think that way. Release your preconceptions. Think in waves, not particles. (This may end up dictating a certain necessary radius to the tube, say, 1/8 or 1/4 wavelength of the free air resonance, something like that.)
As a practical arrangement, cut a tube in half, axially. You've got two hemispherical cabinet backs. Place MDF across the fronts, mounting drivers up the middle, but spaced out a little bit, so that there's room for slots an inch or two wide (whatever the math says, I haven't broken out the books to work this out in detail, it's just a thought experiment) between each driver. You can analyze this as slots, or as ports. (I know in this day and time, everyone likes to use tubes for ports, but way back when they just had holes in the fronts of the cabinets.)
This idea has annoyed me ever since I first thought it up. I'm not saying that there <i>is</i> any benefit, just that there might be. Cogitate on this and see what you can come up with, pro or con.

Ok, trying to get a visualization here...

Are you suggesting that the slots be located on the MDF baffle or in the back of the enclosure?

Ok, only other thing I can think of right now, is where (if) wave cancellation from each of the drivers in the array is going to be a factor. For whatever reason, I'm visualizing wave interactions occuring at the very point in which the cabinet is slot loaded, maybe cancelling each other out? Or perhaps, if spaced properly, an even more focused point of energy at which the cabinet could be slot loaded? Hmm, I'll further partake in this discussion when I can clear my head and think logically about this...
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.