Need Help with DIY Subwoofer Selection

[Argroft]

If using the Crown XLS 1500 with two DVC31088 12" subs, I'm assuming I am to use one sub per channel. Am I correct in assuming that since the DVC31088 is a dual 8 ohm voice coil sub, I should be able to wire it for and impedance of of either 4 or 16 ohms? If so, wired for 4 ohms, I should see 525W per channel, which should be more than acceptable for the DVC31088's 350W RMS rating. OR would it be better (if using with 2 subs) to run the amp in bridged mode, then wire each sub in series then wire both in parallel with the amp for an 8 ohm load? I don't have a lot of experience using dual voice coils or using them with 2 channel, bridgable amps.

Also, here's an update of the table enclosure with a solid mahogany top.

Opinions?

 

[rojo]

The amp sees pretty much the same load with 8 ohms bridged as with 4 ohms stereo. One configuration isn't better than the other in that regard. But if you run them stereo, you'll be able to level match them to compensate for asymmetric placement if needed. If one is farther away from the primary listening position than the other, you might find it useful to turn the gain down a smidge on the closer one. Or if in the future you get an avr with dual sub correction, or you get a miniDSP or similar, the stereo config will let you flatten each sub individually.

I like the look of the solid top. You know, if this project of yours is successful and you enjoy it, I think there'd be a market for end table subs. As far as I'm aware no one builds them to order (save for maybe Jim Salk). I think Danley played with making a coffee table sub once but it didn't quite take off. *shrug*

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[Argroft]

Just ordered the Crown 1500 XLS, should be here in a day or two. I should be able to get the sub sometime after Friday when I get paid. Is there a specific gauge wire used when hooking up subs?

Maybe you can answer this question: when using a sub in a down firing enclosure, do I need a double baffle on it and does bracing need to be done differently? Thanks.

 

[rojo]

I'd use at least 12AWG internally. That'll let you run your end tables with 30 feet of wire from the amp with negligible signal loss. See this page for a useful guide.

A single baffle should be fine. You could do more substantial bracing, with a spine going from top to bottom and a rib from side to side. It's up to you. Just remember that the more bracing you use, the more you'll need to compensate for its displacement by increasing the external dimensions to keep the tuning correct. Also, your sub will be heavier with each additional brace.

You know, one of these days you're going to have a home of your own and a significant other who's going to insist that she wants the couch and end tables on the other wall. No, she changed her mind. She liked it where it was before. Or maybe try it to the left a little. No, back right. The heavier you make these things, the more you're going to scuff your new floors. On the other hand, the less bracing you use, the more your table tops will vibrate. I'm sure you'll find a worthwhile balance. See http://www.hometheatershack.com/forums/enclosure-volume-calculator/ to figure out what your envisioned bracing will displace. For what it's worth, my SDX12 driver is mounted on a single baffle and the box has minimal bracing -- just a single 1" x 4" beam going from side to side behind the driver. I have an amp, a USB hub, and my miniDSP sitting on top. The hub and miniDSP each have a small square of rubber shelf liner underneath, and they never move.

 

[Argroft]

I don't think bracing will be incredibly needed because of the way this thing is designed. The table consists of the internal box (made like a typical sub box) and the external "table". The table top will be .75" thick mahogany mounted to the already .75" thick MDF box. The sides will a 30/70 mix of MDF and mahogany (also .75"). So in reality, the sides of the box and the top will be 1.5" thick overall while the bottom baffle is .75". Using a weight of 96 lbs per 4' x 8' sheet of 3/4" MDF, I estimate the enclosure to weigh about 130lbs. That is likely an overestimate as I used slightly oversized sizes for each piece while adding about 10% of that calculation to that number to make up for driver and port weight and any other potential additions.

In the design I made, the feet are 6" x 6". That equals a total of 1 square foot of contact area with the floor. From what I've been reading elsewhere, it is preferable to either have floor spikes for minimal contact or some sort of isolation platform. If I choose neither and go with my original design, will I be sacrificing any quality in sound? Also, with 1.5" thick walls, do I really need much (if any) bracing? I could go a ton lighter and a bit smaller if using a veneer, but I don't like the quality versus solid wood.

Also, I greatly appreciate you putting up with me and my constant stream of endless questions!

 

[rojo]

De-coupling from the floor can help you avoid your pictures rattling on the walls and sound being transmitted to other rooms, but I never bother with it. You can always change your mind later if needed, right? You know, since the tables are going to be so heavy, I wonder whether adding brass casters would be worth considering? That'd make them easier to move at the same time as minimizing the area in contact with the floor.

Part of the point of bracing is not just to make the cabinet more inert, but also to break up the resonant frequencies of the walls. Divide the wall in half, and you'll increase the frequency at which both halves resonate, moving the resonance beyond the frequency range of the sub.

That's what I've read, anyway. I haven't seen any sort of formula for determining at what frequency an MDF board of X length * Y height * Z thickness will vibrate, nor how strongly at N1 dB the sub plays before you get N2 milliseconds of ringing. I admit I'm in the minority, but I don't place as much value on obsessive bracing as most other builders. Supporting this, from time to time I see reviewers of entry-level subs express an initial impression of "This thing is light! It's going to be a ringing mess." and then express surprise when their expectations are surpassed. Jim Wilson's review of the NXG NX-BAS-500 is one such review. I may change my mind next year or next week. But for now, I think the added size, weight, expense, and effort needed for extensive bracing exceeds the infinitesimal gains to sound quality. As I mentioned earlier, my SDX12 cabinet has minimal bracing, but it's tight and musical.

So, yeah, I think if you've got 1.5" thick walls, I'd be inclined to agree with your prediction that bracing won't be an issue.

What would your sub cabinet look like still with the black legs but without the racing stripes, I wonder?

 

[agarwalro]

De-coupling from the floor can help you avoid your pictures rattling on the walls and sound being transmitted to other rooms, but I never bother with it.

De coupling definitely helps with the rattles, but, I thought it was about preventing the floor from becoming an inaccurate sub. I've got my subs on Grammas and can feel the bass change (for the better) when I take my feet of the floor. I get a good ab workout any time I settle down for a listening session.

This is more a concern for people with hardwood and/or carpet on concrete subfloor and not if the room is a basement with carpet over a solid floor.

 

[Argroft]

Here's a shot of the design minus the stripes:

I don't care for the design all that much, but only because there's nothing to break up all that mahogany. When the design is used with my speaker enclosures, the drivers help break it up and add a little more visual appeal. I am open to suggestions on design. And the only reason I tried out the stripes on the side was to copy the look I used on my center channel since I like how that one turned out. If need be, I could scrap that design and start fresh, but I think I was headed in a good direction. But, like I said, if you could come up with another idea, I'll gladly take a look into it!

 

[rojo]

Hmm. I like it with plain sides, but my tastes are probably more conservative. I am getting on in years, I suppose. Don't get me wrong, though: I didn't dislike the stripes. I was just thinking that if hiding in plain sight is a goal, then making the end tables less conspicuous / more readily matching other furniture ought to be worth considering.

Ultimately, though, the stripe design is a go to hell design. If you love it, then build it! Anyone who doesn't like it can go to hell. If it's half as appealing as your other builds, it'll be a work of art no matter what.

 

[Argroft]

I like my build to have a little more visual appeal. Usually when I have a panel, I'll do a style & rail design with a raised panel in the center. With this design, I think that would be a bit of a clash of styles. I like the stripe, and I'm not overly concerned with matching other furniture as I'm likely going to be building the other furniture.

 

[ARES24]

I don't mean to nit-pick but I don't think this forum is here to discuss personal furniture preference

 

[rojo]

Yeah, that was close! Thank goodness there are watchdogs such as yourself around to keep the forum from devolving into a cesspool of uncommonly creative woodwork and ideas on aesthetics. Left unchecked, spouses might join and start commenting on WAF. Then before you know it, there goes the neighborhood.

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[Argroft]

I thought it seemed to all go together. That and I'm not sure where else I'd get info on a subwoofer end table. Most "non-audioholic" people don't understand the need for this kind of thing and wouldn't be helpful in this type of thing. Eithe way, my new amp showed up today, so i think I might be starting a build thread on this thing soon. I'll post a link here once I've started it!

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[ARES24]

I am not arguing the need for aesthetics, I am just saying that personal aesthetics shouldn't be crowd sourced Then it just becomes box store design D: