Low Profile Center Speaker

[jefe_de_estado]

First of all, I understand that there will be many issues with wanting to build a low profile box, but I have been mandated by the chief design officer (the wife) that I need to build a smaller center channel. So this probably won't result in the idea speaker, but as long as it has a good WAF, and doesn't sound horrible, everyone will be happy.

So, right now, I'm looking at the Dayton ND90. Seems to have loads of excursion which could help the speaker sound larger.

The only requirement imposed by the CDO is that it must be shorter, so I'm aiming for 4" - 4.5" box height. I can go somewhat wide, ~20" or more, and maybe 14" or so deep.

With that volume constraint, what would be a good use of this speaker. Full range? (is that enough volume to do some sort of TL?), MTM? (I can get away with lobing issues as I don't have seating 30 degrees off axis), MMTMM? MMMM?? MT? I can also get away with the fact that this speaker has pretty low sensitivity, I have a small room and can use the amplifier to balance the center and fronts.

I have a Vifa XT25 with the small flange that I'm currently using and I'm quite happy with it, and would like to use it again in this project to save money (if it's needed).

Any thoughts?

[phenobarb1]

If you really want to keep it below 4" vertical height, what if the front baffle was at a 45 degree angle? Then you could fit a 5.25-5.5" mid-woofer. Not that you really need much depth from a center channel, but it would probably improve power handling. Of course placement of such a speaker would present some issues, as you would either want it to be high, with the baffle angled down, of vice versa. Also internal reflections might be an issue if their is no damping material. Oh well, just throwing it out there.

[mdocod]

All of the ND90/91 series appear to have a very ragged response, If you like the way they look or want to give them a try, my personal gut instinct approach would personally be to use 4 of them MMTMM, with a 2.5 way x-over, using all 4 drivers up to ~750-1000hz and the center 2 up to ~2-4K. The exact x-overs would need to be simmed up, the goal would be to fill in some of the ragged dips in response with proper over-lap in the x-over design.

Alternately, Same MMTMM approach, but with the "T" being a 2" full range and a 2 way x-over around 800hz gentle on the high pass and aggressive on the low pass. A narrow slit 2.5 x-over way could also be emplemented to mild effect here to fill in problem areas.

I would not suggest using them full range unless it's limited to a single driver and on-axis listening. I think combing would be noticeable as you move through the room if you stacked a line of these up sideways.

With the dimensions given, you can go vented or sealed with 4 drivers just fine IMO. For vented, use 1/2" material for the box accept the front baffle and use 550in^3 for the box space and about 250in^3 for the port space. Tune to ~60hz. For sealed, 3/4" material all around. Can't help ya with a TL maybe someone else can comment.

I wouldn't use less than 4 of those woofers, they aren't very sensitive. Using 4 helps get the sensitivity up to something more within the realm of center channel needs for the dynamics there.

If it were me, I wouldn't use them for a center channel. If you want the speakers to sound "bigger" I suggest looking for more sensitivity rather than more Xmax. Also, how much bass extension does your center really need? Do you have a sub implemented in this system? If so, then a simple little sealed box loaded full of higher sensitivity drivers would be best IMO.

At less than half the price: Vifa TC9FD-18-08 3-1/2" Full Range Paper Cone Woofer 264-1062
I would much rather use those. half the moving mass and slightly larger piston size translates to 4dB better sensitivity, only sacrifice about 10% Vd. Could get away with using 2 of them rather than 4 and still have better sensitivity but I would go for 4 anyways. (dirt cheap so may as well)

The tradeoff would be bottom end extension, but I'd rather leave it to the sub/s or front mains to deal with given the space restrictions.

Other drivers I'd much rather use in a center channel with these space restrictions (some of these are pushing size restrictions but could be made to fit with 1/2" top and bottom baffles and some slight carving :
Dayton Audio RS100-8 4" Reference Full-Range Driver 295-352
HiVi B4N 4" Aluminum Midbass Round Frame 297-429
Vifa TG9FD-10-04 3-1/2" Glass Fiber Cone Full Range 264-1064
Tang Band W3-1401SD 3" Neodymium Full Range Driver 264-887
http://www.parts-express.com/pe/show...number=295-338

[jefe_de_estado]

Awesome, thanks for all that info! phenobarb1, interesting idea, but the wife didn't go for it. mdocod, thanks for the fantastic response. I was mainly interested in the big xmax, and didn't look at all the other options. I did notice the raged response, I guess I could XO that out, but that means more XO work and more money. The other drivers I looked at only had xmax of 1mm or so. The vifa doesn't look bad and maybe the RS might work.

I've been shying away from drivers that look shiny and fun to play with (from the eyes of my 3 yo and 1 yo) but the kids have left the current speaker alone for now. I don't care much for grills, I'd like to leave them open.

I'll look at those options and propose a new plan forward. Given that list of drivers would you go with the Vifa or one of the others? I think the biggest issue I have with the Vifa is the added effort it will take to make them flush with the front baffle.

[jefe_de_estado]

Oh, forgot to mention, I do have a sub on the system. It's a really old Optimus 12" DVC of some sort (radio shack special from many years ago). It's boomy, but it does get the job done for now. The biggest issue that I have is the only location in the room where I can put it (in the rear corner) makes it easy to locate sonically. I'd like to have a bit more bass up front to widen the bass sound field. I believe the sub is XO'd at 200hz, and I'd like to drop that down to maybe 150 or lower to push more bass out of the front. The mains are also quite small, so not a whole lot of bass to be had in the front, but it wouldn't hurt to add a bit if possible.

[mdocod]

From a cost perspective, I like the Vifa best, but you're right about the flush mounting.... Just buy a CNC mill and no problem right? hehe..

I like the idea of square and truncated frames if you are willing to take the time to "deal" with that because you can mount the drivers closer.

Comparing the 2 round frame options there, the BN4 vs the RS-100, I'd say pick based on aesthetics and/or impedance requirements or price and work out the details later The RS100 is available in 4 ohm, which may be beneficial or not depending on your amplification. If the ND90s are really more to your liking looks wise then just go for it. I hadn't factored in the fact that the ND90s will make for simpler mounting (can just be surface mounted and they will be "close enough" to flush for government work I suppose). It's still going to be a working speaker regardless of what driver you pick. In looking at the response charts, between all 3 of the options, they all suffer from pretty low sensitivity but the ND90 is definitely the worst. (by around 5dB on average), the chart has it mostly in the 75-80dB range. The BN4 and RS100 chart out in the 80-85dB range, which IMO, assuming the charts are accurate, is a huge benefit.

Plenty of domes to choose from out there that should work fine. It's not going to be hard to "keep up" with any of those drivers IMO. I'd opt for small flange options to give you tighter driver spacing as that is a general rule of thumb that can't hurt. I'd probably offset the center driver upwards a touch as well, again, just rule of thumb stuff.

Eric

[jefe_de_estado]

Ok cool... oddly enough, I do have a CNC router just laying around.... sort of. I have a really high end gantry at work which I can bolt on a router. It's a bit of a bear to program, and if I screw it up, I could jack up the $3k vacuum table. It's an option, but I'd rather not use it if possible, but I do like the look of the truncated frames as well. I'll have to stew on this for a bit. Thanks again for your input!

[CLS]

The directivity of a horizontal MTM might not be optimum if the central unit can't play low enough -- 'traditionally' most of the commercial products by cone-dome combinations are like this.

Search for 'Synegy horn, SH Micro', or 'Bessel Array'. Those might interest you.

[jefe_de_estado]

Finally decided that I'll go with the Dayton RS-100T's. I wasn't too impressed with Vifa's product page which shows a picture of the speaker which looks a bit banged up... So I've been saving up and I'll get the daytons which seem to be higher build quality. Here's a pic of the box so far. Unibox tells me I'll get F3 around 60Hz in a 12.1 L box, 2 - 1.75in dia ports. Which will fit perfectly where I need it to.

I figure I'll fill in the truncated parts of the front baffle with bondo to make the woodworking easier.

Now for crossover design. Any good free software that will help me with a 2.5 way?

[mdocod]

Sounds like a nice plan going so far. I think a 2.5 way is a good idea.

I think the port size is too small. WinISD pro predicts nearly 25m/s air velocity at 50W input (also predicts Xmax limited Pe at ~50-60W for that size box, depending on tuning).

Many people shoot for 10m/s estimated port velocity at Xmax limited Pe. Up to ~15-20m/s in designs with flared ports that are rearward or downward firing seems to be accepted by many designs.

I would go no smaller than 1x 3" dia port, or 2x 2.25" dia ports. A step larger than that would be even better.

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I have been tinkering in speaker workshop for awhile. Once you work out the quirks it seems to work well enough.

Have a tweeter in mind?