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DIY Center channel crossover help!


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#21 of 22 OFFLINE   Mark Seaton

Mark Seaton

    Supporting Actor

  • 600 posts
  • Join Date: Oct 10 1999

Posted February 17 2001 - 03:48 AM

Hi Patrick,

I am working on a somewhat similar project at the moment, alongside wAAAAAy too many others Posted Image. It looks like you have found your way to a good design for a center channel. The thing to remember is that while we do want the front 3 speakers and their response to be as identical as possible, the only case where 3 IDENTCIAL speaker works is when all front 3 speakers are in a similar location with respect to nearby boundarys... The only easy way to do this is with a front projection system, and often a perforated screen. As soon as you throw a speaker on top of a big RPTV you just changed your speaker. You now have a center channel who's apparaent front baffle is MUCH larger than the front right and left speakers.

What this all works out to for a typical home theater center channel is that we would like the driver/crossover complement from the midrange up to be identical to the right and left speakers. The bass range, say below 300-600Hz depending on the speaker, must be addressed for the intended application and placment.

The center channel easily has the most content in a movie soundtrack, so at least a pair of woofers to complement the mid & tweet make a lot of sense. I would suggest going with the largest speakers you can comfortably fit to cover the bass. In the case of your center channel above, take a look at drivers up to 8" to make sure there aren't some better options. As for wiring, I would just go with 8 Ohm drivers, and wire them in parallel. This will afford you some small gains in sensitivity (ie at 2.83V) and simple scaling of the crossover components makes the crossover design no more difficult.

When determining the F3 of the system, check out what your processor is doing when you set the speaker to small. Is the crossover selectable or fixed at 80Hz or other? Take this into consideration in your design, and allow yourself the most headroom possible for that low frequency limit.

One of my current projects is using the same 1" tweet and 4.5" mid in each front speaker, while the right and left speakers make use of 2 sealed 8" woofers each, and then center uses a pair of shielded Vifa 6.5" drivers.

Mark Seaton
Mark Seaton
Seaton Sound, Inc.

#22 of 22 ONLINE   Patrick Sun

Patrick Sun

    Studio Mogul

  • 37,750 posts
  • Join Date: Jun 30 1999

Posted February 17 2001 - 10:28 AM

Brian, Sunosub II is undergoing a bottom endcap overhaul: I'm slicing off my original endcap with three 4" ports (36" long) and replacing it with an endcap with one 6" port (22" long). The original porting was just too long (need to keep the length around 5x the port width, otherwise pipe resonance can show up, and I had some shuddering at high SPLs). The 6" port will be wider than two 4" ports, and I can live with its vent mach number (that's hardly much of an issue anyhow for me).

What's the hold-up you say? I am in need of some parts which I can't quite salvage from the old endcap: the straight leg mounts are nowhere to be found anymore (I've tried 3 Home Depots and 1 Lowe's), I can find the angled leg mounts all day; I am waiting for the dual-input terminal cup to show up at my local audio shop one of these days. I like these because they make it easy to run parallelled connection to the dual voice coils, or running separate amp channels to each voice coil. Does anyone know where I might be able to get those little bitty terminal connectors that SVS uses? Their footprint is about 1"x2.5".

Mark, thanks for the tips and info. Good luck on getting your center channel speaker up and running! I've since changed the design just a little more (But it's in stone since I've actually bought the drivers and corssover components yesterday!). I changed the woofer to the Vifa M18WO-09-08's to get better low end response. True, this is not a shielded driver, but I don't think I'll experience problems with the CC speaker sitting on top of my RPTV. If it does, back to the drawing board! I am still running each woofer in its own compartment (15 liters), but vented with a 2" port (7" long) for each woofer, Fb=44Hz, F3=46Hz-48Hz (on paper). The woofer low pass filter's F3 will be around 400Hz. The final dimensions also went up a little: 28"x10"14".

Just for giggles, I bought the necessary L's and C's to wire up the 2 woofers serially as a 16 ohm load just to see if the sounds is better, same, or worse than when hooked up as a parallelled 4 ohm load. I've designed the crossover such that the tweeter and midrange crossover network is on one 1/4" plywood panel, and the woofer crossover network in on another panel, which can be swapped out for easy comparison between serial/parallel connection. Plus, it'll allow me to add in any additional current dividing resistors network if I need to tame the 4 ohm woofer load's SPL on the woofer crossover panel without disrupting the rest of the crossover network for the tweeter and midrange. I'm going to route in some grooves (on the middle compartment containing the tweeter and midrange) so I can actually slide the panels in and out when I make the changes. It will be pretty nifty.

One of my friends has this kick-butt wood shop in his basement, and he was nice enough to cut up my leftover MDF (from Sunosub projects in the past year) this afternoon for me. I owe him a 12 pack of his favorite beer. I didn't have to buy any wood except for some 2x2's for bracing and a 1/4" thick 2'x4' sheet of plywood. I'm using the plywood the same what I did with my subs, so I can provide the t-nuts I'll be using for the speaker machine screws something to dig into when I hammer/glue them into the screw holes. BTW I really want a table saw now!

I did all the final panel calculations for the dimensions last night and the cutting went off with only a little hitch (had to shave off a tad off the side panel's height, like 1/16" to get everything nice and flush). Otherwise, my numbers were just right. Thank goodness he's a perfectionist, so once I glue/screw/dowel these MDF panels together, I think the box will be very squared up (doing a preliminary panel fit confirmed this for me).

I'll be taking more photos of its construction as well (though probably not as many as I would for the subs).

I'm thinking of just drilling a 1/4" hole through adjoining panels and placing 1/4" dowels through the outside of the panels and using wood filler to fill in the dowel holes as the ends are glued and clamped tight and squared up. Is this is a good idea? I don't like the idea of using wood screws through MDF and then filling in the holes with smaller dowels.

Then I'll decide on the veneering (I'm hoping for light rose wood color for the veneer because it'll match my other front speakers made out of real rose wood). But that's a little while away. If I don't veneer, I'll be painting it some light yellowish/beige/tan color.


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