Need opinion for center channel!

[SQconstable]

I have already built a sealed .6 cubic feet enclosure for a 6.5" 2-way coaxial (vifa) that I'm not going to use. I have decided I may want to build an SR-71 for the center since the main left/right SR-71's are so amazing. My problem is that the hole I cut for the current center enclosure is centered, meaning.. if I add a tweeter to it (in the case of a conventional MT 2-way), it would have to be left- or right-of-center, throwing off the symmetry. My only other choice was to use a Seas coaxial, but the box response sucks (according to WinISD) in .6 cubic feet. It wants more like .3 cubic feet and I dont feel like stuffing styrofoam blocks in there since I've already made it "large". I also wouldn't get as low of a freq response with the Seas, even in the recommended enclosure size, compared to a separate woofer from the SR-71 kit.

Has anyone here ever used a regular 2-way MT ontop of their TV for the center? If so, did you notice a definite symmetry point where you had to stagger the box so that the sound was centered? Did you choose the woofer as the center or the tweeter.. or somewhere inbetween? Where does the center seem like to you?

[littlesaint]

Can you stand the MT vertically the same as the left and right? A horizontal speaker is never optimal. The only reason center channels are done this way is to allow them to sit on a display or fit into the stand the display sit on.

[SQconstable]

Unfortunately I can't make the vertical compromise since I don't have room to stand up such a speaker in front of my DLP, it would be obstructive, and I don't want to put it on a stand beneath/infront of it (child on the way). I could have made a box that stands vertically ontop of the DLP shelf but the aesthetics wouldn't pass wife-approval. I guess I wouldn't like it that way either. In the studio, when we used to mix 5.1 stuff, the center was exactly like the other channels, vertically positioned Dynaudio 2-way MT's... and all were on stands. It's impossible to follow this same setup in the home, especially with a child playing around on the floor. I like the height my 65" DLP is at right now so I wouldn't want to raise it in order to put an identical, vertical MT infront. Given that I would have to put the center ontop of the DLP shelf, I have two choices only: SR-71 on its side, or Seas coaxial. With x-overs and all, they both cost about the same (~$180-190 for 1 center speaker).

My dilemma is regarding the symmetry issue when using the SR71 on its side (bad) versus the Seas coaxial in a larger than optimal box (bad?). The plot I got in WinISD wasn't too nice with 18L, but is that plot the final word? Can someone check the plot with 18L/.6 cubic feet on the Seas T18RE/XFCTV2 (H1333) and T18REX/XFC (H1353) (one is shielded with diff specs)? The Madisound enclosure is .48 including the port, for 46Hz using the XFCTV2, but I'm not sure if they specifically chose that volume for this speaker or if they chose the closest box size in stock to work with it. Finally, if I were able to use either of these Seas coaxials in my .6 cu. ft. box, would I be able to get a better response by modifying it in some way other than simply stuffing it to get the airspace to decrease (like port tube changes)?

What would you go with in the end? SR71 on its side (rear or front ported) to match mains, OR Seas coaxial (which model) and have symmetry? What's the lesser of evils?

[Jed]

Maybe you could do an MTM with the ER18s for the Center Channel.

[SQconstable]

I guess I could do that... I'd have to redo the baffle though (already has woofer hole cut, centered). Would that add to the crossover cost? Could I take the kit crossover from Madisound and add to it for that purpose? Oh yeah, 2 of those ER18's in .6 cubic feet will probably be detrimental considering they need at least .5 for best low freq extension, right? I'm trying to stay well below my center channel shelf's max weight load of 31lbs too. I feel 31lbs is pushing it too.

Haha my wife just posed the posibility of a TMT for symmetry Hmm I wonder how a tweet on each side of the centered woofer would act?!?

[---k---]

comb filtering.

[complet]

There is no problem using the Seas H1333 in a 18L box, except that the driver has limited xmax. In fact everything from 12 - 24L will work "fine".
If you use XO at (60-)80hz there will be no problem with cone displacement.

[SQconstable]

I was looking to use it down to 40Hz. Complet, would you have an issue with the other scenario?

[ThomasW]

Standard crossover frequency for a sub out is 80Hz. That would be a good choice for a single small driver center.

[complet]

I was looking to use it down to 40Hz. Complet, would you have an issue with the other scenario?

I'm fan of Seas, and fan of coax in general, but Seas Coax drivers has one bad thing and that is limited xmax. You should remember that xmech are rather good, so they will not be damaged, but the sound is of course suffering.
Your enclosure is on the big side for this driver, in a smaller box it will tolerate a little more power.
As a stereo hifispeaker with "easy" listening it will work great, but as a center speaker with higher sound level I think HP@40hz will be to hard. Dont expect it to work good lower than 80hz.

[SQconstable]

True, but I've been having better results with the lower highpass cutoff freq of 40Hz in terms of the fullness I'm hearing coming from the center alone. 80Hz hp doesn't get those lows like I want. Eventually I feel like someday I'm gonna just have all-identical full-range speakers with subs in each one. It sounds so good that way. As for now I'm thinking the option of the Seas coax is out of the question since I like to turn it up (without distortion/suffering). I'm not sure why that driver is so expensive anyway.

Ontop of my 65" DLP at the moment is my empty, 18" wide, 7.5" tall, 11" deep center enclosure which I will design the SR71 kit (1/2 a kit hehe). Imagine the woofer hole is dead center. With a tweeter mounted on any side of it, the tweeter's midpoint will be about 5" off-center. I'm sitting about 11 feet away from the center speaker. Does that seem like much of a problem?

While I can't front mount this tweeter infront of the woofer cone, I just had an idea of top mounting it (aiming forward of course), without a baffle of its own. That would be bad, right? In other words, I would suspend the tweeter above the box via a small baffle (maybe 4") with no enclosure behind it. The box would then look like it was flipping you off with its tweeter lol. What's the cons of that design? A pro I can think of is that it preserves the vertical mounting.

[complet]

I agree with you that lower is better, and if you play load the Seas Coax isnt the best choice. But expensive? No I think you get what you pay for. Its a good bassmid with a good tweeter.

You should not use two tweeters, first of all, you dont need it. (What you need more is two bassmids, because of sensitivity and Baffle step.)
One tweeter on top of the enclosure is a good ide, but dont use it without a baffle, that will cause some heavy diffractions. The best thing is to use a little baffle for the tweet with an "unusual" shape. A circular baffle with the driver in the center is as bad as it can be.

Here you will find an good example to follow: http://www.htguide.com/forum/showpos...3&postcount=27

[SQconstable]

Ok, now I'm curious... why have two midbass drivers in the center exactly? If it has to do with sensitivity, couldn't one just turn up the center more? As far as baffle step compensation, it looks like EQ could compensate for that, possibly? I would have originally opted for an MTM design, but >1 cubic feet ontop of a shelf connected to the DLP would have made me worry when it was going to fall. There has to be some real reasons people spend more for an extra midbass driver as well as crossover modification (or are there?) for such an addition. Did the practice of MTM start when someone used a single midbass woofer and thought, "hmm that's not loud enough in the midbass.."? I know there's some interesting things to prove in theory but how evident is this 3dB addition of cone area?

[complet]

First; two tweeters will only give you problems, and you dont need it because you have to lower the sensitivity anyway.

Two midbass drivers can give you 3dB higher sens overall, or used in a 2,5 way, it will give you BSC without loosing 3-5dB sens of the speaker.

To obtain 3 dB higher SPL from one driver, you need double power. If you use eq as BSD, you also need a lot more power, maybe around three times more in the low end. (3 times power = 4,7 dB)
So yes you can do it, but power is expensive.
And you must remember xmax, dist and so on.

IMO a center with one midbass and one tweeter vertical gives you the overall best soundquality, IF you dont push it to hard into high SPL.
With higher SPL two mibass drivers is a better choice

[SQconstable]

I definitely won't use two tweeters.

I like the idea of using 2 woofers in the center, but my mains only have one.

In the case of a vertically aligned MT, how large should the tweeter baffle be for a 27TDFC, to be added to the top of my rectangle box? I would flush mount it, of course. Hmm I could do something neat like angle the tweeter baffle downward towards the listener while keeping the woofer straight ahead. Or would that cause issues?

[SQconstable]

Found this on another thread.. has more detailed info about what I was wondering: http://www.nousaine.com/cen%20chan%201.htm

[SQconstable]

Well it looks like I'll be definitely creating an extended, vertical baffle for the tweeter ontop of my sleek rectangle box. It won't be very attractive, but what can ya do...

I gotta order another pair of these SR71's.

Wait... how large should this tweeter baffle be? How much wood on the outside of this flush mounted tweeter shall there be? Hopefully not as wide as a normal baffle. Could it be wider rather than taller? or does taller become important, just as much as being wider? Hmm.. what if it was a circle...or should it attach to the main baffle as if it were seamless? Trying to understand the purpose of this baffle when there's already about 1.5" of plastic plate around the tweeter driver material itself hehe. Can someone help me understand that? Is additional baffle really going to help create, essentially, a waveguide? If I could simply attach a small baffle with maybe .5" extra wood around the tweeter (with rounded corners), that would look tasteful.

[Dennis H]

Just build a stock SR71 and modify your rack so it can sit upright in it's normal position. If you change the design, you're a test pilot.