Center help

danfuls

Member
2015-01-25 2:44 am
I am building a 7.1 ht setup. It will be 50/50 for music/ht. I'm currently building the Daedalus design linked here: Daedalus

I need help building a center channel. I bought 2 Dayton rs225 4 ohm drivers, and a tymphany xt25dg60 tweeter.(actually 2) I really want to use these drivers in a mtm or wmtw design. If anyone has any ideas on a good midrange to use that would be appreciated. I have X-over 3 pro and have modeled some ideas for a fairly flat fr, but I don't really know enough or trust myself enough to come up with the design. Any and all help is greatly appreciated.

Currently I plan to drive everything with a receiver that can handle a 6ohm load but if I need to upgrade to a receiver with pre outs no problem.

The sub I'm building is a Dayton Es 15 inch Hf in a vented 9 ft enclosure.
 

eriksquires

Member
2013-05-10 4:11 pm
Hi Danflus,

I have the XT25 tweeter, like it a lot but it's pretty directional. That for me is a good thing. I've personally built an MTM with it and a pair of 830991 Peerless 5 1/4" woofers without a midrange, works really well. Here's a link to my blog page about it.

If you are trying to get a wide dispersion, the XT25 is not the tweeter for you. Just look at the 30 degree figures. :) Remember, I love this tweeter, but I like controlled dispersion and room acoustic treatments. If you want to fill a wide listening space the dome version DX25 is a better choice.

Of course, for the widest, and most even dispersion, a center channel with a midrange in the center is almost essential. Still, I'm happy to have avoided the complications in crossover and cabinetry. Here's a 3" midrange I just ran across that would suite your needs. You could probably cross it over quite comfortably at around 4 kHz.

The one negative comment I have so far is that if you had bought the 8 ohm version of the RS225 you could have run them in parallel, giving you a good minimum impedance, better amplifier damping and gotten about 93 dB of sensitivity.

Best,

Erik
 
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danfuls

Member
2015-01-25 2:44 am
I can still return the Rs 225 4 ohm. I just got them really cheap (24 each). I was thinking in parallel they would be 8 ohms and that would be a good thing. Good call out on the tweeter. That makes sense. A lot of my movie watching will be off axis as well. If there aren't any really good designs for the 8 inch 4 ohm daytons I might just build one of the many 6 or 7 inch mtm designs for the Dayton reference line. I just wanted to put the really good deal on the woofers to good use.
 
Nice MTM project there, Erik!
A Speaker Maker's Journey: Introducing the LM-1C
https://www.madisoundspeakerstore.com/approx-5-woofers/peerless-830991-5.25-fiberglass-cone-woofer/

I'm a bit baffled why you want such big speakers in a 7.1 setup. Doesn't the subwoofer or two take care of the bottom end? So the other 7 just do midrange and top really.

Those http://www.daytonaudio.com/specs/specsheet.php?prod=295-376 are 91dB, which is rather loud. Putting them in 8 ohm series doesn't change that. So you'd need a very loud mid to keep up with them whilst keeping things easy to design and good impedance. Maybe this sort of 5" SEAS thing: http://www.seas.no/index.php?option=com_content&view=article&id=77:h1262-08-mca15rcy&catid=46:prestige-midranges&Itemid=463

I'd guess the XT25-60 double magnet tweeter might just be loud enough.

But this seems a bit ill-conceived to me for the bass reasons.
 
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jReave

Member
2012-10-30 4:34 pm
If you lose at least about 4dB to baffle step, the Dayton Audio RS125T-8 5" Reference Woofer Truncated Frame seems like the obvious choice to match your mains. If you're not losing that much to baffle step, then maybe the Dayton Audio RS125-4 5" Reference Woofer 4 Ohm will do the job.

Perhaps if you run that tweeter just a little hot it will make up for the poorer off-axis response. Depends maybe on how finicky you want to be with it.

Since multiple woofers around the room improves the LF response, having a couple more of them in your CC will probably help, but maybe at the slight expense of the woofer's upper frequencies due to intermodulation distortion and that may depend on where you cross them over to the mid (ie. the lower the better).
 

eriksquires

Member
2013-05-10 4:11 pm
A pair of Peerless 830991 ($33 on sale at Madisound) give me a -3 dB around 64 Hz in the 0.75 Dayton MTM cabinet using two ports. A much better cut-off than the 5" Dayton ($30 in volume) drivers have of around 106 Hz. The $3 in cost difference is well worth it I think.

By the way, my actual sensitivity for the center channel was around 85 dB. Not great, but not terrible, and an easy load to drive, always over 4 Ohms.

Plus, I can use the 0.25 cubic foot cabinets to make 2-way speakers for the remaining channels, which is what the LM-1 will be if I ever finish the crossover design. :)

Best,


Erik

If you lose at least about 4dB to baffle step, the Dayton Audio RS125T-8 5" Reference Woofer Truncated Frame seems like the obvious choice to match your mains. If you're not losing that much to baffle step, then maybe the Dayton Audio RS125-4 5" Reference Woofer 4 Ohm will do the job.

Perhaps if you run that tweeter just a little hot it will make up for the poorer off-axis response. Depends maybe on how finicky you want to be with it.

Since multiple woofers around the room improves the LF response, having a couple more of them in your CC will probably help, but maybe at the slight expense of the woofer's upper frequencies due to intermodulation distortion and that may depend on where you cross them over to the mid (ie. the lower the better).
 
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eriksquires

Member
2013-05-10 4:11 pm
I used three of these (4 inch woofer) for a few years in the HT, https://www.madisoundspeakerstore.com/mtm-speaker-kits/hds-home-theater-kit-parts-only/which was okay/fine, but had better results with 6.5" woofers (mtm's).

Thanks for the link Erick, been looking for a small project using two woofers and a xt25.

Doug,

Your link didn't quite make it. Can you re-post the link to the woofer?

Glad you like it. :) I need to post the driver centers. Keep putting it off. If you build a pair please do comment or let me know, I have just the one so can't listen in stereo to the MTM.

Best,


Erik
 
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danfuls

Member
2015-01-25 2:44 am
I've attached a crossover I designed on crossover pro 3. Again I'm extremely novice, but this impedance looks very bad.
 

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eriksquires

Member
2013-05-10 4:11 pm
I've attached a crossover I designed on crossover pro 3. Again I'm extremely novice, but this impedance looks very bad.

Hi Danfuls,

You are right to notice the impedance being bad at high frequencies, but you should change the scale so it's easier to see.

The low impedance at the high frequencies is probably caused by the second parallel components in the woofer section. Add 1-2 Ohms in series with C3 to test this out.

Also, until you know the actual acoustic offsets don't take the schematic too seriously as your phase matching will not be accurate. :) For kicks, add about 1.4" of delay to the woofers. Not sure how you do this in XO-Pro though.

Lastly, remember that your final woofer level will be determined by the cabinet as well as it's location (free space or on a TV stand) so there will be more evaluation needed before you can commit to a crossover.

As for your overall process, I encourage you to read the posting I have here, it's in order. Notice that crossover design doesn't come until the end.


Best,

Erik
 
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eriksquires

Member
2013-05-10 4:11 pm
That makes sense as far as designing the crossover at the end. I guess I would need to know if a build will work with these drivers or if I should just look for another design. When I get back home I'll check out those links. I appreciate the help.

Putting together a quick crossover to see if the drivers could come together easily or not is a great thing to do before spending any money and often a good starting point. Just don't obsess over it yet.

Best,

Erik
 

danfuls

Member
2015-01-25 2:44 am
So I ended up trying a different crossover designer program I downloaded and making it a three way with a 5" Dayton reference driver for mids and a Dayton Audio PT2C-8 Planar Tweeter for the tweeter. How does this look? Do you think I would be good to start building? Or are there design problems here? Any and all feedback is welcomed.

Thanks,
Dan
 

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eriksquires

Member
2013-05-10 4:11 pm
Man, I hate looking at that program's schematics. :)

Make sure you have set it to use 2 woofers instead of one. Add about 1.3" or so to the woofer and about 0.75" to the midrange so you start to get some idea of the phase matching issues.

Your impedance runs just a wee bit low. With a solid amp that's fine. Might want to check some of those paths to ground in the midrange to see if you can boost it to reduce that 3kHz impedance drop.