Not new to DIY, but still a novice

[jeffc52053]

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Currently have 5.1 set-up using Dayton 8", Vifa 3" dome and RT Ribbon as the mains. Center channel is a MTM, surrounds are again PE drivers. Subs are 2 10" JBL's. None of them are "voice matched". Electronics are a Yahama 7.1 Rec., Adcom200 WPC for the subs. I'd like to build something smaller (6.5" ??) that is very efficient. Thought of using Eminence 6.5" and Morel CAT378 horn loaded dome. Sensitivity would come in around 93-95 db @1 watt for dynamic range. Don't like horns....
Any ideas?

[JonMarsh]

Hi Jeff,

I think somewhere there's an old saying something on the order of, efficiency, small size, bandwidth- pick any two. With the right drivers in a flush mount MTM you ought to be able to get up to 92 to 93 dB, but it's a limited set of options- I remember someone having a project like that, especially by eliminating baffle step compensation and choosing the right drivers, got around 92 dB.

one project to look at would be adapting Zaph's waveguide loaded tweeter TMM.

http://www.zaphaudio.com/Waveguidetmm.html

It doesn't meet your request for small, though. It could be reduced in size since you're using subs by building it sealed without the port in a smaller box.

There are four ohm drivers like the RS180-4 and others that will have higher sensitivity for a single 6.5" woofer, with extension below 100 Hz, but for various reasons they don't quite add up the same as using two 6-1/2's. OTOH, there are pro type 6.5" drivers, like the Beyma 6MD38-8, or the 18Sound 6ND430-16 that hit the efficiency mark you want, but start rolling off by 200 Hz. These really more like high power wide range midrange drivers.

usually the best sensitivity you can get with a "standard" hifi woofer is to find a good one with true 8 ohm impedance and about 88 dB or so sensitivity; then paralleling two will get you a total of 6 dB more sensitivity FOR THE SAME VOLTAGE. Then your problem will be an adequately sensitive tweeter, but there are ones out there in the 91-92 range; with reasonable speaker voicing, plus some baffle step, you won't need more than that. Of course, it's pulling twice the current, but a decent solid state amp shouldn't care about 4 ohms.

[jeffc52053]

Not new to DIY, but still a novice

Thanks Jon for the reply. I was thinking of the Eminence as they are rated at 95 db, and with the subs I don't need anything much below 90 Hz (Yamaha crossover point) The mains I have image very well but I'm dissapointed in the Ribbon tweeter. So, I thought I'd try the Morel CAT378 horn loaded dome rated at 93 db. The Eminence has a nasty spike at 4Kw (cone break-up?) that I'll have to get rid of. Also need something to smooth out the impedence rise on the 6.5". If I use all the same drivers I should see an improvement. Looking for lots of detail, air and wide dynamic range. Do you have any experience with the Eminence stuff?

[JonMarsh]

No, I don't. Which one do you mean- the American Standard Series Alpha 6A?

It's got a number of bumps in the impedance curve, indicating cone resonances, starting at 800 Hz. It's Fs is about 125, and it starts to dive there- the problem is, HT crossovers at 90 Hz in small box mode are expecting an Fb of about 80 Hz, and will take that into account- 125 is a bit too high, and you'd have some integration issues. I also note that the VC inductance climbs rapidly, indicating probably no shorting rings or copper in the gap, so midrange distortion may be an issue.

Was it another part number you're looking at?

[jeffc52053]

Thanks Jon for the reply

Yup, that's the one. If the response is that bumpy I think I'll look for another 6.5" Can you recomend a few to look at?

[---k---]

FWIW, if I'm not mistaken, CJD's RS150 MTM sensitivity should be around 91db. Same for the Khanspires.

I don't see the benefits in the high sensitivity, but I also have a beefy 300W amp. Maybe one of these days, I'll hear one that changes my mind.

Probably stepping up to one of the quality designs in Mission Accomplished or a Zaph design would be a big enough step up from what you got now, that you would be happy. Otherwise, I've seen lots of talk of people doing really high sensitivity stuff, but nothing comes of it. (Other than DanN Basslines and Jeff B. Salk speakers, but I think their magic comes from the open baffle which the high sensitivity drivers allow to reality.)

But, what do I know? :shrug: