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Going to a three way may be better (crossover may be more difficult) using somewhat smaller drivers and waveguide for the mtm to facilitate a higher crossover frequency. Whatever you decide to go with, the tricky part is usually finding a suitable waveguide.
The reason for going 2.5 way is to gain bass response from all 3 15" drivers. The lowest driver nearest the floor will run from 20hz to 300hz, and the mtm 15" drivers will run from 20hz to 800hz. So you see this configuration is the only option for this passive design. Going 3 way will sacrifice all the bass output.
Myself, I am thinking 3-way is the easiest, biamped. Take something like the BMS 4540nd on a 10" DDS ENG 1-90 waveguide and cross it to something like the Ciare 8.64ND 8" mid at ~1.7khz (18 Sounds has some nice midwoofer offerings too). The MT would then be crossed over actively to a pair of 15" OB run off a SS brute somewhere around 300hz-400hz. With some care in crossover construction (not cheap to do it right), the MT could be flea amp worthy. The impedance hills and valley of the CD on a WG require a multi part xo, especially with a low dampening factor amp like a SET.
Quote from: JoshK on 18 Oct 2007, 08:25 pmMyself, I am thinking 3-way is the easiest, biamped. Take something like the BMS 4540nd on a 10" DDS ENG 1-90 waveguide and cross it to something like the Ciare 8.64ND 8" mid at ~1.7khz (18 Sounds has some nice midwoofer offerings too). The MT would then be crossed over actively to a pair of 15" OB run off a SS brute somewhere around 300hz-400hz. With some care in crossover construction (not cheap to do it right), the MT could be flea amp worthy. The impedance hills and valley of the CD on a WG require a multi part xo, especially with a low dampening factor amp like a SET. Well I'd try not to dwell into the path of semi active Bastani type of design; lets keep it pure simple passive ala R909. My thoughts on the cross over; for the lowest driver implement a 2nd order filter will effectively cause a 6db/octave rolloff at 300hz which will mate to the mtm 15" drivers with natural OB rolloff. At the mtm portion, implement 1st order filter at 800hz for transient perfect results.
Well I'd try not to dwell into the path of semi active Bastani type of design; lets keep it pure simple passive ala R909.
Quote from: wikin on 18 Oct 2007, 08:47 pmQuote from: JoshK on 18 Oct 2007, 08:25 pmMyself, I am thinking 3-way is the easiest, biamped. Take something like the BMS 4540nd on a 10" DDS ENG 1-90 waveguide and cross it to something like the Ciare 8.64ND 8" mid at ~1.7khz (18 Sounds has some nice midwoofer offerings too). The MT would then be crossed over actively to a pair of 15" OB run off a SS brute somewhere around 300hz-400hz. With some care in crossover construction (not cheap to do it right), the MT could be flea amp worthy. The impedance hills and valley of the CD on a WG require a multi part xo, especially with a low dampening factor amp like a SET. Well I'd try not to dwell into the path of semi active Bastani type of design; lets keep it pure simple passive ala R909. My thoughts on the cross over; for the lowest driver implement a 2nd order filter will effectively cause a 6db/octave rolloff at 300hz which will mate to the mtm 15" drivers with natural OB rolloff. At the mtm portion, implement 1st order filter at 800hz for transient perfect results. 800hz and 1st order seems like it's begging for trouble. Plus what about the rear wave throughout the XO region?
Quote from: wikin on 18 Oct 2007, 08:47 pmWell I'd try not to dwell into the path of semi active Bastani type of design; lets keep it pure simple passive ala R909. Well then you can rule out SETs then IMO. A set amp isn't going to cut it with a passive dipole design if you are actually EQ'ing it (passively or actively) for the dipole roll off. Good luck constructing a design that has flat impedance and benign phase!Edit: I quasi take that back, if you used a SET amp with a lot of gNFB then you could get away with it, but usually SET amps are designed without any gNFB.
Were talking 3x15" driver with high qts per channel doing bass job, you still don't think we'll have enough of low freq?http://www.sonicflare.com/archives/vegas07-vision-of-the-future-emerald-audio.php
Quote from: wikin on 18 Oct 2007, 08:54 pmWere talking 3x15" driver with high qts per channel doing bass job, you still don't think we'll have enough of low freq?http://www.sonicflare.com/archives/vegas07-vision-of-the-future-emerald-audio.phpI guess it depends on what you mean by enough, but it looks like three of those drivers are only capable of producing ~90db at 40hz at full xmax on a reasonably sized baffle. I doubt the emerald speakers are using this driver in particular, with their claimed frequency response and applied equalization.
My point about SETs not cutting it has more to do with the high output Z then power. So to that end I don't think the 211 or 845 would be any better than a 300B or smaller tube. The PP EL84 w/ FB would probably work better because of lower output Z (higher dampening factor). Still I think it is much easier to do this kind of project with a SS amp on the bass. A box normally helps you dampen the woofers and takes *some* off of the amp, in OB this isn't so. Plus with the dipole roll off you need to EQ up the lower end, which take even more power, and usually where the woofer is the most demanding in terms of impedance. Even guys like Lynn Olson, a triode freak like some of us, call for big bruiser amps on the bass (even with hi-eff drivers).
