DDF
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Taking full advantage of the Purifi's main benefits requires some unsavory trade offs:
- TS parameters aim for extreme bass reach to take advantage of the very linear design. This requires very expensive passive radiators
- As Purifi claim in this and this paper, its the IM distortion to watch out for, not harmonic distortion. The main benefit of its very low IM design is fully milked trying to operate the driver higher in frequency, but its off axis radiation is nothing special and directivity matching isn't great enough to take full advantage.
The Purifi tech would work better in a 5" designed for mid/woofer duties. Imagine the modern LS35A that Purifi's tech could achieve?
To me, a truly modern system with the fewest trade offs is one that uses separate sub woofer(s) to allow the mains best placement for imaging, and the subs best placement to control room modes. Toss in as small a box size as possible for better visual integration into the room.
The Purifi 6.5's drawbacks can still be avoided and the modern benefits attained by instead designing it in a small sealed box. Running a quick simulation in Unibox shows a very doable small sealed design:
Being sealed also allows heavy fill to clean up box modes, which was included in the simulation. No "port leakage" or mid range ripples.
Being a small box puts some limits on the tweeter faceplate size that will fit. Luckily, a a quick look shows the Seas DXT tweeter used in the Kii Three provides a nice fit, off axis directivity control with its modest waveguide faceplate, and ability to cross low and hard to give great directivity match.
A quick sim in boxycad (subtracting volume of driver and crossover components) with standard 3/4" MDF at 6L effective volume gives (just add some 1" roundovers) a nice pleasingly small box:
A 150W amp will deliver ~ 102 dB SPL in the mid range (subtract BDC and crossover EQ from the curve below), and a nice 70Hz F3 to cross to subs.
Given its linear design, there's no need for a high pass to protect the woofer, further simplifying integration with a sub. Here's is the displacement required at 150W. It stays within its linear xmax over its intended operating range and just stays below its maximum available throw (14.7mm) at all frequencies.
Running a proper second order high pass for integrating with the sub would take this all pretty much below 10mm, but given the purifi's low IM, I don't think is necessary.
Compare this to a typical vented design 3 times the size (if you could even fit a vent...). Not so pretty
The sealed design takes advantage of the Purifi's real benefits over other drivers, long clean linear throw and very low IM distortion, and does it in a nice small box.
Caveat: I still want to calculate the distortion created by the compression of the air itself in such a small box, but I whipped this off in a quick available lunch hour
- TS parameters aim for extreme bass reach to take advantage of the very linear design. This requires very expensive passive radiators
- As Purifi claim in this and this paper, its the IM distortion to watch out for, not harmonic distortion. The main benefit of its very low IM design is fully milked trying to operate the driver higher in frequency, but its off axis radiation is nothing special and directivity matching isn't great enough to take full advantage.
The Purifi tech would work better in a 5" designed for mid/woofer duties. Imagine the modern LS35A that Purifi's tech could achieve?
To me, a truly modern system with the fewest trade offs is one that uses separate sub woofer(s) to allow the mains best placement for imaging, and the subs best placement to control room modes. Toss in as small a box size as possible for better visual integration into the room.
The Purifi 6.5's drawbacks can still be avoided and the modern benefits attained by instead designing it in a small sealed box. Running a quick simulation in Unibox shows a very doable small sealed design:
Being sealed also allows heavy fill to clean up box modes, which was included in the simulation. No "port leakage" or mid range ripples.
Being a small box puts some limits on the tweeter faceplate size that will fit. Luckily, a a quick look shows the Seas DXT tweeter used in the Kii Three provides a nice fit, off axis directivity control with its modest waveguide faceplate, and ability to cross low and hard to give great directivity match.
A quick sim in boxycad (subtracting volume of driver and crossover components) with standard 3/4" MDF at 6L effective volume gives (just add some 1" roundovers) a nice pleasingly small box:
A 150W amp will deliver ~ 102 dB SPL in the mid range (subtract BDC and crossover EQ from the curve below), and a nice 70Hz F3 to cross to subs.
Given its linear design, there's no need for a high pass to protect the woofer, further simplifying integration with a sub. Here's is the displacement required at 150W. It stays within its linear xmax over its intended operating range and just stays below its maximum available throw (14.7mm) at all frequencies.
Running a proper second order high pass for integrating with the sub would take this all pretty much below 10mm, but given the purifi's low IM, I don't think is necessary.
Compare this to a typical vented design 3 times the size (if you could even fit a vent...). Not so pretty
The sealed design takes advantage of the Purifi's real benefits over other drivers, long clean linear throw and very low IM distortion, and does it in a nice small box.
Caveat: I still want to calculate the distortion created by the compression of the air itself in such a small box, but I whipped this off in a quick available lunch hour
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