I don't know what you mean by the HT case, maybe I have missed something, but if this question is adressed to me, this is the plot of the excursion for the 2-way monitor of the active driver (green) and of one passive radiator (red) at 2.83Vrms. Using this curve, it can be calculated at which SPL level the maximum excursion of 15 mm peak is reached for the passive radiator above 38 Hz for this design.
Of course you can play louder if a more early SPL roll off for low frequencies is applied. But the sound timbre will be different also.
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If you calibrate home theater to THX levels that is 85dBA at the listening position per speaker for a -20dBFS level. This needs a LOT of bass. Most of us realistically are closer to the THX domestic spec of 75dBA. LFE channel is 10dB higher, so I've answered my own question, which is that the is fine for music but the sub is necessary for a good home cinema experience (if by good you mean your kidneys are liquified).
With the 3-way I have in mind, with 2 x 6.5 inch Purifi active drivers and 4 passive radiators on the side walls, the SPL at maximum excursion can become 104 dB at 1m. Indeed, for high power low frequency response, you better choose subs with larger drivers.
Does anyone have links to good research about how to brace/damp a Purifi + Passive Radiator design? I’ve seen the KEF white paper and it’s interesting how they support the magnet itself, but Geddes seems to just prefer a CLD. I’m insanely jealous of everyone who has already had the PTT for months, can’t wait to get it in hand and build an insane 2 way monitor.
What do you guys think of a ultra small speaker build with Purifi drivers?
I'm thinking a very small 6L speaker, with 2 of the 6.5" Purifi woofer front back dual opposed, with a Bliesma T25B-6 in a waveguide. Sealed, active, and DSP, aiming for 20Hz extension with tons of NCore amp power. The Purifi is perfect for super small speaker builds with maximum performance.
Ignore some visual mistakes in the render, but something like this
I'm thinking a very small 6L speaker, with 2 of the 6.5" Purifi woofer front back dual opposed, with a Bliesma T25B-6 in a waveguide. Sealed, active, and DSP, aiming for 20Hz extension with tons of NCore amp power. The Purifi is perfect for super small speaker builds with maximum performance.
Ignore some visual mistakes in the render, but something like this
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Have you simulated two opposed PTT6.5 in a 6L sealed cabinet? The TS parameters are designed for a vented alignment. When you do this, the high compression of the air will change the suspension linearity of the cones and they will lose the low distortion ability they were designed for. 6L is 1L bigger than a LS3/5A which only has 1 sealed 5.25in driver.
Yes. With 250W per woofer the Purifi's can hit about 8mm excursion, which is right at where the BL starts to droop.
Suspension linearity is not really an issue in a small sealed enclosure because the air compliance itself will overwhelm the effects of the woofer's own suspension. The high compression of air will of course bring its own distortion, but that's fine.
My main concern would be the thermal limits of such a design.
As it stands I doubt the Purifi can handle 250 watts even in free air. Heck I'd be surprised if it could handle 100 watts continuous in free air.
Put two of them inside a small cabinet, along with the power amplification, and things are going to get toasty very quickly.
What are you intending on making the boxes out of?
In my opinion the only route you could go would be aluminium. Obviously the ncores need bolting to something thermally conductive but also the output inductors of the ncores tend to run quite hot. From images I've seen online 60-70 degrees isn't unusual and that's in a ventilated case. They are going to heat up the inside of your box even just at idle. Then when you start pumping the watts out...If you do listen with 250 watt peaks, which wouldn't be hard, a pair of PTT6.5s will only give you 95dB at 30Hz and 88dB at 20Hz. With action movies SFX you'll easily use all of that up. I would be concerned with the reliability. Those voice coils are going to heat up very quickly and once the ambient starts to rise...poof. And this is in an empty cabinet. I'm assuming you'd want to do a 100% stuff which will really melt things.
It depends what you want to listen to. If all you want them for is classical music, with its wide dynamic range and extremely seldom use of deep bass, then they'll be okay. If it's for HT use, at decent SPL, or pumping out some modern bass heavy stuff with 6dB dynamic range then you'll need to get creative with the thermal management.
Alu cabinets and some sort of interface between the magnets/top plates of the PTTs to the alu cabinet sides to wick the heat out of the motors. Maybe a thick aluminium cylinder that wraps around the magnet structure with some thermal interface material and then uses heat pipes to send it to the cabinet sides.
I don't see the point in the top firing tweeter either.
As it stands I doubt the Purifi can handle 250 watts even in free air. Heck I'd be surprised if it could handle 100 watts continuous in free air.
Put two of them inside a small cabinet, along with the power amplification, and things are going to get toasty very quickly.
What are you intending on making the boxes out of?
In my opinion the only route you could go would be aluminium. Obviously the ncores need bolting to something thermally conductive but also the output inductors of the ncores tend to run quite hot. From images I've seen online 60-70 degrees isn't unusual and that's in a ventilated case. They are going to heat up the inside of your box even just at idle. Then when you start pumping the watts out...If you do listen with 250 watt peaks, which wouldn't be hard, a pair of PTT6.5s will only give you 95dB at 30Hz and 88dB at 20Hz. With action movies SFX you'll easily use all of that up. I would be concerned with the reliability. Those voice coils are going to heat up very quickly and once the ambient starts to rise...poof. And this is in an empty cabinet. I'm assuming you'd want to do a 100% stuff which will really melt things.
It depends what you want to listen to. If all you want them for is classical music, with its wide dynamic range and extremely seldom use of deep bass, then they'll be okay. If it's for HT use, at decent SPL, or pumping out some modern bass heavy stuff with 6dB dynamic range then you'll need to get creative with the thermal management.
Alu cabinets and some sort of interface between the magnets/top plates of the PTTs to the alu cabinet sides to wick the heat out of the motors. Maybe a thick aluminium cylinder that wraps around the magnet structure with some thermal interface material and then uses heat pipes to send it to the cabinet sides.
I don't see the point in the top firing tweeter either.
- Hi Everyone, I have been looking and looking for a really good tweeter that didn't cost an arm and a leg and I found one that looks very interesting... It's a great New tweeter Design that I'm not sure if anyone has seen or shared it here, it has a new Patented design they call SRT if I am remembering right. I'll provide a link below to a review by Troels Gravesen , he really seemed to like the new tweeter and used it in a new speaker he designed, the ATiRi.
- Also it now comes in a waveguide that I don't think was available yet when
he designed and built his speaker. here's a quote from the website - "The waveguide of course provides a more uniform radiation pattern in the working range, reducing the influence of reflected sound in the listening area. Also, the waveguide increases the sensitivity of the tweeter at the lower frequencies of the working range. Thanks to the wave guide, the design of the crossover between the tweeter and mid-frequency driver is simplified" - which is great because Troels Gravesen already seemed to think in many cases it would only need a 2nd order crossover.
Tweeter Review -
- Viawave GRT-145
The ATiRi speaker Troels designed using the tweeter -
- ATiRi
Here is the page from the website about the driver with the waveguide -
- Viawave
- Also it now comes in a waveguide that I don't think was available yet when
he designed and built his speaker. here's a quote from the website - "The waveguide of course provides a more uniform radiation pattern in the working range, reducing the influence of reflected sound in the listening area. Also, the waveguide increases the sensitivity of the tweeter at the lower frequencies of the working range. Thanks to the wave guide, the design of the crossover between the tweeter and mid-frequency driver is simplified" - which is great because Troels Gravesen already seemed to think in many cases it would only need a 2nd order crossover.
Tweeter Review -
- Viawave GRT-145
The ATiRi speaker Troels designed using the tweeter -
- ATiRi
Here is the page from the website about the driver with the waveguide -
- Viawave
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I have been looking at those Viawaves for a while now. They do look really good. I have been pretty happy listening to a borrowed set of RAALs lately. Although just today I finally got my RS28F and WG300 waveguide dialed in with the PTT6.5 in a TL. They sound wonderful - they sound like much bigger speakers. I have the final XO now - much better voicing. XO still at 3500Hz and still passive Harsch.
This is going to be it for a while.
Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
This is going to be it for a while.
Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
- Hello , If anyone drops by I found another very interesting tweeter , It's new enough that there aren't any reviews of it at parts express.... the wave guide that's part of the design seems to look to me to be really good.... this tweeter is also just come out fairly recently being used in speaker monitor that got a good review. So I wanted to get yours thoughts on it - 
Thank you ,
- Here is the info from parts express, the spec sheet , and a small review.
- View attachment 294-1000-faitalpro-fd371-8-specification.pdf
- View attachment 2 - FaitalPRO FD371 Bullet Super Tweeter 8 Ohm - 170.00 ..pdf
- Wayne Jones Audio Jones–Scanlon Monitors
Thank you ,
- Here is the info from parts express, the spec sheet , and a small review.
- View attachment 294-1000-faitalpro-fd371-8-specification.pdf
- View attachment 2 - FaitalPRO FD371 Bullet Super Tweeter 8 Ohm - 170.00 ..pdf
- Wayne Jones Audio Jones–Scanlon Monitors
It seems a waste to use a 110dB tweeter just to pad it down to 84dB to match the PTT6.5. Also, compression drivers are not known to be lowest distortion - although, maybe running them at millliwatts of power to get 84dB is the way to keep distortion low as it’s hardly working. Not sure why the Scanlon red needs a 150w amp for the tweeter!
They did use the Purifi Drivers.... See the link in the post above for the baby reds!