Purifi PTT6.5W04-01A 6.5" midwoofer

[Selah Audio]

Hi Rick, Dennis just commented on the issues he had with implementing the PTT6.5 on AVSForums:



Not sure how far along development you are, but have you encountered anything similar? Or have you found a box size/alignment that allows the Purifi to realise its potential?

As Dennis noted the key is having the right cabinet volume and passive radiator combination. I've already found one that works great and am looking at another combination as well. I've used the other drivers that Dennis has mentioned and the Purifi has some advantages but of course at a higher cost. The response curves are good for the SB Acoustics woofer but it doesn't have the dynamics and power handling capability of the Purifi. The Scan-Speak has a rougher upper midrange and benefits from a 3-way with a lower crossover point, plus it has suspension limiting and higher distortion.
With the BMR design the Purifi didn't make sense since the cabinet volume wasn't right. It's not designed for operation with a port and that's one reason why they created a companion passive radiator. A port will have too much noise due to the high excursion capability of the Purifi woofer.

 

[bigjacko]

Is it possible to use purifi woofer with low volume sealed cabinet? I know that people always say with low Qts the driver suits port design, but what makes it can't go sealed?

 

[Selah Audio]

Is it possible to use purifi woofer with low volume sealed cabinet? I know that people always say with low Qts the driver suits port design, but what makes it can't go sealed?

It's a combination of Fs (resonate frequency), Qts, and Vas (compliance).

 

[bigjacko]

It's a combination of Fs (resonate frequency), Qts, and Vas (compliance).

I know that Qts and Vas can control the volume of cabinet. One thing I don't know about is how much do people value Fs? Is there going to be no output lower than Fs or Fc? I have modelled the woofer in winisd, if I use sealed cabinet it would be 4.8 liter for Qtc of 0.702. The Fc would be around 75.43 Hz. It does not seem too bad, the only complaint may be not much subbass, but it can be fixed with eq or cross with sub.

 

[Dennis Murphy]

I know that Qts and Vas can control the volume of cabinet. One thing I don't know about is how much do people value Fs? Is there going to be no output lower than Fs or Fc? I have modelled the woofer in winisd, if I use sealed cabinet it would be 4.8 liter for Qtc of 0.702. The Fc would be around 75.43 Hz. It does not seem too bad, the only complaint may be not much subbass, but it can be fixed with eq or cross with sub.

A lot of the engineering that went into the Purifi was intended to increase power handling in the bass with a very large Xmax and a special surround configuration that keeps distortion low during all of those wide excursions. The speaker also has admirable distortion specs higher up where excursion isn't as much of a factor, but a lot of woofers do for a lot less money. It would probably take a lot of EQ to get you really low in a small sealed box, and then I'm not at all sure the driver could sustain those low distortion levels that are a feature of its ported performance.

 

[bigjacko]

A lot of the engineering that went into the Purifi was intended to increase power handling in the bass with a very large Xmax and a special surround configuration that keeps distortion low during all of those wide excursions. The speaker also has admirable distortion specs higher up where excursion isn't as much of a factor, but a lot of woofers do for a lot less money. It would probably take a lot of EQ to get you really low in a small sealed box, and then I'm not at all sure the driver could sustain those low distortion levels that are a feature of its ported performance.

Why does ported has lower distortion? Because ported has less excursion? Are all distortion in woofer related to excursion?

 

[Selah Audio]

Why does ported has lower distortion? Because ported has less excursion? Are all distortion in woofer related to excursion?

The port lowers excursion most for frequencies close to the tuning. Below the tuning excursion increases because the port isn't providing as much support or output. This particular driver is designed to lower IM distortion which affects the upper response when the excursion is greater from low frequency content. If you're not driving the woofer that hard / loud, then this is less important; however, the Purifi also has low inductance and other design features that make the upper end response very good. This would show most in a 2-way design, but also has some benefits in a 3-way. It will handle a significant amount of equalization when used in a small sealed box but you have to balance the factors of bass extension and output capability.

 

[Ilkless]

A lot of the engineering that went into the Purifi was intended to increase power handling in the bass with a very large Xmax and a special surround configuration that keeps distortion low during all of those wide excursions. The speaker also has admirable distortion specs higher up where excursion isn't as much of a factor, but a lot of woofers do for a lot less money. It would probably take a lot of EQ to get you really low in a small sealed box, and then I'm not at all sure the driver could sustain those low distortion levels that are a feature of its ported performance.

It's probably no accident that most designs under development with it are compact 2-ways with waveguides. Its simply not very cost-effective otherwise.

 

[bigjacko]

Thank you all for answering my questions. So seems like it is better suited for 2 way because of low IMD and low distortion at higher frequencies. If it is used in a 3 way is it worth the price? It looks like the best driver at the moment for any woofer. What are other woofers that are as good for 3 way but not that expensive?

 

[Dennis Murphy]

Thank you all for answering my questions. So seems like it is better suited for 2 way because of low IMD and low distortion at higher frequencies. If it is used in a 3 way is it worth the price? It looks like the best driver at the moment for any woofer. What are other woofers that are as good for 3 way but not that expensive?

If you use it in a 3'way, you're pretty much limited to a .5 cu ft box or smaller, and you will probably need the factory passive radiators. So configured, it will go impressively low for that small a box, but there are other excellent drivers that will do as well in a larger box at a lot less cost. And when it comes to tower 3-ways, something like the SB Ceramic 8" will get you lower at a fraction of the price.

 

[March Audio]

Hi Rick, Dennis just commented on the issues he had with implementing the PTT6.5 on AVSForums:

I've given the Purifi woof every opportunity to prove itself in the BMR, including running it with two of the Purifi passive radiators, and I finally gave up. It's a very specialized animal. It performs about as well as the Scan 8545 in a smaller cabinet, which makes it a prime candidate for a premium 2-way in a cabinet of .5 cu ft or less. But even in that application the port has to be too long to fit without bending it and introducing even more port noise. The passive radiators solve that problem, but in a larger cabinet the bass response falls off below 100 Hz and the midbass is thin. Given how much more expensive the woofer + PR's are compared with the Scan, it doesn't make sense to reduce the volume of the BMR cabinet to achieve essentially the same results.

Not sure how far along development you are, but have you encountered anything similar? Or have you found a box size/alignment that allows the Purifi to realise its potential?

Im curious about those comments. The PRs behave very much like the modelling. As said, just need the right box size. As with any driver it needs the correct size of box

This was a free field measurement performed early on when I was experimenting with variations on (small) box size

 

[Selah Audio]

It's probably no accident that most designs under development with it are compact 2-ways with waveguides. Its simply not very cost-effective otherwise.

I'm looking forward to starting my 2-way testing. You can use a tweeter with a waveguide by that's not the only option. I also have a 3-way in mind for the next project. I have worked with many woofers of similar size and this is certainly in the top tier (as it should be considering the cost). Like anything else there's the law of diminishing return, but as they say "better is better".

 

[Selah Audio]

Thank you all for answering my questions. So seems like it is better suited for 2 way because of low IMD and low distortion at higher frequencies. If it is used in a 3 way is it worth the price? It looks like the best driver at the moment for any woofer. What are other woofers that are as good for 3 way but not that expensive?

In my opinion it's a great choice for some 3-way combinations. There are good woofers of similar size for 3-way designs like the SB Acoustics 6.5" (black aluminum or white ceramic/aluminum cone), Dayton ES180, and Seas U18.

 

[bigjacko]

I'm looking forward to starting my 2-way testing. You can use a tweeter with a waveguide by that's not the only option. I also have a 3-way in mind for the next project. I have worked with many woofers of similar size and this is certainly in the top tier (as it should be considering the cost). Like anything else there's the law of diminishing return, but as they say "better is better".

Everyone likes SB acoustic's ceramic driver. I have sb26cdc, a ceramic tweeter from SB acoustic, it is one of the best tweeter out there. For waveguide are you going to design one yourself or use some off the shelf one?

 

[Selah Audio]

Everyone likes SB acoustic's ceramic driver. I have sb26cdc, a ceramic tweeter from SB acoustic, it is one of the best tweeter out there. For waveguide are you going to design one yourself or use some off the shelf one?

I don't have any plans to use a waveguide; however, sometimes I get requests to use specific drivers. One problem I've noticed is that some of the systems implementing waveguides don't even show good directivity control around the crossover point. If you don't achieve that it defeats the main purpose of using one.

 

[phoenixdogfan]

I don't have any plans to use a waveguide; however, sometimes I get requests to use specific drivers. One problem I've noticed is that some of the systems implementing waveguides don't even show good directivity control around the crossover point. If you don't achieve that it defeats the main purpose of using one.

How about more than one of these in a cabinet with a compression driver tweeter?

 

[Dennis Murphy]

How about more than one of these in a cabinet with a compression driver tweeter?

You'll probably be seeing something like that in the not-too-distant future if all goes well. However, it will require two of the 8 Ohm versions in parallel to get sensitivity up.

 

[Absolute]

What about a Kef R11 rip-off with Purifi? How would that go? Never mind the price, the cabinets are straight-forward to DIY

What would be needed to make this work, or will there be other drivers more suited?

 

[Ilkless]

What about a Kef R11 rip-off with Purifi? How would that go? Never mind the price, the cabinets are straight-forward to DIY

View attachment 73081

What would be needed to make this work, or will there be other drivers more suited?

KEF's Uni-Q is head-and-shoulders above everyone's - including Genelec's edgeless coaxial driver - considering how much more excursion Uni-Q has to be built to bear, all with much lesser loading than that afforded by Genelec's massive baffle-waveguide. Genelec has a better system that rewrote the paradigm for coaxial speakers, but at a driver level, KEF is unparalleled for coaxials IMHO.

Unless, of course, the Purifi people manage to replicate the emphatic way in which they solved fundamental driver design issues of midwoofers with coaxial drivers

There isn't an off-the-shelf direct-radiating coax that can approach KEF or keep up with Purifi. SEAS coaxials can be good, but come with nulls at 10 and/or 16kHz on-axis (that contribute to smaller dips in the listening window). Now, dual concentric compression drivers are another story... very interesting space and SOTA drivers are available to the end-user.

 

[Absolute]

I was thinking of the possibility of making a Kef R11 clone with Purifi and the Coaxials from the Reference line (can sometimes be found on the market) which would make the SPL capability rather nice compared to the regular R11.

But I don't know if the coaxials are particularly good at high spls?