Introducing Directiva - An ASR open source platform speaker project

[Zvu]

@Rick Sykora

I'm not sure what will you eventually end up with, but for now i see 3dB BSC (which is not enough in my opinion) and bumped bass. Sure it can be fixed with minidsp so let's wait and see. I'm guessing more refinement is in order.

 

[Rick Sykora]

@Rick Sykora

I'm not sure what will you eventually end up with, but for now i see 3dB BSC (which is not enough in my opinion) and bumped bass. Sure it can be fixed with minidsp so let's wait and see. I'm guessing more refinement is in order.

You are correct on the bumped bass, as I did not do any special BSC comp at this point. As you mentioned, it is easy enough to add. Given the flexibility of an active design, rather leave tweaking until later. In some cases, it may be left for the builder. If I linger on the budget design, will take longer to get to the premium one!

Also agree on a bigger cabinet, but am not willing to pay its shipping premium and Amir’s back will be happier with the smaller box. I prefer slim towers as most else needs to go on a stand anyway. It will likely use 2 woofers, but switch to the 8 ohm version of the woofer. Anyway, have some amps to finish for a customer and build the fancy cabinet Directiva variant before I can think about towers.

By the time we have a solid base design to work from, am hoping will have more folks contributing designs and design improvements.

 

[tktran303]

It will be punchy until port distortion hits the fan. If you do just 4dBof baffle step compensation, you'll get at 96dB (Amirs standard for distortion measurements) with 10V signal (28W). There is +3dB hump at 58Hz and the port distortion goes nuts.

View attachment 116175View attachment 116174

This just isn't a midwoofer for small ported cabinet. With PR, maybe. But ported needs larger volume so floorstander is mandatory if you want to really use that high Xmax and low distortion motor.

As always, I respect your opinion Zvu,

But here I will respectfully disagree.

When I model the Purifi PTT6.5 and then compare it, to say, the Scan-Speak 15W/8530, I find that both model very similarly (same Vas, Fs, and Qts)
The port size requirements and air speed and group delay are also similar etc.

Paul Carmody uses the 15W/8530 in the Carrerra- a 15L cabinet tuned at 38 or 43Hz. and there is nothing wrong with the port tuning or bass there. In fact, it’s delicious, for 1/2 cu ft speaker.

I think the way to look at the Purifi is the same.
‘Great sound in a smaller box’.

Erin from Erins Audio Corner has already shown that it in free air, it can reach 100dB cleanly with 12V input.

In a 2 way design I think trying to eek out every mm of x-max and push it to its suspension limits is not necessary. So I’m not modelling it with 100W of input or trying to use up all 10mm of its x-max.

Furthermore, whether one can hear port turbulences and resonances when the port is rear firing, well I’d like to see some studies on it, but if it’s anything like a woofer’s limits under CEA 2010, then probably it’s hard to discern.

And let’s not forget masking effects. When I have 2 speakers, each playing at 96dB, i have a lot more things to worry about, like other things being driven to buzz or shaking in my room.

So I’m not surprised at Rick’s preliminary audition of these- that the port visual measurements looks worse than it actually sounds.

In my own design of a PTT6.5 in a larger box, documented at DIYAudio, I also don’t have any problems with a vented design in a 3/4 cu ft box.

 

[Wolf]

I did not anticipate that you would do those bevels with a hand saw. I expected you would use the miter gauge on the table saw together with the blade tilted. The limit on how far the blade can be tilted means that it needs to be done with the board on edge. A jig with a runner that slides in the miter gauge slot, and a couple of fancy clamps to hold the work piece to the jig. If you were to ask Norm Abram ("This Old House"), this is what he would say I'm pretty sure. I can't quite visualize the jig in my head at the moment, but maybe if I sleep on it tonight. And yeah, it will be extra work, but once you've built it, you'll for each of the hundreds of these speakers that you sell for meager profit after the prototype.

EDIT: The method I've tried to described assumes that the table saw blade is big enough and extends adequately far above the table, to make the cuts. It also assumes that you're comfortable with that much of a table saw blade sticking up through the table.

A graphic of a jig for this method, as drawn by John Hollander:

 

[Zvu]

Hi Thanh,

...........
When I model the Purifi PTT6.5 and then compare it, to say, the Scan-Speak 15W/8530, I find that both model very similarly (same Vas, Fs, and Qts)
The port size requirements and air speed and group delay are also similar etc.

Paul Carmody uses the 15W/8530 in the Carrerra- a 15L cabinet tuned at 38 or 43Hz. and there is nothing wrong with the port tuning or bass there. In fact, it’s delicious, for 1/2 cu ft speaker.

I will surely hit someone's nerve now but i don't consider Mr Paul a particular authority to admire about loudspeaker engineering. There are people i consider much more advanced. Few dedicated Germans from THIS forum are so advanced in loudspeaker design that i wouldn't know how to compare their work with Paul's. They are probably less known only because of language barrier. Of course, legendary Jon Marsh from HTguide really knows what he's doing. And it's not that there aren't more good designers out there but i just can't see anything from their measurements. That's why i appreciate Amir's here and Erin's work - very high resolution measurements that allows us to see the problems.

I think the way to look at the Purifi is the same.
‘Great sound in a smaller box’.
Erin from Erins Audio Corner has already shown that it in free air, it can reach 100dB cleanly with 12V input.
In a 2 way design I think trying to eek out every mm of x-max and push it to its suspension limits is not necessary. So I’m not modelling it with 100W of input or trying to use up all 10mm of its x-max.

100dB in free air is clean but in ported cabinet lower part of the spectrum for this woofer is highly dependent on cabinet construction and design. If you aren't modelling it for at least 70% Xmax, then you don't need that driver and can get away with other (most likely cheaper one) which doesn't suffer same construction related issues.

Furthermore, whether one can hear port turbulences and resonances when the port is rear firing, well I’d like to see some studies on it, but if it’s anything like a woofer’s limits under CEA 2010, then probably it’s hard to discern.

And let’s not forget masking effects. When I have 2 speakers, each playing at 96dB, i have a lot more things to worry about, like other things being driven to buzz or shaking in my room.

Let's put to side bad rep ported loudspeakers earned through years. I also won't get into my personal experience... JBL invested whole lot of time, money and effort in developing a port with least amount of turbulence, and it is something Augerpro confirmed in his thread at DIYaudio. Kef made flexible port to fight the resonance of port tube and to dissipate part of that energy into heat. That much effort from two companies known for their science based approach in design tells something in itself.

So I’m not surprised at Rick’s preliminary audition of these- that the port visual measurements looks worse than it actually sounds. In my own design of a PTT6.5 in a larger box, documented at DIYAudio, I also don’t have any problems with a vented design in a 3/4 cu ft box.

Rick's first hand experience backed up with Amir's measurements and subjective impressions will shed more light on this mater. I'm saying something we all kinda know - on paper, it could be a problem. Not saying it will become one. so let's see how development of this project progresses since i like the concept a lot.

 

[Rick Sykora]

If you did not pick up on it earlier, I had a brief diversion from Directiva as needed to complete a couple of Hypex amps for someone. Those are done and getting boxed for shipment. The other hurdle is of my own making...

Was not paying attention when I got my QA471 mic preamp and did not realize I would need my QA401 to interface nicely to REW. Thanks apparently to @edechamps who had a hand in the ASIO drivers! Without them, my QA471 investment would be naught. The QA401 is on my workbench hooked to a desktop PC whereas my speaker measurements are done on a notebook PC. It is not convenient to haul around the QA401/471 combo. So rather than do so, am going to order a Focusrite Scarlett Solo. Only downside is it appears it may not arrive for a week. The good news is I can spend the time building the other cabinet and make comparable measurements on it with my UMIK mic.

If anyone has a better suggestion, please let me know. Thanks!

 

[tktran303]

100dB in free air is clean but in ported cabinet lower part of the spectrum for this woofer is highly dependent on cabinet construction and design. If you aren't modelling it for at least 70% Xmax, then you don't need that driver and can get away with other (most likely cheaper one) which doesn't suffer same construction related issues.

I think were in agreement here. If the port or cabinet (or design) can't keep up with the driver, then that's the port's (or cabinet's) problem.

Where do I sign up to buy the AugerPort XL Pro?

 

[Rick Sykora]

So the Dayton has been replaced by a Hypex NC252MP amp. Still a slight bit of hiss when close to speaker. Tomorrow will upgrade the minidsp and see if that improves the noise some more.

In the meantime as I brought my UMIK back online, decided I would try an off-axis measurement. This pic shows 30-35 degrees off-axis (teal) in comparison to on-axis (magenta)...

The usual conditions apply: 75 dB, 1m, 3 msec gate.

Looks pretty good for a first pass crossover design!

 

[headshake]

Still a slight bit of hiss

My fa123 + bliesma t25b have no hiss. I am using a topping 10s out to the plate amp using spdif. The pc is connected to the dac via usb.

What do you have connected to the plate amp?

 

[Zvu]

I think were in agreement here. If the port or cabinet (or design) can't keep up with the driver, then that's the port's (or cabinet's) problem.

Where do I sign up to buy the AugerPort XL Pro?

I guess it is not for sale.

Thing is, i know of no software that can help to predict the loudspeaker tuning with constant curve port. If you'd want to try that, i guess you would have to make different types (diameters and lengths) and then play hit and miss. Buddy of mine prints me two pairs of ports that are used in JBL M2. I will use them for testing (to measure the relation of tuning with that kind of port in regard to straight tube). After that i'll probably give it to other friend who is diying M2 since i doubt it will just happen to tune my 12" midwoofer to the desired frequency.

 

[Rick Sykora]

My new minidsp HD is in place and now able to drive with USB audio. It still hisses slightly. The HD version has a lot more gain flexibility, so may help with noise and in more refined low bass boost.

I loaded my previous settings from its lesser brother and was able to readily reproduce the measurements posted to date.

 

[Rick Sykora]

Directiva plans for a better cabinet are underway!

The back baffle should easily allow the SB passive radiator to be used. The Purifi ones will have to go on the sides.

 

[Selah Audio]

Here's a nearfield response curve for the woofer in a sealed box with a passive crossover.

 

[Rick Sykora]

Here's a nearfield response curve for the woofer in a sealed box with a passive crossover. View attachment 117341

Thanks for sharing!
Am sure there are some folks that are interested in a sealed variant. What is the cabinet volume and damping?

Any sign of the distortion @DDF mentioned?

 

[Plcamp]

Like the project!

I have always been intrigued with https://www.parts-express.com/pedocs/specs/264-1678--peerless-da32tx00-08-spec-sheet.pdf because it’s flat to 1 kHz and Looks to have reasonable dispersion.

 

[Selah Audio]

Thanks for sharing!
Am sure there are some folks that are interested in a sealed variant. What is the cabinet volume and damping?

Any sign of the distortion @DDF mentioned?

I did some initial distortion tests and shared the information with DDF. Looking good so far but I'm going to run a few more tests. The sealed box volume included the d.c. resistance of the inductors in the crossover. Since you're doing an active design your box volume and damping will be different.

 

[Rick Sykora]

We have a front baffle!

Routing was done prior to cutting the final shape as needed the extra surface for my rather large router. The remaining cuts were done on table saw. The angle are simple at 75 degrees at base. We are finalizing bevel. So that will be done later.

The next step will be to route the chamfer on back if woofer cutout leaving some landing pads for the t-nuts I plan to use...

 

[KBSDK]

I must say you chose wisely with the Seas DXT tweeter due to:

• the waveguide ensuring a near constant directivity behavior all the way up to the highest frequencies. No pears.
• it's already proved to do very well in the excellent Kii THREE loudspeaker.

The scepticals can read a test report of the DXT here.

The test report also points to an article about baffle design, edge diffraction, secondary sound sources and their influence on the sound quality of loudspeakers. Might be of your interest for this design.

I would have preferred a more regular front baffle shape for easier wood-work for most people.

I suggest:

• a small rectangular front baffle with a large rounding of the side edges like they did on the Kii THREE.
• place the tweeter off-center according to the article above (and like Purifi do it with their demo speaker SPK4 & SPK5).
• place passive radiators on the sides of the cabinet.
• 3D print the port flare to lower port noise (the STL file is included in the zip packages for the SPK5). Place the port on the back.
• place a Hypex Fusion amp** on the back.

** In my experiences the Fusion amps are superb. Take notice. The built-in DSP and DAC are top notch in my experience.
The flaws in the lesser cabinet design can easily be compensated in the Hypex filter designer. And I find it most convenient having three presets that can be changed by using the remote control during listening sessions when optimizing filters, target curves and what not...

FYI: My Hypex FA253 drives a 6,5" Purifi in a temporary open baffle with Viawave GRT-145 tweeter on the top (no baffle). Linkwitz LX521 bass modules handles the rest. Excellent combo IMHO. Especially following the guidelines by "mitcho" for optimizing the in room response with a preferred house curve.

 

[Rick Sykora]

After some discussion with Amir, he is pretty backlogged with consumer speakers to test, so asked me to prioritize which Directiva model is tested first. After some team consult, have decided to go with the best we can put forward. This results in pushing the budget higher as it will use dual Purifi passive radiators, but also gives ASR members a chance to compare to better commercial speakers too.

With this decision in hand, I ran some Bassbox and VCAD sims and adjusted cabinet volume for isolating the tweeter. This resulted in a cabinet volume of 11.5 liters and a f3 of around 42 Hz.

 

[Digital_Thor]

I must say you chose wisely with the Seas DXT tweeter due to:

• the waveguide ensuring a near constant directivity behavior all the way up to the highest frequencies. No pears.
• it's already proved to do very well in the excellent Kii THREE loudspeaker.

The scepticals can read a test report of the DXT here.

The test report also points to an article about baffle design, edge diffraction, secondary sound sources and their influence on the sound quality of loudspeakers. Might be of your interest for this design.

I would have preferred a more regular front baffle shape for easier wood-work for most people.

I suggest:

• a small rectangular front baffle with a large rounding of the side edges like they did on the Kii THREE.
• place the tweeter off-center according to the article above (and like Purifi do it with their demo speaker SPK4 & SPK5).
• place passive radiators on the sides of the cabinet.
• 3D print the port flare to lower port noise (the STL file is included in the zip packages for the SPK5). Place the port on the back.
• place a Hypex Fusion amp** on the back.

** In my experiences the Fusion amps are superb. Take notice. The built-in DSP and DAC are top notch in my experience.
The flaws in the lesser cabinet design can easily be compensated in the Hypex filter designer. And I find it most convenient having three presets that can be changed by using the remote control during listening sessions when optimizing filters, target curves and what not...

FYI: My Hypex FA253 drives a 6,5" Purifi in a temporary open baffle with Viawave GRT-145 tweeter on the top (no baffle). Linkwitz LX521 bass modules handles the rest. Excellent combo IMHO. Especially following the guidelines by "mitcho" for optimizing the in room response with a preferred house curve.

How can good directivity be optained with a front like Kii3? When Heissmann - you link too - clearly states that the DXT needs a very narrow - almost non existing - front baffle, to get a minimum of disturbance and widening in the response near the X-over......