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Introducing Directiva - An ASR open source platform speaker project

D!sco

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With the DXT you'll want a large chamfer around it. It prefers either as little or as much baffle as possible. On a regular rectangle you'll get some uneveness centered around the 3kHz range. Even the venerable Kii3 with its generous roundovers hasn't fully mitigated this effect.
Is this a waveguide issue? You mean chamfering like the DXT-MON by Heissman? It's a good suggestion. For now I just wanted the Denovo cabinet to work. Everything just barely fits in a cabinet just large enough to hit 40hz. It could probably use a stout center brace as well. How did you all get around this on the R1? Was the baffle wide enough?
 

TimVG

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It's not an issue as much as a feature of the DXT design. I wasn't part of R1, but careful crossover design and a slight on-axis compensation can do wonders.
R2, in the prototype iteration I built has the problem close-to-eliminated, and with my new (larger) roundover bit it should as good as practically managable. The crossover is also quite a bit lower so the vertical radiation is quite good as well for a non-coaxial speaker.

How much all of this matters in practice is up for debate, but since R2 is science-driven it makes sense to want to optimise as much as we can practically achieve.
 

D!sco

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Took me like, 20 minutes in sketchup. I love how easy that software is. I can also move the whole driver array up 9mm. It takes a 1" thick baffle to follow Heissman's model.
Screen Shot 2022-09-02 at 08.49.29.png

Also, I'm pretty sure the passive tweeter XO is basically just yours @TimVG with slight tweaks to the L-Pad and first cap. I learned not to fuss with most of it, but where exactly did you compensate for the baffle? Passives are hard.
 

Jdunk54nl

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Took me like, 20 minutes in sketchup. I love how easy that software is. I can also move the whole driver array up 9mm. It takes a 1" thick baffle to follow Heissman's model.
View attachment 228247
Also, I'm pretty sure the passive tweeter XO is basically just yours @TimVG with slight tweaks to the L-Pad and first cap. I learned not to fuss with most of it, but where exactly did you compensate for the baffle? Passives are hard.
That looks too much like the lsa 80 signature, and I was not a fan of that look in person:
LSA-80_Distilled.jpg
 
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Rick Sykora

Rick Sykora

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It's not an issue as much as a feature of the DXT design. I wasn't part of R1, but careful crossover design and a slight on-axis compensation can do wonders.
R2, in the prototype iteration I built has the problem close-to-eliminated, and with my new (larger) roundover bit it should as good as practically managable. The crossover is also quite a bit lower so the vertical radiation is quite good as well for a non-coaxial speaker.

How much all of this matters in practice is up for debate, but since R2 is science-driven it makes sense to want to optimise as much as we can practically achieve.
Just to pile on a bit here…

Credit goes to @ctrl on the r1 crossover. Frankly, I handcuffed him with stock Denovo cabinet. All the behind the scenes efforts (for both r1 and r2) show the benefit of major chamfering. @ctrl sims for this saved lots of MDF too!
 

Lbstyling

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Just an update that both Rick and myself have resumed work on R2. We both had a bit much on our plate over the past few months, and while I can't speak for Rick, I needed to sort out my measurement rig first so that our data is as accurate and comparable as possible.

Having been able to hear and measure quite a variety of speakers over the past months, I can honestly say that R2 will have been worth the wait.
Ooh you tease!
 
D

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Took me like, 20 minutes in sketchup. I love how easy that software is. I can also move the whole driver array up 9mm. It takes a 1" thick baffle to follow Heissman's model.
View attachment 228247
Also, I'm pretty sure the passive tweeter XO is basically just yours @TimVG with slight tweaks to the L-Pad and first cap. I learned not to fuss with most of it, but where exactly did you compensate for the baffle? Passives are hard.
This looks a lot like the Emotiva B1+. Outside of some 1khz cabinet vibration and being a bit light on bass, these have received mostly good reviews.

k1wi5i12zlde12ofj0pg.jpg
 

D!sco

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Emotiva does very well for their price point. I based it specifically on Heissmann Acoustics' Slanted Chamfer article. I went as close to 40˚ as I could without cutting the side walls. It would be nice if making an ideal closure were easy.
 

DualTriode

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Hello All,

Several months ago I had a couple of 6 1/2 inch drivers in hand and was looking around at possible applications.

@DDF in post 35 leaned away from a sealed enclosure because of potential air pressure distortion. I wondered if a sealed enclosure got a fair audition? So I decided to install the 6 1/2 Purifi driver and test a few variations.

I wanted to go along with using the 0.55 cubic foot Denovo enclosure because a pair will fit on my test bench. A couple of days ago I ran some tests using APx 500 software.

I put a fist full of fluffy pillow stuffing in the sealed enclosure and installed the driver. See the test plots below. I was suspired to see the the Total Q (Qb) of the driver installed in the box testing at, 0.64. A Qb of 0.64 is much higher than 0.50 that was simulated by WinISP.

The measured distortion below 100hZ is primarily benign 2nd HD.

Rule of thumb; A sealed speaker enclosure with a Qb of 0.71 has a F3 very near the speaker Fs. In this case with a little lower Qb the F3 is a little higher, maybe 55hZ.

The Two Tone IMD test shows that the installed 6-1/2 inch Purifi has improved mid-range IMD performance. I extrapolate that the voice coil has reduced displacement due to the added stiffness of sealed air suspension.

It is my impression that the 6-1/2 Purifi driver looses nothing in a sealed enclosure.

Thanks DT


Back when Rick proposed the project, I was hot for the possibility of using a sealed box for smaller size, easy integration with a sub (no high pass filter required) and no port pipe resonances colouring up the midrange.

As it turns out, the 6.5" Purifi's Thiele Small parameters require a very small sealed box size.

Classic acoustic suspension design wisdom is that the air in a sealed box acts as a linear (and linearizing) spring, dominating over the driver's suspension compliance (which has its own distortion causing non linearity).

In reality, the thermodynamics of air show that an air spring isn't really linear and if air is compressed too much, it causes harmonic distortion on speaker's output that can easily exceed the distortion caused by the speaker's suspension.

Linkwitz here estimated the % second harmonic distortion caused by air in sealed box as =0.014*SD (in cm^2)*driver displacement(in mm)/box volume (in L).

I simulated a sealed box for the Purifi, and then used Linkwitz's formula to estimate the 2nd harmonic distortion from the air trapped in the box itself, at different listening levels. Here are the results below, compared to the total harmonic distortion of the Purifi vented prototype measured at ASR.

index.php


The sealed distortion is quite a bit higher than a vented and wastes the Purifi's low distortion potential. I also expect the mids might distort when played simultaneously with loud bass because the air itself is distorting (ASR tests don't measure this).

The 6.5" Purifi is all about playing loud with low THD, but it struggles to pull that off in a sealed box because of its unusual TS params.

I will stay tuned.

Focused on a small 2-way for desktop, every review you look at shows port interference and noise that shows up as distortion after the software calculates the distortion curve.

I found and confirmed the sealed box, due to air compression, distortion calculation on linkwitzlab.com

I calculated with 133 cm squared area moving 2mm on a 14L sealed box at 0.20% distortion. 2mm movement is plenty SPL for my desktop. That is 0.20% is for any 6 1/2 inch driver in a 14L sealed box which is not bad.

I will be testing with APx555, Gras microphones and APx500 acoustic measurement software.
Hello All,

I am not really looking at a new build yet. So far I have the Purifi 6.5 inch driver. I am putting it into the same 0.56 cubic foot Denovo cabinet. The tweeter will wait in its packaging.

I want to go back and examine the assumptions made about a sealed enclosure and compressed air caused distortion.

As far as I can determine the “simulated” sealed enclosure distortion was based on the formula found on the Linkwitzlab.com site. Change in volume due to cone motion times 1.4, divided by enclosure volume all times 100 equals % distortion. My favorite simulator calculates that for a Total Q of 0.71 for the volume of the enclosure at ~0.2 cubic feet. This is most likely the number used in post #35. If the enclosure is increased to the selected Denovo cabinet, 0.56 cubic feet, the volume is increased by nearly 3 times, and the distortion is reduced by 60%. With the increase of volume Total Q is 0.5, a not uncommonly selected design number.

I want to go back and take a closer look at the assumptions in post #8 and #35 and make some measurements.

Do the index.php simulation results that appeared in post #35 still exist somewhere? I would like to see them

Thanks DT
Purifi 6.5in 8R 0.55 Cubic Foot 2Volts input Impedance Magnitude.PNG
Purifi 6.5in 8R 0.55 Cubic Foot TS 2Volts input.png
Pyrifi 6.5in 8R 0.55 Cubic Foot Level and Distortion -_ Smooth.PNG
Two Tone voice  FFT Spectrum.png
 

nc535

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I agree with you. Why should a speaker designer care about the cause of the distortion if the distortion is acceptably low (inaudible) at target output levels? I would think vent pipe resonances showing up in the axial response would be more problematic than any increase in distortion due to air compression effects at SPLs appropriate in the home. If one wants the best of both worlds, use a passive radiator instead of a vent or use 2 mids MTM, or both, cost and space be damned.

If you've got IMD products down "only" 55 db due to a driver, its kind of silly to worry about whether they are down 100 db vs 130 db in the DAC!
 
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Rick Sykora

Rick Sykora

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Hello All,

Several months ago I had a couple of 6 1/2 inch drivers in hand and was looking around at possible applications.

@DDF in post 35 leaned away from a sealed enclosure because of potential air pressure distortion. I wondered if a sealed enclosure got a fair audition? So I decided to install the 6 1/2 Purifi driver and test a few variations.

I wanted to go along with using the 0.55 cubic foot Denovo enclosure because a pair will fit on my test bench. A couple of days ago I ran some tests using APx 500 software.

I put a fist full of fluffy pillow stuffing in the sealed enclosure and installed the driver. See the test plots below. I was suspired to see the the Total Q (Qb) of the driver installed in the box testing at, 0.64. A Qb of 0.64 is much higher than 0.50 that was simulated by WinISP.

The measured distortion below 100hZ is primarily benign 2nd HD.

Rule of thumb; A sealed speaker enclosure with a Qb of 0.71 has a F3 very near the speaker Fs. In this case with a little lower Qb the F3 is a little higher, maybe 55hZ.

The Two Tone IMD test shows that the installed 6-1/2 inch Purifi has improved mid-range IMD performance. I extrapolate that the voice coil has reduced displacement due to the added stiffness of sealed air suspension.

It is my impression that the 6-1/2 Purifi driver looses nothing in a sealed enclosure.

Thanks DT






View attachment 237709View attachment 237710View attachment 237711View attachment 237712

A few considerations here...
  1. @DDF was working with the 4 ohm version of the Purifi driver and you appear to be using the 8 ohm. They are not the same.
  2. Modeling in VCAD puts the f3 of the 8 ohm driver at closer to 78 Hz. The 4 ohm driver would be around 84. So...
  3. While could have done some eq to help the closed box, I chose to go the PR route as Purifi and others had recommended.
When DDF suggested a closed box would be more problematic, it further turned me off to a closed box design, but the more significant issue was the much higher f3 for me. As any followers know, have also invested quite a bit of time on the vented use and think I have a better compromise there. Am still measuring and we will see.

If you want to pursue a sealed enclosure, you will not find me objecting, but need more distortion measurements (notably nearfield ones) to truly demonstrate its viability.
 
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DualTriode

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My point is that the Purifi driver installed in a sealed 0.55 cubic foot Denovo enclosure did not get an audition.

My real world near field test plots show that the air compression distortion only shows up below 100 to 120hZ where the ear is least sensitive. The Two Tone IMD test shows that the LF air compression distortion does not contribute to mid frequency IMD.

Next to be tested is, aperiodic vent and passive radiator. Too much noise from a reflex port for me.
 
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Rick Sykora

Rick Sykora

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My point is that the Purifi driver installed in a sealed 0.55 cubic foot Denovo enclosure did not get an audition.

My real world near field test plots show that the air compression distortion only shows up below 100 to 120hZ where the ear is least sensitive. The Two Tone IMD test shows that the LF air compression distortion does not contribute to mid frequency IMD.

Next to be tested is, aperiodic vent and passive radiator. Too much noise from a reflex port for me.

It did not for the reasons mentioned AND at the modeled f3, a passive crossover would not have been an option. Your measurements did not specify any distance so could not tell if they were near field or not.

As I said, no objection from me, but if you are going to research other options, suggest you start another thread. This one is long enough. Thanks!
 

DualTriode

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It did not for the reasons mentioned AND at the modeled f3, a passive crossover would not have been an option. Your measurements did not specify any distance so could not tell if they were near field or not.

As I said, no objection from me, but if you are going to research other options, suggest you start another thread. This one is long enough. Thanks!

I thought that you might reply with some of your thoughts , perhaps measurement along your path of arriving at the inclusion of the 5 X 8 Passive radiator in your build.

Thanks DT
 
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Rick Sykora

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I thought that you might reply with some of your thoughts , perhaps measurement along your path of arriving at the inclusion of the 5 X 8 Passive radiator in your build.

Thanks DT

We used the SB passive radiator since 2 of the Purifi was expensive (though better overall ofc). I had both on hand and tried the Purifi ones on the truncated pyramid prototype. Though I expected the better cabinet design and better PRs to get a better result, it did not. Rick Craig had already used and so I tried the SB. It modeled well and we went from there. In hindsight, I get very comparable extension using a 2x6 port. I would not hesitate recommending the BR design for someone who wants to save some money and forgo the extra woodworking for the PR.

For the closed box case, we did not consider a Linkwitz transform at the time. For the reasons stated earlier, a sealed design was removed from consideration early on. As I was recently reviewing the 8 ohm version of the midwoofer, I noticed the specs are different than the ones loaded into VCAD. These drivers are new and am sure Purifi continues to improve. Directiva was conceived almost 2 years ago and is meant to allow others to extend and (hopefully) improve. If you intend your efforts to become part of the project, there is certainly room for improvement and/or design variants.

In any case, a new thread is needed. At almost 2000 posts, this one is daunting for newcomers to digest. r2 has been delayed but looks like it is about to restart. I may be busy but If you have other questions, either reference me in the new thread or send a DM. @ctrl was a major contributor to r1 and so may forward specific questions to him. His sims and experience really helped get r1 completed faster AND better.

Hope this helps!

Rick
 
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617

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The new Epique 7" PRs should also be capable and much cheaper.
Wolf, those are quite cheap. Cast frame for fourty dollars is impressive.
 

Wolf

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AND- they have the xmax! I have a pair of the 7" for use with the 5.5" Epique woofers. These PRs really have the throw! The 7" PR I have calculated at more than twice the Vd of the 5.5" woofer. They should be a GREAT match!
 

DualTriode

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...

In any case, a new thread is needed. At almost 2000 posts, this one is daunting for newcomers to digest. r2 has been delayed but looks like it is about to restart. I may be busy but If you have other questions, either reference me in the new thread or send a DM. @ctrl was a major contributor to r1 and so may forward specific questions to him. His sims and experience really helped get r1 completed faster AND better.

Hope this helps!

Rick

Hello Rick and All,

@Rick Sykora , Thanks for your reply,

Am I thinking of a new project? Probably not, possibly so, unknown at this point.

I do have a couple of 6-1/2 inch Purifi drivers to play with and a couple of new 8 inch drivers due in a few days.

I would like a place to post and discuss Purifi driver performance in the Directiva domain.

Will you consider starting the new thread?

Thanks DT
 
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Rick Sykora

Rick Sykora

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Hello Rick and All,

@Rick Sykora , Thanks for your reply,

Am I thinking of a new project? Probably not, possibly so, unknown at this point.

I do have a couple of 6-1/2 inch Purifi drivers to play with and a couple of new 8 inch drivers due in a few days.

I would like a place to post and discuss Purifi driver performance in the Directiva domain.

Will you consider starting the new thread?

Thanks DT

Thanks for the suggestion.

It is live here: https://www.audiosciencereview.com/.../directiva-driver-candidate-discussion.38551/
 
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