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Introducing Directiva - An ASR open source platform speaker project

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Rick Sykora

Rick Sykora

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Sica 6.5" was measured at Dibirama. Much more usable FR than most pro coax drivers, for sure. Tweeter THD appears to be the major weak area.

Been spending a bit more time reviewing potential drivers…

One key aspect for me is availability. Looking at the Sica, I did not find a US supplier and neither of the ones on the Sica website appeared to have it (or any Sica driver for that matter). I want to know that the driver in a new design will be supported for a few years and that others will be able to readily acquire it. :)
 

Biblob

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You just have to cross over high enough. Those measurements look a bit weird too, compared to what we've got. I've measured the 5.5" coax at 109,[email protected] outdoors (both midbass and tweeter active), that got me 1,48% THD @5khz. So my impression is that you can freely play as loud as realistically possible indoors with this tweeter as long as you cross over at 2500-3000.

We've also played 111dB continously at the listening position indoors with no hint of audible compression.
Saying this, am I correctly assuming this 5,5" is what you use in your speaker? :)
 

ctrl

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This post will shed some more light on what led to all the delays regarding the crossover tuning of the Directiva.

I had already mentioned (here and here) the small uncertainty regarding the phase alignment of woofer and tweeter to each other. It could be that the reference points, when measuring the drivers, could have had minimally different distances from the baffle.

Now that Rick has updated his measurement equipment, we can be pretty sure that his measurements should be fairly accurate.
When comparing the measured frequency responses of tweeter and woofer by Amir's NFS and Rick's gated measurements, there are sometimes significant deviations.

Comparison of Rick's gated measurement versus Amir's NFS measurement of the SeasDXT tweeter in the Directiva cabinet without XO, after scaling the sound pressure level:
1630170270516.png

That looks pretty good on the whole - considering that different tweeter (of the same series) and measurement methods were used. There are some deviations, among others, in the effective range of a possible crossover, 1-3kHz, and around 14kHz.

The latter could be due to the "decreasing fine resolution" of the NFS measurement ("fitting error") at frequencies >10kHz. In any case, my own measurements of the SeasDXT in different speakers show a comparable dip:
1630169453571.png
Therefore, we assume that Rick's measurements are more accurate in this area.



Comparison of Rick's gated measurement versus Amir's NFS measurement of the Purifi woofer in the Directiva cabinet without XO, after scaling the sound pressure level:
1630170707720.png

The deviations in the important frequency range 1-4kHz took us*** days and days until we were absolutely sure that the deviations were not due to the measurement equipment.

Either the two Purifi woofers show significant frequency response differences in the range 1-4kHz, or there was a disturbance in Amir's measurement in this range.

It is not about small things, but about values that can change the character of the speaker. Here are the differences of the two measurements, when normalized to Rick's measurement:
1630171005528.png

Currently Rick tunes his speaker in the 1-4kHz range according to his measurements and ignores the NFS for this range.

Reliable measurements are everything on a project that is spread across continents. And only with reliable measurements can VCAD play to its strengths. Otherwise, there are always irritations when auditory impressions do not match the crossover simulations, etc.

*** to be honest, Rick had the work and I thought I knew everything better ;)
 

sigbergaudio

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Saying this, am I correctly assuming this 5,5" is what you use in your speaker? :)

That is correct. It sounds and behaves remarkably well.
 

McFly

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@ctrl I can sympathise with your woofer measurements debacle. Long shot but, looking at the frequencies, being higher than most baffle effects, could the differences be somewhat due to the orientation of the woofers surround since it varies? i.e. measure woofer, rotate woofer 60 degrees, remeasure
 

ctrl

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@ctrl I can sympathise with your woofer measurements debacle. Long shot but, looking at the frequencies, being higher than most baffle effects, could the differences be somewhat due to the orientation of the woofers surround since it varies? i.e. measure woofer, rotate woofer 60 degrees, remeasure
Such a possibility should never be ruled out.

It would be somewhat unusual, since the woofer (and tweeter) was measured on-axis with the measuring microphone aligned centrally on the woofer (and tweeter) and 1m distance from the baffle - @Rick Sykora knows all dirty secrets about the measurements ;) and can provide more details.

In this case, rotating the woofer by 60° would not change anything, since it is measured centered and on-axis.
But if the surround of the woofer is responsible for the deviations, a change of the measuring distance might have an effect.
Rick would have to measure the woofer on-axis with different distances - for example 0.3, 0.5, 0.8, 1.0 and 1.2m. Then the effects of the surround should have different impact.
 

ctrl

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@McFly
My statement above is not entirely correct.
Unless there would be an interaction of the edge diffraction with the diffraction caused by the surround. Then a rotation of the driver would actually have an effect.
 
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McFly

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@McFly
My statement above is not entirely correct.
Unless there would be an interaction of the edge diffraction with the diffraction caused by the surround. Then a rotation of the driver would actually have an effect.
That's more what I was thinking, an interaction between the surround and the baffle edge or the surround and the tweeter "hole". For example the woofer oriented one way will have a clear line of sight to the baffle edge and the woofer oriented another would have the surround in the way. Its just a crazy thought I had briefly when I was measuring my purifi's here, but one of those "its probably too hard to see in my low res measurements anyway". With the Klippel your getting 0.79hz resolution or whatever it is, what's rick getting with the new rig? I'm assuming obviously Amirs measurements and Ricks measurements are in exactly the same baffle, box, and cabinet damping.
 

ctrl

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"its probably too hard to see in my low res measurements anyway"
So if measured carefully, the effect should be measurable even without NFS, despite stronger smoothing.

With good positioning of the loudspeaker in the room (woofer at half ceiling height, no reflection surfaces closer than half ceiling height, position of loudspeaker and measuring microphone is identical for all measurements) the phenomenon should be measurable.

If the measurement is performed at a distance of 0.3m, one could also compare the measurements without gate (with all room reflections).
 

ctrl

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Here is a theoretical view on @McFly's theory that the large deviation between Rick's and Amir's measurements of the Purifi woofer in the frequency range 1-3kHz may be caused by the protruding surround of the woofer and may disappear when the woofer is rotated by 60°.
1630425913279.png

For edge diffraction (r1), the newly resulting phase-inverted radiating sound source at the side edge provides the first minimum (i.e. perfect cancellation of the sound pressure level of the primary and secondary sound source) at 3.2kHz (fmin=n*c/r1 n=1,2...) when interfering with the axis frequency response and a first maximum (i.e. perfect addition of the sound pressure level of the primary and secondary sound source) at 1.6kHz (fmax=(2n-1)*c/2*r1 n=1,2...).

This only describes the expected edge diffraction that occurs in any loudspeaker with side edges. In the frequency response of the tweeter you can see the minimum at 3.2kHz very well.
1630428416162.png
For the woofer, the cone acts as a waveguide and suppresses the interaction with the side edges very well.

The same thing can be done for the protruding surround of the woofer with the distance r2.
The first minimum would be at 5.3kHz and the maximum at 2.6kHz.
1630426924047.png


So the surround itself cannot be responsible for the differences in the measurements, the frequency range of maximum and minimum is too high for that.
The largest deviations of the woofer measurements are in the range of 1.5-2.5kHz.

Could the generated secondary sound sources, i.e. the side edges and the surround, also interfere again and thus be responsible for the deviations - rather not. On the one hand the sound pressure level is very low, on the other hand the distances with (r1-r2) 0.04m are so small that the addition and cancellation of the sound sources is shifted to even higher frequencies.
 

D!sco

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Is there only one driver per tester, or is this a consistent issue from person to person, rig to rig?

PS @ctrl, loved the binding posts audibility thread.
 

pseudoid

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I deserve to get tar'd and feather'd for the following:
1. I had every intention to read all 34 'pages' of replies but only got to the end of page 9 before too many Qs kept popping up in my mind about this project.
2. I miss the essence and the need for taking on such a project that seems very innocent and very simple. "I am gonna make a speaker; what can possibly go wrong?"
3. It is one thing to start planning such a DIY project but it is becoming very apparent that someone maybe biting more than they can chew w/this DIY.
4. Like many before you, you are not only taking on an experiment with a speaker-build but much more. It gets even more complex with your decision to throw in a power amplifier (active) to the mix, yet I see scant discussion even about the cross-over network (passive) design, build, etc.
5. I may have missed the intent of this speaker-build project and I am not certain if it is being planned as a floor/stand, a full-range, a multi-channel or a desktop application.
6. I may have also missed the final enclosure design/dimensions or if this a clone of an existing design or something that has any novelty in its core philosophy that is being omitted in the current marketplace.
7. I may be way off track but I hope this does NOT end-up just like another clone of the famous BBC LS3/5A w/a built-in PA...
The above does NOT mean that I do not wish you the best of luck on this project and beyond.
Maybe someday, 'we' will be able to brag about knowing the famous speaker designer named "Sykora" :)
 
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Rick Sykora

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As @ctrl mentioned in his post, measurement variations due to the Purifi woofer surround are unlikely. I have 4 of the woofers. 2 are older and 2 are newer. Amir has one of the older ones and am currently using one of the newer ones. The new ones measure identically. The older one I have is in an SPK5 cabinet and does not match the newer woofer in the Directiva cabinet.

The good news is the newer ones match. If we need to do some compensating for Amir's being slighty different, we have the power of dsp to do so!
 
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Rick Sykora

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I deserve to get tar'd and feather'd for the following:
1. I had every intention to read all 34 'pages' of replies but only got to the end of page 9 before too many Qs kept popping up in my mind about this project.
2. I miss the essence and the need for taking on such a project that seems very innocent and very simple. "I am gonna make a speaker; what can possibly go wrong?"
3. It is one thing to start planning such a DIY project but it is becoming very apparent that someone maybe biting more than they can chew w/this DIY.
4. Like many before you, you are not only taking on an experiment with a speaker-build but much more. It gets even more complex with your decision to throw in a power amplifier (active) to the mix, yet I see scant discussion even about the cross-over network (passive) design, build, etc.
5. I may have missed the intent of this speaker-build project and I am not certain if it is being planned as a floor/stand, a full-range, a multi-channel or a desktop application.
6. I may have also missed the final enclosure design/dimensions or if this a clone of an existing design or something that has any novelty in its core philosophy that is being omitted in the current marketplace.
7. I may be way off track but I hope this does NOT end-up just like another clone of the famous BBC LS3/5A w/a built-in PA...
The above does NOT mean that I do not wish you the best of luck on this project and beyond.
Maybe someday, 'we' will be able to brag about knowing the famous speaker designer named "Sykora" :)

Lol, just to be clear, am not the primary designer. Am avid speaker builder who was asked to lead this project....

I did end up getting more involved than I had intended and some of this is apparent as some of my mistakes have slowed progress. As others are likely to run into some of the same issues, I have been transparent about sharing my travails. I was hoping that by using the Klippel measurements, I could avoid upgrading my measurement rig, but this has not proceeded as I hoped. So yes, my design inexperience is on full display!

I did know the potential peril of hoping that my inexpensive test rig/environment could sync up well with Amir's Klippel/garage. Along the way, my other mistake was to rush to get a test speaker to Amir and was not careful about checking how well the drivers match. What was "close enough" from my original perspective turned out to be "not all that close" when we were trying to complete the crossover design.:facepalm:

Anyway, am about to share more of this in the build thread. I have heard some very promising results from the prototype to date. Unless you are experienced with active speaker design, my advice would be to hold off until after Amir tests Directiva r1 we make our final determinations. :)
 
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Rick Sykora

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So, too many words when a picture can tell so much more. Here is our dilemma over the Purifi woofer shown below...

purifi driver comparos.jpg


The green and blue overlapping traces are the 2 new woofers (measured today) compared to the woofer in the speaker I sent to Amir. Bear in mind, as @ctrl will attest, my measurement setup is much better today than it was when I made the older woofer measurement. That said, what is shown also aligns with the initial Klippel measurements that Amir made of the speaker. So, at this point, we are pretty confident that his woofer has a different frequency response in the 1.5-4kHz range.

Forgot to mention the curveball from VCAD as the shelving filter sim did not match the minidsp HD shelving filter. Kimmo confirmed this issue, but along with some of my room challenges, this complicated made our long distance design work. Not making excuses mind you as we are experienced technical folk, but keep in mind, also part-time volunteers! :)
 

McFly

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Here is a theoretical view on @McFly's theory that the large deviation between Rick's and Amir's measurements of the Purifi woofer in the frequency range 1-3kHz may be caused by the protruding surround of the woofer and may disappear when the woofer is rotated by 60°.
View attachment 150703

For edge diffraction (r1), the newly resulting phase-inverted radiating sound source at the side edge provides the first minimum (i.e. perfect cancellation of the sound pressure level of the primary and secondary sound source) at 3.2kHz (fmin=n*c/r1 n=1,2...) when interfering with the axis frequency response and a first maximum (i.e. perfect addition of the sound pressure level of the primary and secondary sound source) at 1.6kHz (fmax=(2n-1)*c/2*r1 n=1,2...).

This only describes the expected edge diffraction that occurs in any loudspeaker with side edges. In the frequency response of the tweeter you can see the minimum at 3.2kHz very well.
View attachment 150710
For the woofer, the cone acts as a waveguide and suppresses the interaction with the side edges very well.

The same thing can be done for the protruding surround of the woofer with the distance r2.
The first minimum would be at 5.3kHz and the maximum at 2.6kHz.
View attachment 150706

So the surround itself cannot be responsible for the differences in the measurements, the frequency range of maximum and minimum is too high for that.
The largest deviations of the woofer measurements are in the range of 1.5-2.5kHz.

Could the generated secondary sound sources, i.e. the side edges and the surround, also interfere again and thus be responsible for the deviations - rather not. On the one hand the sound pressure level is very low, on the other hand the distances with (r1-r2) 0.04m are so small that the addition and cancellation of the sound sources is shifted to even higher frequencies.
Thank you for that. Really appreciate your knowledge, resources and input. Did you consider R1+R2? i.e flip R2 over on the Z axis.

Anyway, its far more likely the differences in measurements are due to this;

1630446239796.png


Version 0.95 above.

1630446293882.png


Version 1.01 above

1630446353998.png


Version 1.11 above.

Clearly there have been some tweaks to the woofer along the way. It's just a bastard that the differences are right in the common crossover region. Will have to see if I have any measurements of mine here (I will somewhere) as I was one of the early buyers of the woofers when it became public.
 
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Rick Sykora

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Thank you for that. Really appreciate your knowledge, resources and input. Did you consider R1+R2? i.e flip R2 over on the Z axis.

Anyway, its far more likely the differences in measurements are due to this;



Version 0.95 above.



Version 1.01 above



Version 1.11 above.

Clearly there have been some tweaks to the woofer along the way. It's just a bastard that the differences are right in the common crossover region. Will have to see if I have any measurements of mine here (I will somewhere) as I was one of the early buyers of the woofers when it became public.

Thanks for pointing this out. At least Purifi published the revision changes...

Too often the industry makes changes and just keeps selling the same model without sharing the changes or marking the new versions.
 

ctrl

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Did you consider R1+R2? i.e flip R2 over on the Z axis.

This case does not exist - IMO. The secondary sound sources (SSS), with inverted phase, generated by obstacles (e.g. surround) or abrupt "media transitions" (baffle edge) have a longer time of flight to the listening point (LP), compared to the sound emitted from the center of the driver.

In simplified terms, the extended time of flight to the LP corresponds to the distances r1, r2, and r3 (the path is still somewhat longer, but for simplicity's sake we ignore this here).

It's true that r2 = r3, so r3 need not be considered separately. The time of flight difference between r1 and r3, is the same as r1 and r2.
The case r1+r2 does not occur. There is no secondary sound source which produces this extended time of flight.

1630487343297.png
 

D!sco

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This revisionism has also happened historically with Foutnek's NeoCD 1 ribbon tweeter. They changed the waveguide, manufacturer, and even flipped the positive/negative terminals. As long as the changes are consistent, why not just driver match and DSP accordingly?
 

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If this derails the thread PM me and I'll edit, but I thought some people might be interested in what you can achieve if you have a lot of room for ports, say in the bottom 2/3rds of floorstander, you can suppress about 20 db of port noise using resonance traps - as has been demonstrated in the DIYaudio thread.

Here are my rudimentary results from one nights tinkering. First pic was using a 60mm port for a baseline (didn't record length, you could work it out, looks tuned a bit too low). The second pic and all plumbing/port tinkering thereafter was done with 75mm ID piping. The FR's are not directly comparable, but you can compare the resonant peaks of a simple straight port vs. the spaghetti port I ended up with. The traps are stuffed quite generously with pillow stuffing.

Purifi long stroke woofer 6.5" in a 15L test box (as per directiva). Cabinet walls lined with foam. Port installed to base of box as if it were leaving the woofer chamber and running through the leg of a floorstander or stand i.e. there is no port volume within the woofer cabinet.

ptt6.5w04 15L box, 60mm ID port straight.jpg

ptt6.5w04 15L box, 75mm ID port tuning with traps.jpg

20210708_200512.jpg

20210708_200500.jpg
 
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