• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Introducing Directiva - An ASR open source platform speaker project

OP
Rick Sykora

Rick Sykora

Major Contributor
Forum Donor
Joined
Jan 14, 2020
Messages
3,513
Likes
7,017
Location
Stow, Ohio USA

tktran303

Addicted to Fun and Learning
Forum Donor
Joined
Mar 27, 2019
Messages
683
Likes
1,179
I think the thing with the cone-edge resonance that also important to consider is if:

Whether the baffle dimensions and shape help exacerbate or alleviate the resonance (sim + measure)
Can you notch it out (yes, and easier with DSP)
Does it appear off axis (some drivers’ cone edge resonance seems to be less pronounced the further you go off axis, so if optimising for listening window, it matters less)
Whether there’s a a rise in non-linear distortion associated with it (seems the a slight raise in HD2 is fairly innocuous, if not inaudible)

Of course, no resonance is better than a resonance, which is one of the advantages of the Purifi driver in this regard.
 
Last edited:

MrPeabody

Addicted to Fun and Learning
Joined
Dec 19, 2020
Messages
657
Likes
942
Location
USA
Unfortunately, I do not have any test reports from the ES180. The measurements from Voice Coil are unfortunately not performed on an IEC baffle - what is shown does not look bad.

Fit would in any case the Dayton RS-180P-8, low harmonic distortion (HD) and up to 1.7kHz virtually error-free FR (@1.8kHz small resonance).

For extremely low HD, SBAcoustics would be an option (SB17CAC35-4 or SB17NBAC35-4). But these are designed for larger volumes - that should not be a problem with active tuning.


The directivity of the tweeter in the Directiva cabinet is so even (according to the simulation) that one is very flexible with regard to the crossover frequency.
Starting at [email protected], anything is possible. This also leaves a lot of room for fine-tuning (via listening sessions).

As examples, the simulated crossover frequencies for the Directiva, once with [email protected] and [email protected] (in the middle diagram: on-axis = black, LW = green, IR = orange, SP = blue, DI = red):
View attachment 118547 View attachment 118548

I recall having looked at Dickason's tests of this driver not very long ago. The frequency response he shows is nothing like the one that the manufacturer provides. So you suppose this is due to different baffles? Exactly how are the two baffles different?
 

tktran303

Addicted to Fun and Learning
Forum Donor
Joined
Mar 27, 2019
Messages
683
Likes
1,179
I recall having looked at Dickason's tests of this driver not very long ago. The frequency response he shows is nothing like the one that the manufacturer provides. So you suppose this is due to different baffles? Exactly how are the two baffles different?

Vance mounts in a box which is 8-9” wide IIRC, but he always stipulates how he measures the frequency response eg.

“mounted the ES180Ti-8 woofer in an enclosure with a 15” × 8” baffle filled with damping material (foam). I used the LinearX LMS analyzer set to a 100-point gated sine wave sweep. Then, I measured the device under test (DUT) on and off axis from 300 Hz to 40 kHz frequency response at 2.83 V/1”

Reference:
https://audioxpress.com/article/Test-Bench-Dayton-Audio-ES180Ti-8-7-High-End-Midbass-Woofer

So when you measure that way you will see the baffle step loss, as well as the diffraction issues as determined by the most significant baffle dimension/shape, which is usually the width of the baffle and the shape of this edge.

When you measure a driver in an open-baffle eg. Infinite baffle, or a slightly smaller baffle defined as defined IEC; there’s no baffle step loss and diffraction issues are not evident, but there are dips in the bass due to effects of the rearward radiation wrapping around the front and affecting the response.

Now, to confuse (or improve) things, some manufacturers’ specifications are defined in their own baffle shape AND cabinet size, then stitch together the anechoic response for the low end. Eg. SEAS.
 
Last edited:
OP
Rick Sykora

Rick Sykora

Major Contributor
Forum Donor
Joined
Jan 14, 2020
Messages
3,513
Likes
7,017
Location
Stow, Ohio USA
It has been a long day, but as promised, here are the initial driver responses of the custom cabinet variation...

Directiva Custom Denovo - gated driver fr.png

for reference, here is the Denovo cabinet...
Directiva Stock Denovo - gated driver fr.png

So, my initial thoughts are that my measurement setup are not well matched between the 2 cabinets, but have not done a cabinet as angular as the Directiva custom one either. I did struggle with some setup issues switching back from having the minidsp inline. Will review in the morning and ensure I can repeat the Denovo cabinet results.
 

MrPeabody

Addicted to Fun and Learning
Joined
Dec 19, 2020
Messages
657
Likes
942
Location
USA
Vance mounts in a box which is 8-9” wide IIRC, but he always stipulates how he measures the frequency response eg.

“mounted the ES180Ti-8 woofer in an enclosure with a 15” × 8” baffle filled with damping material (foam). I used the LinearX LMS analyzer set to a 100-point gated sine wave sweep. Then, I measured the device under test (DUT) on and off axis from 300 Hz to 40 kHz frequency response at 2.83 V/1”

Reference:
https://audioxpress.com/article/Test-Bench-Dayton-Audio-ES180Ti-8-7-High-End-Midbass-Woofer

So when you measure that way you will see the baffle step loss, as well as the diffraction issues as determined by the most significant baffle dimension/shape, which is usually the width of the baffle and the shape of this edge.

When you measure a driver in an open-baffle eg. Infinite baffle, or a slightly smaller baffle defined as defined IEC; there’s no baffle step loss and diffraction issues are not evident, but there are dips in the bass due to effects of the rearward radiation wrapping around the front and affecting the response.

Now, to confuse (or improve) things, some manufacturers’ specifications are defined in their own baffle shape AND cabinet size, then stitch together the anechoic response for the low end. Eg. SEAS.

Useful information. I'm a little surprised that Vance would take the measurement this way, where the baffle step and diffraction have such a strong affect on the measurements. I know that I had read his description of the enclosure and baffle, but for some reason it didn't register with me. Now I'm wondering whether Dayton Audio explains the test setup they use to obtain the sensitivity/frequency curve.
 
OP
Rick Sykora

Rick Sykora

Major Contributor
Forum Donor
Joined
Jan 14, 2020
Messages
3,513
Likes
7,017
Location
Stow, Ohio USA
Was able to repeat my previous measurement for the most part. The magnitude of some of the ripples has increased. This caught my attention in the newer cabinet measures and so made me doubt. For now, the only major change was that I upgraded REW. Fo now, that seems the most plausible explanation.

So real fun begins and will put the minidsp back and measure the Z offset delay next...
 

frankschwab

Member
Joined
Mar 16, 2021
Messages
5
Likes
0
OFF-TOPIC


The Grimm LS1 shows that the combination of tweeter with small waveguide and wide baffle does not quite work out.
Please do not misunderstand the LS1 is certainly an excellent speaker, I am purely interested in the directivity of the LS.

1. Grimm LS1
2. Sketch LS1, in the simulation, the LS is upside down, but this does not matter.
3. horizontal FR deg0-90, normalized on-axis (15° steps)
4. Spectrogram +-180° normalized on-axis

View attachment 112980 View attachment 112973 View attachment 112974 View attachment 112977
Thus, starting from 5kHz, down to 1.8kHz, the 45° FR increases by almost 5dB and again reaches the sound level of the on-axis FR.

Measurements in the magazines confirm the simulation, for example here:
View attachment 112984
Source: hifitest.de

But the horizontal radiation pattern is not everything. For example, the (simulated) curve of the early reflections of the LS1 is very balanced:
View attachment 112985
In a wide-baffle design like the LS1, is there a point at which the baffle is wide enough that the shape of the edges ceases to matter?
 

frankschwab

Member
Joined
Mar 16, 2021
Messages
5
Likes
0
Vance mounts in a box which is 8-9” wide IIRC, but he always stipulates how he measures the frequency response eg.

“mounted the ES180Ti-8 woofer in an enclosure with a 15” × 8” baffle filled with damping material (foam). I used the LinearX LMS analyzer set to a 100-point gated sine wave sweep. Then, I measured the device under test (DUT) on and off axis from 300 Hz to 40 kHz frequency response at 2.83 V/1”

Reference:
https://audioxpress.com/article/Test-Bench-Dayton-Audio-ES180Ti-8-7-High-End-Midbass-Woofer

So when you measure that way you will see the baffle step loss, as well as the diffraction issues as determined by the most significant baffle dimension/shape, which is usually the width of the baffle and the shape of this edge.

When you measure a driver in an open-baffle eg. Infinite baffle, or a slightly smaller baffle defined as defined IEC; there’s no baffle step loss and diffraction issues are not evident, but there are dips in the bass due to effects of the rearward radiation wrapping around the front and affecting the response.

Now, to confuse (or improve) things, some manufacturers’ specifications are defined in their own baffle shape AND cabinet size, then stitch together the anechoic response for the low end. Eg. SEAS.
You wouldn't happen to know where I could find the IEC spec on baffle sizes? I'm trying to figure out the minimum size baffle I can test a tweeter on (i.e. above 1.5kHz, usually) to get on and off-axis measurements that aren't disturbed by baffle diffraction.
 
OP
Rick Sykora

Rick Sykora

Major Contributor
Forum Donor
Joined
Jan 14, 2020
Messages
3,513
Likes
7,017
Location
Stow, Ohio USA
Before I start crossover design, went to verify the cabinet tuning. Either there is something amiss or the sims are pretty inaccurate. Bassbox and VituixCAD (VCAD) had different outcomes. Neither is close to reality. I have tried no damping, some Sonic Barrier, added some Acousta-stuf, replaced it with the cotton-based damping (Purifi recommends) and even tried reducing the volume by a liter. Not close to aligning the sims and the measurements. :confused:

There are no obvious signs of any leaks, but planning on a nearfield measure and possibly breaking out my stethoscope. Turning back to the timing for the z-axis offset. It took a little doing, but here is the measurement (using method documented on minidsp site)...

pic removed as found a phase issue in test config and needs to be redone.

Based on the minidsp app note, the delay is the difference between the peaks minus the preprogrammed 1 ms delay. This is 1.14-0.075-1 = .065 ms

The main tricks involved knowing which channel is left on USB (input 1) and then how to set the mix on minidsp HD (app note diagram is shown for a DIRAC device)...
minidsp HD z offset routing.png
 
Last edited:

ctrl

Major Contributor
Forum Donor
Joined
Jan 24, 2020
Messages
1,616
Likes
6,086
Location
.de, DE, DEU
In a wide-baffle design like the LS1, is there a point at which the baffle is wide enough that the shape of the edges ceases to matter?
The shape of the edges will always have an influence. If the radius of the e.g. rounding is increased for a wide baffle, this will always be better than without - for realistic enclosure sizes.
 

digitalfrost

Major Contributor
Joined
Jul 22, 2018
Messages
1,521
Likes
3,086
Location
Palatinate, Germany
I hate T-nuts, and now use threaded inserts when using machine screws.
I had my problems with T-nuts but for the most part they worked fine for me. How do you use threaded inserts with MDF? Is it glued in? Or is the outside self-cutting? How do you make sure it's straight?
 

abdo123

Master Contributor
Forum Donor
Joined
Nov 15, 2020
Messages
7,423
Likes
7,940
Location
Brussels, Belgium
Before I start crossover design, went to verify the cabinet tuning. Either there is something amiss or the sims are pretty inaccurate. Bassbox and VituixCAD (VCAD) had different outcomes. Neither is close to reality. I have tried no damping, some Sonic Barrier, added some Acousta-stuf, replaced it with the cotton-based damping (Purifi recommends) and even tried reducing the volume by a liter. No close to aligning the sims and the measurements. :confused:

There are no obvious signs of any leaks, but planning on a nearfield measure and possibly breaking out my stethoscope. Turning back to the timing for the z-axis offset. It took a little doing, but here is the measurement (using method documented on minidsp site)...

View attachment 118748
Based on the minidsp app note, the delay is the difference between the peaks minus the preprogrammed 1 ms delay. This is 1.14-1.075 = .065 ms

The main tricks involved knowing which channel is left on USB and then how to set the mix on minidsp HD (app note diagram is shown for a DIRAC device).

Input 1 is left and input 2 is right.
 

Wolf

Addicted to Fun and Learning
Joined
Nov 21, 2020
Messages
557
Likes
589
Location
Indiana
I had my problems with T-nuts but for the most part they worked fine for me. How do you use threaded inserts with MDF? Is it glued in? Or is the outside self-cutting? How do you make sure it's straight?

I use the ones with the outer-knife rifling, and the tapered cylindrical exterior. Thread-serts are a knurled style that push in from the opposing side, and also valid.
I use a nut/screw-driver and insert them carefully by hand, or install the bit in the drill press chuck, and lower/rotate the bit by hand- not by power. I do NOT use an ordinary Allen-wrench, as I never seem to keep them straight that way.
A little glue on the exterior thread (or knurled-shaft for the 'serts) does not hurt.
 

frankschwab

Member
Joined
Mar 16, 2021
Messages
5
Likes
0
The shape of the edges will always have an influence. If the radius of the e.g. rounding is increased for a wide baffle, this will always be better than without - for realistic enclosure sizes.
Thank you for all the invaluable information in this thread, in addition to your work on this awesome project! A more vague question, if you don't mind, since I know very little about diffraction: For a speaker with a dedicated midrange, is there a general trend of more or less diffraction of the tweeter's output between a recessed dome midrange (like a Morel MD55), a protruding dome midrange (like the Dayton RS52AN), and a small cone midrange (like the SS 10F/4424G)? I'm guessing that the specific tweeter and the spacing etc... play enough of a role that this can't be generalized, but I really don't know.
 
OP
Rick Sykora

Rick Sykora

Major Contributor
Forum Donor
Joined
Jan 14, 2020
Messages
3,513
Likes
7,017
Location
Stow, Ohio USA
OP
Rick Sykora

Rick Sykora

Major Contributor
Forum Donor
Joined
Jan 14, 2020
Messages
3,513
Likes
7,017
Location
Stow, Ohio USA
So as I mentioned earlier, this is preliminary as am still reviewing the damping, etc...

directiva z.png
 
Top Bottom