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Introducing Directiva - An ASR open source platform speaker project

HooStat

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For comparison purposes, I think it would be valuable to build a version with the unmodified Denovo cabinet. But one step at a time for now
Sorry if you mentioned this already, but are the cabinet volumes the same (or similar) between the planned prototype and the Denovo?
 

maxxevv

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PLEASE NOTE: Just to clarify some misunderstanding over the Directiva tweeter selection. Earlier I had posted that I was finalizing the tweeter selection. The context here was amongst the existing team and sharing some of where I had sought (past tense) help with tweeter selection. Some have misread my post as a though we were still looking for tweeters. I regret if this was unclear, but the Seas DXT is the tweeter we have selected. Later derivatives may consider other tweeters, but for the first implementation, I consider the tweeter selection to be final.

So while @ctrl was simulating directivity, I had been modeling and prototyping the cabinet tuning. If you had not previously noticed, I have posted the effort here: Can Purifi's SPK5 be improved with a passive radiator? | Audio Science Review (ASR) Forum

With the equalization and filtering available with an active design, we can address some of the challenges of getting low bass out of the Purifi woofer more readily than if the design were passive. As you have read, I have tried to ensure the Directiva is affordable. An important part of determining the final cabinet is the volume needed. My prototyping has been with the SPK5 cabinet, so had to consider how ports or passive radiators would fit into the Directiva cabinet. I think I have a handle on a vent size that does not have major misbehavior, but the passive radiator has more potential price/performance considerations.

The SB 5x8 passive radiator is inexpensive, but has a large footprint...
View attachment 113037

So, the other consideration is the passive radiator that Purifi designed for the woofer. Like the woofer, it is pricey. But as it is smaller, it is easier to incorporate on the Directiva back panel.
View attachment 113036

I had to order the Purifi PR and they just arrived today. As it is part of finalizing the overall design, will be taking some time away from posting to finalize the cabinet alignments. Before I do, will preview the proposed final cabinet. While I liked latest design, I had some reservation about its complexity, so I proposed a truncated pyramid. We had some back and forth over the dimensions, how the drivers would fit and angles that would be easier to cut. After more simulations, here is what we designed...

View attachment 113038

This has about the same directivity (maybe a bit better) than the prior cabinet shape. As I mentioned, my plan was to offer options for a choice of cabinet, but this is the one I plan to build and have Amir test. For comparison purposes, I think it would be valuable to build a version with the unmodified Denovo cabinet. But one step at a time for now.:)

If you are still thinking of simulating the SB 2604 tweeters, I have done the 3D model based on the their published datasheet.
Confident that its over 90% accurate if the datasheet provided is accurate.

Let me know if you want it for the simulation.
 

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Zvu

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....After more simulations, here is what we designed...

View attachment 113038

This has about the same directivity (maybe a bit better) than the prior cabinet shape. As I mentioned, my plan was to offer options for a choice of cabinet, but this is the one I plan to build and have Amir test. For comparison purposes, I think it would be valuable to build a version with the unmodified Denovo cabinet. But one step at a time for now.:)

This looks somewhat familiar :)

Pharaoh_1.jpg

https://hificompass.com/en/projects/2-way-systems/pharaoh
 

test1223

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The virtual microphone is located at a distance of 2m in all simulations. The phase shift due to the different signal propagation times of the drivers (driver distance is 0.145m) is only 12°, even at a high crossover frequency of 2.4kHz, it has hardly any influence on the axis frequency response in a crossover with even order.
Yes, but in the vertical it has influence. The floor and ceiling bounce should be considered. If you can't get both good an angle of the speaker cabinet is an option. You will also slightly increase the higher frequencies of later reflections with an upward angle, since there is more free space toward the ceiling of the room. Splitting the front in two parts and angle only one driver is also interesting, or including damping material at the front or side walls into the design process... plenty options with no straight listening distance as a goal everything is much more fussy. From the potential DI about 1,2m listening distance would be good to achieve a good balance between direct sound and later reflections.
 

mjvbl

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Recently I was sort of inspired by the SB26CDC tweeter which seems to be the same as the SB26ADC mentioned in this thread but with a ceramic coated dome.

But I'm a beginner, hence my following question.

The datasheet shows a very wide dispersion for these tweeters. I think what is being shown here is much less roll-off at 60deg off-axis than what we typically see for 1" dome tweeters, and very very little roll-off at 30deg off-axis even beyond 20kHz. Especially the SB26CDC shows a very nice off-axis response, and also there seems to be no breakup up to 40kHz!

But I recall independent measurments for SB26ADC looked a bit different off-axis than the datasheet. Then I see on the datasheet that: mic. distance 31.6cm. Does this have an influence on the off-axis measurment results on the datasheet? (As in mic too close to the baffle.)

sb26adc_sb26cdc.png
 

ctrl

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Yes, but in the vertical it has influence. The floor and ceiling bounce should be considered.
For this reason, I wrote the following paragraph in the referenced post:
In order to get a more complete overview of the simulated loudspeaker, for the possible final versions, all simulated FR (72 pieces for each driver) are exported and imported into VituixCAD to be able to view in advance the simulated loudspeaker according to CTA-2034-A (DI, PIR, LW...).
The CTA-2034-A standard includes an approximation for floor and ceiling bounce, which you can then check in VituixCAD - if the vertical spectrograms and angular frequency responses are not sufficient for the assessment.

If you can't get both good an angle of the speaker cabinet is an option.
Since it is an active concept, aligning the sound origination points of the tweeter and woofer in one plane is not a problem.

For the v8 version presented by @Rick Sykora, the normalized vertical directivity is as follows (crossover is [email protected]):
1613557094969.png 1613557167155.png
... and as @Lbstyling wrote in post#63, you can still improve the vertical radiation a little with a round over of the top edge - at the price of a slightly changed horizontal radiation.
 
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test1223

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@ctrl I want to emphasize that the listening distance and the placement of the speaker is very important. You did a great job so fare. It would be perfect to develop the speaker by optimizing everything for one scenario and communicate with which placement everything works best. With the digital crossover multiple versions for different scenarios would be a good compromise if the scenario didn't fit perfectly.

Since it is an active concept, aligning the sound origination points of the tweeter and woofer in one plane is not a problem.
With direct sound, floor and ceiling bounce you have 3 things and only one parameter if you change the delay. So adding a tilt can help to reduce the high frequency floor bounce and alter the distance of the chassis a little bit. Therefore I mentioned this option. Aiming the 0° Axis of the speaker at the corner of the back wall and ceiling is a very good move to optimize the room reflections. Especially for a wave guide design this is a good move.
 

Morpheus

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Yes, but not done as yet. Drivers are about $800 + $64 for Denovo cabinets + $200 for minidsp 2x4 hd + misc connectors and wire is about $1100 before any discounts or shipping. Would be less if you build cabinets yourself. Finally, you need 4 channels of amplification, would be another $400 or more. Call it around $1500 for active vented version.

Not sure how affordable that seems, but is intended to be a good value. Does that help?[/QUOTE

With 600-700 dollars min. factored in for minidspHD plus 4 channels of amplification, what about just going for hypex 2 way Fusions and keep everything super flexible, tidy and digital till speaker?
 
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Rick Sykora

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Sorry if you mentioned this already, but are the cabinet volumes the same (or similar) between the planned prototype and the Denovo?

That would be convenient, but it is mainly what I am working to determine currently. :)
 
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Rick Sykora

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Hi. Please see my earlier reply to @Lbstyling.
 
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Rick Sykora

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Grotti

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May be a bit of topic, but I am very much reminded of this speaker, which I actually own:

1613562414992.png

The directivity was documented by hometheatrehifi.com :

1613562585447.png

I am very curious, if this radiation pattern will be achived by this project or hopefully being topped (very ugly resonance peak caused by the woofer at 5 KHz....)

Again: sorry for OT.
 
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Rick Sykora

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Recently I was sort of inspired by the SB26CDC tweeter which seems to be the same as the SB26ADC mentioned in this thread but with a ceramic coated dome.

But I'm a beginner, hence my following question.

The datasheet shows a very wide dispersion for these tweeters. I think what is being shown here is much less roll-off at 60deg off-axis than what we typically see for 1" dome tweeters, and very very little roll-off at 30deg off-axis even beyond 20kHz. Especially the SB26CDC shows a very nice off-axis response, and also there seems to be no breakup up to 40kHz!

But I recall independent measurments for SB26ADC looked a bit different off-axis than the datasheet. Then I see on the datasheet that: mic. distance 31.6cm. Does this have an influence on the off-axis measurment results on the datasheet? (As in mic too close to the baffle.)

View attachment 113110

Hi. The short answer is yes, but even with matching measurement conditions, you will are unlikely to match other posted results exactly. If you have not already, suggest you read this: https://www.audioholics.com/loudspeaker-design/understanding-loudspeaker-measurements
 

Lbstyling

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[
Yes digital active is the best way.
You can apply brick wall filter, but you have to be aware, that you don't get pre ringing issues and a higher time delay. So you will end up with some overlap in most cases. QUOTE]

really glad you mention this!

So as active crossovers are being discussed, somthing worth discussing is
May be a bit of topic, but I am very much reminded of this speaker, which I actually own:

View attachment 113122
The directivity was documented by hometheatrehifi.com :

View attachment 113123
I am very curious, if this radiation pattern will be achived by this project or hopefully being topped (very ugly resonance peak caused by the woofer at 5 KHz....)

Again: sorry for OT.

There's no reason why this cannot be matched - the bump at 5khz.

The reality is that the design here would kick it's arse In person though due to the low IMD woofer.

An interesting point will be where the team place the crossover point regarding what this does to max SPL WITH a sub (it will almost certainly be tweeter limited) and if flexibility is available to move it so higher SPL is possible when a sub is added given the active amplification.

The wide bottom cab width is a bigger advantage than you would think as it would allow a 8 inch wide bass cabinet add on.

(On a side note) I personally would go with a side mounted dual opposed bass driver bottom cab if this add on was considered, as KEFs research shows the impulse resp suffers with low cab mass without dual opposed design

Either way, I have reasonable confidence given the wisdom of choices made so far. I expected the cabinet to change from V8 to this shape given the complexity with making the cutting angles of the previous cab.

Really impressed guys.
 

Mashcky

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I’m really excited about this project so far and may even upgrade my ER18DXT.

Does the addition of a bass cabinet (or subwoofer) to turn this into a three-way negate the lower IMD benefit of using a Purifi woofer?
 

Lbstyling

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I’m really excited about this project so far and may even upgrade my ER18DXT.

Does the addition of a bass cabinet (or subwoofer) to turn this into a three-way negate the lower IMD benefit of using a Purifi woofer?

The Purifi 'models' like a high quality 6inch mid driver that has the output of a good 8 or 10 inch.

Your basically asking 'Do speakers improve the quality and output of bass when using multiple 8 inch bass drivers over a single?'

Yes.
But It's a case of diminishing returns. You would want one hell of a quality bass driver to consider it, no question.

I would personally do stereo subs as the bottom cabs perhaps as a better trade off. The added advantage being that you can run them above the usual 100hz cut off for subs as the distance to the mains is low. Again, the SPL capability of the tweeter would be the limiting factor of the design, and that comes back to the crossover frequency.
 

Mashcky

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Your basically asking 'Do speakers improve the quality and output of bass when using multiple 8 inch bass drivers over a single?'
Frankly I'm not sure if that that was my question or not. I think I'm going to review the Purifi thread and others on IMD so I don't derail.
 
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Rick Sykora

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So, rather than have to follow another thread, will post a summary here. Have started using VirtuixCAD and so able to use it to validate the Bassbox info. Here is what I have found:

  1. One Purifi PR is good, but really does not improve bass extension. Dual passive radiators do really help the bass extension (f3 in low 40s). The downside is finding space to mount. The single SB pr gets comparable bass extension, but power handling appears less.
  2. The box cannot get too big. The cabinet volume needs to be around 14 liters to get the bass extension.
  3. A shorter port improves the port resonance significantly and with a HP filter can get the f3 to mid 40s.
Ordered some Denovo cabinets to prototype variations with various cabinet alignments. Will save my MDF for fancier shaped cabinets. :)
 
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Rick Sykora

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@Rick Sykora, option 3, how short is the port you are using? How much bass boost in the HP filter?

Vent is 2 inch diameter and 6 inches long. Will get you bass boost as is on another computer. Recall was around 30 Hz.

EDIT: Is 12 dB LP filter at 30 Hz with Q=1
 
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