Introducing Directiva - An ASR open source platform speaker project

[muad]

Hoffman’s iron law states that you can have it all; and can only choose 2 out of the three of:
deep, small and loud.

Bruno bents the rules by cramming all his class D amps into the speakers. So he could go small and deep loud by using 250W of amplification for every woofer.

Now for choosing the woofers- Well the Purifi wasn’t ready (or necessary) when the BXT was released.

for a 1/10 the price of the Purifi woofer:
https://www.parts-express.com/Peerless-SBS-160F35AL01-04-6-1-2-Aluminum-Cone-Woofer-4-Ohm-264-1564

Here’s great woofer for a small sealed cabinet : 1/4 cu foot sealed yields F10 of 35Hz.

Cramming 8-12 per box only needs 2-3 cu ft.

Add DSP and Ncores and you’ll have 20Hz in room response

Now... how to start a group buy for the first 20 interested builders...

That woofer looks very similar to what is in the BXT. Is it the same woofer? Cuz holy shit that price is excellent

could make a very affordable bass array. Would it work well crossed over at 200hz to smooth out the in room response?

 

[Zvu]

Those are the woofers from Kii.

Bare in mind that the price is at PE. If you buy quantity directly from Tymphany, the price is substantially lower. Bruno gets them cheaper than that.

 

[gingerbeer]

Those are the woofers from Kii.

Bare in mind that the price is at PE. If you buy quantity directly from Tymphany, the price is substantialy lower. Bruno gets them cheaper than that.

Minimum order quantity of 500 from parts express.
Googling I found Components-Shop.hk which has 2600 in stock and suggesting a price of $7.19 each. Each BXT module has 8 drivers (4 front, 2 each side, zero on the back), so this would be circa $150 for 2 BXTs of drivers and several times that for the amplification.

I own a proper set of Kii 3s and they are amazing, but the BXTs are just way too expensive to justify. DIY could be interesting though, but that's rather off topic in this cool thread!

 

[ctrl]

So, Rick provided me with new measurements.

It's about the near field measurements of the Directiva stock (Denovo 0.56 cu. ft.) with the SBAcoustics PR.


First the combined near-field measurements of woofer and PR with baffle-step correction (validity range about up to 300-400Hz)

To make it easier to see how well Rick has reduced the unwanted midrange noise of the PR, here is a linearized plot.

The unwanted noise of the PR is at least 19-20dB below the total sound pressure

 

[Savi]

Really interesting thread nice work. Watched ! Maybe I missed it but have you considered the Dayton pr215 passive radiator ? In the rear face of the pyramidal shape it could have been a nice and cheap solution ? On the rectangular box, the sba fits well.

 

[Rick Sykora]

Really interesting thread nice work. Watched ! Maybe I missed it but have you considered the Dayton pr215 passive radiator ? In the rear face of the pyramidal shape it could have been a nice and cheap solution ? On the rectangular box, the sba fits well.

PR125 is bigger than I like, but will keep in mind for my next order. Thanks!

 

[MrPeabody]

Exactly!

I can't tell whether you noticed that you said "deep, small and loud". There is a sort of three-way tradeoff among how small the enclosure is, how deep the bass goes (which implicitly includes loudness), and how efficient the speaker is. You can make a speaker very small without compromising bass, but in order to do so the driver needs to be very inefficient. You can compensate for the inefficiency with more power, but only to a limited extent, because the amount of amplifier power you end up needing, if you try to take the idea much further than the end of the driveway, is impractical.

 

[MrPeabody]

So, Rick provided me with new measurements.

It's about the near field measurements of the Directiva stock (Denovo 0.56 cu. ft.) with the SBAcoustics PR.
View attachment 121845

First the combined near-field measurements of woofer and PR with baffle-step correction (validity range about up to 300-400Hz)
View attachment 121857
To make it easier to see how well Rick has reduced the unwanted midrange noise of the PR, here is a linearized plot.
View attachment 121859
The unwanted noise of the PR is at least 19-20dB below the total sound pressure

This appears to be a very good result, much better than what we saw before.

I previously did a poor job in saying why the output of the PR needs to be this much lower than the direct output of the driver. There's actually two aspects to it. Avoiding the audibility of the peaks in the PR response is one aspect. The other aspect is that even without those peaks, there would be a comb filtering effect in the same frequency region where those peaks are seen, if the PR response is not this much lower than the direct output of the driver.

Could you please discuss what you mean by "linearized". I think you simply mean that this is what it should look like after frequency contouring is applied, but I'm not altogether certain this is what you mean.

I am surprised by the steepness and smoothness of the upper rolloff. This appears to be a property of the woofer itself, and it seems unusual in this respect. I certainly like the smoothness, but I can't help wondering whether the abruptness may actually make it difficult for the crossover to work as intended. The region most sensitive to this will be a narrow region from the crossover point to one octave above the crossover point. (The graph makes is seem that the sensitive region will extend only 1/2 octave above the crossover point, but this appearance is due to the unusually steep rolloff.)

Excellent work, both you and Rick. Honestly I am in awe.

 

[ctrl]

Could you please discuss what you mean by "linearized". I think you simply mean that this is what it should look like after frequency contouring is applied, but I'm not altogether certain this is what you mean.

Yep, the frequency response was equalized to a flat frequency response - I am at least perfect at complicating simple things

I am surprised by the steepness and smoothness of the upper rolloff. This appears to be a property of the woofer itself, and it seems unusual in this respect.

As I said in the post, the frequency response (which is calculated from the near field measurements) is correct/realistic up to 300-400Hz, after that you can take the response just as a vague guide.
To display the total frequency response of the woofer, I have to merge it with the on-axis far-field measurement (e.g. 1m) of the woofer.

 

[MrPeabody]

As I said in the post, the frequency response (which is calculated from the near field measurements) is correct/realistic up to 300-400Hz, after that you can take the response just as a vague guide.

Oh, now that you mention it, I recall reading where you wrote that!

 

[Lorenzo74]

Hoffman’s iron law states that you can have it all; and can only choose 2 out of the three of:
deep, small and loud.

Bruno bents the rules by cramming all his class D amps into the speakers. So he could go small and deep loud by using 250W of amplification for every woofer.

Now for choosing the woofers- Well the Purifi wasn’t ready (or necessary) when the BXT was released.

for a 1/10 the price of the Purifi woofer:
https://www.parts-express.com/Peerless-SBS-160F35AL01-04-6-1-2-Aluminum-Cone-Woofer-4-Ohm-264-1564

Here’s great woofer for a small sealed cabinet : 1/4 cu foot sealed yields F10 of 35Hz.

Cramming 8-12 per box only needs 2-3 cu ft.

Add DSP and Ncores and you’ll have 20Hz in room response

Now... how to start a group buy for the first 20 interested builders...

and this woofer is proved to work in the kii three. However, I’m expecting B.Putzeys is going to use the 6.5 and 4 inch (same size of the kii three) in the next cardioid studio monitor to go deeper without bxt. And you can do 2x6.5 purifi in the back, 2x6.5 purifi on the side and MTM in the front with DXT and 2x4 purifi ...

maybe out of scope but there is anyone here interested into DSP programming to achieve cardioid bass from about 50Hz?

4x 6.5 purifi, 1x4 and dxt could be ok. don’t know if the kii three design is under any patent or copyright

make sense?
best

 

[Juhazi]

"don’t know if the kii three design is under any patent or copyright"

Non-commercial "copying" for private use is free. The basics behind Kii3 or D&D8c are simple physics, no secrets. However making them work takes good understanding with compromises and some experiments - audio range 30-20.000Hz is wide, then add highish spl to reach...

 

[Rick Sykora]

So, along with some really nice weather, Directiva took a back seat to paying work for the last couple of days. Have to finish up the work in the morning and should be back to wrapping up the initial model.

Want to take another run at a lower crossover point. Once this is done, will wrap up the work to date and publish the VCAD project. Then will ship to Amir for a Klippel run to determine final design tweaks.

 

[Lbstyling]

See if you can get Amir to make the measurement points really high when he tests it. The sound field bubble will be the most interesting part to view for me.


Always wondered what sticking a velvet like material on the cabinet outside would do to the sq. I have a feeling it would improve it a little as it softens edges and stops the aerodynamic surface effect.

Just thinking out loud. If doing it, I would go with Alcantara myself.

 

[Rick Sykora]

See if you can get Amir to make the measurement points really high when he tests it. The sound field bubble will be the most interesting part to view for me.


Always wondered what sticking a velvet like material on the cabinet outside would do to the sq. I have a feeling it would improve it a little as it softens edges and stops the aerodynamic surface effect.

Just thinking out loud. If doing it, I would go with Alcantara myself.

Amir will be doing 2 spins - on-axis for each driver (and eventually together), Given his current workload, this is all i can ask.

I have tested F53 acoustic felt applied in many ways around the front baffle. Will see if I can find the measures, but results were not as beneficial as I thought. In some cases, made things worse.

I was replacing deteriorated Sorbethane from the tweeter faceplates on Signet SL280 speakers.

 

[Rick Sykora]

Well along with taking some time for my wife's birthday, the weather here has continued to be unseasonably nice and I needed to cut some lawn, resurrect the deck gazebo and do some power washing. With all of us vaccinated, it was the first time my family has been together since last summer. The last couple of days have had some rain, so I got back to my hobby and worked on Directiva...

Have been working on amplifier alternatives and still looking for something to help make it more affordable. Currently, the best option seems to be the Hypex Fusion amps, but have not bought any as yet. The only other cheap amp I have around is a Dayton APA150. Am going to swap it in and see how it compares to the current Hypex NC252MP. Notably, am interested in whether it may be noisier. As for the speaker, had to recalibrate my test stand to ensure I could reproduce my earlier results. This was done readily and I started to use the other configuration profiles in the minidsp to test lower crossover points.

I did a quick check at 1600 Hz and quickly saw I needed to look over the individual driver performance again. The simple set the driver to the same crossover frequency and LR24 slopes was not working. The main issue is the tweeter low-end rolloff and the LR24 now produced a steeper acoustic slope, This investigation would be better modeled in VCAD, so I left it to later. I did play with a little lower crossover and found that 2200 worked as well as 2400 Hz. Here are some measurement results from that round. So, first, let's revisit the on-axis performance...

Should look familiar, and if it does not, take my word it is almost identical to the 2400 Hz crossover. This should not be too surprising as both frequencies are roughly in the middle of the driver's overlapping responses. The main reason to push a lower response was that I had seen some distortion issues with the woofer at higher output levels. So, decided to check. Here is the distortion at about 80 dB...

This looks pretty good and so decided to push the design considerably harder. So, here is a look at 95 dB...

Clearly something going on around 400 Hz that might warrant further investigation, but pretty good overall and none of the 2-3 kHz ugliness I had seen earlier. For the sake of simplicity, may just forgo any attempts to lower the crossover point unless directivity or another issue suggests a need to reconsider.

 

[Rick Sykora]

As for that rise in distortion around 400-500 Hz, is likely the the passive radiator. It is primarily 2nd order with some 3rd order mixed in. Realized I posted without the legend, so fixed it this time...

 

[Skeptischism]

@Rick Sykora i'm not sure if youve caught any of the discussion over at the streamer thread about multichannel dacs? agreed hypex is a great solution for all in one, with DSP, but there may be other ways to get around it. how much power do these babies want?

 

[Lbstyling]

As for that rise in distortion around 400-500 Hz, is likely the the passive radiator. It is primarily 2nd order with some 3rd order mixed in. Realized I posted without the legend, so fixed it this time...

View attachment 123943

Not that you want the hastle, but I assume the larger passive radiator version would solve this distortion peak.
Without that peak, you would be well under 0.1% distortion at 95db. What you have is already quite something for a standmount!

Here is the Revel m106 for reference at 96db...

Big money Revel 328BE floorstander:

Without the 400hz peak, your nearer the 328BE than the m106.

By the trend, your design looks like it is likely otherwise capable of clean output at 100db+ without auditable distortion

(debatable around -48db 'ish' for me, but not even slightly 'offensive' until at least -28db from 400hz to 7khz for me personally)

 

[Rick Sykora]

@Rick Sykora i'm not sure if youve caught any of the discussion over at the streamer thread about multichannel dacs? agreed hypex is a great solution for all in one, with DSP, but there may be other ways to get around it. how much power do these babies want?

Am only only loosely following but am interested to see a proposal. As I often said, expect that there will more than one solution.

Not sure how to answer the power question as it is a function of how loud you listen and how far you are away. I have not measured, but expect sensitivity to be in the upper 80s without any crossover compensation. If woofer is boosted to tweeter level, may be in low 90s.