Directiva r2 project: market requirements gathering

[sarumbear]

There is no need really. First of, one cannot eq only the backside of the woofer, so any eq is just amplitude and possibly phase. You can still do a passive filter design from mid to tweet. The passive crossover is still on a DSP channel. With an all-passive system it might impossible to do if you need phase adjustments.

You can filter the rear emission of the woofer via an acoustic filter. The rear emission of the woofer is in reverse polarity of the front energy. That is the first requirement for the cancellation. An acoustic filter will EQ and adjust the sound energy passing through. All acoustic treatment devices do just that.

About no need, what is not needed?

 

[sarumbear]

Maybe it's the language barrier but this is what I've been implying for a while now in this thread. I'd be happy to do some prototyping from January onward. I'm actually already using a similar system.

View attachment 160484

Do you have any information on the acoustic filter on the sides that you can share with us? And, what does the polar diagram looks like? Also, what size are those drivers?

 

[abdo123]

I found this on the D&D website, which explains a lot. How I missed it before, God knows. I blame the wine



What they are doing is ingenious. They are leaking the rear energy of the midrange driver through two acoustic filters on each sides. As the rear energy is in reverse polarity the output from the ports cancel the emissions from the side, forcing the otherwise omnidirectional pattern of the narrow baffle to become cardioid. This normally cause pronounced FR anomalies due to cancellations and additions, but they corrected them with the DSP.

Very clever indeed.

Now who is there to design a passive acoustic filter?

I'm really surprised that you didn't know this already, this, the W371A and the Kii 3 are pretty much the biggest innovations in Audio in the last decade.

the only 'negative' thing is that the woofer also exhibits lower sensitivity because of the leakage, THD can quickly reach 10% @ 100Hz in Erin's review. For 12000$ a pair you would expect more output.

@TimVG 's design is overcoming this with bigger compression woofers i think.

 

[sarumbear]

I'm really surprised that you didn't know this already, this, the W371A and the Kii 3 are pretty much the biggest innovations in Audio in the last decade.

I have not been involved with speaker design after winding down Silver 5L operation at the end of 90s. I'm now 71 and started to get involved in speakers as a hobby. My market knowledge is very old. Thanks to you guys I am learning about those new designs every day.

the only 'negative' thing is that the woofer also exhibits lower sensitivity because of the leakage, THD can quickly reach 10% @ 100Hz in Erin's review. For 12000$ a pair you would expect more output.

@TimVG 's design is overcoming this with bigger compression woofers i think.

Are you talking about the two woofers at the rear or the midrange unit on the front?

 

[abdo123]

I have not been involved with speaker design after winding down Silver 5L operation end of 90s. I'm now 71 and started to get involved in speakers as a hobby. My market knowledge is very little. Thanks to you guys I am learning about those new designs every day.

Are you talking about the two woofers at the rear or the midrange unit on the front?

the midrange unit in the front is reproducing the cardioid range alone.

 

[voodooless]

You can filter the rear emission of the woofer via an acoustic filter. The rear emission of the woofer is in reverse polarity of the front energy. That is the first requirement for the cancellation. An acoustic filter will EQ and adjust the sound energy passing through. All acoustic treatment devices do just that.

I think I partially miss understood your post.. got my last wisdom tooth pulled today, so deal with it My comment was more about the apparent DSP correction. That’s something that should really not be that hard to do. The acoustic part is way more complex.

I think most of the DSP magic of the D&D is in the bass section for compensating the rear wall reflections.

BTW: are there any limitations about the malleability of the speaker defined? The R1 can do with a simple off the shelve enclosure. All of these passive directivity control measure need complex enclosure designs. Something to keep ik mind probably.

One could possibly devise a Kii like setup with 3 channels: one for bass, one for the two side woofers, and the last one for mid/tweeter. That would probably mean a much more simple enclosure.

 

[sarumbear]

the midrange unit in the front is reproducing the cardioid range alone.

That drive unit works above 100Hz. Do you mean distortion above that as well?

Erin finds distortion levels to be low. From his review:

[*]Speaking of distortion, I didn’t have any complaints even at much higher than typical listening levels (>100dB at 4 meters). At one point I was listening to these speakers at 105dB in my living room without a hint of mechanical trouble. I backed off the volume simply because those levels, full-range, are dangerous.

 

[voodooless]

I'm really surprised that you didn't know this already, this, the W371A and the Kii 3 are pretty much the biggest innovations in Audio in the last decade.

Home or studio audio that is. The working principle of the W371A has been used in pro audio probably decades (mostly large concerts)

 

[sarumbear]

I think most of the DSP magic of the D&D is in the bass section for compensating the rear wall reflections.

8C has no rear compensation in the bass, below 100Hz.

 

[voodooless]

Erin finds distortion levels to be low. From his review:

Subjectively yes! Objectively not really. You do loose quite some efficiency with those slots. Along the same lines we can also conclude we don’t need an expensive Purify.

 

[abdo123]

Erin finds distortion levels to be low. From his review:

This observation pushes me to think that Harmonic distortion is not as big deal as we think it is, specially in upper and sub-bass. 10% 3rd-harmonic should be 'theoretically' very audible.

 

[voodooless]

8C has no rear compensation in the bass, below 100Hz.

There is no need to have it below 100 Hz. Usually the effect is between 200 and 350 Hz. You cannot compensate anything with only the front woofer, so those rear woofers must do something there as well.

 

[sarumbear]

Subjectively yes! Objectively not really. You do loose quite some efficiency with those slots.

But how can you know? Do you have the specs of their drive unit by itself?

Besides, why would a drive unit's 2PI efficiency be changed by what has been done to its rear energy?

 

[sarumbear]

There is no need to have it below 100 Hz. Usually the effect is between 200 and 350 Hz. You cannot compensate anything with only the front woofer, so those rear woofers must do something there as well.

Please read D&D's note that I copied.

 

[abdo123]

Besides, why would a drive unit's 2PI efficiency be changed by what has been done to its rear energy?

I thought open baffle designs have lower sensitivity in general, isn't this theoretically something in between?

 

[TimVG]

Do you have any information on the acoustic filter on the sides that you can share with us? And, what does the polar diagram looks like? Also, what size are those drivers?

15" drivers.
Basic rockwool, and plenty of it I believe D&D use Akotherm - polyester based.
It's very much trial and error, and I don't believe there are any set methods of calculating yet the precise specifics, yet. The version I have right now is basically a prototype and I'll be experimenting more from January onward. Here is a polar of this prototype compared to a sealed enclosure (which was wider by about 10cm so not exactly apples to apples, also do not mind past 1kHz, different crossovers). I'd have to experiment furhter with the amount and density of the filler material, and size of the 'vents'.

 

[sarumbear]

I thought open baffle designs have lower sensitivity in general, isn't this theoretically something in between?

Not at all. This is like a vented design with a very lossy and low Q resonant port. Baffle is still the same baffle.

 

[Rick Sykora]

Given the size limitations, one probably has to pick one of the two, at least if you want directivity control < 100 Hz.

Also, even if directivity control <100 Hz would be audible, how useful would such a setup be if there are already multiple subs in play? Those will probably not have the same controlled directivity, so will the mix make sense?

As a stand alone solution it might work though.

The quest for more/better directivity reminds me of a question from one of my mentors. Do you want more cheese on your pizza?

In my experience, more/better/controlled directivity is a feature without a clear benefit. Once you have good directivity, how much better is it to have more or different? ...

Suggest we need clearer ties between the benefits of different directivity features with their benefits.

 

[sarumbear]

15" drivers.
Basic rockwool, and plenty of it I believe D&D use Akotherm - polyester based.
It's very much trial and error, and I don't believe there are any set methods of calculating yet the precise specifics, yet. The version I have right now is basically a prototype and I'll be experimenting more from January onward. Here is a polar of this prototype compared to a sealed enclosure (which was wider by about 10cm so not exactly apples to apples, also do not mind past 1kHz, different crossovers). I'd have to experiment furhter with the amount and density of the filler material, and size of the 'vents'.

View attachment 160491

As you use a 15" driver I assume you want to control directivity to around 50Hz? 8C controls directivity above 100 Hz. You will need a very large acoustic filter to work at such a low level. I personally don't know of a material that works such low levels but mechanical filters may work.

 

[TimVG]

The quest for more/better directivity reminds me of a question from one of my mentors. Do you want more cheese on your pizza?

In my experience, more/better/controlled directivity is a feature without a clear benefit. Once you have god directivity, how much better is to have more or different? ...

Suggest we need clearer ties between the benefits of different directivity features with their benefits.

From speaking with designers of such loudspeakers, if you can get rearward cancellation down to where it no longer destructively interferes with the frontwall (the back of the speaker), or down to the transition frequency - whichever comes first - that's probably the point of diminishing returns.