Directiva r2 project: market requirements gathering

[TimVG]

can you describe it in layman terms because i didn't really get it.

also double bass arrays are nothing to be joked about. instant disqualification for a domestic setting.

There is no destructive interference between subwoofers and a front wall. I reference the DBA because it shows how defeating the rear wall reflection, is much more effective.

 

[Rick Sykora]

As far as I can see, it’s really going nowhere.. but that is a discussion for another day probably

While software solutions are very flexible, they are also less stable (as I’ve seen personally). Also some people might want to use an integrated solution with amps like Hypex offers. Or just cobble together something from AliExpress parts.

I would guess that the DSP section is not part of the Directiva offering? So anyone can choose whatever they like? In that case some ground rules need to be set so enough options are possible. Like #channels, IIR or FIR (how many taps) etc. We’re there any for the R1?

No, r1 was open to DSP alternatives. The cost/performance of the minidisp HD made it an easy choice to use while designing. Already doubling the amp channels was a consideration as was trying to keep TCO reasonable.

Would like the initial r2 to have a hybrid crossover. This would allow more drivers without needing more dsp or amp channels. Also allows the minidsp HD to continue to be used as a design tool AND be the minimum requirement for deploying. That said, if members want even more controlled radiation, am not going to stand in the way. Only question for me is whether it is r2.x or r3…

Would like to see r2 designed for extensibility, but if cost or something prohibits, then it will be an r3.

 

[ctrl]

In order to cancel rear radiation like in a cardioid design a la 8C or Kii3 you have to feed the rear woofer via a filter, in reverse polarity and level change.

I thought a "real" cardioid radiation pattern we have already excluded, because too complicated for simple DIY.
And we take the second best and try to control the directivity still to a certain extent below 800Hz.

 

[abdo123]

There is no destructive interference between subwoofers and a front wall.

why? does the laws of physics simply change?

if the front wall is infinitely rigid (reinfornced concrete) and if the subwoofer is far enough so 1/4 wavelength is within the subwoofer's bandwidth you should have a boundary interaction.

It's important to keep in mind that with each room (unless you have a central room) there is at least one wall that is (infinitely) rigid, unless you live in the US with mostly framed walls on the exterior. to put a cardioid speaker against that one rigid wall could make the world of a difference.

Since i live in a sky scraper i would love to have a design that can be placed against a rigid wall.

 

[sarumbear]

While this is true for the Kii3, it is not true for the 8C - the polar pattern is being controlled without DSP and the result is achieved acoustically. The DSP in the 8C has other purposes.

I stand corrected. 8C does not have a cardioid pattern below 100Hz. It basically has an integrated subwoofer made of two drive units at the back that works below 100Hz. It only has controlled directivity above 100Hz.

 

[D!sco]

Would like to see r2 designed for extensibility

In what way? Flat to 40hz without a sub and no distortion wasn’t enough? Humor aside, what could actually be gained without using subs?

 

[sarumbear]

Since i live in a sky scraper i would love to have a design that can be placed against a rigid wall.

Check Kii3

 

[TimVG]

why? does the laws of physics simply change?

if the front wall is infinitely rigid (reinfornced concrete) and if the subwoofer is far enough so 1/4 wavelength is within the subwoofer's bandwidth you should have a boundary interaction.

It's important to keep in mind that with each room (unless you have a central room) there is at least one wall that is (infinitely) rigid, unless you live in the US with mostly framed walls on the exterior. to put a cardioid speaker against that one rigid wall could make the world of a difference.

Since i live in a sky scraper i would love to have a design that can be placed against a rigid wall.

But depending on the distance between the source and boundary, it can be constructive or destructive interference. Personally I don't believe a controlled radiation pattern in a loudspeaker will help you with your neighbours

 

[abdo123]

But depending on the distance between the source and boundary, it can be constructive or destructive interference. Personally I don't believe a controlled radiation pattern in a loudspeaker will help you with your neighbours

bass doesn't escape to my neighbours, the floor, ceiling and outerwalls are all made of reinforced concrete.

My current setup is flat to 40Hz and never had any complains .

bass doesn't escape to my neighbors, the floor, ceiling and outer walls are all made of more than 20 cm deep reinforced concrete.

room accoustics are hell though, which is making me consider floor to ceiling line arrays and cardioid speakers. or perhaps a gigantic horn with controlled vertical directivity as well.

 

[voodooless]

A hybrid design, so active/passive would probably be most effective with a passive mid/tweeter crossover, and then the rest active. low bass passive components are big and expensive, and are still suboptimal.

 

[TimVG]

bass doesn't escape to my neighbours, the floor, ceiling and outerwalls are all made of reinforced concrete.

My current setup is flat to 40Hz and never had any complains .

bass doesn't escape to my neighbors, the floor, ceiling and outer walls are all made of more than 20 cm deep reinforced concrete.

room accoustics are hell though, which is making me consider floor to ceiling line arrays and cardioid speakers. or perhaps a gigantic horn with controlled vertical directivity as well.

Here a comparison of a closed vs passive cardioid. Although not exactly the same cabinet for both (settled on narrower for the cardioid) it actually has decent cancellation down to the bass range. Don't mind >1kHz, different crossovers etc.

 

[sarumbear]

I thought a "real" cardioid radiation pattern we have already excluded, because too complicated for simple DIY.
And we take the second best and try to control the directivity still to a certain extent below 800Hz.

I really want to understand how D&D 8C works. How they achieved almost perfect directivity (5dB difference between 250Hz and 4kHz). I cannot remember the polar diagram of a generic 8" driver mounted in a closed box. Does anyone have any examples?

Does 8C (chart below) fallow a generic driver's polar diagram between 100Hz and 2kHz? If yes, the the main trick of 8C is their perfectly implemented waveguide (other than the integral subwoofer)

 

[voodooless]

Does 8C (chart below) fallow a generic driver's polar diagram between 100Hz and 2kHz?

No it doesn’t. Reason are the resistive slots on the sides that interfere with the off-axis response to make it narrower. Otherwise pattern control would be lost around the baffle step frequency.

 

[Rick Sykora]

In what way? Flat to 40hz without a sub and no distortion wasn’t enough? Humor aside, what could actually be gained without using subs?

As I listen to r1 in stereo, I have most of what I need...

We do know that the Purifi woofer will be challenged by the bass in some music. So, I would like to have the extra bass output that only more woofers can provide. My wife would also be happier if no subwoofers were needed.

Some will want r2 as r1 cannot produce the bass energy needed for larger rooms. Am also interested in what even better directivity might yield.

 

[TimVG]

I really want to understand how D&D 8C works. How they achieved almost perfect directivity (5dB difference between 250Hz and 4kHz).

By controlling sound leakage out of the enclosure through acoustic resistance. The designer(s) of the 8C provided me with some tips and pointers while I was making my own, much larger, model and it's not easy to get perfect.

 

[sarumbear]

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

The 8c has side vents that produce a wavefront that is derived from the back energy coming off the midrange driver, to cancel out the midrange energy that tends to bend around the cabinet corners. In this fashion the side and backside of the loudspeaker cabinets do not produce energy and therefore do not excite the listening room with reflections. And so, by taking the local acoustics out of the equation, the listening experience comes much closer to the actual recording.

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?

 

[Rick Sykora]

Check Kii3

..and prepare to save up! They are not inexpensive.

 

[voodooless]

Some will want r2 as r1 cannot produce the bass energy needed for larger rooms. Am also interested in what even better directivity might yield.

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.

 

[TimVG]

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?

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.

 

[voodooless]

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?

There is no need really. First of, one cannot eq only the backside of the woofer (with a DSP), 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.