Directiva r2 project: market requirements gathering

[voodooless]

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

Totally agree. That would really help in defining an engineering target.

 

[sarumbear]

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.

Using specially made custom wave guide for the tweeter and a narrow baffle it is possible to have controlled directivity above around 400Hz.

It is possible to integrate an extended range "subwoofer" that works up to 400Hz that is made of multiple drive units on that narrow baffle.

That is similar to Revel Performa 3 which I suggest the route we take for r2.

 

[TimVG]

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.

Here's a clearer difference with some contour lines drawn. It works pretty well in the bass range. There was no clear goal but trying to understand what happens practically speaking with these systems. I made 3 or 4 versions. Some more succesful than others.

 

[sarumbear]

Here's a clearer difference with some contour lines drawn. It works pretty well in the bass range. There was no clear goal but trying to understand what happens practically speaking with these systems. I made 3 or 4 versions. Some more succesful than others.
View attachment 160492

How do you reduce 20Hz at 180 degrees by almost 10dB and where have you measured that?

Is that a simulation or actual measurements?

 

[TimVG]

Is that a simulation or measurements?

How do you reduce 20Hz at 180 degrees by almost 10dB?

Oh these are measurements. I don't have any software to simulate this.

ME Geithain produces similar results in their loudspeaker in a similar way.

 

[voodooless]

Using specially made custom wave guide for the tweeter and a narrow baffle it is possible to have controlled directivity above around 400Hz.

How would that work on a baffle that is only 30cm wide at best? What kind of special is that waveguide to make that work?

 

[sarumbear]

How would that work on a baffle that is only 30cm wide at best? What kind of special is that waveguide to make that work?

Just look at the D&D 8C front

 

[sarumbear]

Oh these are measurements. I don't have any software to simulate this.

ME Geithain produces similar results in their loudspeaker in a similar way.

View attachment 160493

View attachment 160495

I am very interested to understand how you have achieved 10dB cancellation at 180 degrees and at 20Hz. Can you share us the details?

 

[voodooless]

Just look at the D&D 8C front

Why? That waveguide does not control pattern down to 400Hz. It doesn’t need to, crossover is at 1250Hz.

 

[TimVG]

I am very interested to understand how you have achieved 10dB cancellation at 180 degrees and at 20Hz. Can you share us the details?

Basically the entire space behind the driver is absolutely stuffed with compressed rockwool, to the point where there's just eough space for the driver. The rest is what you see. There's no secrets.

 

[sarumbear]

Why? That waveguide does not control pattern down to 400Hz. It doesn’t need to, crossover is at 1250Hz.

I copied what I said below.

Using specially made custom wave guide for the tweeter and a narrow baffle it is possible to have controlled directivity above around 400Hz.

I think I made it pretty clear that I was talking about a waveguide for the tweeter.

 

[sarumbear]

Basically the entire space behind the driver is absolutely stuffed with compressed rockwool, to the point where there's just eough space for the driver. The rest is what you see. There's no secrets.

So it is a closed box with extra high compliance? That is nothing different to any sealed box, which has an omnidirectional polar pattern below around 70Hz. Stuffed rockwool will simply increase the effective internal volume, nothing else.

How and where did you measure the speakers?

 

[dc655321]

Using the forum's Search feature to explore thread titles containing "8C" or "Cardioid" is a great way to dig a little deeper.
Much has been covered locally...

c.f. this

 

[voodooless]

I copied what I said below.



I think I made it pretty clear that I was talking about a waveguide for the tweeter.

Again: how does that give us directivity down to 400 Hz? The baffle step of the 8C is about 450Hz, so yes it does some pattern “control”, but at that point it already radiates 180 def. It won’t match the waveguide. So yes there is some control, but it’s much wider that one would like to see in a constant directivity system. In any case any baffle of the same size will do this, there is no magic in the D&D.

 

[voodooless]

So it is a closed box with extra high compliance? That is nothing different to any sealed box, which has an omnidirectional polar pattern below around 70Hz. Stuffed rockwool will simply increase the effective internal volume, nothing else.

How and where did you measure the speakers?

The point of the stuffing is not the volume increase, but rather the slowdown of the sound wave so that they come out of the slots delayed enough to cause the cardioid effect.

 

[D!sco]

Had a thought for the bass extension cabinet. Haven't really been through the hard part, but this SB Acoustics 8" sub is designed to work in a .5 cu ft sealed enclosure, like the one the R1 was built in. It could be fitted below in a 3-way configuration and DSP controlled. I'd need to model the R1 frequencies and x-over to start digging in though.

 

[TimVG]

So it is a closed box with extra high compliance? That is nothing different to any sealed box, which has an omnidirectional polar pattern below around 70Hz. Stuffed rockwool will simply increase the effective internal volume, nothing else.

How did you measure the speakers?

Did you not see the pictures I posted before? It's exactly the same principle as used by D&D.

In bad weather I measure in an old church, using gated measurements. In good weather I'd like to move outside from some groundplane measurements. The gated measurements are certainly not perfect in terms of resolution, although relative levels still come out well.

Since then I've got a better mic stand ..

 

[sarumbear]

Basically the entire space behind the driver is absolutely stuffed with compressed rockwool, to the point where there's just eough space for the driver. The rest is what you see. There's no secrets.

The point of the stuffing is not the volume increase, but rather the slowdown of the sound wave so that they come out of the slots delayed enough to cause the cardioid effect.

I was asking information about the the slots, which is the crucial part contrary to what @TimVG says, the "secret"

 

[TimVG]

I was asking information about the the slots, which is the crucial part contrary to what @TimVG says, the "secret"

The slots are just what you see. Simple slots of a certain length and width, no thicker than the material itself.
Combined with a lot of rockwool between the slots and the driver. If one has time, one can experiment with the size and location of the slot(s) and the damping material until the desired pattern is achieved.

 

[voodooless]

I was asking information about the the slots, which is the crucial part contrary to what @TimVG says, the "secret"

Well, they were in plain sight, so from that sense, no secret