Directiva r2 project: market requirements gathering

[abdo123]

Also one can argue how useful controlled radiation in the modal range is. It makes sense for PA applications, but in the home..

it's incredibly useful because it removes speaker boundary interaction with the back wall. you're basically removing 25% of the modal issues. and not only that but also removing a fundenmntal audio reproduction issue that cannot be solved with room correction.

 

[sarumbear]

Yes, you're correct. Although what voodooless implies is, such as in the D&D patent, one can alter the size, position and resistance of the vents to create different cancellation patterns.

A vent is a Helmholtz resonator, like the pipe of an organ, it resonates at a single frequency. Resistance simply changes the Q of the resonance. You can have multiple vents but that will make the FR non-flat.

 

[TimW]

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?

@Rick Sykora has mentioned keeping the channel count down so that the miniDSP 2x4 can continue to be used. I like the idea of an active directivity control design which would probably require more channels, so I'm just trying to make a case for that by showing that there are many options for electronics.

 

[sarumbear]

@Rick Sykora has mentioned keeping the channel count down so that the miniDSP 2x4 can continue to be used. I like the idea of an active directivity control design which would probably require more channels, so I'm just trying to make a case for that by showing that there are many options for electronics.

There are indeed many options but do we need such complicated, patented even, designs on a DIY project? Do we also have to constrain the design to active only?

 

[TimVG]

A vent is a Helmholtz resonator, like the pipe of an organ, it resonates at a single frequency. Resistance simply changes the Q of the resonance. You can have multiple vents but that will make the FR non-flat.

Well, in practice it is possible to get a well behaved system as a result. Just look at the D&D 8C. My own experiments were also quite succesful, although I have to admit, I've not been able to work out anything yet to predict the response.

 

[TimW]

There are indeed many options but do we need such complicated, patented even, designs on a DIY project? Do we also have to constrain the design to active only?

We don't need to, but there are already plenty of conventional passive DIY designs out there.

 

[TimVG]

it's incredibly useful because it removes speaker boundary interaction with the back wall. you're basically removing 25% of the modal issues. and not only that but also removing a fundenmntal audio reproduction issue that cannot be solved with room correction.

100Hz, to take a number, is well over 3 meter in terms of wavelength, that backwall isn't going to do any more harm then every other boundary is going to do If within 1/4 wavelength, the reflection and source will be indistinguishable and behave as a point source anyhow.

 

[voodooless]

I did say "at least 400Hz" meaning the crossover frequency will be 400Hz or over. Do you expect to have a drive unit on a 3-way speaker where the midrange driver to work lower than 400Hz?

I just have you an example and asked you why you think it must to be >= 400 Hz.. care to finally answer?

 

[abdo123]

that backwall isn't going to do any more harm then every other boundary is going to do

I think you would be surprised by how much one boundary adds to the the mess that is a domestic room, in-wall mounting alone usually limits the error rate of the FR to ~5db above the 3 main axial modes.

 

[voodooless]

@Rick Sykora has mentioned keeping the channel count down so that the miniDSP 2x4 can continue to be used. I like the idea of an active directivity control design which would probably require more channels, so I'm just trying to make a case for that by showing that there are many options for electronics.

That seems sensible. Is that for 1 or two speakers? Otherwise you’ll eternally be stuck with a 2-way.(unless you go part-passive)

 

[TimVG]

I think you would be surprised by how much one boundary adds to the the mess that is a domestic room, in-wall mounting alone usually limits the error rate of the FR to ~5db above the 3 main axial modes.

Again, for the low range it wouldn't make any difference. Since the transducer and reflection are 1/4 or less of a wavelength apart they are acting as a point source. If you want to tackle a boundary, take the rear wall.This is why double bass arrays work as freestanding solutions.

 

[sarumbear]

I just have you an example and asked you why you think it must to be >= 400 Hz.. care to finally answer?

You need a mid range driver small enough to match a tweeter's radiation pattern. 3-5" is the sweet spot for a 3-way design. Such a small diameter cone will limit the maximum SPL the driver can generate below around 400Hz.

 

[abdo123]

Again, for the low range it wouldn't make any difference. Since the transducer and reflection are 1/4 or less of a wavelength apart they are acting as a point source. If you want to tackle a boundary, take the rear wall.This is why double bass arrays work as freestanding solutions.

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.

 

[sarumbear]

If you want to tackle a boundary, take the rear wall.This is why double bass arrays work as freestanding solutions.

Hence the discussion about cardioid speakers...

 

[TimW]

That seems sensible. Is that for 1 or two speakers? Otherwise you’ll eternally be stuck with a 2-way.(unless you go part-passive)

For R1 the 2x4 was intended to be used for both speakers. I don't know if Rick considered using two 2x4's but it would make more sense to use something else IMHO. With a multi-way design it might make more sense to go with a part-passive design anyway so that outputs can be reserved for multiple subs if desired.

 

[voodooless]

You need a mid range driver small enough to match a tweeter's radiation pattern. 3-5" is the sweet spot for a 3-way design. Such a small diameter cone will limit the maximum SPL the driver can generate below around 400Hz.

Well, those are more design choices. If those are fixed, then yes, it will have those consequences. But it’s by no means in iron rule. I can easily divide a different design that will allow for a much lowe crossover.

 

[ctrl]

However, as this is DIY project my comments were tailored for standard 2-3 way speakers in a simple box that are suitable for a DIY project. Helsinki has a unorthodox shape but it is a passive speaker. On the other hand both D&D 8C and Kii3 are extremely complicated speakers with multiple amplifiers. Kii3 has five power amps driven by an integral DSP in each speaker and has a remote control! Neither designs are within the realms of a DIY project.

I tend to agree that it might be worth another look. However to lower complexity, one probably would like to keep the number of channels per speaker to 3 or 4.

3-4 channels of DSP per side for each speaker makes sense because affordable 8 output devices are fairly common.

Four channel DSP plate amps are rather rare. Therefore, it would probably be desirable, if possible, to limit the project to 3 channels.
This means that only one DSP channel is available for the bass module.

If I interpret the thread so far correctly, then the bass module must not be too wide (0.25-0.30m?), but still deliver a lot of sound pressure level and still control the radiation in a certain frequency range.

In order to minimize a possible directivity error at the crossover frequency from the top speaker to the bass module, we need to think about up to which frequency the radiation by the top speakers can still be controlled.
For typical cabinet shapes directivity is controlled down to 700-1000Hz for a 2-way top, for untypical shapes it might be possible to control directivity (to some extend) down to 400-500Hz with 0.3m baffle width.

Now I'm wondering if it's possible to design a bass module that requires only one DSP channel and allows some directivity control using passive elements (slots and-or passive components).
This actually leaves only a bass module with slots or a module with offset drivers at the side or rear (open baffle has already been ruled out as far as I know) - i.e. a 2:2 or 3:1 arrangement.
Here is an example (sectional drawing) of a 3:1 arrangement with three 8'' woofers in the front one in the rear.

Or am I missing a simple solution possibility?

 

[sarumbear]

Well, in practice it is possible to get a well behaved system as a result. Just look at the D&D 8C. My own experiments were also quite succesful, although I have to admit, I've not been able to work out anything yet to predict the response.

I am not sure it is possible but you seem to be confident. I wish you luck.

However, 8c use multiple drive units fed via a DSP to control the polar pattern. Both 8C and Kii3 use multiple drive units controlled via DSP. They are not passive design.

 

[TimVG]

I am not sure it is possible but you seem to be confident. I wish you luck.

However, 8c use multiple drive units fed via a DSP to control the polar pattern. Both 8C and Kii3 use multiple drive units controlled via DSP. They are not passive design.

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.

 

[sarumbear]

This actually leaves only a bass module with slots or a module with offset drivers at the side or rear (open baffle has already been ruled out as far as I know) - i.e. a 2:2 or 3:1 arrangement.
Here is an example (sectional drawing) of a 3:1 arrangement with three 8'' woofers in the front one in the rear.
View attachment 160481

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. This requires two power amplifiers and two DSP outputs as passive filters that change level at low frequencies (100-200Hz) and high operating levels are almost impossible in reality.