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Constant directivity speakers (DSP) for DIYers

hvbias

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Looking to compile a list of what constant directivity speakers are available for DIYers that can use DSP (ie MiniDSP, Acourate, etc)

Geddes? Unsure, someone more in the loop will have to tell me what the situation is with his kits.

Bill Waslo, link for one project, there is another which is larger also on DIY Audio.

Linkwitz page.

I will keep this post updated, need help from you guys!
 
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jtwrace

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Looking to compile a list of what constant directivity speakers are available for DIYers that can use DSP (ie MiniDSP, Acourate, etc)

Geddes? Unsure, someone more in the loop will have to tell me what the situation is with his kits.

Bill Waslo, link for one project, there is another which is larger also on DIY Audio.

I will keep this post updated, need help from you guys!
Earl Geddes is retired. As a former Abbey owner, they were pretty awesome though. That said, if you send him an email he **might** have something he can offer.
 

andreasmaaan

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Looking to compile a list of what constant directivity speakers are available for DIYers that can use DSP (ie MiniDSP, Acourate, etc)

Geddes? Unsure, someone more in the loop will have to tell me what the situation is with his kits.

Bill Waslo, link for one project, there is another which is larger also on DIY Audio.

I will keep this post updated, need help from you guys!

Gedlee speakers were constant directivity, but only from the upper-midrange (700-900Hz depending on the speaker) to the top of the audio band.

Is this adequate for your purposes in terms of "constant directivity"?

I'm not aware of any DIY kits that are truly constant directivity, i.e. right down at least as far as the upper bass (Schroeder frequency range in most domestic rooms).
 

andreasmaaan

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I'm not sure if this DIY offering ever got off the ground. There's still a link up for expressions of interest. It's a Danley-style Synergy horn kit, which I think uses minidsp as the crossover. The designer is based in Australia, though.
 

dc655321

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Good timing on the post, @hvbias.

I've challenged myself to embark on a diy project incorporating some of the best ideas from (IMO) one of the best-engineered systems of today, the D&D 8c. Details (hints?) on the acoustic design are there for the searching, and I'll be doing the DSP engine myself as that is the most familiar design component to me.

I am interested to see what you find and the directions you take.
 
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hvbias

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Gedlee speakers were constant directivity, but only from the upper-midrange (700-900Hz depending on the speaker) to the top of the audio band.

Either you and I (or another member) had this discussion in another thread a while back :) They aren't of interest to me, I am primarily looking to compile a list of what is out there.

For my own use I am going with a K-402 horn and custom midbass horn, but this isn't exactly something that has plans, etc (also very expensive with the TAD compression drivers) so I am leaving it off the thread. My old thread about them here, though I am not using that folded midbass horn.
 

andreasmaaan

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Either you and I (or another member) had this discussion in another thread a while back :) They aren't of interest to me, I am primarily looking to compile a list of what is out there.

For my own use I am going with a K-402 horn and custom midbass horn, but this isn't exactly something that has plans, etc (also very expensive with the TAD compression drivers) so I am leaving it off the thread. My old thread about them here, though I am not using that folded midbass horn.

Ha, yes. Could well have been me. I'm quite in favour of the Gedlee approach FWIW. My point was just to clarify how exacting your standard of "constant directivity" was for the purposes of the thread.

Also as I know members are aware, speakers like Kii Three and D&D 8C make no claim to (and do not achieve) constant vertical directivity or constant bass directivity either, so it's a "how long is a piece of string" type question.
 

Cosmik

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Good timing on the post, @hvbias.

I've challenged myself to embark on a diy project incorporating some of the best ideas from (IMO) one of the best-engineered systems of today, the D&D 8c. Details (hints?) on the acoustic design are there for the searching, and I'll be doing the DSP engine myself as that is the most familiar design component to me.

I am interested to see what you find and the directions you take.
I was just about to ask whether anyone was considering trying their own version of the Kii Three. A few years ago, I might have gone for it as a challenge, but I'm just not all that bothered now; I can get by with ordinary monkey coffins (DSP'ed of course).

(I may change my mind if I get to hear the Kii Three/8C...)
 

dc655321

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I was just about to ask whether anyone was considering trying their own version of the Kii Three. A few years ago, I might have gone for it as a challenge, but I'm just not all that bothered now; I can get by with ordinary monkey coffins (DSP'ed of course).

(I may change my mind if I get to hear the Kii Three/8C...)

It was reading about your system that got me thinking of undertaking this project in the first place. Thanks for sharing that.

After I get through some optimizations, I'm starting to think about the integrate-convolution-engine-to-ALSA state, and would like to get your take on a few points (use LADSPA or make an ext-plugin (probably)? r2r or r2c in FFTW?, etc). I hope you don't mind if I pester you with the occasional question (via PM, or another thread).
 

Thomas savage

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It was reading about your system that got me thinking of undertaking this project in the first place. Thanks for sharing that.

After I get through some optimizations, I'm starting to think about the integrate-convolution-engine-to-ALSA state, and would like to get your take on a few points (use LADSPA or make an ext-plugin (probably)? r2r or r2c in FFTW?, etc). I hope you don't mind if I pester you with the occasional question (via PM, or another thread).
Documenting the process in a dedicated thread would be brilliant for the forum but totally understand if you can’t be arsed.
 

dc655321

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Documenting the process in a dedicated thread would be brilliant for the forum but totally understand if you can’t be arsed.

I'd like to get much further along before sharing/documenting, but yes, I agree.
I post some work, hopefully the smart cookies on ASR throw stones at it, I learn from them and make the product better...
Sounds good to me!
 

DonH56

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There were one or two on Parts Express in kit form a while back, have not looked recently.
 
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hvbias

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What is the main difficulty in doing what the Kii/8c do? Is it the rear wave timing that won't be easy with something off the shelf like MiniDSP?
 

dc655321

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What is the main difficulty in doing what the Kii/8c do? Is it the rear wave timing that won't be easy with something off the shelf like MiniDSP?

If your minidsp has enough channels, sure you could emulate the Kii Three behavior. In some respects that may be the simpler path.
The 8c achieve a similar goal passively. Therein lies the challenge (and smarter acoustic design, IMO).

Similar means to an end though...
 

andreasmaaan

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I don't know enough about MiniDSP, but it would need to be capable of user-controlled all-pass phase filtering to work in the way the DSP in the Kii Three does. Is this something MiniDSP modules are capable of? Last time I used one it was the original 2x4 but I guess things have progressed a lot since then...
 

DonH56

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Yes, but I suspect figuring out exactly how much delay to add could be tricky...
 

Burning Sounds

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Martijn Mensink

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Yes, but I suspect figuring out exactly how much delay to add could be tricky...

The basic principle of a cardioid is quite simple: take two speakers and feed the rear speaker with a signal that has inverse polarity and a delay that corresponds with the propagation delay for the sound of the front speaker to travel the distance to the rear speaker. Build it, measure the results and tweak it slightly to achieve maximum rear-rejection.

Cardioid%20subwoofer%20implementation%201.jpg

Source: http://www.jerryleemarcel.com/OnLin...oretical approach to cardioid subwoofers.html

A practical issue you'll encounter is that when you measure the front-driver and rear-driver at the back of the enclosure, as a result of driver directivity and box shading their amplitude responses are not identical. For perfect cancellation you need a perfect match in amplitude and perfect anti-phase. Use EQ on one driver to match the amplitude. The drivers will behave more or less minimum-phase, so after matching the amplitudes with EQ and optimizing the delay, you'll get perfect cancellation. The final step is to apply global EQ to both drivers to make the response flat on-axis again.
 

DonH56

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Yes, of course, but in practice in a real room you'll have to do sweeps over frequency and account for SBIR/reflections and so forth. But, I have not tried it, so it may be really simple. It should still be a minimum-phase system albeit frequency dependent. I doubt miniDSP has an app for that but it should be pretty simple to do. Maybe I am overthinking this; it happens...
 

FrantzM

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Hi

I did like the Geddes approach. I have been looking to purchase one of his speakers, I have said in another post, the logistics to bring the pairs that I found, were not attractive... at least so far. I wouldn't like to get my hands on an Abbey 12 .. Not necessarily end game but ...
Carry on, I am most interested and am feeling the DIY love .. but with woodworking skills put in the corner of flat-pack ;)... Still the bang for the buck level of DIY is often off-the-chart and with the availability and afordability of powerful DSP solutions ... One can built a rather awesome system with a modest cash outlay...
 
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