[dburna]

A separate thread I started on monitors for a small space mentioned the topic of constant directivity (CD) speaker designs.  Looking about in this circle, I didn't find a thread that tackled this topic.  Thought I would start this as a place to discuss CD, specifically:

1. What is constant directivity (technically)?  How does it work?

2. What are the pros/cons of such a design?

3. Who are the CD manufacturers (and products) on the forefront of this approach?  Ideally, it would be great to get a short-list of CD speakers.

Thanks to all in advance for contributing,  -dB

[sonicboom]

Ideally it's Constant Directivity that you want (a subset of controlled directivity). In simple terms, the characteristic of a CD loudspeaker is one where the frequency response at any axis say within a window of +/- 45 Deg from the center axis, is constant within the entire passband of the speaker.

So, if you were to measure either on-axis or at 40 deg off-axis, the frequency response would look the same throughout its range. (actually the  off-axis would be a few DB down, but the shape would be exactly the same). Contrast this with the typical speaker where the frequency response drops off faster with increasing frequency the further away you go off axis. IOW, an on-axis measurement would be flat, at 20 deg off-axis (all else being equal) it would exhibit a drooping response and at 45 degrees it would droop even more as the frequency increases.

[dburna]

So, if you were to measure either on-axis or at 40 deg off-axis, the frequency response would look the same throughout its range. (actually the  off-axis would be a few DB down, but the shape would be exactly the same). Contrast this with the typical speaker where the frequency response narrows with increasing frequency.

Coolness.  Now, does this have any impact on "taking the room out of the equation"?  If not entirely successful, does this at least reduce the effect of room impacts?  Or is that still a different kettle of fish?

Thanks, -dB (who will never get to put audiophile room treatments in his house)

[Randy]

A separate thread I started on monitors for a small space mentioned the topic of controlled directivity (CD) speaker designs.  Looking about in this circle, I didn't find a thread that tackled this topic.  Thought I would start this as a place to discuss CD, specifically:

1. What is controlled directivity (technically)?  How does it work?

2. What are the pros/cons of such a design?

3. Who are the CD manufacturers (and products) on the forefront of this approach?  Ideally, it would be great to get a short-list of CD speakers.

Thanks to all in advance for contributing,  -dB

amphion - http://www.amphion.fi/en/products/argon3s/

[sonicboom]

From various psychoacoustic studies we know that the reflected sound and its relation to the direct sound plays a big role in our auditory perception. The theory behind the controlled directivity benefits, is that the spectral content of the reflected sound is the same as that of the direct arrival. This cannot be the case with a typical non-CD speaker, since the reflected sound from the side walls, emanates from the speaker's off-axis and hence has diminishing frequency content the higher up we go. Only a CD speaker can give a consistent spectral content from the lows to the highs between the direct and reflected sound.

[poseidonsvoice]

http://www.acousticfrontiers.com/20131129controlled-directivity-speakers-open-up-your-acoustic-treatment-options/

http://www.acousticfrontiers.com/201435speaker-off-axis-controlled-directivity-speakers/

http://www.acousticfrontiers.com/2014420speaker-off-axis-coaxial/

http://www.acousticfrontiers.com/speaker-axis-constant-bandwidth-transducers/

http://www.acousticfrontiers.com/speaker-off-axis-understanding-the-effect-of-speaker-toe-in/

http://www.gedlee.com/Papers/directivity.pdf

http://www.gedlee.com/Papers/Philosophy.pdf (start with page 4: The acoustics of small rooms - Mid to High Frequencies)

Read. Then re-read. For the Acoustics Frontiers articles, the question/answer sessions that are there after the articles are very enlightening to read as well.

Best,
Anand.

[mresseguie]

I believe the monitor speakers in the link below are CD speakers. I have been to the showroom (and will visit it later this year). I did not listen to this pair, but I did listen to three pairs of their horn speakers. I really enjoyed what I heard.

Michael

http://www.lals-audio.com/eng/product/product.asp?smenutitle=Classical+One&book_id=112&hot=&Category1_ID=473&Category2_ID=474&anclasspro=&nclasspro=A035&MenuTitle=Classical+Series&pagetitle=Classical+One

[richidoo]

A CD speaker sounds better in any room because the reflections hitting the listener from all directions and after all delays still have flatter frequency response than a non-CD design whose off-axis frequency responses are not as flat as the CD speaker.  If you have an untreated reflective listening room, then a CD design is helpful in lessening the negative effect of the room.

A speaker's "power response" is the collection of all off axis frequency responses taken as a whole. CD speakers have good power response. Many modern speaker designers say that power response is what we really hear, and is the primary determinant of good speaker performance, meaning "sounds good" or listening enjoyment.

In short, it's OK to have room reflections as long as the reflections also have flat frequency response, just like the on-axis FR.

[jtwrace]

dB-

It's really important to know that many manufactures claim they have a waveguide with CD but the fact is that they don't.  They're FAR from the actual goal.  I think I can think of 5 right now that actually succeed at it and none are on this forum.

[dburna]

dB-

It's really important to know that many manufactures claim they have a waveguide with CD but the fact is that they don't.  They're FAR from the actual goal.  I think I can think of 5 right now that actually succeed at it and none are on this forum.

I'd like to get a list of "true" CD manufacturers.  I can ask separately (via PM) for your list of same, but I think others would benefit as well.  Do you mind "publishing" them as a reply to this thread?

Thanks,  -dB

[richidoo]

I believe the monitor speakers in the link below are CD speakers. I have been to the showroom (and will visit it later this year). I did not listen to this pair, but I did listen to three pairs of their horn speakers. I really enjoyed what I heard.

A circular horn like this one resists defraction better than a naked tweeter in a box, but technically is not a "constant directivity" horn per se. It does impart some frequency variable directivity. The woofer also have frequency variable directivity, so if they complement each other then it can be a constant directivity design. The SP Tech speakers were designed with directivity control in mind and used circular/spherical profile horns like this. A good example of the complementing directivity of different size cone woofers is the Revel Ultima speakers which achieve constant directivity using this approach of 5 different sized transducers with xo freqs placed to create precise CD below the tweeter and the waveguide assures CD for the tweeter's bandwidth.

Don Keele says a nominally "constant directivity" horn has some conical section in it. http://sound.whsites.net/articles/waveguides1.htm

[JLM]

Duke LeJeune's Audio Kinesis speakers are CD.

And I believe the JBL 305 up to the M2 professional speakers are all CD.

[DaveC113]

Here's some measurements on various speakers:

https://www.princeton.edu/3D3A/Publications/Tylka_AES139_3D3ADirectivity.html

There's room for personal preference in the shape of the horn/waveguide and it's associated dispersion pattern. I prefer LeCleac'h profiles myself (RIP JM LeCLeac'h), lots of info available... Here's a comparison of LeCleac'h vs Conical. The CD waveguide as used by Geddes and others is a conical but with an oblate spheriod throat transition.

http://www.jhsaudio.com/conical.html

And DIY Sound Group has a variety of horns/wgs/speaker kits and drivers available:

http://www.diysoundgroup.com/

[Folsom]

I'm really wanting someone to impress me with a CD speaker now. Thus far I haven't heard anything that stood out, but would like to hear the M2 at least. It has a few other things going on besides CD that I find pretty cool.

[Armaegis]

It's really important to know that many manufactures claim they have a waveguide with CD but the fact is that they don't.  They're FAR from the actual goal.  I think I can think of 5 right now that actually succeed at it and none are on this forum.

I too would like to know what this list is...

[Rick Craig]

Here's a link that has some good information. Be sure to read both parts.

http://www.tnt-audio.com/intervis/david_smith_e.html

[lowtech]

No need to reinvent the wheel.  http://www.linkwitzlab.com/Constant_directivity_louds.htm

[Nick77]

Wayne Parham of Pi speakers has been at this for a long time and happily caters to the DIY community. I enjoy my DIY Pi4 speakers with JBL bass driver very much.

http://www.pispeakers.com/Technologies.html

http://www.pispeakers.com/Pi_Speakers_Info.pdf

[FullRangeMan]

Controlled Directivity is mechanical devices to narrow the drivers emissions imo, like the felts used in the famous Duntech 2001 tweeters, but as all in audio there will be some that will golden the pill.

[jtwrace]

Controlled Directivity is mechanical devices to narrow the drivers emissions imo, like the felts used in the famous Duntech 2001 tweeters, but as all in audio there will be some that will golden the pill.

You are joking, right?