Controlled directivity speakers

rblnr

Member Sponsor & WBF Founding Member
May 3, 2010
1,880
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#1
Most of you probably know this -- these are speakers designed to take the room out of the equation -- the radiation pattern above 100 - 200 hz usually is cardioid or heart shaped. The goal is to greatly reduce or eliminate the first reflections from the sidewalls and floor and ceiling. The reflections that do hit your ear are later in time and blur the sound less.

Amphion, Gradient, Emerald Physics are some dynamic speakers that work this way, some horns works this way and some planars have a limited dispersion window or a null on either side as well. Some speakers have shallow waveguides on the tweeters that go part of the way toward controlled directivity and also increase efficiency.

I own a pair of Amphion Ions and have heard Gradients several times -- the clarity and imaging you hear almost jumps out at you. Now there are other aspects that contribute to the success of each of these -- time alignment, open baffle design, first order crossover, dipole bass to name a few -- but the sound is very distinctive and true.

As most rooms are untreated, and to the manufacturer, unpredictable, I wonder why more speakers aren't designed this way. Seems to make a lot of sense. Any ideas?
 

Mark Seaton

WBF Technical Expert (Speaker & Acoustics)
May 21, 2010
319
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42
Chicago, IL
www.seatonsound.net
#2
Most of you probably know this -- these are speakers designed to take the room out of the equation -- the radiation pattern above 100 - 200 hz usually is cardioid or heart shaped. The goal is to greatly reduce or eliminate the first reflections from the sidewalls and floor and ceiling. The reflections that do hit your ear are later in time and blur the sound less.
Controlled directivity has become the latest buzzword used equal or more often by those who don't understand the realities as those who do. :rolleyes:

Some friends just did some comparisons with some quality speakers with very high directivity and were quickly sobered by the reality that it doesn't give you a free pass on the setup. Improved directivity *reduces* the early reflections and can greatly help with clarity, intelligibility and the audibility of natural decay in instruments and sounds.

It can make a bad room sound less bad, and changes how the speakers interact with the room possibly changing where you might want to direct your first efforts in acoustic treatment. It won't "take the room out of the equation," but rather reduce the significance of the effect.

As most rooms are untreated, and to the manufacturer, unpredictable, I wonder why more speakers aren't designed this way. Seems to make a lot of sense. Any ideas?
It's harder and requires much more understanding and measurement to get useful results. There are often more pitfalls in the various methods which need to be navigated to not destroy the many things home audio enthusiasts enjoy in the process of achieving more controlled directivity. The biggest hurdle faced is really the integration of the multiple devices used...

Cardioids and dipoles allow a bit more flexibility, but by definition, most efforts to control directivity require minimum sizes to control above a given frequency. That required size almost insures significant spacing between one device and another in a 2, 3 or 4 way system. This spacing creates hurdles in maintaining smooth off axis response and can create strong lobes which make placement of a speaker more fickle. A good example would be old-school multi-way horns where many efforts had good performance per section, but the integration of the whole was always a major hurdle.

As usual, blind pursuit of one metric can result in significant compromises in other very important qualities.
 

rblnr

Member Sponsor & WBF Founding Member
May 3, 2010
1,880
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#4
Controlled directivity has become the latest buzzword used equal or more often by those who don't understand the realities as those who do.

Some friends just did some comparisons with some quality speakers with very high directivity and were quickly sobered by the reality that it doesn't give you a free pass on the setup. Improved directivity *reduces* the early reflections and can greatly help with clarity, intelligibility and the audibility of natural decay in instruments and sounds.
Didn't mean to suggest it's a free pass or no brainer. And some manufacturers have been at it for a long time, flavor of the month status notwithstanding.

The speakers from Amphion and Gradient I've heard pull it off well. Difficulties acknowledged, the approach makes a ton of sense to me.

Mark, can you elaborate on this:
most efforts to control directivity require minimum sizes to control above a given frequency. That required size almost insures significant spacing between one device and another in a 2, 3 or 4 way system. This spacing creates hurdles in maintaining smooth off axis response and can create strong lobes which make placement of a speaker more fickle. A good example would be old-school multi-way horns where many efforts had good performance per section, but the integration of the whole was always a major hurdle.
and btw, are you Chicago based? Am a native and go there all the time. Would love to hear your stuff if you're set up for that.
 

Mark Seaton

WBF Technical Expert (Speaker & Acoustics)
May 21, 2010
319
2
18
42
Chicago, IL
www.seatonsound.net
#5
Still, it would seem like a move in the right direction and does not require us to wear 3D glasses.
Absolutely. Sorry to be a bit of a wet blanket earlier.

The point I should have more directly made is to check out speakers claiming such with interest, and quickly find out exactly what the manufacturer actually means by "controlled directivity."

Cardioids and dipoles are the only ways to really shape directivity over the entire bandwidth, where most speakers shift toward full spherical radiation below some frequency. Where that happens and the nature of that transition from having directivity and not is a huge determinant in the realized benefits from a designers efforts to control directivity. Yes, talking about designs is much less exciting being a realist. :p

Didn't mean to suggest it's a free pass or no brainer. And some manufacturers have been at it for a long time, flavor of the month status notwithstanding.

The speakers from Amphion and Gradient I've heard pull it off well. Difficulties acknowledged, the approach makes a ton of sense to me.
My comments above weren't meant to imply it wasn't a very important and worthwhile goal. My point was to not transfer your experience with a few products talking about controlled directivity to all waving the flag. The few mentioned are much more the exception than the rule in the larger market.

Mark, can you elaborate on this:
most efforts to control directivity require minimum sizes to control above a given frequency. That required size almost insures significant spacing between one device and another in a 2, 3 or 4 way system. This spacing creates hurdles in maintaining smooth off axis response and can create strong lobes which make placement of a speaker more fickle. A good example would be old-school multi-way horns where many efforts had good performance per section, but the integration of the whole was always a major hurdle.
Any horn, line or spaced set of drivers creating directivity in some or multiple axis will only do so above the frequency where the spacing is significant vs. the wavelength of the frequency being reproduced. As a general approximation, you find the start of forward directivity around and above the frequency where the spacing or size is around 1/2 wavelength (ex ~13.5" @ 500Hz or ~6.75" @ 1kHz) and the system is fully omnidirectional below roughly 1/8 wavelength (ex <125Hz for 13.5" or <250Hz for 6.75"). There are plenty of other variables relating to exactly how they behave in this range and above, including boundaries like the floor, but it is a very useful reality check to keep in mind, especially when we realize that similar directivity around 125Hz comes with dimensions of 54" (4.5 FEET!).

A dipole or cardioid works from a somewhat different perspective, where you essentially trade off efficiency/output for size to get directivity from smaller devices.

and btw, are you Chicago based? Am a native and go there all the time. Would love to hear your stuff if you're set up for that.
I live at the north edge of the city and our office/warehouse is just outside of the NW city limits in Morton Grove. We don't yet have a demo system at our shop, but do have many customers who welcome demonstrations. Best bet is to post on our forum noting what you are interested in hearing or give us a call. There are some very nice systems with Catalysts in Michigan, near Atlanta, in the SF Bay Area, with SubMersives in in many places. Hopefully later this summer we'll have some better local options to have a listen. You are certainly welcome to come by and see what we're up to.
 

Steve Williams

Site Founder, Site Owner, Administrator
#6
Mark

I wish I understood what you were saying. Great to see you posting here. You need to come to our BAAS mtg on June 27
 

Mark Seaton

WBF Technical Expert (Speaker & Acoustics)
May 21, 2010
319
2
18
42
Chicago, IL
www.seatonsound.net
#7
Mark

I wish I understood what you were saying. Great to see you posting here. You need to come to our BAAS mtg on June 27
Hi Steve,

I don't believe I'll be in the area on the 27th, but I will be in the area in the next month or two for another meet in Berkeley. Hopefully you might be able to make that one this year. I will keep an eye on the BAAS meetings as it's not all that hard to get out to the area with many friends customers out there.

As for understanding the above, the first concept of importance is wavelength. Sound propagates at a known speed through air plus/minus a small % for variations in temp, humidity and barometric pressure. The frequency tells us how often the pressure goes from zero-max-zero-min-zero and starts over again. 100Hz is 100 of these full cycles per second (=Hertz). 1000Hz is 10x as many of these cycles per second. Since sound propagates, a fixed distance will be covered during each cycle of max-min and back to zero. This distance is known as wavelength. Here is a simple image where you can visualize the relative increase and decrease of air pressure over distance for a constant sine wave. The top waves are of course for lower frequencies, and the lower waves are higher frequencies:


Many things in acoustic behavior are directly related to wavelength or a fractional wavelength (1/2, 1/4 and 1/8th most commonly). Resistive treatments must be a significant fraction of a wavelength from a boundary (often thickness from the wall) to be effective. This is why 2" thick panels don't have much effect on the 108" wavelength of 125Hz.

Similar ratios come into play with speaker operation. What we commonly call "beaming" of larger drivers or tweeters is this exact effect. 16kHz has a wavelength of ~0.85". A 1" or larger tweeter will be more directional at this high frequency where it is radiates without any directionality at 1/10th this frequency (1.6kHz) as the tweeter is very small as compared to this lower frequency. As with most things in sound, everything is relative.

A bit easier to follow? :)
 

Steve Williams

Site Founder, Site Owner, Administrator
#8
definitely Mark

It is refreshing for me to follow you and the growth of your company as all reports are nothing short of remarkable.
 

rblnr

Member Sponsor & WBF Founding Member
May 3, 2010
1,880
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NYC/NJ
#10
Mark --

Appreciate the primer. Obviously there's no free lunch anywhere. Like everything else, there is not necessarily a best technology, it's the quality of implementation that counts. I'd be interested to hear the what and whys of the initial design choices that go into your speakers. I'll make a point to listen to them.
 
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muralman1

New Member
Jul 7, 2010
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Sacramento Ca
#11
Mark, I understand, and agree with what you are communicating, if not the particulars.

My speakers, The Apogee Scintilla, has been deemed a cardioid emitting speaker. I have found that a believable sound can be heard all over the room. While a lot of folks prefer pin pointing images, I shy away. On those systems, we all have to take turns in the listening seat, where we will have to locate the median point of reference. The sonic stamp suffers outside the sweet spot.

When I am enjoying a live classical music performance, say a quartet playing Mozart, The sound is not pin point. Not at all. All string instruments behave as a cardioid when played. Of course, the audience can easily differentiated between the individual performers - even direction. This is the same situation with my cardioid. When listening to the Kingston trio, the three are obviously standing left center and right. I just don't have to be in a sweet seat to image that.
 

Bjorn

New Member
Oct 12, 2010
140
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Norway
#12
I think high directivity is very important in rooms we're talking about. Early reflections are very detrimental and speakers with controlled directivity will reduce the level of these substantially compared to a speaker with much dispersion. It's not substitute for acoustic treatment, but a great aid. It also reduces the need for dampening and you can have a livelier room.

If one wants very good intelligibility, clarity, loacalization, image, etc. reducing early reflections are vital. To reduce the early reflections enough with a speaker with much dispersion, can be difficult. And you easily end up with a overdampened room that sounds too dry.
 
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Jul 1, 2010
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#13
I'll definitely qualify as one of Mark's one of those who "does not understand the realities," but I've heard a few "controlled directivity" speakers and what I heard was bad dispersion, bad off-axis FR. Now I'm sure there is a place and a set up for this approach, but I suspect it's not the place most civilians live in. What I've heard is an extremely narrow sweet spot. In one example, small Martin Logan hybrids, I'd describe them as slightly recessed in the lower midrange with a very sweet, clear, transparent upper midrange. All around a really nice-sounding speaker for the money when you're sitting right there, that chair. Stand up and they turned to cardboard.

It's all a series of compromises and I'm sure a really well-designed "controlled directivity" speaker is great for the dedicated listener. In the average living space I think you'd get a lot better sound from cardiods or omnis with really good off-axis response and a reasonably non-reflective room.

One man's guess...

Tim
 

Face

New Member
Dec 13, 2011
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#14
I'll definitely qualify as one of Mark's one of those who "does not understand the realities," but I've heard a few "controlled directivity" speakers and what I heard was bad dispersion, bad off-axis FR. Now I'm sure there is a place and a set up for this approach, but I suspect it's not the place most civilians live in. What I've heard is an extremely narrow sweet spot. In one example, small Martin Logan hybrids, I'd describe them as slightly recessed in the lower midrange with a very sweet, clear, transparent upper midrange. All around a really nice-sounding speaker for the money when you're sitting right there, that chair. Stand up and they turned to cardboard.
What you heard were either very poorly described or poorly designed speakers. A well designed controlled directivity speaker will have wide, uniform off axis up to 90*. Which will give a wide sweet spot, along a few chairs, wide couch, etc...something most hifi speakers cannot do. As far as being recessed in the mids, again, that sounds like either poor voicing or a poor design. As far as standing up goes, you're correct that they can sound very different there. As you mention below, it'll all about compromises.


It's all a series of compromises and I'm sure a really well-designed "controlled directivity" speaker is great for the dedicated listener. In the average living space I think you'd get a lot better sound from cardiods or omnis with really good off-axis response and a reasonably non-reflective room.

One man's guess...

Tim
Cardioids will actually have a smaller sweet spot due to their side cancellation...similar to a open baffle or dipole speaker, but with much less room interference.

directivitysonogram16oc.jpg
 

Nightlord

New Member
Dec 30, 2012
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Sweden
#16
Don Keele's CBT speaker have a wide and a very uniform response. Early vertical reflections are unavoided to large degree without any treatment. A speaker evolution in many ways. These speakers not only sounds great in sweet spot but also in other parts of the room.
http://www.xlrtechs.com/dbkeele.com/CBT.php
On my list of speakers I want to listen to, those are extremely high up. (I assume you meant to say avoided, not unavoided)

Ps. Hej namne!
 

Bjorn

New Member
Oct 12, 2010
140
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Norway
#17
On my list of speakers I want to listen to, those are extremely high up. (I assume you meant to say avoided, not unavoided)

Ps. Hej namne!
Best speakers I've ever heard. And first speakers I think sounds good even in a narrow room without horizontal treatment. Even better then a waveuguide speaker like Geddes Abbey. Of course, treating early reflections gives a sharper image. The speaker kit from partsexpress is an amazing bargain. IMO, no exotic speakers out there can compare to the CBT design. Despite of using diamond or beryllium drivers.....

Yes. Meant avoided. Reflections in the vertical plane will be below -20/-25 dB with no treatment in a room with normal height. And no floor bounce. You need a good subwoofer system though and it's an advantage to have the flexibility to cross over a bit high.
 

Bjorn

New Member
Oct 12, 2010
140
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Norway
#19
I'm generally not a fan of line arrays, but would love to hear those.
There's a reason they are called CBT and not line arrays.
I don't believe there are any line array speakers that have a great powerrespons. As far as I know, which Don Keele shows in his papers as well, they have a lot of lobing.

So don't misjudge CBTs for being traditional line arrays. The overall response is much more even and there's no trouble sitting in nearfield.
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
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#20
Has anyone heard these yet? The only thing that turns me off is having to go through an A/D and D/A conversion in order to use the digital crossover.
 

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