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--- What should they do? --- Design of loudspeakers --- Loudspeaker evaluation --- Accurate stereo --- Whatever happened? --- 

--- Room acoustics --- Sound field control --- Other designs --- System design ---



-- Other designs --
"Controlled Directivity" loudspeakers

"Controlled Directivity" loudspeakers  ----  Linkwitz Lab inspired designs  ----  Engineering information  ----  DIY designs

On this web page I want to provide links to engineering information, to websites or forum discussions for the purpose of spreading learning and knowledge about controlled directivity loudspeaker designs. The material should be current and updated to reflect progress that has been made. I will need your help with that and invite you to give me links. The list would serve as a quick entry point to find out where and what the action is. It should therefore also point to relevant activities in languages other than English, since much can be learned from pictures and graphs.  

I expect that the list will point to different design approaches. It would be important to know the design objectives and to what degree they were met. To be added to the list please send me an email with the subject DESIGN LIST, with your URL, and with a 50 to 200 word statement of your specific Design Objectives. I will look at the website or forum to determine whether the loudspeaker design or some of its aspects are a contribution to the field of controlled directivity loudspeakers from my point of view and appropriate for the purpose of the list. 

Loudspeakers in a domestic setting are used in rooms that are acoustically small in the bass region where the wavelengths are long (e.g. 7.8 m at 50 Hz) and which become increasingly larger as frequency increases and wavelength decreases (e.g. 3.4 cm at 10 kHz). At the low end of the spectrum there can be problems in the response due to room modes and at higher frequencies due to specular reflections. The room can participate in the sound reproduction process at many frequencies depending upon the absorptive and diffusive properties of surfaces and objects in the room and to the degree that these are illuminated by the sound waves emanating from the loudspeakers.

Loudspeakers tend to radiate uniformly into all directions at low frequencies where the radiating surfaces and cabinetry are small compared to the wavelength. They tend to beam the sound at high frequencies because the radiators are typically larger than 1/8th of a wavelength. Thus a loudspeaker, which is flat on-axis, radiates a different spectrum at angles off-axis, where the response is no longer frequency independent. Consequently reflections of the sound from different parts of the room that reach the listener will have different spectral content than the direct sound. The effect of reflections upon imaging from a stereo system has only been studied to a limited degree. It is often assumed that reflections can only have negative effects. This seems reasonable because reflections can only degrade the accuracy of a direct signal. But 2-channel stereo is about creating an illusion in the listener's mind. Neither the microphone signals, nor the ensuing ear drum signals at the listener, are accurate representations of a natural occurrence, of a natural hearing situation. The ear drum signals, though, contain cues from which the listener forms an auditory scene in his mind. If this scene is believable, then great enjoyment can be drawn from it.

The ear drum signals also contain cues about the room, though colored in the case of a loudspeaker that radiates a different spectrum in different directions. It has been my observation that a spatially more open and 3-dimensional auditory scene is created in one's mind when the loudspeakers radiate uniformly in all directions like dipoles or omnis do. The auditory scene has great clarity and distance but not the hard edges and closeness that a highly directional loudspeaker tends to produce

A dipole is the only radiator that is directional down to the lowest frequency. I have observed that it can produce bass output that sounds natural and effortless and unlike what I hear from most box speakers. A dipole source demands large volume displacements because of the phase dependent acoustic short circuit between front and rear radiation. The effect is wavelength dependent and reaches a minimum when the front-to-back distance D equals 1/2 wavelength, at which frequency the rear wave adds in phase to the front wave. Above this frequency the on-axis output decreases and becomes zero for D/l = 1. The radiation follows a cos(a) pattern for D/l < 0.1, but widens considerably above this. In practice this tendency is counteracted by the radiating surface becoming itself larger compared to the radiated wavelength and thus starting to beam. This helps when transitioning in a multi-way loudspeaker to a smaller dipole driver for higher frequencies. But it remains difficult to build a loudspeaker that has the same frequency response at off-axis angles as it has on-axis and where only the overall amplitude decreases with increasing angles. It can be done with small drivers, but then the output volume capability is compromised severely.

Note: The graph is derived from a dipole model consisting of opposite polarity point sources at distance D from each other. The graph differs significantly from that, which is calculated for "Radiation from a rigid circular piston in a finite circular open baffle".  Response widening with increasing D/l is marginal and on-axis nulls are not observed. But the increase in 6 dB/oct on-axis slope and a dominant peak agree with observations and required equalization
See Chapter 13 in the recent book by Beranek & Mellow, "Acoustics - Sound Fields and Transducers", Elsevier-Academic Press (2012)

I do not know how consistent the radiation pattern has to be. Nor do I know that constant directivity over the whole frequency range is optimum. I do know that ORION and Pluto can deliver a very believable auditory scene and that other loudspeakers with different radiation patterns often create a less convincing illusion. The problem must be how a given loudspeaker system blends with the room. Ideally the room and the loudspeakers in it are not part of the auditory scene. That scene should open effortless and untiring in front of the listener, to be enjoyed best with closed eyes.


Linkwitz Lab inspired designs

Daniel Spadini --- LX521 from Switzerland, the French part


Hello Mr. Linkwitz,

It is a long time that I follow your work from Switzerland, the French part. I heard the Phoenix, I build the Orion, Thor, Pluto and of course the LX521.

Since the Orion, I always have a problem with the amplifier. I used two Atoll AV500 (5 * 100W) to drive the Orion. I try then with LM3886, but I was not satisfied. When listen to other systems, I found better clarity and accuracy. I knew that the problem was not the speaker, but the amplifier. So 3 years ago, I started to build my own. A push-pull class A for tweeter and medium, Hypex for Bass. I use +/-16V for the power supply of the tweeter, +/-30 V (I started with 25V for the Orion, but It’s not enough for the LX) for the medium. The two have a quiescent current of 1 A. I use a configuration dual mono. I have one box per speaker. For the bass I use one Hypex 400W for each driver and a power supply of 1200 W (Hypex) per box. I work a lot for the power supply (4 times 100uf MKP and 544'000uf of electrolitic capacitors per box) and I use a fan to regulate the temperature of the class A. I just finish. So now, each box weight 29 kilos! But the result is great. The sound is clear and perfectly defined.

Since you are not providing the ASP anymore, I design my own, but smaller. I integrated a line transformer (Jensen JT-10kb) to separate the ground. I also use AD797 for the input, then LME49990 for the rest, except for the output; I use LME49710 in metal box. It’s a big change in quality.

For the LX, I change only one thing from our design; I add a support in the back of the baffle. I use almost the same technique from the Orion. The baffle doesn’t move at all. The low medium is screw in the front of the baffle and attached to the support in the back. I am happy with that. I also change the esthetic of the V-frame for woofer, the front part.

I created an internet site to explain my work (www.spadiniaudio.ch). If someone is interested to have is system build by me, I can do it. I will not sell kits for the LX521. I will furnish a complete system. I am looking for people around me (in Switzerland). I translate my site in English (sorry for the poor language) for the German and Italian fox in Switzerland.

The DSP way is also interesting, but I wanted to push the ASP to the maximum that I can. Now I did and I am very happy. I think that the DAC is a very important part and should be done very carefully. With the DSP you need 8 of them. The volume control is also a problem for me. I would like to have it in the analogical part. So I will wait and test to find solutions that sound at list similar to the ASP.

Of course, If someone would like to come in my workshop to listen to the LX521, he is more than welcome.

With my best wishes, Daniel Spadini

Go for it!  You know the Terms & Conditions. - SL



Chris Lloyd --- A 3D-printed desktop 'LXmini'


Dear Siegfried,

I hope this email finds you well. I wanted to send a few picture about the experimentation with my LXmini’s. I only really listen to music in without moving around at my computer and so the as you may recall I was somewhat disappointed in my initial listening tests. I decided that i would modify the speakers for use as desktop speakers and see where it took me.

I’m pleased to present my 'LXmini desktops’.
In summary they are identical in electronics, the principal structural changes are that the pipe has been converted into a 9 litre sphere, the bass driver is not firing directly up and the full range is gripped by the magnet rather than held within the 3” pipe. Following my design in CAD, the cabinets have been printed by a 3D printing company for around £200 each. One is yellow in ABS and one is blue in PLA. Acoustically PLA is very damped compared to ABS, but the ABS hold a better finish.

I’m currently doing some comparison listening tests with the LXmini’s. The bass does not go so deep and has slightly more resonance, but to me it sounds good at high volume. There is some loss of clarity in the full range due to the design of the cabinet and lack of diffuser. The dispersion in the room is more forgiving of standing up and this was important to me. Overall they fall slightly short of the LXmini in performance, but they look good (apologies I know that this is not a consideration for you), fit on a desk next to my computer and are a good fit for my listening preferences.

Anyway, I email for two reasons.
First, I’d like to take the opportunity to thank you for the work and information available on the website. It has pushed me to get further involved with loudspeaker design and i am really enjoying it.
Second, I’m sure you are aware of the great advances in 3D printing technology and reducing printing cost over the last few years and I see some users are developing small parts of the LXmini with 3D printers. I see the LXmini design, and how closely it fits with water pipe diameters and pipe couplers etc and wonder how close it is to the ideal for a design of this type. How would you design the LXmini if you had complete freedom of form? I feel like with your knowledge of the design and technological advances you could create something even more special than the your current array of LX speakers. You could sell the 3D print file in the same way you sell the construction plans. I think it would have great appeal.

Thanks again and all the best.
Chris --- Chris Lloyd | www.chrislloyd.com | LinkedIn | +44 7739 117670

Thank you, Chris, for inspiring me and DIYers to explore 3D-printing. The top section of the LXmini is certainly a good candidate for a new form while maintaining its acoustic function. But I have no plans to pursue this at the moment. - SL



Luca Fusina --- Manger driver used as dipole

Modified LXmini using a Manger driver

Manger Audio - Manger History - Acoustical Reality by Josef W. Manger

"Hi Siegfried,

There are a number of things, but in my opinion there are two distinctive differences between my speaker and yours:
1. the polar pattern. In the past you built dipoles, the LXmini is "controlled directivity". My speaker seems to be omni at all frequencies. I haven't investigated yet why, most probably is related to the way the Manger driver works. It's obvious my loudspeakers are omni, just by walking around them when music is reproduced. But I thought I made some mistakes with the measurements so I did them a number of times using variations and they seem to be correct. See attached. I really would like to know your opinion about omni sources related to soundstage etc. ref. my impressions about the LXmini soundstage
2. the driver technology. In my opinion the Manger driver sounds more realistic than cones when reproducing certain things that are important to me, eg voices or sounds eg ringtones, doorbells etc.

Anyway, in my speaker
- low frequencies are handled by a conventional Seas Excel W18 mid woofer, housed in a sealed tower made of 2cm solid Italian walnut panels. There is extensive bracing, plus anti-rumble, felt and sound isolation materials used in European residential construction. Many believe solid wood panels are bad for loudspeaker boxes because of resonances, but I never got MDF or Baltic birch to sound any better,
- main unit is a Manger, mounted on a shaped open baffle; crossover between the Seas and the Manger is 300Hz LR4,
- bottom end is handled by a subwoofer; crossover is a 60Hz LR2.

Thank you again for your time and have a nice Capodanno.  Luca"

Luca had visited me in Corte Madera and heard the LXmini. - SL



Ruediger Franz Rauskolb --- The Ultimate DIY Sound System Is at Hand 


The Ultimate DIY Sound System Is at Hand

Sound System Modular Concept

Meine Wunschliste/Systemkonzept

Baffle Vibrations in Open Baffle Loudspeakers

A call for an open source loudspeaker project

The LXmini+2 with PowerBox 6pro NCore is my answer to a 3-way system solution. - SL





Terms & Conditions - item 6

My conversations with Fitz


I heard these speakers at my place in Corte Madera and was impressed by how similar their acoustic properties were to the LXmini. The LXmini thus proved to be a robust design that could tolerate the changes in mechanical design that the builders of the Beanstalk JCK had made.

To me, some of the neutrality of the LXmini had been lost. The speakers had acquired a character which the designers liked. The JCKs produced a sound, and sound stage, which was truly remarkable, even though the fullrange driver was mounted to a circular baffle that increased the acoustic size of the source. 

I now see that the customer apparently has a choice of baffles to adapt the speakers to his/her sonic tastes. That is not a game I would like to play.  A loudspeaker is a machine (transducer), which should neither add to, nor subtract from the recording, as it converts electrical input signals into air vibrations and illuminates listener and listening space with them.

But if you consider a loudspeaker to be an entertainment device, then that speaker may well impart its signature on every recording it renders. And if the speaker does that particularly well for the sounds you like, then who am I to question this. 

Have fun!      

July 2016

Update - October 2016



I wanted to give you a quick update and let you know the most recent developments. I'm writing this from one of our two demo rooms at RMAF. We have gone through a ground up redesign, rebranding and name change (we are now Ono Audio).

I won't go into the full range of technical changes, but market forces pressed us to develop a passive version. This was, to put is mildly, a very large technical challenge. We ended up having to do a driver change up top (to the Fostex Sigma) and adding a tweeter firing upward into the diffuser, which turned out to be an extremely effective way of getting an omni radiator. This allowed us to run the Fostex full range and keep a lot of the sound character of the active system. End result is very crisp and clear and makes for a very accessible package for those not ready to jump to a fully active system. We still keep the option to run active with a dsp and we were lucky enough to be able to demo both versions at the show. We have moved to the Danville dspmusik and are hugely impressed with the clarity and sheer power of the system.

The response has been overwhelming. We just re-launched yesterday and most of the day today and yesterday was standing room only with a line out the door at some points. Press attention looks to be very favorable as well. A lot of people recognize the LXmini influences and we have had some great discussions about your work and innovations. I would say 20-30 people recognized the LXmini design influence and at least half a dozen have built LXminis or Orions. You have a lot of fans out there.
Ben Huffman

Clearly, Ben's speaker design deviates considerably from my original LXmini. I have not heard the new speaker and will not comment on the latest changes, except to say that they continue in directions, which I would not pursue. - SL 


Engineering information

dbx SF-1A Loudspeaker


Mark Davis:
Loudspeaker Systems with Optimized Wide-Listening-Area Imaging

David Moran reminded me of this AES paper from 1987 in response to my comments about the BeoLab 90. loudspeaker, which controls dispersion via a multitude of drivers in a phased array. A similar approach was used for the dbx SF-1A loudspeaker, but without the benefit of DSP.

At the time of publication I had already given up on box loudspeaker design, because of the difficulties to resolve their panel and internal cavity spurious radiation issues. Inspired by the Quad ESL63 my focus had shifted to open-baffle design with piston drivers and to the beam forming properties of dipoles.
A Loudspeaker Design for Reduced Reverberant Sound Power Output
Sound field control for rendering stereo

This work led to the LX521.4 as demonstrated at the Open House, January 2017.




        SEAS DXT wide dispersion tweeter

DXT Technology by Michael Kragelund

Data sheet

Test: Seas DXT 27TBCD/GB

Test: T2 LS1 Loudspeaker


This tweeter should work well in Rauskolb's Ultimate DIY Sound System above.



Lexicon SL-1 loudspeakers and SoundSteer Technology

stereophile-CES 2017      HomeTheaterHighFidelity-CES 2017      AVSForum-CES 2017

Here is a loudspeaker designed by Ulrich Horbach from Lexicon. It appears that it has a narrowed vertical beam, which can be varied in horizontal width and steered in the horizontal plane towards a listener selected "sweet spot". The black section of the speaker is about  44" tall and has a 14" diameter at top and bottom. It uses twelve 1" tweeters, sixteen 2" midranges, four 6" woofers with 22 channels of amplification (12x tweeter, 8x midrange, 2x woofer) and (I guess) a 3-channel DSP driving twenty remotely programmable delays to control beam width and horizontal direction.
See also Horbach-Keele below.

This loudspeaker could serve as a tool to answer questions, which I raised in a paper presented at the AES 127th Convention in New York, 2009: The challenge to find the optimum radiation pattern and placement of stereo loudspeakers in a room for the creation of phantom sources and simultaneous masking of real sources, Manuscript-2009.
The paper was a follow-on to Room Reflections Misunderstood? from 2007, Manuscript-2007

While the polar pattern is a steady-state response phenomenon, will the impulse response be smeared due to the delay between drivers on the circumference?



BeoLab 90 with DSP controlled and adjustable directivity
Here is an all-out effort by Bang & Olufsen at a controlled directivity loudspeaker, where directivity can be varied from a narrow horizontal beam, what I call "headphones at a distance", to a wide beam and omni. It will be interesting to hear whether the auditory scene is hard-bounded by the speakers in narrow beam mode or whether the speakers and room disappear in wide beam mode. Will it be music or music from a pair of speakers? Also, do the acoustic cavities behind the many cones and the diffracting edges in front of them distract from openness of the auditory scene? How varied is the 4p power response? 







January 2017 - Yesterday, late afternoon, I had the opportunity to listen to these speakers for about half an hour using excerpts from a wide variety of my own demo material, which I had brought with me on a thumb drive. My conclusion: Excellent performance in aspects of neutrality of timbre, of dynamic range, of resolution at all levels, of attack and decay, of spatial rendering in width, depth and focus !!!
The BeoLab90 tops what I have heard from any commercial loudspeaker!

My slight reservations are with the bottom end. Bass is tight, explosive but lacks in spaciousness, which I hear rendered from a dipole bass like in the LX521.4. In fairness, though, I must say that the speakers were set up about 9 feet apart, against a long wall and firing across a narrow (15 feet wide?) store room in Stanford Shopping Center. So plenty of open space to the left and right of the speakers, but little room left behind a listener in the equilateral triangle sweet spot. I prefer a setup where the speaker fires along the long direction of the room.

This morning I listened to some of the same tracks with my LX521.4 driven by two PowerBoxes 6pro NCore in my living room. My sweet spot's distance from the speakers and the distance between the speakers is the same as in the store. The perceived image is significantly larger in all directions on symphonic material, which has venue reverberation in the recording. Also, the phantom scene appeared more open and I felt immediately drawn into the emotional aspect of the musical performance. The bass seemed balaced in proportion to the rest of the music and in character to the size of the venue. But keep in mind that my hearing apparatus between the ears has had a long time to be trained and adapt to the LX521.4's rendering and to draw a maximum amount of information from it. At the very top of the frequency range the BeoLab90 might have more output and maybe sweetness.

We agreed to explore further, to have a more leisurely and private listening session in February or March when the BeoLab90 system is fully dialed in. Yesterday the speakers were set to narrow directivity and there was no time to try other settings. So stay tuned.

Before listening to the music tracks I played two imaging test signal tracks:
01- Introduction and Left-Right Imaging Test.flac from Chesky Records,
02-phantom_12800-100Hz_spaced_100_500ms.wav from Linkwitz Lab

On track 01 the voice halfway between center and right and the voice between center and left, was not clearly located. The voice beyond left was properly located but not the voice beyond right. That perception is due to an imbalance between my left and right ears. Similarly on track 02 the highest frequency bursts are not centered between the speakers, but turn towards the right speaker. The bursts move to the left speaker when I face away from the speakers proving that it is a subjective effect. 
Curiously, my left ear has a stronger high frequency response than my right ear. It is as if my brain were trying to compensate and increase the gain in my right ear for high frequencies, thus pulling the phantom center burst image to the right. The brain adaptation fails in locating the voice beyond the right speaker.




Kii Audio THREE - Controlled Directivity: 4.8dB (80Hz - 1kHz, slowly rising thereafter)
Bruno Putzeys of Hypex Electronics and Grimm AUDIO LS1 speaker fame has started a new company with a team of talented contributors.

 Here is an all-out effort at a compact, controlled directivity and low distortion loudspeaker using DSP and built-in Class-D power amplifiers. At very low frequencies the speaker starts out as omni, then turns into cardioid over more than a decade and then becomes forward directional from a wide dispersion tweeter. DSP is used to control the polar pattern in conjunction with the rear firing drivers and also to reduce driver distortion by deriving feedback control from the voice coil currents of drivers.

I have not heard the speakers, but would expect the highest level of performance, i.e. a speaker that disappears from a 3D auditory scene and is completely neutral sounding in a reverberant space, whether studio or home. 

Hopefully the big-name manufacturers of high-end audio speakers take a lesson from this design and recognize the overriding importance of the polar response of a speaker. Designing for the on-axis response is not sufficient.

Review in AUDIO 09/2015

February 2017 - Today I had the opportunity to listen to the Kii 3 using some of my usual test and demo tracks. The location was a professional mixing studio room with very dry acoustics. I would estimate RT60 to be around 200 ms. The speakers were set up on metal stands in the middle of the large room, essentially in free-field conditions.
   Listening from the equilateral triangle sweet spot the speakers immediately impressed me with their smoothness, clarity and neutrality of timbre. The phantom image was precisely detailed. It had depth and width but little height. It was somewhat like listening to an acoustic scene through a window in a wall at the speaker distance, where the speaker separation and the speaker box height defined the window size. The sweet spot was tight and lateral movement of the head quickly pulled the phantom scene to the nearer speaker. But this was in a very dry and acoustically dead room. Listening from a greater distance and also off axis, the speakers preserved their neutrality, smoothness and clarity but the phantom window boundaries disappeared, making the acoustic scene realistic in the studio. 
   The low end was tight and articulate, and extended quite deep. But the lowest notes could not quite keep up with the higher frequency range at very high volume levels. That is not surprising, given the physical limitations of the drivers and again the dry room.
   The whole experience made me aware again of the importance of the reverberant field in the listening room. For sure it has to be spectrally neutral, which the Kii 3 speakers guarantee to a high degree, because of their wide polar pattern. But the room also has to be sufficiently live so that the ear-brain-perceptual apparatus can draw confirming information from the reverberant field about the spatial data in the direct loudspeaker signals to support the phantom scene illusion. A dry room is apparently a useful work environment, but I normally do not experience sounds in such environment. I prefer a room with RT60 around 450 ms.
   The Kii 3 is an impressive speaker, technically and sound wise, in an extremely compact and versatile package. It probably gives the most accurate conversion of electrical input to a defined acoustic field output of any speaker I know of. For my taste, it needs a lively room and then I would cross it over at 80 Hz to a pair of large dipole subwoofers. Could that be the ultimate?




Horbach-Keele linear-phase digital crossover filters for pair-wise symmetric multi-way loudspeakers - 6/9/10


The Audio Toolbox by Dr. Ulrich Brüggemann (((acourate))) now includes these crossover filters. 

Here is a truly ground breaking, sensible and practical application of DSP to the design of crossover filters and the polar response of large multi-way active loudspeakers. Very exciting work! It avoids lobing of the vertical polar pattern by acoustically tight spacing of the driver pairs.

Application of linear-phase digital crossover filters to pair-wise symmetric multi-way loudspeakers
Part 1: Control of off-axis frequency response,  
PP presentation 1
Part 2: Control of beamwidth and polar shape, 
PP presentation 2
Ulrich Horbach and D.B. (Don) Keele, Jr., 
AES 32nd International Conference
, September 2007



Constant beam-width transducer (Keele)  

Wide and uniform horizontal dispersion and controlled vertical dispersion up to high frequencies without lobes. The large number of small drivers ensures high output capability, especially in the tweeter range. The floor reflection is part of the design. The sound field is already uniform close to the loudspeaker and suitable for near-field listening. SPL falls off at a low rate with distance (3 dB/oct) and is nearly constant over a distance range. This is ideal for a home theater setup with rows of seats. (SL) 



JBL Pro LSR6332

This loudspeaker exemplifies Floyd Toole's loudspeaker directivity requirements. They are the result of extensive listening tests where different box loudspeakers were ranked according to preference. The directivity index increases smoothly from 0 dB to 10 dB, without signs of the two crossovers in its frequency response. Moderately wide dispersion horizontally. (SL)


JBL M2 Master Reference Monitor

I was quite impressed with the wide dispersion, clarity and neutrality of these speakers when I heard them at an AES Convention a few years ago. Only wished they were not vented. The horn compression driver is an ingenious dual diaphragm design by Alex Voishvillo for extended high frequency coverage and low distortion at high output levels.

Alex Voishvillo, Dual Diaphragm Compression Drivers, AES Convention Paper #8502, NY 2011



Genelec 8260A  

An active 3-way loudspeaker with a 10" woofer and coaxial 5" mid and 3/4" tweeter. Smooth transition from omni to +/-50 degree, -6 dB, horizontal dispersion. DSP controlled. (SL)



Directivity in loudspeaker systems (Geddes)

A 2-way loudspeaker with a 15" woofer and compression tweeter. Omni at low frequencies and rapid transition to a beam of +/-40 degree at -6 dB due to a 15" diameter waveguide. The narrow beam widens the sweet spot if the speakers are toed-in to cross in front of the listeners. The contour map would be even more illustrative of reality if it were drawn in polar coordinates with the frequency axis as radius and the angle covering 0 to 360 degrees. (SL)



Danley Sound Labs (Tom Danley)

3-way Synergy Horn SH-50 designed in 2005,
showing HF, MF and LF driver placement. 
"The horn can re-produce a square wave over a wide range of listener positions because the drivers are all less than
l/4 apart where they interact."
This plot is 3 dB per color division, from 30 Hz to 16 kHz.
"The horn can reproduce a square wave form, fair to excellent looking, from about 150 Hz to about 2900 Hz, a range spanning both crossovers. That is possible because the front to back positioning of drivers allows a phase shift free crossover." 
Horn from 50 feet and from 400 feet.


The beneficial coupling of cardioid low frequency sources to the acoustics of small rooms (Ferekidis) 

ATC Loudspeaker Technology Ltd.

Perfect 8

The Naim Balanced Mode Radiator



DIY designs


Cardioid as sum of monopole and dipole speakers - Barleywater - 2/17/15
Note the use of Kirkeby's Inverse Filters for crossover


DIY Loudspeakers - Kimmo Saunisto - 1/30/15
A great variety of Cardioid Bass designs

Ground Sound - Gallery Thomas M. - 11/9/14
A cardioid loudspeaker inspired by the MEG RL901K
Here "dissipation" means "dispersion" of sound.

sondek12 (Mats Svensson) - 3/16/13
My open baffle project on ortho acoustic design ideas
My vision for these speakers was to build a design interacting positively with the acoustical properties in a normal living room, creating a balanced and lifelike reproduction of a recorded sound. I wanted to merge the design ideas of the late Swedish speaker designer Stig Carlsson with the benefits of controlled directivity dipolar designs. The aim has been to create a loudspeaker for conventional placement in a normal living room, using controlled directivity and integrated damping to suppress early reflections from influencing the direct sound, but still to illuminate the room with later reflections for a lifelike apparent source width and sensation of envelopment. I also wanted to use dipolar directivity to assist time intensity trading in order to increase the sweet spot area for believable soundstage reproduction.
Design objectives:
-  Flat on axis response for correct experience of timbre
-  Minimum of early reflections (less than 6-8 ms)
-  Consistent dispersion to assist sensation of apparent source width and envelopment in the reproduced sound 
   (enhanced distribution of later reflections larger  than 6-8 ms)
-  Consistent performance over complete intended dynamic range
-  Designed to work as intended with conventional placement in a normal living room
-  Large sweet spot area for a believable soundstage reproduction

keyser (Martijn Mensink) - 8/1/11 
& previous design approach - 3/17/10   

"- Flat frequency response, on-axis as well as off-axis by designing for a dipolar radiation pattern from the bass range up to the highest possible frequency. 
- Operating drivers largely below the first dipole peak to maintain constant directivity up to about 6.5 kHz. Small U-frame 12" woofers and no baffle at all for the 6" midrange and magnetostatic dipole tweeter.
- Closed box subwoofers will be added at a later date. The stand-alone dipole is currently equalized flat to a little below 40 Hz.
- Sufficient dynamic range. In practice it turns out that at a listening distance of about 3 meters and an average listening level a little over 80 dB(A) and an approximated source material crest-factor of 6 dB and broadband, spectrally dense content, there is no audible compression or distortion. At higher levels the sound becomes a bit congested, but I am not sure if this is caused by the room, the speaker or even my own hearing. This is sufficiently loud for me. I have not yet done any distortion measurements.
- Digital crossovers and equalization. Crossover frequencies are 300 Hz and 2000 Hz, both at 48 dB/oct."

DIPOL+ - 1/17/11
"Diese Seiten sollen keine Bauanleitung für Offene Schallwände sein, sondern Hilfe zur Selbsthilfe geben. Ich versuche, die wichtigsten Grundlagen einigermaßen verständlich zu erläutern und verweise für exaktere Herleitungen und Hintergründe auf die einschlägigen Quellen im Netz." (Rudolf Finke) 
3/28/14 - Download Dipol_Schallwand.pdf or Open_Baffle_Dipoles.pdf for descriptions and results from many dipole experiments. (SL)

6.283 Audio Pages - 4/1/10
"Aristoteles and Platon are reference designs for me from which other projects will evolve."

Monte Kay - 3/19/10
"- Envision a dipole with an acoustic black hole behind it, completely eliminating the rear wave, leaving only the front, frequency invariant lobe.  This best describes my directivity goal.  I utilize open baffle dipole and cardioids as tools to eliminate off axis radiation as a partial means of achieving this.  This design objective requires significant absorption behind the speaker to approximate the acoustic black hole.
- The “CBT” (Constant Beam width Transducer) as described by D. B. Keele has proven to be an effective means of achieving this goal.  My home theatre center speaker combines CBT technology with open baffle cardioids.  This focuses the rear wave at the center point of the CBT arc making it very easy to know where to put the absorption.  Along with the proper absorption, the open baffle CBT very effectively accomplishes my stated objective. 
- Keele and Horbach’s Linear Phase Symmetric Pair approach also accomplishes my objective but with other limitations.  The large surface area in the sum of numerous drivers in the CBT solves other problems not related to directivity making it a much higher performance design over the Symmetric Pairs.  As this is a discussion of directivity objectives, the other advantages are for another discussion."

John K - 3/14/10
When designing a speaker system for home use the objectives of any particular design will depend on the specifics of the application and acceptable trade offs. As such it is difficult to state categorically any specific set of design objectives for a CD speaker. With regard to constant directivity, my current interpretation would be that a CD speaker, intended for use in home environment, should have the ultimate goal of maintaining uniform polar response above the Schroeder frequency. As a rule of thumb, this translates to maintaining uniform polar response form about 100 Hz and above. Specific design objectives for my designs may be found at my website."

cuibono - 3/8/10
"The primary objective is to develop an acoustically transparent loudspeaker that is involving, enjoyable and as life-like as possible.  This means addressing primarily linear distortion issues at all angles of radiation, and secondarily nonlinear distortion issues as they relate to maximum output levels.  This was obtained via the following goals:
1)  To be a full range dipole system.  In this case it is about 30Hz to 17kHz (F-6).
2)  To have as regular a dipole response as possible, defined as -1dB at 30°, -3dB at 45°, and -6dB at 60° relative to the driver's axis.  This design goal takes special attention above 1kHz, due to the midrange driver's basket structure, and the tweeters acoustically large size relative to the frequencies it is producing.  One compromise here is a limitation of output SPL from the midrange.  See post #35 in the Violet DSP thread for final polar measurements.
3)  To be as low cost as possible.  In this case, the total driver cost is about $400usd.
4)  To be have enough output SPL to play music at live levels, while keeping nonlinear distortion below an audible level.
(cuibono = Patrick Fleck)"

MOB3W (my open baffle 3-way) - 3/6/10  
"- Constant radiation up to at least 3kHz
- Symmetrical radiation across the entire spectrum
- Sufficient dynamic range down to at least 40Hz.
- Low distortion
I have made several baffles to test what happens with a midrange woofer on a baffle. I found that for true amplitude and phase symmetry, I had to sink the driver in the baffle. Each midrange has at the backside a construction directly behind the surround that has to be copied at the front. In addition, the slimmer the baffle, the more the radiation remains constant. This way the radiation of the AL130, the midrange in MOB3W, is made constant and symmetrical up to 2kHz. To obtain a radiation that is symmetrical and as much as possible constant for the tweeter, and close to figure-8 at least up to 3kHz, I designed the specific baffle of MOB3W. The AMT2340 tweeter 'sees' as little baffle as possible. It has ridiculously low distortion, not at all like the ESS AMT tweeters and the Eton ER4."

Gainphile - 3/4/10
"Affordable lifelike reproduction of music. It is possible to build full-range dipole loudspeakers with lifelike reproduction capability at relatively low cost. The speakers are built under $500 and well under $1000 as complete systems including active 4-way analog crossovers and 8-channel amplifications. There is clear benefit on the accuracy of the drive signals by using active system. Measurable  transducer distortions and maximum SPL output are tradeoffs with such budget, yet the loudspeakers are uncolored and loud enough to provide listeners with enjoyable presentation."

StigErik - 3/4/10
"True dipole operation over the entire frequency range. Operate all drivers below dipole peak to get better directivity. Decoupled drivers and/or baffles for reduced cabinet and/or baffle vibrations. Active XO and EQ. Choose drivers with good dynamic behavior and low distortion. Use multiple drivers to keep cone excursions far below Xmax. XO the midrange above 300 Hz so its less affected by the typical floor bounce suck-out. I'd like add that my listening room preferences and setup in the room differs somewhat from what is common. I have a LEDE room which kills most of the rear radiation from the dipoles (above 200 Hz). I also like to listen in the near-field - my current listening distance is just 1.8 meters (it should be rather obvious that I dont prefer to have early room reflections....) I also like to position the speakers at 45 degree angle instead of the usual 30 degrees."


Commercial designs

Mellow Acoustics, UK - 3/2/16

Hello Siegfried, 

I have also been working to overcome the limitations of the ESL63 but in a different way. One of the most serious limitations is the sheer size and neither my wife nor I want room dividers! The advantage of using a smaller diaphragm is that the rings and centre disk are smaller, so there is less beaming at high frequencies, giving a more open sound. For bass, I am just using a dynamic woofer in a sealed box. I know it is not a dipole, but it still sounds well integrated with the electrostatic unit and has the advantage of small size. They aren’t the loudest speakers in the universe, but 98dB SPL at 1m (from the electrostatic unit) is good enough for me.

Best, Tim


aaninen - 12/14/15
A Finnish manufacturer of a dipole loudspeaker. Also discussed here.

Gerhard Meier, RoomAudio & BASSGUN, Germany - 9/25/15

Two drivers with opposite polarities are mounted in back-to-back sealed enclosures. Reduced rear radiation of the driver combination is obtained from passively lowpass filtering the rear driver.

Design details.


Dutch & Dutch - 2/23/15

A fullrange, cardioid-like horizontal polar response from 100 Hz to 20 kHz is obtained from a slotted acoustic resistance box behind a 18" midrange driver and a forward radiating constant directivity waveguide with a 1" compression driver. 

The 35 Hz to 150 Hz subwoofer box uses a 18" driver in a vented enclosure and a 15" driver in a rear enclosure to cancel rear radiation.

The on-axis frequency response is controlled via DSP.

facebook page of Dutch & Dutch

MURAUDIO - 11/17/14
Omni directional electrostatic above 450 Hz, becoming acoustically large at higher frequencies. Sealed omni woofers below 450 Hz.

amphion - 11/8/14
Krypton 4 - Cardioid with monopole woofer


Planot Speaker - 11/5/11
A cylindrical radiator with supposedly an omni-directional radiation pattern horizontally. A radically new driver design.

KEF Blade  - 5/25/11
An elevated acoustic point source that smoothly transitions to a forward radiating source with the same acoustic center at higher frequencies

Synergy Horns and Tapped Horns

Benk Cube  
Overhead loudspeaker with 360 degree horizontal dispersion of sound for PA applications

Uniform-directivity loudspeakers using horns.

From some time ago  
A variety of significant speaker designs collected by Roger Russel of McIntosh Loudspeaker fame. 

Theory and technology behind small, single driver omnis. 

A single box stereo loudspeaker with identical drivers on left and right sides and a single, mono tweeter on top. The L and R drivers on the sides are coupled via the internal air volume, which is a spring at low frequencies and becomes a transmission line for distances >
l/8 between the drivers. This causes dipole effects with peaks and dips at various angles. It is claimed that the brain handles such radiation favorably.

Grimm AUDIO  
A wide baffle 2-way loudspeaker with an IIR crossover, which imposes exact LR4 acoustic slopes crossing at 1550Hz. The phase is subsequently corrected using an idealized inverted all-pass filter, resulting in a maximally linear phase response without any pre-echo’s.

musicelectronic geithain gmbh - MEG
RL 901K studio monitor with cardioid response in the bass region. No detail is revealed in a news interview how the two 30 Hz to 300 Hz flow-resistors have been constructed and actively equalized.

Georg Neumann, GmbH  
Directivity smoothly increasing from omni to a  +/-30 degree beam, forward horizontally

Dipole and boundary woofer


Aether Audio  
Omni and low edge diffraction tweeter with low xo frequency 

Amphion Loudspeakers
Omni-cardioid-waveguide tweeter

Rountree acoustics  
Omni and forward radiating ribbon tweeter

Dipole except for tweeter

Perfect 8  
Line dipole with ribbon tweeter

Helsinki - cardioid with dipole woofer
EVIDENCE - cardioid with monopole woofer - 11/8/14

BeoLab 5  
Omni at low frequencies and horizontal dispersion lens for highs

mbl 101



Omni horn

RAAL requisite
Ring radiator

morrison audio

Geddes Loudspeakers 
Omni at low frequencies, transitioning to narrow and constant directivity at highs

Danley Sound Labs
Innovative Synergy Horns with high directivity for PA applications






What you hear is not the air pressure variation in itself 
but what has drawn your attention
in the streams of superimposed air pressure variations 
at your eardrums

An acoustic event has dimensions of Time, Tone, Loudness and Space
Have they been recorded and rendered sensibly?

Last revised: 02/15/2023   -  © 1999-2019 LINKWITZ LAB, All Rights Reserved