Build your last loudspeakers yourself or let us build them for you

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.

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

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.

Constant beam-width transducer (Keele)

JBL Pro LSR6332

Genelec 8260A

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.

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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
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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)

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
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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

DANLEY SOUND LABS - 1/7/11
Synergy Horns and Tapped Horns

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

pSpeakers  
Uniform-directivity loudspeakers using horns.

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

TIMEDOMAIN  
Theory and technology behind small, single driver omnis. 

Stereolith  
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

Steinway-Lyngdorf  
Dipole and boundary woofer

Philips  
Omni

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

jamo  
Dipole except for tweeter

Perfect 8  
Line dipole with ribbon tweeter

Gradient 
Helsinki - cardioid with dipole woofer

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

mbl 101
Omni 

GERMAN PHYSIKS
Omni 

WOLCOTT AUDIO  
Omni

Duevel  
Omni horn

RAAL requisite
Ring radiator

morrison audio
Omni 

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

 

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