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ORION++

From your Living Room to every Concert Hall

ORION+

I can hardly contain myself. I am so excited. I have unlocked the puzzle that PLUTO+ presented me with. Now, ORION has taken again its top position, but it took PLUTO+ to point the way.

When I compared PLUTO+ to ORION I was stunned by the sonic similarity between these very different speakers, when properly set up in my living room, even though one is a monopole over the 8 lower octaves and the other is a dipole over 7 of those octaves, out of a total of 10 octaves for the 20 Hz to 20 kHz frequency range. I felt almost embarrassed that so much less costly drivers could give such outstanding performance, when I had labored over testing and searching for the absolute best.  There even was something about human voice that made me question the correctness of the ORION in comparison to PLUTO+. Attempts to change the equalization of ORION to make pink noise and voice sound more similar on the two speakers were complete failures. The only parameter that was left to investigate was the polar response. I had already concluded that it must have been the polar response that made PLUTO+ so similar to ORION in the first place. ORION is a dipole only to about 1.5 kHz. That is over an octave less in uniformity of polar response than PLUTO+ covers, and missing an important frequency range for voice. A rear mounted tweeter on ORION to extend the dipole range might fix that. Well, it did that and much more.

A second Seas Millennium tweeter is mounted on a separate, flat baffle in the rear of the existing tweeter. The added baffle was necessary to preserve a wide and uniform polar response for the tweeter. I had played with rear mounted tweeters when I first started out with dipoles but abandoned them. The rear tweeter does not contribute to the direct sound coming from the front of the speaker over a very wide angle of +/-60 degrees off-axis. This is due to the relatively wide baffle that I use for ORION. It is also an indication that there is little diffraction effect from this wide baffle and hence the good imaging. Thus under anechoic conditions, or outdoors, one would never hear the rear tweeter from any normal listening position. In a room, therefore, anything that is heard of the tweeter, is heard via reflections off walls and objects. Like many audiophiles, I considered that problematic, especially since the commercial box speakers that used such rear tweeters, and that I had listened to at the time, only sounded more fizzy.

Yet, when I listen to ORION with added rear tweeters, calling it ORION+, I can only say that I have never heard sound reproduced as realistically in its dimensions of space, frequency and time. Sure, it is only an illusion and it all happens between the ears, but the ease with which I fall for the illusion becomes obvious when I switch back to PLUTO+. There the imaging is pin point analytical left to right in an acoustic space that has less depth and height than ORION and which by comparison to ORION+ clearly takes some effort to construct in my mind from the cues given. Sort of a re-programming after having heard ORION+.

ORION+ transports me to the performance venue. I must close my eyes so that I do not get distracted by the glaring visual incongruence between the speakers and room in front of me and the visual acoustic space before me in my mind's eye. It seems so real and in 3D. The phantom size of sources changes with volume level setting and it is more of a distance control like before. But the physical size of my living room does not seem to bound the overall phantom size. Recordings sound louder and more natural in this context, but on some recordings I find myself to further increase the volume level because it sounds more realistic and the room is not becoming overloaded. This is unlike my experience with box speakers. Even massed strings that often sound unpleasant on multi-microphone commercial recordings take on a believable character. The perception of bass also seems to be affected. Most enjoyable are the clearly audible decays of sounds in the spaces between the notes, the subtleties of the musicians' expressions, the texture, the dynamics and plain energy of playing. 

If I sound excited, it's because I am. This is sound playback how it should have been all along. So what is going on when merely adding some rear tweeters can make such a remarkable audible difference at the listening position in front? 

My setup for critical listening It has served me well in the past. Therefore I have not changed speaker placement or toe-in. I do not know if it is optimum for ORION+, but the observations reported here were made with this setup. At some point in time I will investigate its parameter sensitivity. Note the complete reversal of the traditional "live end"- "dead end" layout used in some recording studios. I have nothing to add at this time to the trends that I described on the Room acoustics page, but it is interesting to compare them to a completely different loudspeaker placement described in a 1996 AES Convention Preprint by J. Gerhard, B. Theiss and M. O. Hawksford.

Is B higher or lower than A? See what the mind does!

Normally when listening at 15' (4.5 m) distance from the ORION in chair B the sound stage will have become broader, more diffuse and phantom imaging details are lost. With ORION+ it is like looking at a stage from increased distance. The actors on stage remain in their location and are still spatially bounded. What is lost is the sense of close proximity and envelopment that was experienced with closed eyes in chair A.  (Ariel Ramirez, Misa Criolla, with Jose Carreras on Philips CD 420 955-2) Phantom image creation is a process in the brain. The ESP (Ear Signal Processor) needs input data before the image can be formed. These data are delivered from different CD at different rate and are of different reliability. The ESP has to adapt to the stream. It is like being in a darkroom and watching a photograph come to light in the chemical bath.  Some changes are quickly recognized by the ESP, such as in timbre, where fast switching of input signals can be useful. But it is not easily fooled in the long-term, especially with spatial cues, because it has a few million years worth of experience data stored to compare to.

I find DSP that cancels loudspeaker cross-talk at the two ears impressive at first, but it becomes quickly 'phasey' and artificial. Headphone listening is artificial in spatial terms. DSP for ambience recovery from 2-channel recordings and with four additional speakers for playback lasted longer for me, but the speakers have now all been converted to PLUTO and are put to different use. None of my previous playback systems conveyed the sense of naturalness that the present ORION++ has. It differentiates recordings even more and mostly for the better. All this makes me wonder about the efficacy of room equalization. I think DSP is in for a fight with ESP and not just with physics.

The ORION with rear tweeter added has become quite symmetrical between front and rear polar responses and has reduced output to the sides. The woofer section is fully symmetrical, the midrange not quite, but reasonably smooth in off-axis response variation, and the tweeter with its own baffle introduces only a slight tilt in the vertical polar response because it is not properly phase aligned with the midrange in its crossover region. Thus the speaker radiates essentially the same on- and off-axis sound in the rear as it does in the front. The rear radiated sound is reflected, diffused, and slightly absorbed by the surfaces behind the speaker and the greater path length, before it returns to the front and to the listener. At lower frequencies some of the sound propagates directly around the baffle and interferes with the front sound to form the dipole polar response. But in the tweeter frequency range this effect is practically non-existent and what is heard by the listener is strictly surface reflected sound. 

The listener is presented with two sound pictures, F and R. The first arriving is F, the direct sound from the speaker's front and its room reflections. The later arriving R is the rear sound that is reflected predominantly from the area behind the speaker. This rear sound R has nearly the same spectral distribution from low to high frequencies as does F. But compared to the direct sound F the phase of R is highly de-correlated because of the path length being large compared to the radiated wavelength for higher frequencies. This effect is even increased because for a dipole the phase shift increases with increasing off-axis angle. Therefore R and F add on a power basis at the listener. F contains the phase and timing cues between left and right speakers to form the phantom image location. R is delayed by 12 ms in the above example. I have found in the past that speakers should be placed at least 3 feet from reflecting surfaces so that the delay is greater than 6 ms. This seems to insure that the reflection is no longer perceived as a property of the direct sound and coming from the speaker. While F and R add on a power basis and increase the perceived volume level in the short term of a few milliseconds, they are still correlated in the long term of reverberation and sound decay of the recording venue which is in the order of hundreds of milliseconds. Reverberation and sound decay give strong perceptual cues as to recording venue size and source distance. F appears to be essential to strengthen these cues in the sound field at the listener. The net result of R and F is a highly localized presentation of sources from left to right, in depth behind the speakers, and in vertical height of venue space. The sound field appears more energetic and capable of expressing a wider dynamic range without stress.

What probably has happened here is that the processor between the two ears has been presented with an auditory scene and with sound streams with which it can cope easily. It is like the familiar "cocktail party effect" of being able to tune into a different conversation while all go on at the same time. Different types of loudspeakers and setups create different auditory scenes in a room, some of which we are totally unfamiliar with from human evolution. For example, trying to generate with two loudspeakers the phantom image of a speaking person is a totally unnatural process and our brain needs help to decipher such unfamiliar auditory scene. Apparently the multiplicity of reflected sounds from the two sources, in addition to the direct sound, allows easier recognition of familiar cues provided that those reflections have specific directional properties.

The rear tweeter adds about 3 dB to the high frequency acoustic energy in the room. This gives sweetness and richness to strings, roundness to brass, vastness to applause, and texture to many sounds. It is not possible to obtain the same effect from playing with the frequency response of a forward firing tweeter, though I have often observed that really wide tweeter dispersion reduces harshness and sounds more realistic. PLUTO+ challenged me with its dispersion. I find it particularly interesting that the combined tweeter level had to be reduced only by about 1 dB after the rear tweeter had been added to the front tweeter for dipole action. The two drivers are wired in parallel and with opposite polarity. This increases combined acoustic power output of midrange and tweeters by less than 4/3 or 1.25 dB. Tweeter level adjustment is quite critical and will be room dependent but easily recognized when correct. The ORION tweeter level adjustment changes 0.5 dB between its tick marks.

It was determined by Don Barringer and confirmed shortly after by me, that reducing the rear tweeter level by about 3 dB, while leaving the front tweeter at its optimum ORION level, enhances the wall effect. We live 3000 miles apart and have very different listening spaces. Power and number wise the 3 dB reduction is identical to a 1.25 dB reduction of front and rear tweeter together. The attenuation was obtained by wiring a 2 ohm (5 W, 5%) resistor in series with the rear Millennium tweeter. The resulting 0.7 dB bathtub like frequency response of the rear tweeter might be advantageous.

Also, it is a widely held belief that reflections destroy transients and diffuse phantom images. Reflections must be avoided. Yet they are important for energy distribution in the room. This belief has been slowly changing (e.g. Moulton, Toole), but only for lateral reflections. The space behind the speakers has always been suspect for changing the sound unfavorably, and rightfully so. Almost all loudspeakers illuminate this space unevenly and sonically colored. I now also understand why flush mounted speakers sound off-the-wall to me. They completely lack rear wall reflections and thus important spatial cues.

One might postulate that the wall reflection will add a sameness to all sound playback because the listening room acoustics from reflections right close to the loudspeakers get mixed in heavily with the recorded acoustics. The exact opposite is heard. Recordings become more differentiated, the whole range from dead to wet acoustics is clearly perceived. Furthermore, what is perceived as "distortion" is more readily identified: analog tape compression (Cantate Domino, track 1, PRCD 7762), ringing of the hall (Star of Wonder, track 16, RR-21CD), or spectral discontinuity of phantom sources due to microphone mix (Soular Energy, The Ray Brown Trio, track 2, CCD-4268), etc. The rightness of a live recording really shines (Swing Live, Bucky Pizzarelli, track 7, JD218). The "Volume Control" should be relabeled as "Distance Control". I like it that I can slide quite a few rows closer to the orchestra merely with a button push on my remote volume control. It seems that the ringing of the listening room ultimately limits the maximally tolerable SPL and not necessarily the non-linear distortion of the loudspeaker.

When listening in a room and someone opens a door or window you hear outside sounds, different acoustic spaces. Their perceived character is not changed by having entered and mixed with your living room, though their physical properties are changed.   

What has happened here requires a shift in the prevalent thinking about sound reproduction in a home environment, about room treatment, speaker placement, its polar response, room equalization, etc.. More than ever, the recording becomes the limiting factor. The spatial artificiality in pan-potted studio recordings, or in live recordings with too many microphones, becomes immediately apparent, though that does not necessarily detract from their enjoyment. Should it turn out that front-to-rear symmetry with symmetrical nulls in the polar response, and the smallness of the acoustic source size have to be perfected, then it is easy to imagine baffle arrangements for midrange and tweeter that would achieve this, but which are different from the ORION+. They might lead to unsymmetrical vertical responses due to driver offsets. More to investigate, but not by me until I see a need for it. 

My prototype Wood Artistry's prototype of retrofit kit

Rear tweeter mounting The rear tweeter assembly consists of a baffle (11-3/8" x 6" x 3/8") which is held with two screws to two side supports (6" x 1-3/8" x 3/4"). The tweeter is mounted in the center of the baffle. The slight vertical misalignment (1/4") with the front tweeter should not matter, but the rear tweeter baffle should not be moved closer to the midrange. Four fine thread drywall screws (6 x 2-1/4") which pass through 4 predrilled holes in the side supports then tighten the assembly into the square corner pieces of the ORION. The form of the bracket follows its function and is the result of tests and thought, and will not cause a change to the side panels. It is an easy retrofit. The tweeter baffle can be 3/4" thick if the tweeter is flush mounted for aesthetic reasons. Then there is material to round all baffle sides. Concerns in this area deal with unimpeded air flow from the midrange and adequate baffle area for the tweeter. The ORION+ should sound right even when turned around 180 degrees. The on-off and polarity switches in the photo were for testing purposes only. Equal polarity with the front tweeter causes spatial imaging peculiarities. Turning the rear tweeter off and increasing the tweeter volume brings back the original ORION. I no longer need those switches. The rear tweeter is wired in parallel with the front tweeter, plus to minus and minus to plus. The amplifier sees a 2.5 ohm minimum load. This could be increased to >10 ohm by wiring the tweeters in series, but then the tweeter channel gain of the ASP must be increased by 5 dB. Alternatively, each tweeter could be driven from its own amplifier. Is it necessary to use the costly Seas Millennium tweeter? Maybe not. I will investigate, but do not hold your breath. You might miss out. The crossover frequency is low for polar response reasons and this puts great demands on the excursion capability of both drivers. Even more so now, as I like to play ORION+ at higher SPL than before. The Millennium does the job to my satisfaction, and amazement, and I plan to use identical drivers front and rear to minimize uncertainty.

Front and rear tweeters are wired in parallel. The rear tweeter output is attenuated about 3 dB by its series resistor R*. The value of R* is room dependent and in my and several other cases set to 2 ohm (5%, 5 W, wire-wound), but might fall into a range of 1 ohm to 3 ohm depending on your ORION+ setup. Change R* from 2 ohm in 0.5 ohm increments. Adjustment procedure First set the level of the front tweeter (rear tweeter disconnected) to its optimum value by adjusting the Tweeter level potentiometer on the ASP circuit board.  Optimize the toe-in of the ORION for your room setup. Connect the rear tweeter and determine the correct value for R* by listening to a wide variety of recordings. R* is not a "tone control" but a "room contribution" control. Recordings will vary in showing the "wall effect". Do not adjust R* to compensate for "poor" recordings. You should only adjust for accuracy of your loudspeaker/room system and not for personal preferences. Confirm the toe-in for the ORION+.  Fine tune the combined tweeter level with the ASP board potentiometer. These steps are iterative. They require extended listening periods for learning each time a change is made. Refrain from quick A-B comparisons. 1 dB is a lot of change when it affects almost 4 octaves. The conversion of my ORION in Sea Ranch ended up with the rear tweeter level 1.7 dB lower than the front tweeter and the ASP tweeter level adjustment set to 0.5 dB lower than it was for the front tweeter alone. Again, the remote volume control was now acting more like a distance control. For the production of commercial recordings there are a number of conventions and practices, but no standards other than that the sound in the end comes to you stored in two data channels. Recordings are still works of art and their qualities vary. The "wall effect" highlights that variability but not in a detrimental way. I have not heard a recording yet that did not benefit in some way. The playback accuracy enhancement is most easily heard on classical and live recordings that were done with few microphones. The effect helps to distinguish between natural and artificial sound space in a recording (a matter of consciousness, though). It helps with imaging and clarity. All sound exists in space, time and frequency.

Direction of cone movement for positive amplifier voltage

4/21/07  After extensive testing and extended listening it was found that the rear tweeter should be at the same output level as the front tweeter, provided that some slight, but highly critical, adjustments have been made to the ASP frequency response and tweeter level setting. For specific details see your ORION Owner Support page.  

ORION++

The second plus in ORION++ stands for the THOR subwoofers that I have been using on a permanent basis ever since I introduced the w-ASP and increased the crossover frequency to 50 Hz. I have not heard detrimental effects due to group delay and if anything the subwoofers reduce distortion from the ORION woofers. Now with ORION+ and my higher SPL desires I feel that the subwoofers justifiably have a place in my music playback system. 

In my system the two THOR subwoofers are driven from the four amplifier channels of the AT6012 which are not used by the ORION. Amplifiers cannot be "bridged" internally to the AT6012. Instead I take two of the amplifiers and drive them out-of-phase from their RCA inputs with signals provided by the ORION/THOR crossover/equalizer. A single Thor is connected between the hot (red) output binding posts of the two amplifiers. The two amplifiers appear to deliver enough power in this push-pull mode to Thor though each amplifier sees only half the load impedance. I have not noticed problems with my power demands for the ORION+ even when the AT6012 drives the low impedance of the tweeters in parallel at the same time. The only exception so far has been subwoofer amplifier channel clipping on the door slam of the 'Trucking and Welding Shop' track on my Sound Pictures demo CD. Consequently I switched to using an AT1802 power amplifier to drive the two subwoofers. But I have found that the vast majority of my listening is completely satisfied with the ORION+ bass output volume capability. So I rarely turn on the subwoofers. They remain immediately available when a visitor wants to hear their effectiveness for a particularly demanding piece of music. 

ORION was originally developed to minimize the influence of the room on the accuracy of sound reproduction and the creation of a believable auditory scene in your head. I had not understood to what degree the loudspeaker affects how we hear or not hear the room. Today I will say: the room is rarely the problem, but the loudspeakers and their setup determine the disappearance of the room from our attention. This discovery is extremely exciting and opens the door to a new level of realism in reproduced sound.

Enjoy!

PS

• You have seen Orion in the sky:
  Now see the Orion Nebula
  
• And for some deep humor:
  I could be the fourth mother in My God ....
  
• 2-channel sound reproduction is like Alice in Wonderland.

From the first reactions to this page I can see that people wonder how I can get so excited over an old hat trick like a rear tweeter. Yes, adding the rear tweeter to ORION does nice things, but that is only because of the walls! My excitement is over the wall! It can be your friend! It's the third element in sound reproduction and I have always been fighting it. For the first time I heard consciously what it can contribute and it makes sense to me. If you knew this all along, then I wonder why you kept it to yourself. This could be big! An inconvenient truth?

In October, 2007, I added a page to the Concepts collection with the title:

Room optimized stereophonic sound reproduction

It is based on my paper " Room reflections misunderstood?" that I gave at the 123rd AES Convention in New York. My working title, "It's the wall, stupid", would have been misleading. The rear tweeter ensures full spectrum characteristics to the reflections from all surfaces/objects and not just those from the wall behind the speakers. Measurements of reflections in my room show an abundance of reflections. Rather than being overwhelmed by reflections the ESP seems to use them to advantage. The "Precedence Effect" makes this plausible. The listening room can become cognitively disassociated from the acoustic scene that is presented by the playback of a recording. Certain conditions regarding the loudspeakers, their setup, and the room must be met.

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When you have read this page from the top down, you might have gotten a sense of the developments in understanding the rear tweeter integration and what is happening with it perceptually. My conclusions are explained more generally in the Convention paper. 

Abstract:
In a domestic living space a 2-channel monopolar and a dipolar loudspeaker system are compared for perceived differences in their reproduction of acoustic events. Both sound surprisingly similar and that is further enhanced by extending dipole behavior to frequencies above 1.4 kHz. The increased bandwidth of reflections is significant for spatial impression. Measured steady-state frequency response and measured reflection patterns differ for the two systems, while perceived sound reproduction is nearly identical in terms of timbre, phantom image placement and sound stage width. The perceived depth in the recording is greater for the dipole loudspeaker. Auditory pattern recognition and precedence effects appear to explain these observations. Implications upon the design of loudspeakers, room treatment and room equalization are discussed.

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Rear tweeter level adjustment

The rear tweeter is to be wired in parallel with the front tweeter in dipole polarity. This means that the (+) terminal of the front tweeter is connected to the (-) terminal of the rear tweeter and the (-) of the front tweeter is wired to the (+) terminal of the rear tweeter. The front tweeter is wired to its power amplifier. The tweeter level is adjusted on the ASP circuit board where each tick mark on the potentiometer represents a 0.5 dB change. The total range is +/-2.5 dB around the center position.

In most loudspeaker setup situations the optimum combined front and rear tweeter level is found by fine tuning the potentiometer. It is still surprising to me how significant a change in the sonic gestalt is perceived from a 0.5 dB adjustment in level. This is not observed in an instant A-B comparison but by extended listening. You will know subconsciously when the level is right, just as you know when there is something not quite right. Of course, you will need to use a variety of recordings and not rely on the one recording you always used as a reference. Stick with classical, live jazz, choral, female vocal, etc. Stay away from heavily processed studio recordings. With the correct setting, the sound should be natural and balanced, but not bright. The high frequencies become completely integrated with their midrange fundamentals and do not stand out unless that is the characteristic of the source or the recording. There is space and air to the highs. 

There are apparently setup situations, though, where the optimum tweeter level is difficult to find. In such cases the following procedure is suggested.

1. Disconnect the rear tweeter and adjust the front tweeter level optimally. This will become your reference setting on the ASP potentiometer. You can do this by simply removing one of the wires from either of the rear tweeter's terminals. IMPORTANT! Refer to #43 on the Orion support page if you are using crimp connectors on the tweeter terminals.
2. Using the Orion Test Signal disc on track 2 (1545 Hz), set the tweeter adjustment pot in the ASP for equal voltage across the  terminals of the midrange and tweeter drivers. Measuring directly at the speaker terminals will compensate for any variations in amplifier gain, and any signal loss in the speaker wires. 
3. Listen and check if you have arrived at the optimum setting by varying the level in 1 tick mark increments up or down. If you can pinpoint sound coming directly from the tweeter at the listening position, the tweeter level is set too high. 
4. Turn down the tweeter level (CCW) by two tick marks from the reference just found.
5. Connect the rear tweeter and listen to the system. Play the same recordings as previously used to set the front tweeter level. Note the high frequency balance. It should be very close to what you had with the front tweeter only, but with the obvious improvements in detail and spatial presentation that the Orion+ provides. If necessary, fine tune the ASP tweeter level controls one last time to reach the optimum setting (no more than 1 tick in either direction should be necessary.) 
6. If the high frequency balance becomes considerably brighter after connection of the rear tweeter, or if the treble sometimes takes on a "shouty" character, it may be helpful to add a small amount of series resistance to the rear tweeter. Insert the resistor between the (+) terminal of the front tweeter and the (-) terminal of the rear tweeter. A value between 1 and 2.5 ohms (5W) should suffice in most cases. Start with the lowest resistance available and increase to the next highest value until the best balance is achieved. If necessary, fine tune the ASP tweeter level controls one last time to reach the optimum setting. No more than 1 tick in either direction should be necessary. 

It may take some time to optimize your system but you will be greatly rewarded with credibility in what you are hearing spatially and in timbre.

CAUTION:

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