[Duke]

At RMAF (room 1102) I will be introducing my latest bipolar-type speaker, the Strato Prism.   It's sort of a cross between the Cloud Chaser and the Rhythm Prism: 



What you don't see in the photo is the side-firing woofer and horn.   A combination of geometry and aggressive radiation pattern control relegates the side array's output to the reverberant field, where it significantly increases the amount of reverberant energy that arrives from the sides.  This is the most beneficial direction, according to Floyd Toole and the body of research cited in his book. 

A nice side effect (bad pun intended) is that the Strato Prism can be placed much closer to the wall behind it than my more conventional bipoles.

Since the angle between the toed-in front array and the side array is "twisted" by about 45 degrees (they are 135 degrees apart instead of 180 degrees), I'm calling it a "twisted bipole".   

The result is dipole-like spaciousness and openness along with horn-like dynamics and impact, in a more room-placement-friendly (and narrower footprint) package than my previous bipoles.  Note that my waveguide speakers and my waveguide-style horn speakers (like this one) have consistently won over people who "hate horns", and the Strato Prism likewise has negligible horn signature.

The twisted bipole format will not replace my other bipoles; rather, it expands the number of room situations that can benefit from a good bipole. 

The concept actually goes back to about 1990, when I was a DIY guy.  I did some experiments with several different geometries and the side-firing array sounded the best, provided I observed certain guidelines.  Unfortunately I didn't know anything about radiation pattern control, so the results were mixed.  I actually submitted an article on the design to Speaker Builder magazine, but it was rejected.

Then recently I read Toole's book in which he claimed that reflections arriving from the sides were particularly beneficial.  Well I dusted off my old concept and embarked on a new round of experimenting, and in a simple blind test the basic configuration of the Strato Prism did quite well.   

Note that I am not the first to use side-firing drivers.  I was preceeded by DCM (the Time Window), Acoustic Research (the Magic speaker), ESP (all of their models, I think), and last but not least, Audience (most of their innovative ClairAudient line, though the normal recommended setup is with the second array rear-firing instead of side-firing).   I think I am the first to combine all of the following elements in one speaker:  Aggressive radiation pattern control; 45-degree toe-in of front drivers; second array fires to the side, thus selectively enhancing side-arriving reverberant energy; and vertical offset of drivers, in particular the woofers, to help smoothe the in-room bass.

Since the Strato Prisms can be placed much closer to the wall behind them than my other bipoles, greater adjustability in the bass region is called for.  On the upper rear of the enclosure are two ports, a long one and a short one, and port plugs are provided.   If you aren't getting much boundary reinforcement, leave both ports open.  If you are getting some boundary reinforcement, plug the long port.  If you're getting a lot, plug the short port.  If you are getting a lot PLUS using a low damping factor tube amp, plug 'em both.  The port lengths can also be adjusted.  The locations of the twin ports and two woofers are staggered in all three dimensions, so that the in-room bass sources are each a different distance from the room boundaries.   And like my previous models, the treble can be adjusted by changing a high-quality resistor in a cup on the back of the speaker.

I'm fairly excited about this speaker; I think it challenges my top-of-the-line models for half the price, and in a more placement-friendly package.  And, I think it looks more interesting than most big boxes - not an area where my speakers historically do well.

Preliminary specs:

System Type:  Twisted bipole
Bass system:  Ported, adjustable tuning, gentle roll-off.
Impedance:  16 ohms, tube-friendly
Efficiency:  95 dB/1 watt; 2.83 volt sensitivity = 92 dB.
Thermal compression:  Less than 1 dB at 100 watts (115 dB)
Typical bandwidth, solid state amp:  Mid 30's to 18 kHz
Typical bandwidth, low damping factor tube amp:  Low 30's to 18 kHz
Dimensions:  44" tall by 15" wide by 22" deep
Weight:  175 pounds
Price:  $5,800 plus shipping in walnut veneer (pictured), direct sales only

Woodwork by Swainston Mill & Cabinet of Preston, Idaho.

Thanks for taking a look. 

Duke

[tesseract]

That is so cool, Duke. I have been following your circle for a few months now, and admiring what I see. I read that you were ready to unveil an newer speaker, and something inside of me said.... "bipole Prism". Honestly, I do not know why, it is very odd.   

I think it is great that you bring in a new speaker at the lower end that challenges your upper echelon. This shows you are serious about moving forward. And to do it with an older idea, to give that idea another go-around, that has to be very satisfying for you.

Best wishes, Duke. I'll be keeping an eye on AudioKinesis.

[Will2]

This is an interesting and fun idea Duke - thanks for bringing it to the table.  How would you suggest one thinks about palcement from side walls with this speaker?  Don't feel you have to respond to this before RMAF - I know you must be run off your feet.

Cheers
Will

[pbrstreetgang]

How much of a step up from the regular prism is this?

[Duke]

That is so cool, Duke. I have been following your circle for a few months now, and admiring what I see. I read that you were ready to unveil an newer speaker, and something inside of me said.... "bipole Prism". Honestly, I do not know why, it is very odd.   

Very cool... did that something inside also say "take out your checkbook"??

;^)

This is an interesting and fun idea Duke - thanks for bringing it to the table.  How would you suggest one thinks about palcement from side walls with this speaker?

Thanks, Will!

I haven't figured out the minimum and recommended sidewall distances yet; will experiment at the show (I only have a "real" sidewall on one side at home). 

How much of a step up from the regular prism is this?

I haven't had them side-by-side yet, but the effect of good reverberant energy is to make the timbre of instruments sound richer.   The regular Rhythm Prism is the more room-adaptable of the two.

Gotta go pack for the show now.

[tesseract]

Very cool... did that something inside also say "take out your checkbook"??

;^)

Ha, I have been thinking about your regular Prisms, maybe someday...

Have a great showing at RMAF.

[gsm18439]

How close to the rear wall is practical?

Thanks

[Duke]

How close to the rear wall is practical?

The main consideration is, how much boundary reinforcement you're getting (the adjustable port tuning helps with excess boundary reinforcement, and in the extreme you can plug both ports and have a low-Q sealed box).  As long as you're not getting too much bass, you can get within a few inches of the rear wall.  That being said, image depth is improved by having the speakers out a few feet.

Distance from the sidewall is more of an issue.  I would recommend about four feet or so, and more is better if possible.   But with the twisted bipole, proximity to the sidewalls is still more forgiving than proximity to the rear wall is with a conventional bipole.