The Rhythm Prisms

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Duke

The Rhythm Prisms
« on: 4 Mar 2010, 04:28 am »
The small-room-friendly project I've mentioned elsewhere is now ready to be unveiled.  But my marketing department wants me to be sure and preface the unveiling by pointing out that the new AudioKinesis Rhythm Prisms actually DEFY THE LAWS OF PHYSICS!   (<- note impressive use of the caps-lock key)  That's right folks, they do the physically impossible:  They cram a 12" wide woofer onto the front baffle of a speaker that's only 11 inches wide!





The left channel speaker is the mirror-image of this one.

Their secret, of course, is that the angled front baffle is actually 13.5 inches across, so the 12" woofer (frame size = 12.3") fits easily as long as I don't try to flush-mount it.

The reason for the unorthodox geometry is this:  It allows the use of a large prosound woofer along with my recommended 45 degrees of toe-in without imposing an unduly wide footprint.  In constast, when toed in 45 degrees the Jazz Modules have a footprint a little over twice as wide.

The Rhythm Prisms have the following unusual features:

a)  Very good radiation pattern control (90 degrees in the horizontal plane from about 1.4 kHz on up), especially for a speaker only 11 inches wide.  The built-in toe-in avoids a strong early sidewall reflection and gives an unusually wide sweet spot (which I can explain if you'd like), and the relatively narrow vertical pattern of the waveguide horn (50 degrees) reduces the amount of early floor and ceiling bounce energy.   All of this works in favor of minimizing the undesirable very early reflections in a small room.

b)  Placement close to a wall, and even in a corner, is feasible.  A key factor here is the adjustability of the bass tuning system.  On the back of the enclosure are two ports, one at the top and one at the bottom.  These ports are offset to the inside, as the woofer cone is offset slightly to the outside.  When the speaker is placed close to room boundaries you seal off one of the ports because both of them would tune the enclosure too high.  This lowered tuning avoids bass boom and instead turns that boundary reinforcement into bass extension.  Embracing the principle of spreading out the low frequency sources in the room as much as is practical for the sake of smoothness, you can seal the lower port on one speaker and the upper port on the other.  Now there's significant staggering of your bass sources from the two speakers in all three dimensions.

c)  On the rear of the speaker is a single external resistor in a terminal cup, and this resistor acts as a tilt control for the compression driver.  It is bypassing a certain resistor in the crossover.  By changing the value of this resistor, the compression driver's output can be tilted up or down, which does a better job of adjusting for room acoustic conditions than an L-pad's shelving characteristic, and this single external resistor is much higher quality than all but very expensive custom L-pads.

d)  The drivers are high quality prosound units that have negligible thermal or mechanical compression in normal home use.  This preserves dynamic contrast, and thus preserves the emotion in the music because musicians often use dynamic contrast to convey emotion.

The Rhythm Prisms can easily be used in a medium or large room, and/or out away from the walls, in which case we'd leave both of the ports open.  The port lengths are also somewhat user-adjustable, allowing for further tailoring to a specific acoustic environment.  In a very large room, they would probably need subwoofer augmentation.

These are the speakers that, in prototype form, were judged in an informal blind listening test to be competitive with the more expensive Jazz Modules.  These are the speakers that killed my bipolar fullrange driver project, as for a few hundred dollars more the Rhythm Prisms offered a very significant improvement. 

One of the main goals of this project was to keep costs down, which meant that I didn't have the luxury of using bigbuck drivers that are easy to work with.  Instead I chose drivers that do what I want in the areas of dynamics and radiation pattern, and then designed a crossover that gets them to do what I want in the frequency response domain.  This required me to develop some new techniques (new to me anyway) in order to get satisfactory correlation between my measurements and what I was hearing.   I think I have preserved the dynamic capability of the drivers while achieving very competitive clarity and smoothness.  My marketing department still thinks I've defied the laws of physics (and I hate to burst their bubble).

Specifications:

Type:  Two-way controlled-pattern floor standing bass reflex system

Radiation pattern:  90 degrees in the horizontal plane from about 1.4 kHz on up

Impedance:  8 ohms nominal, tube-friendly

Efficiency:  93 dB/1 watt

Recommended amplifier power:  5 to 400 watts

Thermal compression:  Less than 1 dB at 50 watts (110 dB SPL)

Typical bandwidth, medium room:  45 Hz to 18 kHz

Typical bandwidth, small room:  35 Hz to 18 kHz

Dimensions:  44" tall by 11" wide; depth along long side = 20"

Estimated weight:  90 pounds

Pricing:  $2800.00 a pair, plus shipping

*  *  *  *

June 9, 2010 edit:  I wanted to post this photo on the front page of this thread.  This photo was taken by Albert Porter at the 2010 Lone Star Audio Fest in Dallas, and is used with his permission:



Thank you, Albert!

« Last Edit: 23 Jul 2011, 07:33 pm by Duke »

Russell Dawkins

Re: The Rhythm Prisms
« Reply #1 on: 4 Mar 2010, 04:57 am »
Congratulations, Duke!  :thumb:

This is a logical and attractive design. I like floorstanders for their efficient use of space (and the buyers' money!). The 45º angled baffle is the perfect solution for those who would rather have the backs of the speaker parallel to the wall.

High power handling coupled with high efficiency and an affordable price - what's not to like?

Oh, maybe the baffle being too narrow to flush mount the woofer. I think it would be the final touch for it to be grill cloth friendly for those difficult WAF situations.

Duke

Re: The Rhythm Prisms
« Reply #2 on: 4 Mar 2010, 05:29 am »
Thanks, Russell!

I think I could build grilles if someone really wanted 'em, but if WAF is a top priority I'm probably not going to be competitive anyway. 

A round metal "waffle" grille could also be installed to cover and protect the woofer.

Now in theory there's a sonic improvement to be had from flush-mounting the drivers.  I A/B'd flush-mounted and non-flush-mounted drivers in the design stage and couldn't hear a difference, so went with the configuration that allowed me to keep the price down and the footprint narrow.  I'm not saying that no one could detect a difference (no claim of golden ears on my part), but I don't believe it's a significant factor in this case. 

Let me say a bit about the drivers I'm using.  They are fairly new, and have good but not "boutique" quality motors.  The compression driver uses a polymer diaphragm and has very good articulation in my opinion.  The woofer has unusually long excursion for a driver that has the articulation and top-end extension this one does, which means that it will stay linear at higher sound pressure levels than most people will ever approach at home. 

I am using the same drivers in my MRL system, showcased in another thread.  The Rhythm Prisms have a better crossover than the original version of the MRL, so the MRL will get a crossover upgrade.

Duke
« Last Edit: 2 Oct 2010, 09:25 pm by Duke »

poseidonsvoice

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Re: The Rhythm Prisms
« Reply #3 on: 4 Mar 2010, 06:03 am »
Wow! Talk about, "Set it and Forget it."

Great work. There is definitely a market for controlled directivity loudspeakers that don't require multiple subs, when on a low budget, of course.

Anand.

Duke

Re: The Rhythm Prisms
« Reply #4 on: 4 Mar 2010, 08:35 am »
Hi Anand,

Thank you very much.

Yeah, while I believe wholeheartedly in the multisub concept, in practice it's a very tough sell.  That being said, at some point I'll try the Rhythm Prisms with a Swarm and see how the integration goes.  I suspect that placing the RPs out in the room but using only the top port will give the best integration.

One application I want to explore is home theater without a center channel.  I think the RPs would work quite well in phantom center mode, which might be quite attractive if one isn't using a screen that the center channel can be hidden behind. 

Duke





Duke

Re: The Rhythm Prisms
« Reply #5 on: 4 Mar 2010, 11:09 pm »
It occurred to me that I should probably include in this thread an explanation of why my speakers give such a wide sweet spot with that wierd 45 degree toe-in angle.

The ear determines the direction of a sound source using two mechanisms:  Arrival time and intensity.  With a normal setup (slight toe-in), when you move off to one side a bit the center image moves to that same side, but it moves farther than you did.  This is because the near speaker wins both arrival time and intensity.

With the Rhythm Prisms and their 45-degree crossfire configuration, for the off-centerline listener the near speaker naturally wins arrival time but the far speaker wins intensity.  This is because as you move off to one side, you're moving off-axis of the near speaker but on-axis of the far speaker, so it's actually louder.  Thus the two mechanisms tend to offset one another, and the central image remains near its original location.  This works better in some locations than in others (in other words it's not perfect), but it is a significant improvement over conventional speakers & setups.  At audio shows I often have listeners quite content to remain in a less-than-ideal off-centerline seat even when the coveted center seat becomes available because it sounds fine from over there (my other models have similar radiation patterns to the RP's in the horizontal plane).

Now there are two design elements that are crucial to this working out.  The first is, the off-axis output of the near speaker must fall off fairly rapidly in order for the farther speaker to be louder.  Second, the speaker's frequency response should fall off uniformly as we move off-axis so that the timbre doesn't change for off-centerline listeners, and indeed my speakers are very good at this.  The tonal balance will hold up well anywhere in the room, and even holds up through an open doorway into the next room.

This latter characteristic - the tonal balance holding up well even outside the room - is an indication that the spectral balance of the reverberant field is correct.  This is something unamplified voices and acoustic instruments do well, but relatively few speakers emulate.  I believe that when there's a significant discrepancy between the first-arrival sound and the reverberant energy the eventual result is listening fatigue.  This is because the ear/brain system is constantly analyzing incoming sounds to see whether or not they are reflections, and it does so by comparing them to "sound files" recently stored in short-term memory.  If it's a reflection, the ear ignores its directional cues.  If it's a new sound, the ear figures out where it's coming from.  The way the ear can tell whether or not a sound is new or old is by its spectral content, and it literally takes more CPU power to correctly classify a reverberant sound whose spectral match to the corresponding first-arrival sound is poor.  Over time, this extra CPU usage shows up as listening fatigue.

Since I'm in the habit of doing armchair analyses of loudspeakers by estimating their radiation patterns, I see a lot of correlation between radiation patten discontinuities and listening fatigue.  In particular, many speakers have a flare in the off-axis energy at the bottom end of the tweeter's range, ballpark 2.5 to 5 kHz, which happens to be right where the ear is most sensitive.  If the designer doesn't account for this (and make a compromise between on-axis smoothness and off-axis smoothness), such a speaker is likely to be fatiguing particulary in a small and/or highly reverberant room.

An additional (and more obvious) benefit to minimizing the spectral discrepancy between the direct and reverberant energy is more natural-sounding timbre.  The ear derives timbre from not only the first-arrival sound but also the reverberant energy.  In fact, in most listening situations the reverberant field conveys considerably more sound power to the ears than the first-arrival sound does.   

These are the types of things I try to take into account in my designs, because I believe they are audibly significant. 

Duke


JoshK

Re: The Rhythm Prisms
« Reply #6 on: 4 Mar 2010, 11:23 pm »
Fantastic idea!  Very clever indeed.  Reminds me of some of the old NHT towers.

I'd imagine they'd make awesome surrounds in a HT too!

Duke

Re: The Rhythm Prisms
« Reply #7 on: 5 Mar 2010, 12:18 am »
Thank you very much, Josh!

Good call on the NHT's.  Here's one of the models with the inward-angled front baffle:

http://www.blogcdn.com/hd.engadget.com/media/2009/02/20090224-nht_33.jpg

It looks to me like the NHT is using a much shallower angle, maybe 15 degrees or so, which probably had the effect of putting the listener on-axis.  So in that respect anyway, what I'm doing is different.  BUT as far as achieving the recommended toe-in without the speaker imposing a wide footprint, I'm obviously borrowing a page out of the NHT playbook, adapted to a Geddes-inspired radiation pattern setup.

Duke

timjthomas

Re: The Rhythm Prisms
« Reply #8 on: 5 Mar 2010, 12:38 am »
Hi Duke,

If this question is not appropriate, let me know.  Based on your explanation, it seems to me that a 45 degree toe in would make sense for just about any speaker.

Is that correct?

-Tim

gedlee

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Re: The Rhythm Prisms
« Reply #9 on: 5 Mar 2010, 01:50 am »
Hi Duke

A little too much "fluff" for my taste.  Different speakers for left and right don't seem like a good idea to me when the same speaker pointed in two different directions does the same thing.  They look fine, but I don't like the sharp edges of course.

Good luck however, and I hope you can bring the verbage back down to earth sometime.

zybar

Re: The Rhythm Prisms
« Reply #10 on: 5 Mar 2010, 02:04 am »
Hi Duke

A little too much "fluff" for my taste.  Different speakers for left and right don't seem like a good idea to me when the same speaker pointed in two different directions does the same thing.  They look fine, but I don't like the sharp edges of course.

Good luck however, and I hope you can bring the verbage back down to earth sometime.

Earl,

I know you are friends with Duke, but is your post really appropriate in Duke's thread where he is launching a new speaker?

If you think there is fluff or don't agree with something, send Duke and e-mail or PM.  Don't muck up his product thread.


Duke,

Best of luck with the new speaker.

George

dnewma04

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Re: The Rhythm Prisms
« Reply #11 on: 5 Mar 2010, 02:22 am »
I would say that the 45 degree toe in would make the most sense with a speaker with constant directivity.  Depending on the seating position, it could also make sense for a non CD system like a cone/dome speaker configuration or a ribbon.  What could become a problem is if you are listening to a speaker system without CD, you can get significantly different sound than on axis. 


drphoto

Re: The Rhythm Prisms
« Reply #12 on: 5 Mar 2010, 03:13 am »
 I like it. But I like offbeat looks. (I had a pair of norhs once) What's wrong the the idea of chirality?

 Seems like what I'm after, soundwise for a real world price. Count me as interested. I'm just glad to see designers addressing this issue of dynamics along w/ room interaction.

Duke

Re: The Rhythm Prisms
« Reply #13 on: 5 Mar 2010, 03:18 am »
Based on your explanation, it seems to me that a 45 degree toe in would make sense for just about any speaker.

Is that correct?

Hi Tim,

Well, not really.   In order for the off-centerline soundstaging and tonal balance to hold up well, you need for the off-axis response of the near speaker to fall off rather quickly and uniformly.  You can try it with other speakers, but I can't promise good results.

*  *  *  *
Hi Duke

A little too much "fluff" for my taste.  Different speakers for left and right don't seem like a good idea to me when the same speaker pointed in two different directions does the same thing.  They look fine, but I don't like the sharp edges of course.

Good luck however, and I hope you can bring the verbage back down to earth sometime.

Hi Earl,

Welcome, and thanks for stopping in. 

The purpose of using mirror-imaged speakers is to reduce the footprint width required to get that 45 degree toe-in.  As I've cruised the internet boards it seems to me that a lot of people with very small rooms (like 10' by 12') are looking for something that works well in their limited space, and most of them can't devote a lot of floor space to the speakers.  And at the same time, what a small room really needs is good radiation pattern control along with proper aiming of those patterns (which are things you taught me).   Hence I perceive an opportunity to bring good pattern control to the rooms that arguably need it the most.

So much for cutting back on the verbage!

*  *  *  *

Zybar, I appreciate your intentions.  Earl speaks his mind and if he bothered to wish me good luck, he meant that too.

*  *  *  *

dnewma04, in my opinion your analysis is correct, but to be precise it's a fairly narrow constant directivity that works best.  An omni system has constant directivity, and better than normal off-axis soundstaging, but I think the configuration I use (the essentials of which I learned from Earl) does a better job in this regard than an omni.

Brett

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Re: The Rhythm Prisms
« Reply #14 on: 5 Mar 2010, 05:17 am »
I've just seen this linked from another forum. Flippin awesome.

You just keep coming up with interesting designs. All the best with success for these.

Duke

Re: The Rhythm Prisms
« Reply #15 on: 5 Mar 2010, 07:03 am »
I like it. But I like offbeat looks. (I had a pair of norhs once) What's wrong the the idea of chirality?

 Seems like what I'm after, soundwise for a real world price. Count me as interested. I'm just glad to see designers addressing this issue of dynamics along w/ room interaction.

Thanks, drphoto!

I think that, subjectively, the RPs are especially competitive in the area of dynamics and liveliness (the kind that makes it hard for you to sit still).  Take this with a grain of salt of course considering who it's coming from, but I think that's what will stand out about them in comparison to other speakers in their price range.

*  *  *  * 

I've just seen this linked from another forum. Flippin awesome.

You just keep coming up with interesting designs. All the best with success for these.

Thank you, Brett.  I don't see much point in doing a "me too" design, as then I have to rely on marketing.  If nothing else I hope to make the marketplace a bit more interesting by putting some unorthodox alternatives out there.  In that sense, the Rhythm Prisms are probably as radical as I'm likely to get for a while.

*  *  *  *

My intention is to have "expensive, relatively few compromise" speakers at the upper end of my product line, and "more affordable, but inevitably more compromised" speakers at the lower end.  Instead of scaling by size, I'm scaling by parts and enclosure cost, so that my less expensive models (headed by the Rhythm Prisms) don't compromise on dynamics or radiation pattern control in the horizontal plane.  The Jazz Modules and Dream Makers and Planetariums are going to be a bit more refined, but then they should be considering their higher prices.

It's a juggling of tradeoffs, and if I was making the exact same tradeoff choices as someone else, what would be the point? 
« Last Edit: 11 Jun 2010, 01:08 am by Duke »

Paul W

Re: The Rhythm Prisms
« Reply #16 on: 5 Mar 2010, 02:57 pm »
Hey Duke,

You've scored another innovative design!  Keep up the good work!

(I like the fluff :)

Paul

EthanH

Re: The Rhythm Prisms
« Reply #17 on: 5 Mar 2010, 03:23 pm »
Very cool concept.  I would imagine that with the 12" driver the speakers would go down to 45hz with some authority (a two-way with a 12" woofer that extends to 50hz sounds very different from a 5" driver that extends to 50hz, in my experience), but would you say that the speakers sound full range in-room without a sub?  Just curious.

launche

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Re: The Rhythm Prisms
« Reply #18 on: 5 Mar 2010, 05:24 pm »
I've always liked your thought process and designs Duke.  I think your new direction will be welcomed.  In the past I felt many of your designs were a little too large and expensive (less accessible) for the average hobbyist.  But you as a designer appeared very down to earth, helpful and humble (more accessible).  Now to me it appears your philosophy, designs and character are coming together to reach an accessible point for more people to enjoy what you offer to the audio community. 

Hope that makes sense and good luck.

Abby356

Re: The Rhythm Prisms
« Reply #19 on: 5 Mar 2010, 05:54 pm »
Having had the pleasure of meeting Duke before I feel compelled to second what member "launche" just said. These seem like a very accessible speaker from a very accessible guy. All can say is that I sure hope these will make the trip to LSAF this year...pleeease...

Regards, Daniel.