[Roger A. Modjeski]

Fellow Open Baffllers,

Below is a graph of the Visaton B-200 on Richard's open baffle. We measured it together using the same tone burst techniques that were used at Beveridge on the legendary model 2 SW cylindrical sound electrostats). Bev (Harold Beveridge) was a great fan of tone burst testing and so am I. With a burst you can see the startup at any frequency and the ringing that follows the cutoff of the burst. When I see 2 cycles go into the speaker and 4 come out, I have to wonder what’s going on. The worst speaker I ever tested for this problem was the 4 way KLH electrostat that came out around 1978. It’s crossover was 4 tuned resonant circuits in series. They though it was clever, and it was, until you saw the effect of the resonant elements. That speaker put out 4-5 cycles with only 2 cycles in over the whole audio band. Needless to say, nobody is hunting those speakers these days and their production life was very short lived. I wonder what their test methods were? Surely a large company like KLH has some good facilities.

Another benefit of tone burst testing is that the room goes away because you just ignore anything past 2 milliseconds (that’s anything within 2 feet of the driver. The floor is the first thing to come into play as the speaker is only 3 feet (3 mS) above it. I find tone burst testing to be more enlightening than MLSSA and other computer tests. I've heard a number of speakers designed by computer testing and find all of them to be unmusical. I fear the designer is tweaking to satisfy the computer. I don’t think a flat FFT makes a good sounding speaker, not at all. There are too many other variables.

The graph below is a first run and Richard and I have not moved the mic around to check the response off axis or to see how distance affects the response. It was done at 1 meter on axis, just as a starting point. I was so intent on explaining the procedure to Richard that I forgot to confirm the sensitivity of the speaker. That will be given in our next test.  What the curve does confirm is that there is a rising high end going up to 8 KHz before the fall. I find it most remarkable that a speaker without a whizzer cone could produce such good highs.  This performance along with the high rated sensitivity of the speaker has certainly gotten my attention.

We can also see from the graph that the output falls rapidly after 300 Hz., confirming what I heard in my living room the first time we played the speaker (read the beginning of this thread for Richards report on the activities of that day). That day we only pushed the crossover up to 200 Hz. With a pair of my subs I will try going to 300 Hz and see if the blending is favorable.  

Some notes on the graph: I put 0 dB at1250 Hz because there was a flat area between 1250 and 3150 (the longest one, almost 2 octaves) and not much rise (5dB from there to 8KHz.). The data points are the standard 1/3 octave numbers used in this industry for many years. I always look for anomalies between data points as my oscillator is continuously variable. I was happy to see there were no severe ones. This is rare. Most speakers have some little peak or dip that gives them their signature. A peak is much worse than a dip because we hear it like a bell ringing. A tight dip just means we miss a little and that is not nearly as noticeable.. Think about it for a moment, I have not seen this discussed before and I find it a most important point.

I am still a bit perplexed about the peak from 300-450 Hz. and the 8 dB dip at 630 Hz. There is a 0.5 ohm rise in the impedance at 450 Hz which may explain the acoustic rise in that area.  The impedance rise implies that the driver is loaded less in that region. Anyone have any ideas about that?

At these lower frequencies the room does start coming into the measurements. Richard and I plan to do another run of tone burst testing in a week or so.  We had to take a break and I have been busy in the interim finishing the prototype of the lower cost 245 amp, which I have promised Richard a first listen on his B-200’s.

Roger

Ps. The RM-10 just got a nice review in 6 Moons Audio. Locals can join us for the Champagne.

[JoshK]

Why would you want a rise in the response up towards 8khz?

The 0.5ohm rise at around 450hz...could it be surround resonance?

I have seen tone burst measurements done quite a bit with distortion measurements with the spectrum ultimately displayed, not the response.

I think the polar response would be an interesting chart to observe with this driver.

[Roger A. Modjeski]

Josh,

The treble rise satisfies the current desire for brightness, especially in the younger generation. Seems every young listener I know always has the treble up.

Better too bright than not enough. We can always cut the treble. Most amplifiers, cables  and resulting systems have some treble loss, often several dB by the time the signal gets to the speaker.

roger

[-Richard-]

For anyone interested in Srajan's interesting first exposition into
Roger's RM 10 Mk 2, soon-to-be-fully-developed review...here is the link...

http://www.6moons.com/audioreviews/musicreference/rm10.html

We should all note that Srajan liberally quotes from Roger's posts here
on this AC thread...as if we needed proof that our thoughts and ideas
are being carefully read all over the world by intelligent and passionate
audio enthusiasts as well as intelligent and passionate reviewers...

Roger's quotes from AC helps put meat on the bone for Srajan's first foray
into Roger's audio persona...

It gives the reader a sense of who Roger is, his philosophy behind
his innovative circuit designs and some of the science Roger uses that informs
his circuit design decisions...

Really nice...

I am very very excited about Roger's new lower cost version of his 45 SET
amp...which he is developing at this moment...

And of course our work together in measuring and testing the B200's in OB
is due for another session very soon...

Warm Regards -Richard-

[audiojerry]

Thank you Roger, and thank you Richard for maintaining this high quality and entertaining thread. Please keep us informed

[JoshK]

Josh,

The treble rise satisfies the current desire for brightness, especially in the younger generation. Seems every young listener I know always has the treble up.

Well I am from a younger generation than most audiophiles and I am certainly not in that camp.  I am more in the fletcher munson camp.  

I think the problem with half of the audiophile speakers is that they have way too much upper midrange relative to every thing else to give an exaggerated presense, too much midbass and no real bass to speak of.

[J North]

B200 tests from a German site:

http://www.hifi-selbstbau.de/text.php?id=90&s=read



Adding some "meat" to the B200's in OB (doubling them up):

http://www.diyaudio.com/forums/showthread.php?postid=811094#post811094

[Roger A. Modjeski]

Josh,

The treble rise satisfies the current desire for brightness, especially in the younger generation. Seems every young listener I know always has the treble up.

Well I am from a younger generation than most audiophiles and I am certainly not in that camp.  I am more in the fletcher munson camp.  

I think the problem with half of the audiophile speakers is that they have way too much upper midrange relative to every thing else to give an exaggerated presense, too much midbass and no real bass to speak of.

What do you do in the fletcher-munson camp? I'm really not clear on what you are saying.

[Russell Dawkins]

Louis of Omega says he damps the cast frame of the driver to "reduce peakiness in the critical midrange" I wonder if this has any relation to the peaks and dips observed between 300 and 600Hz. I also notice, on the German measurements, what appears to be remarkably similar frequencies for the dip at around 600Hz and the rest of the data, too, allowing for different measurement conditions - looks like the equivalent of an infinite baffle was used.

[JLM]

In the last 20 years the pendulum has swung from fat, bloated 60 Hz bass to lean, weak bass.

Along the whole way marketing types have pushed the "need" for 20 - 20,000 Hz performance (so we "have" to buy bigger, more expensive, more complicated speakers).

The advantage I see from the graph is in using the B200 in open baffle, so that the non-directional bass notes double up as they radiate from both front and back.

Open baffles just don't produce much bass/mid-bass without EQ.

[-Richard-]

Hi Josh K,

At this moment in time, the B200's used in an Open Baffle design is still in
an experimental stage...

It is in the spirit of investigation and experimentation that Roger is taking
measurements of how the B200 perform under actual room conditions...
given the parameters of my Baffles...to create a ground for considering
an approach for integrating a subwoofer seamlessly into the sonic gestalt...

You should be able to fine tune this approach yourself...if you are adventurous...
to align with your musical tastes and preferences...

Anyone who takes the time to read The Gravity Well of a Dark Star started
by the inimitable DMason...still active in the Red Wine Audio forum...will find a
plethora of insights and information about ways of creating a very effective
baffle design with some kind of subwoofer integration...

The point of that thread (TGWofaDS)...and here I am paraphrasing DMason...
was to allow each of us that felt the lure of adventure, to create and fine
tune our own version of this unique speaker paradigm...which once heard...has
the power to change our ideas of how close we can actually come to creating
the sound of live music in our homes...it is nothing less than revelatory...

As far as I am concerned we are no longer talking about HiFi here...

And in the context of this thread, we are not talking about how "commercial"
speakers sound...here is a relatively new paradigm in sound reproduction
that you can create to fit your own personal sensibility...if you are willing to
experiment a bit yourself...

Or you can wait to see what Roger does with it...he is seriously considering the
possibility of creating his own version of the B200 in OB with his own subwoofer,
active crossover and dedicated amp, that would work with his new
SET 245 tube amps...perhaps as an organic self-contained audio entity...

But here we are getting a bit ahead of ourselves...I am quite impressed with
Roger's wish to make available the extremely time consuming results from
his own experiments with the B200's...it is nothing less than a gift, for all of us
who are taking this new speaker paradigm seriously...

Frankly, I am hoping that Roger decides to become a member of AudioCircle's
Manufactures Circle...he is a wonderful educator...he has done an enormous
amount of original research into the fundamental questions and problems that
surround audio reproduction...and as a resource for REAL INFORMATION
he has no peers...and...his new 245 tube SET amps are incredible sounding...
his new lower priced version should come in at less than $2000...and they
are a perfect match with the faster-than-hell B200's in OB...

The first time I took my OB's to Rogers house/laboratory for a listen with his
new 245 tube SET amp, he was sufficiently intrigued with the sound to pull out
the sub woofer he was using for his own electrostatic speakers (which he
designed himself) along with the dedicated amp and active crossover he was
using...to fine tune them to match seamlessly with my OB's...

The sound we all heard that day was astonishing...and it was that sound that
has peaked Roger's interest to delve more deeply into an even more finely
tuned application of his subwoofer module with the B200's...and hence the
work we are doing together to find out how the B200's react under various
test conditions...

Warm Regards -Richard-

[JoshK]

Hi Richard,

Sorry no powdery purple prose in my writing.    Don't read what I said/asked as dismissive, I asked geniunely, because that is what I do, I questions things.  This is my nature.  I also stated a bit of opinion, but it is a learned opinion and we each have our own.

Roger,
The Fletcher Munson reference was likely used back-asswards.  I was just trying to imply that I think the highs being slightly down from the mids being slightly down from the bass (with no midbass hump) is a sort of balance that feels more natural to me.

[skrivis]

Anyone who takes the time to read The Gravity Well of a Dark Star started by the inimical DMason...

I hope you meant inimitable.

[fabaudio]

Anyone who takes the time to read The Gravity Well of a Dark Star started by the inimical DMason...

I hope you meant inimitable.

I hope so too!!  

 inimical 1;being adverse often by reason of hostility or malevolence
             2 a: having the disposition of an enemy: HOSTILE
 ( Webster's Collegiate )

[-Richard-]

This brings up the vital question of whether god resides more in the conscious
mind or in the unconscious mind...

Or put another way...placing our modern ontologies aside for a moment
with their emphatic imbalance towards the scientific...can reality really be
reduced to the simplistic operation of a cause and effect principle?...

Yet put another way...can we be entirely certain that time only moves in one
direction?

Writing quickly has its disadvantages to be certain...and spelling is one of them...
still...the unconscious mind operates in a kind of parallel universe of sorts...
and has its own sense of humor...which I entirely acknowledge...

The word inimitable is what I meant and thought I had written...I was not certain of
the spelling so I asked my wife Deborah to spell it out for me...I typed it as she
spelled it and that is what came out...

JoshK...I was merely pointing out that you would be a perfect candidate for
a DIY OB project...given your apparent discontent with commercial speakers...
that is exactly the engine that drives all of us that have experimented with the
B200's in OB...a mixture of discontent with present offerings and an adventurous
inclination...

Warm Regards -Richard-

[JeffB]

I just ran an experiment with a subwoofer at home with a small pair of satellites.  The ideal crossover point would seemingly have been about 150Hz.  However this localized lower vocal notes to the subwoofer.  I ended up with 120Hz which kept the vocals out of the subwoofer but seemed to stress the little satellites a bit more.  It is possible that the potentiometer on the crossover lied to me about the true crossover point.  This makes me wonder how you will deal with the B200s rolling off at 200Hz.  Perhaps you need two subs in stereo?

[Occam]

Congrats to all on discovering these revolutionary dipoles.
Here are some pics of my 17yr old Alons with their dipole head unit.

Thats a 8 1/2" x 11" paper on top for scale. They cross passively to the dipole midrange @ 350hz. If your desire is to cross at around 200hz, you're going to need a baffle size of about 15" x 18" +-. Not particulary awkward to mount on top of a woofer.
FWIW

[-Richard-]

Hi Occam,

Your speakers are quite beautiful...and assuming the basic design principle
of form follows function the sound must be superb...I can only imagine that
your musical experiences are enhanced many times over by the aesthetics
of having such beautiful speakers creating your musical world...nice!!!!!

You know Occam, from personal experience, what is one of the best kept
secrets in audio...that OB speakers bring music to life in a way that must
be experienced in order to believe!

General subwoofer thoughts...

The entire implementation parameters of a using a subwoofer with the B200's
in Open Baffle is still an active inquiry...

My woofer thinking for the B200 in OB distillate in this fashion...

Keeping the "sub" woofer as a dipole would be best...to generate that
same incredible sound that the B200 does...so that they can perform in
concert with each other...a similar sonic/musical fabric...

However, Roger Modjeski used his own sub encased in wood (when I visited
him) that was curiously small...it was a simple wood box that wrapped around
his driver very tightly...the effect was that his woofer unit was entirely discreet
looking...very easy on the eyes and simple to integrate in terms of space...
and they sounded incredible...suggesting that the B200's are easy to integrate
subs with...providing the subs are lightning fast and light...

We are not talking about Dinosaur feet crashing here...but a musical
sub that fleshes out the lower frequencies with a nimble and seamless
transparency...

Roger used only one sub...but two might perform better...especially in dipole...
they can easily be placed on the bottom of the OB panels for example
beneath the B200's...perhaps serve as the panels support/foot...

I am thinking of using an active crossover...perhaps a Rane unit...it would be
easy to dial the crossover point to the amp...in my case a low watt SET tube
amp (I am hoping Roger will build me one of his lower priced 245 SET's soon)
then send the lower frequencies to a plate amplifier that is dedicated to the woofer...

That will take any stress off the SET amp and the B200's...so that they are relieved
from having to generate those lower frequencies...keeping their range of
performance optimal...comfortable and linear...

The other issue we must all address is the relatively high crossover point that
the B200 need...perhaps as high as 200 to 300 Hz...please see the initial frequency
curve Roger and I did with my B200's on page 9...

Any plate amplifier one should consider would ideally allow for this fairly high
cross-over point...have its own volume control...and phase control if one wishes
the sub to be independent  of the OB panels...

Roger seems to be moving toward a finite understanding of how the B200's respond
under differing conditions...this would allow him to design an OB and sub around
the B200 using his own 245 Tube SET amps to perfection...

However, this open-ended exploration allows for a great deal of personal
experimentation...assuming one is willing to jump into it...an adventure that
delivers the sonic goods in spades...to say the least...

So let's keep in touch with each other and share information that we gather as
we go deeper into this...

Warm Regards -Richard-

[Occam]

Richard - Actually, it was Roger's frequency plots and discussion of a crossover in the 200-300hz range that prompted my post. And we're really talking woofers here as opposed to subwoofs. At that frequency we really need stereo woofers (or very, very steep crossovers) to avoid localization issues. I'm familiar with Linkwitz's arguments for dipole midrange panels extending down to 100hz due to phase consistency, but I've yet to see a compelling argument or data supporting our ability to detect such below 500hz. Regardless, moving that crossover frequency upwards makes life easier whether we forego dipoles for bass (as in my Alons) or extend the dipole presentation downwards via a H or W frame, alowing a more compact implementation.
Ideally we'd like to extend dipole implementation down as low as possible, but life is full of compromises. As you say, that crossover division at 200-300hz allows the use of low power amps ideal for our musical preferences without concern for issues of bass power and damping/control. And from my perspective, that crossover freqency also allows us to apply dsp/room correction as well as arbitrarily steep lowpass filters where it is most beneficial and easiest to apply. A rather socialist view of audio, to each according to their needs, from each according to their abilities.
FWIW

Edit - a point I failed to make is that if we accept that our primary dipole driver does not have to carry the frequency range below 200-300kz, our choice of driver is far wider. We are not constrained to a high Qts, low Fs driver. It is only when we expect that driver to handle frequencies approaching its free air resonnance that issues of Qts are of any great import. Similarly, because this driver is relieved of lower frequency production, we can now consider drivers with smaller diameters and potentially avoid beaming issues, as well as minimizing constraints regarding linear x-max. This is not to say that the B200 isn't still an excellent choice, but simply that our choices have widened considerably, and choices in the physical construction and SAF are far wider.

[lonewolfny42]

Found a few pictures on the web...Alon speakers...like the one's owned by Occam/Paul.

http://208.185.94.62/pics/speakers/Alon-1-02.jpg [/list:u]

http://208.185.94.62/pics/speakers/Alon-1-03.jpg [/list:u]

http://home.ptd.net/~pgunn/alon2a.jpg [/list:u]