[Brian Cheney]

I'll try to comment briefly on posts from ekovalsky and others about why VMPS is so darn peculiar in so many different ways.

If flat amplitude response is your primary concern, high order slopes and drivers alternately in inverted polarity is the way to go.  Response is considerably flatter in the crossover regions and there is less lobing with frequency.

I use first order networks and in-phase drivers because that emulates live music best.  I add "protection" filter poles outside the passband to protect the mid panels and treble ribbons from damage.  These legs are placed well away from the crossover point and have no sonic impact.  I can remove them and see no change in sound quality or measurements.  The only result of not having these "protection" parts is that the panels buzz and the tweeter diaphragm stretches without them.

We use pots because they allow a 1/20th of 1dB change in level to be effected by the user.  Often such a change is all that is needed to tame hot trebles or a forward midrange. A fixed value does not allow the user to adapt the music to his tastes.  Also, resistors are not made with sufficient tolerances to give me the precision I feel necessary for level changes.  Also, fixed parts change value with age and there's nothing you can do about that.  The pots change too, but all you have to do is move the wiper over one winding and you're back in business. Fixed values are invariably determined by measurement, i.e. whatever meassures flattest with your mic and test gear and environment.  However, bass below 200Hz is boundary-dependent; fixed values do not allow for changes in room or placement.  You're going to be wrong virtually 100% of the time, no matter what you think your measurements tell you is best.

Room correction is best effected passively, with bass traps in the corners and absorption behind and beside the speakers.  Digital correction and EQ are fine if you listen only at the mic position.  Since you are using a single mic and have two ears spaced about 8" apart, this may give strange results.

High order filters have poor transient response and ring like bells behind every note.  If you can handle that you are less sensitive to such garbage than I am.

The new NHT Xd system (digitally corrected 2way with sub) was measured in the exact same fashion before correction and I use, in the ultra-nearfield, one driver at a time.  In room measurements are worse than useless and mislead the audiophiles into making huge corrections that can be simply measurement artifacts like floor bounce and late arrivals.  I've been doing this nearly 30 years and have learned the hard way.  

The PR tuning must be done in very small increments.  While amplitude response changes little with tuning, harmonic distortion changes greatly.  I published curves right on this Forum last year, showing 10% THD at 20Hz on the RMX with the PR untuned and 1% THD with about half a gram of putty removed.  The sound becomes dramatically clearer and the bass response subjectively (emphasis here) somes up when the tuning is done properly.  I invented this bass system in 1979 and was highly gratified to see a Klipsch speaker adopt it a few years later.  Imitation and flattery, you know.

I make improvements as I see fit.  These upgrades are available at low cost or no cost to anyone interested.  I am very concerned that all VMPS owners have the best possible sound at home, since this keeps me in business.  I go to extraordinary lengths to make this happen.

My 58-year-old hearing is unlike yours, I'll wager.  I design and listen in an ideal acoustic enviroment (31' LEDE), yet with the adjustments provided, I can go into a completely untreated room like Corbin Johnson's and get near state-of-the-art sound  from modest equipment and a tight budget, by following the directions set forth in our flyers such as "User Adjustable Bass Damping".

In my book, textbook filter design, driver selection and layout, and measurement techniques are useless.

[meilankev]

Brian,

I just hate wimpy people like you who side-step the questions at hand and then pussy-foot around with your answers.     Just kidding!!!

This was one great post - it gives much insight into your philosophy of speaker-building and of providing long-term satisfaction for your customers.  And as always, you're not afraid to say what's on your mind.  

Wonderful stuff...

Kevin

[zybar]

While I don't agree with many things Brian stated.

I absolutely can respect a man of conviction and beliefs.

I wish Brian and VMPS the best.

George

[ekovalsky]

Thanks for the insightful post, Brian.

Many great speakers, including my current ones, use phase coherent first order designs.  It is demanding of drivers but does result in great sound when properly implemented -- Thiel, Vandersteen, Nola, Eggleston being some examples.

Maybe it was just my specimens, or perhaps I didn't understand what I see , but my two pairs of VMPS had simple first order slopes using a solitary inductor only on the low pass to the woofer ~200hz and low pass to the planars ~ 6khz.  The other filters, high pass to the mids ~200hz and tweeter ~6khz, looked like ordinary second order designs with a cap(s) shunted to the ground via an inductor.   Do you consider this to be a true phase coherent first order design across the full frequency range ?  

I agree that frequency response is not everything, and in-room measurements can be difficult to interpret.  However I have found that flatter response at/near the listening position produces a more natural sound.  Conversely, large measurable dips and peaks do result in audible colorations that distract from the music.

Passive room treatment is definitely helpful in addressing reflections and bass nodes but it absolutely cannot solve all acoustic problems in enclosed spaces.  Bass traps big enough to handle the primary nodes in my room would be gigantic and either very expensive (commercial units) or very ugly (DIY).  The TacT does a pretty darn good job and in my opinion is worth every penny.

And this is my opinion of DSP crossovers -- they must be avoided at all cost if good impulse response, coherent phase behavior , and flat frequency response are not desired.

[Brian Cheney]

You can achieve many desirable measurements with dsp.  I know this well, having exhibited a fully digitally corrected speaker at the 1992 CES.  In spite of sterling measurements in every regard, it was unlistenable and we took it down after 2 hours on display.

Why not move your mic 6 inches in any direction and see what happens to your "corrections".

The first owner of your speakers was so anxious to get rid of them he took an $86,000 loss.  And you will lose a good five figures when you "move on".  I just wonder whether this will be accompanied by snide comments from you on line about the design and execution of Alon products.

[Porcupine]

> And this is my opinion of DSP crossovers -- they must be avoided at all cost if good impulse response, coherent phase behavior , and flat frequency response are *not* desired.

?? I'm confused as to what you meant. Was that "not" intended, or a grammar error?

> However, bass below 200Hz is boundary-dependent; fixed values do not allow for changes in room or placement. You're going to be wrong virtually 100% of the time, no matter what you think your measurements tell you is best.

I've just totally given up on bass forever. I almost always listen to music with the bass knob on the receiver as low as it goes. It is always too hard for me to control my room and speaker placement, etc. And I'm not very fond of bass to begin with.

Maybe I'd love a 626R with no woofer to use as my version of a full-way speaker lol. Probably I'm just being stupid. I don't think music sounds bad at all with zero bass.

[_scotty_]

Brian from your opening post on this thread and the title of this thread
http://www.audiocircle.com/index.php?topic=19670
I gather you are now pre-tuning all systems for the lowest measureable THD
and best transient response before shipping them to the consumer.
If this is the case am I correct in my understanding that any deviation in the mass on the PR introduced by the customer will result in an increase in measured THD and a reduction in the accuracy of bass reproduction?
In otherwords the customer can change the tuning to suit their tastes but
they will pay a penalty in increased bass distortion if they do so.
This makes sense in light of your comments here,

I published curves right on this Forum last year, showing 10% THD at 20Hz on the RMX with the PR untuned and 1% THD with about half a gram of putty removed.

Please correct me if I am misunderstanding your design philosophy or your current practices.
Thank-you,Scotty

[ekovalsky]

You can achieve many desirable measurements with dsp.  I know this well, having exhibited a fully digitally corrected speaker at the 1992 CES.  In spite of sterling measurements in every regard, it was unlistenable and we took it down after 2 hours on display.

Why not move your mic 6 inches in any direction and see what happens to your "corrections".

The first owner of your speakers was so anxious to get rid of them he took an $86,000 loss.  And you will lose a good five figures when you "move on".  I ...

Actually Big B I have no intention of selling them as they are performing at an exceedingly high level.  They have met my expectations and then some, and I have zero buyer's remorse.  For the first time since my Apogee/Muse combo I am 100% satisfied with my audio system.  Other than eventually building out my room, I have no plans to change anything.   I'm using the TacT for two purposes -- integrating the mains and subs with DSP crossover and time alignment and correcting room interactions below 200hz.  For both tasks I don't believe there is a better solution on the market.  I'm not sure what type of DSP was available on the market in 1992, but my guess is that it was rather crude compared to the TacT and DEQX.

Unlike some other speakers I've had, the Alon main towers measure quite flat in-room above 200hz.  And it uses phase coherent first order crossvers on all drivers.  There is no need to perform room correction above 200hz or bypass the factory crossovers.  The only thing replaced by the TacT is the antique DLP-1 that Carl supplies with this system.

And it is worth pointing out that the seller did not take a $86,000 loss (actually it would be a $90k loss based on what I paid, if he paid MSRP).  As a former editor of Fi magazine he got them at an industry accomodation price and only sold them because he got a deal on a pair of Rockport Hyperions with his Sirius III turntable.  Several who have heard both speakers in his room thought the Alons were better.  Harry Pearson and Art Pfeffer seem content with the big Alons too, for what little that's worth.  

I bought these to end my speaker quest and anticipate that I have done so for at least the next ten years.  Each night I spend a few hours with them either with a big smile on my face or in a state of synaesthesia -- and to me that is all that matters.

Sorry if this has wandered off topic.  I'd still like to understand how your current crossover design using 2nd order slopes is phase coherent across the audio band.

[Brian Cheney]

I do not believe any claim that a side-by-side array such as the large Alons uses first order networks.  Lobing in the horizontal plane would be severe, a venetian blind effect audible when any listener turns his head.  

Why don't you open them up and report what you find?

I have explained my crossovers at length. You appear to be contentious for its own sake.

[CornellAlum]

Have you guys ever considered my way of viewing speakers...it's called the "do they make you happy and sound good to you" theory, you should really give it a go, it makes life much easier than these back and forth bitch fests which several non-vmps owners seem intent on creating in the vmps forum:nono:  

[Tweaker]

I do not understand why using digital room correction and equalizing with a mike at the listening position would give "strange results". I have an Ultracurve and have done just that and the results are profoundly, overwhelmingly good. Best damned audio investment I've made besides my RM2's. The mike may have been placed in the space my head normally occupies at the listening sweet spot but no matter where I sit or stand the music sounds better. Even upstairs where I am now typing this it sounds better. The only thing that happened when I moved my head to the left or right from where eq'd from is what usually happens- a slight shift in the sound stage left or right. B, your post was a curious mixture of insights, nonsense, and petulance.  Wouldn't have you any other way!  

[Brian Cheney]

Sometimes room EQ works well, particularly in small rooms.  Among us engineer types EQ (digital, analog, you name it) is called "pushing on jello" particularly when boost is applied.  

If it works for you, great.

I may be a little short today, I'll up my meds.

[ekovalsky]

Medication is good

A few weeks ago I opened the Alon crossover boxes to take a peek.  After studying them and talking to Carl, it seems there is a first order Butterworth network between the the 8" woofers and midrange cones and a quasi-second-order series network between the cones and ribbons of the array.   This gives a rising rate of attenuation to 12dB/octave yet maintains good phase and amplitude behavior through the crossover region.  There are a lot of parts in the boxes (many, many more than in the VMPS) and I'm still not exactly sure as to what exactly is happening in there.  One thing I can say is that no notch filters are used.  

I was not trying to be contentious about the VMPS crossover design.  Rather I was pointing out what was inside my speakers.  That's it.  Unfortunately two people expressing their viewpoints frequently comes across as a bitch fest, while to me it is just good audio discussion.  

Obviously my loudspeaker and electronics preferences have changed rather dramatically in the past few years.  As I've said before I respect the longevity and stability of VMPS and also the fact that Brian designs by ear and is passionate about what he does.  And it was rather fun watching him pick apart some competing systems at CES two years ago.  Some very good sounding speakers have come out of El Sobrante and I had enjoyed some good listening through the RM40 and RM/X.   Unlike in the past, at the present I do think there is a lot of competition for new VMPS speakers.  At some of the firesale prices on use speakers there are still some exceptional values to be had.

Enough bantering, time to listen !