Questions for Roy Johnson of Green Mountain Audio


Could you please answer a few questions for me regarding your continuum 3 loudspeakers? Your previous posts on Audiogon have been supremely enightening. Here goes:

1) The way you implement the tweeter and midrange in the cast marble enclosure appear to be quite unique, yet to the lay eye, there seems to be nothing unique about the bass enslosure. Just looks like your basic ported box, but looks can be deceiving right? What are you doing with the bass enclosure that makes it different?

2) Can you post or e-mail frequency response and impulse response graphs? Of course, they wouldnt be used to judge how they sound, that assessment is made by listening.

3) If you use a sub with the Continuum 3's, can the setup still be time and phase coherant?

4) Within the small group of time coherant speaker manufacturers, are some more time coherant than others?

5) Finally, when will your site be complete?

Why not call him? He is very accessible and likes to talk turkey. As busy as he is right now with all of his new speaker designs, it might be awhile before he becomes aware of this thread.


Yes, why would you ask those question here and in the form of a new topic? I smell a rat!
Wow, you smell a rat? Must be your.............oh forget it!
I was asking these questions on the 'Gon because other potential customers may benefit from seeing his responses. Also, it is nice to have information from manufacturers to look back on. Stop being so cynical Drubin and go enjoy some music.
Hey guys! Leave the speaker builders alone, especially those who are back ordered on gear. I've got speakers on order (not GMAs) and bet that feeling like they have to puruse A'gon and answer this stuff delays getting work done. I really do think this happens. Maybe you could call a dealer.
Your best bet is calling manufacturer directly for those questions. Do not rely on dealers for those questions as they are too often the last people to know. (High End) Manufacturers are known to change things on the fly even at the last minutes. Sometimes the customers get better answered from manufacturers if they follow through with their questions.

I speak from my own epxerience as a dealer.
Thank you for your questions.

My apologies for the delay in response- We are only now returning to "normal" after the success of the Rocky Mountain Audio Fest in Denver. I may not be any faster for a few more months, especially with the CES (actually the T.H.E. Show) coming up in Las Vegas in January.

We are training our dealers in the finer points of our designs, so they can be more helpful. Some dealers do not want to put in the work, and so will be dropped. I do not mind posting some answers here, and will try to avoid marketing expressions, focusing instead on some of the engineering.

Flyingtime2, you ask:
"There seems to be nothing unique about the bass enclosure. Just looks like your basic ported box, but looks can be deceiving right? What are you doing with the bass enclosure that makes it different?"

The size and shape:
Provide both the minimum frontal surface area and the maximum to couple the upper bass with the floor reflection, as far as your ear is concerned. Below 100Hz, this cabinet is just slender enough to "get out of the way" and let your room's wall behind the C-3 help reinforce the woofer's low bass.
The aspect ratio of this woofer enclosure (of the front) was also important. That ratio, taken with the floor's proximity, and the woofer's changing dispersion pattern, provides this "correct radiation resistance" to the woofer (its acoustic load), across the entire "transition range" from 350Hz down to 100Hz. The result is an audibly and measurably smooth output across that range for most listeners.

The physical construction of this enclosure is quite unique. This is explained in our new literature, without revealing trade secrets. We would be happy to mail it--we just finished it. Send your contact info to our new e-mail address:

The port is a 4" Aeroport on top. With the aid of what we refer to as a "Golden-Ratio Baffle" inside, this port turns off very smoothly above 40Hz, and reaches maximum output down at 34Hz.

The cabinet is fairly large, required by this woofer having a highly compliant (floppy) suspension. Since the woofer has a low moving mass, an ultra-compliant suspension is necessary for the woofer to have a free air resonance of 19Hz, which is necessary to porting it at 34Hz. That, finally, is a more linear way to obtain bass below 40Hz, because the woofer then stops moving below 40Hz. The result is higher efficiency and response well into the midrange, from the lighter, stiffer cone. The bass clarity is better at very soft volumes, from the ultra-compliant suspension, and at extremely loud ones, from the cone being asked to stroke less below 40Hz.

Most music seldom calls on a port tuned that far below 40Hz. When it does, the C-3's port and enclosure and woofer resonate with optimal 4th-order Butterworth tuning/damping so the port does not ring on (boom) as much as many ported boxes.

The Golden-Ratio baffle inside effectively makes the box more quiet inside than any I know, after building every kind of enclosure, properly, over the last 20 years. It has the interior quietness above 40Hz associated with the best sealed boxes and transmission lines, without the drawbacks of the T-lines, nor the efficiency decrease of the sealed enclosure. All else equal, a sealed box is always best, but when you design a 34Hz ported system like the C-3's, then you have higher efficiency (because the cone's moving mass can be less), and less modulation distortion up to that 280Hz crossover point and beyond (since the cone strokes less below 40Hz). This is not a new appraoch---it just hasn't been seen in a long time. Many 1970's JBLs and Cerwin-Vegas were designed in this manner, although their enclosures were much noisier inside than ours are, and were structurally weaker. With marketing's push to provide a smaller enclosure, this approach was discarded, and in my opinion, to the detriment of fidelity.

"Can you post or e-mail frequency response and impulse response graphs? Of course, they wouldn't be used to judge how they sound, that assessment is made by listening."

They would be interesting to study, but no, I cannot publish them for two reasons:
All our measurements are done in the analog domain- which doesn't give me hard copy.
I make many measurements, and each gives only a small part of the picture.

I have used all of the well-known digital measuring systems---and for what I need, their resolution in performing certain measurements is limited. For example, the impulse seen in Stereophile does not test below the voice range at best, and so doesn't tell you what the woofer is doing. They tested our original Diamante in 1994.

So you are right- just listen to any music or voice, to find out if anyone did things correctly, and listen to any speakers properly setup of course.

I just returned from taking C-3's to the editor of's a better writer than I will ever be, so look at the way he explains the overall concept of first-order crossovers, and how different firms implement them.

"If you use a sub with the Continuum 3's, can the setup still be time and phase coherent?"
Good question. It cannot ever be time-coherent, only phase-correct at best, and only then by using a decent sub that is not one of those "too small of a box with EQ", but one from REL, or from us for example. The following applies to many speakers---only the crossover point would be changed:

One must use an outboard electronic crossover to supplement a crossover built-in to a sub, or bypass that sub's crossover to use either a "THX" crossover found in some home-theater units, or an outboard electronic crossover with 12dB/octave (2nd-order) Butterworth filter slope for the C-3's at 50Hz or so, and with 24dB/octave (4th-order) Butterworth filter slope on the sub(s) at the same frequency. Those are the "THX" slopes, lifted from pro-sound work. If the sub has a built-in 12dB/octave filter, you would augment that with an electronic crossover having 12/12 slopes. A 12/24 electronic crossover comes from Marchand Electronics or is built for you by dbSystems.

The final result is phase correct, but not time coherent, since the two drivers are now a total of 360 degrees apart in timing -one full wavelength- at the crossover point. You hear then, at best, an extra thump on the kick drum from the time delay (kick drum = 50Hz), and a collapse of large-concert-hall depth on classical music. However, the 12/24 crossover blends well enough that you don't adjust it for every song, and you can hear very easily that the that the sub sounds best up in the plane of the speakers, not off in a corner. A sub will disappear with a 12/24 crossover.

Most of the discourse about room problems with a sub, standing waves, etc., are actually how regular measurements "see" the time delays (and how we hear them) of typical sub crossover circuits. These time-delays sound and measure like room problems, because the delays are on the order of 3-8 feet worth of travel for the wave- 3-8 milliseconds of time delay. In my experience, most of those "standing wave" complaints go away listening to music when you are able to crossover in a phase-coherent manner.

Of course we recommend our just-released 'The Hammer' 12" subwoofer... Fortunately, the C-3 requires no sub in my opinion---I think our owners would support that statement. That extra money is better spent on decent cables and a bigger power amplifier, or a better one, to improve the room-shaking capabilities of the C-3, and to let it show you what finesse in the bass also sounds like.

"Within the small group of time coherent speaker manufacturers, are some more time coherent than others?"
There are those whose version of time coherence is more of a broad-brush approach that include cabinet reflection effects, and driver reflections off each other, in their coherence measurements. There are others who use much felt damping on the cabinet surface. Either approach or a combination of those two always leads to complicated crossover circuits. A manufacturer should also tell you at what distance the "focus" is achieved, but I don't think that is made common knowledge. You just need to compare. Using voice the first time helps a great deal.

When the time-coherence is improved, the image is much sharper and the soundstage deeper with everyone clearly in their own space. A higher-order crossover circuit always flattens that perspective, and presents complicated music as a wall of sound. Depending on the voice you choose to audition, and the order of the higher-order crossover, the crossover may aggravate sibilance, or make that voice sound recessed, may make you more aware of "the sound" of a metal tweeter... and it always prevents you from hearing many nuances you never knew were there.

5) Finally, when will your site be complete?
Our webmaster, Carl McMillan, sent us an email two weeks ago that said he was ill and had been ordered by his doctor to bed rest. We have been waiting for him to get well so the website can be finished. At this point, we do not know when it will be completed.

Thank you for your questions and your interest.

Best regards,
Roy Johnson
Founder and Designer
Green Mountain Audio