[Duke]

One of acoustics master Jeff Hedback's clients was in need of large monitors for his recording studio, so Jeff contacted me about it.  We decided on a large MHM format speaker that would be mounted on big Sound Anchor stands.  Here's a shot of one of the speakers before being crated for shipping:



And here are a couple of early pictures of the speakers installed in the studio; I hope to post higher resolution pictures later:





Photos courtesy of studio owner Carl-Frederic Behrmann. Now you've seen what a real "stand-mount monitor" looks like!

That beautiful studio you're seeing?  Jeff Hedback's design. 

An integral part of the speaker system is a Crown amp with built-in DSP-based EQ.  The DSP is used to tailor the low-end to the room.  Jeff developed the EQ settings based on in-room measurements as part of the service he provides.  Also, the internal cabinet damping technique I learned from him is incorporated into this speaker.

Jeff has told me that the measurements he's getting look very good, in particular the low-end smoothness (much of whch goes back to the acoustic treatment that he specified) and left-to-right in-room consistency.

Carl is very happy as well, which makes us all happy.

[Duke]

Why the MHM format?   

First, unlike conventional MTM systems, the MHM format with a 90-by-50 degree waveguide-style horn does a good job of pattern-matching in the crossover region.   There is some pattern-narrowing in the vertical plane of the woofers relative to the horn in the crossover region, but the discrepancy is less than with most systems.  And our horizontal pattern matching is very good.

Second, this way the system has less early interaction with objects in the vertical plane, like that big recording console.   And if there are things in the way of the lower midwoofer, the upper midwoofer still delivers a clean shot.

Third, with a bit of EQ, we can meet our SPL and bass extension targets while preserving really nice midrange clarity at high levels. 

[Duke]

Before crating the speakers, I listened to them for a while in my living room.  They were sitting on the floor, as I lacked both suitable stands and the muscle to put them there.  I noticed something unexpected:  The image height was about at the center of the upper woofer! 

In retrospect, I'd experienced that once before:  The Classic Audio Reproductions T-5 is also an MHM speaker, with a supertweeter squeezed in.   You'd have never guessed the height of the midrange and tweeter with the grille in place.

My guess is that two mechanisms are at play:  First, the top woofer is the closest to seated ear level, so it's the source of the first-arrival mids.  Second, the ear's ability to localize sound sources in the vertical plane is not only poor but has a distinct anomaly:  We tend to mis-localize a high-frequency sound as coming from a higher angle than it really does, and likewise we tend to mis-localize a low-frequency sound as coming from a lower angle than it really does (this established by controlled blind testing).   So the ear tends to mis-localize the horn's output as coming from higher up than it really does.  Sibilants seem to come from the same height as the rest of the voice.

One implication is this:  The format would work as a floorstander in a home audio setting, but I'd probably have to include a grille because people would tend to believe their eyes rather than their ears.

[James Romeyn]

Duke,
What is the modeled (or measured) bass f3 in the studio?

They look great.  I wish I could have heard them.  Next pair call me and I'll help crate them.     

[Duke]

Duke,
What is the modeled (or measured) bass f3 in the studio?

I don't know for sure what tuning frequency and EQ settings will be the final ones, but the initial settings give an F3 in the lower 30's, I believe.  My understanding is that pitch definition is a very high priority here, which may not be consistent with pursuing deepest possible F3.  The in-room curves that I've seen were suprisingly smooth, which I attribute to Jeff's room treatment more than anything else.

Left to its own devices, the speaker has a fairly high modelled F3 of 82 Hz, with a shallow rolloff below that down to the upper 20's, and a steep rolloff from the mid 20's on down.

If it serves the greater good, the tuning frequency could be lowered and EQ adjusted accordingly to yield an F3 in the upper- to mid-20's.   

[James Romeyn]

You piqued my interest re. smooth bass response attributed to the studio and treatments.  Are studio dimensions Golden Ratio?  Per Real Traps' Room Calculator, even GR dimensions appear to result in audible bass modes (IIRC Ethan Winer states this is the case too). 

I spent $750 for professional plans and too many thousands of dollars (including 3-walled ceiling sofit) to treat my last sound room with at best mixed results (modes decreased but not altogether fixed, too dry, admittedly did not finish the corner traps before we moved).  Humungous quantity of absorption produce only moderate damping of long bass wavelengths, and does not boost response dips.

Does the studio have bass resonators?

What did those puppies (speakers) weigh?  Cabinet panel composition? Internal volume?  12" driver weight?         

[Duke]

Does the studio have bass resonators?

What did those puppies (speakers) weigh?  Cabinet panel composition?  Internal volume?  12" driver weight?         

I'll wait for Jeff Hedback to describe the room treatment. 

Speaker weight is a little over 200 pounds each, if my recollection is correct.  MDF, sprayed on both sides for stability in a humid environment (Haiti), double-thicked in some areas and/or braced in others.   Ballpark 7.5 cubic feet, and each 12" woofer weighs about 23 pounds.   The woofers were shipped separately, just because I was nervous about what the extra weight might do if crates were handled roughly. 

[James Romeyn]

I'll wait for Jeff Hedback to describe the room treatment. 

...each 12" woofer weighs about 23 pounds.   The woofers were shipped separately, just because I was nervous about what the extra weight might do if crates were handled roughly.

Applause!  Smart idea.  Brian and I often considered methods to avoid damage in transit at VMPS, and that was not one of them.  Please correct, but I think force upon impact decreases at the square of decreased weight (10% lighter load = 40% less impact force).  Well worth the effort of packing and shipping 56 lbs of drivers separately.

Nothing makes your day like staring at a 28 lb 12" mid-bass with grotesque chunks of MDF semi-attached, the driver wedged between the crate and what's left of the baffle...at least shipping doesn't cost much these days!  (sarcasm off)

[Jeffrey Hedback]

Hi James,

I'll offer the short version...this is an existing room.  All surfaces are concrete (floor/walls, clg).  When Carl came to me first he was oriented 180 deg the other way.  I turned him around and we aggressively used surface treatments that included: RPG Modex Plate, Primacoustic MaxTrap, RPG, 4" BAD panels, Ready Acoustics 4" absorbers and tweaks to the insulation above the drop grid.

Improvements were solid...but the primary axial mode was still strong and Carl wanted the look of wood on the front walls.  I then took that and designed a membrane absorption system with very broad "Q" to attack the sub 50Hz ringing.  We mutually selected Teak for it's look, availability and density.  the wall system was tuned to Teak's properties.

We'll have actual photos soon.

Shown is the Pre T30 and the current T30.