Studio monitor collaboration with Jeff Hedback of Hedback Designed Acoustics

[Duke]

Multi-award-winning studio designer Jeff Hedback offered me the opportunity to bid on providing custom main monitors for a recording studio he designed, and his client accepted my bid. Jeff specified the tweeter height, outer dimensions, and look-down angle. The installation is in-wall, so the toe-in angle is built into the walls. Jeff helped me arrive at a good horizontal coverage pattern for the application, and provided me with all the input I needed whenever I had questions. The speakers were installed last week, and the studio is opening in early 2024.

The mains use two high-output 12" midwoofers and an advanced constant-directivity horn with a 1.4" throat compression driver in an "MHM" configuration, and the subwoofer cabinets each have a single high-output 21" woofer. The crossover between the midwoofers and horn is passive, and the crossover between mains and subs is active. The subs are EQ'd to get bottom-end extension into the low 20's, and they have plenty of excursion and thermal power handling. Amplification and EQ are by Powersoft.

Arguably one of the most important jobs of studio main monitors is "impress the client", which means impressing the musicians who paid the recording studio and want to hear how their finished recording sounds. With this in mind, the studio owner spent Christmas day (yesterday) listening to his collection of reference recordings. Apparently he is happy with the results, even though final calibration is still to come.

Jeff Hedback also does remote acoustic analysis, design and consultation for home audio applications, and ime his work is outstanding, practical, and exceptionally cost-effective. Here's his website: https://www.hdacoustics.net/

 

[MKR]

Outstanding work here @Duke! My kind of speakers … well done

 

[Duke]

Outstanding work here @Duke! My kind of speakers … well done

Thank you!

I don't think it would be fair for me to name names, but the studio owner said the speakers sounded like a well-known brand he is familiar with, except that mine "has bass".... well, I would hope so!

The enclosure designs seek to minimize distortion in a few ways. The two midwoofers each have their own sub-enclosure, the back of which is angled 45 degrees to break up internal standing waves. The area behind the horn is isolated from the midwoofers and has big openings for ambient air cooling. The ports are arranged symmetrically around the cones to maintain a uniform airload on the backs of the cones to combat cone-rocking, and there are ports both higher and lower than the motor to enable some "chimney effect" cooling.

The tweeter height required for this application is 57 inches (with 4 degrees of tilt-down built into the upper enclosures), in order to fire over the mixing monitors, and that would be way too high for seated listeners in a home audio setting. The subwoofer enclosure would have to be reconfigured, which could bring the tweeter height down to about 42 inches.

The enclosure width is 26 inches (well, not counting the wall it's flush-mounted in!), which is wide enough to have a significant effect on the low-end radiation pattern in a "free standing" application. The modelled directivity index is greater than or equal to that of a true cardioid down to about 100 Hz. The 21" subwoofer could be combined with a delayed-and-inverted 18" rear-firing woofer to provide cardioid behavior down to about 30 Hz. But the resulting speaker would be enormous.

Imo a more realistic home-audio approach would have the "MHM" sections as free-standing speakers covering the range from about 80 Hz on up, then a distributed multi-sub system could take the bottom end down to whatever one's low-end target is.

Actually I'm designing another custom system for a different studio with different requirements (it's a smaller space and therefore has less room for serious bass treatment whose thickness is measured in feet rather than inches), and that system will have four 12" subs distributed in all three dimensions.

 

[Mr. Widget]

Very, very nice! Thanks for sharing!
Are the HF horns proprietary or an off the shelf item?

 

[Duke]

The horn is the Faital LTH142, with a layer of Dynamat on the outside to deaden it.

I tested several horns and compression drivers before making the final choice. The 18Sound XT1464 measured a little better, and the Faital imaged a little better (something that I'm unable to evaluate by measurements alone). Arguably they are both very good but the Faital allowed a bit tighter center-to-center spacing.