A battle of Studio Titans: The Barefoot or Sayers Soffit?

[dbluefield]

Ok kidding

Seriously though -- the soffit design Thomas' aka barefoot --with an adjustable shelf on an inner frame that does not touch the studio side wall frame, and a bezel that does not touch the speaker is interesting.

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=718

Have you built one of these Thomas? It would seem that getting the shelf rigid enough with through bolts might not be as rigid as having a framed in box attached to the studio side frame/wall.

John has obviously built/designed several soffits, all of which seem to have the monitor box frame attached to the studio and inner walls.

Simply put, is a box better than a shelf? Or once packed with insulation are they roughly equivalent? John seems to advise that the monitor box and frame should be as heavy and rigid as possible -- the shelf design seems to challenge this.

Does the design to decouple a shelf from the outer framing (studio side wall) contradict most real world application?

Thomas is there some additional reading I can do?

John, some real world perspective on this?

Thanx guys,

Dave

[barefoot]

Titans!!!

Dave,

I haven't built this soffit design, but I have built speaker cabinets that follow the same principle. The two main points of the design are that you decouple the speaker from the room as well as gaining flexibility for future monitor upgrades. The upgrade flexibility is a self evident plus, but I guess the decupling aspect isn't as self evident. Here is a quote from a private massage I sent John regarding this subject.

• "John, I completely agree that a box should be heavy and emit as little sound as possible. This is very different, however, than the concept of rigidly mounting the box itself. The big issue with speaker boxes isn't the box moving due to the inertia of the speaker cone. The major issue is the walls of the cabinet flexing due to vibration transmission through the driver frame and.... primarily... vibration transmitted via the acoustic pressure inside the cabinet.
  
  Imagine these two cases:
  
  1. A box built with a tubular steel frame (skeleton) and thin plywood panels enclosing the volume. The steel frame is filled with lead. The driver is directly connected to the frame. So, you have an extremely heavy structure holding everything in place, but the walls are relatively flexible.
  
  2. A cylindrical cabinet built with two different diameters of concrete forming tubes. The smaller tube is inside the bigger tube. One end connects the driver and both tubes with a thick round MDF ring. The inside tube is shorter than the outside tube such that each tube has its own round MDF cap at opposite end from the driver. So, you basically have two partially decoupled, relatively lightweight cabinets, one inside the other.
  
  Which of these do you think will perform better? Well, clearly the Sonotube cabinet will perform better. In fact, this type of enclosure will perform much better than even a single walled rectangular box with very thick (50mm) MDF walls. Heavy is good, but it's useless if the walls are flexing. Mounting a speaker tightly inside another plywood box will have little effect. You need to isolate the two cabinets.
  
  This is the reason why I came up with that new soffit mount design. It does rigidly couple the speaker cabinet to the framing increasing its inertia. (In your case I had a heavy steel bracket rigidly attaching the cabinet to one of the ceiling beams. Maybe that wasn't clear from the drawing?) But, this increase in cabinet inertia is a very minor improvement. The major improvement comes from decoupling the cabinet vibrations (except the front baffle) from the room. Speaker cabinets can and do emit quite a lot of acoustic energy. Even though the amplitude of the vibrations is small relative to that of the speaker cone, the surface area of the cabinet is much greater."

So, I didn't mean to suggest with my design that mass and rigidity aren't noble goals. They are. You can flesh out the shelf as much as you like - add extra supports, clamp the speaker down more, or whatever. The main point, however, is that decoupling the cabinet's vibrational energy is much more effective than trying to "clamp" it away.

John has come up with truly outstanding studio designs, and his soft mount design is, likewise, excellent. I've just suggested and augmentation that will give a little more flexibility and a little more isolation from cabinet colorations.

Thomas

[dbluefield]

Thomas,

Thanx for the reply. This is very interesting stuff. I guess the idea is that the studio side ot the soffit wall enclosure should ideally not touch the speaker, enabling the inside of the studio to act more like the outdoors? In other words the only direct path from the speaker to your ear is through the speaker itself -- the wall around the speaker doesn't take speaker cabinet vibrations directly, but provides a physical space around the speaker to "push" all sound in the forward hemisphere?

I'm working on my soffits this month and I can perhaps find a clever way to de-couple the soffit box from the studio-side wall. I’m working on angling the monitors down a bit too. I took a break for today so I can continue with a clear mind. I am using actual string as a vector guide to try to aim the approximate tweeter position directly at ear height.

Rather than a strap, perhaps I can figure a way to wedge the monitors inside the box?

Best,

Dave