Publisher Profile

An Interview with Daniel Khesin of Polymer Audio Research

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master crossover

master crossover

LB: A speaker is comprised of its drivers, crossover (absent in a single driver design), and cabinet. As the cabinet figures so prominently in your deigns, let’s begin there. As with all things in audio, there are multiple approaches to cabinet design. In one extreme are those who eschew the cabinet, opting instead for an open baffle. Then there are those who feel that a cabinet should have properties similar to a musical instrument, whereby the cabinet — typically made of wood — is intentionally designed to resonate. At the other extreme are designers such as yourself who believe a cabinet should be insert as possible. Did you arrive at this position empirically, or by trial and error?

DK: We are not in any particular school of thought or married to any particular technology. A brilliantly designed open baffle, electrostatic, or horn loudspeaker can produce spectacular results and they each present their set of challenges. To say that only dynamic driver speakers in vented enclosures are optimal is just silly. It is simply the approach we have chosen for various reasons and then set out to perfect, or rather take to its technological limit. This is the same as the age old tube vs. solid-state debate; neither technology is inherently superior only the competence of the engineering will determine which one ultimately sounds better.

For example, the open baffle construction offers some very attractive features which I find very appealing. This includes total freedom from enclosure standing waves, uniform radiation impedance on both sides of the cone, dipole cancellation on the sides for easier room integration, and much lower construction cost. At the same time the design presents serious challenges, particularly very limited low frequency extension which can only be boosted with electronic equalization which then introduces significant amounts of group delay. The listener thus has to choose from either having a lot of delay, an extremely wide baffle (which then ruins imaging), or just live with no bass. Another issue is that while dipole radiation helps with room positioning it is obvious that musical instruments do not have this type of radiation, rather they radiate sound equally in all directions. But I can’t promise you that we will never introduce an open baffle speaker which would indeed be very compelling if we can figure out how to overcome some of its challenges.

However, certain things are not even up for debate. The idea that a loudspeaker cabinet should intentionally be made to resonate or act as a “musical instrument” is absurd and a major regression from any advances in audio. If we are to agree that the purpose of audio equipment is to hear the recorded event as it was, then this is only possible if the loudspeaker doesn’t introduce any sounds of its own.

All of our design work is driven entirely by decisions that have a measurable or scientifically plausible basis. Anything that cannot be substantiated scientifically is rejected. However, of course there is a tremendous amount of trial and error but really it is an exercise in corroborating observation with science. If there is an unexpected result it can always be explained.

CNC Shop Area

CNC Shop Area

LB: Those who favor resonant cabinets often claim that with highly damped cabinets, the music seems “held back.” Can you speculate as to what might cause this perception?

DK: It is actually true that if a cabinet is just highly damped that the music will have the sensation of being held back. But in addition to damping, it is very important the cabinet have a very low energy storage. When the cabinet is storing very little to no energy, the opposite sensation of “held back” happens. Since no energy is stored in the cabinet all of the energy generated by the drivers is pushed into the room, creating remarkable dynamics and a live sensation. Our cabinets have practically zero energy storage.

But there is simply nothing worse than resonant cabinets. In addition to blurring information and creating their own sound, they store and release delayed energy creating time smear. The entire cabinet is basically acting as a giant woofer playing at low level. It’s just a complete disaster. You want to hear a symphony orchestra in your room the way it sounds live? It’s never going to happen with resonant cabinets.

LB: Aluminum seems to be the material of choice amongst some of the designers who favor inert cabinets. Please explain why this is so.

DK: Aluminum is a good material. It is orders of magnitude superior to MDF, has very high stiffness, reasonable weight, and is relatively easy to machine into complex shapes. It’s simply a very good material for loudspeakers and it makes sense that it is used by some designers. It’s a smart move.

LB: Your own designs eschew aluminum. Did you experiment with aluminum in your earlier designs or prototypes?

DK: Actually we do use aluminum in some parts of the cabinet. Our construction is mainly a combination of various metals with some extreme alloys for the most critical areas. We certainly did experiment with all aluminum construction and the result was great but we are pushing the edge of what’s possible so we didn’t stop there.

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