Infinite bafflement?

You know, I've always wondered if Acoustic Suspension and Infinite Baffle were exactly the same principle or if there was some difference.. I suspect that a woofer in Acoustic Suspension design has a looser spider and higher compliance since the air restores the excusion, whereas infinite baffle may be a large sealed enclosure where a perfect seal is not as crucial?? anyone else?

An infinite baffle is a very large enclosure (even a closet) compared to an acoustic suspension system. The old Bozaks were an example of an infinite baffle design. The drivers did not have a loose suspension.

is an elctrostatic speaker which is enclosureless an example of an infinite baffle speaker ?

"Infinite baffle" is where the front wave emanating from a driver is completely separated from the back wave... as in, installing your woofer on the front wall of your house...

In real life, it usually means that the low freq driver is installed in a very large sealed cabinet -- large enough so that the pressure produced by the cone's movement produces an insignificant amount of noise compared to the actual music content.

Gregm, So a sealed cabinet performs in fact as an infinite baffle? But with a sealed cabinet one has to do with resonances and standing waves within the cabinet, which are non existent if there is an "open" baffle design, like the Jamo Reference speakers.

Chris

In acoustic suspension the box volume modifies Q (damping). In a pure infinite baffle only the driver's Q plays a role. Normally the box volume and woofer are selected to match in order to get the best out of the combo or combined Q (so this difference is not critical)

In an infinite baffle there is NO rearward sound energy reverberating and causing peaks and nulls in the forward sound field. (In a conventional box speaker the reverberant energy off the rear walls behind the speaker cancels or enhances the forward sound energy that reaches the listener creating a highly bumpy sound field in the bass or less than 500 Hz. In open back panels and dipoles this effect can occur in the mid range - creating an airy or spaced out impression - this is how the ear interpretes comb filtering or a highly "notched" sound field).

In an infinite baffle there is also no edge diffraction occuring as the sound geometrically spreads from the driver and then suddenly encounters the edge of the speaker box and diffracts around it ( think a pure clean bow wave from a boat hitting a pier and creating secondary waves off the pier - after the wave hits the pier or goes around it there is no longer a clean signal)

Therefore an infinite baffle will give an almost perfect sound field (in theory)!

A box speaker mounted in a wall is a sort of hybrid. It approximates an infinite baffle in that there is no rear energy to clutter the forward sound field (i.e. approaches a perfect sound field). However, the box volume is still used to modify the woofer Q to achieve a desired system Q... so the bass response of the driver may be enhanced at what is often regarded as negligible expense to the transient response)

Infinite baffle is a pretty self-descriptive term. If you use Gregm's definition (which is correct), just think of the front baffle of any speaker in which all drivers are front mounted. Now imagine that that baffle is infinitely large. There willl be no front/back wave interaction because the waves are separated by an "infinite" baffle. In the real world the baffle is merely large (not infinitely large), so a large sealed box is required to isolate the rear waves.

Marty

Acoustic suspension and infinite baffle are different. An acoustic suspension is a sealed enclosure that has an air volume less than the equivalent air volume compliance, the Vas, of the driver, usually less than half. An infinite baffle is also a sealed enclosure, but with an air volume greater than the Vas of the driver.

Open baffle, electrostatic, or panel/planar, are not infinite baffle because the back wave is not isolated.

The size of the enclosure is not necessarily an indicator. A driver with a Vas of 12L in a 16L enclosure is an infinite baffle. A driver with a Vas of 34L in the same enclosure is an acoustic suspension.

Hartley woofers (18"/24"woofers) used to recommend mounting their woofers in crawl-space openings/infinite baffle.Where the large crawl-space was the "cabinet" and never reflected to effect the front waveform.

is an elctrostatic speaker which is enclosureless an example of an infinite baffle speaker?

That's "open baffle"; sound emanates from both sides of the panel into the room. There are beneficial cancellations (front to back) but also loss of spl as the sound wave becomes too large for the baffle.
Dazz:

So a sealed cabinet performs in fact as an infinite baffle? ...with a sealed cabinet one has to do with resonances and standing waves within the cabinet...

Exactly. However, if the box is large enough to make the rear wave interaction less significant, there is a "simulation" of infinite baffle. As per Martykl & Shadorne, above.

Ojgalli's explanation is a good one. It all has to do with the relationship of the compliance of the driver and that of the air in the box.

In layman's terms, a sealed box can be either acoustic suspension (AS) or infinite baffle (IB). A small box, with a very compliant suspension will tend to be AS, a larger box and/or less compliant driver will tend to be IB.

By the way, AS is truly one of the landmark developments in the history of audio. In my mind, nothing has eclipsed it, and is probably the biggest reason we have 2 channel (as opposed to 1) audio.