Beolab 5 - Four Questionable Technologies

I haven't heard the B&O Beolab 5 yet, but seriously doubt the lenses are mere marketing drivel. They address a problem that most loudspeakers have.

Briefly, very few loudspeakers generate a reverberant field that has approximately the same spectral balance as the first-arrival sound. This matters because the ear derives timbre not only from the first-arrival sound, but also from the reverberant energy. Driver beaming is the main culprit; it affects more than just the high treble. For example, in a typical loudspeaker when we cross over from the midwoofer (which is beaming) to a small tweeter, the radiation pattern flares out again and we have excess reverberant field energy in the lower treble region compared to the rest of the spectrum. Under most listening conditions, such off-axis response anomalies are audible and detrimental.

The lenses used in the Beolab 5 address this issue by reflecting the midrange and tweeter's outputs uniformly over a 180 degree horizontal angle. As a result, the reverberant energy has very nearly the same spectral balance as the first-arrival sound. This contributes to natural timbre and long-term fatigue-free listening.

Now I might quibble about the width of the radiation pattern used in the Beolab 5, but imho getting the reverberant field right is a fundamental requirement for natural timbre and something that relatively few loudspeakers do well.

Note also that DSP correction works best with a loudspeaker having a uniform radiation pattern. You see, DSP corrects for the microphone location only; if your speaker has an on-axis dip but an off-axis peak at a certain frequency, boosting that frequency to equalize the on-axis response would be a step in the wrong direction. DSP cannot correct the radiation pattern - it works best when uniform radiation pattern is an innate characteristic of the loudspeaker.

I would expect the Beolab 5 to sound very natural when set up correctly, and not be fatiguing over the long haul. In my opinion it's not the only speaker likely to have these characteristics.

Duke
dealer/manufacturer

Hi Hdomke,

My post above focused on what I believe is an under-appreciated aspect of loudspeaker design, namely what sort of reverberant field the speaker sets up, and its effect on timbre. I also place a high priority on a wide listening area.

Two things go into getting good sound over a wide area. First (and imho most important) is that the tonal balance hold up well for listeners who aren't in the central "sweet spot", and second it would be nice to still get some semblance of a soundstage from off to the side.

With a speaker like the Beolab 5, the tonal balance will be good throughout the room because the spectral balance of the first-arrival sound changes little if any as you move around the listening area. The imaging will be best up and down the centerline, but will still be better than average from off-center.

The ear localizes sound by two mechanisms: arrival time and intensity. For an off-center listener in a typical setup (conventional speakers with little or no toe-in), the near speaker of course wins arrival time, and it also wins intensity because as you move off to the side you're moving more on-axis of the near speaker so you're getting more high frequency energy from that speaker. With the Beolab 5, I think that there would be relatively little difference in intensity between the near and far speakers, so the image would still shift but probably not as much as with most speakers.

A technique I use with more directional speakers (90 degree instead of 180 degree pattern) is to toe them in severely such that their axes actually cross in front of the listening position. With this geometry, as you move off to one side the near speaker wins arrival time but the far speaker wins intensity, because you're now more on-axis of its tweeter. As a result, you still get a decent soundstage from well off to the side. I first heard about this technique from the writings of E. J. Jordan, and learned how to implement it using a waveguide speaker from Earl Geddes.

As far as speakers that imho do a exceptionally good job with the reverberant field and therefore tend to sound natural and be non-fatiguing (assuming they don't have other problems), I don't want to wax overly commercial here - some of these are speakers that I have chosen to peddle:

Omni or semi-omnidirectional: MBL, Wolcott, Ohm, Duevel, Shahinian, Morrison, and Mirage.

Wide, uniform monopole pattern: Beolab 5, the imho classic (and sadly discontinued) Snell Type A, Amphion, SP Technology, KEF Uni-Q, smaller Tannoys, DCM Time Window, Pioneer TAD home speakers, some Gradients, two-way Gallos, and to a certain extent many three- or four-ways that have a small diameter cone or dome midrange. Floyd Toole of Harmon Kardon (makers of Revel and many others) advocates this sort of radiation pattern.

Bi-directional with good reverberant field response: Magnepan, fullrange SoundLab, Apogee, Omega Acoustics.

Fairly narrow monopole pattern with good reverberant field response: Classic Audio Reproductions, PiSpeakers, Altec model 14 and model 19 (both discontinued), high-end JBL hornspeakers, big concentric Tannoys, GedLee (or Audio Intelligence - presently not distributed in the US), some Gradients, Emerald Physics (dipole at lower frequencies).

In addition, I build speakers that would fall into one or two of these categories. And no doubt I've left out many worthy contenders.

In general, the wider-pattern speakers out of these tend to be more demanding as far as room size and set-up goes. They also tend to sound more rich and enveloping, like you're sitting near the middle of a concert hall - whereas the narrower-pattern ones have a presentation more like you're up near the front of a jazz club.

By the way, thanks for the links you provided. Peter Aczel mentions the power response of the Beolab 5, and "power response" means "summed omnidirectional response" - so this includes the reverberant field. It's different wording (and a slightly different focus) in talking about the same thing.

Duke