Beolab 5 - Four Questionable Technologies

Oxia
“To place an omni speaker three feet from a corner where the side-wall is made of a highly reflective material like glass is nothing short of a disaster.”
I’m not sure if it matters, but I don’t believe the Beolab 5s would properly be called an omni directional speaker since the speaker covers only 180-degrees.

As Paul Messenger wrote in Ultraaudio:
“The Beolab 5’s elliptical reflectors are shaped to cover a 180-degree semicircle horizontally, and to restrict the vertical "window." Nearly all of a driver’s output is thus directed forward, reducing the proportion of room-reflected sound the listener hears, effectively increasing the efficiency in the listening zone, and creating a speaker whose output is substantially independent of proximity to the rear wall. Because the Beolab 5 effectively has its own built-in "rear wall," it is immune from reflection-induced colorations caused by the actual room wall behind it.”

Hdomke,

You are correct about the 180-degree radiation pattern, and I mentioned that in my post. However, despite the fact that midrange and treble energy is not being radiated towards the rear, the speaker is still radiating full power to the sides and is thus susceptible to early reflections from the side walls. Consequently they should be either positioned well away from the side walls and ideally the walls should have something in front of them to absorb the energy from the speaker (such as absorptive foam, upholstered furniture, drapes, etc.). Hard surfaces like glass are the worst, as it creates a very acoustically live environment. I reckon that if the speaker is positioned close (within 3 feet or less than one meter) from the glass side wall, given that the BeoLab5 radiates full power throughout the mid-to-treble range towards the side (unlike a conventional box speaker whose output sharply attenuates to the sides), the result would be that the reverberant energy coming off the sidewalls would arrive at the listener's ears with sufficient force and vivacity as to obscure and smear musical detail much more so than in the case of a conventional front-firing box speaker in the same acoustic environment.

The BeoLab 5's DSP should be able to auto-EQ the bass to mitigate excessive room gain (bass boom) caused by the close proximity of walls, but the DSP does nothing to cure the early reflections of midrange and treble energy coming off the sidewalls. For that, good old fashioned attention to positioning and acoustic treatment is needed.

Hdomke,

To clarify my statement about Beolab 5 imaging-
I used a double negative:

I was stating tha the imaging problem (like the congestion problem) may be due to poor performance by the speaker or may be due to set-up. I just don't know. That's why I said an in-home demo in a room large enough to get the speakers away from the walls will be essential.

I'm happy that B&O accomodated you. The sound I heard was poor enough in certain, specific ways that I am inclined to believe that (at least) part of the problem HAD to be the set-up, otherwise those rave reviews would be hard for me to understand.

OTOH, Shadome heard a pair that seemed to be set up in a better (though perhaps still less than ideal) way and heard some of the same issues. I am eager to hear about your demo and i look forward to your post.

To sum up:

1) I wouldn't dismiss this speaker until I heard it set up properly
2) The demo I heard was pretty terrible for a speaker in this $ range.

I hope that clarifies.

Marty

the BeoLab5 radiates full power throughout the mid-to-treble range towards the side (unlike a conventional box speaker whose output sharply attenuates to the sides)

Not all conventional box speakers have narrow dispersion ( no side radiation ) - good speakers will have wide dispersion at least as wide as far as it matters (to be affected by side wall reflection to listener).

"Not all conventional box speakers have narrow dispersion ( no side radiation ) - good speakers will have wide dispersion at least as wide as far as it matters (to be affected by side wall reflection to listener)."

Shadorne,

I think that the reason for our disagreement is due to the way that we're each using the term "wide dispersion". I am not disputing that there are conventional front-radiating speakers with wide dispersion, but it is a fact that all conventional front-radiating speaker will become increasingly directional as you go up in frequency.

To illustrate my point, please take a look at the polar response graphs in this website.

http://www.mcsquared.com/speakers1.htm

Notice how the bass is virtually omnidirectional even for a front-firing speaker, but the midrange and treble gets increasingly directional. This happens because the wavelength of sound becomes shorter and shorter as you go up in frequency, hence the sound waves cannot "wrap" around the loudspeaker. Yes, some front-firing designs manage to achieve exceptionally wide dispersion through a narrow baffle configuration, but in the end there is no way to cheat the laws of physics and a front-firing speaking will never be able match the broadband off-axis output of a true omni-directional design. This is why an omni speaker will always be more susceptible to early reflections from nearby surfaces compared to a front-firing speaker (even when compared to a front-firing speaker that has exceptional dispersion), thus greater care in positioning is required.

In the end, my point is that you cannot apply the exact same method of speaker placement to both front-firing speakers and omni speakers. Placing a conventional speaker 3 feet from an untreated wall may have worked for you in the past, but this just isn't going be optimal for an omni speaker. When you switch to an omni speaker, the difference in its radiation pattern simply requires a change in your thinking.