Beolab 5 - Four Questionable Technologies

Shadorne,

Regarding your 1st and 3rd points,

-The Beolab 5 may be a novel design in terms of its unique implementation, but the one technological feature that you seem to be focusing on, specifically the use of acoustic lenses to achieve omni-directional dispersion, has actually been around for a while and is a proven concept (see Hegeman / Morrison, Walcott, Duevel).

-The point that "barely any audiophiles seem to own this design" is your weakest argument as it is an appeal to authority, which is a logical fallacy. The fact that you may know of few audiophiles that own a Beolab 5 speaks more of audiophile-accepted trends, attitudes and prejudices rather than the inherent qualities of the Beolab 5 (or any other non-audiophile accepted product, for that matter).

As Microjack rightly pointed out, you ought to listen first and then let your ears decide.

Shadorne,

I just have a question for you regarding your audition of the BeoLab 5.

You said that the speakers were in a square-shaped room with glass on both sides and no acoustic treatment. How much space was there between the speakers and the side walls?

The reason why I ask is because of the design of the Beolab permits almost 180 degree dispersion throughout the treble and midrange, and the high reflectivity of the glass surfaces would undoubtedly play havoc with the speaker's ability to produce accurate imaging and soundstaging.

I've never heard the BeoLab 5 yet, but I am quite interested in hearing it for myself. So far my most favourable impression of an omni-directional speaker was a Morrison, but that's going back many years. My current speaker is the Merlin VSM-MM, so it would be interesting to hear firsthand how the BeoLab 5 sounds in comparison.

Aside from this, I just have to call you out on two claims you made.

1. "Other conventional box speakers can have wide dispersion and hence a large sweetspot AND image like there is no tomorrow."

It has to be clarified that any conventional front-firing box speaker will be highly directional the higher you go up in frequency. If you observe the lateral frequency response graphs published by Stereophile, typically for box speakers the treble frequencies from 10Khz on up will fall off rapidly the more that you move off axis. "Wide dispersion" in this case just cannot be compared to the dispersion characteristics of a true omnidirectional loudspeaker design, which means that special consideration is required for room positioning, in order to minimize early reflections that can cloud the sound and make it seem congested.

2. "No it is not necessary to sit at precisely the right spot on widely dispersive high quality speakers such as you can find at this price. Location of sound is NOT all about volume level in fact this is a misconception propagated by the industry to try and sell more center channels. You can have one speaker 10 DB louder than the other and yet the sound can come from directly between them....it is timing that tells us the location much more than volume level "

I would agree that your lateral seating position isn't overly critical for a box speaker with wide dispersion if you were only listening for tonality. However, I completely disagree with you that seating position does not matter if you are listening for imaging and soundstaging.

While it is true that the human ear perceives spatial relationships through detection of amplitude and timing differences in the sound that reaches our left and right ears, I think that your example is rather exaggerated, and isn't very helpful to Hdomke's attempt to understand how to optimize his ability to hear proper imaging and soundstaging.

A 10 DB difference in amplitude would make speaker "A" sound twice as loud as speaker "B". Thus if both speakers and the listener were positioned like points on an equilateral triangle, the centre image would be perceived to be shifted toward the side that speaker "A" is on. In practical terms, if you were listening to a vocal track where the singer is supposed to be situated dead centre, now the singer will sound like s/he is standing to one side.

In order to equalize the effect of the amplitude difference, you would have to significantly increase the spatial distance between speaker "A" and the listener, until the increase in arrival time and the attenuation in perceived volume of the sound coming from speaker "A" no longer predominates over speaker "B".

Should anyone auditioning speakers have to go through this? I don't think so. If you want to listen for imaging and soundstaging, then sitting in the sweet spot (equidistant between both loudspeakers) is essential in my opinion.

Shadorne,

Right *after* I had submitted my question to you regarding the positioning of the BeoLab 5 during your audition, audiogon posted this from you.

"In my audition they were about three feet from the corners - so to me the congestion was from the speaker not the placement."

Based on this, I must say that the it's no surprise that the speaker sounded so disappointing. 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. Honestly, the people in the B&O store should have known better. That's about as silly as putting a set of QUAD ESLs 3 feet from a front wall that's made of glass. It's so ridiculous that it boggles the mind.

One must consider that unlike a conventional box speaker, an omnidirectional speaker is radiating almost full-range in all directions. The amount of reflected energy coming off those glass walls would have definitely caused smearing of musical detail and this would almost certainly be a prime contributor of the diffuse sound you heard.

In comparison, a conventional box speaker may be close to flat across its frequency range when measured on-axis and up to about 30-degress off-axis, but as you go further off axis the amplitude of the radiated energy starts to fall off non-linearly across its bandwidth. Therefore you may get away with putting a front radiating box speaker 3 feet from a side wall (although even here, some acoustic damping from furniture or curtains would be helpful), but the same configuration for an omni speaker is just silly.

To quote from Don Morrison: "Yes, the speakers should be brought out from the side and back walls. And yes, there should be room treatment on the side walls to tame the first reflection".

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.

"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.