General Forum

Re: Acoustic lenses

jc — Tue, 11 Jan 2011 11:49:14 GMT

Ofcourse any judgement on a speaker should be down to your own ears, like I did as I listened extensively to the beolab 3's before starting this thread. Every pair of speakers sound different, even from the same manufacturer. Different sounding speakers can all be enjoyable in their own way, I mean there isn't a "perfect sound", just different.

Re: Acoustic lenses

symmes — Tue, 11 Jan 2011 10:00:39 GMT

I can't say I am enjoying the read, but it is an intriguing one. That said, if I am going to part with 11 large for a pair of speakers, I will appreciate and thoughtfully listen to what people say and base my decision on what I, not they, think are my reasons for buying. Actually, I think most people do something similar.

Edit: PS, If that didn't translate as appreciative and friendly, I apologize. I meant it in a positive, taking responsibility, kind of way.

Re: Acoustic lenses

Teletom — Tue, 11 Jan 2011 09:45:11 GMT

jc:

So if we want to haven a "complete" speaker, we will have to save for the Beolab 5...

No, I most certainly would not say the 9's are "incomplete" speakers soundwise.

The frequency response remains generally flat with a few db's frequency rise above 10 kHz. After experimenting for a while (based on several valuable advices of fellow Beowolders) to find the correct placement, I highly admire and appreciate the overall performance of these stunning speakers. I certainly would not part with them.

Re: Acoustic lenses

TheMajor — Tue, 11 Jan 2011 08:39:59 GMT

I have never owned any relevant speakers to comment on this thread but I am enjoying the read.

Re: Acoustic lenses

jc — Tue, 11 Jan 2011 04:12:06 GMT

So if we want to haven a "complete" speaker, we will have to save for the Beolab 5...

Re: Acoustic lenses

Teletom — Mon, 10 Jan 2011 16:26:29 GMT

jc:

The crossover characteristics of the Beolab 3's as discussed above did remind me of a earlier thread about the presumed lack of midrange of the Beolab 9's. Does anyone know if the 9's are designed with comparable crossover frequencies?

Being a three driver speaker the crossover freq's in the 9's are as follows:

The frequency range of the 10 inch woofer is 30 to 180 Hz, being exactly 2,5 octaves. The 5 inch midrange operates from 180 Hz to 2 kHz, which is approx. 3,5 octaves and finally 3/4 inch tweeter takes over from 2kHz all the way up to 20kHz, which is if I' am all calculating correctly 3,3 octaves.

Thinking of the presumed lack of midrange (I have experienced more or less the same) it just reminds me of the following paragraph in Beocentral's productdescription of the BL9's:

Quote "The BeoLab 9 used 3 drive units, described as a 10” woofer, a 5” midrange and a 0.75” dome tweeter. This made for a nominally 3-way loudspeaker, though given the sizes of the drive units and their crossover points the effect was more akin to a small 2-way loudspeaker working in conjunction with a well-matched subwoofer." Unquote

Re: Acoustic lenses

jc — Mon, 10 Jan 2011 14:08:33 GMT

The crossover characteristics of the Beolab 3's as discussed above did remind me of a earlier thread about the presumed lack of midrange of the Beolab 9's. Does anyone know if the 9's are designed with comparable crossover frequencies?

Re: Acoustic lenses

spthomas — Wed, 05 Jan 2011 21:47:21 GMT

Dave Moulton:

The brilliance of the BeoLab 3 lies in exending the low frequency response of the woofer through using passive side radiators with a different resonance than the driven front-firing woofer, thereby teasing almost an extra octave out of a tiny design. I wish I'd thought of that!

Dave, thanks for you comment to my earlier question. One more thought though about your BL3 comment and BL2s and the extra octave, just an observation- do the BL2's get further down in the frequency range for the same reasons? I heard a BL2 in a store years ago that were with BL1s, and as a test track I had an organ piece which featured a soft 64' stop, which is around 8Hz. So this is well below the "spec" but it made a rumble! Later I tried the same track on BL5 and frankly didn't hear so much. Of course the 64' stop was a "resultant" stop, meaning it is really two pipes, neither 64' long for practical reasons, a 32' stop (16Hz low C) and a 2nd rank tuned a fifth above (24) so the beat frequency is 8, this is sometimes done for very low notes on organs. Of course any two tones close in frequency has a beat (major 3rd in equal temperament at some ranges).

Re: Acoustic lenses

Dave Moulton — Tue, 04 Jan 2011 08:53:03 GMT

Good questions:

The shape of the BL11 has little effect on its dispersion, because all of the wavelengths it produces are "large" relative to the device (ca. 3 - 18 meters). It is definitely NOT an acoustic lens!

Regarding the BL2, I've never believed it was "slow" in an auditory sense, as described by many. I've found it to be really nice with BeoLab 3s for both video/film and music. I don't use it in the studio bcause (a) for my production work BL3s alone are better and (b) with 5 BL5s on hand, I can "check the bass" extraordinarily easily! The physics of passive side radiators are well known, and particularly with the mass added on the BL2 there must be some lag, manifested as phase shift, relative to the driven woofer. The difference between that and what I suspect happens with a BeoLab 3 has to do with the difference in size. The BeoLab 3 will have negligible lag (relative to the BL2) because the size of the drivers is so much smaller.

So I'm one of the ones that doesn't have a problem with this, especially on the BL3s. I think they are both great examples of audio engineering!

Thanks for listening!

Re: Acoustic lenses

Alex — Mon, 03 Jan 2011 16:21:06 GMT

Guh, how irritating, I just posted a great big long response then accidentally closed the tab!

I know I can respond to the first question with some degree of knowledge if I may?

The lower the frequencies you're expecting your speaker to handle, the larger your horn or 'directivity device' needs to be. In the case of a subwoofer, this would have to be massive. An 'Acoustic Lens loaded' subwoofer would have to be wider than your average estate car is long. A horn-loaded BeoLab 5 subwoofer would have to be at least 8.5 metres across in order to make the deepest notes directional. This is because longer wavelengths wrap around smaller objects more easily. With an Acoustic Lens, you're trying to STOP the sound from wrapping around the horn, you want it to get directed in the 180ºx30º arc heard in the BeoLab 5, 9 and 3.

A BeoLab 11 is producing notes which have wavelengths as long as 6 metres, even longer in some cases. Even the highest notes it reproduces will have a wavelength of 1.5 - 2.0 metres. All of these are sufficiently long that they can wrap around the tulip design of the BeoLab 11 without being affected by it's shape at all. As the drivers are so close together, their sounds add together almost perfectly and more-or-less double the volume output. The BeoLab 11 is IMO a fantastic design!

As far as the BeoLab 3/2 thing goes, I have some theories in my head, but Dave will have much more knowledge about these two designs than anybody else on the forum! IMO, the tuning of the BeoLab 2 passive radiators is too low. A subwoofer of that size really shouldn't be able to reproduce such low frequencies at the sort of volumes the BeoLab 2 does. The result of this is higher levels of distortion. That's all in my opinion though!

Re: Acoustic lenses

spthomas — Mon, 03 Jan 2011 12:13:08 GMT

Dave Moulton:

I've never auditioned the BL11, and have no opinion of it. However, it will not solve the problem I discussed. 2 drivers (as a general rule) do not have enough bandwidth to cover the 10 octaves of the audio spectrum (say, 20 Hz. to 20,000 Hz.). A good, well-implemented driver might cover 2.5 octaves in a reasonable way. So, 2-way speakers (including the BL3, which actually is a bit more than a 2-way) have serious limitations.

The brilliance of the BeoLab 3 lies in exending the low frequency response of the woofer through using passive side radiators with a different resonance than the driven front-firing woofer, thereby teasing almost an extra octave out of a tiny design. I wish I'd thought of that!

This brings up two related questions:

- It seems like the shape of the Beolab 11 make it almost like a vertical acoustic lens- does it not such a dispersment issue as an ALT since the frequencies are so low?

- There are remarks made about the Beolab 2 being "slow" for bass because of the passive side radiators- if this really an issue, wouldn't it also be a problem with the BL3's? Here is a very positive comment about passive side radiators, but most comments related to the BL2 seem negative.

Re: Acoustic lenses

koning — Mon, 03 Jan 2011 10:08:31 GMT

Alex:

koning:

Let's face it,most B&O buyers did't have the right placements.

i hope that AST would be standard in all beovisions.

AST won't make any difference with this particular issue (tonal balance) unfortunately....

I know...But you don't have a sweet spot in the 5.1 set-up

Re: Acoustic lenses

Dave Moulton — Mon, 03 Jan 2011 09:34:00 GMT

In response to jc's question:

I've never auditioned the BL11, and have no opinion of it. However, it will not solve the problem I discussed. 2 drivers (as a general rule) do not have enough bandwidth to cover the 10 octaves of the audio spectrum (say, 20 Hz. to 20,000 Hz.). A good, well-implemented driver might cover 2.5 octaves in a reasonable way. So, 2-way speakers (including the BL3, which actually is a bit more than a 2-way) have serious limitations.

One of these almost always has to do with a dip in output at the crossover point between the woofer and the tweeter. The other has to do with the bottom two octaves of the spectrum, which are always deficient with a 2-way design (a driver big enough to move the volume of air needed to create an 18-meter long wavelength – 20 Hz.) is too big (and has too much mass, generally) to produce the 10 cm. wavelength - 3 kHz. - at the crossover with the tweeter).

Subwoofers are an attempt to fill in those bottom octaves, and may work more or less well, depending on a lot of things. However, the midrange problem is entirely different, and can only be resolved by changing the woofer into a midrange (which means re-engineering the cossover design, among other things). None of this is easy.

The acoustic lens can actually help the tweeter extend a bit farthr down into the spectrum, but it is a really a dispersion altering dvice, not a spctrum altering device. It can be scaled to fit any spectrum band you want (as in the BeoLab 5, which uss 2 lenses). In the BeoLab 3, the crossover is at a typical frequency (ca. 3 kHz., as I recall), and there is a consequent dip below that which I hear and have to account for when I'm working.

The brilliance of the BeoLab 3 lies in exending the low frequency response of the woofer through using passive side radiators with a different resonance than the driven front-firing woofer, thereby teasing almost an extra octave out of a tiny design. I wish I'd thought of that!

As for the other question on the thread about how to aim Acousic Lens speakers, the answer is, it doesn't matter much. For years, I simply pointed them directly into the room, not at the listener. I've also tried pointing them at each other, away from each other and other sillinesses.

Right now, as part of retirement, I've re-invented stereo (for me) and have arranged my BL5s in a pentagonal array, aiming all five speakers at the listening position. You can read about this at:

http://www.moultonlabs.com/more/happy_accident_a_better_way_to_play_back_stereo/

It works great! I'm quite sure it would also work great with BL9s or 3s. How good is it? One of my colleages auditioned his latest stereo release on it and said, "Ahhh. This is why we do this work!"

Thanks for listening.

Re: Acoustic lenses

Evan — Mon, 03 Jan 2011 04:29:31 GMT

I remember that thread also, about toe-in. I think it sprang up when razlaw had his Beolab 9s pointed in just slightly.

And then there was the comment about how the initial listening tests of ALTs mistakenly had them toed-in.

Re: Acoustic lenses

Alex — Sun, 02 Jan 2011 17:03:34 GMT

koning:

Let's face it,most B&O buyers did't have the right placements.

i hope that AST would be standard in all beovisions.

AST won't make any difference with this particular issue (tonal balance) unfortunately....