Bob Carver announced the Amazing Line Source (ALS) Loudspeakers, which claim to present a huge and majestic soundstage that captures the complete sense of acoustic space that helps make music come to life in our listening rooms. Bob Carver believes you will hear beautiful sound images inside that larger acoustic that will seem so real it will be downright spooky. There will be a soundstage that extends far back from the speakers, and it will be much wider than the speakers.
A solo female singer will appear center stage, up and back slightly, perfectly focused, singing her heart out as if she were in our room, all the while being inside that larger acoustic bubble. It is very, very spooky.
How it works
A line source speaker is simply a speaker so tall and acoustically long that we, the listener, hear a speaker that goes all the way to infinity. Up to infinity and down to infinity, resulting in what a scientist would call a “perfect wave launch.”
The wave from the speaker sounds as if it emanates from a gossamer thin filament running from below the center of the earth to beyond the moon. A pure cylindrical sound wave.
When we listen to such a wave, we find that we can hear musical nuances that we often cannot hear at all using conventional speakers.
“An analogy is to consider a thin pole that is eight feet tall, extending from floor to ceiling. On the pole are mounted 22 lit birthday candles, each a light source. Additionally, imagine the floor and ceiling to be perfectly polished mirrors. When we look down a the bottom of our speaker, we will see lit candles reflected in the mirror continuing all the way down to minus infinity. If we look up towards the top of our speaker, we will see the reflections of candles that go up to plus infinity. Here’s the best part: All these reflections are real light sources to our eyes, as real as any real candle; we can read a book by their light. The candles in the mirrors make light just as well as the actual candles in the room on that pole. Absolutely non-intuitive! Now instead of candles, imagine that we replace them with lots of small loudspeaker drivers. The same holds true for speakers and candles alike; the speakers in the mirror make just as much sound as the speakers in the room, and behave for sound the same way as the candles behaved for light.”
“Here is the next best part: we can remove the polished mirrors and just use the floor and ceiling to make the line source work perfectly,” Bob Carver explains.
The ribbon looks like it’s from Parts Express
Of course it is. Bob Carver designed that ribbon over thirteen years ago for a loudspeaker he ended up developing and calling the Sunfire Cinema Ribbon. The ribbon was built in China by Hi-Vi for Homni, my Chinese supplier for drivers at the time. Shortly thereafter he sold the design to Hi-Vi as part of a joint cooperation agreement for manufacturing tooling, and subsequently it was delivered into the public domain by my intent. Hi-Vi, under the joint cooperation agreement, markets it worldwide and now sells it to Parts Express. Again, it was originally designed for Bob Carver’s Cinema Ribbon and is still used in Cinema Ribbons today. It is truly an amazing ribbon, says Bob.
121dB SPL is an enormous sound pressure level but the numbers that teach us how it does that are comprised of simple arithmetic. First,a pair of the small woofers as utilized in the tried-and-true Cinema Ribbons produce a loudspeaker that has a sensitivity of 89dB SPL. The Cinema Ribbon was designed to absorb all the power that my 200 watt per channel amplifier could deliver. At 80 Hz it’s peak-to-peak excursion is 0.48″. The Amazing Line Source speaker has 22 of these drivers per channel. Since each driver can take 100 watts (92 watts with crossover losses), how much can each Amazing Line Source speaker handle? Well, 92 x 22 is 2,024 watts. At those power levels and at 80 Hz, those woofers are moving back and forth 0.48″. Or, from another point of view, 80Hz/4 (20 Hz) allows equalization and yields flat response down to 20 Hz with a 450 watt per channel amplifier, assuming a room gain of 8dB at 20 Hz (Theoretically it’s 3dB per boundary, and there are three boundaries in a room for each speaker).
Low Frequency Response
A line source that goes from floor to ceiling is a weird, spooky, and interesting thing. Imagine that your floor and ceiling are mirrors, and the line source has 22 candles instead of woofers. If we look at it, we will see candles going up infinitely to the sky and down infinitely below. The amazing thing is that each reflection of each candle generates real light and so do the reflected sound sources of the line array. Spooky because it seems as if it’s something for nothing, and it almost is. The same holds true for the ribbons. Each ribbon, on speech and music, can easily absorb 200 watts rms and there are thirteen of them per channel. Finally, 200 watts x 13 = 2600 watts – a walk in the park for these ribbons!
Each time the area or the displacement is doubled – all other things held constant – the sensitivity increases 6dB. Here is the arithmetic: One ribbon = 89dB. two ribbons = 95dB. Four ribbons = 101dB. Eight ribbons is 107dB, and 16 ribbons would be 113dB sensitivity IF the voltage across each were held constant. Since these ribbons are in a complex series/parallel configuration we must subtract 17dB because the voltage across each ribbon is substantially lower (approximately 20% of the original voltage) yielding 96dB SPL sensitivity. The precise calculation is as follows: There are thirteen ribbons, so 10 x log(13) is 11dB. 11 + 89 = 100dB, and the crossover throws away 4dB, for a net of 96dB sensitivity. That’s the science.
Strictly speaking, nothing is distortionless. However, in hi-fi, if the distortion is below our threshold of audibility we can color it gone. If it’s gone, we can’t hear it and sufficiently distortionless to call it thus.
- Height: 8 Feet
- Cabinet: 1 piece extruded aluminum cabinet
- Number of front firing 8″ ribbons: 13
- Number of side firing 4″ high excursion drivers: 22
- Rated Power: 2,000 watts
- SPL: 121 dB
- Sensitivity: -96 dB
Price and Availability
The Bob Carver ALS speakers will be available May 2012 for $22,000.