Tag: ALS

Posted in Carver Audio

New Bob Carver Designed ALS Speakers

New Bob Carver Designed ALS Speakers

Bob Responds:

I’ve been reading the commentary on my new speaker and find the interest very exciting. Some of the comments I will address now.

One: It can’t be done

My answer: Of course it can. Not only that, but I am used to being accused of inventing things that can’t be done, beginning with the Phase Linear 700 watt amplifier of long ago, all the way to my current high-pressure subwoofer. So I’m used to that.

Two: The ribbon looks like it’s from Parts Express

Of course it is. I designed that ribbon over thirteen years ago for a loudspeaker I 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 I 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 my Cinema Ribbon and is still used in Cinema Ribbons today. It is truly an amazing ribbon, if I do say so myself.

Three: 121dB SPL

121dB SPL is an enormous sound pressure level but the numbers that teach us how it does that are comprised of simple arithmetic. I begin: 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″. Now, my new 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).

Four: 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!

Five: Sensitivity – 96dB

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.

Six: “Distortionless”

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 I consider it sufficiently distortionless to call it thus in my use of colloquial English.

Seven: “fast and loose with hyperbole”

I plead guilty for hyperbole, not guilty for fast and loose; my designs always deliver the performance and the numbers, for real, every time, as evidenced by independent reviewers over and over again through the years. Wait and see.

Thanks guys, your comments and passionate responses to this new loudspeaker have made me think.

Great comments, warmest and best,

Bob Carver