Every design...

August 16, 2016
 by Paul McGowan

...of loudspeaker has its good and bad points. None are perfect. Not even close.

With electronics we can get closer to the ideal, though perfection will always remain an elusive goal.

Single driver loudspeakers, of which we have been discussing as of late, are no different. I have heard many good ones, and just as many bad ones.

Though not a true single driver speaker, Walter Liederman and Mark Schifter's work on the Emerald Physics line of open-baffle single-point speakers always impresses. And there are more, though my goal in this series is neither one of praise nor condemnation of any one design.

As I wrote, they all have their strengths and weakness.

Before we leave single drivers for the divided world of tweeters and woofers, it's probably worth a moment to look at another method of separately enhancing highs and lows with one driver.

The whizzer cone.

Exif_JPEG_PICTURE

I don't know the history of these funneled protrusions but they are a mechanical means of improving high frequency response, one that does not rely on an electrical crossover.

The whizzer cone is a small and separate cone attached to the voice coil. To be effective, designers must decouple the larger woofer cone by the addition of a small bit of flexible material. As the woofer voice coil moves faster, the whizzer cone stays perfectly synched while the larger woofer cone has reduced movement. The idea is that at the highest frequencies the whizzer acts as a tweeter, its small cone area pumping out higher frequencies, while the larger woofer cone relaxes and sticks with lower notes.

These types of cones have fallen out of favor for two reasons: most had a sound to them that wasn't all that natural, and designers had moved on to what is known as the coaxial driver.

Altec 601

Coaxial drivers are not new. This picture is of an Altec Lansing 601 from 1943. Unlike a whizzer cone, coaxial drivers require a crossover. They are, after all, a two-way loudspeaker, with a tweeter and woofer.

That's what we'll cover tomorrow.

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15 comments on “Every design...”

  1. A driver's membrane should transform the electrical signal into a pneumatic sound wave which was sensed by the microphone - - neglecting here effects added by the mixing console. It seems quite impossible to get two membranes of different mass working together in a way that the superposition of their movements create the original sound wave.
    Only a massless (non-inert) driver could follow the signal of the amp. The best approach to a near massless driver is a plasma tweeter showing a most limited sound pressure for frequency below 5 kHz.
    Finally no speaker is able to reproduce the original sound wave fulfilling the requirements for original sound pressure levels. The art seems to be creating sound patterns that come close to the patterns relevant for the recognition of familiar sounds. Obviously there are patterns for timbre recognition as well as localisation.
    Only headphones could come close but lack creating all patterns relevant for localisation and sensed 'body shaking'! 🙂 I remember ideas long ago in the quadrophonic-sound era of combining headphones following the open design with subwoofers!

      1. The ozone problem has been solved according a manufacturer's claim (Acapella Audio Arts) already in the mid 70th of the last century! However the biggest problem with HIFI/stereo is the missing holistic approach based on psychoacoustics and pattern recognition. Marketing guys claim point source behaviour not knowing that a point source is an ideal mathematical concept within Huygen's theories! A point has no dimension!

  2. The father of a childhood friend had one of these Altecs mounted in a wall in the basement that cordoned off the laundry room in an infinite baffle sort of way. It really rocked the rec room when we had a sleep-over. Kingston Trio, the Limelighters, Peter, Paul & Mary, Ray Charles.

  3. I don't understand this :
    "It really rocked (??) the room....". With the Kingston Trio, the Limelighters, Peter, Paul & Mary, Ray Charles ?
    Sounds like music for a retirement home.
    Not exactly AC/DC, Korn, Stones, Metallica, Rammstein and the likes.
    That's what I call rocking.
    😀

    1. I once worked a concert where Ray Charles was the headliner (and fixed the rented Leslie speaker!). I can assure you that by any standards, he rocked the house - or in that case the slope, it was at the Winter Park ski area.

      The Kingston Trio and Peter, Paul and Mary made toe-tapping music and got big, packed venues moving. I once sang on a stage with Pete Seeger on television, and he got people marching with a banjo and his voice.

  4. In the vintage arena, the legendary Altec curvilinear cone had gradual decoupling of the voice coil so the effective surface area decreased smoothly with frequency, and had response to 3KHz in their 15" without excessive beaming. It still required a tweeter, but moved the crossover out of the human sensitivity peak. These were copied by Nick McKinney at Lambda Acoustics, who also incorporated a Faraday to extend to 5KHz.

    One of the most amazing feats is the Thiel mid-tweeter which has a mechanical crossover in an Aluminum diaphragm driver. The metallic resonances are well controlled by MAGIC - or rather, years of dedicated engineering and brilliant development.

  5. Okay, I'm convinced. From what you tell me, there's only one conclusion possible : Peter, Paul & Mary rock.
    And a banjo is the ultimate rockin' instrument.
    🙂

  6. Why can't full range drivers work to cover the entire audible spectrum while headphone drivers can. The answer is that due to the very low required output, on axis positioning, and controlled environment between the headphone and the ears. Headphone drivers can reconcile competing requirements for low and high frequencies at the same time while single driver loudspeakers can't. To produce low frequencies from a speaker you need to move a lot of air. That means a large heavy driver cone with a long stroke. It means high inertial mass. To reproduce high frequencies it must be very light with very low inertial mass and if it is to have any dispersion at all, it must be small. It doesn't have to produce a lot of sound but what it does produce must meet these criteria. Large, heavy, long stroke versus small, light short stroke.

    Loudspeaker drivers are resonant devices. Typically they only have a relatively flat frequency response over about 2 to 2 1/2 octaves,
    sometimes if you are lucky three octaves. There are extraordinary measures that can extend this response over a wider range but those solutions are complex and often require a lot of amplifier power. For example, the CTS driver used as a full range driver in Bose 901 would require six hundred to a thousand times as much power to achieve the same sound level at 30 hz as it does at 1 khz. It has very little response above 10 to 12 khz. It takes a monumental boost at both frequency extremes to even achieve that and there are FR anomalies in the bass boosting the output in the 250 hz range that helps extend the lower bass which has a 12 db per octave falloff that must be compensated for. The equalizer only provides 6. Even with its equalizer it crosses the 1 khz output at about 90 hz and is around 12 db down by 30 hz even with its 18 db boost. This may explain why they are often played at ear shattering levels.

    Headphone drivers are a different story. My favorite, Sony MDR-V6 covers the entire audible range with clarity and neutrality (careful there are fake knockoffs of it out there, Youtube videos can show you how to tell the difference.) They are rugged and have a long coiled cord and have become a favorite of recording engineers which helps explain why they are still manufactured decades after their introduction. The tight seal around your ears gives the driver a load to work into. The volume in front and behind the driver are of comparable orders of magnitude. Loudspeakers do not work into an external load, the so call "room loading" is a complete myth, there is no such thing as the room has hundreds if not thousands of times more air volume than the speaker enclosure. Pull the headphones away from your ears and the low bass is gone. There was only one problem with MDR-V6. It only cost $67 retail back in the early 1990s when I bought two pairs. Not much profit to be made out of it at that kind of price.

    so

  7. Interesting to note how “dueling banjos” was made famous and gained international popularity of bluegrass music in 1972. Deliverance was selected for preservation in the United States National Film Registry by the Library of Congress in 2008 as being "culturally, historically, or aesthetically significant". Bela Fleck pays tribute in concert to Lester Flatt and Earl Scruggs popular song “the ballad of jed clampett” from a television show back in 1962.

  8. I don't have to ask good old Bela.
    I heard some of his music. Never realized it was rock.
    I thought campfire music. And there's nothing wrong with that.

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