President's Message
June 2002

Dear Members,

1.  Panasonic has some new headphones: "Brain Shaker--Extreme Headphones. VMSS (Virtual Motion Sound system) makes it possible to experience truly exciting sound reproduction. Built-in amplifier boosts the bass signal." The VMSS unit transforms bass signals into vibrations which can be felt on the back of the neck through a separate transducer.

2.  Eddie Ciletti writes in Mix (My02) about a mod to the headphone amp in the HHB PDR1000 PortaDat. Users were complaining that it wouldn't play loud enough without distorting. The amplifier runs on single-ended 5 volts. By connecting the ground pin to -5 he doubled the voltage swing. He notes: "...not a user mod because it requires major dissembly; in fact the level of miniaturization [due to surface mount components] could cause severe brain fatigue."

There is a 32 ohm isolation resistor in series with the output which causes some loss of signal, depending on the impedance of the headphones (generally from 12 ohms (Sony MDR-F1) to 600 ohms Beyer DT-990pro)).

[In some tests on the NE5534 op amp as a headphone driver I found that using less than a 50 ohm isolation resistor caused uncontrolled high frequency oscillations when driven into current overload. Nothing I could do would stop it. It puts out 50 ma peak which is sufficient for almost all phones.

The recent BAS headphone clinic tested a variety of headphones. One important factor that is not well publicized is the smoothness of the impedance curve. Since the output impedance of headphone amps is generally fairly high, any variation in headphone impedance will result in a variation in frequency response. We measured the impedance versus frequency for all the headphones as well as sensitivity and frequency response and distortion and will present the results in a future BAS Speaker].

3.  Emory Cook died 19Fe02. Born in 1913, he was known for the left-right binaural disc (1952) and his innovative recording label, Sounds of Our Times. One of his most famous recordings, "Rail[road] Dynamics" was a sensation at the 1951 Audio Fair and sealed Cook's reputation as an audio guru. AESJ AP02. (They were some of the zaniest recordings made. I remember a recording of the Morelia (Mexico) organ featuring the sound of distortion, followed by the buzzing of a fly in the wind chamber. I owned a recording with the sound of earthquakes (speeded up) on one side and the sound of "whistlers" (high frequency electrical disturbances in the upper atmosphere) (slowed down) on the other side. I must have lent it to someone because it disappeared from my collection. I hope someone is enjoying it now.

David Hadaway

President, Boston Audio Society


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updated 11/11/04