AUDIOCLINIC (Q and A) (Jan. 1975)

Pink Noise Revisited

In the September issue, Mr. Giovanelli's answer to Mr. Paul Lutz's letter concerning pink noise was wrong.

In the first paragraph Mr. Giovanelli states:

"If one devises a filtering system, however, this noise could be produced over a portion of the spectrum only. It is this reduced noise band width which we refer to as 'pink noise.' " The 1/3-octave 'pink noise' is a special case of such pink noise, where the spectrum is divided into very narrow segments, each of which is 1/3-octave wide." Random noise produced by a noise generator (which Mr. Giovanelli referred to) is normally what is called "white noise," as it is similar to white light having an equal energy level at all frequencies within the portion of the spectrum being utilized. This portion of the spectrum can be many octaves or any small amount desired, such as 1/3 octave, and it is still white noise. If this white noise is filtered through a network which gives a 3-dB-per-octave attenuation as frequency is increased, you then have pink noise which has equal energy within any octave or fraction thereof, such as 1/3 octave, 1/4 octave, etc. It is this difference between equal energy at all frequencies and equal energy within an octave or fraction thereof, which is of significance. I feel that Mr. Giovanelli's statement was not only incorrect but could very badly mis lead someone who is starting in the audio field as a professional and who has not had formal instruction which would make him aware of the inaccuracy of this statement.

-S. Blair Hubbard; Chief, Branch Audio Production Services

Dept. of the Interior National Park Service

Harpers Ferry, W.V.

A Problem of Boominess

Q. My speakers perform quite well through the upper mid-range and high end. They are plagued, how ever, by a mid-bass peak which seems to place the male voice "in a barrel." Lower strings are likewise hollow and overly resonant sounding. Reduction of the settings of the bass tone controls on my preamplifier by about 8 dB removes the problem, but thins the low bass too much. I know I could opt for different speakers or employ a frequency equalizer, but I wish to avoid undue expense.

Can you suggest a modification to my present system which would solve or ameliorate my problem?

-Ralph L. Price, Jr., Woodbridge, N.J.

A. A possible approach to your problem is to place your speakers in different parts of the listening room, with the hope that a location for each speaker can be found which will minimize this condition. The listening room often contributes more to boominess than do the speakers themselves.

Paralleling Power Amp Inputs

Q. Can I use a "Y" connector in each channel of my preamplifier to drive a pair of mono amplifiers per channel. I have four Advent speakers, and I would like to power each one with a separate amplifier.

-C.T. Lewis; Morrisonville, N.Y.

A. You should be able to use the "Y" connectors to feed two power amplifiers from one channel of a pre amplifier, provided that the total in put impedance represented by the two power amplifiers does not fall below the minimum recommended by the manufacturer of the preamplifier.

Where two power amplifiers are identical, the combined impedance of their two input circuits will be one half that of a single power amplifier.

(Source: Audio magazine, Jan. 1975, JOSEPH GIOVANELLI)

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