A Baffling Quiz
January 1968 Popular Electronics

January 1968 Popular Electronics Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

It is doubtful that as many people today build their own stereo speaker enclosures as was the case back in the 1950s through about the 1970s. During those decades stereo equipment was a really big deal, as evidenced by the large number of articles in technical and hobby magazines. I have posted a couple dozen articles on the subject here on RF Cafe. Topics included equipment reviews and feature comparisons, troubleshooting and alignment, modifications to commercial units, build-it-yourself projects, optimized room layout and construction, and even advice on how to best enjoy your stereo system. Lots of comics appeared in the magazines as well poking fun at how a stereo enthusiast's family members and neighbor might not appreciate the ear drum-busting power capability of your system. There were also quizzes like this one on speaker enclosure baffle design to challenge the stereo buff's technical knowledge (search the list below).

A Baffling Quiz

By Robert P. Balin

Speaker enclosure designs differ mainly in the way they employ baffles, ports, tubes, columns, ducts, and horns to control the sound radiated from the front and back of the speaker. To see how much you are baffled by enclosures, try matching the cross-section drawings (A-J) of commonly used enclosures with the names by which they are known (1-10).

1  Acoustic labyrinth ___

2  Air coupler ___

3  Baffle ___

4  Ducted-port phase inverter ___

5  Folded horn ___

6  Helmholtz resonator ___

7  Horn-loaded reflex ___

8  Infinite baffle ___

9  Klipschorn ___

10  Resonant column ___

<see answers below>

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, and Radio News were published over the years - some really simple and others not so simple. Robert P. Balin created most of the quizzes for Popular Electronics. This is a listing of all I have posted thus far.

Baffling Quiz Answers

1 - D)  An Acoustic Labyrinth is a form of bass-reflex enclosure which uses a folded rear air column designed to be one-quarter wavelength at the low-frequency resonant point of the speaker. The resonant column dampens the resonant peak of the speaker and extends the low-frequency response.

2 - I)  An Air Coupler is an air column designed to be one-quarter wavelength at the speaker's low-frequency resonance point to minimize the resonant peak and provide improved speaker-to-room (free air) acoustic impedance-matching.

3 - G)  The Baffle, box baffle, or Hartley-Turner enclosure, uses a series of vented, sound-absorbent baffles to absorb back radiation and minimize back loading.

4 - A)  A Ducted-Port Phase Inverter is a form of bass-reflex enclosure in which a duct provides additional acoustic inductance to resonate with the acoustic capacitance provided by the volume of the enclosure. The reduced acoustic capacitance requirement permits a more compact cabinet for the same speaker resonant frequency.

5 - F)  A  Folded Horn offers the advantages of speaker-to-room acoustical impedance matching in a more compact cabinet than an otherwise impractically large straight horn design.

6 - B)  The Helmholtz Resonator, or R-J enclosure, is a form of bass-reflex enclosure in which the port, in the form of a narrow, circular slit surrounding the speaker, supplies additional acoustical resistance for improved low-frequency damping of the speaker.

7 - E)  The Horn-Loaded Reflex enclosure is a form of ducted-port phase inverter having the increased radiation resistance and higher efficiency provided by the horn-shaped duct.

8 - C)  An Infinite Baffle enclosure is not really infinite in the sense that all of the front radiation will go forward without refraction, but back-enclosed cabinets do prevent the back radiation from interfering with the sound radiated from the front of the speaker and, in that sense, are considered a practical form of infinite baffle.

9 - H)  A Klipschorn enclosure is a folded, exponential horn which uses the corner of the room as the final flare of the horn mouth, and thereby, in effect, places the listener within the horn.

10 - J)  A Resonant Column is a cross between an infinite baffle and a tuned pipe coupler that provides the large air volume of an infinite baffle in an enclosure design which requires less floor space.

Posted September 5, 2019