Radio Shack Sound Level Meter User Manual download pdf

audioXpress

2007 1

Radio Shack Sound Level

Meter Characteristics

By Daisuke Koya

This article investigates the characteristics of the Radio Shack Sound

Level Meter in regard to its accuracy.

Article prepared for www.audioXpress.com

he Radio Shack Sound Level Meter is a

versatile and economical device, used for

calibrating home theater speaker levels,

subwoofer level matching to main speak-

ers, low-frequency room-mode analysis, and mea-

suring loudspeakers. Conveniently, an output jack

is provided on these sound level meters, which

allows connections to personal computer sound

cards, and permits usage of these devices via PC-

based acoustic measurement programs. But how

accurate is this device and is it the appropriate tool

to be used in the aforementioned activities?

The Radio Shack Analog-Display

Sound Level Meter (referred to here-

after as the RS SPL meter) has seen a

model change. The new version (Photo

1, model number: 33-4050) is more

compact than its predecessor. I assume

that many users still own the older, now-

discontinued version (Photo 2, model

number: 33-2050), so I include it here.

The Radio Shack Digital-Display Sound

Level Meter (Photo 3, model number:

33-2055) features a digital readout of the

sound level instead of a moving needle.

I had access to two of the older-model

RS SPL meters, one new model, and a

digital version. I used these four units for

this study.

FREQUENCY RESPONSE

DETERMINATION METHOD

I devised a method to determine the

frequency response of the four RS SPL

meters. First, I took a reference measure-

ment using a calibrated Mitey Mike II

microphone and a custom-made micro-

phone preamplifier. From its specifica-

tion sheet, the Mitey Mike II has a flat

response in the low-frequency range, to

20Hz. The custom-made microphone

preamplifier was designed to have a flat

frequency response down to DC. I used

LMS, which uses stepped sine signal

acquisition

, to perform all acoustic mea-

surements.

One speaker I used in making this

reference measurement was a 6½˝ two-

way bookshelf speaker with a relatively

flat frequency response (88Hz ~ 20kHz,

±2dB). Because the bookshelf speaker’s

frequency response extends down to only

88Hz (-3dB), I used a subwoofer with

an approximately flat frequency response

down to 16Hz (16Hz ~ 200Hz, ±2dB)

to ascertain the low frequency region. I

measured the bookshelf speaker using

the ground-plane method

and the pseu-

do-anechoic (gated

) method.

I performed both measurement meth-

ods for the bookshelf speaker because

when the RS SPL meter is placed flat

on the ground, its microphone element

edge is about 1cm off the ground. I sur-

mised that this height differential in the

ground-plane measurement may limit

high-frequency accuracy

. Therefore, for

high frequencies (above 500Hz), I used

pseudo-anechoic measurements, which

place the RS SPL meter microphone

Tube, Solid State,

Loudspeaker Technology

PHOTO 1: RS

Sound level meter

(new model).

1 2 3 4

Summary of Contents

Page 1 - Meter Characteristics

audioXpress 2007 1Radio Shack Sound Level Meter CharacteristicsBy Daisuke KoyaThis article investigates the characteristics of the Radio Shack Sou

Page 2 - DISCUSSION

2 audioXpress 2007 www.audioXpress .comelement clear of reflection boundar-ies. I measured the subwoofer using the ground-plane method.

Page 3 - Stereophile

audioXpress 2007 3off. The digital RS SPL meter has a less steep low-frequency rolloff compared to the new RS SPL meter, but still a few decibels o

Page 4 - CONCLUSION

4 audioXpress 2007 www.audioXpress .comrelative accuracy. Using the new or digital meter may not produce ideal results, because its low

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