Radio Shack Sound Level Meter Uživatelský manuál stáhnout pdf (Strana 2)

2

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element clear of reflection boundar-

ies. I measured the subwoofer using the

ground-plane method.

I used each of the four RS SPL meters

to measure the bookshelf speaker and

subwoofer. Then I calculated the differ-

ence between the RS SPL meter mea-

surements and the reference measurement

for both the bookshelf speaker (ground-

plane and pseudo-anechoic methods)

and subwoofer to determine the RS SPL

frequency responses. I spliced differ-

ence calculations for the subwoofer and

bookshelf speaker (ground-plane) around

180Hz. Then, I spliced the ground-plane

and pseudo-anechoic bookshelf speaker

difference calculations around 500Hz to

complete the RS SPL meter frequency

responses. Figure 1 illustrates this process

as a flowchart.

RESULTS

I used a Brüel & Kjær Type 4220 pis-

tonphone to check the absolute dB accu-

racy for all four RS SPL meters, which

Radio Shack claims have an accuracy

of ±2dB at 114dB SPL. The B&K pis-

tonphone produces a calibration SPL of

124dB SPL at 250Hz. Table 1 displays

the dB SPL deviation, from factory set-

tings, referenced to the pistonphone cal-

ibration level.

All RS SPL meters used the “C

weighting” setting, which has the fac-

tory-claimed frequency response of

32Hz~10kHz (±3dB). Figure 2 plots

the four calculated

RS SPL meter fre-

quency responses.

Table 2 displays

general observa-

tions regarding low-

f requency cutoff

(-3dB point) and

mid-band tolerance

(32Hz ~ 10kHz)

from analyzing the

calculated RS SPL

meter frequency re-

sponses.

Table 3 lists the

1/3-octave spaced

low-frequency deviation compared to

the Mitey Mike II and its associated

electronics. Although I used only two

samples of the old RS SPL meter, one of

the new RS SPL meters, and one digital

RS SPL meter—in this study, those who

require some compensation values for

their respective versions of the RS SPL

meters may wish to apply these numbers

for correction when performing ¹⁄₃-oc-

tave low-frequency measurements.

DISCUSSION

The absolute dB SPL the RS SPL me-

ters measured referenced to the B&K

Type 4220 pistonphone were within

±1dB. These RS SPL meters are quite

accurate in the actual sound pressure

level they measure. This is quite impres-

sive for an inexpensive device!

The old RS SPL meters mostly

matched the low- and upper-end rolloff

characteristics of the C-weighting curve

(Fig. 3). However, the new RS SPL

meter deviates from the C-weighting

characteristic in the low-frequency roll-

PHOTO 3: RS

digital-dis-

play sound

level meter.

PHOTO 2: RS

sound level

meter (old,

discontinued

model).

FIGURE 1: Flow-

chart depicting

method to con-

struct the RS SPL

meter frequency

response.

Low-frequency Mid-band tolerance

cutoff (-3dB) (32Hz~10kHz)

Old RS SPL meter (A) 23Hz ±2.8dB

Old RS SPL meter (B) 24Hz ±4.25dB

New RS SPL meter 41Hz ±7dB

Digital RS SPL meter 32Hz ±10.4dB

TABLE 2: Low-frequency cutoff and mid-band tolerance for

the four RS SPL meters.

Old RS SPL meter (A): -2dB SPL

Old RS SPL meter (B): -1dB SPL

New RS SPL meter: -1.5dB SPL

Digital RS SPL meter: 0dB SPL

TABLE 1: Absolute sound pressure level deviation of the four RS

SPL meters referenced to a B&K Type 4220 Pistonphone.

Pistonphone Deviation

1 2 3 4

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