Foster DF62 Microphone Comparison and Noise Levels

29/6/13        Foster DF62 Microphone Comparison and Noise Levels

I wanted to do a quick Post on this microphone curiosity.

I can’t find much on Google about this older, almost Beyer M160 looking microphone, but is says Dynamic Mic, Dual Impedance 50k ohm and 600 ohm, on the side, and the model number, DF-62. Is this Japanese Co. that made it, from 1962 onwards?

http://www.foster.co.jp/en_corporateProfile/history.html

Here’s a Foster DF-1 pic from Ebay:

And a MAF 400 model pic:

I did a rewire so that the (original) broken, then twisted together wires, taped up, bodged up 4 pin locking XLR to jack cable it came with was properly soldered with the other end soldered to a normal 3 pin XLR male end.

Once I DDM tested that pin 4 was cable braid to chassis, and the other 3 were normal XLR pin outs, I tested it against the Shure SV200 into the Fostex MR8 recorder, as it has 2 mic inputs. The output of the Foster was lower signal strength than the Shure, by a small turn of the gain pot. The pins count clockwise on the female side 1-4 from the key at the top.

I placed both mics in front of the 2 X 12 cab speakers about 3 inches away from a speaker each, and played the Gibson GA15 through it.

I also did a quick vocal nonsense test to see how the Foster compared to the Shure, which I had an idea of from doing a vocal test with that against a proper Shure SM58 at college last year.

It was surprising, as I assumed the Foster would be pretty horrible sounding but it wasn’t that different from the Shure, except in output level. The Foster is 600 ohm also, from what limited info I’ve read on Ebay and Google for other Foster mics:

“Impedance 500 Ohm or 25k Ohm dependent on plug in adaptor.”

It seems you changed the locking adaptor cable from XLR to jack plug, which makes sense, as you would then use the jack into a guitar amp or PA system, which expect to see higher input impedance in the 10k-500k range – like a guitar.

I wanted to do an FR curve but couldn’t think of a way at first. The visual spectrum of the recordings when viewed in FLS with the Parametric 2 plug-in, showed some very small differences in response to the two identical tracks, but not much, though you can tell a bit more when panned in stereo and setting the volumes equal each side using your ears. The Shure has more definition, and is more sensitive as it has a little distortion on the Shure track for the volume level I was playing at.

Later, I realised I might be able to do some comparison of FR by measuring the actual output voltages on the oscilloscope using croc clips on the pins, then playing the FLS frequencies through the stereo speakers with the mics in front of them at some arbitrary distance that suited the signal level on the scope, and my ears!

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Note – I always use ear plugs when doing these tests – see the info below on noise pollution level damage, and exposure times.

Read more via the link:

http://www.noisehelp.com/decibel-scale.html

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Odd measurements were taken, but it worked – on an odd level!

You have to ignore the amplitude voltage levels (in mV) as read by the oscilloscope from a practical performance point of view, because I KNOW the Shure has a higher output than the Foster when plugged into standard 600 ohm impedance that Pro Industry mics are designed for. The input impedance of an oscilloscope is high – 1 Mega ohms – so the oddity that is the Foster seems just better placed to send a higher signal to the scope than the Shure (up to 4 times or less – 80/18mV or 38/25dB max reading). The important part – which is the overall relative curve shapes, is that they mirror each other very closely, disregarding the actual output levels in milliVolts. This is great news as it means this mic performs almost as well as the “poor man’s SM58” Shure SV200.
FR.jpg

The shape of the curves overall, is of course completely dependent on the outputs of the M Audio unit, Technics SU800 amp and – most importantly – the output response of my B&W speakers.

On the real recording of the guitar, it was apparent that that Shure had more definition – the Foster was a little “blurry” in comparison, not quite the same clarity, but it was pretty close for an Industry “no name” mic that was probably designed for tape vocals or CB radio or similar decades back, not music, from the WikiP info I could find on 4 pin XLR connectors, the Ebay listings and the Foster webpage:

https://en.wikipedia.org/wiki/XLR_connector#Four_pin

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Noise Dose Formula

 

The generally accepted standard to minimize hearing risk is based on an exposure to 85 dBA for a maximum limit of eight hours per day, followed by at least ten hours of recovery time at 70 dBA or lower (at which the risk of harm to healthy ears is negligible).

Then a “3-dB exchange rate” formula is applied, which means that for every 3 dB above 85 dBA, the maximum exposure time is cut in half.

Noise levels above 140 dB are not considered safe for any period of time, however brief. For children, the World Health Organization recommends no exposure above 120 dB.

 

Maximum Recommended Noise DoseExposure Levels

 

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Noise Level (dBA)

Maximum Exposure Time per 24 Hours

85

8 hours

88

4 hours

91

2 hours

94

1 hour

97

30 minutes

100

15 minutes

103

7.5 minutes

106

3.7 minutes

109

112 seconds

112

56 seconds

115

28 seconds

118

14 seconds

121

7 seconds

124

3 seconds

127

1 second

130–140

less than 1 second

Noise Level Chart

A noise level chart showing examples of sounds with dB levels ranging from 0 to 180 decibels.

dBA

Example

Home & Yard Appliances

Workshop & Construction

0

healthy hearing threshold

  

  

10

a pin dropping

  

  

20

rustling leaves

  

  

30

whisper

  

  

40

babbling brook

computer

  

50

light traffic

refrigerator

  

60

conversational speech

air conditioner

  

70

shower

dishwasher

  

75

toilet flushing

vacuum cleaner

  

80

alarm clock

garbage disposal

  

85

passing diesel truck

snow blower

  

90

squeeze toy

lawn mower

arc welder

95

inside subway car

food processor

belt sander

100

motorcycle (riding)

  

handheld drill

105

sporting event

  

table saw

110

rock band

  

jackhammer

115

emergency vehicle siren

  

riveter

120

thunderclap

  

oxygen torch

125

balloon popping

  

  

130

peak stadium crowd noise

  

  

135

air raid siren

  

  

140

jet engine at takeoff

  

  

145

firecracker

  

  

150

fighter jet launch

  

  

155

cap gun

  

  

160

shotgun

  

  

165

.357 magnum revolver

  

  

170

safety airbag

  

  

175

howitzer cannon

  

  

180

rocket launch

  

  

  

  

  

194

sound waves become shock waves

  

 

Most noise levels are given in dBA, which are decibels adjusted to reflect the ear’s response to different frequencies of sound. Sudden, brief impulse sounds, like many of those shown at 120 dB or greater, are often given in dB (no adjustment).