Exhibits details 10


Status  3 October 1914

We got from Günter Hütter, very kindly, a curious (studio) light-spot 'sound level meter'

Günter told me, that he did not understand how it works (something might be missing), I was intrigued by this artefact and would like to investigate it. Bearing in mind, that we possess another Siemens dB-meter without electronics and when the meter system fails, that we can use the other sound level meter which then is to be fed from the defect meter module.



Viewing the front panel of this curious sound-level indicator

Type-number plate is lacking.



Considering the sound-level meter from the rear towards the front-panel-scale

The two valves left and right are both neon-stabilisers (STV 150/20)


It is clear that we have to deal with a light-spot meter, usually employed in 'sound recording studios'.



Please notice first the situation where the supposed pointer-arm is missing; followed by an imagined pointer arm provision.



The rotating arm lacking its unknown pointer provision 

Visible is, that something was previously being soldered onto it. How it once might looked is unknown to us.

The white square in front, considering the fork on the other side, was meant for damping mechanically its arm movement. A quite logical provision, as sound often changes its magnitude (soundness) rapidly; and the measurement should more or less indicate its peak amplitude.  



L = path of light-rays (beam); PA = imagined (missing) pointer-arm, drawn in 'white' for reason of contrasting against background; MP = imagined meter-pointer, which black shadow should be thrown at the frosted-glass-scale. In my perception, a pointer having a broad-sized plate with in its centre a slit, would have been too heavy

I have to apologise for this a bit clumsy illustration; I miss the skill for accomplishing it better.

This moving-coil meter clearly is lacking a black pointer-needle, which movements are the result of the moving-coil deflection angle. It is not clear to me whether the needle is carried by both fork-ends, or by a single arm only; in  my perception, most likely, by means of both arms. These arms has also to fulfil another purpose: damping the pointer movements, by softly rubbing over the white square; for it I have made this virtual arm section red. On the other arm-side there exists also a thin wire or spring-load - that fulfils this function, likely even with a progressive damping function versus meter deflection.




Viewing the fork-arm fit with a curved wire

However, another option which should be considered, this wire piece is the part that is being left-over and should in some way or another have been mechanically connected onto the previously drawn example; somewhere should also have been incorporated a pointer, which's shadow is than creating a 'dark line' against a white(light) scale background projected at the 'frosted glass' scale-window.

All is my guess, as we have no other parts left.

Owing to a minor mistake, the white square has been moved upwards a tiny bit, hampering its free movement, for the time being.  



Viewing the sound dB-meter apparatus from the rear; serial number 23480

In the centre is the projection-lamp-holder. On the far left is the audio input, which is typically a 'Siemens' product; allowing pin- and wire-connections.



Viewing the dB-meter from the rear, projection module being removed

The green 'Kapsch' electrolytic capacitor apparently is from post war days, other parts might be wartime. Although, we discovered that behind the green capacitor there is mounted a so-called (flat) 'selenium' rectifier cell, likely a product of post war Siemens & Halske. Its wiring is typically of war- or post war-days.

The contacts up are to connect the projection module. Two contacts for the meter, the other two for the projection-lamp.



Upside-down, on both top sides, we encounter two RV12P2000 valves; being from origin a German military valve. However, also used in post-war days 

The long-stretched resistors where also used during wartime days (like in Nachtfee), but the bright blue ones might originate from the post war era

Apparent, the accessibility is not very serviceable, particularly those in front, below the glass-scale. 




Viewing the projection module

Down the magnet of the moving-coil instrument. Please imagine, that light flows from the projection-lamp rightwards via the optical black device towards the (projection) frosted-glass-scale.




For some time Dick Zijlmans gave us this 'dB-sound-meter' device



9Rel Bv 663K9

B-J 47b Nr. 4281

This three right-hand digits (281) are also handwritten on its mounting plate.

Also 10.59 stamped on the meter-housing. I guess, that this points to October 1959.



Viewing the meter from the rear

The 'Tuchel' connector in front were quite well known in previous days in Germany and abroad (Amphenol later purchased the Tuchel company).

On the left-hand side the projection-lamp holder. We have, however, no idea what lamp type was used, voltage and wattage unknown. Both, this meter scale and the previously described meter scale are having much in common.  


By Arthur O. Bauer