Quincke tube adjustment

[physicist]

You can find an explanation of the Quincke tube here:-
https://www.studyadda.com/notes/jee-mai ... -tube/8012

Strictly speaking, the device on the EMG/Expert machines is not really a Quincke tube as that requires two tubes of different lengths to be connected.
It might be better described as a "Quincke" stub as it is a closed end tube in the side of the tonearm air path. Sound waves entering it will bounce off the end and return back to the tonearm air path. If they arrive back 180 degrees out of phase there will be appreciable cancellation of the sound. This is, therefore, a tuned notch filter where the notch frequency depends upon the length of the stub.

[Lucius1958]

Agreed ! It is possible a passing bat may be able to discern differences with various settings but my ears have never been able to hear them !

Love the Flanders & Swann reference...

- Bill

[emgcr]

Well spotted !

[emgcr]

Okay, seriously, I've only been in this hobby for 40 years, so I'm just new at this, but WHAT IS A QUINCKE TUBE???

Here are the details of an Expert All Range tonearm complete with "Quincke tube".

[Marco Gilardetti]

Are there earlier designs using longer quincke tubes? The EMG/Expert quincke tubes seem to be too short to make a significant difference in the frequency range that can be heard with their machines.
I have re-visited my investigation of a longer quincke tube. The attached image shows the frequency response difference with a much longer tube.
The red curve is the frequency response I get when recording Fats Waller's "Copper Colored Gal". The green curve is the response with an extended quincke tube. The difference is shown in the brown curve. The dip at ~1250Hz is consistent with a quincke tube length of ~70mm.

I am absolutely astonished that such a small piece of tube can alter the frequency response as low as around 1 KHz, but if these are actual measurements, 1 KHz it is.

This said, -20 dB at 1 KHz is an abyss in the full centre of the audible spectrum! My next astonishment is that no one seems able to hear that!!! How is this possible?

[physicist]

Marco, the loss at ~1200Hz IS noticeable as I was testing a much longer than normal version of the Quincke "tube". With the standard EMG/Expert tube, the notch is about 3-4x higher in frequency on the maximum extension, and progressively higher as the plug is screwed in.

Here are the recordings:-

fats_waller_copper_colored_gal_normal.mp3

(2.89 MiB) Downloaded 22 times

[JerryVan]

Thanks to those who explained the Quincke tube! Much appreciated! I feel smarter now

[physicist]

I should also point out that the shape of the notch filter is affected by the ratio of tube length to tube diameter. The notch will be sharper for longer tubes. This means that for the normal shorter EMG/Expert "tube", where the effect is at higher frequency, the loss is spread over a much wider frequency range and there is less signal reduction.

The attached spectrum shows the effect of the maximum tube length of a standard EMG/Expert Quincke tube. As you can see, there is minimal effect in the frequency range of actual signal on the record.

[Menophanes]

Here are the details of an Expert All Range tonearm complete with "Quincke tube".

So that is why E. M. Ginn used the old-fashioned style of tone-arm with a T-joint, instead of a smooth curve, between the swivelling section and the main arm! (emgcr's images show that the Quincke tube screws into the outer end of the crosspiece of the T.) I have always been puzzled by this, thinking that the abrupt right-angled joint must surely have a damaging effect on the sound, especially at lower frequencies.

Many years ago, when I had an H.M.V. Intermediate Monarch with a mahogany horn, I introduced a diagonal baffle into the T-joint, thus unwittingly re-inventing the Plano-Reflex concept. It seemed to me that this resulted in a slight improvement in bass response, although I cannot produce any solid evidence of this. I am aware that the Plano-Reflex idea has long been discredited and it may be that I deceived myself about the effect of my idea, but that is how it seemed at the time.

Oliver Mundy.

[Inigo]

I've been always tempted to do that same trick on the gooseneck T section... but never tried it, though. I'm lately procrastinating ...