Cricket Continuity and Polarity Test Set

[Deleted User]

The calibration tape that is offered from The Tape project allows for determining if a person's complete tape playback chain conforms to standard polarity or not. In order to use this tape I needed a Cricket polarity test device. So I ordered one from B&H Photo Supply for a reasonable amount and have had fun checking out my system's polarity. The test set has two parts: the "sender" and the "receiver" and like the names imply one unit sends a special signal to whatever device you want to check (speaker, preamp or amplifier) then the other unit receives this signal and shows with either a red or green LED what the absolute polarity is. Since I have dipolar speakers the green LED showed from the front of the speaker and the red LED showed from the rear.
This "send/receive" capability can also be used to check a cable's continuity as well as microphone polarity. I used to watch the engineers at Polk use a similar device to maintain polarity during speaker testing and design. All-in-all a handy device that is useful and reasonably priced.

F1nut

Early Christmas present to yourself?

mhardy6647

Back when I was really experimenting with drivers and horns to enhance the width of the stereo image from the big boy loudspeakers, I got myself thorougly confused by Altec and JBL's historically variable way of defining + and - on their compression drivers.

One of the local gurus recommend a Cricket, and offered me loan of his. Knowing this fellow, I - gingerly - looked it up on the internet to see how much they cost. When I saw how much (i.e., how little) they cost, I bought a set!

They can be invaluable in matters of polarity. I'd opine that anyone who even wonders about the polarity of... anything... more than once a year should have a Cricket test set in the house.

The worst thing I can say about them is that the build quality is a little skeevy. Other than that, a useful gizmo and a great hifi/audio bargain tool/test device.

[Deleted User]

Putting the 9 volt batteries in the enclosures was a little difficult, but other than that not too bad. As it turns out the Ampex inverts the polarity, according to the calibration tape. I guess if I want to be the consummate audiophile I should reverse the speaker's polarity (and adjust the subwoofer's polarity) when I play a tape on that deck. I suppose I could consider a cathode follower to flip the polarity, at the risk of adding another stage.

pitdogg2

What benefit is there for the deck to reverse the polarity Ken?

[Deleted User]

The idea is that from the recording microphone's diaphragm to the motion of the loudspeaker's element should conform to a standard called absolute polarity. The positive moving part of the audio signal should cause the speakers cone or diaphragm to move forward away from the cabinet or frame in the case of electrostatic speakers. This chain of events can be moved even further back in the reproduction chain all the way to how the microphone reacts to the changing air pressure of sound.
In a perfect world as the microphone captures the sound should be the same way the speakers deliver that sound to the listener.
The Sheffield Labs records always recommended reversing the speaker's polarity when listening to their records. To me it always seems that the sound seems to move out away from the speaker forward when things are in agreement. Different people react differently to changes in absolute polarity.

[Deleted User]

There can be a problem with most consumer level Dolby B decoders and some tape recorders. The way these units work is that they reduce the high frequencies of the incoming audio signal when there is no signal present beginning at 5kHz and above. This is how the effect of high frequency tape hiss is reduced by 10dB. The Dolby processor looks for this signal by changing the incoming AC signal to a DC control voltage that is applied to an FET acting as a variable resistor to raise or lower the high frequency information. The potential problem is how this rectified control voltage is created. To reduce design costs most consumer grade decoders use half wave detectors which only operate on the positive portion of a music signal. As we know music, by nature, is asymmetric and controlling the high frequency response based on what occurs on the positive going portion of the complete waveform will change things.
This means that depending on the absolute phase of the signal produced by the tape deck's output chain will adversely effect the signal coming out of the Dolby decoder. . Professional level Dolby B decoders will use a different method of obtaining this control voltage and will not be as effected by differences in the incoming absolute polarity.