Reproducer calibration?

[jboger]

I've rebuilt two types of reproducers so far, the Exhibition, and a Columbian type for the Standard Model A. Both had thoroughly dried-out gaskets. The improvement in sound quality was enormous. But I recently read an article on Victor sound-boxes and how the different types had different sound reproduction qualities, some better for the bass, for example. And I've read threads here on the Forum in which someone describes the response of his/her recently rebuilt reproducer when playing a record. Sometimes someone describes an unwanted buzzing sound on high notes, again for example. It seems to me the quality of the sound reproduction depends on a number of variables: the horn, the condition of the record, and of course the kind and condition of the reproducer. To test a rebuilt reproducer it would be good to have a calibration source. By that I mean a brand new 78 rpm recording that records a wide range of sustained pitches over several octaves. Once could put such a record on and test the response of the reproducer for various frequencies. Perhaps adjustments could be made to optimize its performance. Does such a recording exist?

[Henry]

Years ago High Fidelity magazine sold a stereo test record (33-⅓ LP) intended to show effective frequency response of speakers. It did this by means of steady tones at different frequencies, from 20Hz to 20KHz, IIRC. There was also a section of sweep frequencies that would show whether one's system was afflicted with buzzing or audible distortion. Of course, there were some other variables that would affect frequency response, such as the pickup and amplifier, so this wasn't a fool-proof procedure. Still, it was useful if only to satisfy the audiophile's curiosity as to whether his set-up was "on the advertised," so to speak. In those far-off days, just about every reputable (and some not-so-reputable) manufacturers claimed that their product delivered 20-20KHz response. Not that there was much that you could do about it if your stuff didn't measure up!

I have the record. I have no idea if such a product were ever available on 78, but I rather doubt it, considering the narrow frequency response of even the best equipment in the 78 era, when such specific claims were rare, if indeed they existed at all.

Others on the board may have information that would answer your question directly. Anybody?

[jboger]

Thanks for the response. You raise some good points. One might not be able to do much about a poorly responding reproducer in certain frequency ranges, as you note. Still it might be useful to disentangle the reproducer's response from just a bad record or bad recording, although you couldn't do so with respect to the horn. I've bought brand new mica through eBay. And I've noticed that some of the layers of mica seem to be delaminated even in the new material (or was I just the recipient of some bad stuff?). There may be some parameters one could adjust on a reproducer depending on how it is made: how much one tightens down on the gaskets, the gauge of the gasket, the material of the gasket, and the condition of the mica; tension on the stylus springs, and so forth. Well, a thought.

[CarlosV]

Actually HMV in England issued a series of test tone 12 inch 78 rpms. I have some of them, not the full series though. It has fixed tones ranging from about 80 Hz to 10 kHz (both extremes inaudible in gramophones), another disc has increasing tones at fixed octave/minute rate. The whole series is made of I think four or five discs (I don't have them in front of me), and from the label it looks like they were issued in the late 30s or 40s. If you keep an eye on UK Ebay you will eventually find these discs, every once in a while they show up for sale.

[52089]

Thanks for the response. You raise some good points. One might not be able to do much about a poorly responding reproducer in certain frequency ranges, as you note. Still it might be useful to disentangle the reproducer's response from just a bad record or bad recording, although you couldn't do so with respect to the horn. I've bought brand new mica through eBay. And I've noticed that some of the layers of mica seem to be delaminated even in the new material (or was I just the recipient of some bad stuff?). There may be some parameters one could adjust on a reproducer depending on how it is made: how much one tightens down on the gaskets, the gauge of the gasket, the material of the gasket, and the condition of the mica; tension on the stylus springs, and so forth. Well, a thought.

You are on the mark with your thoughts about adjusting various parts of the reproducer's components. You can read some more about this in the Compleat Talking Machine, and there are many comments on this board about rebuilding techniques.

Victor did make a series of technical discs with both constant and sweeping frequencies. These are pretty hard to find though.

[bigshot]

Years ago High Fidelity magazine sold a stereo test record (33-⅓ LP) intended to show effective frequency response of speakers.

That may have been the one my brother had... I distinctly remember that the tones above 10kHz would only last five or ten plays before they started getting destroyed, even with my brother's nice Thorens turntable. Eventually, the upper frequencies turned into a mush of distortion. Later on in my career when I was producing a record, I asked the disk mastering engineer about it and he said that it was standard practice to look for frequencies above 15kHz and apply a low pass filter when they were cutting LPs.

[Uncle Vanya]

Years ago High Fidelity magazine sold a stereo test record (33-⅓ LP) intended to show effective frequency response of speakers. It did this by means of steady tones at different frequencies, from 20Hz to 20KHz, IIRC. There was also a section of sweep frequencies that would show whether one's system was afflicted with buzzing or audible distortion. Of course, there were some other variables that would affect frequency response, such as the pickup and amplifier, so this wasn't a fool-proof procedure. Still, it was useful if only to satisfy the audiophile's curiosity as to whether his set-up was "on the advertised," so to speak. In those far-off days, just about every reputable (and some not-so-reputable) manufacturers claimed that their product delivered 20-20KHz response. Not that there was much that you could do about it if your stuff didn't measure up!

I have the record. I have no idea if such a product were ever available on 78, but I rather doubt it, considering the narrow frequency response of even the best equipment in the 78 era, when such specific claims were rare, if indeed they existed at all.

Others on the board may have information that would answer your question directly. Anybody?

Victor issued a "Frequency Record", Victor 84522. Side A was continuously variable pitch sweeping from 10,000 cps to 30 cps, with buzzer signals at 10,000, 9,000, 8,000, 5,000, 4,000, 2,000, 1,000, 500, 200, 100 & 50 cycles. Side B featured 2 bands, 1,000 and 2,300 CPS when played at 78RPM and 433 and 1,000 CPS when played at 33 ⅓ RPM.

This disc is both useful and scarce. I own two good copies which I have used in the past to run frequecny response curves on various machines.

[bigshot]

If you found imbalances in certain frequencies, I don't know how you would correct them. It's not like the soundbox has a built in equalizer. I guess you could rebuild it again using new materials, but I suspect you'd end up in pretty much the same place if you've done a good job on the rebuild.

[Uncle Vanya]

If you found imbalances in certain frequencies, I don't know how you would correct them. It's not like the soundbox has a built in equalizer. I guess you could rebuild it again using new materials, but I suspect you'd end up in pretty much the same place if you've done a good job on the rebuild.

One is limited, but on mica diaphragm reproducers one may change the thickness of the mica, and vary the compliance of the edge gaskets, along with adjusting the tension of the cross tension springs at the stylus bar pivot. All of these greatly affect response, though each adjustment also affects all others. In addition, one may vary the compliance of the connection between the reproducer and tone arm. This is a very important adjustment. It affects low frequency response and can hav a damping effect on midrange peaks.