Interesting Exhibition observation

[scullylathe]

This is in re: the post I made on the Exhibition soundbox on my Victor VI "peaking" at different frequencies. I purchased a new diaphragm, new gaskets, rebuilt the unit as I was taught years ago by a seasoned collector, BUT - it still sounded like crap. After several months of frustration, I finally closely examined it and discovered that I hadn't noticed that the armature plate was bent and it wasn't meeting the two pivot points (the "pointy" things on the Exhibition main casting which need to meet with the two slits ground on the armature saddle) as it should. After bending the plate back to it's original shape and fixing it's position on the soundbox, it now sounds like it should. Odd thing is that I was observing the bad sound when it wasn't working properly and I noticed that it was only a certain range of frequencies that was affected by the damage. (Acoustic recordings, obviously.) I didn't actually do an analysis with my test equipment, but violins were pretty good, but 'dropped out' in certain ranges and 'peaked' in others. The rest of the frequency spectrum seemed OK, but the high mid range seemed to be the most absent. (Only one side of the saddle was meeting with the pivot point.) Strange thing is, that if this is the case with misalignment or other problems in acoustic systems and it causes response issues in only certain parts of the frequency spectrum, it indicates that there is much more to the acoustic system of recording and also validates Bettini's work and many others. (Contact points on diaphragms, etc.) Maxfield and Harrison had the advantage of electronics and by simply placing a better designed horn in the reproduction path it seemed like "better sound", but we all know that a lot of Edison Diamond Disc recordings that we know were made acoustically but sound like early electrics, as well as the fact that I can play many Victor and Columbia acoustic recordings on a rebuilt and well adjusted mechanical reproducer and get much more bass than should be there, it makes sense that mechanical systems also had the possibility of frequency sensitivity adjustment or "EQ" as electrical systems have. It was just too difficult in mechanical systems to predict and adjust for (in whatever way) equalization issues and I don't think a lot of research was done back in the day on HOW diaphragm links, pivot points, diaphragm "spiders" and other parts of the recording and reproducing systems back then affected tonal quality. The main issue was simply putting sound at an appropriate level on the disc. I'd like to hear what others thoughts are on this observation...

[chunnybh]

Tuning reproducers is rarely mentioned. With acoustic recordings having no standard for recording, it was left to the recording engineers how they set up the equipment for each recording. Different labels and the dates they were recorded on played even more havoc with reproduction quality.
A good experiment is to get at least three identical reproducers and "tune" them different. One that plays really well on a Victor might not on an equivalent Columbia record.
Reproducers can also be tuned for different types of music. I have one that simply plays most piano recitals like no other reproducer.

What’s the secret....experiment... and when you find something that works ...don't tamper with it.

[Henry]

You might be interested in reading Paul Edie's test results on the the Concert, Ex., and no. 2, at http://www.victor-victrola.com/Soundbox%20Article.htm

[scullylathe]

Yes, I am aware of Paul's experiments and read that article years ago. As opposed to overall frequency response though, I found it interesting how lack of one pivot point caused a noticeable drop in one frequency range and a harsh peak in another. Once I fixed the problem, the sound returned to normal for an Exhibition. Would have been interesting if those designing recorders back then would have better documented their research on the design of armature suspension, location of supporting edges of the stylus bars, methods of attachment to the diaphragm and the actual diaphragm material used in studio recorders. I'm sure trial and error was a factor in getting the best level and overall sound quality and it is known that the Sooy brothers that worked for Victor each had several recorders they used for different types of recordings. It is also known that mica, glass, rice paper, copper and other materials were used in recorders even though the great majority of reproducers used mica. Unfortunately, because of the relatively simple concept of mechanical sound recorders, designs that worked well were kept a trade secret.

[Phototone]

In the UK, where acoustic playback lasted longer as a preferred playback medium, getting specially tuned reproducers (sound boxes) was more common, and there were several makers of such. Makers such as EMG and Expert (basically the ultimate custom acoustic machines) did this for practically every machine they sent out.