Of Stripes and Recording ...

[Tim Gillett]

...Another aspect that is often forgotten about is the pins/pressers that hold the soundstripe to the soundhead, these are plastic and will wear down and get flat, they can also end up with burrs or raised edges which can mark the edges of the frame on the emulsion side.

Not generally well understood is that these plastic "pressers" were a compromise method to press the stripe against the head's face. It resulted in accellerated and uneven wear on the head itself.

Professional film gear avoided this compromise and at greater expense used proper film back tension to gently hold the stripe against the read head in a more controlled fashion. This was one of my reasons for modifying a semi pro tape recorder to play back 8mm striped sound film. Picture of sound stripes pressed against the sound head with nothing but film tension.

[Lee McCaffrey]

I guess you would need an additional sprocket or capstan after the gate to maintain contact against the soundhead by tension alone (due to the intermittent movement).
Osi the presser pins wear due to the action of running thousands of feet of film against them under pressure. It's expected wear and tear but lubricating prints will reduce it. As the pins wear an edge will develop which can lift and start scratching the emulsion side, or lint can become snagged which in turn can mark the film

[Brian Fretwell]

The difference betweel tape and film that meant all projectors had pressure pads is the thickness of the base which gives a lower flexibility. Tape will mould itself to the heads with less pressure so heads should last longere.

I don't know about Sendust heads in reel to reel tape recorders, but later Akia ones offered "Glass and crystal ferrite" heads, I assume also for longer life.

[John Taylor]

what is the CLA value when relapped?

I think we do all forget sometimes, no matter what the design or make of projector, these heads have done very well, decades of good service and quality sound, the Sendust heads are among the best proven for a long life. I dont know what the cost of relapping would be but I'm sure a replacement projector would be so much easier.

BTW, I thought I would just add one thing to finish off my two pence worth, If you dont know what your doing and you try relapping your heads, it will be the best way to totally **** them up. Dont try this at home

[Osi Osgood]

This may be an assinine question, but could one use ELMO 🧲 heads in, for instance, an Eumig projector? If they are of the same size, magnetic configuration, and wiring?

[John Taylor]

It would nake a eumig a much better machine but in a word, no.
100% different in every way.

[Lee McCaffrey]

I don't think 35mm or 70mm mag uses pressers to contact the stripe to the heads, just film tension.
You have to think of the magnetic heads as being one part of a whole, including the amplifier circuits etc. Swapping the soundhead to a different model would most likely entail replacing the entire audio section including recording.
Given that super 8mm sound doesn't have a particularly high frequency response to begin with the heads would have to get pretty worn out before being detrimental to performance, however the balance head will go first being that much thinner to begin with

[Tim Gillett]

...Given that super 8mm sound doesn't have a particularly high frequency response to begin with the heads would have to get pretty worn out before being detrimental to performance, however the balance head will go first being that much thinner to begin with

Not particularly high frequency response compared to the much faster linear speeds of 16mm, 35mm, 70mm! Those magnetic formats could potentially reproduce audio frequencies well above human audibility. In those much more luxurious formats for sound and picture, magnetic not optical sound was for many years the premiere format for both film sound production and presentation on release prints. Magnetic was the high fidelity format. This in spite of the fact that magnetic stripes were more fragile than optical tracks, and magnetic heads took a beating. They went to all that trouble and cost for the better sound fidelity of magnetic.

If we think magnetic stripe on Super 8 had poor upper frequency response what was the alternative? Optical on Super 8? Its response was worse. Well maintained Super 8 mag stripe exceeded 16mm optical in high frequency response.

Perhaps we forget or have never experienced how good Super 8 stripe sounded like, or could sound like. In my experience, the weak link was and is so often the projector playback. With slow film stripe speeds it becomes a wavelength game. The slightest "spacing loss", meaning a separation of the stripe oxide from the head gap by a few microns, and the treble takes a nose dive. Often the main contributor is head wear, wear so apparently insignificant we'd need strong magnification even to see it. It's easy to get used to poor highs and conclude it was always like that or that "it sounds OK to me".

That's why a reference playback can be instructive. In my playbacks of one customer's old live Super 8 mag stripe films I measured a useable upper response limit around 15 kHz. Here is a short excerpt from one of that customer's mag striped films: and it's the poorer performing balance stripe.

https://youtu.be/wBRSRIflDq0?si=EkeAnc4vbWzJ8jgl

[Lee McCaffrey]

Interesting stuff about the upper frequency response of super 8mm magnetic, I had no idea it could reach 15kHz. Most projector manufacturers never posted that high a frequency response in their specs, I think Bauer/Beaulieu reported 12kHz and Elmo 13.5kHz for the GS1200 (all at 24fps)
WRT mag audio I've been fortunate enought to attend a few repertory 70mm 6-track screenings and the magnetic sound was a revelation.

[Osi Osgood]

That sounded quite good! I do not have too many high quality super 8 audio recordings, but some really are standouts! One new one, JAWS stereo 600ft super 8 is one of the standouts! The high end clarity is really outstanding!

[Tim Gillett]

I guess you would need an additional sprocket or capstan after the gate to maintain contact against the soundhead by tension alone (due to the intermittent movement).

Yes another capstan and flywheel but unfortunately to damp out flutter from the intermittent movement at the gate, many quite expensive projectors including 8mm relied on a simple dancing arm under spring pressure. It dealt with the worst flutter but introduced wow. Another advantage of playing back film soundtracks via a dedicated sound player is the absence of this introduced wow.

[Osi Osgood]

Oh, and I agree with the statement about optical sound not beating magnetic sound, as much as I enjoy those darlings. The optical soundtracks of the late 70's throughout the 80's however, are quite superior.

[Tim Gillett]

Interesting stuff about the upper frequency response of super 8mm magnetic, I had no idea it could reach 15kHz. Most projector manufacturers never posted that high a frequency response in their specs, I think Bauer/Beaulieu reported 12kHz and Elmo 13.5kHz for the GS1200 (all at 24fps)

That's interesting. At 15 kHz there was admittedly not much signal to noise which is why I mentioned 15 kHz as an upper limit. 12 kHz or even lower would be more realistic I guess, but only with everything well maintained.

WRT mag audio I've been fortunate enough to attend a few repertory 70mm 6-track screenings and the magnetic sound was a revelation.

Yes compared to the 35mm optical of the day it was a jump up. I remember going with my parents in 1965 to see a screening of My Fair Lady in 70mm at The Ambassador's, one of our city's premier cinemas. Both picture and sound knocked me over.

[Tim Gillett]

Oh, and I agree with the statement about optical sound not beating magnetic sound, as much as I enjoy those darlings. The optical soundtracks of the late 70's throughout the 80's however, are quite superior.

Yes thanks probably to increasingly better film stocks and Ray Dolby!

[Osi Osgood]

Well, optical sound never made the jump to stereo on super 8, though it was a possibility. They were able to print optical sound on both the main and balance/sprocket area, though these tended to be used for duo language track capability, as the optical sound print of Star Trek 4 proved. That screenshot is somewhere in this forums records, if someone could find it.