Gramophone Test No. 6 - Victor Constant Note Record No. 6 (110-160 Hz) on the EQB B-43 (80 Hz) Horn

I recently came across a copy of Victor Constant Note Record No. 6, one of the company's technical records from the 1920s--It only covers 110 Hz to 160 Hz, but still gives some interesting information about the homemade 80 Hz horn's bass response.

As the the lowest note on the record is 30 Hz above the horn's theoretical cut-off frequency, I played each note for the full length, and then played the 110 Hz note again, using the motor's speed control knob to slow the turntable rotation and lower the pitch, making an improvised sweep from about 120 Hz (with the motor running slightly too fast) down to around 40 Hz (with the motor running just fast enough not to stop).

Assuming my phone's microphone has a reasonably smooth low frequency response, the results indicate that--at least in its current position in this particular room--the horn is slightly deficient in bass from around 140 Hz to 120 Hz, but then has a peak in its response around 110 Hz, below which the response drops off rapidly, but with another small peak around 80 Hz. There might also be very small peaks around 60-65 Hz and 47-50 Hz; when taking the plot spectrum for ~5 second-long snippets of the sweep at progressively later points in time after the 80 Hz peak, I saw very small peaks appear around those frequencies, moving down in pitch with time. The same peaks showed up in the plot spectrum for the whole sweep, but they were much smaller even than the 80 Hz peak, so they probably wouldn't have much effect on the overall sound quality, assuming they are in fact from the record and not just from ambient noise.

The plot spectrum for each note also shows high levels of harmonics compared to the result obtained from some sweeping note tests I did a while ago using an online tone generator and a modern speaker in place of the soundbox (not posted in a video), with the harmonics being least present in the 160, 150 and 108 Hz notes, which are also the loudest notes--as I don't see the harmonics in the grooves of the record, I suspect that they might be the result of horn resonance, although I'm not knowledgeable enough on the subject to say for certain.

Record information:
Victor 84503-A (take 1) / -B (take 1); recorded in Camden, New Jersey, c. 19 January 1926. Side A contains notes at 160, 150, 140 and 130 Hz; side B contains notes at 125, 120, 115, and 110 Hz. Played with a Burmese Colour Needle.