EMG Gramophone Equations/Frequency Responses?

[Ethan]

Does anyone know the frequency responses—especially the low-end cut-off frequencies—of the EMG Mk IX and Mk Xb (not the Oversize)?

Based on the length measurements that Graham Rankin gave in the thread about the vertical-horned EMG, and assuming a roughly 1.5” horn throat diameter, I found the equations pictured below for the Mk IX and Xb's respective approximate horn contours, which would indicate roughly a 100 Hz cut-off for the Mk IX and 80 Hz for the standard Xb—Does that seem accurate to those of you who have heard them in person?

EMG Mk IX equations, assuming ~1.5" diameter throat, 58.5" length, and 22" diameter mouth--I wasn't sure whether that was the inner or outer throat diameter, but the contour is about the same either way. The top equation assumes a 1.5" outer diameter and 1/16" wall (1 ⅜" inner diameter), and bottom one assumes a 1.5" inner diameter.

EMG Mk Xb equations, assuming ~1.5" diameter throat, 82.5" length, and 29.5" diameter mouth.

[Inigo]

How interesting! Thanks!
But as per the horn mouth perimeter being the cutoff wavelength, or 80% of it, as per others, we have:

22" mouth -- 69.12" wavelength = 1.76 m -- 194Hz, or 155Hz if the 80% rule is considered

29.5" mouth -- 92.7" wavelength = 2.35 m -- 144Hz, or 116Hz if 80% rule is used

[anchorman]

What are you using to draw the curves? And can they be exported as an autocad file?

[Ethan]

Mouth perimeter is definitely another way to look at it—based on what I’ve read about horn design, EMG mouths seem much too small to give even responses down to their cut-offs, but they appear to manage it quite well, so apparently there’s more to it than that—maybe very long horns are more forgiving about small mouths?

The 100 Hz and 80 Hz that I mentioned are based on the flare, so it could well be that both that and the mouth size play a role—I have heard that the Xb Oversize has the same flare as the Xb, but with an extended mouth (i.e, larger x-value at the mouth) and I believe it’s supposed to be able to go down to about 80 Hz. I’ve tried recording videos of EMGs playing late-‘20s electrical records from a speaker that goes down to 60 Hz, but there isn’t much below around 150 Hz—presumably due to the responses of the microphones used to make the videos and that I used to record them playing.

I used Desmos to draw the curves—it’s a free online graphing calculator; as far as I know, there’s no way to export the graphs as anything, but I could be wrong. I believe there’s a way to create an account (although I don’t know whether that would be free), which I think lets you save graphs, so you might be able to export from there.

[anchorman]

I used Desmos to draw the curves—it’s a free online graphing calculator; as far as I know, there’s no way to export the graphs as anything, but I could be wrong. I believe there’s a way to create an account (although I don’t know whether that would be free), which I think lets you save graphs, so you might be able to export from there.

My previous attempts used excel, and then exported the values from the spreadsheet to autocad as a script to make curves that can be used either in autocad or elsewhere. I'll have a look at Desmos, thanks!

[anchorman]

The 100 Hz and 80 Hz that I mentioned are based on the flare, so it could well be that both that and the mouth size play a role—I have heard that the Xb Oversize has the same flare as the Xb, but with an extended mouth (i.e, larger x-value at the mouth) and I believe it’s supposed to be able to go down to about 80 Hz. I’ve tried recording videos of EMGs playing late-‘20s electrical records from a speaker that goes down to 60 Hz, but there isn’t much below around 150 Hz—presumably due to the responses of the microphones used to make the videos and that I used to record them playing.

There may be a high pass filter in youtube that cuts out the lower frequencies. Or there may just not be much below 150hz on those records. When I played the test record the other day, you could faintly hear down to 50 or 70hz still even out of the little horn on the portable, but it may have been overtones I was actually listening to. Perhaps more important on some level than reaching all the way down deep is the ability for stuff above cut-off to not be rolled off so hard as it is with a smaller horn?

[anchorman]

there is definitely a high pass filter on the iPhone microphone. And probably most other phones that people use to record these videos. Some 3rd party software can bypass these filters. The better spectrum analyzer programs will do so.

[Orchorsol]

roughly a 100 Hz cut-off for the Mk IX and 80 Hz for the standard Xb—Does that seem accurate to those of you who have heard them in person?

This seems approximately right to me, or a little above those figures - from memory, around 85-90 Hz for the Xb and 75-80 Hz for the Xb Oversize.

Some years ago Bjørn Kolbrek (who co-authored 'THE' vast text book on audio horns in recent years, mentioned by Graham in another thread) visited Graham, Ian Maxted and myself and made numerous measurements on various EMGs and Experts - both from frequency test 78s using various soundboxes, and by injecting frequencies from a tone generator. Fascinating stuff!

[Henry]

In my experience, the actual low frequency response of these machines might be understated. For reference purposes, the lowest note of the piano, sub-contra A, is 27.5 Hz (a' = 440 Hz). The lowest note of a contrabassoon is sub-contra Bb, c. 29 Hz, which is the lowest pitch emitted by an orchestral instrument. I have a recording in my collection of a vocalist singing "Asleep in the Deep" which reaches down to great D, 72.4 Hz. This is on a VV-XI with Exhibition.

Incidentally, "60 cycle hum" is a rather sharp contra Bb (actual pitch in equal temperament @ a' = 440, 58.27 Hz). In the US, the dial tone of a telephone is small f, 174.6 Hz.

[Inigo]

Don't know if there are filters in YouTube, but recordings of grand organ have pretty low notes which I hear in my pc speakers very well... Check this
https://youtu.be/6sevZ7U0Rus