Frequency Response of Big HMV and Victor Re-Entrant Horns

[PeterF]

Over in the "Music" section, there was a thread not long ago about the Victor Frequency Record, a 12" Victor electrically-recorded record with a continuous sweep tone moving from 10,000 Hz to 30 Hz:

http://forum.talkingmachine.info/viewto ... =3&t=15711

This thread had piqued my interest on how the Victor Frequency Record would sound on various big machines, so I set about finding a copy, and was recently successful. I played it through both a Credenza (6' horn is commonly assumed) and an HMV 194 (2nd biggest horn of the re-entrant HMVs, estimated by some at 7' total length). I used the same excellent-condition HMV 5a reproducer on each, with the same medium-tone tungstone needle, and recorded them under identical conditions with the same device - all of this to minimize variables.

It's not the most fun record to listen to, and is at some points actually shrill and painful to hear. There's a buzzer that sounds at certain milestone frequencies. You can definitely hear that the systems' frequency responses are peaky, as the overall loudness of the tone varies widely as the frequency changes. As a side note, it also seems like my own ears' frequency responses are not even close to identical, since I noticed variation across the width of my head as the frequency changed, making for a side-to-side panning effect. It's almost like hearing stereo coming out of a Victrola, which is pretty weird to experience.

I'll soon be posting the videos to youtube, in the hope that someone with a spectrum analyzer will be able to give us a bit of info on the differences between the two big horns' responses, and will post the links here.

(I posted a very similar version of this note in Music earlier today but on afterthought decided to re-start it here in Machines since that's more appropriate for the topic.)

[Nat]

Interesting, and I look forward to comments and YouTube. But a thought: as a violist, I know that the appeal of the sound of a given instrument is very personal and largely unquantifiable: an instrument (or bow) that I love may not appeal to you as much as another. Metal horn vs wooden horn is another issue, quite apart from measured frequency response.

There's also the matter or "psychological bias:" a pair of recent blind tests, by way of example, compared Stradivari and various old instruments with new instruments, and the conclusions in both cases were in favor of the modern instruments, as well as very mixed as you went down the list.

But I do look forward to reading further developments and envy your chance to make the comparisons! It's an endlessly fascinating subject!

[Wolfe]

Blah, blah, blah.

Let's have it right here, right now, right on the table. The results of the test.

[RAK402]

I am looking forward to the results, sir!

[phonojim]

A spectrum analysis based on Youtube audio won't really tell us much. To run a proper analysis you would need an acoustically dead room, a calibrated microphone with known flat response to beyond both ends of the spectrum you are analyzing. In addition, your test record should be verified to insure that all tones are at the same level or the differences noted so that you can allow for them in the final analysis. I would also suggest that you use both Victor and HMV reproducers to rule out any inconsistencies there as it is my understanding that they are of at least slightly different designs. Ideally, I would think that an electronic driver used with an amplifier which could be equalized to give a flat acoustic signal into the horn over the frequency range desired would be the best way to go.

Jim

[ChuckA]

Years ago I was interested in the frequency response of the Credenza wood horn and the metal horn in the 8-9. I don't have the plots anymore, courtesy of a hard drive crash, but I remember a few results. I built a driver that attached to the back of an orthophonic reproducer and used a studio quality mike set up 3' away and on center of the horn opening for my "listening" device.

My source was an audio generator that I swept manually across the spectrum from 50Hz to 10,000Hz and measured the output of the microphone, through a flat gain preamp, then plotted the frequency response on graph paper. What I found was that the wooden Credenza horn had a -3dB frequency response from 150Hz to 5,000Hz and the metal 8-9 horn from about 300Hz to 6,000Hz. This pretty much confirmed what I could hear in that the 8-9 had a slightly brighter sound than the Credenza.

I also did a test using the Western Electric test records and the reproducer/horn combination, but for the life of me I can't remember the results. I did this almost 30 years ago.

If I were to try this again I would use a calibrated test microphone which are ruler flat out to 15,000Hz, these have dropped into the $200 range, and use an HP 35665 audio spectrum analyzer with it's built in swept sine test function to plot results.

Chuck

[Orchorsol]

I have a selection of UK-issue test records on HMV, Decca and Parlophone which I (and I know others) have found invaluable for making checks on high quality machines such as the EMGs and Experts I'm passionate about. Subjectively, these achieve an amazingly flat response across a wide frequency range; the various permutations of soundbox model and tuning give different treble cutoff points and bass response, as well as other differences. I would love to make scientific tests one day, and am finding this thread very useful as food for thought!

[PeterF]

This is by no means a scientific or sophisticated thing, just a fun exercise to compare two machines I luckily happened to have sitting right next to each other. No flat mic or acoustically dead room or any of the rest...just two machines recorded under near identical conditions to see what happens. I'll be able to post the recordings tonight.

The mention of a spectrum analyzer is intended to see the relative curves, not absolute curves showing actual frequency response of the machines. I just want to see which is peaky where and how the top and bottom ends compare.

[Henry]

Keep in mind that our subjective impression of amplitude, commonly referred to as "loudness," varies with the frequency (pitch) of a given tone. For example, high frequency sounds are very directional; small changes in elevation of the head above and below the source will strongly affect one's impression of loudness, as will turning the head to different angles to the point source. This is just one reason why precise measuring devices, rather than the human ear, are necessary to properly evaluate the acoustical characteristics of a sound source.

[PeterF]

Here's the Credenza: http://youtu.be/wr7KKjlRpig

And here's the HMV194: http://youtu.be/ZNjTLql5Hrk