The Talking Machine Forum — For All Antique Phonographs & Recordings

That's interesting, I assume much of it is theoretical and difficult and costly to test methodically, other than through listening. Can you recommend a text that explores the relationships you describe? I'd like to learn more.

I found several papers about design of exponential and tractrix horns, and downloaded from the web. You can google yourself, but later when I have access to my hard disc, I can provide the exact articles on sound transmission that I used.
BTW, the final mouth angle in Percy Wilson's book is not 41 degrees, but he mentions to be desirable 45 degrees, although he also indicates that their own experiments have lead to the conclusion that 42 degrees is a minimum, and results are very similar to 45 degrees. He does not mention the fact that the horn areas can be halved etc regarding the solid angle of sound dispersion at the mouth. This I have taken from other papers related to horns and sound transmission.

Brilliant. I've been looking for more info on horn construction and just found your Youtube channel. Looking forward to reading this thread in its entirety!

Thanks!

When you did the calculations for the horn length, did/does that include the length of the tone arm and the connecting piece between the tonearm and the horn?

anchorman wrote: Thu Oct 27, 2022 2:04 am When you did the calculations for the horn length, did/does that include the length of the tone arm and the connecting piece between the tonearm and the horn?

Yes for the tone-arm; no for the internal conduit—the internal conduit is constant-bore and small diameter, so (according to Modern Gramophones, at least), it shouldn’t have much effect on the soundwaves going through it. The tone-arm is tapered, though, so it does act as part of the horn/horn length—I measured the diameter at the narrow end of the tone-arm I used at 23/32”, the diameter at the large end at 1 ⅜”, and the length at about 14”, which gives a cut-off frequency of about 100 Hz, so I used that as the cut-off frequency when designing the horn. Ideally, the internal conduit would have been tapered, too, so that the entire thing, from the soundbox to the horn mouth, had the same flare (in which case the tone-arm and the conduit would both have contributed to the horn's length), but the 100 Hz contour flares quickly enough at the tone-arm outlet that the curvature would have become quite tight.

I think I read somewhere that adding constant-bore sections near the throat does lower the resonant frequency of the air column inside the horn because it increases its length, and maybe boosts the bass at that frequency as a result, even though it doesn't change the official cut-off frequency--I'm not sure about that, though; I could just be making it up from bits and pieces of horn articles that I only half understood...

Hi Home-made gramophone Lovers,

That sounds great!! Congratulations!!

By the way, this is one of my home-made gramophones. The bell diameter is about 33". I use Collaro electric motor and Credenza's tonearm and Credenza's brass reproducer or Meltrope II soundbox. I use my hand-made susudake needles or thorn needles.

Hideki

Hideki, I surrendered years ago to your charming achievements in gramophone things, your yt videos, your singing, and all that. On me you have an unconditional fan. I already knew your emg-esque handmade gramophone, and it's great! Probably by one of your videos playing it...

Inigo wrote: Sat Oct 29, 2022 5:39 am Hideki, I surrendered years ago to your charming achievements in gramophone things, your yt videos, your singing, and all that. On me you have an unconditional fan. I already knew your emg-esque handmade gramophone, and it's great! Probably by one of your videos playing it...

Hi Inigo,

I am planning to put up some videos on youtube, but I need to buy a USB connector to transfer videos from iphone to my laptop. I am a 70-year-old retired teacher and kind a lazy about those tech. things. Anyway I will do so in a near future. Thanks.

Hideki

Ethan wrote: Fri Oct 28, 2022 6:35 pm
I think I read somewhere that adding constant-bore sections near the throat does lower the resonant frequency of the air column inside the horn because it increases its length, and maybe boosts the bass at that frequency as a result, even though it doesn't change the official cut-off frequency--I'm not sure about that, though; I could just be making it up from bits and pieces of horn articles that I only half understood...

That bit about bits and pieces of horn articles that I only half understood sounds familiar… but it’s good to be learning new things even if I don’t fully understand the mechanics of how they work just yet.

Calculating the length of the horn is proving a little troublesome for me, as I still don’t know if I should calculate the taper of the horn (in this case meaning just the large external structure) from where the horn begins at the end of the conduit from the one arm, and how the ultimate tone arm and conduit length will effect the ideal shape of the rest of the horn. I suppose the best practice would be to start with a soundbox, figure in the length of the tonearm and conduit needed, and then calculate the rest of the horn based on the conduit opening, but as of yet I still don’t have a truly suitable tone arm, and want to make the system compatible with a number of different sound boxes. It’s likely that making the parts function their best somewhat independent of the other parts is a goal at odds with achieving the best sound quality.

My plan at the moment is to make the end of the conduit to a standard size, either that of the EMG, or the expert, or perhaps even whatever standard size and taper the Victor horns used, so that the horns are interchangeable.

Perhaps one of our colleagues who understands these things better could explain how extending the length of the horn ahead of the conduit end will interact with the ideal horn taper? As it is, I’m still grappling a bit with how to best achieve the curved section, which really ought to have a non cylindrical cross section to help the sound waves along the outer edge of the curvature to travel in unison with those along the inside edge of the curve.

The theoretical thing is to consider everything after the soundbox neck as part of the same sound pipe, so the taper law must include the tonearm, the conduit and the horn. I think this is the design of EMG and Expert gramophones.
Other thing is what we can do with our means, with a fixed tonearm, basically. So the things where we have freedom to design must respect the selected design laws, and this includes the conduit.
This said, Percy Wilson makes us understand that not being too faithful in the small diameter parts of the piping doesn't have onerous consequences in the final results. So if the true design starts at the horn throat only, the sound is likely to be good. He also mentions that adding a fixed bore pipe in the path doesn't change the sound noticeably, what makes me think that a cylindrical tonearm and conduit should not impair the sound, starting the expansion only from the horn throat. The EMG Colonel made experiments with a long fixed bore hose attached between the tonearm base and the horn throat, and the sound was also good. Watch this video: https://youtu.be/Czq9WfGWbVA