Questions Regarding Horn Design and Dimensions

Discussions on Talking Machines & Accessories
TN Allen
Victor Jr
Posts: 47
Joined: Sat Sep 22, 2018 11:24 am
Location: Blue Hill, Maine

Re: Questions Regarding Horn Design and Dimensions

Post by TN Allen »

One half of the oyster is milled, though with flaws. This is a learning project, a significant challenge. There are flaws, though given the material is imperfect insulation foam, and this project requires unusual demands on software and the Haas, it still seems promising.

One interesting and possibly troublesome characteristic of the 8" thick block is an unexpected low frequency resonance. I'd never have suspected 8" of this foam could "sing", nonetheless is does when bumped or rubbed a certain way.
Attachments
20211104_160337.jpg

User avatar
dzavracky
Victor IV
Posts: 1262
Joined: Fri Oct 25, 2019 11:37 pm
Personal Text: college collector
Location: Knoxville Tennessee

Re: Questions Regarding Horn Design and Dimensions

Post by dzavracky »

Wow very nice! Looking forward to seeing the finished product.

David

TN Allen
Victor Jr
Posts: 47
Joined: Sat Sep 22, 2018 11:24 am
Location: Blue Hill, Maine

Re: Questions Regarding Horn Design and Dimensions

Post by TN Allen »

Thank you.
Regarding finishing, I don't plan to do much more than glue the 2 halves together, attach the printed throat pieces, toneam and platter assembly, in order to listen to the sound.
If it is promising, I'll make and attach the turned or milled mouth extension.

I may trim some of the blocks' excess, but most of what will remain visible may not be very attractive. The really attractive part, in my opinion will be the inner horn.

TN Allen
Victor Jr
Posts: 47
Joined: Sat Sep 22, 2018 11:24 am
Location: Blue Hill, Maine

Re: Questions Regarding Horn Design and Dimensions

Post by TN Allen »

More progress, the second half is started, and one of the throat pieces is shown being printed. The vertical surfaces intersecting the horn opening will be trimmed later.
Attachments
20211115_121312.jpg
20211115_121343.jpg

User avatar
Inigo
Victor V
Posts: 2278
Joined: Mon Dec 18, 2017 1:51 am
Personal Text: Keep'em well oiled
Location: Madrid, Spain
Contact:

Re: Questions Regarding Horn Design and Dimensions

Post by Inigo »

Nice! :)
Inigo

TN Allen
Victor Jr
Posts: 47
Joined: Sat Sep 22, 2018 11:24 am
Location: Blue Hill, Maine

Re: Questions Regarding Horn Design and Dimensions

Post by TN Allen »

The throat sections are printed and fitted to the foam spiral. The weight on top was to try press the 2 halves together in order to listen to the phone through the horn. While the bass increased, it was not impressive. The phone has insufficient volume to provide any sense of the horn's efficacy.

In designing the throat section I should have reversed the direction of the exit toward the exterior top or bottom of the horn, rather than toward the center. I could print an alternative section to connect to the tonearm, but as the parts are already fitted, I'll probably continue with the existing design. This will require cutting more of the lower block away to mount the tonearm, but that's a quick job compared to printing another section. Each of the present sections required more than 8 hours print time, and the two together required 10 to dissolve the support material. They were printed entirely "entombed" to provide adequate support to maintain dimensional stability.

I'll probably epoxy the throat sections to the block, then spray foam around the sections to fill the rough cavity I carved. There are overcuts and flaws in the horn contour that need filling, then it can be painted to harden the surface somewhat. I may trim some of the excess off the exterior of the blocks before gluing the two halves together. It's all quite rough at present, but will suffice for testing, making it more presentable makes sense. Unfortunately my band saw throat opens to only 14", so I can't trim the halves once assembled, but it can be rough cut and then easily sanded and ground into a more attractive shape.

I think they will need to be glued in order to adequately seal the horn volume.

I'm still thinking of ways to assemble the platter and tonearm to the blocks. This may require a short straight section between the tonearm base and the receiving end of the printed throat section.

There are several changes I'd make were I to do this again.
Attachments
20211120_123515.jpg
20211120_123154[1].jpg

User avatar
Inigo
Victor V
Posts: 2278
Joined: Mon Dec 18, 2017 1:51 am
Personal Text: Keep'em well oiled
Location: Madrid, Spain
Contact:

Re: Questions Regarding Horn Design and Dimensions

Post by Inigo »

It looks nice. I'm sure a tonearm with gramophone soundbox will produce much more air pressure than the phone, and the volume should be quite considerable. For increasing the bass you'll need the external flare you're planning to make. The bass capacity of the horn depends greatly on that. A common rule is to end the flare so that its perimeter is at least 80% of the maximum wavelength you want to transmit. Of course the length of the horn goes together with this final size through the exponential law. You will also increase it.
End demi-angle of the flare to the axis is also recommended to be no less than 41 degrees (Wilson). Be ready to make a HUGE final external section with the flare.... For 150 Hz it should have a diameter of 24" at the mouth, kind of EMG IX or Expert Junior?
Last edited by Inigo on Wed Nov 24, 2021 1:24 am, edited 1 time in total.
Inigo

TN Allen
Victor Jr
Posts: 47
Joined: Sat Sep 22, 2018 11:24 am
Location: Blue Hill, Maine

Re: Questions Regarding Horn Design and Dimensions

Post by TN Allen »

You are too generous regarding its rough look.
I cobbled it together today with an Orthphonic tonearm and a platter I "motorized" a few months ago. There are losely connected joints in the sound path, and daylight in places between the halves. Nonetheless, the sound is good enough to warrant continuing with the project. This will require filling a few areas in the spiral, cutting down part of one block to shorten the straight section between the tonearm pivotting flange and the 3D printed sections, then painting the spiral contour, and at last gluing the halves together to eliminate leaks. I continue to puzzle over the exterior. It goes without saying it can be made more attractive.

I recorded the cobbled assembly playing various records, but have had difficulty posting the video to YouTube. I live in an area with poor internet service, my slow connection all but stalled uploading the video. I'll try again when I have access to a faster connection, and provide a link. Listening was informative.

The current mouth is ~16" in diameter. No doubt the 24" x 31" dia. extention might make a significant difference. I'll decide whether to make it after hearing the current asembly completed.
Attachments
20211123_112735.jpg

TN Allen
Victor Jr
Posts: 47
Joined: Sat Sep 22, 2018 11:24 am
Location: Blue Hill, Maine

Re: Questions Regarding Horn Design and Dimensions

Post by TN Allen »

Remarkably the video made it onto YouTube. It is rough but gives a sense of the sound. The 60Hz. hum is the shop electrical system. I moved around trying to get a sense of the sound at different angles and distances. As I explain in the text accompanying the video, the shop acoustics are awful.

https://www.youtube.com/watch?v=6hoKI7mJFyA

User avatar
emgcr
Victor III
Posts: 899
Joined: Mon Jul 02, 2012 9:57 am
Location: Hampshire, England.
Contact:

Re: Questions Regarding Horn Design and Dimensions

Post by emgcr »

What a useful machine shop ! Actually I didn't think the acoustics were too bad for some of the positions---attractive reverb' !

Well done with construction so far and I quite agree that the sound is really very good and certainly it is greatly worthwhile progressing the project---extremely interesting. It is amazing just how good the sound actually is with so many unfinished details which says a lot for the W&W mathematics and design I think. We found the same thing with the Krakenhorn (partially destroyed EMG Xb Oversize) where great chunks of the physical bell were misshapen and actually missing : https://www.youtube.com/watch?v=ojs88ChMdag

So wonderful that we all continue to learn every day. Many congratulations and thank you so much for sharing this priceless information and experimentation !

Post Reply