8" MID HORN (development thread)
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Category: Plans
Forum Name: New Projects Forum
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URL: https://forum.speakerplans.com/forum_posts.asp?TID=103297
Printed Date: 19 April 2024 at 8:17pm
Software Version: Web Wiz Forums 12.06 - https://www.webwizforums.com
Topic: 8" MID HORN (development thread)
Posted By: luthier
Subject: 8" MID HORN (development thread)
Date Posted: 11 February 2019 at 1:22am
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So I'm planning on having a go at making a 8" mid horn, the design criteria is: - 350hz to 2khz (and above if possible) - highest sensitvity I can achieve, hopefully 104 - 105db (+/- 3db in pass band) at 4pi - Maximum depth of 412mm driver + horn - Maximum width 498mm So far I've been modeling on hornresp based around the B&C 8pe21, I have started with this driver due to it's massive EBP and reputation in horn loaded designs. My issues at the moment are: - Getting the horn to play above 2khz - Controlling the dispersion/measuring the dispersion - Lack of sensitivity - Length of the horn - Is a 14:1 compression ratio too high for an 8" driver? Also, I'm planning on trying to get hold of a trial of COMSOL futher down the line, to model the horn accuratley, has anyone on here any experience with it or similar?    |
Replies:
Posted By: MattStolton
Date Posted: 11 February 2019 at 10:20am
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My only comment would be that, without a phase plug, you may get some cancellations in the mouth of the horn, as upper frequency waves bounce from side to side, forming standing waves in the mouth. 2KHz wavelength is approx. 17cm, so any dimension of this order of magnitude will lead to some issues. To get low frequency control, your mouth will be big, so top end will be affected. ------------- Matt Stolton - Technical Director (!!!) - http://www.wildingsound.co.uk" rel="nofollow - Wilding Sound Ltd "Sparkius metiretur vestra" - "Meter Your Mains" |
Posted By: Mircea Bartic
Date Posted: 11 February 2019 at 12:51pm
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looks like you want to build something like this: http://www.bluearan.co.uk/index.php?id=SONMR8XT&browsemode=manufacturer" rel="nofollow - http://www.bluearan.co.uk/index.php?id=SONMR8XT&browsemode=manufacturer ------------- general manager & head designer at nexus-acoustics research http://www.facebook.com/nexus.acoustics.research" rel="nofollow - http://www.facebook.com/nexus.acoustics.research Ex Nexus_3 |
Posted By: studio45
Date Posted: 11 February 2019 at 2:21pm
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14:1 does seem like a lot - most 8" horns I've seen are only about 2 or 3:1 You could try modelling an existing horn and see what the graphs look like? Because I would doubt Hornresp's accuracy in the upper midrange. I think it tends to show more of a roll-off than will actually happen IRL. And I don't think it models phase plugs at all well. For example I have some phase-plugged horns here, designed for the 8PE21. (very approximate values from quick measuring) S1 = 77cm2 (annular slot around plug) so about 2.85:1 ratio S2 = 838cm2 (mouth) L12 = 27cm Exponential profile Throat chamber approx 264 cm3 (driver cone volume minus rear part of plug) Rear chamber volume approx 1.25 litres (2.5litre back bowl, assuming driver takes up about 50% of space) Rear ch depth 10cm See how you get on....These horns do actually work quite well in real life. The plots don't necessarily suggest that! ------------- Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA |
Posted By: snowflake
Date Posted: 11 February 2019 at 4:43pm
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you aren't modelling the directivity. model a single section horn and use the directivity tool to get an idea of how much directivity you gain at different frequencies. then go back to modelling a multi-section horn and aim for a power slope that decreases with frequency (approx -3dB per octave). making your first throat section much shorter will give you this slope and help the very high end. make it just 2cm long and the flare cutoff is about 2kHz. should give a flat on axis sensivity to about 3kHz. this is often called 'rubber throat'. the throat you have will also cause a lot of distortion at high levels. faster flare rate where the throat is small reduces this problem too.
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Posted By: ceharden
Date Posted: 11 February 2019 at 7:28pm
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14:1 ratio is practical in any shape or form. Even HF drivers with complex phase plugs don't go that high. For a cone driver I would say 3:1 is probably a realistic maximum. You have to also take into account path length matching. All areas of the cone need to have a similar path length to the exit of the horn and a small circular throat is probably about the worst for that. It would also be very hard to avoid a large front chamber without a phase plug. I recommend reading this: http://www.centauriaudio.com.au/diy/plugs.html" rel="nofollow - http://www.centauriaudio.com.au/diy/plugs.html |
Posted By: luthier
Date Posted: 11 February 2019 at 9:16pm
Completely understand, the plan has always been to design a horn flare with a phase plug for the very reasons you mention.
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MattStolton wrote:Posted By: luthier
Date Posted: 11 February 2019 at 9:19pm
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I've actually got two sitting in my workshop as a temporary solution and a base line. I plan on A/B testing against them. My issue with them is the low end extension and big dip just after 2khz. Also I just want to learn more about horn design.
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Posted By: luthier
Date Posted: 11 February 2019 at 9:20pm
I've actually got two sitting in my workshop as a temporary solution and a base line. I plan on A/B testing against them.
My issue with them is the low end extension and big dip just after 2khz. Also I just want to learn more about horn design. |
Posted By: luthier
Date Posted: 11 February 2019 at 9:25pm
Well that is incredibly useful to know. Thank you for such a detailed reply! Is there any other software you know of that might model this type of horn more accurately? I'm currently looking into LEAP and COMSOL. |
Posted By: luthier
Date Posted: 11 February 2019 at 9:26pm
Got it, cheers! I'll bare it in mind.
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Posted By: luthier
Date Posted: 11 February 2019 at 9:28pm
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Right, that's matches up to what I've been reading. Interestingly I've been on that website quite a lot recently, I'll have to take another look.
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Posted By: luthier
Date Posted: 11 February 2019 at 9:30pm
Right, that's matches up to what I've been reading.
Interestingly I've been on that website quite a lot recently, I'll have to take another look. |
Posted By: luthier
Date Posted: 12 February 2019 at 10:24am
This should be fun, there was a warning on the last tutorial saying ' if you are not an expert in this field you should not be using this software as you will not understand what you are doing'. Hopefully in the process of learning the software I can begin to understand what I'm doing, it might be a steep learning curve.
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Posted By: sgarfa
Date Posted: 12 February 2019 at 4:23pm
 this is the model (1/4 to speed up the calculations) for a mid with b&C 8mbx ,I wanted to study the behavior of the phase plug in comsol was fine with the complete parallel with inventor, anyway I became crazy, in the end I made a quick script with akabak..simulated..make de 3d drawing.. milled the mold ... stop..I think I'm not smart enough to comsol ------------- http://www.soundcloud.com/ramirez_amd" rel="nofollow - Ramirez_amd TECHNO |
Posted By: luthier
Date Posted: 12 February 2019 at 7:40pm
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[QUOTE=sgarfa this is the model (1/4 to speed up the calculations) for a mid with b&C 8mbx ,I wanted to study the behavior of the phase plug in comsol was fine with the complete parallel with inventor, anyway I became crazy, in the end I made a quick script with akabak..simulated..make de 3d drawing.. milled the mold ... stop..I think I'm not smart enough to comsol [/QUOTE=Glad it's not just me finding it tricky!
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Posted By: luthier
Date Posted: 17 February 2019 at 9:14pm
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So with a little more time playing on Hornresp and thanks to all the input I have recieved on here I've managed to get this. When moddeled as one horn off Axis I gain massive sensitivity over 450hz + 10db in places so I'm just focusing on the most useable frequency range. 
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Posted By: luthier
Date Posted: 17 February 2019 at 9:24pm
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I've also been practing modeling horns in Solidworks as I can export the CAD file to COMSOl when I manage to learn to use the bastard thing. Here's a few pictures, they're just experiments really, I'm not planning on using any of the files. I'm just trying to get the hang of using the more complicated equation driven curves. Here's a Hyperbolic horn equation:  Here's what I made with the hperbolic horn equation:  |
Posted By: luthier
Date Posted: 17 February 2019 at 9:32pm
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What I've gathered so far is: - I need a small VTC under 100cc - s1 needs to be at least 72 in order to stay at/below 3:1 compression ratio - a slow flare rate at the begingng of the horn smooths out the graph - a large mouth is important to increase linearity - displacement is 1mm over the 1mm xmax at 300hz which hopefully won't be an issue - Lining the rear chamber is very important to stop waves reflecting Also installing a virtual machine to sim in Akabak is a right pain! |
Posted By: sgarfa
Date Posted: 18 February 2019 at 10:23am
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really a good job,what angle of the dispersion you want? ... if I were you I would make a different dipersion between horizontal and vericale..in any case you could also use a mid with closed back ... so as to simplify a little the thing ------------- http://www.soundcloud.com/ramirez_amd" rel="nofollow - Ramirez_amd TECHNO |
Posted By: luthier
Date Posted: 18 February 2019 at 7:04pm
Thank you! I'm aiming for a 60 x 40 dispersion, although I've not been very successful in measuring the current dispersion. I'm modelling the horn as one segment and looking at the directivity: Polar map, beam width and dispersion pattern. A closed back mid would certainly make things easier, if I can find one with suitable T/S parameters I'll go for it.   
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Posted By: toastyghost
Date Posted: 18 February 2019 at 7:55pm
https://www.bcspeakers.com/en/products/lf-driver/8-0/8/8NSM64-8 It's good enough for the d&b GSL 
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Posted By: fatfreddiescat
Date Posted: 18 February 2019 at 8:30pm
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For the mid and high sections it may well be worth thinking of them as wave guides as opposed to horns, in this case where horns primary goal would be to present a load to the driver and a wave guide to control directivity. All but the conical horn will have uneven dispersion versus frequency. The type of cabinet your working on I think dispersion over it's working range is critical to a good outcome, especially as you looking to use them in arrays. https://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides.html http://mariobon.com/Articoli_storici/Horns_measurements_ETF2010d.pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.536.5361&rep=rep1&type=pdf http://www.gedlee.com/Papers/paper.aspx PS finally getting somewhere with 'Inventor'
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Posted By: luthier
Date Posted: 18 February 2019 at 9:43pm
Very glad you mentioned this driver I simmed it a few weeks ago on a previous horn I was modelling and it didn't look great. Now though, different story. With the 1.5L chamber a larger S1 and reduced compression ratio I managed to get this:    Group delay and Xmax limit me to a hpf around 330hz which isn't a problem, think I found my driver! |
Posted By: luthier
Date Posted: 18 February 2019 at 9:48pm
Makes perfect sense and confirms all my fears. Thanks for the reading material I'll get started on it! Glad to hear your getting on with Inventor, I've still been meaning to get around to having a play with it! |
Posted By: fatfreddiescat
Date Posted: 18 February 2019 at 9:54pm
No worries re inventor, you got enough on your plate and making a great read so wouldn't want to distract you.
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Posted By: bass*en*mass
Date Posted: 24 February 2019 at 6:48am
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James/Timebomb got a pair of 18sound 8sm610s for sale rel. cheap, heard those on custom horns, not a bad choice imo.. ;) |
Posted By: luthier
Date Posted: 24 February 2019 at 9:23am
| Thanks for the heads up, I'll sim them later today. |