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Midrange compression driver development |
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JulianDA 
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Joined: 29 May 2018 Location: Soest, Germany Status: Offline Points: 156 |
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 Posted: 09 December 2024 at 1:12pm |
-We will do "the real measurements" outside when we have constructed a horn from glasfiber.
-All measurements that i posted in my latest post were gated at 14ms. I am also pretty sure that the dip is caused by reflections. -The vertical scale of all measurements is 1dB per increment as stated in my post. The microphone was shifted by 10° for each new measurement in the "directivity-graphs" starting with 0° as the first measurement. -> This means the desired 60° directivity in the horizontal plane is reached by the 4th measurement (purple) and 50° in the vertical is between the 3rd and 4th (orange and green) -We are eyeing on the B&C DE360 as the HF Driver over this Horn. The desired Crossover is somewhere between 3000-3500Hz but it can be higher if thats a possibility. But i would like the midrange horn to be well behaved a good bit higher than crossover. We will see how this turns out with the glasfiber horn and optimised phaseplug. |
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JulianDA
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Joined: 29 May 2018 Location: Soest, Germany Status: Offline Points: 156 |
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Posted: 03 February 2025 at 6:19pm |
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We build the first horn from GRP. Its not the prettiest and still needs a lot of cleaning and finishing, but there will be some measurements -hopefully outdoors- that follow in a few weeks.
This is the current state of it:   |
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smoore
Young Croc 
Joined: 30 March 2011 Location: N.Devon Status: Offline Points: 966 |
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Posted: 21 March 2025 at 3:11pm |
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Good work! Looks solid! Any developments?
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JulianDA
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Joined: 29 May 2018 Location: Soest, Germany Status: Offline Points: 156 |
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Posted: 26 March 2025 at 2:53pm |
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Yes, there are developments. I still did not get to measure the horn/driver combination outdoors, but the work still continued.
For the phaseplug development i now use mostly impedance measurements to spot resonances. This worked with great success! The following graph shows a comparison in impedance and frequency response of 3 different phaseplugs measured on the GRP-Horn.  -The first one (green) is the original PP constructed from the results of my simulation. -The second one ("purple") has shifted PP entrances by 2mm <- seemed like the right direction -The third one (red) is the newest PP which has shifted PP entrances by 4mm This is the newest PP (in the pictured version with a twist in the outer channel for path-length-matching)  The first frontchamber cavity resonance at ~2,6kHz is almost completely suppressed. It seems like shifted entrances by 3,5mm will be perfect. The second frontchamber cavity resonance at ~4-5kHz is a bit more complicated. It should also be suppressed by now. The problem at this point is that the driver itself has strong resonances (You can see them in the impedance and response measurements in the drivers datasheet: https://www.bcspeakers.com/en/print/lf-driver/6-5/8/6nsm51-8 ) Things i learned: - Impedance measurements are a perfect tool for spotting resonances and working on them! especially when good fr-measurements are difficult to do - the hump between 1-2kHz comes from the driver itself and has to be EQed or dealt with in the crossover - extending the center of the plug, like previously suggested, makes no difference now that the horn is perfectly adapted to the PP - the resonances of the diaphragm around 4-5kHz will probably be a problem in the future
- matching path-lengths makes things worse. My reasoning is, that matched path-lengths are only valid if both PP entrances are driven in phase with each other. This condition may not be met with the realities of a real diaphragm that does not move piston-like at those frequencies The next development will be changing the areas of the PP-channels. Right now the outer channel has a bigger area than the inner one. I will test same area channels and channels where the inner one has the bigger area. Edited by JulianDA - 26 March 2025 at 3:06pm |
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Timebomb
Old Croc 
Joined: 11 October 2004 Location: Lancaster Status: Offline Points: 2763 |
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Posted: 29 March 2025 at 9:27pm |
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Looks nice :) Some good work gone into it! You making me think about doing one for the Celestion CN0617M or the CN0515M, i had a play with them last year.
Are you matching the path length so that the two path lengths are the same? Or are you accounting for the time it takes for the wave to travel through the paper diaphragm to the outer ring?
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James Secker facebook.com/soundgearuk
James@soundgear.co.uk www.soundgear.co.uk |
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Line Array
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Joined: 19 March 2022 Location: New Jersey, USA Status: Offline Points: 204 |
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Posted: 30 March 2025 at 10:15pm |
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fun project but i think what QSC did in their 4-way Cinema speakers with a phase plug on the 10" midrange is more interesting ...
it appears they used a 10" B&C driver that has a nasty resonance in its response and they designed a phase plug that tuned that resonance out ... they have a replacement parts page where you can find out the models of drivers they use ... or you can call them ... i don't see much value in taking a midrange driver that is already optimized to work without a phase plug and then adding a phase plug to it but if you can do what QSC did and actually use a phase plug to equalize response of an otherwise flawed driver then that is pretty cool most dedicated midranges probably will use some kind of soft felt paper that damps the resonance but if you can suppress a resonance with a phase plug you could use a driver made out of harder paper, say carbon fiber impregnated paper that was maybe on its own quite peaky in response and create something unique ... maybe that is already what you're doing in which case i apologize ... you can't really horn load a cone midrange because the horn would get impractically large - you can only really waveguide load it in which case the function of a phase plug is slightly different than in a horn ... in a horn you're padding out the volume of the cavity that would otherwise short out HF like an acoustical capacitor ... in a waveguide you can use a phase plug like QSC did to EQ the nasty out of the driver, or maybe to slightly narrow the effective diameter for better dispersion ... or both ... anyway good luck
Edited by Line Array - 30 March 2025 at 10:28pm |
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JulianDA
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Joined: 29 May 2018 Location: Soest, Germany Status: Offline Points: 156 |
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Posted: 18 April 2025 at 2:00pm |
Thanks James :) I matched the lengths just geometrically and started my iterative prototyping from there. Everything else was to much guesswork for my liking. Keep us updated if you go through with your project! I will be following it with great interest! Its always nice to inspire people to start new projects :) |
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Teunos wrote: