Quad 12" Isobaric Ported Sub |
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vertx
Young Croc Joined: 14 March 2012 Location: Sydney Status: Offline Points: 578 |
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Posted: 31 July 2017 at 2:54am |
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Would something like this be possible?
I'm imagining something like a simple 2x12" GSub type ported cabinet but with the 12"s in isobaric push pull configuration, four per cabinet, using a driver like the BMS 12n630, maybe with a slight v-baffle to save some space. Run 30hz - 120hz. Opinions? Are their any commercial designs doing something like this? Weight to SPL ratio could be decent. Edited by vertx - 31 July 2017 at 2:57am |
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FrederikMA
Registered User Joined: 19 July 2017 Location: Copenhagen Status: Offline Points: 76 |
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Here's Gunness' paper on the benefits of manifold in the EV MT4 from 1986:
http://fulcrum-acoustic.com/assets/pdf/whitepapers/loudspeaker-manifolds-high-level-concert-sound-reinforcement-1986.pdf |
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MarjanM
Old Croc Joined: 10 February 2005 Location: Macedonia Status: Offline Points: 7810 |
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Isobaric loading will make using smaller box for lower cutoff possible. But you will lose about 3db in sensitivity.
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Marjan Milosevic
MM-Acoustics www.mm-acoustics.com https://www.facebook.com/pages/MM-Acoustics/608901282527713 |
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vertx
Young Croc Joined: 14 March 2012 Location: Sydney Status: Offline Points: 578 |
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EDIT: link was referring to manifolds
A small, 4x12" manifold cabinet run 30-80hz might work well though. Edited by vertx - 31 July 2017 at 1:41pm |
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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[QUOTE=FrederikMA]Here's Gunness' paper on the benefits of manifold in the EV MT4 from 1986:
http://fulcrum-acoustic.com/assets/pdf/whitepapers/loudspeaker-manifolds-high-level-concert-sound-reinforcement-1986.pdf[/QUOTE] isobaric and manifold loading are two different things. assume the OP means the latter. didn't realise the manifold loading gave better low frequency response as well as reducing high frequency distortion. so how do you calculate the optimum front chamber size? |
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vertx
Young Croc Joined: 14 March 2012 Location: Sydney Status: Offline Points: 578 |
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So I sort of had this in mind visually, which is isobaric
But these EV manifolds look really interesting too, and I think was what I was looking for in terms of output/SPL per cab size Edited by vertx - 31 July 2017 at 1:48pm |
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MarjanM
Old Croc Joined: 10 February 2005 Location: Macedonia Status: Offline Points: 7810 |
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Isobaric loading will not give you more spl. In a volume that is enough for a classic 2x18 reflex box, you will go much lower, but not louder. You will lose 3db in sensitivity.
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Marjan Milosevic
MM-Acoustics www.mm-acoustics.com https://www.facebook.com/pages/MM-Acoustics/608901282527713 |
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FrederikMA
Registered User Joined: 19 July 2017 Location: Copenhagen Status: Offline Points: 76 |
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Sorry for the confusion caused. Strictly speaking Isobaric and manifold are two different subjects but in practice one may also benefit from manifold loading in an already multiple driver configuration such as an isobaric.
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FrederikMA
Registered User Joined: 19 July 2017 Location: Copenhagen Status: Offline Points: 76 |
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Snowflake, regarding your question of optimum front chamber. The shorter the driver to driver distance is the better the low frequency coupling. For attenuation of unwanted upper harmonics, you can go for a 1/3 wavelength (120 degree phase) of the driver to driver distance. That will be the lowest possible frequency attenuated by destructive interference and attenuation will most likely start to happen at higher frequencies than this.
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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the paper above seems to say there is no point putting the drivers closer than the radius of the diaphragm as the reactive component is already infinite at this distance. also the compression ratio at this point would be ~3:1 and likely to cause problems if any less. with an 18" driver and 20cm spacing the attenuation would begin above 570Hz which seems about right. the paper says you have to be careful not to damage mid-band sensitivity but doesn't say any more about it. |
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FrederikMA
Registered User Joined: 19 July 2017 Location: Copenhagen Status: Offline Points: 76 |
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Yes, in the band of a subwoofer or woofer the wavelengths involved allows quite some driver distance. I did some (to me) quite revealing sims of a hyperbolic horn using 4 18sound 12nd610 in a manifold compression chamber like the ev subs. The system design feature of hornresp suggested a horn of around 160cm and a fairly small throat for a single driver, but simulating 4 drivers decreased optimum horn length to less than 130cm and a throat of around 800sqcm, resulting in a shorter and more open horn than is traditionally considered a loading optimized horn. The 12nd610 is a very light, high BL, low-excursion driver. Other heavier cone/higher power/higher excursion drivers simulated the opposite, requiring a longer horn and higher compression ratio per driver for more drivers. Unfortunately an "ms sans serif" problem doesn't allow me to enter hornresp to get exact values and take some pics for you at the moment. My point is that this reactive component of a manifold introducers some very interesting elements of ingeneering including driver selection. |
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Elliot Thompson
Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5172 |
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Manifolds are only good to 50 Hz. That would not be classified as a Sub in this day in age.
Best Regards, |
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Elliot Thompson
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