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Quad 12" Isobaric Ported Sub

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vertx View Drop Down
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    Posted: 31 July 2017 at 2:54am
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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Post Options Post Options   Thanks (1) Thanks(1)   Quote FrederikMA Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 8:01am
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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Post Options Post Options   Thanks (1) Thanks(1)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 9:17am
Isobaric loading will make using smaller box for lower cutoff possible. But you will lose about 3db in sensitivity. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 9:36am
Originally posted by MarjanM MarjanM wrote:

Isobaric loading will make using smaller box for lower cutoff possible. But you will lose about 3db in sensitivity. 


Ahhh ok thought there was a general gain in sensitivity for isobaric, the document above shows this is dependent on frequency with preference to low frequencies.

EDIT: link was referring to manifolds

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The on-axis frequency response of the direct-radiating system is shown in Figure 17 and the response of the manifolded system is shown in Figure 18. Comparing the two curves, there are several differences that are readily apparent; below 70 Hz the manifolded system has substantially more output than the direct-radiating system; above 100 Hz the manifold has slightly less output; and above 200 Hz the manifold rolls off abruptly.... 

....From 70 Hz to 100 Hz the manifolded response is very similar to the direct-radiating case. 
 

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 10:23am
[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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Post Options Post Options   Thanks (0) Thanks(0)   Quote vertx Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 1:38pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 3:11pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote FrederikMA Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 3:17pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote FrederikMA Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 3:42pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2017 at 7:22pm
Originally posted by FrederikMA FrederikMA wrote:

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.


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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Post Options Post Options   Thanks (0) Thanks(0)   Quote FrederikMA Quote  Post ReplyReply Direct Link To This Post Posted: 01 August 2017 at 11:54am
Originally posted by snowflake snowflake wrote:

Originally posted by FrederikMA FrederikMA wrote:

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.


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.


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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 01 August 2017 at 1:40pm
Manifolds are only good to 50 Hz. That would not be classified as a Sub in this day in age.

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