Quad 12" Isobaric Ported Sub
Printed From: Speakerplans.com
Category: Plans
Forum Name: Ported Enclosures
Forum Description: Post all your reflex and bandpass and 'other' boxes with holes in stuff here...
URL: https://forum.speakerplans.com/forum_posts.asp?TID=98969
Printed Date: 20 April 2024 at 6:22am
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Topic: Quad 12" Isobaric Ported Sub
Posted By: vertx
Subject: Quad 12" Isobaric Ported Sub
Date 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. |
Replies:
Posted By: FrederikMA
Date Posted: 31 July 2017 at 8:01am
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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 |
Posted By: MarjanM
Date Posted: 31 July 2017 at 9:17am
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Isobaric loading will make using smaller box for lower cutoff possible. But you will lose about 3db in sensitivity. ------------- Marjan Milosevic MM-Acoustics www.mm-acoustics.com https://www.facebook.com/pages/MM-Acoustics/608901282527713 |
Posted By: vertx
Date Posted: 31 July 2017 at 9:36am
EDIT: link was referring to manifolds
A small, 4x12" manifold cabinet run 30-80hz might work well though. |
MarjanM wrote:Posted By: snowflake
Date Posted: 31 July 2017 at 10:23am
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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%5b" rel="nofollow - 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? |
Posted By: vertx
Date 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  |
Posted By: MarjanM
Date Posted: 31 July 2017 at 3:11pm
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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. ------------- Marjan Milosevic MM-Acoustics www.mm-acoustics.com https://www.facebook.com/pages/MM-Acoustics/608901282527713 |
Posted By: FrederikMA
Date 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. |
Posted By: FrederikMA
Date 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. |
Posted By: snowflake
Date Posted: 31 July 2017 at 7:22pm
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. |
Posted By: FrederikMA
Date Posted: 01 August 2017 at 11:54am
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. |
Posted By: Elliot Thompson
Date Posted: 01 August 2017 at 1:40pm
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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, ------------- Elliot Thompson |
Posted By: darkmatter
Date Posted: 01 August 2017 at 2:36pm
I think you simply need to download and install the font "MS Sans Serif Regular".
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Posted By: snowflake
Date Posted: 01 August 2017 at 3:46pm
why only good to 50Hz - surely that depends on the drivers and size of box? |
Posted By: FrederikMA
Date Posted: 01 August 2017 at 5:04pm
Void Nexus X goes to 36Hz -3dB http://voidacoustics.com/docs/products/Nexus_X.shtml" rel="nofollow - http://voidacoustics.com/docs/products/Nexus_X.shtml |
Posted By: Elliot Thompson
Date Posted: 01 August 2017 at 8:08pm
Where did you see it says it is a Manifold? The Manifold is a patented design from Electro-voice from the 1980's that uses 4 or 2 18-inch Drivers. Best Regards, ------------- Elliot Thompson |
Posted By: snowflake
Date Posted: 01 August 2017 at 9:01pm
you can see the manifold mounting on the picture in the link above. I haven't read the whole EV patent but I wouldn't think they would have limited it to 18" drivers, would they? patent will have expired by now anyway. |
Posted By: Elliot Thompson
Date Posted: 01 August 2017 at 9:55pm
I do not see an internal picture of the design so, I am not going to assume it is indeed a Manifold. From historical standpoint, Rog tends to create his own designs (with great pride) despite from a spectator point of view it resembles another design when it comes to bass cabinets. A prime example is the PD 1850/186 and the Cerwin Vega B 36. Best Regards, ------------- Elliot Thompson |
Posted By: RoadRunnersDust
Date Posted: 01 August 2017 at 11:58pm
The EV Manifold Technology is pretty much just about considering a moving diaphragm as a piston and loading them into a Manifold so as to unify their output. It's used on the HF and MF units from the MT series, its not solely an LF principle, nor is it restricted to 18" drivers. Turbo did something very similar with the V2 device on the later TMS-3s... Which, amusingly, used the same HF driver as some of the MT series HF units yet achieved a much better result (at the cost of expense) ------------- www.guildfordcablecompany.co.uk" rel="nofollow - www.guildfordcablecompany.co.uk |
Posted By: Contour
Date Posted: 02 August 2017 at 8:25am
| B36 and 186 horn have different folding. |
Posted By: mobiele eenheid
Date Posted: 02 August 2017 at 9:27am
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But from a spectator view (the outside) they might look the same, which is the point Elliot is trying to make. That being said, you can see the drivers in the central (manifold chamber), that are mounted as they would in a manifold, you can see the ports and there's only about 40 litre per driver to play with, so there isn't exactly much else you can do that makes sense. The patent has expired and he is the first to cram 8 x 12" drivers in such a small enclosure. Let's ask Aman Gebru! |
Posted By: cravings
Date Posted: 02 August 2017 at 9:28am
| i think that was the point elliot was making. that at a glance, they might appear similar. but they're actually different. |
Posted By: FrederikMA
Date Posted: 02 August 2017 at 1:36pm
| So in the search for a high cabinet size to output ratio I guess it's about finding drivers with suitable Thiele Small parameters for a small volume reflex manifold or finding drivers with higher sensitivity to compensate for the reduced sensitivity of the isobaric loading. In practice i would suspect the reflex manifold to win out on sheer output to cabinet size, disregarding the allegedly reduced distortion of some kinds of isobaric loading. |
Posted By: snowflake
Date Posted: 02 August 2017 at 3:29pm
I thought people were saying they didn't know what was inside (although it seems likely they are a bass-reflex with manifold mounting). |
Posted By: ceharden
Date Posted: 02 August 2017 at 9:15pm
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http://emacoustics.co.uk/docs/products/i-12.shtml" rel="nofollow - http://emacoustics.co.uk/docs/products/i-12.shtml Four 12" drivers in isobaric pairs....
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Posted By: Risc_Terilia
Date Posted: 02 August 2017 at 10:45pm
| 404 |
Posted By: ceharden
Date Posted: 02 August 2017 at 11:15pm
| Try now, not sure why copying and pasting the original link from the address bar didn't work |
Posted By: flinnt45
Date Posted: 21 August 2017 at 3:54pm
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Look at decware for a quad box ------------- JAH Kreator Hi Fi |
Posted By: _djk_
Date Posted: 21 August 2017 at 6:56pm
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A little work in a box program with isobaric designs will probably have you changing your mind. While you only lose 3dB in efficiency, you lose 6dB in maximum output capability (model it and see). The Qts of the BMS suggests a small equalized and vented alignment (6th order) might work the best. A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB). A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB). A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB). RCA was the first company to use equal-pressure coupling (isobaric) in a loudspeaker. They used a 12 coupled to a 15 to reduce the box size by a factor of 4x. The drivers were in series, and the inside 12 received more power (the penalty for a small box that went deep in the bass) ******************************* RE: nope
In Reply to: http://db.audioasylum.com/mhtml/m.html?forum=hug&n=152776&highlight=30hz+djk&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dhug%26searchtext%3D30hz%2Bdjk" rel="nofollow - RE: nope posted by Scholl on December 13, 2010 at 14:46:43:
We have a fixed box size and cut-off frequency. Each box requires a different driver to be optimum for the box type (2nd, 4th, 6th). This can be seen as if you would convert a 2nd to a 4th the reference efficiency cannot change, but the 4th would go about 1/3 octave lower. In theory we should be able to see about a 3dB difference in a 2nd vs a 4th if the box size and cut-off frequency are kept constant (which we do, 84.55dB vs 87.56dB). What you need to ask is how the 6th can be 91.54dB, an increase of 3.98dB? The answer lies in the optimum driver having a lower Qts which in turn raises the mid-band reference efficiency, but causes the deep bass to roll off. There is no such thing as a free lunch, and there isn't one here either. The deep bass roll-off is compensated for by the bass boost in a 6th order system, typically 6dB at the box tuning frequency. That's cheating! Well, sort of. Comparing output at Fc (2nd order) vs Fb (4th and 6th order), the 6th order is only about 1dB more that the 2nd order, and is actually 2dB less than the 4th order (low Qts drivers have no low bass). But the mid-band reference efficiency really is 6.99dB more that the 2nd order, or 3.98dB more than the 4th order. The 6dB boost in the 6th order is mainly at Fb and drops off rapidly above there. An octave above Fb the boost has declined to only 1.5dB or so. Distorting is not excessive as the largest boost is at Fb and does not cause excessive cone motion. Levels of F1 in program material tend to be on the order of 6dB~10dB lower than F2 on most musical instruments, so the boost at Fb doesn't eat up all the power on real music. The 6th order vented system looks to be a free lunch (violate the Iron Law), but as we see, doesn't. Keele's actual examples were for a 2nd order with a 15, 4th order with a 10, and 6th order with an 8! See example 2 on page 29 of the pdf (which was pg.28 of the actual paper) From examining various equations for efficiency and LF cut-off I have concluded the optimum driver for the highest efficiency and lowest cut-off would have a Qts=0.312 and be a 6th order system with an Fb=F3=Fs=Faux with the filter (Faux) having a Q=2. I can address alignment jamming (using non-optimum drivers) if desired.
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Posted By: FrederikMA
Date Posted: 07 September 2017 at 8:53am
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Tanks for sharing your findings DJK - quantifying these tradeoffs (and then to build a functioning prototype) is how we will raise the bar of the DIYs! This link shows quite a few variations of the 6th and 8th order bandpass. [URL= ][/URL] https://www.the12volt.com/caraudio/boxes6.asp#1" rel="nofollow - https://www.the12volt.com/caraudio/boxes6.asp#1 I have 8 lab12 drivers sitting that i wish to use below my 4 double punishers when doing bass heavy gigs. So I've looked at the 6th and 8th order from 50Hz to as low as the cabinet will play in a reasonable small enclosure. The above link however opens up to some variations which hornresp does not allow me to sim. Which direction would you choose with such a narrow (1 octave) bandwidth? Best regards, Fred |
Posted By: bass*en*mass
Date Posted: 14 September 2017 at 5:01pm
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4 double punishers running as "kicks" could do with some more lowend spl`ability than another 8 lab12s in "any" cab could offer imo.. (like 4x double 21"s in a low and narrow tuned bandpass for example, at 25/30-45hz you need sheer Sd and xmax/displacement, the more the better..) that said, if i`d own 16 lab12s i would either just use/build more puns and run at slightly lower cutoff/power if required or swap to labhorns and proper kicks - depending on sort of gigs/transport/Tops etc. obviously.. |
Posted By: FrederikMA
Date Posted: 14 September 2017 at 9:21pm
The system consists of 3way hornloaded midtop and puns to match the sound of the midtops as i think this is more crucial than lowend extension (like labhorns). I was considering selling the lab12s but thought they could justify staying if used in such a cab. Although i think your are right about the labs not being sufficient under puns, i do not plan to invest in several 21s to use in a two-part bas configuration. The c-weightedFletcher-Munsoncurvewhalesongsubharmonic search is simply a black hole for good intensions and engineering. I will probably just sell the labs and build more puns down the road then! Best regards, Fred |