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-   -   Isobaric tapped horns (http://www.diyaudio.com/forums/subwoofers/229628-isobaric-tapped-horns.html)

Cal Weldon 8th February 2013 07:37 PM

Isobaric tapped horns
 
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I have 4 - 6.5" drivers but only room for two rather small cabinets. Any chance of making this work?

Patrick Bateman 8th February 2013 07:40 PM

Well of course.

I can't figure out why more people don't go isobaric with tapped horns.

The primary limitation on subwoofer output is xmax (as long as you have enough power.)

Therefore, isobaric tapped horns can generate more output per square foot than conventional loading.

Isobaric loading is kinda pointless for front loaded horns, because the back chamber is so small already, but in tapped horns, BLHs and vented boxes it makes a lot of sense.

Also, going isobaric reduces thermally induced distortion by spreading the heat between two motors.

Note that you don't have to do them clamshell; there are ways to mount them in a tapped horn so that you can still keep S1 very small. (Basically put a piece of wood there that couples the face of the two cones together.)

Cal Weldon 8th February 2013 07:47 PM

Thanks for the quick response. Good to know. I couldn't see why not but I'm pretty low on the speaker genius ladder. I like the idea of making them small [read WAF] and yes, the coupling of the drivers would likely be on either side of the baffle piece rather than actual clamshell.

Cal Weldon 8th February 2013 08:04 PM

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I don't see a design program for tapped horns on a mac. Here's the driver specs, can someone plug the numbers and give me a horn that is approximately the simple shape shown in the fist pic? I think tuning it to 50 Hz is probably low enough?

I would appreciate that greatly.

Patrick Bateman 8th February 2013 08:05 PM

Quote:

Originally Posted by Cal Weldon (Post 3361618)
Thanks for the quick response. Good to know. I couldn't see why not but I'm pretty low on the speaker genius ladder. I like the idea of making them small [read WAF] and yes, the coupling of the drivers would likely be on either side of the baffle piece rather than actual clamshell.

A few random observations:

1) Vented boxes, tapped horns, and BLHs have a lot in common. A BLH and a tapped horn with the same volume and length will have nearly the exact same response.

2) If you don't mind the wonky group delay curve, a vented box with a really big vent can rival the output of a tapped horn of the same footprint. Obviously, if the tapped horn is bigger it's generally going to have more output.


The thing I find compelling about the isobaric designs is that power is SO CHEAP right now. I can buy a 4000 watt amplifier from Wal Mart and have it delivered to my doorstep for under $300. With that type of power on tap, ten cubic foot horns start looking kinda silly.

Also, I think the Geddes 'multi-sub' approach sounds great.

Plus, Geddes keeps saying thermal modulation is A Big Problem and maybe he's right. An extra voice coil sure doesn't hurt things.

Do you have Car Toys in BC? They were doing the Alpine Type S for $99 recently. It's a good candidate. 14mm of xmax, a flat BL curve, and a 2.6" voice coil. Not too shabby for the price.

Cal Weldon 8th February 2013 08:14 PM

The drivers are now in a bipole ported enclosure. I was hoping by running the isobaric I could halve the size of the cabinet and conceal the drivers.

I really don't need anything more. :) I have loads of amps, loads of speakers, I just want to downsize the ones on the TV in the kitchen area to make them look better and save a little room.

Cal Weldon 8th February 2013 08:16 PM

Quote:

Originally Posted by Patrick Bateman (Post 3361632)
ten cubic foot horns start looking kinda silly.

That's small compared with some of the crap I have. :)

ghettosynth 8th February 2013 08:51 PM

Quote:

Originally Posted by Patrick Bateman (Post 3361602)
Also, going isobaric reduces thermally induced distortion by spreading the heat between two motors.

Doesn't it take twice the power for the same output meaning that each coil receives the same power that it would in a single driver cabinet? I was under the impression that you would have, modulo other factors, roughly twice the heat since each driver will get as least as hot as it would in a single driver cabinet.

I also don't understand how xmax comes into play since each driver is being driven by exactly the same power that it would receive in single driver cabinet? Does the reduction in cabinet size have some affect on the xmax?

Also, to model in hornresp, assuming that the horn dimensions allow for two drivers, do you simply halve the vas, recompute cms et al., and adjust the DC resistance and impedance according to how you wire the drivers?

tb46 8th February 2013 09:07 PM

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Hi Cal,

This driver is not suited to vented enclosures (Qts=1.081), and the Sd indicates a size of about 5.5", I would guess at a relatively small Xmax :-). Just stuff them into a 1cft sealed box if you want to try them isobarically.

Anyway, here it is in Hornresp, TH isobaric pair:

Regards,

tb46 8th February 2013 09:13 PM

Hi ghettosynth,

To model isobaric driver arrangements in Hornresp:

- enter the driver as you normally would, and
- under Edit - Driver Arrangement select Isobaric, and however many isobaric configurations you want Hornresp to use, e.g. 2 iso pairs in series with 2 parallel branches.

Hornresp will do the calculations for you.

Regards,


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