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isobaric constant pressure bandpass horn

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turbo7 View Drop Down
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    Posted: 10 August 2019 at 10:44am
Hey,

did anybody try to build an isobaric "constant pressure" bandpass horn ?

I do not find anything anywhere, all i found is an isobaric transmissionline.

I would like to have a "cone-to-cone" placement. At an isobaric paralell circuit, VAS of the 2 drivers is 1/2 that of a single driver, Re is 1/2 of a single driver due to paralell wiring, as well as Le.

I thought it would be appropriate in very limited space to have a closed horn chamber and isobaric placement of another driver sitting in the bandpass chamber before the horn throat.

Any input is welcome Clap
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2019 at 4:00am
Because Vas is half that of a single driver, you can make the chamber half the original (single driver) volume but the horn has to stay the same size. So if your chamber is the main part of the cabinet (like a reflex cabinet) you can decrease it to 50% of it's original size. Because the horn is usually a large part of a band pass horn, the smaller chamber volume doesn't change the overall cabinet volume that much.

Half the Vas also means efficiency (of the chamber part) is 3 dB lower. Plus the Sd of two isobaric mounted drivers is the same as a single driver, so that's a loss compared to the Sd of two drivers.

All that combined is probably the reason it isn't used that much in PA where high output is the main priority. And if it's used in PA it's usually just in reflex or closed cabinets because that's where the volume decrease is most noticeable.
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Chris Grimshaw View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris Grimshaw Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2019 at 10:35am
FWIW, I wouldn't bother.

You can get the same effect by simply using a better driver, which will also have more mechanically-limited output, and lower distortion.

Chris
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turbo7 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote turbo7 Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2019 at 12:32pm
thx for the input,

true, i understand it is a trade off between size ( volume ) and efficiency. the rear chamber of a bandpass horn is mostly small anyway and the second driver eats up volume as well, so there is no or only a little win in less volume. But:

what i find attractive is, that driver nonlinearities are reduced which as well means less distortion.

Another interesting fact is, if i load hornresp with the new "virtual driver", which means 1/2 VAS 1/2 Re 1/2 Le, while Sd and all other parameters stay the same as with one driver only, this is the output: grey is isobaric constant pressure, black is one driver only. Is it correct to simulate with a new virtual driver or did i forget something ?

Power input: 1w 8 Ohm on the black, single driver, 2x 1w 4 ohm on the isobaric



Edited by turbo7 - 11 August 2019 at 12:49pm
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2019 at 4:06pm
I think you need to simulate the isobaric cab with 1 watt total input (ie, 0.5 watts per driver) in order to make a meaningful comparison with the single driver cab. Otherwise any output gain can be explained by the fact you're putting twice as much power in!
Studio45 - Box Builder Commotion Soundsystem -Mobile PA
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turbo7 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote turbo7 Quote  Post ReplyReply Direct Link To This Post Posted: 11 August 2019 at 4:36pm
Yes i got confused ( and still am ) because - i have 2 coils that means i actually have 2x the power, input . So That would equal 1w each 8 Ohm coil or 2w into a 4 Ohm load vs 1x 8 Ohm 1w load. still confused lol

in theory, the isobaric 2 drivers would have -3dB in spl but having twice the power handling because of 2 coils this nulls out more or less. If i put in 0.5 watts, i am getting worse spl than with one driver, which is confusing again because it should stay the same


Edited by turbo7 - 11 August 2019 at 4:46pm
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godathunder View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Posted: 13 August 2019 at 6:00am
I would have thought that the bph would filter a lot of the distortion anyway so I'm not sure that the improvement would be anywhere near as significant as in a reflex. Just based on instinct, happy to be proven wrong
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