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antiG View Drop Down
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    Posted: 06 March 2011 at 8:26pm
just a couple of questions about using constant directivity HF horns:

I'm designing a pair of full range cabs with a 12" (reflex loaded) and a 1" (+ passive crossover @ 2K), sometimes to be used full range as monitors, somtimes as mid tops.

When using the cabs as mid tops and sending them 200hz and up from an active crossover, is it ok to have the active crossover's constant directivity setting switched on for that whole range (200-20k)?  Does the setting only effect the higher frequencies or will it have some effect on the mid?  Will it run OK through the passive crossovers?  Active crossover is an old style behringer super x pro.  Passives are beyma fd250.

And.. Are there any drawbacks to having a constant directivity horn on cabs that will sometimes be used full range with no constant directivity setting available?  Do you lose any quality or coverage using a constant directivity horn with the setting not engaged compared to a non-constant directivity horn?

Thats pretty much it, any help appreciated Smile
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http://www.electrovoice.com/sitefiles/downloads/EV_PABible-07-Add06-Constant_Directivity_White_Horn_Paper-1980.pdf

CD eq should only change the frequencies the horn deals with, 3Khz +


Edited by lgosdset - 06 March 2011 at 8:32pm
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antiG View Drop Down
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thanks thats a helpful bit of reading, i see theyve got the rest of the bible on their website as well, will have to get at that.

so the CD setting is a slope up from 3k then, any anticipated problems with putting that through the 2k passive crossover?
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colint View Drop Down
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Originally posted by antiG antiG wrote:

thanks thats a helpful bit of reading, i see theyve got the rest of the bible on their website as well, will have to get at that.

so the CD setting is a slope up from 3k then, any anticipated problems with putting that through the 2k passive crossover?



You shouldn't have any problems with it, but you will lose a bit of the hf punch without the eq in.
 I have a system with large 2" cd horn's and have tried it without the eq slope, It still sounded OK but you'll know the difference, The hf sort of "come's alive" with it engaged but sounds mediocre & a little dull without.
When using as foldback/monitors you may have some problems with feedback with the eq in due to the extra gain so try it either way?

The 2k crossover should be fine.


Edited by colint - 06 March 2011 at 9:04pm
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Originally posted by antiG antiG wrote:

just a couple of questions about using constant directivity HF horns:

I'm designing a pair of full range cabs with a 12" (reflex loaded) and a 1" (+ passive crossover @ 2K), sometimes to be used full range as monitors, somtimes as mid tops.

When using the cabs as mid tops and sending them 200hz and up from an active crossover, is it ok to have the active crossover's constant directivity setting switched on for that whole range (200-20k)?  Does the setting only effect the higher frequencies or will it have some effect on the mid?  Will it run OK through the passive crossovers?  Active crossover is an old style behringer super x pro.  Passives are beyma fd250.



Yeah it'll only affect higher frequencies. Its basically an EQ curve/boost that's applied, wont cause any problems to the passive crossover Smile

Originally posted by antiG antiG wrote:

And.. Are there any drawbacks to having a constant directivity horn on cabs that will sometimes be used full range with no constant directivity setting available?  Do you lose any quality or coverage using a constant directivity horn with the setting not engaged compared to a non-constant directivity horn?

Thats pretty much it, any help appreciated Smile




While not totally technically accurate, think of it this way:  High frequencies naturally start to "beam" and become focused more and more narrowly at the front of the cab. The idea of a constant directivity horn is to "spread" these out and try and make the horn as evenly dispersed as possible across the whole frequency range, meaning you can array them more accurately without any gaps in HF coverage.

However because the high frequency energy is now much more spread out, combined with the fact that there is less energy in high frequencies anyway, there is less of it "per area" or "per person" and it needs boosted to even it back out again and stop it from sounding dull and lifeless.

So the answer is yeah, if you just plug your signal straight into the back without any CD eq then it will sound very dull and lacking in HF.  

And the other point to consider is that ALL speakers need to be crossed over. Even large 18" or 21" subs still should always have a low crossover enabled to cut out everything below 30 or 40 Hz (depending on the design etc) to stop too low a frequency getting to them and blowing them.

Similarly with your tops, even when used "full range" they should still really have a high pass enabled to cut everything below 60-80Hz out (again depending on the model)  because 30 or 40 hz hitting them at significant volume will almost certianly cause the 12" cone to over-excurse and possibly cause damage.

k


Edited by kevinmcdonough - 06 March 2011 at 9:05pm
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antiG View Drop Down
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thats great thanks for the input

one thing i'm still not sure on though - what gives better sound quality (within main area of coverage):

contant directivity without the EQ boost
non-constant directivity

or will they sound about the same

on the HP filter stuff, yeah certainly will have the full range high passed at 50 or 60 when available
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colint View Drop Down
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CD with EQ!
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antiG View Drop Down
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haha please stick within the options!

versatility is the key to this project, would really like CD horns for when the cabs are used as mid tops, but its no use having them if the HF sounds terrible when the cabs are driven full range with no processing
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Originally posted by antiG antiG wrote:

thats great thanks for the input

one thing i'm still not sure on though - what gives better sound quality (within main area of coverage):

contant directivity without the EQ boost
non-constant directivity

or will they sound about the same

on the HP filter stuff, yeah certainly will have the full range high passed at 50 or 60 when available



lol both will sound bad for different reasons. CD with no EQ will sound dull and lifeless, where as a non-cd horn will be very uneven sound good DIRECTLY in a straight line in front of the cab, but the HF will rapidly drop off even one or two steps to the side.

k
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antiG View Drop Down
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so its a typical case of deciding where to make the compromise then

will go for the CD horns as theres no complications with the 12s or passive crossovers

then test them to see how much sparkle they lose without the EQ and go from there..

oh yeah, do CD horns maintain a wider dispersion than non-CD horns even without the EQ?

thanks for all the help Smile
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"oh yeah, do CD horns maintain a wider dispersion than non-CD horns even without the EQ?"

Cd horns (try to) reproduce the power response of the driver inside their specified opening angle. So yes, CD-horns try to maintain the dispersion in a range they're designed to.

I wouldn't call 40x20 degree CD horn a wide coverage version. You need to specify what's wide.
90? 120?

Also take account to fit the horn directivity with the directivity of the 12" driver near crossover frequency.

"versatility is the key to this project, would really like CD horns for when the cabs are used as mid tops, but its no use having them if the HF sounds terrible when the cabs are driven full range with no processing"

You can usually make the cd-correction in passive filter quite easily. Just by-pass the L-pad resistors with suitable RC-series circuit or RCL-series circuit (JBL-studio monitor way).

Andy
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A horn is simply a 3D object that constrains the expansion of sound waves.

To realise how they work it is useful to think of sound waves as a series of bubbles. Low frequencies with long wavelengths are big bubbles and high frequencies with short wavelengths are small bubbles.

If a bubble travels down a horn (or waveguide), as long as the cross sectional area is smaller than the bubble then the bubble is constrained, or controlled, by the horn. With a traditional exponential horn the angle between the horn walls is constantly increasing the further from the throat you get. Once the cross section of the horn is larger than the bubble, the bubble loses contact with the walls and it no longer sees the horn. Larger bubbles have to travel further down the horn before they stop seeing the horn and therefore the wall angle is wider. As the bubbles get smaller (higher frequencies) they see a horn with a narrowing angle between the walls. This causes a narrowing of the dispersion pattern with increasing frequency.

A constant directivity horn has straight walls. The angle between them therefore remains constant and the dispersion pattern remains constant over the usable bandwidth.

The bandwidth is set at the lower end by the mouth dimensions. Where the wavelength of the sound is larger than the mouth dimensions the horn has little control over directivity. The upper frequency limit is set by the dimension of the compression driver exit. Once the wavelength is smaller than the throat diameter the sound doesn’t see the horn and it is only influenced by the compression driver.

By modifying the acoustic radiation resistance the diaphragm sees, the horn can influence the power output and efficiency of the drive unit. However, all drive units, cone and compression, have an upper response frequency above which the power output falls at 6dB per octave. The on axis sensitivity is usually maintained above this frequency because increasing directivity concentrates the power into an increasingly smaller area. By maintaining a constant directivity, the on axis response more accurately follows the power response. This is the reason corrective eq is used to flatten the response. The horn doesn’t actually change the power response as such but as stated in other posts, the power is spread out more. A good CD horn can require in excess of 12dB boost above 10KHz. 
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