Which Horn for linear response down to 20Hz? - Page 6 - diyAudio
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Old 13th August 2005, 01:08 PM   #51
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Quote:
Originally posted by Cortez
Have they created something speacial and more, then a simple, but huge horn with strong speakers ?
They look like big scoops to me.


Rob.
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Old 13th August 2005, 01:10 PM   #52
Mark Kravchenko
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I'll try some modeling to. Maybe our two hamsters spinning on squeaky wheels will come up with something. The idea of lowering the limit of the horns response is great. But it has to be done with the same clean sound that we crave from the beasts. With what I have read it is really an expanded version of reactance annulling. The idea being that there could be a smooth roll off of 12 db/octave below the horn system cutoff. Come to think about it why could it not be equalized a bit and get the true sub cut off?

Regarding the size of boxes and the pic posted.

Sure there are smaller horn subs. I have studied a great many. Some are even reflex loaded below horn cutoff. They have definite peaks and dips in their output. The boxes are manageable in size.

I said what I did because from the direct radiator side of the argument they will come up with a 4 cubic foot over amped and Eq'd that has response to 14hz. They exist. And they have output down to the basement and volume to match. The kicker is the amount of power that they require. Kilowatts! Plus there is a difference in the distortion components the two different boxes produce. Short of using a servo.

But then again if you use a level playing field a servo could be incorporated in a horn to. The servo combined with John's idea would get the most bang for the buck. There is also Graham Maynard's phase coherent low end Eq circuit. The point to keep in mind is that the response below horn cutoff decline steeply at 24 db/octave. With an enlarged rear enclosure it should roll off at 12 db/octave. The active Eq will take a lot of power but work.

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Old 13th August 2005, 03:37 PM   #53
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I don't understand the emphasis on EQ'g a horn below cutoff in the last few posts. Isn't that just begging for excursion problems? On the other hand enlarging the chamber on a rear horn moves the point where excursion increases rapidly to a lower frequency.

Is the Imperial a scoop? If take a scoop and make it's horn length 2m and make it's chamber size well over 100L, then yes. I think that changes the sonics quite a bit compared to typical scoops.
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Old 13th August 2005, 04:44 PM   #54
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Quote:
Originally posted by johninCR
I don't understand the emphasis on EQ'g a horn below cutoff in the last few posts. Isn't that just begging for excursion problems? On the other hand enlarging the chamber on a rear horn moves the point where excursion increases rapidly to a lower frequency.

Is the Imperial a scoop? If take a scoop and make it's horn length 2m and make it's chamber size well over 100L, then yes. I think that changes the sonics quite a bit compared to typical scoops.

I think its more that in a home environment the horn will never get near its x-max. This allows a fair bit of boost before problems arise.

I won't be boosting the labs I'm building - they'll be crossed right on the lower limit of the horn loading.

Re: the imperial. I haven't seen inside one - I think I'd have to pay for the plans. The 21" scoop I linked to has a 2.44 metre length, and a very quick rough calc gives approx 75L rear chamber. (If the rear chamber is what I think it is on the plan )

Whats the mouth size on the imperial ? - The scoop I linked to has a mouth of 3984 cm2, and it states in groups of 4 the loading is down to 28Hz. (35Hz for 1 unit)

Cheers,

Rob.
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Old 13th August 2005, 05:54 PM   #55
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I use three sub horns loaded against the front wall and concrete slab floor. They get down into the teens at 125 db levels no problem. Mine are loaded with three eighteen inch JBL 2242H's.

Stargate Horn System (Obsolete)

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Old 13th August 2005, 06:02 PM   #56
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Here is one I built designed to go up against a wall. It has a 25 Hz flare and is loaded with a JBL 2241 18" woofer. It requires a 6 db boost at 20 cycles to get below 20 with authority.

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Old 13th August 2005, 06:12 PM   #57
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Rob,

I came up with about the same chamber size for that 21" super scooper, but that's for a 21" driver and the imperial was designed for a single 15". The scoops are designed for max efficiency, however, the Imperial was originally designed as a full range unit, so they sacrificed some efficiency for deeper extension which was a better match for the acoustic XO between the front radiation and horn output at about 90hz. BTW the imperial's mouth is 7600cm2 and it was designed for in wall installation and use as a single unit in mono.

The route I'd like to try eventually is an rear loaded horn array, at least to find out if what HornResp is telling me is real, and that is strong output more than an octave below Fs. If I can find someone to give me 24-32 of the CSS WR125ST's, I could make a sub unnecessary except for subsonic HT content.
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Old 13th August 2005, 06:34 PM   #58
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Quote:
Originally posted by RobWells


They look like big scoops to me.


Rob.
Greets!

Depends on the 'scoop's' design gain/BW. If a typical BLH designed for wide BW such as the Imperial's, then it's nothing more than a BR with a huge expanding vent, ergo has a relatively large filter chamber/throat and terminating at a shorter length/larger mouth. Limited BW 'scoops' are closer to being compression driven, with higher gain over a narrower BW via a smaller filter chamber/throat and longer pathlength to get to the minimum aceptable mouth area.

The former has greater acoustic (box) efficiency, while the latter has greater acoustic power, ergo lower distortion/higher SQ until the driver goes into thermal power or mechanical overload, which can be at quite low power if the CR is high, so only prosound drivers designed for the app/abuse should be used IMO, even in a HI-FI/HT app as half roll surround suspended drivers sound really obnoxious when they deform. Obviously, any driver suitable for a BR/TL app will work in a typical wide BW design BLH.

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Old 13th August 2005, 07:21 PM   #59
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Would the DECWARE Imperial plans work with a single Tannoy 15-inch dual-concentric per side? Just curious.

Thanks,
Deon
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Old 13th August 2005, 08:03 PM   #60
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Quote:
Originally posted by johninCR
Rob,

I came up with about the same chamber size for that 21" super scooper, but that's for a 21" driver and the imperial was designed for a single 15". The scoops are designed for max efficiency, however, the Imperial was originally designed as a full range unit, so they sacrificed some efficiency for deeper extension which was a better match for the acoustic XO between the front radiation and horn output at about 90hz. BTW the imperial's mouth is 7600cm2 and it was designed for in wall installation and use as a single unit in mono.

The route I'd like to try eventually is an rear loaded horn array, at least to find out if what HornResp is telling me is real, and that is strong output more than an octave below Fs. If I can find someone to give me 24-32 of the CSS WR125ST's, I could make a sub unnecessary except for subsonic HT content.
Hi John,

The photo of the imperials that was posted had 2 x 15's (I think they're 15's) per cab. Therefore I was thinking it would need more rear chamber than a single 21"

Thanks for the input GM. Nice to have your experience chiming in.

Rob
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