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Author Topic: Matching up TS specs for horn loaded 18" driver  (Read 858 times)

Sam Saponaro Jr

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Matching up TS specs for horn loaded 18" driver
« on: November 09, 2019, 04:37:52 am »

OK looks like I will be needing to buy a couple 18s for some old BH800 cabs(posted few weeks back about possibly buyin them).Turns out one has no driver. And finding an original will be quite hard to do.
 Been reading threw TS specs(I know enough to be dangerous lol). Was trying to match up the specs of the original RCF L18-851K to modern drivers. From my limited knowledge the B&C 18tbx100 seemed like a good match based on QTS and VAS specs being similar. Same with the B&C 18rbx100 and RCF L18P300.
 Asked at usspeaker and was suggested a Faital 18hp1010 . The VAS is very close but the QTS is higher. Im sure they know more than me about drivers but am unsure what makes them suggest this one over others with closer Q specs.
Im a bit confused as to what to look for as far as matching up specs and how close they need to be. What specs should be spot on and what have room to play etc. All I really know is driver selection is crucial with horns.
For reference the original RCF L18-851K specs are
Fs 38.7
VAS 200
QTS .35
QMS 6
QES .38
BL 21.7
CMS .13
MMS 128
VD .468
Xmax 4.5mm
« Last Edit: November 09, 2019, 04:41:42 am by Sam Saponaro Jr »
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Chris Grimshaw

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #1 on: November 09, 2019, 05:21:28 am »

Here's a curveball: the RCF driver may not have been optimal for the cabinet.
Best bet is to figure out the Hornresp inputs for the cabinets, and then simulate some drivers.

Chris
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Sam Saponaro Jr

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #2 on: November 10, 2019, 05:16:05 am »

Hum.....that would be something. I know the original design was based on another driver. But I allways figured EAW used what was best in their cabs(at that time of course).
Hornresp.....not sure on that,I know I had a hell of a time figuring out bassbox one time and quickly gave up. That and I have no clue on how to measure up the horn and wouldn't trust myself to do it right.
Wish I had access to a few drivers I'd just stick um in and A/B um.
« Last Edit: November 10, 2019, 05:22:18 am by Sam Saponaro Jr »
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Chris Grimshaw

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #3 on: November 10, 2019, 07:04:41 am »

Hornresp is okay. You'll need to go around the cabinet with a tape measure and come up with a drawing of the internals. I'll give you a hand with the Hornresp inputs.

Chris
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Mal Brown

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #4 on: November 10, 2019, 10:52:59 am »

why not call EAW ?   I had an early set of the bent horn 18's from them in the early 80's.  They were RCF loaded.   Which RCF I couldn't tell you...
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Sam Saponaro Jr

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #5 on: November 10, 2019, 09:23:32 pm »

Chris,
I found this which contains outter box measurements
 http://eaw.com/docs/2_Legacy_Products/Loudspeakers/BH/BH800R_BH800P.pdf
 
http://eaw.com/docs/2_Legacy_Products/Loudspeakers/BH/BH-800-LR_MR-102-LR.pdf
I also found this which shows a cross section view of the cab.
I wont be able to get to the actual cabs till I pick them up.



 
« Last Edit: November 10, 2019, 09:30:47 pm by Sam Saponaro Jr »
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Patrick Cognitore

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #6 on: November 11, 2019, 12:40:37 am »

Was trying to match up the specs of the original RCF L18-851K to modern drivers.

Depending on which model BH800 it is the cab could've use an RCF LF440R (unless that's another designation of the same woofer you listed).

I don't have specs for the above, just came across it in some old EAW specs sheets I've got.
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Chris Grimshaw

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #7 on: November 11, 2019, 04:05:45 am »

Having looked at the internals, I'd pause for a moment. The low-frequency cabinet shown in the PDF is a front-loaded horn with a fairly short path. You're looking at something that'll be really really efficient above about 70Hz, and be seriously limited (as in, whatever the driver in a sealed box can do) below that.

I'd strongly urge you to reconsider your purchase plans unless you're planning on running a dedicated <80Hz cabinet below this one.

Chris
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Peter Morris

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #8 on: November 11, 2019, 06:38:57 am »

OK looks like I will be needing to buy a couple 18s for some old BH800 cabs(posted few weeks back about possibly buyin them).Turns out one has no driver. And finding an original will be quite hard to do.
 Been reading threw TS specs(I know enough to be dangerous lol). Was trying to match up the specs of the original RCF L18-851K to modern drivers. From my limited knowledge the B&C 18tbx100 seemed like a good match based on QTS and VAS specs being similar. Same with the B&C 18rbx100 and RCF L18P300.
 Asked at usspeaker and was suggested a Faital 18hp1010 . The VAS is very close but the QTS is higher. Im sure they know more than me about drivers but am unsure what makes them suggest this one over others with closer Q specs.
Im a bit confused as to what to look for as far as matching up specs and how close they need to be. What specs should be spot on and what have room to play etc. All I really know is driver selection is crucial with horns.
For reference the original RCF L18-851K specs are
Fs 38.7
VAS 200
QTS .35
QMS 6
QES .38
BL 21.7
CMS .13
MMS 128
VD .468
Xmax 4.5mm

I don't think you will find a driver to match that, but you should be able to find a driver to work in that box.

Make a model of the horn in HornResp and test some drivers - You just need the fold/box dimensions - EAW says it has a flare rate of 44Hz (I assumed exponential 1500mm long - just a guess)

When I did that with a VERY ROUGH GUESS it looked like a B&C 18RBX100 or 18PZB100 would work and match the frequency response of the L18- 851  - with the 18PZB100 being the loudest, and the RBX having slightly less Xmax issues ... the original 851 seems to run out of Xmax easily.

FWIW a block of 4 Sim-ed to be -3dB at 43Hz ... one box about -3dB at 58 - 59 Hz
« Last Edit: November 11, 2019, 06:47:56 am by Peter Morris »
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Chris Grimshaw

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Re: Matching up TS specs for horn loaded 18" driver
« Reply #9 on: November 11, 2019, 08:38:13 am »


FWIW a block of 4 Sim-ed to be -3dB at 43Hz ... one box about -3dB at 58 - 59 Hz

I got slightly higher frequencies - probably different interpretation of the cabinet. Seems to me like it wouldn't keep up with modern subwoofers if deep bass is required. Given the weight and size of those boxes, I'd take a decent 2x18" ported box every time.

Chris
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Re: Matching up TS specs for horn loaded 18" driver
« Reply #9 on: November 11, 2019, 08:38:13 am »


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