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Determining overall speaker sensitivity

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Posted on May 26, 2023 at 12:02:40
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005
 Can one, and if so, how does one determine the overall sensitivity of a speaker with multiple drivers? The speakers concerning my question are: JBL 4647 enclosures w/ 2225 woofers (97db) and 2445J drivers (111db) into 2380 horns. XO is JBL 3115A at 500Hz. Woofers are 8ohm and drivers are 16ohm.

 

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RE: Determining overall speaker sensitivity, posted on May 26, 2023 at 14:40:46
Bill Fitzmaurice
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Posts: 5337
Location: New England
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 97dB.This assumes that you've padded the level of the HF horns to match the woofers, which is SOP.

 

RE: Determining overall speaker sensitivity, posted on May 26, 2023 at 20:32:21
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005
 Bill: "padded the level of the ... horns"?

 

RE: "padded the level of the ... horns"?, posted on May 27, 2023 at 04:57:25
Bill Fitzmaurice
Industry Professional

Posts: 5337
Location: New England
Joined: October 20, 2002
 Yes. The usual method is with an LPad. If you don't do that the HF horns will be some 10dB louder than the woofers, even after taking into account their higher impedance.

 

RE: Determining overall speaker sensitivity, posted on May 27, 2023 at 05:48:53
Scholl
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Joined: March 8, 2001
 +1 JBL is good with specing reference efficiency and the 500hz crossover will probably shave off any response rise.

 

RE: "padded the level of the ... horns"?, posted on May 27, 2023 at 11:31:25
Webnick
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Posts: 925
Location: So. California
Joined: October 3, 2005
 Explains why I'd set the XO "HF Boost" to -6db?

 

RE: "padded the level of the ... horns"?, posted on May 27, 2023 at 12:52:23
Bill Fitzmaurice
Industry Professional

Posts: 5337
Location: New England
Joined: October 20, 2002
 Even that is probably a bit hot. Being 16 ohms lowers their 2.83v sensitivity by 3dB, but that's still 11dB higher than the woofers.

 

RE: "padded the level of the ... horns"?, posted on May 27, 2023 at 13:41:34
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005
 Well, if I can't lower the output any more via the XO, what analog method(s) is preferred?

 

RE: "padded the level of the ... horns"?, posted on May 27, 2023 at 19:04:46
Bill Fitzmaurice
Industry Professional

Posts: 5337
Location: New England
Joined: October 20, 2002
 LPad.

 

RE: "padded the level of the ... horns"?, posted on May 28, 2023 at 00:18:53
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005
 Or I suppose I could simply match the drivers, no? H woofer with H horn or J woofer with J horn? I'll investigate whether the H 8 ohm is superior to the J 16 ohm; go with one or the other. Also wonder whether simply changing the diaphragm from 16 to 8 will do the job.

 

RE: I could simply match the drivers, no?, posted on May 28, 2023 at 05:04:14
Bill Fitzmaurice
Industry Professional

Posts: 5337
Location: New England
Joined: October 20, 2002
 No. No matter which driver you use horn loading makes it more sensitive than the direct radiating woofer. The only way to level match them is via reduction of the input voltage to the HF driver, by either an LPad or by bi-amping.

 

RE: I could simply match the drivers, no?, posted on May 28, 2023 at 10:00:31
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005



So, Bill, isn't my XO (3115A) doing just that, where this XO is designed to work with a low frequency impedance of 8 ohms and a high frequency impedance of 16 ohms?

 

RE: I could simply match the drivers, no?, posted on May 28, 2023 at 12:26:20
Bill Fitzmaurice
Industry Professional

Posts: 5337
Location: New England
Joined: October 20, 2002
 You're looking at two entirely different concerns. Crossover components are chosen to deliver the desired crossover frequency and slope with the specific impedance of the drivers being used. That has nothing to do with level matching, which as I already said can be realized with an LPad or with bi-amping.

 

RE: I could simply match the drivers, no?, posted on May 28, 2023 at 15:51:34
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005
 I see. But aren't the level controls included with the XO for that purpose (perhaps not in the same way, but have a similar effect)?

 

RE: I could simply match the drivers, no?, posted on May 28, 2023 at 19:14:56
Bill Fitzmaurice
Industry Professional

Posts: 5337
Location: New England
Joined: October 20, 2002
 They are there for that purpose, though I would say -6dB is inadequate. Without seeing measured response it's only an educated guess.

 

RE: I could simply match the drivers, no?, posted on May 29, 2023 at 09:17:59
Webnick
Audiophile

Posts: 925
Location: So. California
Joined: October 3, 2005
 Thank you for your insight Bill. More research to do.

 

RE: I could simply match the drivers, no?, posted on June 6, 2023 at 14:36:18
claudej1@aol.com
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Location: Detroit
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 as opposed to a Scientific Wild A$$ Guess! (SWAG)

 

RE: I could simply match the drivers, no?, posted on June 8, 2023 at 22:06:23
KanedaK
Audiophile

Posts: 2417
Location: Brussels
Joined: April 27, 2010


  		You could use Crites 3636 auto formers to match the level of the horns to the woofers. You will need to use the correct parallel resistor to bring back the impedance seen by the network to the correct value.
You can find more information here (parallel resistor values would be the same with Crites autofiormers, assuming an equal attenuation):

 

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