For a 3-way designed for sub crossing at 80Hz - what are the implications of multiple woofers? - Page 2 - AVS Forum
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post #31 of 37 Old 04-20-2013, 05:28 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

I don't know what you mean by instantaneous power need or dynamic peak handling. Those are mainly marketing terms, not engineering terms. Speaker output is measured in decibels, not watts. The decibel output limit for a woofer is determined by the maximum cone displacement. If one driver lacks adequate displacement adding a second driver doubles the displacement, allowing for 6dB additional output.

I think i generally understand, but let me know where my understanding goes off the rails...

Using this SPL calculator

If I am sitting 18 feet from my speakers which are close to a wall (some boundary reinforcement)...

...and say I like my basic level to be 80db at the listening point

...to deal with a 20 db peak I would need 300 watts in order to have 100db at the listening point

So, if i have one driver then it needs to handle short bursts of 300 watts.

If I have a two driver system, does each driver see 150 of those watts, or do both see 300?

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post #32 of 37 Old 04-21-2013, 06:08 AM
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Forget about watts. You need to model the drivers you intend to use in a modeling program like WinISD Alpha Pro and look at the maximum SPL chart to see what they're capable of. And forget about SPL calculators as they're only accurate outdoors. Indoors room reflections make speakers work literally twice as well as a simple -6dB/distance doubling would indicate, so a -3dB per doubling of distance is a more likely scenario.

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post #33 of 37 Old 04-21-2013, 07:29 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Forget about watts.

But don't you ultimately have to determine if the speakers can handle the amount of power it will take to get them to the desired volume levels? Also to determine if the amp you have can attain those levels without clipping?

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You need to model the drivers you intend to use in a modeling program like WinISD Alpha Pro and look at the maximum SPL chart to see what they're capable of.

I understand that this is truly part of the process to determine the truw sensitivity and FR of a speaker system vs the drivers in it. Sounds like learning to play with this software is something i need to look into - thanks.

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And forget about SPL calculators as they're only accurate outdoors. Indoors room reflections make speakers work literally twice as well as a simple -6dB/distance doubling would indicate, so a -3dB per doubling of distance is a more likely scenario.

Seems the calculator I used was closer to the -3db per doubling. I entered 17 feet, which would be just over four doublings (1->2, 2->4, 4->8, 8->16) and they suggest -14.3db for distance but add back 3db for proximity to a wall. Is there a better way to determine the maximum power needs for power handling considerations?

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post #34 of 37 Old 04-21-2013, 02:35 PM
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Originally Posted by rick240 View Post

But don't you ultimately have to determine if the speakers can handle the amount of power it will take to get them to the desired volume levels?
Modeling tells you that. What program are you modeling with? What are you using to calculate the crossover frequencies? What are you using to calculate the crossover components? I think you may be in way over your head with this.

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post #35 of 37 Old 04-21-2013, 03:32 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Modeling tells you that. What program are you modeling with?

I downloaded WinISD Pro and may play with it a bit.

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What are you using to calculate the crossover frequencies?

Pulling them out of the air based on FR charts coming with the drivers and comments here on resonant frequencies, etc.

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What are you using to calculate the crossover components?

Wasn't really planning to go that far. I'm just trying to understand some basics and maybe a bit further so i can have intelligent conversations when I commission getting these built (likely Salk/Murphy like my last set of speakers).

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I think you may be in way over your head with this.

I'm trying to avoid getting that deep - just want to understand principles.


I do appreciate your sharing your knowledge.

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post #36 of 37 Old 04-21-2013, 06:29 PM
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I'm trying to avoid getting that deep - just want to understand principles.
IMO stick with a tested design.

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post #37 of 37 Old 04-23-2013, 08:13 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

IMO stick with a tested design.

But that would take all of the fun out of it wink.gif

Besides, the designs I'm considering are all tested. I'm just seeking some knowledge about the designs.

Also, I'll be lucky if the budget allows for the upgrade to happen this year - so I have lots of time to better understand concepts, evaluate (on paper and by forum) various drivers, and ultimately make reasonable requests of those with the skills i don't have when the time is right smile.gif

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