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Author Topic: well, efficiency of multiple boxes raises up to....???  (Read 7565 times)

Tamas Tako

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well, efficiency of multiple boxes raises up to....???
« on: January 17, 2006, 03:14:48 pm »

Hi,

Tom, Mark, Ivan and all the other people here (please forgive me if your name wasn't there..) I have a question regarding efficiency here...

If one would build a large stack from

a/ Double 18" vented boxes
The efficiency of one 2x18" vented cabinet is around 95..98 dB
Say 100dB for easier calculation...


b/ Horn loaded subs ( TH 112/115/Vortex or whatever)

The efficiency of one Horn loaded cabinet is say around 106dB
in this particular case for easier calculation.


If you have 2, 4, 8, 16, 32, 64 pcs in a stack, how the efficiency raises in both a/ and b/ cases?

I mean having two boxes instead of just one, You would get 3 dB more efficiency and 3 dB more power handling giving 6dB more max SPL.
But efficiency can not raise up to more than 100% right?
And the number of boxes where the 100% efficiency would be reach is not infinite....

So I guess:
Doubling the number of boxes not always results 6 dB max SPL gain anymore. If you have 64 instead of 32 you may only get 3 dB more SPL and this only becouse of the increased power handling and no efficiency increase...

Sure I know SPL can be increased not just by efficiency and input power, but with more directivity as well... (see BDEAPs)

At some point you neither get more directivity when you already reached the dimensions where the majority of the stack is working under quarter space conditions, however this can be true always just for a part of the stack and not for the speakers on the both ends... So you may get more and more boxes to work with increased directivity and with increased radiating impedance due to the sound (air) pressure generated by the other boxes...


So my question is, If Horn loaded boxes have or have not any advantage in this manner when they are used in big stacks?

SO If I use 64 pcs of 2x18" vented cabinets Do I get less Max SPL than using 64 pcs of Horn loaded Subs if the total input power is the same in both cases?

I mean If I only can reach an efficiency of say 120dB 1W 1m including directivity in both cases, then I get the same max SPL when feeding with the same total power, right?

Clear, that I could reach this efficiency margin with horns easier and with less cabinets. Maybe with just 16 pcs...
But what if I add there some more horns? I gues there should be a border somewhere, above I dont get more efficiency, I just can pump more watts into the speaker...


I am wondering if this all is true or not?

If anyone has to say something about this I would appriciate any explanation!

Thanks,

Tamas



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Paul O'Brien

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #1 on: January 17, 2006, 03:38:48 pm »

You have 2 terms mixed up here, Sensitivity and Efficiency.

Sensitivity is the sound output level resulting from a given input signal and measured at a given distance from the driver, usually indicated as ??spl@1w/1m in spec sheets.

Efficiency if the amount of that input signal that is actually converted into sound, while the rest is dissipated in heat, soaked up in back emf, produces cone movement....Not usually found in any spec sheets. This is typically between 1-10% for direct radiator designs, and up to 50% for horn loaded designs.

There is a limit to the maximum efficiency you can achieve,(directly related to the box type) but the more boxes you stack together the higher the sensitivity.

For example.. it doesn't matter how many reflex boxes you stack together, you'll never reach the efficiency(amount of sound output per watt) that a stack of horns will produce from the same power. Because of the horns efficiency advantage, it will take fewer horns and less power to match the bigger reflex stack.
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Paul O

Tamas Tako

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #2 on: January 17, 2006, 04:01:52 pm »

Hi,

Thanks for your reply, however I am afraid, you don't really understod me.
I was not wanting to mix the two terms sensitivity and efficiency. However they ara sisters. Efficiency shows you, how many acoustic watts you will get when you put one electronic watt into the device in  %.
Sensitivity shows you how many accoustic watts you will get for an 1 watt input if you know the coverage pattern.... So you see the are almost the same if you add that directivity is an important part of the difference between efficiency and sensitivity. The fact, that one of it is in dB and the other usually in % doesn't matter If you imagine that distortion can be figured in % and in dB as well....
This is why I was writting about directivity coused sensitivity gain where the efficiency remains the same at the same time...



Anyway thanks,

Tamas
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Paul O'Brien

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #3 on: January 17, 2006, 04:30:56 pm »

I agree they are all related, Sensitivity, Efficiency and Directivity, but they are seperate entities, and an array of reflex boses will have increased directivity in a plane just like an array of horns will have increased directivity in a plane. The biggest difference will be that the horn array will be louder at a given distance, with the same input power and number of boxes used. This is a direct result of thier higher efficiency.
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Paul O

Tamas Tako

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #4 on: January 17, 2006, 04:45:05 pm »

Well yes maybe I should edit my post and write efficiency where I mean Efficiency and sensitivity where I mean sensitivity...

I am not sure you will get more SPL in the farfield with horns than with direct radiators when the 1m SPL is the same... I also read earlier some post that the radiator is the driver and 1m far from the horn means 3-4m from the driver and the inverse square law should be used this way.  I have measured this and this is not true!

Tamas
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Paul O'Brien

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #5 on: January 17, 2006, 05:01:19 pm »

Tamas Tako wrote on Tue, 17 January 2006 16:45


I am not sure you will get more SPL in the farfield with horns than with direct radiators when the 1m SPL is the same... I also read earlier some post that the radiator is the driver and 1m far from the horn means 3-4m from the driver and the inverse square law should be used this way.  I have measured this and this is not true! Tamas


OK.. from what I understand when measuring a speaker systems sensitivity, the test position is 1m from the "radiating surface" of the cabinet. That's essentially right at the cone for direct radiators, but at the mouth of a horn loaded box.
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Paul O

Tamas Tako

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #6 on: January 17, 2006, 05:08:47 pm »

Yes.
This is How I understand and what I have measured
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Walt de Jong

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #7 on: January 17, 2006, 05:41:52 pm »

These are measurement on a stack of 2,4 and 6 Punisher horns. This was done outside with about 1200W into each Punisher. In the farfield the inverse square law applies. In the nearfield some strange effects are noticable. Horizontal axis is distance in metres from the stack. Vertical axis is dB(c)

http://img14.imageshack.us/img14/2388/meting246punishers5ok.jpg

Best regards,

Walt
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Antone Atmarama Bajor

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #8 on: January 18, 2006, 11:35:09 am »

Horns Don't measure the same as Direct Radiators  up close.

     Horns have more of a linear Air coupling.  You should compare measurements with Direct radiators at 100W 10m instead of 1W 1m.

Antone-
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Michael_Elliston¶

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Re: well, efficiency of multiple boxes raises up to....???
« Reply #9 on: January 20, 2006, 12:12:23 am »

Walt - that is a great measurement ! nice to see some one bothering to both do it,and post it up !
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