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Author Topic: JTR releases new 2x18 Subwoofers - info here  (Read 4908 times)

Ivan Beaver

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #50 on: May 09, 2019, 06:49:34 pm »



FWIW, my simulations show dramatic changes in the low corner when 16x cabinets are used - from 52Hz to 34Hz.

* This would go some way to explaining the observation that large horn subwoofer stacks "throw" the sound a long way, with lower-than-expected levels near the stacks.

Chris

I will admit I have never stacked up that many horns to see what happens, 4 is the most I have done, but I did not see any trend at that point.

Part of the reason the horn levels up close are not as loud as expected (but are correct in the far field) is due to the fact that the acoustic center is not at the front of the cabinet, but rather a distance behind.

So a bit of expansion has happened (inverse square law kinda) before the sound gets out of the cabinet.

That is another reason subs (expecially large ones) should be measured at a far distance.  I like 10M, because it is a 20dB  loss, so you just drive the signal 20dB harder (a voltage factor of 10) and the math becomes real easy :)
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Art Welter

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #51 on: May 09, 2019, 11:14:48 pm »

Not counting power compression, and 4, or 5, or is it 6 dB SPL increase in the real world when doubling subs? 😉
Caleb,

In the real world doubling subs and power will result in a +6dB increase in low frequency output, plus additional gain due to the larger frontal area reducing rearward radiation. That said, as the center to center distances in the larger array become more than a 1/4 wavelength apart, they will have more upper band off axis reduction due to comb filtering, so will be less than +6.

This also furthers the "horns go way lower in multiples" myth, because the reduction in upper response makes it appear there is relatively more lower response.

Art
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Roland Clarke

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #52 on: May 10, 2019, 05:51:29 am »

My take on this Art is that the increase in frontal area helps extend baffle step, but multiple cabs even putting out the exact same sound are very much not a single horn of the correct length with a mouth area large enough to lower the horn cut off response to 20-30hz.  When you look around, there are a whole bunch of front loaded horns with lower response -3db points of 38-40 hz and they are all of a reasonably generic size.  Itís perhaps understandable that to produce anything that breaks out of this mold requires a different design (tapped horn, bandpass, etc) or has to be much larger, I think that Danley have demonstrated this.

Much like the fact most double 18ís are of a fairly generic size, performance is going to be reasonably within similar bounds give or take driver quality and parameters, and port geometry.
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Caleb Dueck

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #53 on: May 10, 2019, 10:42:08 am »

Caleb,

In the real world doubling subs and power will result in a +6dB increase in low frequency output, plus additional gain due to the larger frontal area reducing rearward radiation. That said, as the center to center distances in the larger array become more than a 1/4 wavelength apart, they will have more upper band off axis reduction due to comb filtering, so will be less than +6.

This also furthers the "horns go way lower in multiples" myth, because the reduction in upper response makes it appear there is relatively more lower response.

Art

6dB is the theoretical number, yes.  I mentioned this based on an old post Ivan did about a test he did where he found 5dB-ish was more the real world average sum. 
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Ivan Beaver

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #54 on: May 10, 2019, 11:01:11 am »

6dB is the theoretical number, yes.  I mentioned this based on an old post Ivan did about a test he did where he found 5dB-ish was more the real world average sum.
There are different factors that will affect any measurement.

Things such as actual physical position of the mic vs the cabinets (remember that they are not in the same physical location-which would result in the +6dB), or a single mic placement vs mic placements over the intended coverage area etc.

How close you are to the sources (again mic placement), freq of interest (you may not get +6 depending on the mic placement vs freq), sometimes the actual placement of the cabinets (depending on the position of the woofers vs port area and how they are coupled to the other cabinets and at what freq) and so forth.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!
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