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Old 13th September 2012, 01:00 PM   #41
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How did you get to 124dB for 8 drivers from 82dB with 1 driver
I think its more like ▒91dB/W/m with 8 drivers if one is 82dB/W/m
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Old 13th September 2012, 01:40 PM   #42
tb46 is offline tb46  United States
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Hi sangram,

Post #40: "...at 82dB per sub as per my estimates, eight units will be 124dB/1m, and I might be able to get about 110dB at listening position with 1 watt..."

You might want to simulate this in Hornresp. I'll attach an example SPL comparing 1 (light grey) v. 8 (dark line):

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File Type: jpg 1_v_8_SPL.jpg (32.0 KB, 147 views)
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Old 13th September 2012, 02:50 PM   #43
AndrewT is offline AndrewT  Scotland
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double the output (+3dB) over a restricted frequency range by doubling the Sd.
quadrupling the output (+6dB) over an even more restricted frequency range by quadrupling the Sd.
eight ytimes the output (+9dB) by using 8times the Sd over a much reduced frequency range.

The restricted frequency range comes about because the "width" of the sound source is becoming bigger as more drivers are added to the array.
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Old 13th September 2012, 02:53 PM   #44
AndrewT is offline AndrewT  Scotland
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Tb,
are you allowing Hornresp to increase the input power as you add more drive units to the array? Hornresp lets you input drive voltage. It then uses your s/p arrangement to generate the correct driver voltage.

The +17dB with 8units looks like +9dB from 6times the input power and another +8dB from the added Sd of the array.
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Old 13th September 2012, 03:22 PM   #45
sangram is offline sangram  India
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My understanding was that halving the impedance doubles the input power to the array, I was simplifying by adding +6dB for each driver which is incorrect.

I stand corrected. Thanks to tb46 and AndrewT, and for bart-west for pointing out the error. I can only hope that the lower than originally estimated SPL will be enough. I suspect given the casual approach to (and expectations from) the project, I might still be able to get away with it. I'm shooting for reasonable output in a 20x22 room between 30 and 60Hz, so a very narrow-band sub with some usable output down to about 27Hz - mostly for home theater.
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Old 13th September 2012, 09:59 PM   #46
tb46 is offline tb46  United States
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Hi AndrewT,

The Hornresp Multiple Speakers function maintaines the input Eg, and handles the resistance according to the series/parallel connection you specify. In this case 8 in parallel (see: Post #40). There was a long discussion on the subject of multiple speakers, and resulting combined SPL (as handled in Hornresp) somewhere here in diyaudio.

Gotta run.

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Old 16th November 2012, 03:49 PM   #47
sangram is offline sangram  India
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tb46 and Andrew, thanks for your help. I finished this project today. I'm running the 8 as two groups of 2 ohm arrays, off 8 chipamps (also configured as 4 parallel/channel x 2 channels) with active cooling.

The subs have far more headroom than either my ears or the 90dB/W Wharfedale speakers I'm using them with. This is more than adequate for home theater usage, is able to go far louder than I will ever need them to, low bass is pretty good though being very basic drivers they do not have much below 25Hz. I do have enough headroom to apply EQ so maybe that's next on the cards.
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