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Multi-Way Conventional loudspeakers with crossovers

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Old 19th January 2002, 06:14 AM   #21
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Quote:
Originally posted by Kilowatt
I thought that the bottom end of my system (the big one that has caused much controversy on the forum) wouldl put out about 144dB peak. I figured that out using this equasion: (10log W)+speaker sensitivity. I was wrong. I have now learned that every time you double the number of speakers, it goes up 6dB. Each speaker is 96.4dB@1W@1m. There are eight speakers, so this would make 114.4dB@1W@1m right? There is 7200W of power. Plug this into the equasion and I get 153dB (YIKES!).
each speaker is 96.4dB@1W@1M and there are 8 of them.....
add 6 dB each time you double the number of speakers.... so in this case you double 3 times which is 18dB increase.... you then also know that if the total power delivered to the 8 speakers is 1W then each speaker will get 1/8W .... now take 3dB for each time you halve 1W to get 1/8W .... you do this 3 times ... 1W --> 1/2W --> 1/4W --> 1/8W which means each speaker will be down 9dB now add the efficiency of a single driver + the gain you get from having 8 drivers - the loss because each driver sees less of the power ........ 96.4 + 18 - 9 = 105.4dB@1W@1M then add the gain for 7200W which is about 38.6dB which will give a total of 105.4 + 38.6 = 144dB SPL @ 1M for the bass so max output from the total system would be 147dB .... know you also need to allow for @ least 20dB headroom so you would never operate the system above 127dB SPL @ 1M rms continuous.
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Old 19th January 2002, 06:33 AM   #22
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Ok, thanks, I guess my original figuring method worked after all, though it was a little different approach, so it's 147dB peak total system SPL. I still don't know how to divide it up 50%, 15%, 35%.

What exactly is that 20dB headroom thing all about? Is that 127dB figure the average music power? Perhaps that number would go up if it's playing White Zombie, and down if it's playing Simon & Garfunkel. Is that true?
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Old 19th January 2002, 06:38 AM   #23
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Music has big peaks #$%$#$^$% big peaks..... so you've gotta allow for them .... if that 7200W amp clips then those speakers are gone you play the watever @ an average of 20dB below the systems output so that its got some hope of handling the peaks without melting down .... oh i mean clipping.... tho in this case they are probably the same thing of course, some of the time it will be quieter than this also... thats just the average program level.
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Old 19th January 2002, 07:13 AM   #24
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if that 7200W amp clips then those speakers are gone
So it's to allow for peaks. I see. So, why is it that if a 200W amp clips a little, it's no big deal, but if my 7200W amp clips, it catastrophic? Those speakers can handle that 7200W just as well as a smaller set of speakers can handle smaller power levels. Just wondering. I do know that clipping is always hard on speakers, so I would of course want to make sure it doesn't clip ($1400 worth of speakers!), but would it really be that bad?

Maybe I should wire the speakers for lower impedance and make the voltage gain a little lower, this way I could get the full 7200W RMS and have plenty of room for large peaks. It would also make designing the amp a lot easier. What do you think?

Now for the redundant and still unanswered question: what is 35% of 147dB?, what is 15% of 147dB?, how do I figure it out? I am tri-amping, <300Hz gets 50%, 300-1500Hz gets 15%, >1500Hz gets 35%.
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Old 19th January 2002, 07:28 AM   #25
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cause when the 7200W amp clips it will output about 300VDC into those poor speakers ... as for different wiring arrangements, you'll need to work out how many amps the system will draw.... then you've gotta work out how to supply all the current. If you keep your original plans, each of the 1800W Amps will have to supply 25Amps on the peaks and 150V.... now you've gotta work out how to supply each of the 4 big amplifiers with 25Amps that alone is a challenge.
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Old 20th January 2002, 02:20 AM   #26
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Kilowatt.... are those 8 woofers shared between 2 channels ie 4 drivers per channel stereo? if so the maths is different to that which is above.... i redo it if need be
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Old 20th January 2002, 02:31 AM   #27
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You may or may not know that I have changed my design slightly to make it easier for me to design. The amp will have 8 channels, each 900W into 12 ohms. Every other channel will be out of phase, so 1800W into 24 ohms x 4 would also be possible, but I will just hook up one speaker to each of the 8 channels. Each of the + (red) speaker terminals will be labeled either + or - according to their phase to make it easier to hook the speakers up so they run in phase. The output devices will be mounted on opposite sides of 4 big, thick walled pieces of square aluminum tubing that I got from a recycling plant. These will be cooled in the same manner as freezer, with a compressor and liquid/gas refrigerant. It will be very cool (in both ways).
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Old 20th January 2002, 02:35 AM   #28
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OIC ... but that didnt answer the question ... are 4 of those speakers for the left channel of a stereo setup and 4 for the right channel?
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Old 20th January 2002, 02:47 AM   #29
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Yes, 4 for right and 4 for left.
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Old 20th January 2002, 02:58 AM   #30
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ok


well i'll correct my maths...

4 woofers per channel @ 96.4dB@1W@1M each...
so add 12dB because there is 4 drivers....
now each driver will get 1/4 the power so subtract 6dB
so 102.4dB@1W@1M

now each speaker is gonna get 900W so for the 4 speakers that is 3600W .... so add 35.6dB

which gives 138dB @ 1M.............

now that is the bass for 1 channel.......

so total RMS output for 1 channel will be 3dB higher than that or 141dB

and total RMS output for the system will be 3dB higher again which will be 144dB

Less 20dB headroom for a total continuous RMS system output of 124dB SPL @ 1M
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