LM4780 : good choice for 3 way active speaker ? - Page 3 - diyAudio
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Old 9th April 2013, 09:41 PM   #21
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FYI the 4780 has tiny pins which are a PITA to wire up vs. the 3886. That alone would push me toward the 3886 if you are doing point-to-point dead bug.
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Old 10th April 2013, 09:12 AM   #22
AndrewT is offline AndrewT  Scotland
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A 4ohm driver that is specified as 90dB/2.83V @ 1m is actually drawing 2W for that 90dB.
An 8ohm driver that is specified as 90dB/W @ 1m is also 90dB/2.83V @ 1m.

The 8ohm driver is delivering twice the volume for 1W as the 4ohm driver is when actually supplied with 1W = 2V i.e. 4ohm should be specified as 87dB/2V @ 1m to show true sensitivity to power input.
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Old 10th April 2013, 09:40 AM   #23
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Andrew, the convention is mostly per 2.83V so we have a single yardstick. DCR for an 8 ohm driver is rarely more than 7 ohms in any case (if one can find an 8 ohm driver). And even then it's probably only actually 8 ohms in 3 places.

No, this convention works in a voltage driven world. The designers can decide on whether their amps an manage it (and how they are going to spec their power output.
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Old 10th April 2013, 09:45 AM   #24
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On that basis every manufacturer that makes available both 4ohms and 8ohms drivers will show the 4ohm driver as twice as efficient. Balderdash.
No, the manufacturer will show the sensitivity in manner that allows the user to decide which he/she requires and select the power to be delivered to that choice of driver as appropriate.
It can only be done by comparing apples to apples, i.e. dB/W
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Old 10th April 2013, 02:03 PM   #25
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No, not balderdash! It has been thus for at least 35 years. I suggest you go back and look at spec sheets from Seas, Vifa, Tang Band, Scan Speak and even KEF if you can find them. All set to 2.83V, precisely so you can compare apples with apples (being voltage driven devices powered by voltage amplifiers).

And yes the lower Z ones show up as more efficient, though rarely by 6 dB because the magnetic circuit is usually saturated.
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Old 10th April 2013, 03:38 PM   #26
AndrewT is offline AndrewT  Scotland
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SPL is related to input power or related to supply voltage squared.
and it's 3dB not 6dB
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Old 11th April 2013, 01:21 PM   #27
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Andrew, you really are a frightful know-all aren't you?

F=BIl, f=ma, a determines level. Halve the resistance, double the I, level doubles, Ie.6dB.

Works the same way when you put drivers in parallel.

My comment was that the magnet does not usually allow you to realise the full 6dB.

Last edited by ChristianThomas; 11th April 2013 at 01:35 PM. Reason: Error on power
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Old 11th April 2013, 02:57 PM   #28
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Quote:
Originally Posted by AndrewT View Post
A 4ohm driver that is specified as 90dB/2.83V @ 1m is actually drawing 2W for that 90dB.
An 8ohm driver that is specified as 90dB/W @ 1m is also 90dB/2.83V @ 1m.

The 8ohm driver is delivering twice the volume for 1W as the 4ohm driver is when actually supplied with 1W = 2V i.e. 4ohm should be specified as 87dB/2V @ 1m to show true sensitivity to power input.
Thanks, i didn't suspect that, but it makes sense.
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Old 12th April 2013, 06:48 PM   #29
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i see no point in dB/W @1m.
but dB/2.83V @1m makes a lot more sense.
why negotiate the power, when they are all -as pointed out- driven by voltage?
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Old 13th April 2013, 09:35 AM   #30
AndrewT is offline AndrewT  Scotland
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Because we buy our equipment by power ratings.

The amplifier is power rated.
The speaker output is power rated.


If, as I have suggested a few times on this Forum, that we specify amplifiers by Vout into rated load, then it would make a lot of sense to use a voltage sensitivity.

But, that is not the way we specify amplifiers. We insist on using power ratings instead of voltage ratings.
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