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Old 19th January 2012, 02:16 PM   #11691
6L6 is offline 6L6  United States
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Originally Posted by KatieandDad View Post
Can you equate that into dB/W sensitivity ?
Sensitivity in an 8-ohm speaker is given at 1W/1m.
4-ohm speakers are shown at 2.83v/1m. This is not actually the same thing.

A rule of thumb is to subtract 3db from the 2.83v/1m reading to make equivalent to 1W/1m. It's close enough for government work.
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Old 19th January 2012, 02:22 PM   #11692
Salas is offline Salas  Greece
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To reach nominal power of 25W for F5 on 8 Ohm, 14VRMS must be attained. Keep that in mind for system gain when an average modern music recording on CD can show 0.7V median output level, and F5's voltage gain is 5.6 times or 15dB.
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Old 19th January 2012, 02:25 PM   #11693
AndrewT is offline AndrewT  Scotland
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Your scope reads Vpp, not Watts.

90dB/2.83Vac @ 1m means apply a voltage of 2.83Vac to the 8r0 resistor and without adjusting the source/amplifier transfer the speaker to the set up and measure the SPL at 1m.

If the speaker is accurately equivalent to a 8r0 resistor across the whole audio bandwidth then the source/amplifier is delivering 1W to the speaker and you have a dB/W @ 1m measurement.

if the speaker deviates from that idealised 8r0 equivalent then the power delivered to the speaker using that 2.83Vac is no longer an equivalent in Watts. It is a voltage sensitivity measurement. That is what B&W have stated. A voltage sensitivity measurement.

If however, the tester measures both the rms voltage and the rms current passing into the speaker then the operator can adjust the source/amplifier to input exactly 1W into the test speaker and then measure the SPL at 1m. This answer results in the power sensitivity dB/w @ 1m.

If one knows that the speaker is actually 4ohms equivalent and the manufacturer quotes either the power, or the voltage, sensitivity then you can swap between the two specification by simply adding or subtracting 3dB from the stated figure.
If one does not know the speakers equivalent impedance, then one cannot apply the correction for equivalency.
If the manufacturer is transparent and honest, both the power, or voltage, sensitivity and the actual equivalent speaker impedance will be given. These two measurements allow valid comparisons to be made and for predictions of SPL relative to drive from any amplifier.

90dB/2.83Vac @ 1m driven with pink noise band limited to 40Hz to 18kHz and showing an equivalent impedance of 6.2ohms, tells all.
regards Andrew T.
Sent from my desktop computer using a keyboard

Last edited by AndrewT; 19th January 2012 at 02:28 PM.
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Old 19th January 2012, 02:33 PM   #11694
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I'm perfectly aware of the maths.

When I said 5.8W I was assuming an 8 Ohm load and just measuring the pk-pk violtage.

The DM683 has a normal B&W horrible impedance curve.

I seem to recall it varies between about 2 Ohms and over 2K.
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Old 19th January 2012, 09:49 PM   #11695
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The F5 TURBO ought to take care of that.

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Old 19th January 2012, 09:55 PM   #11696
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You such a tease.....

Get back to work now !
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Old 19th January 2012, 11:12 PM   #11697
6L6 is offline 6L6  United States
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...can you at least give us the simplified schematic with some hints as to the differences???

Pretty please??

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Old 19th January 2012, 11:17 PM   #11698
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Click the image to open in full size.
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Old 19th January 2012, 11:44 PM   #11699
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Here is how the F5 Turbo sound

Ramones - Surfin' Bird - YouTube

Eweribady know the Bird is a winner
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Old 19th January 2012, 11:49 PM   #11700
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Thumbs up F5 Turbo

Well let me guess: the F5 Turbo is a combination of a Modified F5 with a modified BA PP output stage that makes a F5 Turbo

Don't shoot

Be nice to animals.
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