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6L6
diyAudio Moderator

Join Date: Oct 2010
Location: Denver, Colorado
Quote:
 Originally Posted by KatieandDad 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.

 19th January 2012, 02:22 PM #11692 Salas   diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece 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.
 19th January 2012, 02:25 PM #11693 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders 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. eg. 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. Last edited by AndrewT; 19th January 2012 at 02:28 PM.
 19th January 2012, 02:33 PM #11694 KatieandDad   diyAudio Member     Join Date: Nov 2011 Location: UK 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.
 19th January 2012, 09:49 PM #11695 Nelson Pass   The one and only     Join Date: Mar 2001 The F5 TURBO ought to take care of that.
 19th January 2012, 09:55 PM #11696 Bksabath   Banned   Join Date: Dec 2007 You such a tease..... Get back to work now !
 19th January 2012, 11:12 PM #11697 6L6   diyAudio Moderator     Join Date: Oct 2010 Location: Denver, Colorado ...can you at least give us the simplified schematic with some hints as to the differences??? Pretty please?? __________________ Illustrated Build Guides - Pass F4 - Pass B1 - Pass F5 - Pearl 2 - O2 HPA - Hagerman Bugle 2 - Pass Aleph J - Me at BA '13 -Pass F5Turbo - BA-3 Amp - BA-3 Preamp - F6 AmpCampAmp
 19th January 2012, 11:17 PM #11698 Malotron   diyAudio Member     Join Date: Sep 2005 Location: Honolulu
 19th January 2012, 11:44 PM #11699 Bksabath   Banned   Join Date: Dec 2007 Here is how the F5 Turbo sound Ramones - Surfin' Bird - YouTube Eweribady know the Bird is a winner
 19th January 2012, 11:49 PM #11700 Audiofanatic   diyAudio Member     Join Date: Oct 2002 Location: The Netherlands, Utrecht 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 Audiofanatic __________________ Be nice to animals.

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