Power needs analysis...

**JonMarsh** · 16 March 2005, 16:31 Wednesday

I have found many mainstream manufacturer's data for efficiency to be anywhere from slightly off to outright lies. Descrepencies of up to 4-6 dB.

The Studio 60's are a floor standing two way in what is referred to as a 2.5 configuration, as the seond woofer is rolled out relatively low and provides baffle step compensation of the bottom end. Good 7's that will deliver low end extension in a larger cabinet like this typically have a nominal sensitivity around 87-88 dB. The second driver essentially provides the additional output needed in the conversion from 2pi space to 4 pi space because of the baffle size (baffle step compensation). Considering the "Anechoic" rating from Paradigm is 88 dB, that's probably an "honest" FTC style rating.

.

Recalculate based on that, not the more optimistic 91 dB rating.

Note, 3 dB = 2X the amplifier power.

~Jon

**ajpoe** · 16 March 2005, 16:37 Wednesday

Thanks John, I was hoping one of you smart guys would chime in. If I recalculate at the rating of 88, then I'd need 64 pure watts to achieve the DD standard instead of 32 since it starts at 3 db less. Since the Rotel conservatively provides 120 watts x 5, I'd say its safe to say that I have plenty of power. I calibrated my system and I'd have to have the volume around 82 on my 1068 to be at the directors intended levels. This is extremely loud and I generally watch a movie around 70-72 if its DTS or 72-75 for DD (the later if no girls are present... why don't chicks like loud movies? LOL)

**hidefdvd** · 16 March 2005, 18:23 Wednesday

Try this db calculator. It should give you an idea how many watts your using to reach reference level. The other 3 speakers in a 5.1 setup add to the overall db level.

Peak SPL Calculator

http://www.myhometheater.homestead.com/splcalculator.html

**JonMarsh** · 16 March 2005, 20:00 Wednesday

Originally posted by ajpoe

Thanks John, I was hoping one of you smart guys would chime in. If I recalculate at the rating of 88, then I'd need 64 pure watts to achieve the DD standard instead of 32 since it starts at 3 db less. Since the Rotel conservatively provides 120 watts x 5, I'd say its safe to say that I have plenty of power. I calibrated my system and I'd have to have the volume around 82 on my 1068 to be at the directors intended levels. This is extremely loud and I generally watch a movie around 70-72 if its DTS or 72-75 for DD (the later if no girls are present... why don't chicks like loud movies? LOL)

Don't forget there are peak to average issues- you may playback at an average SPL in the mid 70's to 80's, but short term peaks can be 20 dB higher. Still, I agree that the Rotel your should be up to the job just fine.

**ajpoe** · 17 March 2005, 11:12 Thursday

Originally posted by JonMarsh

Don't forget there are peak to average issues- you may playback at an average SPL in the mid 70's to 80's, but short term peaks can be 20 dB higher. Still, I agree that the Rotel your should be up to the job just fine.

John, I was under the impression that the rating of 106 db for DD was at the peaks and that normal dialogue and more quiet scenes would be much less. So as long as my power/sensitivity calculations are fine to those peaks at 106 db, everything should be fine. Is this a correct assumption? According to the charts, I only need 64 pure watts to achieve this, but I have some cushion just in case.

**JonMarsh** · 17 March 2005, 11:23 Thursday

That should be a correct assumption. Of course, some peaks are longer than others... and the unfortunate thing that comes out is that multi-channel receiver power ratings have a lot of gamesmanship involved- often power rating is quoted mainly for 2 channels driven out of 6 or 8 (5.1, 7.1), then somewhere in fine print they may have a rating with all channels driven, in which case the power supply is working very hard, there's a lot of voltage ripple on the power supply rails, and the sound quality suffers. For this reason alone I would recommend having a 3 dB power margin over calculated results, unless using seperates with clearly defined ratings for all channels driven simultaneously.

But I'm a bit of a stickler and luddite....

**AndrewM** · 17 March 2005, 11:28 Thursday

Oh just go pick up a nice pair of 600W monoblocks already

Andrew
High effeciency and high power make a nice combo

**ajpoe** · 17 March 2005, 14:07 Thursday

Originally posted by JonMarsh

That should be a correct assumption. Of course, some peaks are longer than others... and the unfortunate thing that comes out is that multi-channel receiver power ratings have a lot of gamesmanship involved- often power rating is quoted mainly for 2 channels driven out of 6 or 8 (5.1, 7.1), then somewhere in fine print they may have a rating with all channels driven, in which case the power supply is working very hard, there's a lot of voltage ripple on the power supply rails, and the sound quality suffers. For this reason alone I would recommend having a 3 dB power margin over calculated results, unless using seperates with clearly defined ratings for all channels driven simultaneously.

But I'm a bit of a stickler and luddite....

Excellent! I have a 3 db margin based on my calculations (or very close) and Rotel is rated all channels driven at 8 ohms 20 hz - 20 khz. :T

Andrew, 600 watt monoblocks would be nice... if you'd like to donate a few, i'd be more than happy to keep them warm for you! :B

**Kingdaddy** · 17 March 2005, 16:04 Thursday

That chart would be of use only for an active system where the drivers are directly coupled to the amps output. Passive crossovers dissipate as much as 80% of the input power into heat, so I've read. So it depends on how many passive components and how much series resistance is in the crossover.

Power needs analysis...

Power needs analysis...

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