[Dave Milne]

I know, I know... too much is never enough, especially when it comes to volume or bass.


But seriously, I recently upgraded my high-end two-channel system to 7.1. The front L-R are large Dynaudio WMTMW towers that are quite efficient ([email protected]). I'm driving them with Bryston 4BST. 400+Wpc (26 dbW) into the 4-ohm Dynaudios yields 117+dB. Each speaker. Without room gain. Center is a slightly smaller Dynaudio "Twynn" (~90dB/1W) driven by 400W.


My question is... do I really need anywhere near that output capability in the surrounds? They're also Dynaudio, nicely timbre matched, but much smaller. They're about 87 db @1W. I'm driving them with 200wpc, but am considering going to a Bryston 8B (4 x 120W=21 dbW) to save rack space and "brand match" the rest of the system. The result would be surrounds with a full 10dB lower capability than the LCR --but still respectable 107 dB. Is this wise? Is there some sort of "reference level" the movie industry uses that defines the max output requirement of surrounds?


BTW, I have two large (280 l) vented, equalized subs with JBL 2245H 18" drivers, so bass is not an issue.

 

[fs1]

If they can do 107dB, then that's actually over reference levels which is 105dB peak (for transients) for all channels, and 115 dB for the LFE. Check with AVIA calibration disc.

 

[John Kotches]

The figures you cite are for a listener at 1m. Don't forget to figure in losses for distance from the speakers.


If you can, get a voltmeter and measure the SPL with a 2.83v input to the speaker, this will tell you your sensitivity at the seat.


Regards,

 

[Mark Seaton]

Hi guys,


As John explains, these values of 105dB are AT the listening position. In open space, sound falls off at 6dB per doubling of distance. This would imply a 1M requirement of 117dB for a mere 13-14' listening distance. In reality, this attenuation is somewhat less in a more reverberant room, but if your room is well treated, expect 4-6dB of loss per doubling of distance.


Now there is another issue in that at 400W of input power, most speakers will suffer from some form of thermal compression, typicaly at least 3dB. Then there is the matter of if your speakers can actually reproduce these levels without significant distortion. Some may do it for a limited range, but most fall appart in the midrange and upper bass region. A single 6.5" woofer won't have a chance.


In my own system I have a newer speaker of ours which is 95-96dB sensitivity, with very low distortion past 110dB @ 1M. My own playing with amplifiers has had me being more comfortable with amplifiers of 200W @ 8 Ohms or better to get the full potential out of the speaker. Of course some of the very conservatively rated higher end amps have proven quite good, I generally can find their limits in a larger room. In our large office space, I can almost use up the peak (would go deaf if it was continuous) power of a QSC PL 236 which does 1100W into the speaker's 4 Ohm bass load. To keep this all in perspective though, I still get plenty of clean sound for most from a modest little Adcom 535II (65 or 80W?).


Regards,