AVS Forum banner
Status
Not open for further replies.
1 - 6 of 6 Posts

· Registered
Joined
·
4,354 Posts
Discussion Starter · #1 ·
20ft (l) x 8ft (h) x 40ft (L)

very dead sounding ( highly absorbant )

4ft floor ( last one )

wood floor with carpet all over

speakers: 2 high sensitive fronts (98dB), 91db rears, 2 subs (99db)

fronts can "take" 500w easy, subs 2000w, rears: 200w


how much watts would you "feed" these given these data, in order to have DISTORTION free ( ziltch! nada!) sound but still a powerful sound (stereo, multichannel)

target: 90-95dB average (with peaks way higher of course :D )


thanks
 

· Registered
Joined
·
1,876 Posts
With a 98db efficient speaker you would not need a very high power amp to drive them to your desired sound levels.


But your desire to have that level be low in distortion depends more on the QUALITY of the amplifier used (no receivers) than the watt output and on the ability of the speaker to play loudly without breakup. Two speakers which are equally efficient could have very different abilities to play loudly. The efficiency rating measures only the loudness at 1M when 1 watt of power is applied. It tells nothing of how well the speaker performs when driven by 10 or 100 times the power.


BTW I know of no speakers at ANY price that are truely zilch!, nada! distortion free.
 

· Registered
Joined
·
430 Posts
David,


It is impossible to answer your question as we know nothing about your speakers' distortion characteristics or sound quality, just as Carl noted.


However, we can use some basic room acoustics calculations for determining the in-room SPL produced by your system. From your description, I am estimating the equivalent absorption area A of your room to some 50 m^2. The reverberant field SPL Lp produced by your front pair of speakers for an input of 1 W (or usually more correctly, 2.83 V) per channel may be roughly calculated as:


Lp = Lw + 10*log(4/A) = 98 + 3 + 10*log(2*pi) + 10*log(4/50) = 98 dB


This means that using 100 W (+20 dB re 1 W) of input power will produce a whopping 118 dB SPL, usually enough for even a hard-core headbanger. Actually, IMO, the capability of producing clean peaks of 115 dB (sounds loud but not overbearingly so) should be a design criteria for a high-end system. Your system will produce 115 dB with just 50 W @ 8 ohm, but as stated previously, I have no way of telling what the actual sound quality will be like at this level.
 

· Registered
Joined
·
4,354 Posts
Discussion Starter · #4 ·
Iceman and Carl


hi :)


and thanks for the comments.


of course, distorsion-free is "impossible" but you get the picture.


the listening positions ( 2 rows ) are at 5.5 and 7.2meters or so but the total length of the room ( HT - living room ) is 17meters in fact (don't know if the total length has an influence ).

100w would be "enough" for the fronts but "true" 100watts: it's a class AB amp (Denon 4800), so let's its efficiency is around 50-55%. that means the real watts outputed even at mid level (70% of total power ?) is not very high. I suppose 200watts of high efficient amp (switching for instance) would give much more headoom and cleaner power.


do you think there exists a sort of formula to estimate the watts needed given all these data such as speakers efficiency, room size, room absorption, listening distance etc etc ?


don't misunderstand me however: the current system can give insane sound pressure with very low distorsion already.


best
 

· Registered
Joined
·
1,876 Posts
There is no such formula as it depends on the relationship between the specific amp and your speakers.


Some speakers present a tough load on your amp, going down to 1-2 ohms on occasion. These speakers require much more current capability than speakers that are close to an 8 ohm load full range. Different amps have different abilities depending whether they are driving easy, resistive loads or difficult low impedence loads.


If you are reasonably happy with your current setup you ought to try to audition several amps from local dealers and see whether they are worth the additional cost to your ears. Without knowing where on the planet you are located I won't even speculate how easy or hard this might be.
 

· Registered
Joined
·
430 Posts
David,

Quote:
100w would be "enough" for the fronts but "true" 100watts: it's a class AB amp (Denon 4800), so let's its efficiency is around 50-55%. that means the real watts outputed even at mid level (70% of total power ?) is not very high. I suppose 200watts of high efficient amp (switching for instance) would give much more headoom and cleaner power.
I am not quite sure what you mean, but the efficiency of an amp has nothing to do with actual power output. An amp rated at 100 W will output a maximum of at least 100 W regardless of efficiency (provided that the manufacturer is serious). Efficiency is the ratio of power output to power input where power input in this case is the power supplied by the mains. If you are not bothered by the extra heat produced by a conventional, inefficient, design, efficiency should not be a concern.



The expression for calculating in-room SPL is the one I used above:


Lp = Lw + 10log(4/A)


Simplifying this expression without boring the readers with details, you end up with the following "cookbook formulas":


Max SPL "live room" = speaker sensitivity + 10*log(154*amp power @ 8 ohm*number of channels/room volume)

Max SPL "dead room" = speaker sensitivity + 10*log(77*amp power @ 8 ohm*number of channels/room volume)


Room volume in meters^3.


The amp is considered ideal (constant voltage source) - a fairly good approximation for most amp/speaker combinations. For all but the most extreme speakers, the reduction due to current limitation in the amp is no more than 2-3 dB even for mid-fi receivers.


Note that as soon as you are more than 1 m or so from the speakers, the sound waves reflecting off the walls dominate over the direct sound and the SPL becomes constant regardless of distance from the speakers. This condition is known as the reverberant field.


(Disclaimer: The expressions above are only roughly valid and oversimplified not to complicate matters too much. Still good approximations, though)
 
1 - 6 of 6 Posts
Status
Not open for further replies.
Top