How Much Power Do I Need ?

[betty boop]

Noticed someone ask about this question in another post.

How much power, how many watts do I need,

It basically comes down to the sensitivity of your speakers, how loud you want to go and how far you sit at listening position which will determine how powerful an amp you need.

keeping in mind when talking amp power we're talking quality watts here. we're not talking the 1000w pmpo that you've seen on the chingwa htib at cash converters. a dead give away usually is have a look at the maximum power consumption of the amp in question if the power claims of the number of channels driven doesnt total up to less than the maximum power consumption - you know someones telling some fibs ! typically you'll find quality amps have power consumption and power suppies often 1.5x the power claims to allow for inefficiency of the amp plus to allow some dynamic range

as an illustration, I've done a run through with my speakers and amp as an example.

speaker efficiency : 90db

amp power : 255w or 24dbw

listening distance : 3.3m

Starting with speaker sensitivity 90db

subtracting 10db for my listening distance (sound level reduces at 6db for each doubling of distance over 1m)

adding 3db because there are 2 speakers

gives 90-10+3= 83db

thats my speakers sensitivity at listening position, given my amps power which is 255w or 24dbw and will determine the maximum peak output I can acheive at listening position. which in my system would be..

83 + 24 = 107db

which is about right and what I've experienced as peaks with the odd excursions I've taken them out to !

anyways hope helps anyone else wondering or just or just curious about these things.

ps there is also this simple little calculator which also gives similar result plus also to specifiy if speakers are near walls or near corners.

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

[2Brix]

Very helpful and clear example. Could you also comment about how people might assess whether their speakers are capable of handling the max SPL they calculate for their own values of speaker efficiency/amp power/listening distance. My speakers have a stated max SPL but many speakers just have a stated RMS power rating or suggested amplifier power range.

[betty boop]

Very helpful and clear example. Could you also comment about how people might assess whether their speakers are capable of handling the max SPL they calculate for their own values of speaker efficiency/amp power/listening distance. My speakers have a stated max SPL but many speakers just have a stated RMS power rating or suggested amplifier power range.

I couldnt tell you that perth -ed, it would be something you'd have to talk to the the speaker manufactuer about. most will give you a maximum handling in watts and a suggested amplifier range. ofcourse keeping in mind its the unclipped power capability of the amplifier we are talking about, and thats where many amps come unstuck clippign to produce the power claimed which is a sure fire way of destroying your speakers if sending the amp into clipping.

[Cameron]

Of course, at this level of playback, cone breakup will colour the midrange and treble if they are run wideband.

[betty boop]

Of course, at this level of playback, cone breakup will colour the midrange and treble if they are run wideband.

depends on the quality of the speaker I suppose, some will do a better job than others. some will have no hope, probably very much depends on the design I suspect.

[Azz123]

Great Article Al.....

What about 4 ohm speakers? If you've got 4 ohm speakers, do you use the (higher) applicable 4 ohm output of your amp?

My Dyn's are 4ohm and only 87dB. The Elektra is 185wpc for 8 ohm - does that equate to 370w for a 4 ohm load?

[joz]

Great Article Al.....

What about 4 ohm speakers? If you've got 4 ohm speakers, do you use the (higher) applicable 4 ohm output of your amp?

My Dyn's are 4ohm and only 87dB. The Elektra is 185wpc for 8 ohm - does that equate to 370w for a 4 ohm load?

In this case the amp would double into a 4 ohm load.tho if your speakers could hack it I think your ears would give up first.

370 watts continuous is a lot for any speaker or ears in a domestic situation.

But its nice if your system can work well under these conditions,not that you'd be running full steam continuously.

Nice to have the headroom.

But this power is usually the domain of pro audio,few domestic speakers are capable here.

Then of course there are the advocates of 99db+ sensitivity speakers driven by flea power 5 watt valve amps which go just as loud domestically.At 2 watts power they are bloody loud with plenty in reserve.

Horses for courses

.

Edited December 27, 2007 by the joz

[betty boop]

In this case the amp would double into a 4 ohm load.tho if your speakers could hack it I think your ears would give up first.

370 watts continuous is a lot for any speaker or ears in a domestic situation.

But its nice if your system can work well under these conditions,not that you'd be running full steam continuously.

Nice to have the headroom.

But this power is usually the domain of pro audio,few domestic speakers are capable here.

Then of course there are the advocates of 99db+ sensitivity speakers driven by flea power 5 watt valve amps which go just as loud domestically.At 2 watts power they are bloody loud with plenty in reserve.

Horses for courses

.

quit right there joz thats a lot of power to be feeding a speaker, and az you'd need to check how much power your speaker can handle, also probably check with arthur re what the T7 does with a 4 ohm load, not all amps double when going into 4 ohm. also keeping in mind that with most speakers the impedance qouted is a 'nominal' and woudl wary in reality based on freq.

working on a 4 ohm load, 87db senstivity and say the T7 can deliver 370w youd get

87-10+3=80db

assuming amp is 25-26dbw

youd get a peak possible of 105-106db.

that is a peak spl and things would be working at their max to acheive that sort of levels. this isnt about max spls but I guess more about choosing an amp /system based on the kind of levels your after, plus knowing the kind of dynamic range - headroom given a speaker amp combination.

joz how much was the sensitivity of those lowthers we heard that were running off a 2w or so amp if I remember, would be in the 99db + I'm thinking and yeah quite able to get to some spls in an intimate setting. that varkley amp too was interesting too as still had a massive power supply ! yes defintely the other approach with things.

[Azz123]

working on a 4 ohm load, 87db senstivity and say the T7 can deliver 370w youd get

87-10+3=80db

assuming amp is 25-26dbw

youd get a peak possible of 105-106db.

that is a peak spl and things would be working at their max to acheive that sort of levels. this isnt about max spls but I guess more about choosing an amp /system based on the kind of levels your after, plus knowing the kind of dynamic range - headroom given a speaker amp combination.

From the specs of the Focus 220

Sensitivity (2.83 V/1 m) 87 dB

IEC Long Term Power Handling >250 W

Impedance (nominal) 4 Ohms

I don't know if IEC is somewhat like PMPO....

One must remember this is talking about running at full noise and is mathematical..

Even though dB's have been removed for distance, room gain is added in a real world scenario?

For me runnig at full noise is not something that happens EVER.

If I can do -10 on my AVR for one song I've got neighbours out bopping on their front veranda's.

As the joz said - "if your speakers could hack it I think your ears would give up first"

[betty boop]

From the specs of the Focus 220

Sensitivity (2.83 V/1 m) 87 dB

IEC Long Term Power Handling >250 W

Impedance (nominal) 4 Ohms

I don't know if IEC is somewhat like PMPO....

One must remember this is talking about running at full noise and is mathematical..

Even though dB's have been removed for distance, room gain is added in a real world scenario?

For me runnig at full noise is not something that happens EVER.

If I can do -10 on my AVR for one song I've got neighbours out bopping on their front veranda's.

As the joz said - "if your speakers could hack it I think your ears would give up first"

hi az, yes it is mathematical and theoretical to give some idea as to the limits and whats required to acheive realism if thats whats intended.

IEC is just anoher way of measuring where its done at 1khz if I'm right, I wouldnt discount it, I've seen measurements where its figures corelate pretty well especially if the amp ha a linear response which many typically do.

re the point of -10db vol level keep in mind that is just related to the reference level you might have calibrated your levels at, in that 0db might give a listening level of 85db or 75db. however even at -10db theres nothign stoppign you gettign swings in dynamics taking you over the 100db mark. In the linked example you could be easily listening to a voilin concerto peaking at 60 odd db at realistic levels to then have brass percussion come in at 110db or so. also pretty common if watching movies an the like where also keep in mind your sub will be responsible for a lot of the spl given the amount of air it can move and large powerful amp driving it.

[yamapro]

From the specs of the Focus 220

Sensitivity (2.83 V/1 m) 87 dB

IEC Long Term Power Handling >250 W

Impedance (nominal) 4 Ohms

I don't know if IEC is somewhat like PMPO....

One must remember this is talking about running at full noise and is mathematical..

Even though dB's have been removed for distance, room gain is added in a real world scenario?

For me runnig at full noise is not something that happens EVER.

If I can do -10 on my AVR for one song I've got neighbours out bopping on their front veranda's.

As the joz said - "if your speakers could hack it I think your ears would give up first"

G'day Azz,

Just wondering if you calibrated your avr to 75db? If so -10 will still be 10db below the reference level that your song was mastered at! So to get your neighbours bopping away that must be one loud track!

As Al has stated IEC isn't a bad guide and in terms of the Dyns, i think it is stating that they will happily handle 250w continuously over a long period of time, (admittedly that is generally measured over a pretty narrow Frequency bandwith) - which i think means that they would be comfortable with dynamic power of two or so times that, so they are very capable of achieving huge dynamic swings with decent amplification!

All of which you would expect from a speaker as gorgeous and capable as the 220 (nice gear by the way )

[Trofius]

So do these type of calculations apply to subs aswell? If so, no wonder i havent turned the beast to 11 yet..

2 speakers in a box each rated to 350w @8ohms wired in series, and have 91.2db as a sensitivity, amp is 525w into 8 ohms (1000w @ 4ohms) 2.4m from sweet spot.

so is this correct 91.2 - 9 + 3 = 85.2 speaker sensitivity

so max spl would be about 85.2 + 27 = 112.2db, thats prety scary in a room 4 x 5m

I dont even want to think about what Joz' beasts are capable off (dont they have a 98db sensitivty, or is it more)

[yamapro]

Hi Mick

Your calcs are pretty close but there are a few variations...

Firstly, is your measured sensitivity accurate for the drivers in the box they are in? You may find them to be more or less sensitive depending on the box properties.

Also, especially with subs you may well get quite a bit of room gain (measuring and Eq-ing will tell you this), it can be quite considerable if your subs are mounted near corners or in close proximity to for example the rear wall...

Of course whatever your SPL at 1w is then you have a dynamic range of +27db (or +30 if you are indeed delivering 1000+watts) which is pretty staggering and just one of the reasons DIY subs are a great project

[betty boop]

So do these type of calculations apply to subs aswell? If so, no wonder i havent turned the beast to 11 yet..

2 speakers in a box each rated to 350w @8ohms wired in series, and have 91.2db as a sensitivity, amp is 525w into 8 ohms (1000w @ 4ohms) 2.4m from sweet spot.

so is this correct 91.2 - 9 + 3 = 85.2 speaker sensitivity

so max spl would be about 85.2 + 27 = 112.2db, thats prety scary in a room 4 x 5m

I dont even want to think about what Joz' beasts are capable off (dont they have a 98db sensitivty, or is it more)

hi trofi, big spls from subs defintely easy with the big drivers moving a lot of air and with big amps behind them. I cant tell you about efficiency in the box, I do know box and box type and porting whether plugged or not can also impact on easy of driving and efficiency. also with subs it might be easier to get high spls at one freq point but the tough part is to get a smooth response flat across the freq range which is both room and position related..an yeah as per yam certainly will get some room gain which will impact as well but also nulls to content with.

joz's jbls are 95db efficiency which would work from him not needing a big huge amp to get huge spls out of them.

[Trofius]

yep well i did make the box slighlty bigger than needed, and no impossing amp help this again..

the amp is only pushing at most 525w into 8 ohms as tehy are wired in series, so the amp sees 8 ohms rather than 2! (they must be 4 ohm speakers i forget)

As for room gain i have opted aginst it, the sub is completely open in front and behind, i notice different areas are more bassy but the seating position sounds good, the front door is actually 9db louder, open or closed! and the dunny is about 4db louder than the lounge room, lol but it is very boomy and woofy more a wave of pressure rather than a defined note. My bro and law didnt even relise how much difference it made he could hear the sub, (his mates have them set to kill so everything distorted) until i turned off teh power amp to all the main speakers so it was just the sub, and he heard what it is actually putting out, smooth deep velvety bliss

The sub does work well, and is quite flexible i feel, i have the gain on 5, which works nice for music, a definete extension of piano, and double bass type sounds, and nice and explosive for movies, the extra head room is obvious, and i am glad i got the Dayton amp.

when i did some measurements the sub at seating position easily got to 100db, the pictures etc were vibrating etc was very cool , lol the spl meter wont go much higher, and i started to get some freaky feedback which ment that 3/4 on the power nob was it. But as mentioned the frequency of a sub is much more listenable to at higher volume i find high pitch noises can hurt at high volumes.

ie i had a grin when testing the sub @100db, But even at 80db with all speakers playing in my small room it IS too loud, and i start to get reflections that make it less than ideal.

then i soppose it takes a lot more power to drive a bass note than a high end note hence the amps behind subs..

In relation to Joz' subs i must have been confused with another JBL 18 i have seen that was 98 or 102db sensitive, pro jobbies.

damm i think i just dribbled a whole lot of stuff, lol i think a bit is on topic...sorry just did an 8am to 11pm day the brain/body is dead... but still in top gear..

Edited December 29, 2007 by trofius

[joz]

quit right there joz thats a lot of power to be feeding a speaker, and az you'd need to check how much power your speaker can handle, also probably check with arthur re what the T7 does with a 4 ohm load, not all amps double when going into 4 ohm. also keeping in mind that with most speakers the impedance qouted is a 'nominal' and woudl wary in reality based on freq.

working on a 4 ohm load, 87db senstivity and say the T7 can deliver 370w youd get

87-10+3=80db

assuming amp is 25-26dbw

youd get a peak possible of 105-106db.

that is a peak spl and things would be working at their max to acheive that sort of levels. this isnt about max spls but I guess more about choosing an amp /system based on the kind of levels your after, plus knowing the kind of dynamic range - headroom given a speaker amp combination.

joz how much was the sensitivity of those lowthers we heard that were running off a 2w or so amp if I remember, would be in the 99db + I'm thinking and yeah quite able to get to some spls in an intimate setting. that varkley amp too was interesting too as still had a massive power supply ! yes defintely the other approach with things.

Hi Al I think your correct here,if I remember correctly (probably not) Mohans Lowthers were about? 100db effecient.

His huge 5 watts class A amps? was putting out approx .5 -.75 of a watt to acheive about 75-80 db in that listening room at the seating position.

With the amp only using 10% of power and easily reaching 80db,it could easily double or triple power output for those extreme dynamics.

Where as if for the most of us if your already pumping out 50-60 watts continous most amps would have little or even no chance of tripling output without maxing out into clipping.

[joz]

In relation to Joz' subs i must have been confused with another JBL 18 i have seen that was 98 or 102db sensitive, pro jobbies.

Hi tofius,hows the fish?

Anyhow your right there is another another 18" driver, but as far as I know its a bass driver not a sub driver.It only goes to about 30-40 hz.

Edited December 29, 2007 by the joz

[betty boop]

there is this simple little calculator here too guys,

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

jsut a matter of pluggin in the numbers and it works out for you. also has selections if speakers near walls or corners.

for my calcs above gives same result of 107db if not near walls, for near walls adds 3db to take to 110db and if near corners adds another 3 db to take to 113db as a peak spl.

[norpus]

The THX Home Cinema certification calls for a flat power response from the subwoofer down to 20Hz with an SPL of at least 105dB

http://www.subwoofer-builder.com/SPL-comparison.htm

Note, doing 20Hz takes twice as much power (and more excursion) as doing the 40Hz (where most smaller box subs are happy at.)

I recall JA measuring my front IB at nearly 130dB at the throat (no room gain) so I think I have the THX spec covered

[betty boop]

The THX Home Cinema certification calls for a flat power response from the subwoofer down to 20Hz with an SPL of at least 105dB

http://www.subwoofer-builder.com/SPL-comparison.htm

Note, doing 20Hz takes twice as much power (and more excursion) as doing the 40Hz (where most smaller box subs are happy at.)

I recall JA measuring my front IB at nearly 130dB at the throat (no room gain) so I think I have the THX spec covered

hehe I recall that one too, poor JA he probably needed a few reds following that one to get the kidneys back in order ! hehe

this clarification from the link above re thx certification probably helpfull...

The THX Home Cinema certification calls for a flat power response from the subwoofer down to 20Hz with an SPL of at least 105dB

You might also note that none of these speakers do 105dB@ 20Hz, so I guess THX certification is pretty hard to estimate from the anechoic response. However, the actual specification is in-room at the seating position. According to Adire Audio, room gain can add around 6dB@10hz, 4dB@20hz and 2dB@40hz.

I had a look at the THX site to see if any of these make it. The Velodyne DD15 and DD18, and Triad Platinum Powersub are THX Certified, as is B&W's 800-ASW, but the 400-ASW was not listed

my dd15 is indeed thx ultra2 certified and yeah would make sense to measure inroom and at listening position, and room gain certainly would help to achieve the flat to 20hz @105db requirement.

[yamapro]

More useful contribution there Max,

why don't you do us all a favour and disappear once and for all?

This will be the last correspondence i enter into.

[geoff888]

Most manufacturers claims of sensitivity are over-rated (often by 2-3dB) when compare to actual measurements which would make the calc. inaccurate.

[betty boop]

Most manufacturers claims of sensitivity are over-rated (often by 2-3dB) when compare to actual measurements which would make the calc. inaccurate.

yes need to keep in mind in the calcs that the manuafacturers could be overating sensitivity. that is stated in the original reference material qouted I believe. that does not make the calculation method innacurate it jsut means your assumptions are flawed and a overating of 2-3db in sensitivity will result in 2-3db less in the final result same goes with power claims from amp manufacturers as suggested in the original post as well

in the end this is just a guide, a quick handy means of getting an idea theoretically what your system is capable off. and given a speaker the kind of amp power needed to achieve the kind of spls required to recreate realistic levels if that is what your chasing

[hb20c]

very helpful post. The calculator actually helped me improve my hi-fi setup's sound. Thanks!

[simo_crf]

Very helpful thanks guys