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betty boop

How Much Power Do I Need ?

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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 by the joz

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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.

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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 :)

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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.

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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.

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

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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 :)

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All,

Just remember;

3 dB is a just noticeable increase in volume

10 dB is generally to be twice as loud.

Alanh

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Just a bit of a correction

0.25bd - 0.5dB is regarded as just noticable (theshold of being able to pass a blind test)

3dB is easily noticable

10dB is equivalent to twice as loud

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Drizt,

3 dB is for the general public who are not trained to detect differences. It also depends on whether it is measured on noise excluding headphones or with background sound, it also depends also on the nature of the sound under test ie tone music or speech.

All,

For those who don't know 10 dB is 10 times the power

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A 3db change in level represents the smallest significant change that can be heard by a person with normal hearing..

It is not the least audible change in sound level one might notice .

C.M

Edited by Tweet

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A good thread and would be very helpful to a lot of folks I'm sure.

But in regards to how much power is needed, I'm wondering how much do people allow for dynamic headroom/transient peaks on average. For live music some things I've read they say transient peaks can be as much as 25dB while recorded/compressed can still be upto as much as 10dB. Depending listening distance and speaker sensitivity this can start getting crazy in terms of power needs from a amp if you like reference levels or higher. Classical can have some pretty decent transients.

EG: myself I often tend to be a bit of a loud listener lol, though it depends on what I'm playing and my mood. While my room isn't large the listening distance is 5m-6m, my speakers are fairly sensitive but I tend to learn towards quite powerful amps because of my listening habbits and I don't like to overdrive a amp for obvious reasons. I tend to err on as much power as possible with the idea to work the amp as little as possible and using common sense to not just crank the volume to insane levels. Too little or too much power can be a issue either way.

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The dynamic range of an orchestra is very wide indeed, in the range of 70db to 100 db above ambient noise levels so you are never going to have sufficient power reserves to compete with that, let alone the amplifier and the loudspeakers to deliver it.

Most modern loudspeakers have an efficiency of about .1 to .2% at best unless one goes to horn loading, but then two of such monsters in your room may make it a little difficult for other amusements.

Most 'quality' amplifiers usually only boast a 2 - 3 db headroom over their rated power levels and at possibly elevated distortion levels too, so don't expect anything substantial in power reserves.

Remember your ears do not have a linear frequency response, and neither linear in dynamic range.

So, in the end one has to ask one's self this question ..." What is HiFi anyway ?"

C.M

Edited by Tweet

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