How much power is needed for each driver in active 3-way setup with sub

Dear all,

I have spent some time in trying to find info on how much amplifier power is needed for “sufficient head room” for each driver in an active three way setup. -Especially the mid/high and the high drivers.

I do believe that I have sufficient power for the sub’s (UREI 6290 2x600 @4ohms) and the low/mids (Crown CTS 8200, 8x200W@4ohms). But how much do I need for the “mid/high” and “high” driver.

The basics is that the need for power goes down with frequency. This of course subject to each driver, cabinets and the room it self. But assuming a perfect room and perfect drivers in their respective frequency window how would you suggest a normal power distribution would look like? What size of power amp would be needed for each driver?

Let’s assume 3-way system with a subwoofer and all drivers have the same “linear” sensitivity of 90db and all are 8ohms. Assume filter slope of say 18db and that all drivers have power capacity in their respective band.

Sub up to 80Hz
Low/Mid between 80-1.000 Hz
Mid/High 1000-10.000 Hz
High from 10.000 Hz and up

Given normal listening how much power would you use for each element? Is there any difference between music and movie’s? I understand that “the more the merrier” but that is beside the point. The relationship is the interesting point and from that it is easy to adjust for actual sensitivity for each driver.

My gut feeling is that there is really little need for power above 1kHz and that one could do with as little as maybe 30 watts. But that is just a guess on my side.

In reality it is a fully active 3-way 5.1 system with;
Two SUB1500 subwoofers in closed cabinets, driven by a UREI 6290
Each of the 5 other speakers use;
Dual 8” low/mid drivers with about 93db sensitivity in parallel operation in closed boxes, driven by a Crown CTS8200
Mid/high is 2451 driver on 2231 horn (JBL DMS-1) with 110db sensitivity, no amp yet
Tweeter is Ti025K with I guess about 92 db sensitivity, no amp yet

Thank you for input
//RoB

It simple all you need to do is determine what you want as the max SPL level at your listening position. Scale the amps accordingly. I use 100 watts per driver and I can hit about 113db peaks clean for my stereo pair. More obviously if I am running in HT mode. That number is based on my woofer sensitivity of 98db from which all other driver levels are based. I can get more from my mids and compression drivers but simply don't need it. That is on the conservative side not allowing for any advantages due to using multiple amps, amp headroom. So what you need is base speaker sensitivity and listening distance plus what ever your max spl number is. Play with the calculator to see what numbers it comes up with. I listen at an average level of about 85db that gives me about 30db of clean headroom which is a good number.

http://www.doctorproaudio.com/doctor...n.htm#calc_spl

You can use as much power as you want but after a certain point it just turns into a watt contest with no real gain. The real advantage is to start with a high system sensitivity. I use all the same amplifiers for all drivers as I had enough SPL based on the woofer sensitivity and they were readily available.

In your case the tweeter is the limiting factor as far as max spl is concerned. I have a 1.5" compression driver up top so I don't have any limiting up there.

Rob:)

Hi Rob,
Thank you for your input.
I agree that this would be the appropriate mathematical approach given evenly distributed energy over the frequency range and that we are assuming average levels. Certain type of noise has this characteristic.

I don’t think music and/or films do have evenly distributed energy over the frequency range. There is much more energy in the lower regions and I guess my question is what power requirements that translates into over the audible spectrum. Assuming normal mixed music and movie’s how much power headroom is really needed to handle the absolute level and the peaks.

My sub’s are JBL SUB1500’s in closed cabinets and I feed them with 2x600W in 4 ohms RMS (UREI 6290). The calculator gives that such setup would give a max SPL of 106db at 4 meters assuming that the SUB1500’s are at 90db sensitivity.

This means that since my 1,5” 2451 drivers on the 2332 horns are about 110 db they would need 7W to get to the same level and my tweeters (only used above10-12Khz) would need about 600W to give 106db assuming the same sensitivity as the SUB. I don’t think my tweeters would live very long…. J

Starting from the sub’s, all the drivers above should need to produce less SPL with rising frequency regardless of sensitivity and still do accurate music reproduction. Hence I would need less power in the high regions compared to the low regions. But I don’t seem to be able to figure out how much less or how it varies over the frequency spectrum.

What is the energy spectrum of music?

Regards
//RoB

http://en.wikipedia.org/wiki/Equal-loudness_contour

Note how the bass frequencies require far more SPL for the same apparent loudness level.
This is why Bass speakers have to be BIG and need a lot of power!:eek:

Quote:

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Starting from the sub’s, all the drivers above should need to produce less SPL with rising frequency regardless of sensitivity and still do accurate music reproduction. Hence I would need less power in the high regions compared to the low regions. But I don’t seem to be able to figure out how much less or how it varies over the frequency spectrum.

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Average power may be lower but peaks may not be.

http://sound.westhost.com/bi-amp.htm

Rob:)

We are hitting 40w (McIntosh meter) on a tweeter with 100db/1w/1m. Flat phase, and flat impedance. Crossover at 850Hz.

Thats LOUD. But man, it pays off to have good headroom. No strain whatsover.

Quote:

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Originally Posted by jcrobso

http://en.wikipedia.org/wiki/Equal-loudness_contour

Note how the bass frequencies require far more SPL for the same apparent loudness level.
This is why Bass speakers have to be BIG and need a lot of power!:eek:

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Sorta kinda... bass drivers need to be big due to the physics of sound. It is absolutely possible to create a woofer that will produce 20Hz and only be 2" in diameter... but it will play very softly.

In any event, a zillion years ago there was a chart someone published that I used for contemporary music that broke up the power requirements for various bands of the spectrum. It was something like 50% of the power is below 250Hz, 25%-35% between 250 Hz and 1KHz and 15%-25% above 1KHz... this will obviously vary based on musical type but it is more or less accurate for most music.


Widget

It seems no sense in having a 500W amp feeding the tweeter or the driver so my point is, was does make sense?

If the reasoning under the link provided above is correct, the ”equal power point” is around 250 Hz.

Wanting extensive bass as with the .1 (subwoofer) channel in films probably moves the point lower.

The below table is from the link above.

XO Frequency in Hz / Power to Bass (%) / Power to Mid+High (%)
250Hz / 40% / 60%
350Hz / 50% / 50%
500Hz / 60% / 40%
1.200Hz / 65% / 35%
3.000Hz / 85% / 15%
5.000Hz / 90% / 10%
12.000Hz / 95% ? / 5% ?

Source of table is here.

Given this table I get to something like this.

My JBL SUB1500 subwoofers should be fed as much as I can afford or they can stand !

For the 5.1 system I can use Rob’s suggestion above and decide how loud I want to play and dimension power amp's after that. If I feed my dual 8” woffer/mids with 125W each (250W power amp / 8”s in parallel). The calculator shows about 109 db SPL max.


Source of calculator is here.

My XO introduces the 1,5” 2451 drivers at 1.000Hz (like in DMS-1) and according to the table above they would need about half of the power above 1.200Hz. Given that the sensitivity is 110db the calculator gives me 12W for 109db for one driver/horn. And as their need is only half of the power above 1.200Hz it comes to 6W.

The tweeter needs less than 10% of the power if cut-off above 5.000Hz in table above and probably much less for me using XO point at 12kHz. The tweeter is 92db sensitivity and the calculator gives me 800W to get to 109db SPL. As it only needs 10% of the power above 5kHz, or less, it comes to 80W or less for the appropriate SPL level. ….Assuming it can handle it….

So from the above conclusions I would get

* Sub’s = as much as possible and not really included in the reasoning… (OT, new 2x900W amp replacing UREI 6290 tonight)

* Dual 8” woofers/mid’s @ 94db and 80-1kHz = 250W for 109db SPL (125W per driver)

* 2451/2332 mid driver @ 110db and 1kHz to 10Khz = 6W for 109db SPL (given that the Bi-Radial link is compensated electronically and does not effect sensitivity as with passive filters)

* Ti025K dome tweeter @ 92db and 12Khz and up = <80w for 109 db SPL. Probably 40W is enough from a simple calculation.


Does this make sense???

//RoB

Quote:

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Originally Posted by Mr. Widget

...
In any event, a zillion years ago there was a chart someone published that I used for contemporary music that broke up the power requirements for various bands of the spectrum. It was something like 50% of the power is below 250Hz, 25%-35% between 250 Hz and 1KHz and 15%-25% above 1KHz... this will obviously vary based on musical type but it is more or less accurate for most music.

Widget

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This falls in line with what I've always used as a rule of thumb. I remember a Cerwin-Vega publication that espoused the line that half the power in music was below 200Hz, half above...

Quote:

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Originally Posted by sebackman

* 2451/2332 mid driver @ 110db and 1kHz to 10Khz = 6W for 109db SPL (given that the Bi-Radial link is compensated electronically and does not effect sensitivity as with passive filters)

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Hi

Even if the conpensation is done before the amp, you still need to take it into account. If you compensate, say, 10dB at 10khz then you have to consider the sensitivity to go from 110dB at 1khz to 100dB at 10khz in your calculation

Hi pos,

That depends if you do bi-radial compensation by amplifying above 2 kHz or if you attenuate below 15 kHz, as with passive bi-radial circuits, to flatten the curve.

I'm amplifying in the filters using the same inputs as JBL states for their big monitor DMS-1, which use the same horn and driver combination as I do. They are acctually doing both, they amplify by high shelving 12db/oct +10db @ 8,28kHz and attenuating Q0,25 -1,5db @ 3,24Khz for the 2450SL on the same horn as I'm using, the 2332. I use 2451 with SL membranes so that should be the same or very close I guess.

I'm using digital filtering and can't really do large amounts of attenuation as the only way of doing that in the digital domain is by dropping "bits" and that means reducing resolution. -Especially on low listening levels. As long as there’s head room in the digital domain amplification is normally fine. In my simple "non sientific" tests the loss of resolution is clearly audible. -And I'm feeding full digital signal to my filters so it cannot be a A/D issue.

But does the above play with numbers make sense?

//RoB

IMHO you are creating a problem for yourself with those low sensitivity tweeters.

The numbers seem correct, they will need a huge amp to keep up, but will they stay alive for long?

Pos is also right about the compensation - it doesn't matter where it is done, you will need the extra power.

Regarding the frequency spectrum and power needs - that is entirely dependent on the music. The fact is that, given driver(s) with 100dB/1m sensitivity, it will take 10W to produce 110dB/1m regardless of frequency.

The complexity of the signal will add to the power needs, as Rod Elliot showed in your link.

I have lots of music, where the voice is the most power demanding off all the instruments. It depends on the mix/music.

Agreed, I made a misstake in the calculation above.

As the driver/horn dropps from 2kHz I need to compensate with more power. Say that the dropp is 10db, then I would need about 10 times the above stated power according the calculator. So I would need about 60W to the driver to compensate for the sensitivity drop.
So;

* Dual 8” woofers/mid’s @ 94db and 80-1kHz = 250W for 109db SPL (125W per driver)

* 2451/2332 mid driver @ 100db and 1kHz to 12Khz = 60W for 109db SPL (it is probably less because as the bi-radial compensation needs more boost in higher frequencies the need for power is reduces as per above, so the real need is probably lower...)

* Ti025K dome tweeter @ 92db and 12Khz and up = <80w for 109 db SPL. Probably 40W is enough from a simple calculation due to the fall off in program information in higher frequencies.


Does this make sense?


//RoB

My guess is that 40W for the tweeter wil cause compression. I think other tweeters might be better suited for you.

Thank you for input. You are probably right.

Unless you want to use the 2405/077 there is not really too many JBL alternatives that runs flat beyond 20kHz. (I cannot fit 2404) I know you cannot really hear up there but I think that the overall "experience" get's more enjoyable if the top end is there. I have no real explanation to why but if I tune the XO’s to 16kHz, which is about as high as we can hear, the sound is different if the tweeter is in or out. It should not matter at that frequency, but it does regardless of filter type or slope (max 48db/oct in my system, no low pass on driver/horn). At least to my ears.

The Ti025 comes from the Ti10K which is rated at 300W (I think) with a cut off at 3Khz. With the above reasoning it should get about 45W RMS in such setup (15%). I will have a cut off at 12kHz or higher so the power is probably lower than my estimated 40W so I think (hope) I'm good.

This entire exercise is really driven by that I want to update my amps and the market seems to offer only very meaty monster amps with >7x150W (+30 Kg) or smaller units with 7-8x40W @ 8ohms or less. To get a 7x150-300W monster to rum my 2451/2332 above 1kHz and the Ti025k above 12kHz does seem like a little overkill…..

I need at least 7 separate amps for mains, rears and center. Sub's and lows amps are already in place (Crown @ 5x250W/Urei @ 2x600W).

I will probably by one of the small amps and do some measurements.

Comments?

Regards
//RoB

For the tweeter you can also use the 2407 on a small 6" square PT waveguide (90° pattern control up to ~15khz in my tests), but that is probably too big for you application if you cannot fit a 2404... It is also much less efficient than the 2402/3/4/5 at these frequencies.
I think the problem with using a dome tweeter as a super tweeter is not that much about efficiency, but more about directivity: they are typically already too large to maintain a large directivity (>=90°) above 10khz, let alone past 20khz, so even if you do reach these frequencies on axis you will not get much of that "air" at your listening position.
Ok there is one solution left: try to find a 045Ti ! (it seems it is not that much efficient either, by the way). It is good to past 30khz, with a narrow throat that warrant for large dispersion capabilities up high.

Regarding the amp, I don't think you should worry too much: if you find a good 7 channel amp then why bother about "too much power" ? You will spend more if you try to find specific power amp for each component, and you will loose a lot of rack space for nothing more (for not having more than needed in fact).
And you can also choose a low power multi way amp, and bridge some channels for the low mids if you need extra power there, for example.
Plus, I think there is one thing you have to consider with these multiway amps: the power supply is (in most cases) common to all channels, so if one channel use less power, others can make more use of the power supply and dynamic capacity, in a way.

I have heard good comments about the Ram-Audio T serie:
http://www.ramaudio.com/t.htm