# tri-amping

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#### Kilowatt

How do I calculate the SPL that each section of a tri-amped system must produce by itself to achieve optimal power distribution among the 3 sections?

#### AudioFreak

Is this for Hifi or Pro Audio / Sound Reinforcement?

#### Kilowatt

It's for my big system that I want to build, you know the one. It's for hard rock and heavy metal music, kind of a monster hi-fi thing.

The low crossover frequency will be 300Hz, that part of the system will produce up to almost 144dB. As for the other two parts, that's what I want to figure out, so I know what to do for amps and speakers for mid/high. I plan the upper crossover frequency to be 3000Hz.

#### subwo1

Kilowatt, I prefer about 20dB greater capability for bass than for the range above. So if you require 2000 watts, say, for the lows, that would mean 20 watts for the rest. But it doesn't hurt to have reserve capacity either way to avoid clipping and provide a little flexibility. The speaker system plays a role in the determination also.

#### Kilowatt

Ok, I guess my question is more like this:
The total dB level shall be 147dB. According to a chart that I saw, with a xover frequency of 300Hz, the SPL should be divided evenly between mid/trebble and bass. So the subwoofers would produce 144dB, or half of 147dB right? The upper xover frequency is 3000Hz, so the SPL should be divided such that the mids produce 35% and the tweeters produce 15%. The subs, of course, produce 50%. 50+35+15=100%. What is 35% and 15% of 147dB? How do I figure it out? These figures are all subject to change, so I need to be able to calculate this stuff.

thanks

#### AudioFreak

Half of 147dB SPL is 141dB .... twice that of 144dB SPL is 150dB SPL.... also these should be peak values.... allow @ least 20dB headroom which would mean if the bass was capable of 144dB peak then it should be run @ about no more than 122dB SPL continuous even less in practice this would give about 120-130dB SPL continuous for the system.... and half the total power of the system should be for below 300Hz .....

#### CHRIS8

And this should make losing 90% of your hearing darn near effortless.

-Chris

only 90% ?!?!?

#### Geoff

Hearing Damage

Quote:

"Temporary reduction of hearing sensitivity, as indicated by the increase of hearing threshold level, occurs after exposure to loud sounds. This can become permanent if the exposure is prolonged. The louder the sound, the shorter the exposure time to produce permanent impairment. Damage is greater if the sound contains impulsive components caused by percussive elements in the source.

Hearing impairment is of a band centred around 4kHz (bark 18 in the cochlea), irrespective of the nature of the sound causing the damage. As damage increases with further exposure, the band broadens, reaching in some cases down to 1kHz.

Exposure levels and times are regulated in industry. Maximum permissible levels are shown in the following chart:

90dBA 8 hours
93dBA 4 hours
96dBA 2 hours
99dBA 1 hour
102dBA 30 mins
105dBA 15mins
108dBA 7.5 mins
111dBA 3.75 mins

It should be noted that with disco music and headphone listening, levels well in excess of 100dBA are possible. The danger is therefore obvious"

#### sandro

I was amused reading these theoretical calculations for 140-150 db on bass!
C'mon guys, are we engineering a kind of acoustic weapon to sold to the Pentagon?!

I guess Geoff is completely right in his post, and that, given a defined budget, is much better to invest in quality rather than quantity.

Let's remember that if we talk about music reproduction (if our goal is to realistically reproduce the sound of an F14 taking off from a carrier at 1 mt, of couse the story is different...) it is insane to aim at an SPL higher than, say, 115 db/1mt, and only if we have available a room as big as a castle salon and a listening point of more than 4-5 mt.
Otherwise, apart from ear damage, all the energy that we put in the room will make everything resonate out of control. We'll have a big noise but a very poor music or event reproduction.

Also, talking about acoustic, classical and normal rock music, the lion share of energy distribution is taken by the midrange section, especially the human voice is the 'instrument' who has the higher need of continuous power. Below 150 Hz we don't have that much, and above 4000 the power percentage is negligible (and that is a good thing, this way we can use extremely light tweeter coils)
Of course heavy metal and others 'non natural' (*) sounds (like home theatre special effects) may have an energy distribution more on the bass side.
bye
sandro

(*) I don't mean by that to say that HeavyMetal, rave etc. are not good, just that this music has a different energy balance.

#### AudioFreak

I believe kilowatt is trying to build this system for outdoors use... having said that, i would probably quite happily listen to this system @ a rock concert from about 50-100 meters away... i reckon @ that distance the output should have dropped to a sane level quite frankly i cant see the point in this project and i believe it will most likely deafen kilowatt the 1st time he cranks it up but it is his hearing .... i guess all we can do is try and advise against it....

#### haldor

Come on now. Poor kilowatt. Every time he starts a thread we all jump on him and tell him why what he wants to do is either impossible, unsafe, unwise, immoral or unpatriotic. Live a little, he's young, whatever he melts, implodes, fries or breaks off of his anatomy will probably grow back.

Lets see, direct rectification of power mains, 147dB levels. What's next, atomic power cells, carcinagenic speaker coatings? I can see it now, Ralph Nader is going to do an expose on kilowatt "Unsafe at any volume!". They will show training video's in high school electronics classes about kilowatt like the old drivers ed movies that tried to scare us into being good drivers "Blood on the Highway" move over, here comes "Audio Carnage"!

Kilowatt, what everone is saying about high sound levels is true (just like all the other warnings and good advice you have gotten in the past). There is an SPL competition for car audio systems that hits insane volume levels (160 dB+), but nobody is anywhere near the cars during tests.

The fact is that systems that do what you want already exist, they are called PA's. If you really just want a concert PA of your very own thats cool, but you will probably save money and end up with something that really works if you just save up your nickels and buy a used rig. That way when you get tired of it (or go deaf) you can either sell it to some audio production company or else go into business providing sound reinforcement (I think this option is easier if you are deaf).

Phil

#### sandro

Allright, let's go with humour, (Kilowatt, it's just amusement we're not attacking you)!

It remembers me a great book from Douglas Adams ('The restaurant at the end of Universe' I guess), where the concert of the galactic-trendy rock group was planned as follows:
- One desert planet was setup with soundwalls and amplification system
- The sound engineers worked in concrete bunkers on the other side of the planet
- The listening area was the planet nearby
- The group played from a starship orbiting around, while the lead guitar ( being in suspended death status for fiscal purposes) was playing trough a medium.

Anyway, such a sound system is intriguing, if we find somebody willing to finance it I would be happy to participate in the project group!

sandro

#### haldor

sandro said:
- The group played from a starship orbiting around, while the lead guitar ( being in suspended death status for fiscal purposes) was playing trough a medium.
sandro

I love that sandro. I had forgotten about that scene from the book. I especially love the dead guitarist. I guess this is like the ultimate DI (or would that be MI for Medium Input).

Kilowatt, I hope you haven't taken offense at my attempt at humor. I enjoy your ideas, there are some real gems that pop out of them. For example, I had never considered direct rectification of AC mains being even a remote possibility until you mentioned it. Turns out that it is possible (at least in the USA, although still not very wise or marketable).

Thanks Kilowatt and like William Wallace in Braveheart said to his friends before the first big battle, "just be yourselves".

Phil

#### Kilowatt

Hey, I know direct line rectification is perhaps dangerous, I have been told about the risks, but It's my only practical option here. I also Know that 147dB is very dangerous, but I don't plan on being near the speakers at such levels. Ear protection is also an option, duh!

Anyway, 144dB is half or 147dB isn't it? Not 141. Each time you double output power, it goes up 3dB right? (I am willing to be corrected on this, but only if you can provide links to several articles saying otherwise.) And these are, of course peak levels, not average, unless you drove the amp with a sine wave, which would be a nasty thing to do other than into a dummy load for testing. So, can I get some help on this instead of being "attached" or "amused over"? How do I divide decibel values?

#### haldor

Sorry again if I ticked you off Kilowatt,

Here is an excellent writeup on how to do whatever kind of dB calculations you need.

http://www.prosoundweb.com/studyhall/lastudyhall/dB_calculations.shtml

AudioFreak is right about the 6 dB change being half the SPL. You are correct that doubling an amplifiers power results in a 3 dB change in SPL, but that isn't double the SPL, 6 dB is.

It's confusing, but be careful not to mix up SPL and Watts they are both measured in dB, but there are lots of different kinds of dB's running around out there and they aren't all the same.

Phil

#### AudioFreak

kilowatt.... when you have 2 identical signals you gain 6dB .... double power add 3dB, double voltage add 6dB, double acoustic power add 6 dB

#### Phage

yes you are correct kilowatt, sound pressure doubles every 3db. Sound perception doubles every 10db. The scale is logorithmic so to divide the level by 2 just subtract 3. I just did some quick calculations and found that:

power difference factor = 2^((dB1 - dB2)/3)

the "power difference factor" is how many times more energy dB1 is than dB2
dB1 is the higher dB number
dB2 is the lower dB number

perception difference factor = 2^((dB1 - dB2)/10)
the "perception difference factor" is just how many times louder it sounds

#### AudioFreak

Phage said:
yes you are correct kilowatt, sound pressure doubles every 3db. Sound perception doubles every 10db. The scale is logorithmic so to divide the level by 2 just subtract 3. I just did some quick calculations and found that:

power difference factor = 2^((dB1 - dB2)/3)

the "power difference factor" is how many times more energy dB1 is than dB2
dB1 is the higher dB number
dB2 is the lower dB number

perception difference factor = 2^((dB1 - dB2)/10)
the "perception difference factor" is just how many times louder it sounds

Phage... this could be a little misleading for kilowatt...

if you double the amplifier power than you gain 3dB as you stated and if you increase the amplifier power 10 fold then you gain 10dB and the sound appears twice as loud but if you double the acoustic power ie double the number of speakers, you gain 6dB so if you've got 2 speakers producing the same material (like @ the crossover point, then you gain 6dB so both speakers must be -6dB @ the crossover point to keep a flat response.... however, if you have 2 speakers producing different signals eg. anywhere other than @ the crossover point, they add together to give an rms increase of 3dB SPL

#### Kilowatt

What a coincidence haldor, I just read that article last night, trying to find answers to my question. It does have some good information, but didn't say anything about what I am trying to figure out, working with fractions or percents of dB levels.

I'm starting to get the hang of it, but it's a bit confusing. I thought that the bottom end of my system (the big one that has caused much controversy on the forum) wouldl put out about 144dB peak. I figured that out using this equasion: (10log W)+speaker sensitivity. I was wrong. I have now learned that every time you double the number of speakers, it goes up 6dB. Each speaker is 96.4dB@1W@1m. There are eight speakers, so this would make 114.4dB@1W@1m right? There is 7200W of power. Plug this into the equasion and I get 153dB (YIKES!). This will be half of the total SPL, so the total SPL must be 156dB right? (AudioFreak: "however, if you have 2 speakers producing different signals eg. anywhere other than @ the crossover point, they add together to give an rms increase of 3dB SPL"). It is a tri-amped system, so I must know how to divide that upper 153dB up among the mids and horns. Let's say the xover frequency is 1500Hz, so about 35% goes to the horns, 15% to the mids, and the other 50% to the big-*** thing. I'm still not quite clear on how to figure out how much SPL the mids and treb speakers must produce. You must ecuse me, I'm fairly new to such dB calculations, so, I would like it if someone would enlighten me on how to do it. Thanks.

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