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speaker 101 basics

 
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Old 11 Sep 2011, 10:15 pm
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Default speaker 101 basics

Speakers 101
first lil about me,
i have been doing car audio for 25 years,
i have worked at a car audio shop, ihave built boxes,
that have won sound comps,
i have workd at a comercial sound reseller
and have made and designed sound systems for comercial use,
i can rebuild woffers, build boxes from scratch,
and my best aspect,
doing the math,
before the internet you had to use a calulator, lol,

this is a lil, boring, but its very basic,


Spl Ė sound pressure level, big woofers and lots of woofers make large spl,
Think the bass you feel that is spl
The other end is sound quality, and not usually rated in spl, more in decibels, or db,
And rated in competions in how clean it sounds and how accurately its is reproduced,

Some go all bass some go all sound quality,
I thought a system that can be clean and give a good boom, was usually the best,
So thatís where ill be heading,

So first letís address the ways to cheat a system and get it to produce more than our accepted laws allow,
Laws,
For a system to be heard as louder you need about 3 dbs in sound
Every time you double the power you get that perceived increase in sound hence 3 db,
More later on that,
How to cheat those laws,

In general,
Every time you double the woofer count you gain a 3db in perceived sound,
Porting when done right can yield a 3 db boost in a desired area, say 30 Hz, (wow that car really hits hard) done wrong can make it lose db
Band pass, can yield a 6db boost in the 30-45 Hz area, but sounds ehhh
(Wow that car hits hard what song is that?)

Free air
Ported
Sealed
Air suspension,
Letís hit this really quick, in simple form,

Take a trash can lid in your mind,
Grab the handle and shake it back and forth, to and fro
Youíll get hardly any resistance and lots of movement up down and sideways,
I.e. sloppy

Now take that lid and add a rubber surround and toss it in a big cylinder,
And shake back and forth, slop will be minimized, but not much resistance, and not a lot of power to move it
(Free air) not very clean sounding still sloppy

Put a bottom on that cylinder now itís sealed, on one side,
Shake it back and forth
Much harder to shake (takes more power)
The air provides a vacuum when extending,
And when it is returning it tends to get to 0 positions much faster due to the air press inside giving the woofer added resistance,
Now lots of people think adding fills to this kind of box,
Makes the woofer magically think itís in a bigger enclosure,
, not really,
What fill does is not for the air but for the sound waves in side the box,
They hit the rear of the box then bounce forward and hit the cone,
Making the woofer reverberate when it should not be,
Hence sounds unclean,
The fill breaks that sound wave and prevents it from hitting the cone again,
Hence sounds much cleaner at a lower power setting,
Sealed is my preferred set up,
I like clean tight bass,
But this requires the most power per decibel,


Now stick a port in the cylinder
and lets assume itís to the frequency we want
say 30 Hz,
The port doesnít actually produce much sound,
itís for an air release, and intake
And should have a knerfed edge to reduce whistle
Itís just to make the woofer more efficient at the 30 Hz,
Hence a bass boost at that level, usually 3 db is the goal
Think of it as a 2 stroke power band, itís where every thing is working just right and flowing really well,
So the woofers get efficient at that 30 Hz level,

Then you can step it up to a band pass box, usally 4th order
the boxes are set up to make that 30-40 Hz even more efficient and work very well but sound very unnatural, thatís great for that bass not sound quality, usually a 6 db increase in that rage

Air suspension, is its whole own thread and im not up to date on it,
Basically volume isnít as crucial, and you just power the crap out of it,

POWER

Some people think rms is the end all about what a speaker can do, thatís just not enough info to make any determining facts as to what the speaker will do,

Think of it this way, 1 vehicle has 1000 hp, and one has 100 hp
Thatís not a guarantee that the 1000 hp is a faster ,
Say a 100hp bike, vs. a 1000hp, Mack truck,
there are lots of variables,
The manufactures hit on the rms because itís easy to make it sound impressive, and sell
1000 watts looks better than 280,
That doesnít mean ones louder than the other,
until you know the rest of the #s
So along those lines
,
100 watts to an 8 inch woofer usually does more
Than 100 watts to a 15 inch woofer,
as it has 3 times the woofer to move,
So that rating is called, sensitivity,
Sensitivity has a direct relation on how many decibels you can achieve out of a given speaker,

Rms is only how much power a speaker can take

There are some things in the audio world the learned take for granted as law,
Though there are exceptions,
Generally when a woofer size increases,
The sensitivity goes down,
When you add size to the voice coil,
You add power handling capability...
And lower sensitivity

Generally an 8 inch woofer usually has from 85-95 sensitivity

Say you found an 8 inch with 100 db sensitivity,
And a 200 watt rms would be about 122 decibels loudness

An Average 15 has 80-90 sensitivity and say 1000 watts rms

Take the same graph,
And deduct the difference from 100 to what ever your sensitivity,

80 sensitivity would give you 109 db at 1000 watts
90 sensitivity would give you 119 db at 1000 watts
NOW THATíS DB, not spl.
Spl is much harder to figure out, and thatís basically the bass you really feel

GRAPH
1watt produces 100 db
2 Ė 103
4 Ė 106
8 Ė 109
16 Ė 112
32 Ė 115
64 Ė 118
120- 121
240- 124
480- 127
1000- 129
2000-132
4000-135
8000-138

Ok, letís dispel
Some myths bout amps,

heres the law

Converting Watts to Amps

The conversion of Watts to Amps at fixed voltage is governed by the equation
Amps = Watts/Volts

For example 12 watts/12 volts = 1 amp

And it works in reverse

Converting Volts to Watts

The conversion of Volts to Watts at fixed amperage is governed by the equation
Watts = Amps x Volts

For example 1.5 amps * 12 volts = 18 watts


So what does that mean to me joe, ???
you ask,


Say on a great day, your pt alt puts out 120 amps,
and your getting the full 14.6 volts to the amp you want to use,

Your max amp you can use and not clip is 1752 watts,
How do you cheat this fact
Capacitors, they store the power in the amp and dump it when needed,

Stiffing caps near the amps can release the power ondemand
and put a band-aid on a poor power supply

Now I have an earthquake d2
thatís supposed to be 2000 watts, at 2 ohm,
I use it for 2 @15 inch earthquake subs 1000 watts each,
And it pulls about 50 amps,
Thatís a lot,
It blows 40 amp fuses, and once in a great while will pop a 50, safe with a 60,
So letís do the math
14.6 volts x 60 amps,
is about 860 watts, out of a 2000 watt amp???
so thats 430 max watts to the woffs
the woofers are 97 sensitivity,
so lets do the math
240 watts should be 121
480 watts should be 124
add 3db for 2 woffs, combo
i should be around 124-127 db,
i spike the top which is 125 on the db metter
then you can use an a weight, which is an avarage db over time,
it holds about 122-125, exactly what it should be,,
hope this help understand woffers a bit,

joseph
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Old 11 Sep 2011, 11:24 pm
xwing777's Avatar
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Default Re: speaker 101 basics

Good write up.
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