Uploaded by rumreich on 01.02.2010

Transcript:

This video is about how to design your own subwoofer box.

The first step is to choose the

subwoofer driver that you’d like to use. I’ve chosen

The Infinity

1252W 12-inch sub. It's a

top seller right now.

So once you pick the driver, you want to find a specsheet for that driver.

You’ll find the Thiele/Small parameters and there are three numbers that you’ll need.

The first is called fs

and here it is free air resonance, fs,

for this driver.

It's 24.23 Hz and I’ll write that down.

The second number

that you need is called Qts, total Q. Qts for

this driver 0.48. I’ll write that down also.

The last number

You need

is Vas,

compliance volume. On this specsheet it’s shown in

cubic feet and liters.

I will

write down the cubic feet. I prefer to work in cubic feet but

the software will handle either one, you just need to keep track of

which you've chosen, so 3.48 cubic feet.

The next step in doing the design is to use some

speaker design software and

I like to use the Subwoofer Design Toolbox for this.

So the first thing we need to do is enter those three numbers into the software. So fs

was

24.23

Qts

0.48

Vas in cubic feet,

(we could have chosen liters,

we chose cubic feet)

is 3.48 cubic feet

Now the first thing we're going to do is see

how this

driver acts in a sealed box,

and the software lets you choose sealed, ported and other types of boxes too.

We’re going to start with sealed

and I’m just going to choose a

half cubic foot,

0.5 cubic foot box and see what happens.

So update the plot.

Now if you're not used to looking at these frequency response plots

they show you the bass response.

Think of it as the loudness of the bass

versus frequency, so here at the higher frequencies we’re

near zero dB, but as you start to get lower and lower,

there's a point where it just starts to fall off

and so

for this speaker

we’re

-3 dB

at about

49.6 Hz. Up here it shows

it's called data tracking you can see

where this cursor is so

it looks like about 49.6 Hz.

Well, our goal is

40 Hz

or maybe even better.

So let’s see if we can do a little bit better.

I'm going to put

a data description in here.

We’ll call this

sealed box

and it’s

0.5 cubic feet.

So the next thing I want to do

I’d like to keep all these curves up here I’ll just add a data set

and

the next one I want to show will also be a sealed box.

But let's make the box one cubic foot.

So I’ll

put the box volume of one.

I’ll put

1.0 up here.

I’ll update the plot, so now this plot shows

the red line is the sealed

.5 cubic foot,

the green line is the sealed one cubic foot. Well you can see what happens here,

we got an improvement. Now we’re -3 dB

At about 41 Hz compared to

about 50 Hz before, so that's a good improvement.

Let’s try making it even bigger, let's try a 2 cubic foot sealed box.

I’ll add a new data set,

we’ll call that sealed 2.0,

make the box volume two cubic feet,

update the plot.

Well now, something interesting happens which is, it’s a little bit better

than one cubic feet,

but not much.

And so we've kind of hit the point with this speaker where making the box

bigger

doesn't really do much for us and so when that happens

it means it's time to look at a ported box.

So what I'm going to do

is

I’ll leave the sealed .5 and sealed 1 up there, but I’m going to

now play a little bit with some ported boxes.

Let's

have a ported box with a volume of

two cubic feet.

Now with a ported box

there's one more number that you need to

add. With a sealed box, the only number

you need to worry about is the volume of the box. With a ported box

there's this other thing here

called port frequency.

That has to do with how you tune your port.

Well, the software recommends a value

to use and were going to take its recommendation. I’ll just

double click here,

it’ll put that value in there,

we will update the plot

and see what happens.

So the yellow line is showing us a properly tuned

port in a

two cubic foot box. Well

now we’re

30 Hz at the

-3 dB frequency

and we were not able to get that out of a sealed box. Only by going to ported

were we able to squeeze that extra 10 Hz

out of the system.

This shows one of the

rules of box design, which is you always have a

small box that’s sealed, and a large box

that's ported.

I’ll just fix up the description here, this should say ported.

Let’s

add one more data set.

let's try a ported

four cubic feet.

Well you can see a similar thing that

happened before, which is we're starting to run out of steam.

Now here we have -3 dB at

about 23 Hz, so yes it's an improvement but

you can't just keep increasing the box size forever and keep seeing those improvements.

The design process is you usually start out with a sealed box,

increase it until you get

your design goal of 40 Hz and then

if you can't get there,

switch to ported

and once again keep increasing the box size and hopefully you'll be able to

hit your

35 or 40 Hz goal.

In later installations of this,

I’ll talk about how to use the

port design tool,

the enclosure design tool

and the woofer selection tool.

If all you're doing is a sealed box, you don't need the port design tool.

The woofer selection tool helps you choose woofers, we just

knew we wanted that Infinity and didn't have to mess with that here. But if you're

shopping for woofers, you will want to use that tool.

And the enclosure design tool helps you

build the wood

cabinet, to make sure that you've got the volume that you need.

The first step is to choose the

subwoofer driver that you’d like to use. I’ve chosen

The Infinity

1252W 12-inch sub. It's a

top seller right now.

So once you pick the driver, you want to find a specsheet for that driver.

You’ll find the Thiele/Small parameters and there are three numbers that you’ll need.

The first is called fs

and here it is free air resonance, fs,

for this driver.

It's 24.23 Hz and I’ll write that down.

The second number

that you need is called Qts, total Q. Qts for

this driver 0.48. I’ll write that down also.

The last number

You need

is Vas,

compliance volume. On this specsheet it’s shown in

cubic feet and liters.

I will

write down the cubic feet. I prefer to work in cubic feet but

the software will handle either one, you just need to keep track of

which you've chosen, so 3.48 cubic feet.

The next step in doing the design is to use some

speaker design software and

I like to use the Subwoofer Design Toolbox for this.

So the first thing we need to do is enter those three numbers into the software. So fs

was

24.23

Qts

0.48

Vas in cubic feet,

(we could have chosen liters,

we chose cubic feet)

is 3.48 cubic feet

Now the first thing we're going to do is see

how this

driver acts in a sealed box,

and the software lets you choose sealed, ported and other types of boxes too.

We’re going to start with sealed

and I’m just going to choose a

half cubic foot,

0.5 cubic foot box and see what happens.

So update the plot.

Now if you're not used to looking at these frequency response plots

they show you the bass response.

Think of it as the loudness of the bass

versus frequency, so here at the higher frequencies we’re

near zero dB, but as you start to get lower and lower,

there's a point where it just starts to fall off

and so

for this speaker

we’re

-3 dB

at about

49.6 Hz. Up here it shows

it's called data tracking you can see

where this cursor is so

it looks like about 49.6 Hz.

Well, our goal is

40 Hz

or maybe even better.

So let’s see if we can do a little bit better.

I'm going to put

a data description in here.

We’ll call this

sealed box

and it’s

0.5 cubic feet.

So the next thing I want to do

I’d like to keep all these curves up here I’ll just add a data set

and

the next one I want to show will also be a sealed box.

But let's make the box one cubic foot.

So I’ll

put the box volume of one.

I’ll put

1.0 up here.

I’ll update the plot, so now this plot shows

the red line is the sealed

.5 cubic foot,

the green line is the sealed one cubic foot. Well you can see what happens here,

we got an improvement. Now we’re -3 dB

At about 41 Hz compared to

about 50 Hz before, so that's a good improvement.

Let’s try making it even bigger, let's try a 2 cubic foot sealed box.

I’ll add a new data set,

we’ll call that sealed 2.0,

make the box volume two cubic feet,

update the plot.

Well now, something interesting happens which is, it’s a little bit better

than one cubic feet,

but not much.

And so we've kind of hit the point with this speaker where making the box

bigger

doesn't really do much for us and so when that happens

it means it's time to look at a ported box.

So what I'm going to do

is

I’ll leave the sealed .5 and sealed 1 up there, but I’m going to

now play a little bit with some ported boxes.

Let's

have a ported box with a volume of

two cubic feet.

Now with a ported box

there's one more number that you need to

add. With a sealed box, the only number

you need to worry about is the volume of the box. With a ported box

there's this other thing here

called port frequency.

That has to do with how you tune your port.

Well, the software recommends a value

to use and were going to take its recommendation. I’ll just

double click here,

it’ll put that value in there,

we will update the plot

and see what happens.

So the yellow line is showing us a properly tuned

port in a

two cubic foot box. Well

now we’re

30 Hz at the

-3 dB frequency

and we were not able to get that out of a sealed box. Only by going to ported

were we able to squeeze that extra 10 Hz

out of the system.

This shows one of the

rules of box design, which is you always have a

small box that’s sealed, and a large box

that's ported.

I’ll just fix up the description here, this should say ported.

Let’s

add one more data set.

let's try a ported

four cubic feet.

Well you can see a similar thing that

happened before, which is we're starting to run out of steam.

Now here we have -3 dB at

about 23 Hz, so yes it's an improvement but

you can't just keep increasing the box size forever and keep seeing those improvements.

The design process is you usually start out with a sealed box,

increase it until you get

your design goal of 40 Hz and then

if you can't get there,

switch to ported

and once again keep increasing the box size and hopefully you'll be able to

hit your

35 or 40 Hz goal.

In later installations of this,

I’ll talk about how to use the

port design tool,

the enclosure design tool

and the woofer selection tool.

If all you're doing is a sealed box, you don't need the port design tool.

The woofer selection tool helps you choose woofers, we just

knew we wanted that Infinity and didn't have to mess with that here. But if you're

shopping for woofers, you will want to use that tool.

And the enclosure design tool helps you

build the wood

cabinet, to make sure that you've got the volume that you need.