I couldn't find a picture of the back, but it's not very interesting.

It's just a flat panel that's closed. And, so what I want to do is in the

guitar amplifier that you're building, if you just want to use it for a guitar, you

can just put it in a simple little open box.

Basically of any size that you like but if you want to try to enhance the

frequency response of bass frequency so you can use this.

As a bass practice ampliflier and get a little more bass out of it.

Then we can follow the following simple example calculation, which is following

exactly the examples that Rob gave in his Week 5 lectures.

So, let's go on the assumption that we want to build this base cabinet.

Now, there's a, the data sheet for the the MCM speaker that comes with a kit.

The model 55-2970. now of course you can go out and buy any

small speaker that you want. And, hopefully, you can find the

Thiele-Small parameters for that speaker but there is a data sheet that goes with

the MCM speaker. And the, the key parameters for the

speaker box design are the resonance frequency, the total Q factor of the

speaker, and the equivalent volume of air that gives the same compliance as the

speaker and so those three parameters are the ones, those three fields, small

parameters are the ones that we need to use to do our design.

So and this is the frequency response down here, the frequency response and

this is the impedance versus frequency of, of the, of the speaker.

We'll put the the data sheet up on the website so you can download it and look

at this in detail. So let's just run though that example

quickly. So, the FS was 40 hertz for the speaker,

the total Q was .424 and the equivelant volume compliance is about 27 liters.

So, we want to make the closed box Q one. If that's our design goal, to make it

one. So the Q closed box over Qts is about

2.36, and So then the main design equation Vas over Vbox, this is the

volume of the box we're looking for is Qcb over Qts squared minus 1.

And plugging in the numbers, this comes up to 4.57 the ratio of Vas to Vbox.

And so the box volume then should be Vas over 4.57 or about 5.89 liter or 5890

cubic centimeters. So that's the total volume of the box

that you would like to enclose the speaker in to give it the optimal base

response. So now you have to choose your 3

dimensions, the width, height, depth of the box.

And so if we follow the guideline of using the golden ratio so we use 0.618 to

1 to 1.618. we find the, the dimensions that satisfy

that are about 11 by 18 by 29 centimeters.

So this is still a nice compact design, This is a little over a foot tall.

something like that the speaker fits nicely in, in a box of this size and it's

only about maybe 4 inches deep or so. So there's your there's your base

amplifier, using the speaker. Of course, if you get another speaker, it

will have, you'll have other dimensions. Now the other thing it, about this is

that we measured a few of these speakers. We have a small setup for measuring the

field small parameters. And there's about for an inexpensive

speaker like this, there's about a 20% variation from one speaker to the next.

So, you can take this calculation too seriously because the speaker that you

have maybe quite different from the one that on the data sheet and the one we

measured. But anyway, this gives you a guideline

for for making a better base response with the amplifier.

Okay. So now that covers all of the sort of the

background and the design background and any of the theory that we wanted to

cover, which is prerequisite to building the amplifier.

Of course, it's not prerequisite. You could just build the amplifier and

see how it sounds. But now we have, all of the pieces are

you have an understanding of all of the pieces of this.

Now, the rest of the lecture this week is going to be Dave going through the

details of designing the amplifier and showing how to put it together and, how

how it should sound and a few of a, a few pointers for testing the thing along the

way. So you'll know you're on the right track

or not. So, good luck and I hope you'll enjoy.

Bye.