1986 Toyota MR2 - We’ve got a damn great hump...

Not trying to thread hijack here, but looks like you’ve been poking around my record collection. 👍

I approve of people with varied musical tastes.
I always used to say that I had a varied musical taste but I had to draw the line at jazz which I just couldn't stand.
Of course I've come to realise that I quite like some jazz and that a lot of the pop music I enjoy has a strong jazz influence.

So there we go, wrong again. It's a good job I don't mind being wrong. Especially when you learn or discover something new.

James

This made me smile so much. Someone who has similar music spectrums is a rare thing indeed. My 6 disc changers tended to have a Genesis/Phil Collins album, a Yes or ELP album, 2 trance nation discs, a Delirious album, and a Jungle or D&B disc. Radio stations similarly eclectic, depending on mood and journey 😂

Totally agree,
I too have eclectic music tastes,
I've always said I like everything from Bach to Black Sabbath, ( although no lover of Country or Rap, as in curse word !!)
Nigel

I’ve spent more time fiddling with the sub woofer. Adjusting it and readjusting it. This is bad news because it suggests something is wrong with my frequency response. Now that’s not any sort of news. Stick a large speaker in a small wooden board paired with front speakers that are too small, put them in a tiny car and you are never likely to achieve studio quality sound.

I’ve heard a load of sub woofers over the years. By and large they sound somewhere between terrible and really horrific. Done properly you can’t tell that you have a sub at all. But then you’ve spent a load of money on something you don’t notice so a lot of people turn the up too much so you know you have one. The other ‘problem’ with subs is that you shouldn’t be able to hear where they are in the room (or car in this case). But that only works if the crossover is set to a pretty low frequency. Set it too high and your ears can locate where it is.

My dash speakers won’t go low enough so I have to have the crossover set a bit higher meaning I can hear where it is. I can set it to so it blends in really nicely but then you don’t get the sub bass that I want to hear so I’ve got it a little loud too. The Vibe amp has a ‘Bass Boost’ control. It’s an EQ centred at 45 Hz. Adds a pit of punch. I had a chunk of that dialled in but I’ve backed it off a little so the sub blends in a little better.

Yeah… I can’t quite get it right, but, I’m being hyper critical and it’s pretty bloody good for what it is.
If you sit in the passenger seat and listen to it things are actually better. You don’t feel it so much but there is more distance for it to merge into the car and so it’s harder to hear where it is. I might do a rebuild and move it to the other side of the car one day. But first I want to listen to it while on the road and that means actually having a car that’s legal. Like having an actual MOT and stuff.

Anyway, during this extensive testing I did notice this…





It might not be immediately obvious but the centre bulb in the dash illumination has gone out.
Well that’s of no consequence so we’ll just pretend we didn’t see it. Right?

We didn’t see it… Right?

We didn’t…

Ah poo. I can’t unsee it and it’s going to annoy me even though I can’t actually drive the car anywhere. Let alone drive at night.





I’d forgotten how many screws you have to take out to get this apart. And to make life marginally harder the light switch is on the binnacle on the MR2 so when you’ve taken it all apart you can’t turn the lights on to test it. Well, I mean I did, but it’s awkward.

The bulb was fine.





So I just reseated it and retensioned the contacts and it’s fine.
Yes, I did try thumping the top of the dash before I took it all apart.

Anyway that’s all fixed now.
What, you want proof? Really!? Ok. Here you go.





See! Would I tell you porkies?

In the next episode we’ll either get back to filling those holes in the bumper (remember that?) or we might modify the pop up headlights to make them less irritating.
“But, James, why are they irritating?”

I do like a leading statement to arouse interest.

James

I don't understand any of this crossover sub frequency stuff at all.

I particularly wondered why they are called woofers, do they have something to do with dogs?

OMG





We might come back and chat about this one day after I write some stuff about crossovers. I've got to admit I find it a bit, er, disquieting. ...If that's the right word... Or even any sort of word.
(Yes I know that's the number of views not the number of people reading but it's still a ridiculous number.)

Anyway, thank you all for reading. It's lovely to have you all along for the adventure. 

James

Apparently I would tell you porkies ‘cos we are talking about crossovers.

We’ll keep this simple. No sums. Almost no numbers. Just a couple of drawings. Just a very basic look at what they do and why we want them. If you want to go deeper we can.


The lowest frequency you can hear is about 20Hz. The highest is about 20,000Hz. For decent hifi we want the response to be flat between those end points. So for a particular power across the frequency range we want the same volume out of our speakers.
There is a lot wrong with those statements. For a start, at the low end there comes a point where it’s too low to hear it but you can still be aware of it. You start to feel it. If you’ve never done it go to a cathedral and listen to somebody playing a big pipe organ. The sound is unbelievable. The biggest pipes can get down to a few Hz.
If my assumptions of my audience demographic are correct, none of you can hear 20kHz. About the only people who can are youngsters and they probably aren’t reading this ‘cos they are mucking about on X or something. Your hearing’s high frequency sensitivity drops off as you get older.

Even when you could hear to 20kHz most of you would have had a notch at 15625Hz. That was the line frequency of an old tube TV. I’m not sure if we actually went deaf at that frequency or if our brains just filtered it out. Young people that have only watched flat screen TV’s don’t have that 15625 notch and they go nuts if they walk into a room with a tube TV in it. They can hear a loud whistle but they can’t work out where its coming from. It’s really funny. (He says speaking as an old person.)

No loudspeaker driver can do the whole 20Hz - 20kHz range. You need a little one to do the high frequency stuff, a middle sized one to do the mid frequencies, and a big one to do the bass.
That said, a reasonable sized, say 4 to 6 inch mid in a well designed box will get pretty low. Bigger the better. But you aren’t going to get really low bass.

Ok, so let’s put a couple of drivers in a box, a little tweeter and a bigger mid, and see what the frequency responses do. Later we might add my sub to the drawing and see what my problems are.





We can see the mid driver can get a fair way up the frequency range. And the tweeter gets a fair way down. So there is a range of frequencies where both are working. What does that do to the overall frequency response? Well we get more volume out of it where both drivers are active and add together.





Oh dear. We’ve got a damn great hump in what we hoped would be a flat response. That won’t do.
What we ideally need to do is design the drivers differently so the mid doesn’t get quite so high and the tweeter doesn’t get so low. Just nicely so that they bump into each other. Well that’s not going to happen and there is an easier way of dealing with the problem.
We should put the signal going to the tweeter through a little electronic circuit called a high pass filter that knocks off some the lower end of its frequency range. And put the signal going to the mid through a low pass filter that knocks off a bit off the top of its frequency range.





Now the two drivers bump nicely into each other. The overall frequency response is now flat.





Let’s call these two filters a crossover. That’s it, we are done.
There is another reason why we need to filter the low frequencies off the tweeter. The tweeter is a small delicate little thing. Stick a few hundred watts of bass up it and the winding inside it (called the voice coil) will melt really quickly.

There are two ways of doing crossovers. Almost all are built into the speaker cabinet and are called Passive Crossovers.





The audio power amp outputs the full range of frequencies to the speaker. Then the filters in the speaker split it up into the ranges need by each driver.
This works well. I’m listening to some passive crossovers in my speakers as I type this and they are great. They do lose a bit of level from the system though but that’s rarely a problem.

The other way is what we do in professional audio. Or really high end home hifi. Or anywhere we need loads of control so car hifi is a good example.
We can have an active crossover first. Active because it’s a powered circuit. This splits the audio band into ranges which then feed a power amp for each driver.





Power amps aren’t cheap so this is an expensive way to do it. But it has the advantage that it’s more accurate in the frequency split part and it’s more easily adjustable. In a proper recording / mixing studio you can tune the speakers to the room they are fitted in if you want to.
In the stuff I work with the active crossover and power amps are built into the speaker cabinet. You just plug it into the mains, feed it sound, and enjoy your wonderful tunes.

So that’s part one of the story. Happy so far?

James

Ah... You know I was trying really hard to keep my terminology clear but I know I'll have screwed it up somewhere. It's complicated because in real life we use 'speaker' to mean different things.
I was trying to use this terminology...

What I'm trying to call a driver is this -





That's a mid / bass. A tweeter is -





The problem is that those things above are also called speakers.



When I'm writing 'speaker' I mean some drivers in a cabinet.





Or these if you want something better -







To complicate matters in my industry a 'speaker' also includes the amplifier that drives it.
We use a lot of these things.





That thing in the back is the active crossover and power amps that run the drivers in the front.
Undoubtedly I'll have mixed my terminology somewhere in that post. And I'll continue to mix my terminology. Sorry.

James