Tweeters

carl.halvorsen · Post by **carl.halvorsen** » Mon Jul 21, 2003 5:08 pm

Friends,
I boughr a pair of tweeters for my 91. I vaguely remember reading somewhere
that there is already a crossover somewhere in the speaker circuit of the MX5.
Does someone recall this? Or does someone have some advice on wiring them up?

Carl

Post by **zorruno** » Mon Jul 21, 2003 6:40 pm

What are they? Do they come with a crossover inbuilt? Aftermarket 'addon'
tweeters usually come with a cap inside (usually just an electrolytic
capacitor in series - simple highpass filter - you'll see it in the back).
If not, the same cap from Jaycar/DSE is only a few bucks.

What are the mounting options - can you mount and swivel to change angle?
Are they recess mounted or surface? I can suggest my preferred location for
tweeters in cars, but not if they are surface mount with no adjustment...

There are highpass filters for the headrest speakers in the factory stereo.
(FWIW Jeff Anderson in the US gets paid by people to remove this for better
sound - my personal thoughts are to remove the headrest speakers entirely,
but that's another story)

zorruno

Grant · Post by **Grant** » Mon Jul 21, 2003 11:31 pm

Capacitors when used as high pass filters for tweeters must be non polarised
type. Slightly dearer than standard but readily available from Jaycar or
DSE. Got tweeters in mine so if you can't find out what the value is let me
know and I will have a look.

Grant

carl.halvorsen · Post by **carl.halvorsen** » Tue Jul 22, 2003 7:37 am

They are Blauphunk ( without checking the spelling on the box!!).
100 watt max, 50mm and can be mounted flush or surface.
The crossover is not inbuilt. There is no cap inside.
Are you able to send me a simple drawing showing the connection in series of
an electrolytic
capacitor ?
I guess DSE will be able to advise me.

Carl

Grant · Post by **Grant** » Tue Jul 22, 2003 8:13 am

Just did some quick calculations. You must have a capacitor in series with
the tweeter to prevent the bass frequencies from destroying the tweeter.
They will sound worse without the capacitor, especially when the bass notes
destroy them!
To calculate the value, you need to know the:
Z (impedance) of the tweeters. Usually 4 ohms in a car speaker.
f (frequency) of the crossover or lowest frequency for the tweeter

From the following formula:

C = 1000000/ (2*Pi*f*Z)

The answer is in uF (microfarads)

So for Z of 4 ohms and f of 1000Hz

1000000/(2*3.141*1000*4)

you will need a 40uF capacitor. At 2000Hz you will need a 20uF capacitor and
so on.

Just connect the capacitor in series with one of the leads to the tweeter
(usually the + lead) and that's it. It is essential you use a non-polarised
capacitor. Most electrolytic capacitors are polarised so chech you get the
correct type.

Here endeth the lesson!

Your speakers are Blaupunkt. If I remember correctly it stands for Blue
Spot. Something to do with the production in the early Bosch factories when
they started making electronic equipment. Quality marking I think.

Grant.

carl.halvorsen · Post by **carl.halvorsen** » Tue Jul 22, 2003 8:50 am

Thanks Grant.
Its great to have some experts in the club.
I have some basic electronic knowledge so with your advice I will be on the
right track. Stay tuned.

Carl

carl.halvorsen · Post by **carl.halvorsen** » Tue Jul 22, 2003 2:52 pm

Hi Grant
The impedance is 4 ohms
and the minimum frequency is 3000Hz ( 3000 - 30,000).
I did the calculation and get .075384
Does that mean I require a .075 uF capacitor?

Regards
Carl

Gary Morrison · Post by **Gary Morrison** » Tue Jul 22, 2003 4:50 pm

Hi Carl,

For -3dB approx at 3kHz you need a series capacitor of 13uF. I'd use a 10uF
cap as none of this is hugely critical. Theoretically that will give you a 3dB
point of about 3,800Hz with 4 Ohms. The 4 Ohms is only a nominal figure
anyway, and its better to err on the high side frequency-wise than the low. In
a car the tweeter will be so many wavelengths away from the woofer/mid that
its pretty non-ideal anyway.

gary

On Tue, 22 Jul 2003 14:52:48 +1200, carl.halvorsen wrote:

Hi Grant
The impedance is 4 ohms
and the minimum frequency is 3000Hz ( 3000 - 30,000).
I did the calculation and get .075384
Does that mean I require a .075 uF capacitor?

Regards
Carl

Grant · Post by **Grant** » Tue Jul 22, 2003 5:41 pm

As Gary suggested, the 10uF will be fine. DSE have a 10uF at 50 volts for
$0.95 on their web site so go for that. My 1992 has Sony tweeters mounted in
the doors (part of the V spec option, I assume) and they certainly help the
sound. I also have speakers in the headrests (4" for $30.00 a pair from The
Warehouse) which are a vast improvement over the factory ones. I'm sure
better quality ones would help here as well, but I'm not prepred to spend
the money. My door speakers are some I bought from Repco. Relatively cheap
but sound quite good. The originals had been replaced by junk speakers
before I bought the car.

Good luck wand enjoy the improved sound.

Grant.

carl.halvorsen · Post by **carl.halvorsen** » Tue Jul 22, 2003 6:45 pm

Thanks Garry, Grant and zorruno for your help. I will be knocking on DSE's door
tomorrow morning.

Cheers,
Carl

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