Modifying mission 705 crossover - falling at the first hurdle!

[silentphoenix]

Heya,

Im on my way to build my own mission 705 like speaker (I've sourced all the drivers, but need to build a cross over). I've read up on the basics of crossovers (multi way, multi order circuits) but still struggle with understanding the difference between various types of orders (Butterworth, Linkwitz-Riley...).

I've got the crossover design for the mission 705:



I'm planning to use black gate standard caps for the 470uf and 10uf, and 4 x elna silmic 2 1uf in parralel for the 4 uf cap. Haven't thought much about inductors or resistors yet. This is assuming I stick to the design above.

To me it looks like a relatively simple second order crossover network, but what I don't understand is:

1) Why is there a resistor in the tweeter circuit? At first I thought it was reduce the current/voltage(?) across the tweeter to reduce the sound from the tweeter is this true?

2) Can I change the tweeter cap to 4.7uf (I can get a 4.7uf black gate standard electrolytic cap - saves the hassle of making a 4uf cap with 4 x elna 1uf ones). If so, how does it change the resitor and inductor?

3) Why don't the tweeter-mid have the same value caps and inductors?

4) Why doesn't the mid range use a narrow band filter, but instead a low pass filter?

5) As 3 but, why don't the mid-sub have the same value caps and inductors?

6) Why is there a resistor in the sub circuit? I'm guessing the answer is related to question 1 or is this a zobel circuit?

Other general question I have are:

Would I benefit from a higher 3rd order x-over circuit?
Are there any other recommendations?

Thanks in advance

[KevinP]

1) There is a resistor to pad down the sensitivy of the tweeter. Tweeters are generally more sensitive than mids/woofers, so levels must be brought down to match

2) do not use electrolytic cap in tweeter circuit. I don't even think they make electrolytic caps that small. I'm sure you can find a couple of 2.0 ufd poly caps to use in parallel

3) why would they? Different drivers, different circuits... crossovers have to be matched to drivers, they are not generic values thrown together

4) see above

5) not sure - could be some sort of EQ circuit

[silentphoenix]

Originally posted by KevinP
...

2) do not use electrolytic cap in tweeter circuit. I don't even think they make electrolytic caps that small. I'm sure you can find a couple of 2.0 ufd poly caps to use in parallel

...

Thanks for that - it was really helpful! So, the circuit uses 4 caps all in:

1) 4uf in the tweeter - options:

- 3.9uf mundorf mkp polprop. or 3.9uf claritycap SA (I guess i'd have to change the inductor if I do this too?)
- 2 x 2uf claritycap SA in parallel
- anyone like to point me to a 4uf polyprop cap in the UK for about less than £10?

2) 10uf in the mid range - options:

- 10uf blackgate lytic
- 10uf soniqs sax polyprop.
- 10uf claritycap SA

3 and 4) 470uf in the bass - options:

- 470uf blackgate lytic

At the moment im tending towards 2 x 2uf claritycap SA + 10uf blackgate + 470uf blackgates.. that sound OK? What are other peoples suggestions.

Also, how complicated would it get if I add another 8ohm driver into the mid range (same spec as the other mid range)?

Thanks again

[KevinP]

If you add another driver to the midrange you've just changed the impedence and sensitivity, and would have to alter the x-over accordingly. I would strongly advise against it, this being a 3-way things would get complicated quickly

[Tancrède]

Hi silentphoenix ot other on this Forum.

Do you remember the name of the 705 speakers components: Speakers are Mission or other brands ????? Including the tweeter.

I have the occasion to buy a set of them, and i have to verify if the are original woofers, mids and tweeters.

The price is 400$ canadien, so around 200 sterlings.

Thanks

Tancrède

[sreten]

Originally Posted by silentphoenix

Heya,

Im on my way to build my own mission 705 like speaker
(I've sourced all the drivers, but need to build a cross over).

Thanks in advance

Hi,

If they are not the original drivers, there is little point
in slavishly copying the 705 x/o, if they are it is.

I get the feeling that your chucking expensive
components at something you don't understand.

rgds, sreten.

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