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Old 18th January 2004, 06:27 PM   #1
Vikash is offline Vikash  United Kingdom
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Default Help with first crossover

After much work on the speaker rebuild, I've finall got round to considering the xover.

I've ripped the old one out and done my best to draw a diagram of what it's doing (pic attached). I'm really lost here, because I don't know whether to just replace each component with a same value higher grade component, or reassess the crossover design completely (considering a different enclosure and changes in driver T/S parameters over the years). Do I need to mic measurements to design from scratch?

There's no markings on the inductors, so I don't know their values. Can someone also tell me what the resistor's job is in this scenario? (absolute newbie to this!)

I know that this is a second order design, but thats about it. So all help is much appreciated.
Attached Images
File Type: gif xover.gif (4.7 KB, 362 views)
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Old 23rd January 2004, 12:02 PM   #2
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Hi Vikash,

Your post seems to have gone un-noticed (which is unusual considering the content)..... Must have been busy lately

I haven't designed any xovers yet, but after playing around with a mic and speaker workshop to do some measurements I'd highly recommend doing the measurements.

I was doing it on my existing speakers so I could learn a thing or two before starting on my next project. What did I learn? I learnt that no matter what xover freq's I used it wasn't going to help, because the drivers didn't have enough overlap!!!! If I was trying to tweak by ear I never would have been happy because it wasn't possible!!!!! The mic showed that up straight away, and in some respects, the existing crossover point's are probably reasonably optimal for the particular drivers, which is somewhat of a fluke since they are stock ones I bought from Jaycar years ago.

The resistor looks like half an Lpad but my guess is it's there to change the impeadance of the driver probably an 8 ohm speaker and being changed to 4 Ohm, though I imagine it would also attenuate it somewhat.

edit: Woops doesn't help when the history doesn't show the graphics.... make that 2.8 Ohms if the two woofers are 8 ohms...... Maybe my math is screwy!!!!!!! (or as I discovered with Lpads, Ohms law doesn't necessarily apply).

Tony.
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Old 23rd January 2004, 01:54 PM   #3
Vikash is offline Vikash  United Kingdom
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Hi Tony,

Thanks for replying. I have the jig v2 and SW ready to go. After going through the SW tutorial again I realised that I need the FR measurements. Now this takes me back to getting hold of some Panasonic WM61 electrets which I've found problematic in the UK. I refuse to go for an inferior one, or the Monacor one without a fight.

I considered buying 100 last week from digikey, but I need to know there is enough demand by the UK DIYers. (Start shouting if you're out there)

The midbass drivers are ~10 Ohms. Lemme check a tweeter...4.2 Ohms.
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Old 23rd January 2004, 02:02 PM   #4
Rudolf is offline Rudolf  Germany
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Hi Vikash,
I can only help you with the resistor. Itīs a very crude kind of impedance linearisation. The lowpass for the woofers wouldnīt work, if it was influenced by a high impedance peak at woofer resonance. The resistor helps to "cut" the impedance peak to a much smaller value.
I have no clue how to get the inductor values, if you donīt even know the x-over frequency.

Rudolf
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Old 23rd January 2004, 03:24 PM   #5
Vikash is offline Vikash  United Kingdom
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Hi Rudolph,

That makes sense. When I was measuring the T/S params for the drivers I was concerned about the high impedenace at FS: ~ 150 Ohms.

I suddenly remembered that I could measure the inductors with SW. But this is moot since I now realise that a new enclosure = new xover.
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Old 23rd January 2004, 04:07 PM   #6
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hi

i saw the effort you have put into constructing those cabinets ,

i could help with explainig the cross - over , but i think it could do with a total revamp

for one

the tweeter can be c/o ved at 18 db per octave

i can easily give you 12 db , 18 db , 24 db c/o designs which you can make easily , (knowing you have tried your hand at voice coil winding !)

these are the things i would like from you

the type of sound you are looking for , your personal taste

for eg i dont generally prefer c/o inductors in the woofer line , like them direct , with may be a notch filter if i find a spectrum peaky , impedance correction too would depend on my amp to speaker current ratio to ones desire for a flat responce

to use some of your c/o parts please send me the henry of each coil , or the swg and the size , plus if it has a ferrite core / bobbin

upon designing a c/o and test s we can then proceed to build in a notch filter and impedance correction if required

suranjan

transducer design engineer
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Old 23rd January 2004, 04:09 PM   #7
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hi

another thing i would require is the frequency responce of your drivers , in this condition an approximation would do ,
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Old 24th January 2004, 12:52 AM   #8
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Quote:
Originally posted by Vikash
Hi Tony,

Thanks for replying. I have the jig v2 and SW ready to go. After going through the SW tutorial again I realised that I need the FR measurements. Now this takes me back to getting hold of some Panasonic WM61 electrets which I've found problematic in the UK. I refuse to go for an inferior one, or the Monacor one without a fight.

I considered buying 100 last week from digikey, but I need to know there is enough demand by the UK DIYers. (Start shouting if you're out there)

The midbass drivers are ~10 Ohms. Lemme check a tweeter...4.2 Ohms.
I ended up purchasing 11 wm60-AY mics from digikey (11 seemed the best number for me to get a reasonable unit price, when postage and handling was factored in, without wasting too much if I couldn't find anyone who wanted one). I wasn't sure about the 61, it looks a bit better on paper in some respects, I wasn't so sure about whether it was as flat, after seeing Eric Wallins tests on it (and considering Mr Linkwitz says the 60 is really flat).... Also wasn't sure if the linkwitz mod was applicable to it.

Tony.
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