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Old 13th November 2009, 04:19 AM   #1
asiquis is offline asiquis  Canada
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Question To crossover or not or ?

I am looking at a woofer that is fairly flat and has a natural 12 db roll off at
5000 Hz (Silver Flute W20RC38-04)
I am looking at a ribbon tweeter that needs to be crossed over at at least4500 hz (according to manufacturer RT1CA HiVi)

If I run the woofer without a lowpass how then does one determine the highpass frequency and slope for the tweeter?
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Old 13th November 2009, 05:59 AM   #2
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I believe you could try putting a "mock" 2nd order (12dB) LP filter at 5,000Hz in Passive Crossover Designer (hopefully it should do nothing to the FR response) and then put in the values for the tweeter. This way you should be able to mimick the LP filter.

Alternatively, you could try putting the woofer in PCD by itself with no crossover and just have one for the tweeter. I think this works, though I've never tried it.

Also, don't forget that you may need an L-Pad if the woofer is too efficient due to the lack of an LP filter.

You will need SPL Trace if you don't have any .frd or .zma files for Passive Crossover Designer.
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Old 13th November 2009, 07:31 AM   #3
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Wouldn't taking 12dB/octave from a 12dB/octave slope mean it's 24dB/octave?

Unless, of course, the Passive Crossover Designer doesn't account for the rolloff of the woofer/tweeter.

Personally, I'd low pass the woofer - at the frequencies you're talking of, it would be starting to beam.
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Old 13th November 2009, 10:25 AM   #4
Andy G is offline Andy G  Australia
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I'd use a different top end. Your mid/woof should not be crossed much higher than 2.5-3kHz, and its best to choose a tweeter that can match the mid/woof
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Old 13th November 2009, 04:54 PM   #5
Pano is offline Pano  United States
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Second what Andy said, but if you want to try it, here is how.

Since your woofer has a 2nd order roll off at 5K, you need to be near that with the tweeter. A simple 2nd order high pass at ~5K is a start, but will it actually give you a 5K 2nd order acoustic roll off? To simulate you'll need to get the tweeter FR into software and throw filters at it until you find one that gives you a curve to match the top of the woofer. That should not be too hard.

But then the real world kicks in and you'll find that you probably need to spread the crossover frequencies a bit to make up for the driver offsets.

Do you have the software to do the sims?

EDIT: I just took a look at the HiVi driver and it's going to be very hard to get a 2nd order acoustical roll off at 5K. 3rd order is easy. 3.2uf and 0.65 mH or there abouts. Nice 3rd order roll off at 5K.
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Last edited by Pano; 13th November 2009 at 05:11 PM.
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Old 14th November 2009, 03:21 AM   #6
asiquis is offline asiquis  Canada
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Quote:
Originally Posted by panomaniac View Post
Second what Andy said, but if you want to try it, here is how.

Since your woofer has a 2nd order roll off at 5K, you need to be near that with the tweeter. A simple 2nd order high pass at ~5K is a start, but will it actually give you a 5K 2nd order acoustic roll off? To simulate you'll need to get the tweeter FR into software and throw filters at it until you find one that gives you a curve to match the top of the woofer. That should not be too hard.

But then the real world kicks in and you'll find that you probably need to spread the crossover frequencies a bit to make up for the driver offsets.

Do you have the software to do the sims?

EDIT: I just took a look at the HiVi driver and it's going to be very hard to get a 2nd order acoustical roll off at 5K. 3rd order is easy. 3.2uf and 0.65 mH or there abouts. Nice 3rd order roll off at 5K.

My son was doing some google searching and found this interesting speaker
DECWARE / Small High Efficiency MTM Towers MG944

What might the thoughts be on this??

I was thinking crossover at 5000 and it looks like this one is at 8000?
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Old 14th November 2009, 04:25 AM   #7
Pano is offline Pano  United States
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Interesting find. So someone is using these drivers and making it work.

Maybe the electrical high pass on the tweeter is 8K, but I don't see how the acoustical could be - too much gap with the woofer.
My 1st guess for a x-over for this combo would be the afore mentioned 3.2uF+0.65mH on the woofer along with about ~0.3mH on the woofer.
Not quite sure about the inductor on the woofer because I can't tell what the impedance is. But I think you'll need something on the woofer to get it to blend right with the tweet.
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Old 14th November 2009, 05:24 AM   #8
dheming is offline dheming  United States
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The crossover Steve uses in these is just a single cap with the tweeter run reverse polarity.
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Old 14th November 2009, 11:42 AM   #9
FE3T is offline FE3T  Norway
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I am doing the exact same thing with a Morel 8,5" papercone and a Audax 34mm dome. besides the L pad for lowering the tweeters output 4db only a 6,8uf cap on the tweeter are used.

Last edited by FE3T; 14th November 2009 at 11:47 AM.
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Old 14th November 2009, 12:33 PM   #10
gfiandy is offline gfiandy  United Kingdom
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I wouln't run this woofer without a xover. It starts to break up at about 1KHz (you can see the bump in the SPL trace) from here up its off axis response will be getting worse and worse. By the time you get to 5KHz it will be a tight beam. Also the peak at approx 4KHz of about 5dB will make this speaker sound quite unpleasant on axis, this is because 4KHz is the point of maximum sensitivity for the human ear so you really don't want a peak here. The top end of woofers output also tend to have a large amounts of distortion so whilst the sweep shows a 5dB peak here there may also be harmonics from lower frequencies adding to this which will make it sound even brighter and harsher. I would cross this speaker over with a tweeter at no higher than 2.5KHz (lower if you can find a tweeter that extends down further) and try to suppress the peak at 4KHz as much as possible.

Some people like the forward sound you get from wide open woofers describing it a live sounding. If you like this then ignore what I have said above. I tend to like acurate, easy to listen to speakers and find any distortion gives me listening fatigue very quickly.

A good way to get an idea of the effects I am describing is to run a graphic equaliser on a song you know well and turn up the 4KHz region. Since not many people have graphics these days this used to be quite hard to experiment with however now all you need to do now is download iTunes and use the graphic equaliser on that (It's mysteriously under the view menu rather than tools).

If you want to simulate the response of your xover system on axis, you can do it by downloading speaker workshop and SPLTOOLS SPLTRACE. Use spltrace to copy the response from the data sheet into a file that speaker workshop can use. Then do the same for the tweeter you have chosen. Then you can design and simulate a xover. This is quite a long winded process, there are several tutorials on the web about it but you will have to search for them as I can't remember the sites.

Regards,
Andrew
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