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Multi-Way Conventional loudspeakers with crossovers

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Old 17th December 2002, 08:50 PM   #21
Kram is offline Kram  United Kingdom
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hello,
Kelticwizard, i allready have one of those cobles you were on about and it was connected to my PC too.
Anyway, i ran that RMAA program and the graph response should be below,

the response dosent really look too good, it seem as though it dosent make it to 15kHZ. I is however just the onboard sound card and not a PCI slot type.

Kram.
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Old 18th December 2002, 02:29 AM   #22
Wizard of Kelts
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Your sound card is better than my sound card, which isn't saying much, LOL.

Overall, I would say your sound card is pretty good. You are -1.5 dB-not -3 dB-from 19 Hz to 15,000 Hz. Pretty good, I would say.

I wonder why we were getting such outrageous readings when we tested your AR tweeters? Gad, could your microphone have been that bad? Or your AR tweeters?

One thing, you might want to check your "multimedia" in your Control Panel to make sure there is no boost or anything in the mic input. Mine has a selection in the mic section for bass boost-not in the Line In section.

Anyway, if you have a mic handy-any mike-check some selected tones from 13,000 Hz down to 1000 Hz through your tweeter. You can see that the tweeter should be flat down to 1300 Hz or so, then goes down. Let's see what the mic reading is.

You can either use the oscilloscope, or measure directly from the mic leads with your digital multimeter. When you measure, see if you can get a 2 digit reading on the multimeter. Your tweeter should be able to take up to a 4 volt tone from 13000 Hz to 1000 Hz. Let's see how flat the mic is.

I am going to work on Crossover Simulator to figure the values we need. The author, F4ier, a member here, said that it takes into account notch filters, etc.

I believe I could design a crossover for you "by the numbers", but phase has everything to do with acoustic output with crossovers, and this notch filter adds another wrinkle. That is why I think we should have some sort of method of measuring that is reasonably accurate. It doesn't have to be that accurate, just want to make sure that we are not wildly off.
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Old 19th December 2002, 12:06 AM   #23
Bose(o) is offline Bose(o)  Canada
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Quote:
Originally posted by kelticwizard



C) The TW010E1 might have been selected by you for it's cost. However, it's .4 inch, (10 mm) diaphragm would make it a good choice for anyone who wants good dispersion above 12,000 Hz, regardless of cost. What was the size of the driver that crossed into your tweeter? Generally, "beaming" is what causes harshness, and too large a driver for the frequency causes "beaming". I would think that for a 6,000 Hz crossover to be used, the midrange should be five inches or less-preferably less.
My driver is 5.25", beaming occured when I had had only the mid/woofer rolling off naturally both, low-end and high-end.

"beaming" causes harshness. Wow! I didn't know that, well, my driver is not succeptible to mid-beaming. Thanks for the tip!

Soundcards, oh man, c'mon you guys don't suffer poor performance and awful acoustic output! Even a Soundblaster Live! Value would be great. Response is ine to me except fro that little blip in freq.


Keltic, what and where is this "wrinkle" you speak of? Phase plot, where?
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Old 29th December 2002, 02:12 AM   #24
Wizard of Kelts
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Well, Kram, it's been awhile since I checked back on this. I am contacting another member tonight. However, just one thing I want to report.

If you want a quick-and-dirty crossover just to get this project moving, use a 7.8 uF capacitor in series with the tweeter. This will give you a 6 dB crossover at 3400 Hz, which is where your woofer will rolloff naturally.

Fancier crossovers will take a little longer to put together, and as I mentioned before I am contacting someone else.

You mentioned in the previous thread that you might consider leaving the anomaly at 2000 Hz in if necessary. Well, this simple crossover will leave that in. I would prefer to give you a crossover that takes that roughness out. However, I just want to give you the option of having a crossover to put in in case you decide that you want to wrap the project up.

One more thing. The Audax website is down, so you cannot see all the stats for the TM025F1. However, Solen of Canada, a very respected retailer, lists the Re as 5.7 ohms and the Le as .04 mh. Anybody who wants to jump in and help on this crossover might wish to know that.
http://www.solen.ca/aud.htm

Incidentally, if you choose to use electrolytic capacitors, which are not the best for crossover work, use the nonpolarized kind. The others are useless. Also, do not use tantalum under any circumstances. Poly caps are fine-a little more expensive but not too much. They will make a difference on a fine tweeter like the Audax.

Hope to post more soon.
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Old 29th December 2002, 02:54 AM   #25
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Hi Wiz

Do you still need the formula for phase shift for notch filters?

Sorry if I upset you on the other thread, but it looks like they don't want to take any notice of experience anyway
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Old 29th December 2002, 03:53 AM   #26
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Yes, the formula for notch filters would be a great help. Thank you.
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Old 29th December 2002, 10:41 PM   #27
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Hi Wiz, here is the schema and calcs for a notch filter, sorry it's a bit rubbish, but my scanner has just decided to misbehave, I hope you can make it out ok...
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Old 30th December 2002, 12:47 AM   #28
Bose(o) is offline Bose(o)  Canada
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thank you as well.

How would you use the phase equation?? What's it for? Does it calculate for a smoother phase response?
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Old 30th December 2002, 01:10 AM   #29
Wizard of Kelts
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Bose:

Phase is very important in crossovers. It is too long a story to go into here, but let me say this. If two loads are entirely out-of-phase-that is, 180 degrees apart-they will cancel each other and you will have nothing. No output.

In fact, airlines have begun to use "anti-noise" in some planes where the immense noise from the jet engines is sensed by microphones, then electronically put 180 degree out-of-phase and then played through loudspeakers in the passenger area. Although there is a little delay because of the sound has to travel through the microphone and amp, the it is close enough to being completely out-of-phase, (180 degrees apart) from the source that the sound is deadened considerably.

As it is with sound, so it is with electronics. When you combine two signals that are completely in phase, you get double the amplitude of the signal. If they are out-of-phase, combining them will result in something less than double the amplitude and might even result in total cancellation, (no output at all).

It gets more complex than that. Capacitors make a signal go out-of-phase in one direction, and inductors the opposite way. If you have an amp with a capacitor in series with an inductor, at the frequency where the capacitor and inductor both have equal ohms, you get complete cancellation. The amp see zero ohms, and blows. The only ohms the amp will see is the DC resistance of the wire it took to wind the inductor-every inductor has some DC resistance. That is it. If the wire in the inductor had a resistance of 1/8 of an ohm, the amp sees 1/8 of an ohm-even though both the capacitor and the inductor are 30 ohms or more at that frequency!! Heck, they could both be 10,000 ohms at that frequency-it wouldn't make a difference.

I will search the web for a website with a quick-and-dirty explanation for this-it really is not that complex an idea in it's basic form, (though it leads to some mighty complex figuring when you have resistors, capacitors and inductors in series and parallel all in the same circuit).
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Old 30th December 2002, 01:27 AM   #30
Bose(o) is offline Bose(o)  Canada
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So, it's like noise-cancelling headphones. How do you apply this to your crossover however? Where does the value of pheta degrees fit in? Just post the site if this answers the question. Thanks a lot for the info! You learn something new everyday.
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