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Old 10th July 2011, 06:18 PM   #21
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Inspired, very nice.
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Old 10th July 2011, 07:02 PM   #22
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Quote:
Originally Posted by Toppsy View Post
I might make up another pair of tubes with the face plate cut to a 5-deg slope to match that of the front baffle the FH3's.
1st comment Chris had when i suggested we throw some of these togther.

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Old 10th July 2011, 07:25 PM   #23
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Quote:
Originally Posted by Bob Brines View Post
The point that dynablaster is trying to make is still unanswered. The diffraction that he is addressing is baffle step diffraction. As long as the operating frequency of the tweeter is high enough that 1/2 wavelength is shorter that the width of the tweeter faceplate, baffle step won't occur and Olsen's drawing do not apply. Edge diffraction is an entirely different phenomenon. Since the design under consideration is a dome tweeter, the edges will be illuminated well within the operating bandwidth and will be a consideration. The horn loaded Fostex designs are directional and do not illuminate the edges.
Thanx Bob, a better explanation than i had as i was reading towards your post.

To add to what has been said on this subject:

Assumming a tube just slighly larger than the bezel (3") baffle step is at ~4500 Hz, so should be a non-issue.

Edge diffraction on the other hand will be an issue. Because the "enclosure" is circular all secondary emmittance from the edges will be the same distance in time from the primary emittance of the dome.

There are 3 major techniques to minimize the issues.

1/ Add a round over and flush mount the tweeter. Won't take much of a round-over at the frequencies involved. Adding some "enclosure" width also pushes the baffle step frequency down which won't hurt.

2/ Minimize the amplitude of anything gettling to the edge. This is where the felt comes in. A star-shaped cutout around the dome is recommended, preferrably cut at an angle from the perpendicular. And use the higest quality felt you can find, as you don't have much room to work with, not too dense or it will, in itself become a reflective "wall". The felt could be wrapped around any round-over to compound the efficacy of using both.

3/ Don't make the "baffle" a circle. In effect the star-shaped (or non-circular) cut-out in the felt has a virtually similar affect.

dave
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Old 10th July 2011, 07:34 PM   #24
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must it be felt or could Alcantara do the job?
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Old 10th July 2011, 07:40 PM   #25
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Alcantara is synthetic, i doubt it would be naerly as effective as wool or cotton felt.

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Old 11th July 2011, 09:29 AM   #26
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Quote:
Originally Posted by Toppsy View Post
When I asked my mate Chris for some feedback on how he was getting on with these tweeters, I got this reply. He is using these tweeters mounted atop his Mark Audio CHP70 Frugal Horn Mk3 speakers:



I'd call that a result
My initial listenings were very positive, but some recordings could make me wince, so I've been messing about pushing the corner frequency of the high-pass filter upwards.
The starting point was with a 2.2uF cap, giving a corner frequency of 9000Hz.
I've ended up shoving the corner frequency up to 13000Hz, using a 1.5uF cap, and I am much happier with the sound I'm getting - there is nowhere near the same amount of presence band energy coming off the FH3/CHP-70/supertweet combination now, and things sound very nicely balanced.

Nothing particularly scientific about about the process - I just subjectively listened as capacitors were changed, and stopped when I felt that things sounded right.

I should also add that my thoughts are about the sound I'm getting in my room, and with my gear.
YMMV
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Old 19th July 2012, 02:59 PM   #27
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So I'm a total newb, just getting into speaker building and learning all about x-overs. Can someone tell me how to x-over is done up? Do I need a cap on both sides (positive & neg)? Does the resistor just go on the positive side? And I assume its done in series with the cap between the tweeter and the resistor. Thanks in advance.
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Old 19th July 2012, 03:15 PM   #28
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Hi mwfair,
Without getting complicated, the audio signal is AC so that means that it continually changes back and forth so it matters not which side the cap goes on although you often see it on the + side. There is no need for a cap on either side, just the one as the signal has to complete the circuit by going through all components. There really is no + and -, those are just phase indicators. That means that in most cases (perhaps all nowadays) if you apply a DC voltage to the + side it will translate to outward diaphragm movement.
Again it matters not which side the resistor goes on. If it is a simple resistor (not an L-Pad) you can put it before or after the cap or even on the - side if you wish.

This is a very basic look at things and there may be others that have advice on the hows, whys and whatnots but I hope this will help you understand the most basic of circuits.
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Old 20th July 2012, 02:49 PM   #29
mwfair is offline mwfair  United States
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Thanks, for the clarification.
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Old 19th June 2013, 12:20 AM   #30
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sorry for the old thread resurrection - i'm hoping someone can point in me in the direction of the resister values used in this tweeter. thanks!
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