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
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
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.
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.
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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