however for good educated guess you you need to work out the cap value whos capacitive reactance ( Xc ) equals the impedance of the device at the selected X-over frequency.
I will probably test out the bulltet tweeters on the existing set-up using the same caps as I use for the silk-domes. Bit for the new baffles I will be using active crossovers for the tweeters so does this still apply?
Nuuk said:So the impedance curve is for academic interest!
Maybe. Maybe not. It gives you an idea for a starting point.
I choose caps that give me an XO about an octave above where i think it should be. Then keep adding parallel caps (i have a big stash of 0.1 uF for this) until the tweeter becomes a bit too noticable, then back off a bit. It will take a while of listening and it is by ear, but the curve gives you your starting point and shows if you have any little wrinkles to deal with.
The ballpark here is to start with 1 uF and work your way upwards (i'd guess you won't reach 3 uF) -- this is for an 8 ohm tweeter. Larger values if the actual impedance is lower, smaller if higher.
dave
Nuuk said:I will probably test out the bulltet tweeters on the existing set-up using the same caps as I use for the silk-domes. Bit for the new baffles I will be using active crossovers for the tweeters so does this still apply?
So you will connect the amp direct to the tweeters ? - I've often wondered about this - is it safe. Turn on thump etc.
So you will connect the amp direct to the tweeters ? - I've often wondered about this - is it safe. Turn on thump etc.
I ran my active system for over two years with the amps connected directly to the drivers (woofer and tweeter). However, I did use Velleman speaker protection modules so the connection was not made until everything had 'settled down'.
Now I must make the decision whether I use protection again! (I will need to buy another module for a start).
So the impedance curve is for academic interest!
In this case YES !.
Watch the impedance curve of the FT17H :
FT17H
It is flat !!! Between 5 to 20 khz the impedance is equal to the its nominal value : 8 Ohms...
...and since you will use THIS value to calculate the value of your cap.
Just a question of common sens...
In this case YES !.
Watch the impedance curve of the FT17H :
That's good newsLionel but I think Dave was offering to see if the Radio Shack tweeters have the same impedance curve.
Nuuk said:I think Dave was offering to see if the Radio Shack tweeters have the same impedance curve.
Exactly. They are in their pods so i need to dissassemble to get past the XO.
The scale on the Fostex FT17 sheet is a bit deceptive. Very squashed scale & the impedance magnitude axis is logarythmic. Still pretty flat.
dave
OK chaps, the Radio Shack bullet tweeters are now playing in my open baffles and sound pretty good to me!
I have installed them with a 1 uF cap and no padding. I decided that the Goodmans 201's would be a close enough match in sensitivity and that appears to be the case.
The change in tonal balance is immediately discernable. After a listen to a few Jack Johnson tracks, I put on Roger Waters (Amused to Death) and with this CD the changes are even more apparent. All those little sound effects are moved further out into the room such that they surround the listening position even more than before.
After an hour of continuous listening I haven't heard anything that I dislike but I'll need to listen to many more recordings to find out if these are my 'final' tweeters.
I have installed them with a 1 uF cap and no padding. I decided that the Goodmans 201's would be a close enough match in sensitivity and that appears to be the case.
The change in tonal balance is immediately discernable. After a listen to a few Jack Johnson tracks, I put on Roger Waters (Amused to Death) and with this CD the changes are even more apparent. All those little sound effects are moved further out into the room such that they surround the listening position even more than before.
After an hour of continuous listening I haven't heard anything that I dislike but I'll need to listen to many more recordings to find out if these are my 'final' tweeters.
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