[capace]

I enjoy fostex drivers and have tried several including 103,127 & 167.  But this time I am thinking about getting the 207e, and the ft17h tweeter.

Do I have to worry about time alignment with the tweeter.  I'll probably be running the 207e full range and then doing a 2nd order butter worth configuration on the tweeter. along with an l-pad to match sensivity.

The tweeter of course will be as close to the 207 as possible.

Thanks for the input.

[planet10]

General practisw is to just use a single cap. I like using a small cap & a high XO such that the  roll-off brings the tweeter down to the right level at the XO.

I did this with a set of T90 on top of my Fonkens -- there is a big sensitivity difference here and the cap was set for about a 80k nominal XO. Worked well.

dave

[rjbond3rd]

Hi Dave, do you mean 18k for the crossover frequency?  80k would be impressive.

[planet10]

No 80k. A 1st order XO up there brings the ~105 dB T90 down to the 90 dB level of the FE127eN at about the 15k roll-off of the 5". I never got a chance to really fine tune it, i was just making the T90s used before shipping them off to the UK.

dave

[capace]

Interesting, that adding a cap way above 80k would do that to the tweeter?

Also I would be using the ft17 not the t90.

Using a 1st order cross over. Wouldn't that still cause issues with time alingment. I'm big novice at building cross overs. I may not understand how that works.

[planet10]

Also I would be using the ft17 not the t90.

With FT17 & FE207 there is much less difference in sensitivity so you would XO much lower.

Yes time alignment and comb filtering will always be an issue, but with an XO this high the ear is not as sensitive as it is in the critical midrange/telephone band-width.

dave

[rjbond3rd]

Hi Dave, shame on me for doubting you!  I'm a newb and would have (unimaginatively) used a resistor but your technique sounds cool and interesting.  But wouldn't the tweeter's response "never" get flat?  Would it not be rising at 6 db/octave basically "forever", i.e. only flatten out once it reaches 80kHz?

[SET Man]

Hey!

   I have been using 167E with FT17H for a while now.

   With the 167E running fullrange and the FT17H with just a 0.47uf cap.

   With your 207E I think you might want to try caps between 0.68-1uf first since I think the 207E is not as extended on top as the 167E.

Take care,
Buddy

[planet10]

Would it not be rising at 6 db/octave basically "forever", i.e. only flatten out once it reaches 80kHz?

Electrically yes, acoustically no. And audiably for less than an octave.

dave

[capace]

I'm guess I'm not understanding? If I did go the the t90, and used and XO of 80k, would that not negate the whole concept of the XO, being that hi.

Also would that not allow all the lows to hit the tweeter and thus kill it?  Maybe I'm missing something.

[planet10]

I'm guess I'm not understanding? If I did go the the t90, and used and XO of 80k, would that not negate the whole concept of the XO, being that hi.

Also would that not allow all the lows to hit the tweeter and thus kill it?  Maybe I'm missing something.

I think you are. With the 207 being some 4 dB more efficient than the FE127eN i was using, the XO would need to be lower and then when one also considers that the 127 goes higher than the 207 a biy lower yet.

You need to knock the T90 down by about 12 dB so that is 2 octaves above where you want to XO it, so if 12k then set a nominal XO at 48k

The FT17 is 98.5 so you only want to loose about 5 dB so a bit less than an octave, say 22-23k

With the XO as high as it is, there is little worry about LF getting to it and killing it.

You dial the XO in by ear, i suggest starting a bit higher than estinated and then add small caps until it is a bit too much and then back it off a bit. Once you have found a suitable value you go out and buy a really good cap.

dave

[capace]

Thanks!