What's the lowest frequency I could x-over a 27TBFC/G using 2nd order slopes?

[fjhuerta]

Hello all,

I know the SEAS 27 TBFC has been crossed over as low as 1.4 KHz, 4th order acoustic, without many issues.

I'd have supposed that meant the tweeter could work at 2.8 KHz, 2nd order. But browsing through Zaph's site, I've noticed the relationship between x-over frequencies when changing orders isn't lineal. I saw him recommending, for example, 2 KHz LR4/2.5 KHz / LR2 (for some other tweeter).

So, I'd suppose the SEAS could be close to 1.4 KHz LR4 / 2 KHz LR2, or something similar?

[mackintire]

It also depends on how hard you are driving the tweeter. In one design you may be driving the tweeter to 102db, in another you may be driving it to 110db.

Tweeters have Xmax too and often you end up with more distortion the more you ask your tweeter to do.

So LR4 at 3K may be able to play cleaner louder than say LR 1.5K. Every tweeter/ woofer combination and setup is going to be a little different.

[Dave Bullet]

Have a go at my system excursion spreadsheet elsewhere on this site (look at my postings). I've driven the 27tdfcg down to 1.3KHz (as Mark K did for one of his 1"/8" 2 way designs with I think the 27tbfc/g) and the woofer will hit the excursion limit the same time as the tweeter (I have about 5dB baffle step mind you factored into the design).

PS: system I'm talking about was LR4 acoustic both slopes (more or less).

PPS: How much peak power do you want to dump into them, conversely, what peak SPL do you have in mind?

Dave.

[fjhuerta]

Have a go at my system excursion spreadsheet elsewhere on this site (look at my postings). I've driven the 27tdfcg down to 1.3KHz (as Mark K did for one of his 1"/8" 2 way designs with I think the 27tbfc/g) and the woofer will hit the excursion limit the same time as the tweeter (I have about 5dB baffle step mind you factored into the design).

PS: system I'm talking about was LR4 acoustic both slopes (more or less).

PPS: How much peak power do you want to dump into them, conversely, what peak SPL do you have in mind?

Dave.

Hi Dave,

I'll be sure to look for your spreadsheet. That will definitely come in handy.

I don't expect to go higher than 60~80W RMS. Reason being, the system has 2 4.5" woofers with 4.5mm Xmax. I'd probably go with 80W because I'll be using a sub with them, but it's not a high SPL system by any means.

[JonP]

Have a go at my system excursion spreadsheet elsewhere on this site (look at my postings). I've driven the 27tdfcg down to 1.3KHz (as Mark K did for one of his 1"/8" 2 way designs with I think the 27tbfc/g) and the woofer will hit the excursion limit the same time as the tweeter (I have about 5dB baffle step mind you factored into the design).

PS: system I'm talking about was LR4 acoustic both slopes (more or less).

PPS: How much peak power do you want to dump into them, conversely, what peak SPL do you have in mind?

Dave.

Hmmm... I'll be looking for that Dave...

I remember Sigfried Linkwitz has something like that on his site, more oriented to larger drivers, though probably you could dial the cone size down to tweeter size...

BTW, Mark K's design was with the RS28, though a 27Txxx should be able to handle down there...

I recall reading someplace that tweeters are perhaps less predicitable in how clean they will be at a certain amplititude, vs their published Xmax and cone size. Best is always to do distortion measurements, if you can. But, you should be able to get in the ballpark of what's possible and not, by looking at those driver specs...

[Dave Bullet]

Been away for a while....

The spreadsheet from memory was just a rearrangement of SL's formulas. His website offers a calculation which you input TS params for a driver (I think the example he provided were small diameter pistons - such as dome tweeters) and it gave you the SPL and power for a given excursion. I just changed to say "give me the max SPL at either the thermally or excursion limtations for the average and peak thermal limited power of the driver"

I didn't do much testing of the spreadsheet, so wouldn't be surprised if you find a few errors.

[Dave Bullet]

Hmmm... I'll be looking for that Dave...

I remember Sigfried Linkwitz has something like that on his site, more oriented to larger drivers, though probably you could dial the cone size down to tweeter size...

BTW, Mark K's design was with the RS28, though a 27Txxx should be able to handle down there...

I recall reading someplace that tweeters are perhaps less predicitable in how clean they will be at a certain amplititude, vs their published Xmax and cone size. Best is always to do distortion measurements, if you can. But, you should be able to get in the ballpark of what's possible and not, by looking at those driver specs...

Quite true. The spreadsheet only shows you the power breaking point (ie. when xmax is reached) - not how much distortion is being generated as driver non-linearities increase. Sure it may not blow up, but it may sound like mother-in-law in the backseat with a megaphone in the process.

[NyxOne]

Quite true. The spreadsheet only shows you the power breaking point (ie. when xmax is reached) - not how much distortion is being generated as driver non-linearities increase. Sure it may not blow up, but it may sound like mother-in-law in the backseat with a megaphone in the process.

Please forgive me for hijacking this thread but the "mother-in-law in the backseat with a megaphone" comparison is funniest I've seen in a while!!! I never thought of distortion like this before! LOL!!! :rofl:

NyxOne

[fjhuerta]

The lowest I could take the 27TBFC/G was 2.6 KHz.

It didn't have a thing to do with distortion.

The frequency response in the lower treble simply wasn't enough to go any lower. Even if the tweeter's distortion were up to it, there was no simple way to shape the response enough.

But it sounds lovely at 2.6

[alias2]

The lowest I could take the 27TBFC/G was 2.6 KHz.
It didn't have a thing to do with distortion.
The frequency response in the lower treble simply wasn't enough
to go any lower. Even if the tweeter's distortion were up to it,
there was no simple way to shape the response enough.

But it sounds lovely at 2.6

http://zaphaudio.com/audio-speaker17.html

http://zaphaudio.com/BAMTM.html

2.0KHz 4th order L/R with a cap, inductor and L-pad.
1.45Khz 4th order L/R with a resistor, cap and inductor.
It does not get much simpler than these.

/alias2.

[fjhuerta]

Those are 4th order filters (as a matter of fact, I used the BAMTM's filter topology on another project of mine). For this project, I wanted a 2nd order one.

[Finleyville]

May I ask what you are pairing the 27TBFC/G with to a 2nd order? That tweeter is my current favorite and I am looking for a little larger project than my coveted Zaph L18 pair.

May I recommend TWO L18's for a TMM config? Maybe an all metal Seas three way? hahaha! :T

[fjhuerta]

I used a pair of W4-1658sb's. The project is on this site.

[fjhuerta]

Here's the link:

http://www.htguide.com/forum/showthread.php4?t=32196

Interesting little project. I learned to love 2nd order filters. They sound really great.

[alias2]

Those are 4th order filters (as a matter of fact, I used
the BAMTM's filter topology on another project of mine).
For this project, I wanted a 2nd order one.

Your right of course, but seeing the tweeter itself rolls
off with a second order function from ~ 2KHz a pure
second order acoustic roll off is not possible it will
have to be quasi 2nd order and eventually 3rd.

/alias2.

[fjhuerta]

Yeah.

I was reading Zaph's other projects, and his 2nd order bookshelf had to use the Vifa XT25, since he said the 27TBFC/G didn't have enough power at the lower end.

I wish I had been paying more attention to that paragraph! Still, the crossover came out just (barely) fine.