Curvy Changs - Modifications to Design?

[bmwman91]

First off, let me thank planet-10 / Dave for all of his help via email. I have gained some useful information from that.

So I had been thinking of building a nice SB Acoustics MTM pair as my next project, but I really wanted to do something different than my previous projects (running TM pair with a gigantic ported sub, tri-amped & filtered with DCX2496). A friend has been building Fostex BLH's and some crazy 10' long loaded horns for a few years and I always liked the aesthetics and efficiency.

Obviously the Changs are not horns really, but they look really cool and apparently have great performance. It seems that the driver of choice, the Fostex FE207E, does well, but it looks like it really sort of dies above 10kHz (which is pretty respectable for an 8" driver). I would LIKE to avoid adding a tweeter if possible since I find simplicity to be elegant. The FE206E seemed to go all the way to 20kHz but it is unavailable and might not be suited to the CC. There is also the F200A that seems to get all the way up, but the price is a tad heinous at $480 each!

So anyway, I will likely end up running an FE207E with a tweeter crossed over with a capacitor somewhere in the 8-12kHz range (any recommendations on the setup?). If people have better suggestions I am all ears. What sort of cone excursion do you get in the CCs? Is it tightly controlled like a horn, or is typical bass-reflex behavior the case here? These don't get the boost in sensitivity that horns do, either?

Since I haven't had any involvement in the design of these speakers, I probably should not be mucking around with changes to them. But, I enjoy the fabrication process and the challenges posed in it, and it is always nice to add custom touches when possible. See the renders below for some a rough idea of what I was thinking. The middle model really has not been changed much...just some simple round-overs.

I am more interested in the possible effects of the model to the right with the tapered bass enclosure & approximated circular arc for the mouth deflectors. Were things like this ever experimented with? Reducing sharp angles wherever possible can help with reflection formation & such, right? Of course, I may be putting too many assumptions in here that I really don't have the capability to simulate; I am guessing that I will be told to stick with the original design (which wouldn't come as a surprise).







Thanks everyone!

[planet10]

Originally Posted by bmwman91

So anyway, I will likely end up running an FE207E with a tweeter crossed over with a capacitor somewhere in the 8-12kHz range (any recommendations on the setup?)... What sort of cone excursion do you get in the CCs? Is it tightly controlled like a horn, or is typical bass-reflex behavior the case here? These don't get the boost in sensitivity that horns do, either?

Most people use FE207 with a tweeter. FT17 is the budget choice. FT96 if you have deeper pockets. They can be XOed at 12-15k with a cap + L-Pad, or you can try my preferred method of using the XO roll-off to attenuate the tweeter. XO high enuff that the tweeter level has fallen off enuff to meet the 207 at the right place.

The middle model really has not been changed much...just some simple round-overs.

I am more interested in the possible effects of the model to the right

Middle is OK. Right is going backwards toward Bruce. Unlikey to work as well as either.

dave

[bmwman91]

Originally Posted by planet10

Most people use FE207 with a tweeter. FT17 is the budget choice. FT96 if you have deeper pockets. They can be XOed at 12-15k with a cap + L-Pad, or you can try my preferred method of using the XO roll-off to attenuate the tweeter. XO high enuff that the tweeter level has fallen off enuff to meet the 207 at the right place.



Middle is OK. Right is going backwards toward Bruce. Unlikey to work as well as either.

dave

If the FE207 + a tweeter is the preferred method then I will probably go that route. Can you point me toward a good thread with the preferred l-pad & XO design?

I figured that I probably wouldn't be able to improve on it with an uneducated shot-in-the-dark. I'll just stick with the design that the people who know what they are doing came up with. Any chance a middle-right hybrid would be decent? (keep the square bass enclosure, but use the pseudo-round deflectors)

What sort of power can I run to these before non-linear excursion becomes an issue?

Thanks.

[planet10]

FY17 + 207 is covered pretty well, IIRC, in the curvy Chang thread.

The middle variation is OK, the waveforms affected will not see any of the differences.

dave

[planet10]

Originally Posted by bmwman91

Reducing sharp angles wherever possible can help with reflection formation & such, right?

At the frequencies involved there are no reflections just an expanding volume. Changing the rate of change of that volume screws things up.

dave

[planet10]

Originally Posted by bmwman91

What sort of power can I run to these before non-linear excursion becomes an issue?

Loud enuff with not much power that sustained useat those levels will cause hearing damage. 3-20 watt amp recommended. Preferablly with a high output impedance.

dave

[bmwman91]

Originally Posted by planet10

FY17 + 207 is covered pretty well, IIRC, in the curvy Chang thread.

The middle variation is OK, the waveforms affected will not see any of the differences.

dave

Well, it looks like I will go with a nice, stock CC, as the designers intended. Veneering round features is not something I really wanted to mess with anyway.

Originally Posted by planet10

At the frequencies involved there are no reflections just an expanding volume. Changing the rate of change of that volume screws things up.

dave

I sort of figured that this would be the case. I suppose that the design's apparent simplicity masks the fact that there is deliberacy behind every dimension. (I should trademark that, it's pure marketing gold!)

Originally Posted by planet10

Loud enuff with not much power that sustained useat those levels will cause hearing damage. 3-20 watt amp recommended. Preferablly with a high output impedance.

dave

Hmmm...well, I suppose that I won't run them from my Behringer A500's then. I have been wanting to build my own amp for a while now anyway (probably using a design from Rod Elliot's site). It sounds like a tube amp is suited well to this also, although I don't want my first mains-level electronics project to be a tube amp (I want to live).

Is there a simple answer as to why high output impedance is desired? Everyone is always trying to go the other way in pursuit of the maximum damping factor.

[planet10]

Originally Posted by bmwman91

(probably using a design from Rod Elliot's site).

Have a look at the firstwatt F2 or F2J (i'm assuming from comments made that the former can be converted to the latter)

dave

[bmwman91]

Quick one...where is the (simulated) lower roll-off frequency with these? The Chang PDF has a sim plot showing flat extension down to ~40Hz...where do the CCs end up (start of roll-off & -3dB)? I know that the room is a major part of it, but someone indulge me please!

[Scottmoose]

The same.