taming harshness of fostex FF125WK

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I have been playing with my new OB setup for a couple of months now, and after an initial honeymoon with sound of the FF125WK, I am now noticing a certain harshness to the sound (most probably in the 5-10khz region) and was wondering if anyone has witnessed addressed this issue.

I know that Dave (Planet10) said that some zig two-way glue on the back of the foam surround does help a bit, and I'll be doing this.

Another option is to fully Enabl these cones, but I don't know what kind of coating is needed and if/where microgloss would need to be applied.

I have previous experience with Enabl'ing my AN super12, so the technique would not be a problem.

Anyway, my setup is a double H-frame 15 inch subs with FF125WK on a flat panel, crossed actively using a 2x4 miniDSP...

Regards

Nick
 
I had the same problem with the my Fostex 127's - a cone break up produces a peak in the response around 7kHz. I tried Dave's tri-foil treatment but it didn't help and I don't believe eNable will help either. As I understand it, you need to use the zig on the back of the cone near the surround (I don't think it's on the foam you want to place it). I want to try this on my FE127's when I get the time.

I do have one FE127 still doing duty as the centre in my home theatre. It's been running for a couple of years and I'd guess it now has around 250 hours on it. The dust cap has been bodged in by inquisitive fingers too. It now sounds a lot better.
 
frugal-phile™
Joined 2001
Paid Member
I know that Dave (Planet10) said that some zig two-way glue on the back of the foam surround does help a bit, and I'll be doing this.

Goes on the part of the surround that is attached ro the cone and a bit onto the cone.

This driver gives a good idea of the EnABL patterns i tapped out.

FF125-chocolate-spice-comp.jpg


dave
 
frugal-phile™
Joined 2001
Paid Member
I had the same problem with the my Fostex 127's - a cone break up produces a peak in the response around 7kHz. I tried Dave's tri-foil treatment but it didn't help and I don't believe eNable will help either.

Measurements (done by Mark Fenlon in the big anechoic chamber) show otherwise.

Comparison-FE127eN-FRx.gif


But yes, despite what the measures say, even after treatment the ear can pick out a slight edge, a ghost from the 7k peak.

dave
 
has no one made a notch for it ?

Any measurements ?

And yea, it can measure flat but it can be "ringing down" in the time domain (waterfall plot) especially so close to the nasty 8khz range............

6khz (tang band 4" bamboo), not too bad unless you really know what it is doing and defitinely know it shouldn't be there. 6khz adds a nice clang to cymbals........

Norman
 
Measurements (done by Mark Fenlon in the big anechoic chamber) show otherwise.
But yes, despite what the measures say, even after treatment the ear can pick out a slight edge, a ghost from the 7k peak.
dave

was this the full enable treatment, just the tri-foil or something else ?

I only did the tri-foil and I didn't put on the cone the coatings that are used as a base for the enable so there may be quite a difference ??
 
I don't have my 125WK in a cabinet yet, but I selected based on listening and comparing while in Japan. i had the impression that when you listen a bit off-axis, it was nicely musical without extra components.
Otherwise i expect that you'll have more success with an equalizer like the deq2496 than with classic notch filters.
 
Last edited:
Agreed,

Its' a nice 4" driver, very natural sounding [in a box]. Using a .75mh/7ohm resistor for a filter (need to add small cap). We tried a larger coil (2.5) but ran into some other issues. The filter helps a little bit - to sweeten them up.

I had a handful of light country music the other day (son's) I was very surprised how well they sounded, very full/lifelike. Wife and son agreed - "hey, that does sound nice".

As many know, I have been testing them in boxes for a long time now - I do feel that they need a good bit of damping material to calm them down.
 
Dave, thanks for chiming in.
I'll be applying the zig glue today.
As for the Enabl process, does it involve any microgloss?

ODougbo, the reason I went with the FF125WK was that I wanted a two way OB with the full ranger covering everything from 150-200hz upwards and the FF125WK fit the bill just right with a good HF extension, a low enough Fs and an x-max that wold not make it strain or distort.

Below is my close mic measurement waterfall (3cm from dustcap) of the FF125wk on the OB board (60x45cm). It clearly shows the ringing at ~7khz. I'll measure later to check if the zig will cure any of it.

P.S: while there are lots of posts about the FF125WK, none addresses the issue I'm having in my setup
 

Attachments

  • ff125wk close mic.jpg
    ff125wk close mic.jpg
    86.1 KB · Views: 551
Everything above ~1.5KHz is resonance. That's how wideband drivers produce HF / extend their upper BW limit. Some frequencies more strongly than others, to be sure.

I've not heard this before. It has been my understanding that these lightweight cones do work at high frequencies (i.e. not relying on parasitic resonances for everything), especially some of the new MA drivers, and that perhaps the dust cap is responsible for helping too. Not saying you're wrong, only expressing my surprise - I guess I learned something new :)
 
has no one made a notch for it ?

Any measurements ?

And yea, it can measure flat but it can be "ringing down" in the time domain (waterfall plot) especially so close to the nasty 8khz range............

6khz (tang band 4" bamboo), not too bad unless you really know what it is doing and defitinely know it shouldn't be there. 6khz adds a nice clang to cymbals........

Norman

Yes I tried a notch filter. Does not work. Pay attention to P10. You might read the thread "What's the attraction".
 
I've not heard this before. It has been my understanding that these lightweight cones do work at high frequencies (i.e. not relying on parasitic resonances for everything), especially some of the new MA drivers, and that perhaps the dust cap is responsible for helping too. Not saying you're wrong, only expressing my surprise - I guess I learned something new :)

We can't beat the laws of physics. A wideband moving coil drive unit is only pistonic (itself a debateable word / definition) over a restricted BW. Everything above that is controlled resonance or vibration of the cone & any additions e.g. whizzers: another way of saying 'breakup.' The question is not really whether the driver is resonating, but how well controlled this resonance is. That's a big part of the science of designing them, and probably the hardest thing of all to do well. There are various methods. Some units use decoupling rings (those ridges you see on some cones) to progressively reduce the effective cone size as frequency increases. Some vary the cone profile and / or thicknesses. Some add strategic damping at certain points on the cone surface to damp regions where it rings more than others (the points often refered to as 'breakup'). Some more or less progressively decouple the main cone & hand over to a central dustcap attached to the end of the VC -essentially a central tweeter, turning the driver into a 2-way coax with mechanical XO. And so on. All have their advantages and disadvantages. But the constant is that it's resonant action. Same applies to conventional tweeters incidentally, esp. at the top end of their BW.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.