Just listened to some Fostex T50RPs today... WOW!

[superdux]

thx for the advice guys, i will try doublesided tape and flipping the lip and hopefully get my HM5 pads on!

 

[DHT 4 ME]

Hi guys.
 
First post here and this thread is the reason I joined. Thanks so much for all the sharing
 
I have to wonder why nobody has focused on stiffening the baffle instead of just damping it heavily.
I would think that some carbon fiber spars like the ones in RC airplanes glued to the back of the baffle would increase the stiffness incredibly around the driver and move the primary resonance up above the point where the mass was higher than the moment of inertia. You could damp it with stiffeners too if you so desired.  .040x.250 spars glued on edge would really stiffen the baffle and give some added diffusion.
Even a matrix of them on edge would be better, sort of like a honeycomb open face sandwich.
 
Anyhow, I have ordered my pair and am formulating a plan of attack based on my ME schooling, by numerous past speaker projects and what has been uncovered in the thread.
 
Thanks again

 

[hans030390]

I have to wonder why nobody has focused on stiffening the baffle instead of just damping it heavily.

I have a tube of QuikSteel that I had to use on a plastic reservoir in my car. I've always wondered if it might work well in the T50RP instead of the typical plasticine-type material. I didn't get a sense of how much mass it had, but it certainly hardened like rock (or, steel...I guess). It would just have to be applied very careful and quickly! It's dry within a few minutes, so it doesn't give you much room for error. Still, I imagine that would greatly help stiffen the baffle if used properly.

 

[DHT 4 ME]

Hans
 
A 1mm x 5mm  carbon fiber  superglued on edge is so much stiffer than Quick steel could ever be with a fraction of the weight.
If you add too much weight you move the resonance mode down to an area where is is more likely to be excited by the driver.
 
This should also help bass precision and midrange clarity. Much like the ultra stiff baffles on my Theil CS5i.

 

[Armaegis]

Well if you're going to the work of glueing down stiffening braces on the baffle, you're only a short iteration away from machining new baffles. I would be curious what a higher stiffness plastic or even solid metal baffle would sound like. 
 
We've been mass damping with plasticine (which should bring the resonant point up) and vibration damping with dynamat so far. 

 

[DHT 4 ME]

Armaegis,
 
A machined baffle would be the ultimate but is obviously beyond the majority of DIYers.
 
BTW adding a soft mass like Plasticine will lower the frequency. Think of it like a mass hanging from a spring. The more mass on the spring the lower the frequency of oscillation.
 
The Plasticine lowers the Q of the resonant system however the system gets more flexible as the stiffness to mass ratio moves in the wrong direction for fidelity and bass precision.
 
Adding a very light extremely stiff spar will greatly increase the resonant frequency, make it easier to damp and have better precision.
 
Think about the difference between a poly woofer and the ceramic Accuton.

 

[Armaegis]

Oh whoops, I knew that about the resonant point going down. Got the wires crossed in my head. 
 
The part about lowering the Q makes sense. I suppose that's the tradeoff between extra stiffness and extra mass. In the grand scheme of things though... how significant is the baffle resonant point compared to the acoustic resonance in the chamber? I'm thinking at this point it's probably the last thing to tweak. Earpad/seal and cup mods seem to do the most, with reflection disks coming in shortly after. 

 

[eltocliousus]

My highly modded T50RPs gave up it's last legs today after a soldering job gone bad, not my best moment, Bluemonkeyflyer kept my spirits up and in keeping good spirits, tree ornaments! Merry almost-here Christmas!
 
 

 

[kalbee]

is there any easy way getting those shure or HM5 pads on? think i´ve got too big hands, they keep on slipping off while applying.

http://www.head-fi.org/t/452404/just-listened-to-some-fostex-t50rps-today-wow/8415#post_8413435

 

[eltocliousus]

Quote:

http://www.head-fi.org/t/452404/just-listened-to-some-fostex-t50rps-today-wow/8415#post_8413435

 
I found that new Shure 840 pads are quite a tight fit and often slip off themselves, it helps to give them a bit of a stretch before popping them on.

 

[Nevod]

geetarman49,
FraGGleR,
 
Thanks!
I may though just directly wire internal wires to a cable put through the stock hole and just remove the jack socket assembly. I just want to be minimally destructive.

 

[bluemonkeyflyer]

Quote:

Hans
 
A 1mm x 5mm  carbon fiber  superglued on edge is so much stiffer than Quick steel could ever be with a fraction of the weight.
If you add too much weight you move the resonance mode down to an area where is is more likely to be excited by the driver.
 
This should also help bass precision and midrange clarity. Much like the ultra stiff baffles on my Theil CS5i.

Interesting. Where do you source carbon fiber and what sort of tool is needed for cutting?

 

[hans030390]

Hans

A 1mm x 5mm  carbon fiber  superglued on edge is so much stiffer than Quick steel could ever be with a fraction of the weight.
If you add too much weight you move the resonance mode down to an area where is is more likely to be excited by the driver.

This should also help bass precision and midrange clarity. Much like the ultra stiff baffles on my Theil CS5i.

I see. Well, you might be on to something! Are you planning on trying the carbon fiber out?

 

[DHT 4 ME]

I am planning on trying this next week.
 
You can get the Carbon FIber at any serious hobby shop that does RC planes and the like.
You can cut it with a Zona saw or other small razor saw. It glues extremely well with cyanoacrylate (super glue).
 
I have looked at the Thunderpants mod and it has a new thick wood baffle that is surely more rigid and wonder how much this
new baffle adds to the improved sound.
 
What this all boils down to is looking at mitigating resonance in one of 3 ways, you can  dampen it,  diffuse it or you can move it.
 
Time to play.

 

[micmacmo]

Quote:

Hi guys.
 
First post here and this thread is the reason I joined. Thanks so much for all the sharing
 
I have to wonder why nobody has focused on stiffening the baffle instead of just damping it heavily.
I would think that some carbon fiber spars like the ones in RC airplanes glued to the back of the baffle would increase the stiffness incredibly around the driver and move the primary resonance up above the point where the mass was higher than the moment of inertia. You could damp it with stiffeners too if you so desired.  .040x.250 spars glued on edge would really stiffen the baffle and give some added diffusion.
Even a matrix of them on edge would be better, sort of like a honeycomb open face sandwich.
 
Anyhow, I have ordered my pair and am formulating a plan of attack based on my ME schooling, by numerous past speaker projects and what has been uncovered in the thread.
 
Thanks again

 
Welcome aboard, DHT 4 ME. It's great to have new ideas in this thread.
 
Part of the reluctance of many of us to stiffen the baffle is that it likely falls into the realm of a non-reversible mod. Cheap though they be, our T50RPs are something we tend to be a bit conservative about.
 
On the issue of damping with newplast/plasticine/tungsten putty, check out BMF's original incremental mod post and charts 28 and L1 in particular. There isn't much difference between dampened and undampened baffles. As BMF points out, though, the 10g newplast per baffle he uses isn't a large amount. 
 
Quote:

In the grand scheme of things though... how significant is the baffle resonant point compared to the acoustic resonance in the chamber? I'm thinking at this point it's probably the last thing to tweak. Earpad/seal and cup mods seem to do the most, with reflection disks coming in shortly after. 

 
I tend to agree with Armaegis here. My most recent mods don't include any baffle dampening and I can achieve a relatively flat FR without obvious ringing.
 
Out of curiosity, if I were to put my finger lightly against the baffle, would I be able to feel a resonating baffle?