Fostex T50RP Incremental Mods and Measurements

[bluemonkeyflyer]

Quote:

Yup! I had to pull the layers apart like you did. Although, I didn't get 20 layers, more like 5-6 at the most. So, I used two layers of my 5-6 layer stacks to make up the 20mm height you recommended. All that denser cotton in there might be the reason I have too present highs and not enough bass. Whatcha think?

 
I suspect there's a good chance that your highs are too high because your cotton is still too dense. Maybe you can separate them into more layers? The "fluffier" the better.
 
Here's what I'm using now in place of Rite Aid "Natural Absorbent Cotton" which has been discontinued:
 
Rite Aid "First Aid Rolled Cotton" 
 

 
 
Separated into 20 individual layers. You can see 1 layer at the bottom of the ruler:
 

 
 
Preparing "First Aid Rolled Cotton" for Effective Dampening
 
1. Separate the roll of dense cotton into 20 individual layers.
 
2. Divide into 2 parts of 10 layers, each. UNcompressed, 10 layers = approximately 2 cm thick.
 
3. Cut 10 layers to fit the cups = 2x7x7 cm.
 
4. Cut 1x7x7 cm fiberglass and place over the top of the cotton.
 
This is my initial DBV #3 build with "First Aid Rolled Cotton" followed by tuning one or more of the following variables (individually) to achieve the desired frequency response:
 
* add/remove cotton
* add/remove fiberglass
* tweak the size and number of holes in the stiff felt over the rear driver grids
* tweak the size of the paper treble reflectors
 
Prepping Rite Aid "First Aid Rolled Cotton" results in 'similar' performance compared to Rite Aid "Natural Absorbent Cotton."

 

[chrislangley4253]

Yeahhhh. my cotton is so much more dense than that stuff. :'(

We gotta find a good source of cotton! The rite aid stuff looks pretty good when you separate the roll like that, definitely a lot better than what I'm working with.

 

[onefatsurfer]

I recommend you guys try these.. They're incredibly soft and separate very easily.

http://www.abesmarket.com/organic-essentials-100-pure-organic-cotton-non-gmo-cotton-balls-triple-size-80-count.html

I got them at harmon drugs, but they're available online under this name and "swisspers"

 

[HumanSaurusRex]

How did you guys close the baffle port? Like this without the notch?
 

 

[bluemonkeyflyer]

Quote:

How did you guys close the baffle port? Like this without the notch?
 

 
The notch keeps your options open during tuning. If you want to close the baffle port temporarily, stick on a tiny piece of masking tape. If you want it closed permanently, use hot glue, silicone, self-adhesive felt, or Dynamat.

 

[HumanSaurusRex]

Thank you for your fast answer! Do you recommend dynamat on the ear side with #3 ?

 

[bluemonkeyflyer]

Quote:

Thank you for your fast answer! Do you recommend dynamat on the ear side with #3 ?

 
My pleasure.
 
I have duplicate DBV #3 mods. Some have Dynamat and some do not. I cannot tell any difference with vs without Dynamat.

 

[HumanSaurusRex]

Did you ever try "Simplified and Consolidated Pictorial for DBV #3" with Stax SR-007 or LCD-2 pads?

 

[bluemonkeyflyer]

Quote:

Did you ever try "Simplified and Consolidated Pictorial for DBV #3" with Stax SR-007 or LCD-2 pads?

 
No, I haven't tried either. DBV #3 (and variations) were tuned for 840 pads, only. Using different pads will change the FR. Basically, pads with deeper/larger interior volume will decrease bass quantity. See the incremental mod graphs for an idea of how each component performs using 3 different pads: Stock T50RP pads, Shure 840 pads, and Fischer FA-003 pads.

 

[HumanSaurusRex]

Okay, thanks. Last question: does an amp like a fiio e17 improve the sound or does it just turn up the volume?
Modded my T50rp today and I'm really happy with after removing some cotton.

 

[bluemonkeyflyer]

Quote:

Okay, thanks. Last question: does an amp like a fiio e17 improve the sound or does it just turn up the volume?
Modded my T50rp today and I'm really happy with after removing some cotton.

 
Excellent! Happy to hear you're happy.
 
I have not tried Fiio gear. I use a Dacmini with 1-ohm output impedance mod.

 

[chrislangley4253]

Quote:

Okay, thanks. Last question: does an amp like a fiio e17 improve the sound or does it just turn up the volume?
Modded my T50rp today and I'm really happy with after removing some cotton.

It will mostly turn up the volume, unless the dac in your current source is particularly bad or your source is particularly underpowering them. The land of dacs and amps .. Is confusing. I'll send you a PM with some more info to help you decide if you need one or the other

 

[Congo5]

 Has anyone done efficiency measurements to determine power requirements of the T-50 DBV#3?
 
I measured mine today:
 
1k sine wave from BK Precision 3020
 
modded t-50's....3.23v=104db      4.14v = 110db
 
so if math is correct 3.2v squared divided by 50ohms is 204mw ....0.064amps
 
4.14v would be 342mw
 
If so than a target of  250mw sounds right to me>>>?

 

[chrislangley4253]

Quote:

 Has anyone done efficiency measurements to determine power requirements of the T-50 DBV#3?
 
I measured mine today:
 
1k sine wave from BK Precision 3020
 
modded t-50's....3.23v=104db      4.14v = 110db
 
so if math is correct 3.2v squared divided by 50ohms is 204mw ....0.064amps
 
4.14v would be 342mw
 
If so than a target of  250mw sounds right to me>>>?

I haven't done any math, but I can say that they definitely don't need more than 2.5x gain with a Redbook 2Vrms source. I'm prolly gonna drop the gain on my O2, but waiting to finish my mods first.

 

[kingoftown1]

I haven't done any math, but I can say that they definitely don't need more than 2.5x gain with a Redbook 2Vrms source. I'm prolly gonna drop the gain on my O2, but waiting to finish my mods first.

I've always been happy with 1x gain on all of my mod configurations( DVB#3 and variants included)