[dhruvmeena96]

Just finished a set of universals using the RAB 32257 design by dhruvmeena and Choy Wei De. I wanted to build something inexpensive to use with a Bluetooth adapter while at the gym or climbing. This is only the second set of universals I've built. Previous builds include three iterations of customs with Knowles GV, one universal with GV for my girlfriend, and a B6 + zobel ciem that I'm currently working on.

I think these sound great for a sub-$100 build. Bass reproduction is lacking a bit and treble could use a bit more taming to prevent fatigue. Overall, the quality for price is amazing and the work put into the zobel and tubing (dhruvmeena & Choy Wei De) for this is very impressive.

Following Choy Wei De's post for the tubing didn't take much time at all and I was able to finish it within 20 minutes. The zobel took a bit longer just because I was working with 0805 & 1206 size parts. I used uv solder mask to protect the joints and prevent shorts when compressed into the very small shell. The shell I used was perfect for this build, which is nice because I couldn't fit anything larger into them.

I think they turned out pretty nice and I'll definitely feel more comfortable using them at the gym than my customs.

Question
What is that blue thing after zobel(in series to driver). If it is a resistor, please remove it. Any resistor will go in between zobel and mmcx(not in between driver and Zobel)

Suggestion
Use brown damper, white is for treble head.

Compliment
Best color scheme(blue foam tips) with blue shell. It looks sexy AF. And also blue gloves....

 

[wolkegeist]

I’m trying to build a dual RAB 32257 plus a sonion tweeter (E25ST001). I understand zobel for RAB but idk how to wire the tweeter. Any advices? And what is the length of tubing and damping I need for a balanced sound?

 

[dhruvmeena96]

I’m trying to build a dual RAB 32257 plus a sonion tweeter (E25ST001). I understand zobel for RAB but idk how to wire the tweeter. Any advices? And what is the length of tubing and damping I need for a balanced sound?

Hmmm
Since there is no zobel for EST.

They are going to share the zobel.

Zobel on MMCX according to RAB series or parallel.
(Series means inductance and resistance double, parallel means 1/2)

EST with 940nF cap(470nF cap parallel).

You gonna ask why not 1uF. Well you can go for that too, but this is the sweetspot I came with while testing value near 1uF on EST.

I think, its better to do RAB-p(green damper) + EST

That's gonna save 1 RAB, plus you would have a better extended response and mature tuning.

 

[wolkegeist]

Hmmm
Since there is no zobel for EST.

They are going to share the zobel.

Zobel on MMCX according to RAB series or parallel.
(Series means inductance and resistance double, parallel means 1/2)

EST with 940nF cap(470nF cap parallel).

You gonna ask why not 1uF. Well you can go for that too, but this is the sweetspot I came with while testing value near 1uF on EST.

I think, its better to do RAB-p(green damper) + EST

That's gonna save 1 RAB, plus you would have a better extended response and mature tuning.

Thanks for the advice!
Can you explain further about RAB-p?I made one RAB build before, but not with zobel, I put 10ohm resistor in series with RAB and green damper 10mm away from driver. So the sound is mid focus, but I want more treb and bass so I think I can wire another RAB as woofer and EST as tweeter.
LIKE this?

 

[Caluub]

Question
What is that blue thing after zobel(in series to driver). If it is a resistor, please remove it. Any resistor will go in between zobel and mmcx(not in between driver and Zobel)

Suggestion
Use brown damper, white is for treble head.

Compliment
Best color scheme(blue foam tips) with blue shell. It looks sexy AF. And also blue gloves....

It is a 20ohm resistor that is green because of the solder mask. It was my understanding that it should be there. Are you suggesting that I should move it so that it is on the positive leg of the mmcx but before the zobel instead of after? Or do you suggest that I remove the resistor entirely?

I will try brown dampeners. Also, would you suggest removing the tape from the vent in the driver?

 

[dhruvmeena96]

Thanks for the advice!
Can you explain further about RAB-p?I made one RAB build before, but not with zobel, I put 10ohm resistor in series with RAB and green damper 10mm away from driver. So the sound is mid focus, but I want more treb and bass so I think I can wire another RAB as woofer and EST as tweeter.
LIKE this?

Wire a zobel circuit on the + and - of MMCX(parallel to circuit)

RAB-p is resonator + horn + zobel + brown damper
I think I have mentioned it somewhere in thread

 

[dhruvmeena96]

It is a 20ohm resistor that is green because of the solder mask. It was my understanding that it should be there. Are you suggesting that I should move it so that it is on the positive leg of the mmcx but before the zobel instead of after? Or do you suggest that I remove the resistor entirely?

I will try brown dampeners. Also, would you suggest removing the tape from the vent in the driver?

You mean to add the 20ohm to driver before it hit zobel

Which changes the Q factor of driver for Zobel to work effectively.

You driver will turn 42ohm DCR

And the zobel is made for 22ohm DCR.

Shift the resistor on mmcx leg

Mmcx - resistor - zobel - driver

 

[Caluub]

You mean to add the 20ohm to driver before it hit zobel

Which changes the Q factor of driver for Zobel to work effectively.

You driver will turn 42ohm DCR

And the zobel is made for 22ohm DCR.

Shift the resistor on mmcx leg

Mmcx - resistor - zobel - driver

Okay, I will move it. Should the tape be left on the driver vent?

 

[dhruvmeena96]

Okay, I will move it. Should the tape be left on the driver vent?

Your choice
RAB32257 distort less than RAB32033
But when you remove tape, it distorts higher than 32033 while mimicking it


Well,I think, you should remove the resistor all together actually, if you find the response brighter.

If you want to really add, then add 10ohms only. Resistor in series was used for crossover purposes to damp the impedance and bass curve

And change to brown damper.

 

[wolkegeist]

Hmmm

EST with 940nF cap(470nF cap parallel).

You gonna ask why not 1uF. Well you can go for that too, but this is the sweetspot I came with while testing value near 1uF on EST.

You mean 940nF cap parallel to EST or series?
BTW do you have any suggestion on EST damping or tubing?
Thanks in advance!

 

[dhruvmeena96]

You mean 940nF cap parallel to EST or series?
BTW do you have any suggestion on EST damping or tubing?
Thanks in advance!

Series

EST is capacitor and tweeter high pass happens when you use series cap

If using RAB-p design

Take the half or double the amount of tubing length
1mm ID(because RAB-p is with horn, so compensate ID of EST, we have to go smaller dia....dont worry about roll off due to smaller ID tubing, as EST doesnt have roll off....so smaller ID effect will be negligible)

Recommended is double for sparkle and airy treble

 

[Caluub]

You mean to add the 20ohm to driver before it hit zobel

Which changes the Q factor of driver for Zobel to work effectively.

You driver will turn 42ohm DCR

And the zobel is made for 22ohm DCR.

Shift the resistor on mmcx leg

Mmcx - resistor - zobel - driver

Moved the resistor as recommended. I seem to be getting much better quality now. Next I will try with a brown dampener instead of white.

 

[Caluub]

Update: brown resistor is slightly better. You really have to be focusing on a difference to notice. Slightly warmer, less fatiguing.

 

[dhruvmeena96]

Update: brown resistor is slightly better. You really have to be focusing on a difference to notice. Slightly warmer, less fatiguing.

I think it is smooth enough and not at all fatiguing. But everyone eardrums and canal react differently.

Brown damper had a purpose when we finalised it. White damper had least impact on treble(grey and white were acting same on HF, even though white damped the 3kHz region more than grey) while green was killing our top end extension. 8kHz to 11kHz sacrifice was there in brown, but was not killing response like green.

Remove the 20ohms series resistor, so that you can make t less brighter


The series resistor only goes in when its worked with other drivers

 

[Caluub]

I think it is smooth enough and not at all fatiguing. But everyone eardrums and canal react differently.

Brown damper had a purpose when we finalised it. White damper had least impact on treble(grey and white were acting same on HF, even though white damped the 3kHz region more than grey) while green was killing our top end extension. 8kHz to 11kHz sacrifice was there in brown, but was not killing response like green.

Remove the 20ohms series resistor, so that you can make t less brighter


The series resistor only goes in when its worked with other drivers

Will removing the series resistor increase response in mids?

EDIT: Removed the resistor. After removing I enjoyed it more with the white dampener than the brown.