Bohlender Graebener RD50 transducers advice

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Juhazi

Juhazi

Member
Joined 2007
Electric and acoustic response are very different. I guess someone here can give a suggestion by simulation in VCAD2.
First try to find datasheets of your drivers, with T/S parameters and axial response graph. Also tell dimensions of the intended baffle and position of the RD in it.
 
kmj

kmj

Member
Joined 2004
My intent is just to make a box/baffle out of what I have in the garage and a box for the woofer somewhere close to the dimensions needed. Since I havn't heard anything like these drivers or an amplifier with power enough I just want something approximately close to try them out.
Cheap box or baffle from old closet doors and cheaper crossover parts.
 
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M

metzb1

Member
Joined 2010
kmj said:
My intent is just to make a box/baffle out of what I have in the garage and a box for the woofer somewhere close to the dimensions needed. Since I havn't heard anything like these drivers or an amplifier with power enough I just want something approximately close to try them out.
Cheap box or baffle from old closet doors and cheaper crossover parts.
Click to expand...
That sounds like a good plan. Looking forward to hearing your impressions of them. They are somehow special in my opinion.
 
kmj

kmj

Member
Joined 2004
That sounds like a good plan. Looking forward to hearing your impressions of them. They are somehow special in my opinion.
Click to expand...

I have parts for some different amplifiers but to get something quick I decided to just make two pairs of LM4780 for a 4-channel amplifier and I got a soundcard from a friend that should enable me to use an old laptop as music source and active filter.
Enough to run some tests.
 
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C

Calleberg

Member
Joined 2011
Just order a couple of 100uF Capacitors from Conrad.se for now. It's wise to have some caps in there anyway if you are planning on using a DSP for filtering. If you want to be slightly scientific when moving forward swap those out with an MKP capacitor (or a bipolar in parallell with an MKP) that has atleat some (2-3dB) attenuation at fs, since thats were excursion is going to be at it's maximum if things go south.
 
kmj

kmj

Member
Joined 2004
Calleberg said:
Just order a couple of 100uF Capacitors from Conrad.se for now. It's wise to have some caps in there anyway if you are planning on using a DSP for filtering. If you want to be slightly scientific when moving forward swap those out with an MKP capacitor (or a bipolar in parallell with an MKP) that has atleat some (2-3dB) attenuation at fs, since thats were excursion is going to be at it's maximum if things go south.
Click to expand...
Thanks!
 
kmj

kmj

Member
Joined 2004
Hello again.
I have made the decision to crossover at 1000Hz to a pair of 8" 4ohm drivers and I am looking at a 4th order crossover (see attached screenshot).
For the caps I have a bunch of 10uF caps that I'll put in parallell and then add smaller caps to get closer to the specified value.

When it comes to the coils I have a pair of the larger ones of 1.8mH (R=0.49) but also 4pcs of 0.68mH with R=0.71 (0.7mm diameter).

So, the question is regarding the wire thickness of the coils.
The info from BG states that the notch filter should have a coil with a thickness of 1mm.
Does this go for all coils in the crossover or could I use thinner somewhere (the 0.68mH I have at hand)?

Or thicker perhaps? received_1157803105365385.png
 
C

Calleberg

Member
Joined 2011
A generic filter of any kind is for the most part not going to give you a very good frequency response. But the further from the drivers own natural roll off the chosen crossover frequency is, the less terrible it will be. :) Use whatever coils you have, but add any series resistance of coils to the driver impedance. But have in mind it´s going to be far from perfect. and because of that, don´t spend time worrying over details, Just get it done the cheapest way possible.

Another thing that WILL affect the filter response are the drivers impedance curves, you can ignore that for now. Just be aware that your filter is going to be suboptimal at best.

This can all be fixed, but the only really good way to get there is to measure the actual summed response of what you have cobbled together and take it from there.
 
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kmj

kmj

Member
Joined 2004
Calleberg said:
A generic filter of any kind is for the most part not going to give you a very good frequency response. But the further from the drivers own natural roll off the chosen crossover frequency is, the less terrible it will be. :) Use whatever coils you have, but add any series resistance of coils to the driver impedance. But have in mind it´s going to be far from perfect. and because of that, don´t spend time worrying over details, Just get it done the cheapest way possible.

Another thing that WILL affect the filter response are the drivers impedance curves, you can ignore that for now. Just be aware that your filter is going to be suboptimal at best.

This can all be fixed, but the only really good way to get there is to measure the actual summed response of what you have cobbled together and take it from there.
Click to expand...
Thanks!
Just what I wanted to hear.
 
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