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DIY inspired Buchardt S400 – Crossover design


Major Contributor
Forum Donor
Jun 5, 2020
8 ohm is standard, 4 ohm is for specific driver arrangements as necessary. Most amps don't like lower ohm ratings and thus the standard.
The Buchardt speakers use the 4 ohm drivers.

Thomas Rainer

New Member
Jul 23, 2022
Dear all,

After hours of reading on the web and especially on the ASR forum, I’m finally decided to start designing my first DIY speakers.
Initially I wanted to start with a tower speakers but I reconsidered my plan by first trying to take experiance first with a 2 Way Bookshelf speaker.

This project will be not very original as I want to make an inspired version of the Buschardt audio S400.

In that regard, I was planning to use :
-SB17NBAC for the woofer ;
-SB26STAC for the tweeter with a 3D printed wave guide ;
-SB15SFCR for the passive radiator.

The woofer SB17NBAC as an Sd of 118cm² and a Xmax of 7.17mm (so 84.6cm^3 of displaced volume)
The passive radiator as a Sd of 178cm² and à Xmax of 11mm (so 195.8cm^3 of displaced volume)
So the passive radiator can displaced 2.3 time the air volume of the woofer which looks in the rules.

I was planning to use a 18L box and tried to simulate that in WinISD and it look like I could obtain a 50hz low at -3db.
So first, what do you think of this driver selection ?

Then come the hard part for me as I have no skills in crossover design and I know it have a huge rôle in the final result (I only know how to read a crossover schematic and good at welding components)
By looking at the frequency response of the drivers, I was thinking of using a crossover point somwhere beetween 1500 and 1800hz.
View attachment 199150
View attachment 199151

This leads me to ask you few questions :
-How do you select the nominal speakers impedance as the woofer is available in 4 and 8 ohm ?
-Does a generic crossover always lead to a bad result ?
-Is there any active crossover module that can be used with numerical output for 2 FDA « budget » amplifier ? ;
-Othrewise, where to start from and which software do you recommand for passive crossover design ? (Go back to school is an acceptable answer ;-) ;

I also plan to order a UMIK-1 as I know it will be necessary to adjust parameters in every cases.

Thanks !
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