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DIY inspired Buchardt S400 – Crossover design

Chromatischism

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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

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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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Madslide

Madslide

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I had to make a short break in the project during the summer.
I will share my drawings at the end of the project only if I consider it is successful.

For now I'm staring the box construction. It's just a start and only 3 panels are currently sticked (I have to work on the inner "barrier").
 

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Madslide

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Few pictures of the prototype built. Cables are not the final ones but what I had on hand…

I started to make my crossover using the MiniDSP, but the current result is not really relevant as I did my measurement in room and it seems there is a lot of reflexion. Need to find time and space to do that with the adequate conditions. However, I'm already conquered by the sound of this speaker which seems to fill the whole room even though I only tested one.

Few questions:

What is the best SPL level I should focus on or I should work with for the crossover adjustment and why ?
On many response graphs I see an SPL level close to 85/90db as a target for the curve. It’s way too high level for an everyday listening so my thinking is, why do the crossover is adjusted so high whereas most of the people don’t listen that high. This question is also related to the non linear hearing humans a equipped. If the tunning is good at 85db, the result will be not in standard condition around 70db.

Is there any benefits to choose a an high crossover (2600/2800hz) versus a lower one (1800/2000hz).
I tried both and even if the response curve looks good, it’s way much detailed and accurate close to 2650 than with a lower value.

Any remarks or comments on my build are appreciated. It’s my first speakers so I may have done some mistakes.
 

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phrog

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Few pictures of the prototype built. Cables are not the final ones but what I had on hand…

I started to make my crossover using the MiniDSP, but the current result is not really relevant as I did my measurement in room and it seems there is a lot of reflexion. Need to find time and space to do that with the adequate conditions. However, I'm already conquered by the sound of this speaker which seems to fill the whole room even though I only tested one.

Few questions:

What is the best SPL level I should focus on or I should work with for the crossover adjustment and why ?
On many response graphs I see an SPL level close to 85/90db as a target for the curve. It’s way too high level for an everyday listening so my thinking is, why do the crossover is adjusted so high whereas most of the people don’t listen that high. This question is also related to the non linear hearing humans a equipped. If the tunning is good at 85db, the result will be not in standard condition around 70db.

Is there any benefits to choose a an high crossover (2600/2800hz) versus a lower one (1800/2000hz).
I tried both and even if the response curve looks good, it’s way much detailed and accurate close to 2650 than with a lower value.

Any remarks or comments on my build are appreciated. It’s my first speakers so I may have done some mistakes.
You can make quasi-anechoic measurements in-room using the method outlined in this thread. https://www.audiosciencereview.com/...ents-spinoramas-with-rew-and-vituixcad.21860/

For measurements, the only advantage to measuring at louder volumes is that it increases the signal-to-noise ratio. In a relatively quiet room, lower volumes should work just fine.

Picking the ideal crossover point is tricky, as there are a lot of things to consider.

1. The 6 inch woofer will start to beam around 2000ish Hz
2. The tweeter will have more distortion the lower it plays
3. The crossover frequency will affect the off-axis vertical response. Lowering the crossover frequency will widen the vertical range at which the response is good, but setting the crossover point such that the center-to-center spacing is 1.2 to 1.4 times the wavelength at the crossover will yield the most consistent vertical reflections. You can read more about that here. https://www.audiosciencereview.com/.../ctc-and-the-cea2034-spec.37277/#post-1311644
4. Probably some other things I forgot to mention

That waveguide looks really nice. I'm sure they'll sound great once you get the crossover done.
 

Paweł L

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Looks nice. I usually set the level at 2.83V (1W/8ohm) at the amp out which is the norm for frequency test at 1m distance, just to be compatible with others. The level would somewhere in the 85-90dB @1m for most woofers. The tweeter will be a few dB higher. As for the x-over point, lower may give better transition regrading directivity, but most tweeters like the higher point distortions wise. It depends how the two drivers transition from one another. Usually it's a compromise, especially with passive crossover design as the phase (time) alignment can't be delayed as with most active designs.
BTW, what drivers are you using? Is it the 8ohm version of 17NBAC or 4. The 26ADC in it's waveguide looks great
 
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Madslide

Madslide

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Thanks for the answers and advices.
So i'm using the 8ohm version of the NBAC.

I worked a little on the active crossover and here is the current result with the goal to follow the marginal line around 78db.
-Yellow line is the tweeter
-Orange line is the mid/bass woofer
-Red line is both without any EQ on the DSP
-Green line is after DSP EQ. I also added a 40hz high pass filter otherwise bass are too punchy for me.

I did not played yet with the inner plate position to check if and how it affect the response.
I'm open to any comment to see where I could make changes.
 

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Tangband

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Thanks for the answers and advices.
So i'm using the 8ohm version of the NBAC.

I worked a little on the active crossover and her is the current result with the goal to follow the marginal line around 78db.
-Yellow line is the tweeter
-Orange line is the mid/bass woofer
-Red line is both without any EQ on the DSP
-Green line is after DSP EQ. I also added a 40hz high pass filter otherwise bass are too punchy for me.

I did not played yet with the inner plate position to check if and how it affect the response.
I'm open to any comment to see where I could make changes.
Looks nice .
I would try a slightly lower dsp crossover , maybe everything from 1,7 KHz and go up to 3 KHz . The sound will be slightly different even if the frequency response looks the same. Theres always a tradeoff getting good directivity and low distortion . So in the end , you have to decide what sounds the best with music and ears.
You also have to tune the passive radiator with different weights . Try different and settle for the tuning that sounds best.

Use a 18 dB/oct dsp HP filter 5-10 Hz below the tuning frequency . This is very important for good sound .

In the Hybrid projekt , I also played with the tilt of the waveguide frequency response. 1 dB more energy at 10 KHz is audible . This is easily done with the dsp .
In this speaker the sound was the best with a crossover at 2,3 KHz , but the directivity measured best at 1,8 KHz .
The scanspeak ringradiator didnt like crossovers lower than 2 KHz .
8CE7AF85-52EA-4BD7-8AAD-414FC974CE04.jpeg
 
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Paweł L

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I used the 17NBAC-4 (Qts around 0.41 when it settled down) with the same passive rad in 17L box, stuffed with Dacron to avoid reflections, tuned to 34-35Hz. The bass is quite ... pronounced, I would say and very different in character from the old 17NRXC-4. I think HiFi Compass measured the 17NBAC-8 - beware of that 3kHz bump and cone break-ups past 4kHz.
As for the measurements, seems that your level is too low, or environment noise is too high. You should be able to measure the slopes another 20-40dB below your current level. I always put tick Dacron blanket on the floor between loudspeaker and microphone if I measure at home to absorb reflections - 1m MLS freq resp 17NBAC-4/Kartesian with passive X-O on the pict. Better results can be done with outside measurements: loudspeaker on top of 2m ladder, as they could be valid to 200-300Hz anechoic. With Ground measurements you can get pretty decent low frequency measurements. Don't worry about cranking the drivers past your current level if you can obtain more valid measurements.
 

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Chromatischism

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Looks nice .
I would try a slightly lower dsp crossover , maybe everything from 1,7 KHz and go up to 3 KHz . The sound will be slightly different even if the frequency response looks the same. Theres always a tradeoff getting good directivity and low distortion . So in the end , you have to decide what sounds the best with music and ears.
You also have to tune the passive radiator with different weights . Try different and settle for the tuning that sounds best.

Use a 18 dB/oct dsp HP filter 5-10 Hz below the tuning frequency . This is very important for good sound .

In the Hybrid projekt , I also played with the tilt of the waveguide frequency response. 1 dB more energy at 10 KHz is audible . This is easily done with the dsp .
In this speaker the sound was the best with a crossover at 2,3 KHz , but the directivity measured best at 1,8 KHz .
The scanspeak ringradiator didnt like crossovers lower than 2 KHz .
View attachment 233227
Nice looking speaker. Why was the ring radiator chosen?
 
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