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Small 2-way speakers with linear on-axis and power response characteristics (Scan Speak and SB Acoustics drivers). H&V off-axis measurements included

I like that idea. What is the part number for the normal face-plate version? I can't seem to find it.

You can pour a flat baffle with a horn shape easy with an open 1-peice mold. An open mold also means don't have to vent it and you can shake the bubbles out of it easily.

I was thinking of this one https://www.scan-speak.dk/product/d2606-920000/

But it's maybe not the same driver, it was a very wild guess based on the name of it, probably better to have the correct one to take measurements of the horn etc.

Would love to see what you come up with.
 
I was thinking of this one https://www.scan-speak.dk/product/d2606-920000/

But it's maybe not the same driver, it was a very wild guess based on the name of it, probably better to have the correct one to take measurements of the horn etc.

Would love to see what you come up with.

The more I look at it mechanically the more it looks like the same driver but with different flanges on the top. The spec difference must be entirely due to acoustic changes from the wave guide. All that said it's somehow cheaper with the wave guide in it.
 
Another one in process, pcb design from @wineds. All componens from soundimports.eu :)

 

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Another one in process, pcb design from @wineds. All componens from soundimports.eu :)

Those cabinets look great, nice work!

You’re a bit ahead of me. I’ve got all the parts, and x-over assembled (also using @wineds board design).

I haven’t had a chance to start on the cabinet yet and waiting on the little PCB lugs to get here from the UK - lol.

Did you use a router /circle jig for cut outs?

IMG_6510.jpeg
 
Those cabinets look great, nice work!

You’re a bit ahead of me. I’ve got all the parts, and x-over assembled (also using @wineds board design).

I haven’t had a chance to start on the cabinet yet and waiting on the little PCB lugs to get here from the UK - lol.

Did you use a router /circle jig for cut outs?

Nope i used CNC :)
Btw. i created pcb mount if you have 3d printer and some M3 5mm heat inserts (3mf in mechano23-xover-mount.zip). I recommend to use foam sound dampening touching the pcb to eliminate vibration transmitted to the pcb.

I already put them together without sound sound dampening (waiting for order) and the sounds good but vocals are somehow very directional (almost hollow like). Its little bit strange. Maybe it will help sound dampening or i made mistake somewhere.
 

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Nope i used CNC :)
Very nice! I don’t have one those, unfortunately- lol. (Wish I did though!!)

Agree on foam under the PCB, I did that on the c-notes I built and it seemed to work well. I like the PCB mount, that’s sweet!

For the dampening, any thoughts on best placement? I was thinking 1/2 or 1” foam on the bottom, back, and 1/2 way up the side walls..? (Sonic barrier from PE).
 
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Inspired by the purifi blog post on reducing THD (link) I did some experiments with the crossover.

The new traps
traps.jpg
(4.7uF,0.11mH/0.14ohm, 47ohm)

The test interface: two pairs of wires per cabinet, one is to insert the new trap (parallel resonance circuit in series with the midwoofer) and the other pair is for switching on and off the original trap (opens or connects the 0.82uF cap branch). Interface holes drilled in the least visible place, i.e. in the bottom panel. After the tests they will be filled with epoxy.
test_ifc.jpg


Impact on the system spl: +-0.5dB from the original characteristic (green). The lower curve: both traps enabled, the higher curve: only new trap enabled.
spl.jpg
(5dB/div)

Finally, the impact on THD. The 2.3kHz THD peak was attenuated by 5dB so THD was reduced by almost half. With the new trap it's 0.8% 87dB. (In the original article the reduction was about 10 dB)
thd.jpg
(5dB/div)
 
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I already put them together without sound sound dampening (waiting for order) and the sounds good but vocals are somehow very directional (almost hollow like). Its little bit strange. Maybe it will help sound dampening or i made mistake somewhere.
While you wait for your damping there are a couple of things you may want to check to make sure you don't have a cabinet leak or standing wave issues inside the cabinet:
1) Did you add a gasket to the tweeter? My tweeter was supplied without a gasket so I had to buy some speaker gasket tape for the tweeter, making sure that it also covered the side holes I had to make for the tweeter terminals to fit through the baffle
2) Although plastic would not be my first choice of material for crossover boards (I used 6mm mdf), you may want to consider rubber grommets rather than foam to isolate them (stronger and more robust). Rubber grommets screwed down into the base at each corner should help mitigate any board vibrations
3) I have mentioned in a previous post the lack of current research regarding speaker damping materials, but what seems to be generally accepted is that natural materials with complex fiber structures (natural wool, denim, felt etc.) are better than artificial fibers (polyester, foam, rubber) at absorbing standing waves inside speakers. You may want to experiment with this.
4) Damping should be placed on all internal walls except the baffle and the floor (if the crossover is placed there). it's particularly important that the rear wall is fully covered (with cutouts for the port and speaker terminals).

Further details in the assembly instructions at the bottom of this page: https://nbaudio.com.au/blogs/projects/customer-project-mechano-23
 
While you wait for your damping there are a couple of things you may want to check to make sure you don't have a cabinet leak or standing wave issues inside the cabinet:
1) Did you add a gasket to the tweeter? My tweeter was supplied without a gasket so I had to buy some speaker gasket tape for the tweeter, making sure that it also covered the side holes I had to make for the tweeter terminals to fit through the baffle
2) Although plastic would not be my first choice of material for crossover boards (I used 6mm mdf), you may want to consider rubber grommets rather than foam to isolate them (stronger and more robust). Rubber grommets screwed down into the base at each corner should help mitigate any board vibrations
3) I have mentioned in a previous post the lack of current research regarding speaker damping materials, but what seems to be generally accepted is that natural materials with complex fiber structures (natural wool, denim, felt etc.) are better than artificial fibers (polyester, foam, rubber) at absorbing standing waves inside speakers. You may want to experiment with this.
4) Damping should be placed on all internal walls except the baffle and the floor (if the crossover is placed there). it's particularly important that the rear wall is fully covered (with cutouts for the port and speaker terminals).

Further details in the assembly instructions at the bottom of this page: https://nbaudio.com.au/blogs/projects/customer-project-mechano-23
Thanks. Yes looks like reflections in cabinet were cause of the problem. After dampening they sound good :)
 

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Inspired by the purifi blog post on reducing THD (link) I did some experiments with the crossover.

The new traps
View attachment 425673(4.7uF,0.11mH/0.14ohm, 47ohm)

The test interface: two pairs of wires per cabinet, one is to insert the new trap (parallel resonance circuit in series with the midwoofer) and the other pair is for switching on and off the original trap (opens or connects the 0.82uF cap branch). Interface holes drilled in the least visible place, i.e. in the bottom panel. After the tests they will be filled with epoxy.
View attachment 425671

Impact on the system spl: +-0.5dB from the original characteristic (green). The lower curve: both traps enabled, the higher curve: only new trap enabled.
View attachment 425670 (5dB/div)

Finally, the impact on THD. The 2.3kHz THD peak was attenuated by 5dB so THD was reduced by almost half. With the new trap it's 0.8% 87dB. (In the original article the reduction was about 10 dB)
View attachment 425672(5dB/div)

Looks great. So this will be the new crossover design going forward?
 
Looks great. So this will be the new crossover design going forward?
This is nothing new, exactly such absorption circuits, parallel circuits of capacitor, coil and resistor, were published by Bernd Timmermanns in the 90s for various loudspeakers for tweeters and midrange speakers, also for later modifications of existing loudspeakers.
 
Looks great. So this will be the new crossover design going forward?
Also looks like simple modification. Just adding this trap circuit between WT+ and speaker terminal. If Im not mistaken.
 
Btw. any recommendation for project with coaxial driver and subwoofer driver ? :)
 
I just trimmed the soldered leads and made sure I only had cable tie joins on the component side. Then just screwed it to the back panel with self tapping screws. But you could use a mount if you wish.
Thanks for the reply.
 
Better to screw it to the base (if it fits) and put damping on the back panel where it can best absorb rear waves from the woofer.
Is there any risk of interference from the back of the mid-woofer magnet? vs mounting it on the rear panel?
 
Is there any risk of interference from the back of the mid-woofer magnet? vs mounting it on the rear panel?
In terms of electromagnetic interference between crossover and woofer, the risk is low - there are a few forum threads on this topic such as this one:


In terms of physical interference, you want to make sure no crossover components touch the rear of the woofer, so you may need to anchor the board towards the back of the floor rather than the front. In our case we turned the board around 180 degrees (with longer connections to the terminals) to give plenty of room for the board. Damping the rear wall is the most important consideration though (in my view) and the sound of our speakers is excellent.
 
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