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surprisetech

New 3-way Speaker Build has finally started.

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I've been planning to build a new 3-way pair from scratch for some time and it's finally happening.

 

The last upgrade I did on my main speakers was to increase the box size from 70 to 118 litres by adding plinths to the bottom of the existing enclosures, replacing the 10" bass drivers with 12" Peerless 830669's, fitting appropriate ports and rebuilding the crossovers.  I've been really happy with the results, but always planned to upgrade the aging mids & tweeters and build new enclosures from scratch with better materials and a really nice finish.

 

I've been really happy with the Peerless woofers, so they are being re-used.  

Did quite a bit of research into mids & tweeters that would match with the 830669s and with each other, and finally settled on SB Acoustics SB15NRXC30-4 5" Mid-Bass drivers and SB26ADC-C000-4 Tweeters.

They're both a very good match for the woofer in efficiency and both have really good off-axis response in the bands they will be operating in.

I also picked the SB15NRXC30-4 because it has an Fs of 41 Hz.  This allows me to have a fairly low woofer-mid crossover of 350Hz, so that each of the 3 drivers will only be responsible for about 3 to 4 octaves.  I'm looking at a mid-tweeter crossover of 2800Hz, so all 3 drivers will only be operating well within their comfort zone.

 

The new enclosure will be 130L front-ported and the midrange driver will have its own 3L chamber behind it that I'm making up out of heavily damped poly pipe.

 

I don't really have the time or tools to build the boxes as well as I would like, so have got a custom furniture builder doing it for me.  Should be picking up the semi-assembled boxes soon to do the internal treatments.

 

 

 

SBNRXC30-4.jpg

SB26ADC-C000-4.jpg

830669front and back.jpg

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Do you have any illustrations as to what the final speaker will look like?

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20 hours ago, Cardiiiii said:

Do you have any illustrations as to what the final speaker will look like?

 

Yes. I had to do very detailed drawings for the cabinet maker.

Material is 18mm furniture grade birch ply.

Photo is from the maker when the basic assembly was done and before he started on rounding the edges, bracing, etc.

Front and Side.jpg

IMG_8575(2).jpg

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Crossovers (Mark 1) were built a couple of months ago.

I've chosen to go with 2nd order slopes all round to start with and have included Zobel networks for the woofer & mid.

(It's OK, the solitary bi-polar electro is only in a zobel network)

No doubt there will be some changes when I can start testing.

 

Once I'd chosen to go with the 350Hz bass-mid crossover, sourcing the choke for the woofer was an interesting exercise.  The Jantzen C-Coil finished up being my best option to keep the DCR to an absolute minimum and eliminate any chance of saturation without breaking the bank.  I can see why so few commercial 3-way designs crossover this low!

 

The plan is to embed this enclosure into the back of the speaker box so that the crossover components will be accessible for mods by just taking its lid off.  i.e. without needing to open up the speaker box.  This should make fine-tuning the crossover and doing measurements much easier.

Crossover Mk1.jpg

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The midrange chambers are ready.  I had a few different ideas of how to approach this and although the technique I settled on might be amusing, I think it should be effective.  It's a little over 3 litres which according to WinISD would give me a flat response to more than an octave below my crossover frequency. So plenty of margin there.

 

Due to the close proximity of the chamber walls to the driver in a midrange enclosure, and the chamber itself being inside a speaker box, I wanted rounded surfaces throughout.

So I used a length of 150mm diameter stormwater pipe, a melamine bowl and a 75mm end cap all glued together with polyurethane adhesive after preparing the mating surfaces with coarse sandpaper.

 

Outside is covered in Car Builders Sound Deadener to make it non-resonant and the inside is lined with thick felt at the rear and thinner felt around the sides to kill off internal reflections.  I'll add some polyester fill when doing the final assembly.

 

I'm planning to use liquid nails or the polyurethane adhesive to attach them to the back of the baffle and provide a complete seal, in conjunction with a couple of small L brackets to make sure they are centred over the midrange cutouts.

 

Creative and/or comic comments all welcome!

 

Mid chamber Final_8462(2).jpg

Mid chamber Final-internal_8464(2).jpg

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Ha, very good! Just don't try taking them on a plane.

 

Can you see the colour coding from outside the speaker? Oh, and is red for driver +, or crossover +?

 

I'd be flattered to be one of your mids.

 

I'm more worried about the thickness of your panels, especially the baffle. Hope you use lots of bracing.

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15 hours ago, BioBrian said:

Ha, very good! Just don't try taking them on a plane.

 

Can you see the colour coding from outside the speaker? Oh, and is red for driver +, or crossover +?

 

I'd be flattered to be one of your mids.

 

I'm more worried about the thickness of your panels, especially the baffle. Hope you use lots of bracing.

 

Thanks Brian.  All good points.  

I'll be wiring the mids with care and will be treating the terminals on the back of the chamber as the speaker terminals (red for driver +).

 

As for panel thickness/stiffness.  I'm fairly confident I have this covered, but I do have a contingency plan.

The choice (and extra expense) of the birch ply gives me the stiffness of 25mm MDF, but without the weight. (And a nicer finish)

All the panels are biscuit-jointed and also have battens on all the insides of the joints.  The panel shapes and the narrower widths at the top should also help.

Yes, there will be lots of bracing done with more of the 18mm birch ply and I've still got 10 sheets of the Sound Deadener to install on the insides of the panels as well as a thick dense felt.

 

The contingency plan is that the design allows me to glue an additional layer of the ply to the back of the baffle if necessary.

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Was able to make some progress on the weekend.  

The crossover enclosures are now embedded into the removable section of the rear panel with PU glue, so no chance of air gaps.

Inside surfaces of these panels including the back of the crossover box have the adhesive bitumen pads and 10mm felt.

Wiring from the crossover to the inside of the box will go via the IP68 rated cable gland.  Might add a little silicone just to be sure before I tighten the gland.

 

Having found the odd insect or spider inside speaker boxes over the years, I also vermin-proofed the Port tubes with some grille cloth.

 

The midrange chambers and ports are installed (PU glue again) and I did add another layer of ply on the back of the baffle around the woofer.

11a-Crossover in rear panel-1.jpg

11a-Crossover in rear panel-2.jpg

12a-Port Tubes2.jpg

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Picture of the midrange chamber installed in the box.

 

14-Mid Chamber Installed2LR.jpg

Edited by surprisetech

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