New 3-way Speaker Build has finally started.

[surprisetech]

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.

 

 

 

[Cardiiiii]

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

[surprisetech]

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.

[surprisetech]

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.

[surprisetech]

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!

 

[BioBrian]

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.

[surprisetech]

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.

[surprisetech]

Boxes ready for pickup tomorrow night.

[surprisetech]

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.

[surprisetech]

Picture of the midrange chamber installed in the box.

 

Edited September 11, 2017 by surprisetech

[surprisetech]

So; I should have been listening to these last night, but my plans came unstuck while I was checking the crossover wiring with the multi-meter before the speakers were connected.

When I was building the crossovers, the barrel of the soldering iron briefly touched one of the poly caps.  It only left a small mark on the cap, so I didn't worry about checking it then, but turns out it turned the cap into a 28.3 Ohm resistor!

Replacement ordered from LSK last night, so hopefully can replace during the week and have them ready for the weekend.

 

DIYer warning.  The Dayton poly caps are great value, but do appear to have a thin skin, so be careful when soldering.

***

[surprisetech]

On a brighter note, the finished assembly is looking pretty good.

Will be working on some grilles next.  The sloping baffle and the protruding surrounds on the mid & woofer probably expose the drivers to a higher risk of damage and more dust, so I'm going to make some grilles that don't interfere with the appearance too much and can be easily removed for serious listening.

 

[Guest]

Excellent DIY there !

Nice work with the butyl Car Body Deadner there Mate, I know of another high quality bass unit made from ply that could do with a liner of that stuff @BioBrian

[surprisetech]

10 minutes ago, 125dBmonster said:

Excellent DIY there !

Nice work with the butyl Car Body Deadner there Mate, I know of another high quality bass unit made from ply that could do with a liner of that stuff @BioBrian

Thanks.

The sound deadener helps, but good bracing is still very important.

[Guest]

No worries, would be lovely to listen to, excellent build

 

Have found over time with ply even the tightest boxes, usually larger 100 liter sealed ones will sometimes "ring" a little on final testing and the butyl rubber totally fixes all that.

 I hope you get hundreds or more hours of listening pleasure from them

 

matt

 

[Swarm]

Looks darn good

[Cardiiiii]

Well done! Looks amazing!

[BioBrian]

Eagerly awaiting further reporting, we can handle it...

[surprisetech]

On 15/10/2017 at 8:49 PM, Cardiiiii said:

Well done! Looks amazing!

 

On 14/10/2017 at 2:54 PM, Swarm said:

Looks darn good

 

On 11/09/2017 at 2:53 PM, 125dBmonster said:

No worries, would be lovely to listen to, excellent build

 

Have found over time with ply even the tightest boxes, usually larger 100 liter sealed ones will sometimes "ring" a little on final testing and the butyl rubber totally fixes all that.

 I hope you get hundreds or more hours of listening pleasure from them

 

matt

 

 

On 15/10/2017 at 9:05 PM, BioBrian said:

Eagerly awaiting further reporting, we can handle it...

 

Thanks guys.

Fine tuning has stalled at the moment - got busy with cleaning up the block, some family stuff and needed to put in some extra time at work.

 

However, I can report that while I'm already very happy overall, I'm really pleased with the bottom end.  The big rigid box is paying dividends.  I've always preferred a single large woofer to smaller bass driver arrays. 

I know the quality of smaller bass drivers has come a long way in the last couple of decades, but I still suspect that it's mainly aesthetics that pushes most manufacturers to go with multiple smaller woofers rather than a single large driver.

Fortunately, my wife grew up in a home with transmission line speakers, so has understood the need for big boxes from any early age!!

(Fun fact:  Sd (effective cone area) of one 12" driver = 2.5  8 inch drivers = 4.5  6 1/2 inch drivers.)

 

The mids are definitely portraying a more natural timbre and imaging seems much better.  I am noticing though that the upper-mids dominate on a fair bit of material, so I'll need to look into that.

 

 

[surprisetech]

Well 2018 was a pretty hectic year with my parents transitioning to care and a few other challenges, so not as much happened on the DIY front as I had hoped.

However, I finally got back to fine-tuning these speakers over the Christmas break.

 

There was a hump in the upper midrange that was obvious in measurements and noticeable on some types of music.

Problem was my 2nd order midrange low-pass filter was not adequate to suppress the rise in the driver's response from 3.5kHz to 9kHz (see pic) leaving the mid with an almost flat response up to about 8kHz instead of the intended 2.5kHz, which when combined with the tweeters response, produced the hump and no doubt other interactions as well.

 

Rather than mess around with a notch filter I decided to go to 4th order filters for the mid-tweeter crossover.

Looking at the mid's impedance curve I also decided that the zobel network on this driver was unnecessary and may have also been contributing slightly to the problem.

Mid and Tweeter with the 4th order 2.5kHz filters are now wired in phase and woofer is wired in reverse as the Woofer-Mid 350Hz filters are still 2nd order.

Owing to the values I needed, I had to order my bits from Hifi Collective in the UK this time.  Very happy with the service, postage costs and delivery time.  Prefer to use Speakerbug or LSK if I can, but in this case neither had the range of inductor values that I needed.

 

With 4 extra components I then had to spend some time sketching layout options to make sure the chokes could be positioned and oriented correctly to minimise interactions.  End result is pictured.

 

So the hump is now gone and listening to NY & Crazy Horse, Roy Buchanan, etc. doesn't grow fatiguing any more.

I'm also certain that the stereo imaging and soundstage have improved.  Instruments that seemed to move around a little with pitch are now more stable.

[BioBrian]

I'm curious about how you decided upon cap and coil values, and why a 2nd order filter couldn't work for your mid (did you try a series cap/resistor across the low-pass coil?).

 

Personally, I would have chosen a larger mid, for possibly more comfortable crossover to both the woofer and tweeter.

 

If you feel like sharing, I'd love to hear more about your design process. Sure others would, too.

 

Sorry to hear about the distractive year - know the feeling well! (I also had father issues).

 

Thanks for your fascinating update.

[surprisetech]

15 hours ago, BioBrian said:

I'm curious about how you decided upon cap and coil values, and why a 2nd order filter couldn't work for your mid (did you try a series cap/resistor across the low-pass coil?).

 

Personally, I would have chosen a larger mid, for possibly more comfortable crossover to both the woofer and tweeter.

 

If you feel like sharing, I'd love to hear more about your design process. Sure others would, too.

 

Sorry to hear about the distractive year - know the feeling well! (I also had father issues).

 

Thanks for your fascinating update.

Yes, happy to share my reasoning.  Every choice has it's pros and cons.

I went with this particular mid for a couple of reasons:

- It has extremely good off-axis response right across the pass-band that I wanted (and beyond).  I take particular note of 30deg off-axis response curves, as that is closest to the angle at which we do most of our listening. (unless using toe-in).  When originally researching midrange drivers I was surprised to see how many start to fall away soon after 1kHz on their 30deg response.

- Being primarily designed as a compact mid-woofer, it has very low Fs for its size, decent power handling and very similar sensitivity to the woofer.  Since I wanted a fairly low 350Hz crossover point, this all made for an extremely comfortable transition to the woofer using 2nd order filters.  Larger drivers that I looked at generally had higher efficiency and would have required attenuation.

- It has low inductance and an extremely tame impedance curve which is good for the crossover to the tweeter.

- It has very low distortion even at higher listening levels.

 

The only downside with this choice (AFAIK!) is that rise in the response above 3.5kHz that you can see in the driver response graph in yesterdays post.  Even in the 30deg curve, the peak at around 5.7kHz is 5dB above the level at 2k.  So up to that point, the 2nd order filter was merely flattening that peak rather than providing 6dB of cut.

I thought about filtering out the peak, but figured the cleanest solution with the most predictable results was to change the Mid low-pass and Tweeter high-pass filters to 4th order.  Values were obtained from the calculator on the mh-audio website which allows a good range of variables to be entered.

[Nickelle]

Great speakers, i built my Dallas 2's many years ago now, i dont even know where they are but i hope they are still performing well. They did not get as far as the Birch timber finish solution. I built them for a friend and the idea was to get them sprayed in an autoshop in black, they would have lost some of their visible bulk then i am sure. But they were sold on straight away, you definately need a partner with musical appreciation for these monsters. Built to exact Dallas 2 specification, I did fill the voids with catty litter at the top and river sand at the bottom, sealed in plastic bags.

 

 Nearly finished, cd for scale.

 

Plans.

[surprisetech]

4 hours ago, Nickelle said:

Great speakers, i built my Dallas 2's many years ago now, i dont even know where they are but i hope they are still performing well. They did not get as far as the Birch timber finish solution. I built them for a friend and the idea was to get them sprayed in an autoshop in black, they would have lost some of their visible bulk then i am sure. But they were sold on straight away, you definately need a partner with musical appreciation for these monsters. Built to exact Dallas 2 specification, I did fill the voids with catty litter at the top and river sand at the bottom, sealed in plastic bags.

 Nearly finished, cd for scale.

 

Thanks.  The Dallas 2s came up really nice.  There's some complex woodworking in that design.

My partner is very understanding.  Her dad was into his hifi and his Silcron Transmission Line Speakers are now in my 2nd system.

Her hobby is horse riding, so I also get some leeway because you can guess which of our hobbies impacts our lives the most!!