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Multi-Way Conventional loudspeakers with crossovers

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Old 11th August 2007, 11:28 PM   #1
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Default Construction journey-Active 3-way

It begins last December...

I have finished my sealed, Linkwitz transformed subwoofer a few months before. I love the bass it provides - clean, solid, no boom.

The one problem is that my main speakers, built 3 years ago, are transmission line. On their own they have very good bass, nice and tight, smooth, controlled. Combined with the sealed EQ'ed sub, there is an overlap/cancellation problem. Phase the sub one way, bass production is reduced. Phased the opposite way, bass is annoyingly increased, muddy, incoherent.
I tried moving the sub to different locations, but due to it's size, I don't have many options for room placement.

So, I decide the best thing is to build a new pair of sealed speakers - three way and make them actively driven to boot.

I have built a few speakers, and I am not a fan of the rectangular box, plain and simple types. I prefer to make it architecturally interesting, it should look stunning and sound sublime.

For inspiration, I looked to Reference 3A. Their L'Integral Nouveau is a speaker design that I admire, with its graceful curved baffle with contrasting colour to the body.
I decide this will be what my new speakers will look like.
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Old 12th August 2007, 12:24 AM   #2
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Typically, I work without plans, just a rough idea of how I want it to be. Most times this works.

I start with a sheet and a half of 5/8" MDF. This is enough to get all of the pieces for both speakers.

Cut and assemble the body, which has a divider between the woofer chamber and the midrange/tweeter chamber.

Cut the pieces for the baffles. The baffles are 2 layers of MDF, the first is glued, clamped and screwed to the body (as shown in picture below). Given the fairly gradual bend, I felt confident that the MDF would bend without resorting to kerf cuts.

My plan is to build the speaker, finish the baffle in high gloss piano black, then add a layer of 1/2" maple veneer particle board to the body with silicone rubber as the adhesive. This would be my version of CLD and also give the contrast in finish that I am looking for.
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Old 12th August 2007, 12:32 AM   #3
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Here's a shot of the back. The body is put together with yellow carpenters glue and 16 gauge 1 3/4" airgun nails.

Other than the divider between the woofer and midrange, there is no internal bracing. The widest span is near the bottom of the body on the sides where it is ~11".
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Old 12th August 2007, 01:26 AM   #4
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As I said, I don't work from plans. That comes back to bite me is the ***, when I locate the divider a little too close to where the midrange is (as seen in the picture). I need to carve out some material to accommodate the big magnet on the driver.

The drivers are:
-Seas CA21REX08. Good ~90dB efficiency, low Fs (31) and a Qts suitable for sealed enclosure.

-Max Fidelity pro411m8. I don't have much information on these midranges, and I have emailed a slacker at Max for specs, but haven't heard anything. My testing shows Fs at ~110Hz. Efficiency is up there, as this is a pro driver, perhaps at 95-96dB.
In the end it's how it sounds, and this sounds good, very clean, detailed midrange.

-Scanspeak D2905/9300. Silk dome, 90dB efficiency. Very nice sounding tweeter.

Picture quality: my camera, when it's in the mood, can add accents to make things interesting (white spots).
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Old 12th August 2007, 02:06 AM   #5
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These speakers will be driver by active crossover amps as detailed in this thread:

Active filter plus LM3886 - one board

Using passive crossovers for every speaker up till now, I'm tired of all the tedious work involved with getting it right. I always wind up with a crossover that is more complex than I wanted it to be, losing efficiency along the way. Dynamic range also seems to suffer from too complex filters.
My choice of DIY active filters and amps adds a hugh level of complexity to the project, but I believe it will be worth the extra effort.

The crossover frequencies are at 310Hz and 3100Hz and the filters have a 4th order (24dB per octave) slope. They are a Linkwitz-Riley alignment, giving flat response in the crossover region.

Anyhow, not to waste a post without a picture, here's the backside of the speaker:
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Old 12th August 2007, 02:52 AM   #6
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Those are gorgeous looking speakers and should sound at least as gorgeous! Please keep us informed as the build progresses. I have not seen the References before and they are very clean, simple, and somewhat organic - great platform to follow.
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Old 12th August 2007, 03:14 AM   #7
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Hi sdclc126,
Thanks for the compliments.

I am playing catch-up with this build as much of it is complete, so expect a few more posts to bring my progress up to date.

I hope they do sound gorgeous when finished. I did get one together for a quick listen, albeit with a passive filter, and I can say it sounded quite good. Having lived with 2-ways for 3 years, a high efficiency 3-way can open your eyes.

Yes, the shape of the L'Integral attracted me. Normally, I would not blatently copy an original design, but in this case, I couldn't resist.
A shame that I could not make the baffle from solid Corian, like the original. Oh well, next time.
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Old 12th August 2007, 03:39 AM   #8
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Time passes...other projects are started and finished:
New Compact TL Project

Spring comes, and with it comes my desire to resume work on these speakers.
Before I can do anythig else with them, the baffles need to be painted. The arrival of warm weather means I can start this.

My painting process has been explained in other threads, but in a nutshell: 8 coats of primer, 10 coats of finish, coloursand and polish.
The picture below shows them after they have been primed. That would have been in the early part of May. I then let the primer cure completely then sanded smooth before finish paint.
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Old 12th August 2007, 07:38 PM   #9
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It takes about 2 weeks for the urethane based primer that I used to fully cure. I then repair any little blemishes with automotive spot putty and sand the entire baffle with 400 grit paper.

It's now ready for paint.
It takes much of a Sunday to apply the ten coats of paint. Temperature and humidity are factors for spraying this many coats in a short period.
Why so many coats? Well, in order to get the final result (piano black), you need to coloursand the paint. This is wet sanding the paint with very fine (2000 grit) paper. Experience has shown me that in order not to cut through the paint into the primer below, the paint has to be thick. So far, 10 coats seems to be the right thickness, especially with the cheaper spray equipment that I have.

No problem, a few cold beers, a sunny Sunday, take my time and paint. Other things to do while waiting for each coat to flash off like working on my tan.
Ah, but don't get me wrong, don't spray in direct sunlight.

Heres a pic after the speaker has been painted and let dry a few days:
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Old 13th August 2007, 03:25 AM   #10
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I waited a full month before colour sanding the baffles. The paint takes a long time to cure, and I not really in a hurry anyway.
Sanding goes well, no burn through the paint layer.

Next comes polishing. I use a 7" high speed buffer for this and polishing compound. This goes as expected, with good results.
This type of finish is impressive, but can be very difficult to do without the proper preparation and knowledge. Once polished, every tiny imperfection will show up, so you can't scrimp on the prep work (especially sanding).

As mentioned earlier, I temporarily installed the drivers for a quick listen. Slung together crossover, close to the 300Hz and 3000Hz of the active filters crossover frequency. As it was only one speaker, I had to pair it with one of my T line mains.
First off, it's so much louder, I have to turn it down. Sound quality is very good, good bass production.
I'm very encouraged.
Here's a shot of the speaker with it's drivers installed:
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