Magnus', Urban's and Mike's ProAc 2.5 project page

The ProAc 2.5 is a really good speaker. It cost about 4000 euros or more in just about any high quality HiFi store. I don't know who they are, bot some people "out there" wanted these speakers so much, that they started building "look alikes", trying to get their clones as close to the "real thing" as possible. I believe they got pretty close. This is the story on how I used directions found on the web to build my own speakers.

I will divide my efforts in the following parts:

• People
• The pile of wood
• Building the boxes
• Mounting the speaker elements
• Building the crossover
• The deed is done!

News

People

As for now (august 2002), we are four people getting the parts for the speakers.

• Me
• Michael Karllson
• Urban Svensson
• Rolf Arnesson (my steaph fater, long distance member)

I've ordered parts for five sets of speakers. Urban and I will build two pairs each. My steaph father, Rolf, will build his in Sweden (I'm in Geneva, Swizerland). I ordered speaker elements for him though.

The project

The pile of wood

The first hassle was to get the wood. OK, we found a place in Geneva where we could get the wood and it wasn't too expensive. The problem was that I don't speak french. They didn't speak any language but french. When I went there to pick it all up, it took me about 10 minutes before they understood that I wanted my MDF boards. I had to call up Michael on my cellphone (he speaks french) and he just had to tell them his name, and they were happier than ever before; "Monsieur Karlsooooooooonnnn..."

Just for your information... It took me about one hour and a half to carry all the MDF from my car to my apartment. On the picture there is MDF for four pairs of speakers. I have one more set of MDF + all the left overs. I'm not kidding you when I say that there was some 200 kg - 300 kg of MDF in my car. Don't do it without help. It is painful!

Building the boxes

Here is the drawing I used. I found it at ProAc 2.5 clone site. I didn't completely follow it.

Building the boxes was not that hard. The trick is to buy the wood in a shop where they have computer controlled sawing. I got mine with a tolerance of fragments of a millimeter. I didn't even need clamps when I assembled the boxes. Everything fitted really tight.

To get the boxes sealed and airtight we used plenty of glue on the joints.

Here you can see how nicely they fit together.

I got all the wood (one sheet of 19mm and one of 25mm) for just about 300 CHF (equals about 200 euros). This was enough for five pairs of speakers. Make sure you have some friends who wants good speakers as well before you go out and get the wood... The price I mention here included the cutting of the wood. I recommend eveyone who wants to cut the wood themselves to save money; DON'T!!! You'll never get it as good as they do in a professional shop.

On the picture above, Urban (UrSV) is filling up the holes and leveling out uneven corners. This is very important in order for the laminated wood to stick properly. After the lamination, we cut out the large holes with a router. This was done on my balcony in the middle of the night. I wonder what my neighbours were thinking...

Mounting the speaker elements

This was actually the hardest part of the project. Two holes had to be cut out and sinked (4 and 5 millimeters respectively) for the woofer and the tweeter. For this, I bought (yet another reason for building speakers... a reason for buying tools) a router. I found a cheap Black and Decker for 79 euros at in a local store. It worked perfectly. As a guide for making the holes I sacrificed the plastic cover from a box for some screwdrivers. That and some patience made a perfect couple for making the wholes. If you don't have the guide or a router, go to a local carpenter to get the wholes made. I've heard of people having that done for around 40 euros. That's cheap if you want it to look good. I've read some recommendations that one should wait with the holes until after you've put on the laminated wood. I agree. It was really hard to wait, since the boxes were standing there just waiting for some speaker elements. Ok, you probably can do it before and have a "sneaky preview" on how they sound, though then you'll never finish them. The speakers will stand there in your livingroom forever looking ugly.

You can see how professional we are, using the vacuum cleaner and everything. Well, what could we do. Even if the neighbours didn't like it, it would not have been any use to complain, since I don't speak french yet. The tricky part was to not make the hole the whole way through the MDF and leave one millimeter. Othervise the router would have got stuck in the insulation on the inside (which by the way is 7 mm bitumen asphalt + 50 mm insulation material). The last piece was done by hand (actually using a knife). When this was done, one of the small tasks left to do, was to drill small holes for the screws we used for the speaker elements.

Building the crossover

Here is the drawing of the crossover:

This is the crossover recommended by another ProAc 2.5 clone site.

Eventually I couldn't wait any longer. I was visiting in Gothenburg (september 2, 2002) and went to my favorit parts supplier, Tema Elektronik. Even after moving to Geneva I still haven't found a better place to buy parts. The guy there is never pushing for crappy parts and he tells me when I'm being too cheap. He is also a valuable source for knowledge on "everyday" electronics. So, to start with I have bought crossover parts for about 45 Euro for a pair of speakers.

I skipped PCB's for the X-overs and used a piece of wood (leftover from when I put in new floor in my bedroom). This sucker is connected p2p (pin to pin) and fixed to the wood using hot glue. Hot glue is a really cool invention. For now, I have the X-over outside the speakers. This allows for easier tweaking of the filter. New capacitors are on their way already...

The deed is done!

Here are some pictures of our finnished speakers. They look really good! We are particularily happy with the cherry wood, which turned out pretty good.

On the picture below, you can see that I and Urban was using different techniques for laminating the top of the speakers. Urban was aiming for the symetry of the natural lines on the wood. I was making some kind of a pattern, using triangles fitted together.

Also look at the difference of the location of the bass port. I put mine a little bit lower than Urban. I will never admit that I used the wrong measurement... Many people on the net have told me that this doesn't matter when you use a bass port. It should not have too much of an impact.

Parts

The boxes

• 19 mm MDF board, one sheet ( about 1220 x 2400 mm ), price: see 25mm
• 25 mm MDF board, one sheet ( about 1220 x 2400 mm ), tot price: 300 CHF for four pairs of speakers, about 40 euros per pair
• Glue
• Screws, price: 15 euro for 700 screws, about 2 euros per pair
• Sound damping insulation: 15 euros
• Bitumen, asfalt board: 20 euros
• Cherry wood for lamination: 60 CHF (=40 euros)
• Contact glue: 40 CHF (=25 euros)

Drivers

• Scandspeak D2010/8513 - 3/4" tweeters, 2 pieces
• 2 st Scanspeak 18W/8535- 7" midrange/low, 2 pieces

Crossover Components

• 1.5 mH inductor, 2 pieces: 6 euros / piece
• 0.83 mH inductor, 2 pieces: 6 euros / piece
• 0.25 mH inductor, 2 pieces: 6 euros / piece
• 5 ohm, 5W resistors, 2 pieces: 1 euro / piece
• 47 ohm, 5W resistors, 4 pieces: 1 euro / piece
• 3.4 uF capacitor, 2 pieces: 3 euros / piece
• 4.7 uF capacitor, 2 pieces: 3 euros / piece
• 8.5 uF capacitor, 2 pieces: 3 euros / piece

Grand total

Misc

• Speaker input posts, 2 pieces ( 63 SEK = 7 euros )
• Internal wires, a couple of meters ( got it for free )
• Ports (140 mm x 75 mm (inner diameter), 2 pieces ( 2 euros )

References

Since one of my goals is to help other people getting started as well, I'll just go ahead and list my references and links on the web.

Links in no particular order:

• ProAc 2.5 clone page - A site on how to build the ProAc 2.5 clone
• Troels Gravesen - A guy who really has tested some different solutions for crossover filters
• Swedish ProAc 2.5 clone page - A guy in Sweden built a pair of ProAc 2.5 clones and documented the whole thing (in swedish)
• Minic - A web-store for HiFi in swedish
• Audio components - The place where I bought the speaker elements. They give great discounts if you buy in quantity and pay in advance.
• Troel Gravese's measurements and tweaks for the X-over

E-mail addresses

• Magnus Lubeck: kmg@skip.informatik.gu.se
• Urban Svensson: N/A
• Michael Karlsson: N/A