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Multi-Way Conventional loudspeakers with crossovers

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Old 8th November 2009, 03:02 AM   #1
pheonix358 is offline pheonix358  Australia
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Default Doesn't get much easier.

I am posting this series to show others that there are 'other' ways to build speakers, either a build that any one can do with only a jig saw, or other builds that allow those that have talents in fields other than woodwork to achieve a finish that is limited only by the imagination.

I have 30 years experience and am well known to Aussies, or at least my designs are. One of my designs in particular sold thousands and met with acclaim. I wish I could find that article from the Western Australian Audiophile Society, it was a real hoot. Perhaps another Aussie could post it.

This first one is simple! But first we need to step back and correct a misconception that some have.
There is a perception that the only way to properly design a speaker is to first choose your drivers and then design your enclosure based on a particular 'alignment'. Strictly speaking this is only one way to do it.

Take a Morel MW115S driver. This is IMHO a wonderful small driver. In a closed box the volume varies from a low 0.112L (Qtc 1.2) to a high of 1.2L (Qtc 0.5) Anything between these limits is valid.

The thing to consider is that a driver exists in a sealed enclosure on a continuum of volumes. Sure there are limits at either end but notice that the continuum is from 0.112 to 1.2 Litres, a facter of ten. This can be graphed in a 2 xy graph.

For a ported enclosure we can use a xyz graph with volume and port tuning for any driver. In the case of the MW115S, volume per driver is anywhere between 1L to 2.5L.

The example I will be using uses the 2.5L per driver tuned to 75Hz.

Now, take a drive to your nearest car parts place. Buy a pair of ready made enclosures designed for a 6*9 speaker. Take them home to the kitchen. Put a largish plastic bag in one of the enclosures and using a measuring jug, fill the enclosure with water, measuring as you go. Mine turned out to be 5.1 Litres. Now pour the water out and remove the plastic bag.

Picking a driver or drivers is now just a matter of using your favorite software program and see how your chosen driver will go.

HINT: Drivers with a Qt close to 0.38 to 0.42 will be much more forgiving of variations of port tuning.

The MW115S has a Qt of 0.37 and for the lowest f3 needs 2.5 Litres. Two will fit in the enclosure and room is left for a small tweeter.

Next find two pieces of timber that just cover the front and cut holes for the woofer(s) and Tweeter.

Mount this to the box with 4 to 6 screws and then follow your cuts so you cut out the baffle. Plastic ports can be cut to length and fit in the bottom or top of the enclosure. Mount your drivers and connect them to the plate that is already in place. Line the walls with dampening material and you are good to go.

Many small drivers up to a single 5 should work well. You will need a small tweeter, I used a Morel MDT40. The MDT41 would look better since it can be worked into an appropriate sized round hole. A little silicon will keep it in place. See attached photos.

I will cover crossovers in a future post.
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Old 8th November 2009, 03:22 AM   #2
dave_gerecke is offline dave_gerecke  United States
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Nice little writeup you did here. You just helped inspire me a bit. I happen to know where there's a pair of cabinets like that I can get for free. I gave them to a friend to use in the rear of his truck cab. He never got to it, and then sold the truck. New truck doesn't need. They now sit in his barn. Now I'm going to have to go get them and do the butchering you showed.
The nice thing about those cabs it that you can usually find them cheap at yard sales and flea markets. At least here in the states.

Peace,

Dave
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Old 8th November 2009, 03:25 AM   #3
pheonix358 is offline pheonix358  Australia
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Thanks Dave, It's an easy build and not all speakers need to be 'the best in the world.' These do duty as nearfield speakers for my computer. Much better than computer speakers!

Terry
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Old 8th November 2009, 03:35 AM   #4
dave_gerecke is offline dave_gerecke  United States
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That was one thought I had for them, although I really don't care too much about the sound out of my PC. I focus on the big setup. I was thinking of using a config like that as a sort of MTM, perhaps with a sub under each one for really low bass duties.

Peace,

Dave
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Old 8th November 2009, 05:11 AM   #5
pheonix358 is offline pheonix358  Australia
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I am trying to work out if these should be in this forum or in 'Construction tips' Problem here is that they tend to get lost pretty fast.
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Old 8th November 2009, 04:30 PM   #6
Pano is offline Pano  United States
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Doesn't get much easier.
Quote:
Originally Posted by pheonix358 View Post
T not all speakers need to be 'the best in the world.
Indeed! I usually enjoy the more fun projects here. Modest goals, good sounds and lots of fun.

Thanks for the thread.
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