The LM-1 Driver Locations

Living in an apartment I don't really have a chance to build my own cabinets, so I relied on cabinets from Dayton Audio. For the satellites I'll be using a version of these:

Dayton Audio TW-0.25CH, $175/pair or their curved-side brethren. I like the square sided cabinets as it makes it easier to place the speakers on their sides.

Update: September 2016: It seems the straight sided cabs are gone and only the curved TWC-0.25 versions remain.

Of course, you can save the $220 for the cabinets by making them yourself. You will need to maintain the front baffle dimensions (7.5" x 12") as well as inner volume of around 0.3 cubic feet for the tuning to remain accurate.


It's been too long since I touched a CAD program. I would really date myself if I explained which program I liked the most.  So instead, you get to see my hand-drawn artwork here! Rejoice.

Measure Twice, Cut Once

It's always good to do a full-size mock-up if you can, and given the size of the front panels this was straightforward. Please note that to make the pictures more interesting I've turned some of them around.

The LM-1 speakers are meant to be listened to in a traditional, tweeter over woofer arrangement. They will also play horizontally, if necessary but it's not my intention to make these speakers "landscape mode."  It's just me being a little creative with the camera.

After locating all the important points, I placed the drivers on the paper to visually inspect the resulting design.


Note that the tweeter is in fact offset. This should reduce edge diffraction. You may center it instead, but you MUST maintain the driver distances. This means two things. The driver to driver distance as seen to the right, but also how the drivers are mounted. If you move either driver towards or away from the listener you throw off the perfect crossover integration.

I have hand drawn the driver locations.  As you would expect, the woofer is centered across the vertical axis, and I've tried to maintain equal spacing to the left of the woofer and to the right of the tweeter. You could probably center the tweeter instead and it would be fine.

Measurements are taken from the closest corner.

I also measured the distance from the edge of the baffle to the flat side of the woofer.  I'll use this to put masking tape down before routing the outer diameter of the driver.

Despite the woodworking being quite limited, there's still going to be quite a bit for me to do.  I'll need to drill pilot holes, measure, decide if I really want to add stuffing or a port, re-measure. There's a lot to do before I can really get down to the business of crossover design.

Woofer Mounting

There is no doubt that flush mounting provides the best measured sound due to the minimization of diffraction effects from the sound coming off the driver ring and hitting the cabinet front. However, cutting these drivers in is a real pain so I have surface mounted them instead.

Inner Chamfer

You must chamfer or round-over the inside of the woofer holes. The Dayton cabinet faces are an inch thick, more than enough to block most of the back of the woofer basket.  Of course, this is not needed acoustically for the tweeter, but I may do so just to make it easier to get to the terminals.

Outer Chamfer  

The Dayton baffle has a round-over on the edges that is about 1/2" round. If you build your own you should strive for a round-over or chamfer as well to reduce edge diffraction effects.

Bass Reflex Port

After much useless soul searching, I did finally include a bass reflex port in mine. 1 1/2" and 4" long gives us a very useful -3 dB point around 55 Hz. Not a boom box, but very useful with a subwoofer crossed over anywhere between 50 to 90 Hz.  Locate it directly behind the tweeter.

Must you port? No, you don't have to. You can also seal the port after including it, but you'll loose about 20-30 Hz in low end response.  If you are OK with about an 80 Hz -3 dB point then you can leave the port out. This may be a better option if you are absolutely sure you will only run the speakers with a subwoofer, as the maximum excursion will be better controlled, and you'll get more maximum output. Meh. Really not worth a lot of thought. The point is, ported or not the crossover stays the same.

Padding

Sonic Barrier

Experience has shown that the majority of vibrations in Dayton cabinets happens in the front section, before the middle brace, so cut the Sonic Barrier and coat all 4 sides of the front with it. The Sonic Barrier will also help increase the apparent cabinet size, so we get a few extra Hz of bass extension.

For the rear, cover the back wall with Acousta-Stuf (or similar), and stuff a little into the sides.  If you don't do this you'll get a little extra boom from the speakers.