Some basic ?s re: speaker construction

[fvoelling]

I'm building the Modula MT out of MDF. The crossovers are built (not tested yet), and I've cut the cabinet walls, braces, and baffle cutouts. Since I have no experience with veneering, I'll keep it simple and just paint it black for now.

As I was trying to figure out in which order to glue the cabinets together, it dawned on me that there is the issue of being able to access the inside afterwards (to line the walls, mount the crossovers).

Once the cabinet is assembled, my only real access will be via the woofer cutout. I know the Parts Express cabinets have a removable front baffle, but I'd prefer not to have screws visible on the front. I could make the back of the cabinet removable for easy access, but I'm using the flared port from PE that will be attached to the back and the brace, in effect tying the two together.

My current brace is similar to the one in the PE cabinet. I've seen pictures in the Modula MT thread that show a partial horizontal and partial vertical brace combination installed in the top half of the cabinet. This would allow sufficient space for access to the inside from the front woofer hole, and may be my best option.

For testing, do you guys leave the crossovers outside the cabinet (I could do that by running the wires through the port), or do you just test everything without the box first? I suppose using a binding post plate would have made this a lot easier.

With respect to location of the crossovers, does it matter whether they're mounted horizontally or vertically, in front of or behind the brace?


Thx,
Frank

[joecarrow]

I managed to get my entire crossover to fit on the front and back of a sheet of irregularly shaped (thin) MDF, which I was able to slide in through the woofer hole on my Modula MT. You need to be careful about how your inductors are oriented in relation to each other (the forum has some good references on the topic- one such is a link to http://www.troelsgravesen.dk/coils.htm)- but it can be done.

The key thing is to make sure that all parts of the inside of the cabinet have wide open paths for airflow- don't let your crossover board or braces split your box into separate cavities. I placed my port behind my tweeter, and oriented my crossover board vertically so that the air space on either side of it had a clear shot to the port and the rest of the box. I'm sorry to say that I didn't take pictures as I was going. If you leave a baffle (front or back) removable, mounting the crossover firmly to a wall is also a great way to go.

I first tested my crossovers outside the cabinet with the woofers and tweeter just laid out on the floor. I played music really quietly through them just to make sure that I hadn't made any horrible mistakes, such as bass coming out of the tweeter. Honestly, I was so excited about it that I couldn't wait to get them into boxes.

I'd definitely recommend testing inside the box in such a way that you can still correct things if they don't sound right. Its not that hard to mess up driver polarity, and you might at first say to yourself, "Gee, this doesn't sound quite right. The drivers aren't distorting and there seems to be high and low sounds, but something is just wrong", and then realize that the tweeter is reversed.

If a crossover is wired poorly enough, it would be possible to cause damage to the tweeter or your amp- so you should definitely go over it methodically to make sure you didn't make an easy goof. I've definitely caught a few major errors after thinking I was done and taking a break for a sandwich, then coming back and retracing my steps.

If this is your first time building, take your time and trust your gut. Building your own is totally worth it, and I don't think you'll be disappointed.

[technimac]

The baffles were the last part to be glued onto my Modula MT's, but everything was already installed inside first. That made it easy to clamp on a baffle, test the crossovers, then go for the glue.

Clamping the baffle on prior to gluing makes it easy to assess the SQ with everything in place, and even then, the crossover is easily accessible through the woofer opening after glueing.

HTH,

~Bruce

[fvoelling]

Thanks for the advice! I particularly like the idea to just clamp on the baffle during testing.

It would also seem to make sense to line the walls prior to assembly, unless it is necessary to seal the seams from the inside after glue-up. Is it?

Frank

[JonW]

Frank,

For what it's worth, I made a rear access panel in my Modula MT's. It's much easier to just glue up the boxes. But if you ever want to get in there again...


Images not available

[Rich Jura]

You might already know

but your 'T' nuts are on the wrong side.

Later
Rich

[technimac]

It would also seem to make sense to line the walls prior to assembly, unless it is necessary to seal the seams from the inside after glue-up. Is it?

Not likely...... :W
I used polyurethane glue for this. It "foams" slightly while setting up and fills any small voids that may exist. :T
The front baffle is "rabbeted" on the inside, so the glue has lots of surface area to make a good seal.
On this baffle it's actually laminated, with a panel of 1/4" HDF glued (with PVA) to the inside.



I also don a disposable latex glove and run my finger around the inside of the joint to smooth any excess glue that squeezes out after it's clamped.
Finally, after trimming the outside of the baffle with a flush trim bit, I bondo any voids that may remain on the outside.

[JonP]

Sounds like you're getting a lot of good advice...

FWIW, I did mine a different way, I split the crossover into two halves, highpass and low pass, and put them on two separate pegboard boards. It turns out you only need one wire, from one half of the crossover to the other, besides the ins and outs.

These are (barely!) able to move around my slightly unconventional bracing, and come out the woofer hole. So, they are removable out of a solid box.

Look on the Modula MT thread, at the beginning where other's construction pics are is a link to my Photo-bucket account... I actually didn't know I was in there till a few days ago... not that I mind... Guess I need to reverse the order of the pics, so they show in forward rather than reverse chronological order, but what the hey... There are some pretty good pics of the crossover boards and their placement.

HTH...

[JonW]

You might already know... but your 'T' nuts are on the wrong side.

Yeah, oops. A newbie mistake. They were the first speakers I ever made. Maybe not a good example for someone asking how to build cabinets. At least they have not fallen apart yet.

[Rich Jura]

It would take up way too much bandwidth to list my mistakes, the worst of
which custom modified two of my fingers.

Later
Rich

[JonW]

Ouch. Sorry to hear that.


I've been wondering if this might be a good investment:

http://www.sawstop.com/

It's crazy expensive ($4k) but they have a cheaper version expected in the near future:

http://www.sawstop.com/products-contractor-saw.htm

[---k---]

I've been wondering if this might be a good investment:

http://www.sawstop.com/

It's crazy expensive ($4k) but they have a cheaper version expected in the near future:
http://www.sawstop.com/products-contractor-saw.htm

Those come up all the time. My thinking is that no one can protect me from my own stupidity. If it isn't the saw, it will be something else. Shoot, last night I burned one of my fingers bad enough to blister it with hot glue! A piece of felt slipped out of my hand as I was trying to position it, and the glue on the back burned me. Ouch!

For me, its always something! I just need to slow down and take my time. I also keep meaning to take a woodworking class from the local community college so I learn some of the basics safety, rather than "learning on the job".

[JonW]

If it isn't the saw, it will be something else.

But it might be worth investing in various little things to stay safer, here and there. Try and minimize chances of an accident. Although at $4,000 for a saw... your point is taken. I just ordered myself a respirator and filters for woodworking. And this weekend I’m going to try and set up a system to vent air from my basement wood shop to outside, to get rid of the fine particulate dust that isn’t so healthy.

I also keep meaning to take a woodworking class from the local community college so I learn some of the basics safety, rather than "learning on the job".

Now that’s a good idea. :T I should look into that.

[Dennis H]

But it might be worth investing in various little things to stay safer, here and there. Try and minimize chances of an accident.

Common sense is your best defense, Jon, and nothing will keep you safe without it. Like don't light your bunsen burner near an open beaker of ether.....

[ahaik]

Biggest danger is over comfidence, people tend to become overcomfident over time.
You need to remember that these tools can hurt you badly whenever you work with them.

[JonW]

Common sense is your best defense, Jon, and nothing will keep you safe without it. Like don't light your bunsen burner near an open beaker of ether.....

Common sense. Yup. :T

I've actually seen people try to light a bunsen burner near ether. (I stopped them.) Those people don't usually last too long in the sciences.

Biggest danger is over comfidence, people tend to become overcomfident over time.
You need to remember that these tools can hurt you badly whenever you work with them.

Agreed. I'm always a little scared when I use these loud and powerful tools. I think that's a good thing. I just use them on the odd weekend so I never get too comfortable with them. I'd imagine if you used them every day, for a living, that's when you're going to get overconfident or complacent and increase your odds of an accident.

[Concillian]

Common sense. Yup. :T

I've actually seen people try to light a bunsen burner near ether. (I stopped them.) Those people don't usually last too long in the sciences.

This reminded me of when I was a teenager at an international Boy Scout Jamboree. Hundreds of camping kids and every site had propane appliances. Someone did something very wrong to a propane tank or something attached to it. Either the valve got knocked off or something, but the sound was unmistakable ... a propane tank was venting it's contents.

What was the response of 90% of the people there? Run towards the sound to see what was happening.

I couldn't help but think to myself "what the hell are you people doing?" while I told what friends I could to run AWAY from the potential explosion.

Luckily nothing happened, the contents dissipated with no further event. As a teenager, the sight of such a large display of lack of common sense for safety was rather astounding.

[JonW]

As a teenager, the sight of such a large display of lack of common sense for safety was rather astounding.

And now that your older... and you've had more time to observe humanity... now how do you feel about people? :P