Couple questions for first speaker build

[mugdecoffee]

I'd been wanting to build a pair of speakers for a while and finally took the plunge this summer. Right now I've pretty much finished up the bare cabinets and am waiting for a pair of drivers and a couple cross over components to finish them up. So far everything's gone well but I have a couple of questions.

With this being my first build, some of my cuts aren't absolutely perfect and so after gluing the panels together, some panels jutted out just a little bit. I ground down the seams which made the surface smooth but now the box isn't perfectly square especially around a couple of corners. You can't really tell by looking but the boxes don't quite sit flat. Would I be able to add a layer of bondo to make up the missing MDF? Would it be better to grid down everything until it was level? As a backup solution, I figure I could always just add some spikes.

Secondly, do you usually glue on the front baffle? That would make the strongest/most airtight bond but it bothers me that the entire box would be glued together with no way to fix anything later.

[Nebby]

Bondo'ing back to a perfect square is a difficult proposition but you're welcome to try I guess.

I'm personally a fan of removable baffles though you can still have decent access to the inside of a glued front baffle box via driver and port holes (assuming you use screw mounted or friction mounted ports).

[luvdunhill]

I would go the spike route personally. Perhaps use some threaded inserts with a threaded spike.

I always glue the baffle and have bonded material to the walls and even added interior cavities without problem. The fact that your joints are perfect might further underscore the need to glue the baffle if you're concerned at all about airtightedness.

[Nebby]

You can always slather glue on the interior joints to make sure it's airtight

[swt61]

I always cover all the interior seems with NP-1 (a type of flexible caulk) even though they've been glued. It's added insurance for an air tight fit.

As for the slightly out of square dilemma, either choice will work. You'll want a decent belt sander to flush up the edges, or if you go the Bondo route make sure you use a mud knife (knife for floating sheetrock seems) that's wider than your speakers, so that you can use the cabinet edges as a guide for filling the Bondo to the correct level. It'll take more than one application, and a little previous Bondo experience will go a long way.

I like to glue the baffles on sealed speaker enclosures, and even on ported enclosures I'd be sure to use a foam seal of some kind. Krazy Foam self adhesive sheets from Hobby Lobby work well for this.

[mugdecoffee]

It sounds like bondo takes some skill to apply and I'm not sure I'd end up with worse looking cabinets. I also don't have a belt sander, only a cheap orbital palm sander. For the baffle, those foam sheets sound perfect. Would you stick them on the front of the cabinet then screw the baffle on? Also more generally, how important is sealing? Will a small air escape cause a significant change in sound? Is it somewhat less important in a ported enclosure?

[luvdunhill]

Do you have the ability to measure the impedance to tune the port?

[swt61]

Well if you happened to be planning a Port A weekend sometime soon I'd offer my shop to you. Bring Shelly and we'll have a micro meet.

You can do it with a palm sander too, but start with about 80 grit paper to sand the bulk away.

I stick the foam sheets to the back of the baffle after I've sealed the back of the baffle with lacquer, then screw the baffles in. Maybe Nate has a pic of the boxes I made in the same mannor for him?

Oh here's one...

You can see all the screw holes I recessed with a countersink bit.

[recstar24]

Damn that is some fine woodwork.

[Nebby]

Dang that's a lot of screws! I think I did about that much for my sub panels....

No rebate for the speaker cutout, swt?

[aardvark baguette]

I know those...

[swt61]

Those were just some quick and dirty boxes for a pair of Cicada drivers Nate had. I used that many screws more for the aesthetic than for any other reason. We used a stainless, torx screw that looked pretty cool IMO. Kind of an homage to Harbeth.

[Nebby]

Ahhh, I see Very nice result for a quick and dirty box. Better than I could do with a lot of time and effort.

[Dusty Chalk]

Ahhh, I see Very nice result for a quick and dirty box. Better than I could do with a lot of time and effort.

QFT. One man's quick and dirty is another man's time-consuming and effort...-ful.

No double-entendres intended, but I see 'em coming.

EDIT: Effort-laden?

[Dusty Chalk]

effortvescent

Nice, I like.

[mugdecoffee]

Do you have the ability to measure the impedance to tune the port?

We measured impedance of simple circuits in one of my electrical engineering labs with some software but the soundcard interface might not work well with low impedances. I could if there was a way to measure impedance with a function generator and scope. The design I followed (Overnight Sensations - undefinition) specified a 6" port. Would tuning still be necessary?

Well if you happened to be planning a Port A weekend sometime soon I'd offer my shop to you. Bring Shelly and we'll have a micro meet.

You can do it with a palm sander too, but start with about 80 grit paper to sand the bulk away.

I stick the foam sheets to the back of the baffle after I've sealed the back of the baffle with lacquer, then screw the baffles in. Maybe Nate has a pic of the boxes I made in the same mannor for him?

I'd actually be thrilled to work in a real shop but I won't have a car this year. If the bondo is doable without a fancy sander I'll give it a shot. I have a few days until the drivers come anyways. Do you use any special screws to attach the baffle? Right now I have some basic drywall ones. Those boxes look amazing. Once I get everything together I'd love some finishing tips.

[luvdunhill]

Would tuning still be necessary?

the idea would be that you could account for the box losses (via gaps at the seams, or not using the exact same wall covering / port geometry / crossover volume as the original design) by tuning the port. also, it's possible to track down box resonances using the same method.

[swt61]

Do you use any special screws to attach the baffle? Right now I have some basic drywall ones. Those boxes look amazing. Once I get everything together I'd love some finishing tips.

As far as function, the basic drywall screws will work great. They're designed with a high shear strength, and therefore tend to break far less often than say stainless steel, those look pretty, but have a low shear strength.

Do predrill for the screws with a bit slightly smaller than the screw diameter though.

[n_maher]

They looked pretty ok with the drivers installed.

[Emooze]

"Pretty ok" is an understatement. I think they look damn awesome. I like the exposed screw heads too.

[swt61]

Thanks. And don't get me wrong, I'm not saying I cut any corners, and aesthetically I loved how they turned out. I was just referring to the fact that they were simple boxes, with no real need for internal bracing or complex angles.

I'm a big Walnut fan, and thought Nate might be as well, so I wanted them to be nice.

[Nebby]

They are indeed very nice! I didn't notice the sides were also walnut until Nate posted that picture. Very cool!

[swt61]

The bottoms and the backs are Black, because I only had a limited amount of Walnut veneer on hand.

[johnwmclean]

Really nice speakers, I’m totally jealous. I love single point imaging speakers. I’ve been thinking about a nice pair of Fostex’s for a while, this has given me some incentive to kick start the project.