Cab Builder Question

[Ben Esparza]

I plan on building a cab using PL adhesive, screws, and brad nails. Would removing the screws after the PL sets be a wise decision or should I leave them in place? I'll be setting the wood joints into rabbets and dados which will give a little more adhesive surface area.

What do you guys think about removing the screws versus leaving them in place?

[dave zilla]

I'm a cabinet maker by trade but have never built a cab. I would say leave them and not bother pinning unless you are using them as a holder whilst screwing.

Basically you've put them in if you pull them out there will be a weak spot

[gregoire1]

I built a BFM Omni several years ago with PL glue. Once it dries, screws are no longer necessary. I removed the ones that would interfere with my rounded-off edges but left the rest. No problems yet.

[billfitzmaurice]

The screws are only there to hold the parts in place until the PL sets. I always pull them on the edge of the cab where they'd interfere with rounding the corners. With a well designed cab the rabbets and dados are also unnecessary.

[Ben Esparza]

All makes sense. I would be using plenty of Bondo to fill the holes left by the screw removal. The brads will be used just to keep things in place for the screws. I've built with pneumatic finish nails and they can sometimes that a different route than intended. 1" pneumatic brads are easier and safer. Thanks.

[MontanaBassDude]

Hi, Ben - you can see photos of my recent fEARful cab build here: fEARful

It's a darn solid cab, and used no rabbets or dados, because I'm not smart or patient enough to re-calculate the cuts, and I didn't want to change the interior volume of the cab. I just used PL and rubbed it deep into the plywood with a rubber-gloved finger. Then I used screws (countersunk) to hold it all together. Check out the photos.

[will33]

Simple butt joints are plenty strong in the corners. You need the bracing out in the middle of the panels to stop flex and vibration...raise the resonance high enough to not interfere with the sound......a bit different approach if you're not used to it. Crossbracing is a bit easier and stronger than the spines. Use that where you can...put a spine where you can, like if a driver is in the way or something.

[will33]

Finally figured out how to get that damn diagram.

[billfitzmaurice]

Originally Posted by will33

bracing...raise the resonance high enough to not interfere with the sound...

That's another commonly accepted concept that's not quite right. Bracing prevents the panels from flexing. It also raises the resonant frequency of the panels. But it's the flex prevention that makes the cab work better, not the raising of the resonant frequency. You can accomplish the same thing with added mass, but that doesn't necessarily raise the panel resonant frequency; depending on the topology it can actually lower it.

[will33]

Originally Posted by billfitzmaurice

That's another commonly accepted concept that's not quite right. Bracing prevents the panels from flexing. It also raises the resonant frequency of the panels. But it's the flex prevention that makes the cab work better, not the raising of the resonant frequency. You can accomplish the same thing with added mass, but that doesn't necessarily raise the panel resonant frequency; depending on the topology it can actually lower it.

Hmm....I was coming from the angle that everything has a resonant frequency....steel, ice, our bodies, everything. Intuition says making something stiffer would raise it but I guess then concrete buildings would be immune from earthquakes. Or does that cross the line from soundwave to shockwave...like in bombs?


Getting a little OT here....just brace the box good.

[will33]

Originally Posted by will33

Hmm....I was coming from the angle that everything has a resonant frequency....steel, ice, our bodies, everything. Intuition says making something stiffer would raise it but I guess then concrete buildings would be immune from earthquakes. Or does that cross the line from soundwave to shockwave...like in bombs?


Getting a little OT here....just brace the box good.

Actually, that doesn't make a whole lotta sense if you think it through.

I think it stems from "tighter drumskin, higher pitch"----"stiffer cab panel, higher pitch when you tap on it". Like playing a cajon.

[billfitzmaurice]

Originally Posted by will33

Actually, that doesn't make a whole lotta sense if you think it through.

I think it stems from "tighter drumskin, higher pitch"----"stiffer cab panel, higher pitch when you tap on it". Like playing a cajon.

A method of vibration damping used by Wharfdale in the 50s-70s was to make a double skin of plywood and fill the inch space in between with sand. It worked very well, but did not raise the resonant frequency of the panel. If raising the panel resonant frequency was the key to good results we'd build cabs out of sheet metal.

[dhsierra1]

Originally Posted by billfitzmaurice

A method of vibration damping used by Wharfdale in the 50s-70s was to make a double skin of plywood and fill the inch space in between with sand. It worked very well, but did not raise the resonant frequency of the panel. If raising the panel resonant frequency was the key to good results we'd build cabs out of sheet metal.

so then really the point is to minimize the amplitude of the panel vibration w/bracing etc and not increase the resonant frequency? So is it a misconception that it's easier to control/dampen higher frequencies when working w/wood cabinets? Just trying to clarify the concepts, thanks, Bill.

[billfitzmaurice]

Originally Posted by dhsierra1

so then really the point is to minimize the amplitude of the panel vibration w/bracing etc and not increase the resonant frequency?

Yes.

So is it a misconception that it's easier to control/dampen higher frequencies when working w/wood cabinets?

There's generally no need to dampen higher frequency vibrations of the cab, as they're of insufficient amplitude to color the speaker response. They may be there, but if they're down 30dB compared to the driver output you can't hear them anyway.

[dhsierra1]

Originally Posted by billfitzmaurice

Yes. There's generally no need to dampen higher frequency vibrations of the cab, as they're of insufficient amplitude to color the speaker response. They may be there, but if they're down 30dB compared to the driver output you can't hear them anyway.

I'm sure this varies a lot based on cabinet design, size, bracing scheme, etc but is there a certain frequency (range) where you lose the effect of coloration? I know some guitar speaker cabinets go to a fair amount of trouble to add coloration due to panel vibration like the old Fender combos.

[Philonius]

THIS is why I love Talkbass. Sand filled cabinets? They must have weighed a ton. For FOH PA's, or audiophiles gone 'round the bend?

[BassmanPaul]

Originally Posted by billfitzmaurice

A method of vibration damping used by Wharfdale in the 50s-70s was to make a double skin of plywood and fill the inch space in between with sand. It worked very well.

My father had one of those, SFB3 IIRC. It was the speaker system I learned how to play bass using so it would be 1962.

[will33]

Originally Posted by billfitzmaurice

A method of vibration damping used by Wharfdale in the 50s-70s was to make a double skin of plywood and fill the inch space in between with sand. It worked very well, but did not raise the resonant frequency of the panel. If raising the panel resonant frequency was the key to good results we'd build cabs out of sheet metal.

We built some things similair years ago as isolation panels to put between amp/mic rigs when recording multiple tracks/sources live. Seemed to work as far as reducing mic bleed from one rig to the one beside it.

Of course we didn't know what Wharfdale or resonant properties were, just trying to stop sound using brute force and a concrete wall wasn't practical. Of course these weren't that practical either, heavy as hell, but they were little walls filled with sand, carpeted on either side.

[dhsierra1]

Originally Posted by Philonius

, or audiophiles gone 'round the bend?

think that's bad? Check out the old Plasmatronics speakers using gas plasma for the tweeter. You had to have tanks of helium. Think of the karaoke potential at parties w/those

[will33]

Originally Posted by Philonius

THIS is why I love Talkbass. Sand filled cabinets? They must have weighed a ton. For FOH PA's, or audiophiles gone 'round the bend?

Ya, can learn something new here all the time.