Ultra Light Weight Bass Cabinet

[robthebassplaye]

OK, so this is the first thread I have ever created....

I am a 53 year old bass player, and lugging heavy gear has gotten the best of me over the years. I'm 5'6", not in great shape, and I am fortunate enough to have a fantastic career and job, which allows me to play bass as a hobby (for the last 40 years). I've played everything from Madison Square Garden, Lincoln Center, and pubs with 2 old guys who didn't even know they were in the pub... So, I've seen it all.

I have a lot of great bass guitars, and a lot of great bass amps. But, I needed something lighter, louder, and better sounding than I could find...

I'm an engineer by formal training (Columbia University, NY) so I took a formalized approach to this build, and I documented it every step of the way.

My goal on this build was to make a bass cabinet under 30 pounds, over 120 db-spl, and flat from 30-18K. No, really, I mean flat... No coloration, just loud, clean, and light. That is the exact opposite of what most typical bass cabinets will do. A lot of bass players will say they count on the sound of the amp and the cab, but I wanted this to be clean, with any coloration happening before it hit the amp. Thats just my preference, your milage may vary...

Before I decided how to construct the cabinet, I performed a lot of experiments measuring the response of panels from various types of material (that is, I designed some accelerometers, mounted them to a few types of panels, and measured the response of those). That helped my decide on the construction technique.

It became clear very early on that a low mass, high stiffness type of structure (such as extruded foam with fiberglass) was superior in almost every way to any form of wood, or other honeycomb composite.

I have a lot of the data for the design parameters captured, and I would like to share that with everyone who cares to review it. I also used some technical tools such as L&T, Eminence Designer, and P-Spice in the creatino of this beast, and I have all of the engineering data and documentation for that available as well, for those who are interested.

So, let's get on with this...

Has anyone else taken on this type of build? What were your experiences? I will post everthing I have on this, let me know what you are interested in...

Rob

[robthebassplaye]

Originally Posted by robthebassplaye

OK, so this is the first thread I have ever created....

I am a 53 year old bass player, and lugging heavy gear has gotten the best of me over the years. I'm 5'6", not in great shape, and I am fortunate enough to have a fantastic career and job, which allows me to play bass as a hobby (for the last 40 years). I've played everything from Madison Square Garden, Lincoln Center, and pubs with 2 old guys who didn't even know they were in the pub... So, I've seen it all.

I have a lot of great bass guitars, and a lot of great bass amps. But, I needed something lighter, louder, and better sounding than I could find...

I'm an engineer by formal training (Columbia University, NY) so I took a formalized approach to this build, and I documented it every step of the way.

My goal on this build was to make a bass cabinet under 30 pounds, over 120 db-spl, and flat from 30-18K. No, really, I mean flat... No coloration, just loud, clean, and light. That is the exact opposite of what most typical bass cabinets will do. A lot of bass players will say they count on the sound of the amp and the cab, but I wanted this to be clean, with any coloration happening before it hit the amp. Thats just my preference, your milage may vary...

Before I decided how to construct the cabinet, I performed a lot of experiments measuring the response of panels from various types of material (that is, I designed some accelerometers, mounted them to a few types of panels, and measured the response of those). That helped my decide on the construction technique.

It became clear very early on that a low mass, high stiffness type of structure (such as extruded foam with fiberglass) was superior in almost every way to any form of wood, or other honeycomb composite.

I have a lot of the data for the design parameters captured, and I would like to share that with everyone who cares to review it. I also used some technical tools such as L&T, Eminence Designer, and P-Spice in the creatino of this beast, and I have all of the engineering data and documentation for that available as well, for those who are interested.

So, let's get on with this...

Has anyone else taken on this type of build? What were your experiences? I will post everthing I have on this, let me know what you are interested in...

Rob

Here are some more details_

[Mike Arnopol]

The Thunderchild is another example of a very flat, hifi cab based on the 3012lf. I have one and it sounds amazing. I'm like you---I want to start with a neutral palette and use EQ and other electronics to color my sound to my liking.

[smeet]

So... How does it sound???

Interesting. I don't know much about speaker design, but I am embarking on a fEARful 15/6/1 build as soon as all the materials are delivered.
Do you have any idea how your speaker compares to the fEARful line?
What drivers did you use?

The lightness seems great. But it seems like it might be fragile? If I sat on the cabinet, would it collapse?
There appears to be no bracing. Maybe I'm not familiar with the materials used, but are they stiff enough to not flex at high SPL?
I would love to see more details on the build.

[Mike Arnopol]

They're plenty strong.And super rigid. Dropped mine from 3 ft.(not on purpose)---no problem. Actually the surface is harder than the Italian poplar plywood cabs commonly made today. The surface of the composites doesn't dent like the plywood.

[countrybass007]

Hope your cab build works out well. I'm several+ years older than 53, and lugging all the big heavy cabs were getting a bit much for me too. I ended up with an Orange Tiny Terror Bass Amp and an Orange SP212 cab. Under 50 lbs. combined and sounds great. My "big rig" now is a PJB BG800, and at 78 lbs. is still well under the old 135 lb. 810 cab. I feel fortunate that they make alot of great sounding lightweight bass gear now.

[smeet]

So Mike, you are familiar with this material? I thought fiberglass composite was different than a couple of layers of fiberglass cloth over foam.

The Thunderchild is a wooden cabinet, is it not?

[robthebassplaye]

Originally Posted by smeet

So... How does it sound???

Interesting. I don't know much about speaker design, but I am embarking on a fEARful 15/6/1 build as soon as all the materials are delivered.
Do you have any idea how your speaker compares to the fEARful line?
What drivers did you use?

The lightness seems great. But it seems like it might be fragile? If I sat on the cabinet, would it collapse?
There appears to be no bracing. Maybe I'm not familiar with the materials used, but are they stiff enough to not flex at high SPL?
I would love to see more details on the build.

Absolutely not fragile - very strong, you can stand on it, jump on it, drop it out of the trunk - it's very strong.

I used Eminance neo drivers, 12", 6.5" and a horn. Bracing is not required, as the material has such a high resonant frequency that you don't need to do this. Bracing in general for plywood is used to move the resonant frequecny higher (the smaller the unbraced areas, the higher the resonant frequency). But with this type of composite construction, the mass is so low, and the stifness is so high, that it doesn't really requie barcing to move the fundamental frequencies any lower.

Rob

[robthebassplaye]

Originally Posted by smeet

So... How does it sound???

Interesting. I don't know much about speaker design, but I am embarking on a fEARful 15/6/1 build as soon as all the materials are delivered.
Do you have any idea how your speaker compares to the fEARful line?
What drivers did you use?

The lightness seems great. But it seems like it might be fragile? If I sat on the cabinet, would it collapse?
There appears to be no bracing. Maybe I'm not familiar with the materials used, but are they stiff enough to not flex at high SPL?
I would love to see more details on the build.

Also, because of the material, there is a lot less phase distortion. It's a very pure sound, perhaps not to everyones likeing, since some folks really like their bass amps and cabinets to have a certain sound. But, this is flat, pure, and accurate. Really noticable, if you do a side by side comparison.

Rob

[Petebass]

"It became clear very early on that a low mass, high stiffness type of structure (such as extruded foam with fiberglass) was superior in almost every way to any form of wood, or other honeycomb composite."

Bazzinga!!!

There have been several cabs built this way by forum members. Do a search for the word "composite" in the amps forum and they will all appear. I have built 2. Zac2944 has built 3, and he is really the guy who introduced this concept to this forum. His initial build thread was very thorough and contains everything you will need for the construction phase. You can find it here.

DIY Lightweight Composite Cab Build

[Petebass]

Oops I just spotted the PDF. Nice job!!!!

[greengoblin]

Very nice! Something I would like to try one day...

What did you do with the speaker mount? Any bracing for the foam around the speaker mount, did you use a sleeved nut/bolt configuration?

[tjh]

Rob, nicely done ... I have worked fairly extensively with foam, creating sets for theater, but they have not needed to be transported, etc, and only needed a limited life ... what did you use for adhesive on the joints, and did you fiberglass the entire shell inside and out, or just joints on the inside, or?? .. also, any particular reason why you chose fiberglass cloth vs. mat ? ... and what have you selected for grill material? thank you

[SactoBass]

I have a question, and I am sincere when I ask this:

If a cab is too light, will it jump around on stage?

It seems that having motors and cones vibrating back and forth inside the box (particularly with large excursion woofers and hitting low notes) that a cab shell that is excessively light would want to move around on stage.

Just askin...

[Rufus]

Any plans for a 210?

[Petebass]

Originally Posted by SactoBass

I have a question, and I am sincere when I ask this:

If a cab is too light, will it jump around on stage?

It seems that having motors and cones vibrating back and forth inside the box (particularly with large excursion woofers and hitting low notes) that a cab shell that is excessively light would want to move around on stage.

Just askin...

This is the most common question I get about these cabs.

The short answer is no. If the cab jumps around or walks, it's because the panels are vibrating...... Which means you have bigger problems than the can being too light. Stiffness, strength, and mass are three seperate things which.can to a certain extend be manupulated seperately. This thus of construction favours stiffness and therefore panel vibration is no problem.

[will33]

All good points. Have you considered component spacing? Cluster together, as close to a single point source as possible, etc. At least less than 1/4 wavelength at crossover frequency?

[robthebassplaye]

Originally Posted by tjh

Rob, nicely done ... I have worked fairly extensively with foam, creating sets for theater, but they have not needed to be transported, etc, and only needed a limited life ... what did you use for adhesive on the joints, and did you fiberglass the entire shell inside and out, or just joints on the inside, or?? .. also, any particular reason why you chose fiberglass cloth vs. mat ? ... and what have you selected for grill material? thank you

I decided on the fiberglass cloth material, and wrapped the entire cabinet in it, inside and out (there are some photos in the pdf I think of that). Initially, when I put the foam pieces together, I used epoxy filled with glass beads to basically hold it together, but the real strength comes from the fiberglass cloth. Putting this on both sides of the foam, from a mechanical perspective, is what reallly provides the stiffness and strength.

For the grill, I used a simple wooden frame and speaker cloth, mostly because this would be lighter than a metal grill, and I'm not that hard on gear, so I didn't think it needed that much protection.

I attached a photo of the cabinet with the grill. It's a little old fashioned, but I like the look personally.

[robthebassplaye]

Originally Posted by Petebass

This is the most common question I get about these cabs.

The short answer is no. If the cab jumps around or walks, it's because the panels are vibrating...... Which means you have bigger problems than the can being too light. Stiffness, strength, and mass are three seperate things which.can to a certain extend be manupulated seperately. This thus of construction favours stiffness and therefore panel vibration is no problem.

Petebass is correct, if it is built properly, there should not be any motion. In fact, I have plots of the accelerometers I used to design my box, both during the initial investigation of what material to use, and after the build, so I actually measured the displacement of the walls of the cabinet.

I also measured (with the accels again) a few standard wooden bass cabinets, and the displacement of those walls is an order of magnitude larger than what you see in a composite based design like this.

I've attached my analysis and data from the accelerometer testing, but the bottom line is that the data proves (which you could easily guess ahead of time) that the composite structure is much stiffer than the plywood. What is interesting is the harmonics of the primary mode, and how much more quickly they are dampend, that, I believe, is why this cabinet sounds SO MUCH BETTER than anything else.

Take a look at the attachement, I'd love to get some technical feedback...

Rob

[robthebassplaye]

Originally Posted by Rufus

Any plans for a 210?

Hi Rufus,

No, to my ear and tastes, a 2x10 cabinet is always stuck somewhere in the middle of what I really like. It's allmost never loud enough (not that I play loudly), and never seems to have enough "punch" (I know, that means something different to everyone, so it's a personal thing), no matter how large you make the cabinet, or how well you do the porting. I like 12's and 15's, to me those are drivers that can move enough air coherently, rather than 2x10...

But, these composite constructino techniques can be used on cabinets designed with the standard speaker cabinet tools (I prefer Emenince Designer, but again thats a personal preference, there are free tools out there that work great as well). Also, you can go to some of the speaker drivers websites, and they have plans for some of these cabinets.

Bottom line, based on my measurements and analysis, anything you build with a composite technique will sound cleaner and more accurate than a cabinet constructed from plywood. So, it depends if you like that kind of sound.

Rob