Ultra Light Weight Bass Cabinet

[GrowlerBox]

I think it's another great demonstration of the fundamental value of the design that it can be arrived at independently by engineers not working within the constraints applied by marketing departments. It's no surprise at all to me that Rob's cabinet would look very similar to a previously well-designed and constructed cabinet. Kudos to both!

 

[::::BASSIST::::]

I guess the question is how "independent" is it?

...exactly the same drivers and exactly the same crossovers, with almost exactly the same internal air volume, and a box tuning that is very close as well.

At any rate since the fEARful plans are free people are free to do what they want with them with varying results of success.

As a side note, I am reluctant to "go there" in this thread as there are enough petty squabbles on TB, but I have a hard time leaving this alone and not pointing some things out to those who might not have otherwise made the connection.

...And if someone is genuinely interested in a composite cab like this they can head over to Link Removed

 

[Bredian]

I guess the question is how "independent" is it?



At any rate since the fEARful plans are free people are free to do what they want with them with varying results of success.

As a side note, I am reluctant to "go there" in this thread as there are enough petty squabbles on TB, but I have a hard time leaving this alone and not pointing some things out to those who might not have otherwise made the connection.

...And if someone is genuinely interested in a composite cab like this they can head over to Link Removed

Don't think that is surprising, considering the guy was not on a budget, he's a pro engineer in a related field, the drivers are the best of the best, its a natural to find them. The calculation models determine the speaker box volume, I'm a novice, but would probably get close. I was on TB for several months before discovering the whole DIY thing going on here. Hard to go back to the "store".

Like the OP, I immediately wondered about the honeycomb composites I've been seeing promoted by a supplier/inventor in the building industry, but the glass over foam looks easier and more accessible. Labor intensive.

There are available brand built boxes that are similar, but probably not as good, but demonstrate all the same thinking, ports, volume, crossovers....

I think is speaks volumes to the validity of the models and designs.

(I've even looked through BFMs projects to see if they're composite friendly)

 

[Bredian]

On second thought, the dimension mix looks significantly different, but the volume is likely the same.

ROB - not a rush, but how you attached speakers to the composite baffle will be of interest. Robby has been through some evolution there.

Side material thickness?

 

[Smallequestrian]

I guess the question is how "independent" is it?



At any rate since the fEARful plans are free people are free to do what they want with them with varying results of success.

As a side note, I am reluctant to "go there" in this thread as there are enough petty squabbles on TB, but I have a hard time leaving this alone and not pointing some things out to those who might not have otherwise made the connection.

...And if someone is genuinely interested in a composite cab like this they can head over to Link Removed

Go where? There's not a hint of an issue. He obviously did his own cabinet design and he used a different port type and different outside dimensions.

 

[1n3]

Rob,

Welcome to TalkBass. Thanks for posting this. It's clear you've gone to a LOT of work to build and document this cab.

It is remarkable how you arrived by different routes at endpoints so similar to others here. In your choice of drivers, cab volume, and crossover, you're close to a fEARful. And your construction methods are close to what was done by zac2944, Petebass, and Robby Hoinsky.

There are some differences too, such as your porting choices. I don't recall ever seeing a cab with both front and rear ports. Curious as to how you arrived at that configuration. On page 8 of your first PDF (As-Built Dual 7.85" Ports vs Other Port Options), I'm not sure what I'm looking at. What is the Y axis?

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.

AFAIK, you are the first builder to do this. This sounds like some great basic research. Can you share more details?

 

[::::BASSIST::::]

Go where? There's not a hint of an issue. He obviously did his own cabinet design and he used a different port type and different outside dimensions.

Yeah, maybe I am just reading too much into it. There are similarities but perhaps they are just a coincidence. I am far from an expert on these things.

 

[GrowlerBox]

Yeah, maybe I am just reading too much into it. There are similarities but perhaps they are just a coincidence. I am far from an expert on these things.

The point is that they are not just a coincidence; the problem of designing and building a light-weight cabinet with great power-handling capabilities that could faithfully reproduce the entire tonal spectrum of the bass presented itself to two different engineers, and they each came up with a solution. That they are so similar (porting details aside) attests, in my mind, to the validity of the design and the process each went through in its realisation.

The testing of the cabinet materials adds another fascinating layer. Again, far from detracting from what Robby achieved, I thinks this adds (or perhaps, subtracts) weight to the value of his approach.

 

[billfitzmaurice]

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.

It's widely accepted that by moving the resonant frequency higher via bracing cab vibrations are controlled; IMO that conclusion is not correct. Cab vibrations aren't controlled because the resonant frequency of panels is raised, they're controlled because the panels are too stiff to flex. The raising of panel resonance is a by-product of bracing, not an end unto itself. In this case if the panels are stiff enough not to flex then they don't need to be braced not due to panel resonant frequency issues but simply because they are stiff enough not to flex without bracing.

 

[robthebassplaye]

It's widely accepted that by moving the resonant frequency higher via bracing cab vibrations are controlled; IMO that conclusion is not correct. Cab vibrations aren't controlled because the resonant frequency of panels is raised, they're controlled because the panels are too stiff to flex. The raising of panel resonance is a by-product of bracing, not an end unto itself. In this case if the panels are stiff enough not to flex then they don't need to be braced not due to panel resonant frequency issues but simply because they are stiff enough not to flex without bracing.

Awesome, thank you for this post, Mr Fitzmaurice. This was exactly the kind of discussion I wanted to have with someone on this forum... It was getting a little dishartening reading things about weather or not I copied someone elses design, who cares, and why would I do that anyway? I spent a boatload of time designing this, before I ever started to build it. And, I've put all the design details out there for anyone to use if they want.

So, anyway, back to resonant frequencies etc... Maybe it's the terminology, but bracing absolutely does raise the resonant frequency of any panel. By definition, making the area that can vibrate smaller will raise the fundamental node, and that is what bracing does.

Stiffness is the term used to describe the resistance of an ELASTIC body to deform under pressure. A composite structure, such as a fiberglass covered foam core, is NOT an elastic body. It is rigid, up until it's breaking point. That is why the fundamental resonant frequency is so high. And, in my opinion, why the cabinet doesn't vibrate.

Are we saying the same thing?

Thanks,
Rob

 

[Petebass]

I'm no an engineer so I just want to clarify I'm understanding this correctly. If the harmonic patterns are different between a braced and non braced cab, how would this manifest in terms of sound? For example, if two identical cabs were built and one was braced and one wasn't, how would a frequency response graph differ between the two cabs assuming the non braced can was already fairly stiff?

 

[robthebassplaye]

Rob,

Welcome to TalkBass. Thanks for posting this. It's clear you've gone to a LOT of work to build and document this cab.

It is remarkable how you arrived by different routes at endpoints so similar to others here. In your choice of drivers, cab volume, and crossover, you're close to a fEARful. And your construction methods are close to what was done by zac2944, Petebass, and Robby Hoinsky.

There are some differences too, such as your porting choices. I don't recall ever seeing a cab with both front and rear ports. Curious as to how you arrived at that configuration. On page 8 of your first PDF (As-Built Dual 7.85" Ports vs Other Port Options), I'm not sure what I'm looking at. What is the Y axis?



AFAIK, you are the first builder to do this. This sounds like some great basic research. Can you share more details?

Hi! Thanks for the questions! Thats exactly the kinds of discussions I was hoping to have on this forum.

So, here goes about page 8 and the porting options.

These are actual measurements (not something theoretical) of the cabinet with different porting opitons. The X axis is frequency, the Y axis is dB (but only relative to itself).

What I was doing was changing the port lenghts and measuring the low frequency performance. I did this outdoors, so that there would be absolutely no room effects (even I don't have access to an acoustic chamber that will be accurate below 100 Hz, and I'm fairly certain that if I don't have access, no one does, given my job

So, this was a design of experiments kind of thing. I'd build it with different port lengths, measure it, and then listen to it. That is what led me to the final "as built" configuration. I wasn't sure that the standard acoustic formulas would hold up in a cabinet that was super stiff, beacuse I didn't know if the software I was using had been "tweeked" for real world effects (such as plywood stiffness, vs the resonances that exist (or don't exist) for a composite wall).. Turns out they were not tweeked, but being anal and an engineer, I wasn't taking anything for granted.

The porting (front and rear) turned out to be more of a practical decision. Fitting 2 ports on the front baffle would have been the best theoritical way to do it, but I was running out of room (and structure) I was worried about how strong this composite wall would be, but I'm not worried any more - it's stronger than anything I could have imagined!

In my opinion, as long as the rear port is at least a quarter of a wavelength away from the rear wall, there should not be any noticable effects. In actual use, this cabinet sounds freakin' awesome (to me). But, you have to remember that room acoustics, especially at low frequencies, play a large part in the perceived audio quality.

Thanks for this post! Did I answer your question?

Rob

 

[robthebassplaye]

I'm no an engineer so I just want to clarify I'm understanding this correctly. If the harmonic patterns are different between a braced and non braced cab, how would this manifest in terms of sound? For example, if two identical cabs were built and one was braced and one wasn't, how would a frequency response graph differ between the two cabs assuming the non braced can was already fairly stiff?

Hi Petebass,

OK, this is awesome. Now were having some good conversations!

Often times, things like this will not show up in a frequency response curve. Thats why it's always really important to listen to things.

Harmonics, which I believe are what result from different bracing techniques, may not show up in a frequency response plot. And, the harmonics that do exist will totally effect the perceived sound - even harmonics vs odd harmonics have a very different sound, and really can't accurately be captured in a frequency response curve.

So, in my opinion, the stiffness of the composite build reduces all harmonics (even and odd - thats what I measured, have a look at the data, so I believe it's true). And, reducing those harmonics (any harmonics) makes the cabint more accurate in my mind.

You can search on the internet for opinions about those even and odd harmonic effects and how they sound - that would be an entirely different and Huge thread! Some folks prefer even, others prefer odd harmonics. I do know that they sound different. But, in a composite build, those harmonics are allmost non existant.

You can see that on the accelerometer data that the harmonics (even or odd) die out much more quickly on a stiff structure such as the fiberglass composite, relative to a plywood panel. I think that effect is audible and noticable.

Anyway, THANKS so much for the question, these are exactly the kinds of conversations I wanted to have on this forum.

Did I answer you question?

Rob

 

[BogeyBass]

Really, what I want to do here is have serious technical discussions, thats the only reason I'm on line here.

Thanks,
Rob

Cool, first of all i do believe you reached your goal of building a lighter cabinet.

Otherwise as far as your opinion on the fiberglass being a superior material.
I would say its the opposite. Wood offers superior damping and reduction of resonance with the tradeoff of higher weight.
Foam/Fiberglass composite offers lighter weight. with the trade off of less damping and more resonance.
your test data clearly shows that the composite material has more resonance. Shown by much stronger upper harmonic energy.

[Invalid or Expired Link Removed]

[Invalid or Expired Link Removed]



If we were to label anything as being superior it would be a material that shows a significant reduction of the fundamental frequency and of course the upper harmonics. If the fundamental was reduced then we would be achieving the goal of finding a better material that is damping the actual original frequency.

Otherwise as far as why the composite shows odd order harmonics could be one of 2 things.

1) The waveform itself is simply symmetrical in nature and would show a somewhat typical spectrum. A very strong rise of even order 3rd harmonic and a set of strong odd ordered higher harmonics. similar to your composite graph

2) hopefully not, it may be possibly that the traducer signal was strong enough to cause symmetrical distortion on the electronics side. I dont know how much voltage the accelerometer was putting out, and dont know the voltage of the system used to get the signal. I'm sure its not an issue.

Otherwise its great you posted this, because over the last few days i have been looking into accelerometers and software to test a multi layer baffle that i built.

Seems like you already have a great system, i wish you could do the same 95 hz test with a small test piece of my multi layer baffle. I think it may be easy for you to recreate. aside from the other sillyness in this thread i have some photos and diagrams in this thread about it.

I'm interested in seeing how it performs, hopefully i might be able to spark your interest.

[Invalid or Expired Link Removed]

the idea is that all the vibration is obviously coming from the speaker. Any vibration or energy coming into a enclosure would be from the frame of the speaker mounted to the baffle and the baffle is connected to the rest of the enclosure.

I wanted to isolate and reduce as much vibration as possibly right at the source the speaker and the baffle.
so blah blah blah without making this post any more longer. its what i came up with. I could fill up a few pages on why it works but i will spare us from that.

aside from the somewhat thread high jack, sorry hope you dont mind, its just so related to what ive been looking at for the last few days.

 

[robthebassplaye]

I guess the question is how "independent" is it?



At any rate since the fEARful plans are free people are free to do what they want with them with varying results of success.

As a side note, I am reluctant to "go there" in this thread as there are enough petty squabbles on TB, but I have a hard time leaving this alone and not pointing some things out to those who might not have otherwise made the connection.

...And if someone is genuinely interested in a composite cab like this they can head over to Link Removed

Hi Bassist,

I'd like to assure you that I arrived at my design absolutely independantly. In fact, I'm a bit embarresed that I did not find some of these other builds while doing my research - so that fact alone is a barb that stings... I'm relatively new to TalkBass... And, being an Engineer that "redesigned the wheel" so to speak, is a bit embarrising and not good for one's reputation, so I'm not thrilled about that either. But, I think I did a lot of research and experiments up front that had not been done before, and hopefully that is worth something.

So, I'm mostly embarresed, and it's ok if you want to point that out.

All I want to do is to contribute to the knowledgebase of cabinet construction. I have no financial interest in any of this (there certainly are folks who do have a financial interest in things on this forum, but I am not one of them, nor do I think thats a bad thing). Everyone needs to make a living.

I want to share the technical information I have acquired with anyone who cares to acquire it. I'm just a part time, hobby kind of bass player.

I'm not sure if this put's your mind at ease, but I am definately not out to eat anyone elses cake... All the work that was done prior to my (First ever on the internet) post clearly is ground breaking, and I definately acknowledge it as such.

Thanks,
Rob

 

[Mike Arnopol]

As far as copying---there are only a few drivers that will work in this type of application. Unless one is going OEM, you've got one driver (3012lf) to use. (I'm trying the Beyma---looks promising)If one has never heard of Talkbass or Fearful they still would likely be looking at the few 6 1/2 mid drivers. (I used 6 1/2 Audax pro sound drivers 20 years ago---the newer 18 sound and Faitals are higher power handling but don't necessarily sound better)Not to lessen the impact of Greenboy who is really doing the bass community a great service, but these choices are pretty common sense. I just built a composite cab. Wanted something as small as possible using a 3012ho. After modeling I realized that my cab was VERY similar to the Barefaced Midget. I wasn't trying to copy it---it was just common sense as far as enclosure size and tuning.

 

[robthebassplaye]

Cool, first of all i do believe you reached your goal of building a lighter cabinet.

Otherwise as far as your opinion on the fiberglass being a superior material.
I would say its the opposite. Wood offers superior damping and reduction of resonance with the tradeoff of higher weight.
Foam/Fiberglass composite offers lighter weight. with the trade off of less damping and more resonance.
your test data clearly shows that the composite material has more resonance. Shown by much stronger upper harmonic energy.

[Invalid or Expired Link Removed]

[Invalid or Expired Link Removed]



If we were to label anything as being superior it would be a material that shows a significant reduction of the fundamental frequency and of course the upper harmonics. If the fundamental was reduced then we would be achieving the goal of finding a better material that is damping the actual original frequency.

Otherwise as far as why the composite shows odd order harmonics could be one of 2 things.

1) The waveform itself is simply symmetrical in nature and would show a somewhat typical spectrum. A very strong rise of even order 3rd harmonic and a set of strong odd ordered higher harmonics. similar to your composite graph

2) hopefully not, it may be possibly that the traducer signal was strong enough to cause symmetrical distortion on the electronics side. I dont know how much voltage the accelerometer was putting out, and dont know the voltage of the system used to get the signal. I'm sure its not an issue.

Otherwise its great you posted this, because over the last few days i have been looking into accelerometers and software to test a multi layer baffle that i built.

Seems like you already have a great system, i wish you could do the same 95 hz test with a small test piece of my multi layer baffle. I think it may be easy for you to recreate. aside from the other sillyness in this thread i have some photos and diagrams in this thread about it.

I'm interested in seeing how it performs, hopefully i might be able to spark your interest.

[Invalid or Expired Link Removed]

the idea is that all the vibration is obviously coming from the speaker. Any vibration or energy coming into a enclosure would be from the frame of the speaker mounted to the baffle and the baffle is connected to the rest of the enclosure.

I wanted to isolate and reduce as much vibration as possibly right at the source the speaker and the baffle.
so blah blah blah without making this post any more longer. its what i came up with. I could fill up a few pages on why it works but i will spare us from that.

aside from the somewhat thread high jack, sorry hope you dont mind, its just so related to what ive been looking at for the last few days.

OMG - this is the best discussion ever!

You are correct in your analysis of my charts, but take a look at the scales. They are not accurate, and thank you for seeing that. They are just accurate relative to the same measurement.

They are just relative levels, so you can only compare the numbers to what was taken at the same time for the same test - unfortunately you cant compare one run against another...

In other words, it's sort of hard to intrepret.

But, I do know that the levels (ie the displacement) of any resonances in the composite are much lower.

Also - these graphs were taken from a worst case scenario - I did conclude that they resonated at 95 Hz (for the test panels, not the final build, which was much, much higer and not included in those charts). So, these are at the resonant node, and as you would expect, plywood does dampen out faster. That makes sense, of course. But the fact that the levels of the composite are so much lower really is what is important to me.

So, therefore I think that my original conclusions are still correct. A composite build has much lower levels of resonance than a plywood build. Also, I posted the mechanical/structural prpoerties of plywood, and from that, I think you can draw the same conclusions. Yes - you are correct, that the plywood does dampen out faster, but in fact, the composite starts from a much lower level, and never really needs to have all of that dampening... It's just low.

Also, you are correct that wood has superior damping properties, but it has a larger fundamental resonance, so most of that dampning goes into mitigating that.

Dampeing is a different property than stiffness.

I would be really, really happy to test and measure your materials, if you would like. Please keep in mind, I have absolutely no financial interest in any of this, I'm just an engineer wanting to spread valid engieering data around...

Or, I am absolutely very happy to send you all of the details of my test setups, for you to measure this. It's not that expensive (less than $200 USD).

Really!

Rob

 

[robthebassplaye]

Awesome cab, and nice thorough documentation of what you did/how you did it. I built a composite cab a little over a year ago and it's still going strong! My goal for it, as a 1x12, was to come in under 20 lbs and its right around 19.5~ which I was ecstatic about.

These builds to me are just fun ways of attempting new ways of speaker (cab) design. I've built a few cabs from plywood, but working with fiberglass and this type of technology was exciting and interesting to me. I would love to do another cab (a second identical, a 12/6/1 like yours here, or a fEarful 15/6/1) when I have the financial resources for it. After making one of these, there's so much I feel that you learn that could help improve/quicken the process for the next time.

Again, Great build and thread! I hope to see more in the future

Yikes - hoping to see more in the future???

This was a boatload of work, and as much as I love the cab, I dont think my marriage will support another one of these...

But, just beacuse I wont be building anymore in the future, I would still like to stay in touch. I want to help spread the technical info about these...

Rob


Rob

 

[robthebassplaye]

As far as copying---there are only a few drivers that will work in this type of application. Unless one is going OEM, you've got one driver (3012lf) to use. (I'm trying the Beyma---looks promising)If one has never heard of Talkbass or Fearful they still would likely be looking at the few 6 1/2 mid drivers. (I used 6 1/2 Audax pro sound drivers 20 years ago---the newer 18 sound and Faitals are higher power handling but don't necessarily sound better)Not to lessen the impact of Greenboy who is really doing the bass community a great service, but these choices are pretty common sense. I just built a composite cab. Wanted something as small as possible using a 3012ho. After modeling I realized that my cab was VERY similar to the Barefaced Midget. I wasn't trying to copy it---it was just common sense as far as enclosure size and tuning.

Thanks!

I really just want to contribute technically to the field! If it's not technicial info, I'm just not that interested... It's not a business, nor anything else for me... It's just the fun of having insightful technical conversations...

Rob

 

[seanm]

In my opinion, as long as the rear port is at least a quarter of a wavelength away from the rear wall, there should not be any noticable effects. In actual use, this cabinet sounds freakin' awesome (to me). But, you have to remember that room acoustics, especially at low frequencies, play a large part in the perceived audio quality.

Interesting thread. In practical terms, how far away from the wall does a rear ported bass cab need to be to reduce noticable effects?

Sounds like you built a real winner.