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Ultra Light Weight Bass Cabinet

#81
Passinwind said:
He's not too roughed up about it, judging from his posts in his own forum. ;)
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Greenboy and I talk on the phone probably a lot more openly than most "competitors" do. He is impressed by Rob's build, and so am I.

Comparing notes, Greenboy and I have independently come up with several virtually identical "designs on paper", because we have similar goals and are looking at the same collection of available drivers to work with. So that sort of thing happening here isn't surprising.

As one who builds plywood cabs, I don't hesistate to concede Rob's points on the superiority of a good foam-core composite build (points well made by Zac and Petebass and Robby Hoinsky, but I think Rob's in-depth hands-on research is unique).

Putting on my armchair designer's hat for a minute, I see a lot to like in Rob's design choices apart from the composite cabinet. I like his driver choices; I like his box size; I like his innovative porting arrangement. Let me talk about the latter a bit:

Rob's porting architecture invites hot air to exit the top port and cool air to enter the bottom port, which is something that was recommended to me by an engineer at Eminence. Also, spreading out the ports in all three physical dimensions will somewhat stagger the way they interact with room boundaries. In practice I don't know how much of a difference this might make in a large venue, but in a small room (like a living room) I believe that spreading out the low frequency sources has audible benefits.

Given the height of the cab, I might have tried to vertically align the mid and tweet, but can't say for sure that would make an audible difference.

I do have a minor question, Rob. Is your box tuned to 48 Hz (page 2 of your PDF), or 52 Hz (page 8 of your PDF)?

Thanks!

Very nice job sir.
 
#82
robthebassplaye said:
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
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No worries. Hope it all works out for you. :)
 
#83
DukeLeJeune said:
Greenboy and I talk on the phone probably a lot more openly than most "competitors" do. He is impressed by Rob's build, and so am I.

Rob's porting architecture invites hot air to exit the top port and cool air to enter the bottom port, which is something that was recommended to me by an engineer at Eminence.

Very nice job sir.
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Hello Duke,

Thank you for the very kind comments.

And, I definately did talk with an Eminence Engineer - Mr Jerry McNutt (or McJerry as he is known in the industry). So, definately kudos out to him and Eminence, I should also have stated that more clearly up front. Without good drivers, a good cabinet is impossible to design.

He definately advised me to put ports on the top and the bottom, and that would have benificial cooling effects for the drivers. He wasn't sure about the front / back effect, didn't sound like that had reallly been tried before.

I have tried to measure the effects of that design (ports on the front and the back), but the problem is that the only theoretical effect the rear port will have is in close proximity to a wall, and once you do that, (at least for me), thats inside, and then the room comes in to play.

So, I don't have any viable method to measure its effect that I could stand by.

This would be a GREAT topic for a discussion, how could you measure this effect (aside fo the standard equations and analysis)???

Rob
 
#84
DukeLeJeune said:
I do have a minor question, Rob. Is your box tuned to 48 Hz (page 2 of your PDF), or 52 Hz (page 8 of your PDF)?

Thanks!

Very nice job sir.
Click to expand...
Hello Duke,

Sorry, I missed your real question, regarding the box tuning.

So, from my perspective, and this is coming from someone who is anal and really puts a lot of stock into numbers and measurements, it is 52 Hz as measured. I was aiming for 48Hz, but for whatever reason that didn't happen, and wasnt able to happen given the physics of the box. I wanted (and had hoped) to design it for a lower frequency.

I think there are a lot of designs out there that have a theroitical number, but probably very few (including famous, mass marketed cabs) that have an actual measured number lower than this - it's really hard to achieve.

Based on other posts I have seen from you, I know that you understand this, but I want to state it again for others reading this - there are THREE VARIABLES for any kind of cabinet design - Low, Light and Loud. And making any one of those more important will impact the other. So, a loud box (ie with a higher SPL output) will have a harder time with low notes, and with being light. Heavier boxes, and boxes that are larger and more structurally sturdy, can definatley go lower in freq response, and possibley louder.

This build was an effort to mitigate one parameter, (light),

So, althought 52Hz "sounds" high, my bet is that is is actually lower that a lot of the production cabs out there. I have not measured them, so I don't have a basis for that statement, but based on what I know about this, I belive it's accurate.

Also, In my opinion (again, I'm trying to stay out of trouble here), it is not the fundamental tone of the bass note that is important, but rather the harmonics of that note that give it the quality that people like to hear. In my book, it's not the harmonics of the cabinet that you want, it's the harmonics of the instrument and strings.. I know that might be a bit confusing to some, and I'm sure that requres an entirely different thread and topic as well!

Thanks,
Rob
 
#85
Petebass said:
The Kappalites are amazing drivers. I think even Greenboy would acknowledge that once you decide to use them, and if you follow a logical path, the rest of the cab kinda designs itself. Good design is good design no matter where it came from! So lets move on eh!!!
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Yup - sounds like a good idea to me. Thanks, Petebass!

Rob
 
#86
::::BASSIST:::: said:
No worries. Hope it all works out for you. :)
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OK, thanks for the "no worries"... and "the hope that it all works out for me"...

But, I'm actually not trying to make anything work out for me, and I think that perhaps that is some of the misconception. I could care less if anyone thinks this cab build is a good idea, or a terrible idea.

I'm set in life, I have a great job, great family, and I will definately not be in the bass cabinet business, --- ever. Based on what I know about the MI industry, thats just too hard to compete in, and I am definately not interested, even for a few $K per week.

So, really, I don't care, except at a technical level. Thats why I've put any post on here....

I got that message across to other folks that DO have a business interest in this area, I'm pretty much a non-completitor in their eyes. I just want to have technical discussions, and I think they understand that. And, I think thats OK with them...

I'm just looking to have high quality technical conversations about these topics.

So, let's all step up the technical discussion !!!

Hope that helps put things in perspective,

Rob
 
#87
Passinwind said:
He's not too roughed up about it, judging from his posts in his own forum. ;)
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You know, I'm such a nubie at this (and that is really hard to say when you are 53 years old...). But, where can I find that forum??? I know I've tried to find it, but without sucess....

Thanks (Sorry to be such an inept dude...).

Rob
 
#88
robthebassplaye said:
I'm just looking to have high quality technical conversations about these topics.

So, let's all step up the technical discussion !!!
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I agree - technical discussions on TB should help open a lot of eyes and promote good innovative thinking for the future. Unless we educate people into learning how do design properly and innovatively, we will be stuck with the same old expert opinions. One reason the experts dont talk in detail is they dont want to give away their "secrets"! However, in most cases its prior art and just that others dont have the confidence and experience to use it to best effect.

Having seen a number of cab designs with unusual formats and materials, I can see that many people on here would respond well to technical discussions before embarking on their next projects.

Yes, the small, low and loud physics cannot be broken but most people are not at the limit of the physics and compromises are made due to poor design. There is therefore potential to get closer to physical limits. :D
 
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#90
Bass Unique said:
I agree - technical discussions on TB should help open a lot of eyes and promote good innovative thinking for the future. Unless we educate people into learning how do design properly and innovatively, we will be stuck with the same old expert opinions. One reason the experts dont talk in detail is they dont want to give away their "secrets"! However, in most cases its prior art and just that others dont have the confidence and experience to use it to best effect.

Having seen a number of cab designs with unusual formats and materials, I can see that many people on here would respond well to technical discussions before embarking on their next projects.

Yes, the small, low and loud physics cannot be broken but most people are not at the limit of the physics and compromises are made due to poor design. There is therefore potential to get closer to physical limits. :D
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WaHoo! Thank you so much for weighing in.

I could not agree more. Let's open up those discussions. All I want is for the best technology to be available to all the bass players out there. After all, for me, thats what it's all about. I'm a tech geek, clearly...

As far as breaking the laws of Physics, it's really hard to do. But, there are pretty simple design rules that are not expensive, that make a big difference. So, getting the word out here about that is a good thing, I think. Some of those rules are really easy to latch on to.

We can define the limits of the technolgy, describe how to hit those limits, and then its up to everyone (individually) to decide how close to those limits they want to get...

And, getting close to the limits of technology has always cost big bucks. Think about any technology, that is just the way it works..

(Thats probably why building this kind of cabinet was krazy expensive for me, and probably will be for anyone else who is going to try it). But, maybe, someday, those things will change.

Imagine if you could build this type of cabinet for the same dollars as any other wooden cab...

So, very cool, and thanks for that focus - we should all think along those lines...

\Rob
 
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#92
Bass Unique said:
It seems that some people think that these forums are not for very technical discussions. If this is the case, should be ask for a new forum called "Technical discussions" where we can go in to as much detail as we like - for those that are easily confused, they can use the normal forums?

Do we ask the moderators or is the view that we can do this in "Amps" anyway?
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NOOOOO, keep it coming, great subject, mostly over my head tbh, but it seems there are enough folks here that do understand
 
#93
rad bassman said:
NOOOOO, keep it coming, great subject, mostly over my head tbh, but it seems there are enough folks here that do understand
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Yo Rad Bassman,

Thanks for that comment! To me, it seems like accurate data, and real data, can only benefit this kind of community.


So, all I want to do is get facts out there.

And, to be clear, not everything is black and white. There are some things - especially in audio - that are not clear and are subjective.... One persons objective opinion about audio quality will not be the same as anothers....

So, it's imortant to keep the mind open, and to stay focused on whats going on...

Thanks
Rob
 
#96
Hey Rob , really nice build!
Love those DIY things like yours or Greenboy's etc....

I would be the prefect target for one of those if was not such a big fan of integrated active PA boxes. :bassist:


Talking about PA boxes , why do you all end up with Eminence drivers ? ( question to all engineers and DIY'ers )
There are a lot of other drivers out there : JBL , EV , RCF , etc... there is no other alternative as far as power/weight/etc.. is concerned ???
 
#97
Hello, again.. Obviously my questions aren't in the technical end, methinks you have that covered... but more how this was built.. I recognized the West System epoxy in the pics. I have used this before in my R/C model race boat days.. I'm just curious, since obviously you have thought long and hard about everything that went into this.. is there an advantage to using West Systems over other epoxy systems?? Did you research foam materials other than polyester i.e. polyurethane, klegecell, etc? Is the 1-1/2" thickness a calculated parameter? Ever consider vaccum bagging?

Just trying to make a decision whether its worth it for me to try a little prototyping...
 
#98
fokof said:
Talking about PA boxes , why do you all end up with Eminence drivers ? ( question to all engineers and DIY'ers )
There are a lot of other drivers out there : JBL , EV , RCF , etc... there is no other alternative as far as power/weight/etc.. is concerned ???
Click to expand...

The short answer, the Kappalites are simply the best driver for the application.. I am certain no stone was left unturned when guys started developing these cabs.. I've ran a bunch of 'em myself through the ol' ISD.. If I thought I could design something better w/different components, I would have done it.. There's a reason I am where I'm at...
 
#100
robthebassplaye said:
You know, I'm such a nubie at this (and that is really hard to say when you are 53 years old...). But, where can I find that forum??? I know I've tried to find it, but without sucess....

Thanks (Sorry to be such an inept dude...).
Click to expand...

Hey Rob,

Looks like someone else posted the link. Welcome to Talkbass, by the way.

I have done some crossover modeling in LTSpice myself. Have you looked into using some subcircuit models for the speaker loads, rather than just using 8 ohm resistors? Also, did you measure frequency response on the actual baffle installed on your cab, or at least model baffle step and diffraction effects?

Nice build. I have a fair amount of experience working with composites for watersports toys, and if I ever bother to build any more DIY cabs I would prefer that sort of construction to wood by a large margin.
 

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