DIY Lightweight Composite Cab Build

[GGman]

Adjust the kerning better on the word Lite

A few more logo ideas. Thanks to those who posted/PM'ed suggestions.


Here's a different font and more subtle color scheme. A little less Nascar.

Here's a different logo.

 

[GGman]

I would bet some college around Boston, or even MIT, would help you measure it with what they have. Or some research lab/company.

That is something I'm trying to understand better. What happens on paper (or on Winisd) and what happens in the real world are two different things. I believe that my port calculation were accurate because the nature of the physics behind those calculations is fairly straight forward. Frequency response is whole other ball of wax. WinISD assumes your signal is a perfect sine wave. Your bass produces a much more complex signal.

For now I'm limited to testing with only a SPL meter and sine wave signal generator. I'm looking into getting an test mic and running RTA software for more accurate analysis. I doubt I'll ever have access to an anechoic chamber, but the backyard will work for now. The neighbors give me the strangest looks when I'm sweeping text tones. I live in a very dense city neighborhood just outside of Boston. I just hope they spare me so I don't have to explain.

 

[zac2944]

http://www.laminatorwarehouse.com/di_films.shtml I'm using the 7/3 DI (10 mil), but I have a few others here. It is polypropylene. You can get this stuff a number of different places, but each has its own qualities. The CP is less stiff, for example.

I did some quick searching on matweb.com and polypropylene film looks to be at best only 1/10th as stiff as fiberglass/epoxy when considering flexural modulus. If you're designing an equivalent to plywood a good flexural modulus to use is about 7-9 Gpa for the plywood and consider it monolithic.

The nice thing is that it is just iron on, so it is 100 times quicker than FG/epoxy.

Be careful with the iron on the XPS. It has a glass transition temperature of about 203F (95C). If you get it too hot it will try to out-gas and expand.

Also, how will you do the corners? This could be tricky with film.

I did a test and one ply is near as stiff as plywood, but less strong (kind of like what you found out during your testing). Luckily I can put multiple layers of the film over each other and that will substantially increase stiffness and strength. I can do the calculations too (we do them to calc wing strength), but I have no idea how strong or stiff they need to be! Do you have any info on that?

Adding more film will make it stronger and stiffer, but will also make it heavier. You can stiffen up your cab without the weight penalty by thickening your core. This adds little weight, but increases your stiffness dramatically.

Use the plywood modulus data above to calculate the stiffness of 1/2"-3/4" ply and try to design a sandwich panel to match that stiffness.

I just went back and read that you put 27 ozs of E glass on each side. Yes, that would be strong. That would make a good strong slope fuselage.

I wanted the baffle to be very stiff, so I used all that glass and a thicker core. It really is rock solid.

I was going to make a build thread once I figured out if it would work or not. I have a couple of pics.

Cool. Can't wait to see it.

 

[AndreasMergner]

I did some quick searching on matweb.com and polypropylene film looks to be at best only 1/10th as stiff as fiberglass/epoxy when considering flexural modulus. If you're designing an equivalent to plywood a good flexural modulus to use is about 7-9 Gpa for the plywood and consider it monolithic.

Polypro is also 1/3 the weight, and with a 1" thickness compared .5" thickness, the polypro will be 4/3's the strength for the same weight of laminate.

Be careful with the iron on the XPS. It has a glass transition temperature of about 203F (95C). If you get it too hot it will try to out-gas and expand.

In practice it is not a problem.

Also, how will you do the corners? This could be tricky with film.

You need to pleat or cut it. It is not that hard to do. If you are going to cover it with carpet, it's not a problem at all. If you are painting, you need to do a neat job.

Adding more film will make it stronger and stiffer, but will also make it heavier. You can stiffen up your cab without the weight penalty by thickening your core. This adds little weight, but increases your stiffness dramatically.

Yes, definitely. I agree. Luckily the film is not really that heavy.

Use the plywood modulus data above to calculate the stiffness of 1/2"-3/4" ply and try to design a sandwich panel to match that stiffness.

I can tell that just one layer is stiffer....it's just not as strong. I think 2 or 3 layers will be better although 1 would do if you used carpet and were a little bit careful handling it.

 

[Khronic]

Wow! What a great idea, build, and thread.
Zac you knock me out.
I finally thought of something to add. Check out Invalid Link Removed from a couple of years ago.

 

[zac2944]

Wow! What a great idea, build, and thread.
Zac you knock me out.
I finally thought of something to add. Check out Invalid Link Removed from a couple of years ago.

Thanks for the props.

About that patent. What caught your eye there? The tie-blocks? Surfboard makers have been using that technique for years. IMHO, the weight it adds isn't worth the added peel strength you gain. If you needed a cab that was bomb proof it might be worth it though. I haven't had any delamination issues yet so I wouldn't be so quick to add tie blocks.

 

[billfitzmaurice]

Did some more testing yesterday. Things in the neighborhood quieted down in the evening so I gave it a go. I used the same procedure as last time, except I pointed the cab up and took measurements from above.

Here's a look at my ghetto testing set up:

.

Measuring like that you'll get a 1/2 wave cancellation dip based on the distance from the front of the cab to the ground and back again. If the total distance is 3 feet, for instance, you'll see a dip at roughly 190 Hz.
The best way to do it is with two measurements. The first is ground plane, with the cab facing normally and the mic on the ground, preferably 2 meters out, which gives a reading 6dB less than 1 meter, which you compensate for by using a 4 watt signal. There can be no large obstacles or walls within at least 50 feet. This gives an accurate 1/2 space measurement, but only up to where the baffle is 1 wavelength across in the smaller plane. With a 2 foot wide baffle, for example, that's about 565 Hz.

Make the second measurement as shown in the picture, with the mic at 2 meters high on-center with the tweeter if there is one. This will give the 1/2 space result above the baffle step frequency. Combine the two results for 1/2 space broadband. In the transition octave between the two measurements average them, above and below that use each individually.

 

[zac2944]

Measuring like that you'll get a 1/2 wave cancellation dip based on the distance from the front of the cab to the ground and back again. If the total distance is 3 feet, for instance, you'll see a dip at roughly 190 Hz.
The best way to do it is with two measurements. The first is ground plane, with the cab facing normally and the mic on the ground, preferably 2 meters out, which gives a reading 6dB less than 1 meter, which you compensate for by using a 4 watt signal. There can be no large obstacles or walls within at least 50 feet. This gives an accurate 1/2 space measurement, but only up to where the baffle is 1 wavelength across in the smaller plane. With a 2 foot wide baffle, for example, that's about 565 Hz.

Make the second measurement as shown in the picture, with the mic at 2 meters high on-center with the tweeter if there is one. This will give the 1/2 space result above the baffle step frequency. Combine the two results for 1/2 space broadband. In the transition octave between the two measurements average them, above and below that use each individually.

Thanks for your input Bill! I went into testing these cab blind and based my setup on some info I've picked up here and there on the web and a lot of assumptions. It was a learning experience more than anything.

The two step approach you describe makes a lot of sense. I new I was probably picking up some interference due to the boundaries in my test area, but since it was my only option at the time I had to neglect it. I'll have to give your method a try next time.

I'm planning another build and test once the 3012s are released. This time around I hope to have enough cash on hand to shell out for a Behringer measurement mic (ECM8000) and a copy of TrueRTA. Call me a geek, but I love designing and testing. I'd really like to get better at testing and learn better procedures. Using a SPL meter, PC generated test tones, and logging data into Excel takes a long time. Not to mention all the neighbors I must have pissed off!

Can you recommend any good sources for info on speaker testing and procedures for the non-professional? Would joining AES be a good source for this type of info considering I don't work in the industry? I am an M.E., but work in the printing industry. Maybe money would be better spent on a good book or two.

 

[billfitzmaurice]

Can you recommend any good sources for info on speaker testing and procedures for the non-professional?

The definitive text:
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Would joining AES be a good source for this type of info considering I don't work in the industry?

Not really. Being a member gets you discounted pricing on archived AES articles and their various books, but you'd need to order a pre-print everyday to make it worth the membership cost. AES today is very much theoretically oriented, too much so IMO, the average article has math that would make even an EE's head spin.

 

[alexclaber]

The best way to do it is with two measurements...

Very useful info Bill! I'd guessed it had to be something like that because of the baffle step - I suppose the other way of doing it would be to dig a hole in the ground exactly the same size as the cab and then you could do one measurement from up above!

This time around I hope to have enough cash on hand to shell out for a Behringer measurement mic (ECM8000) and a copy of TrueRTA.

I finally bit the bullet and these arrived this week. Much better than all the bodges I've used up 'til now! Am going to get some measurements done ASAP and hopefully my simple design, The Compact, will act as an effective control measure as it should plot out very similar to Eminence's own data, so if that comes out right then I'll know my methods are reliable.

Alex

P.S. Got some other interesting designs on the go too but that's another topic!

 

[billfitzmaurice]

Very useful info Bill! I'd guessed it had to be something like that because of the baffle step - I suppose the other way of doing it would be to dig a hole in the ground exactly the same size as the cab and then you could do one measurement from up above!

That is an option for taking a half-space measurement in one pass, the other being an anechoic chamber with a flush mount in one wall.

 

[Crockettnj]

lol

I was checking the tuning freq of a cab in my classroom after hours and I guess the swept sine signals caught someones attention. One of the physics teachers walked by, shook his head, and mumbled something about digging holes in the courtyard.

I get the reference now.

 

[Foz]

T...AES today is very much theoretically oriented, too much so IMO, the average article has math that would make even an EE's head spin.

True... but if you subscribe to the AES library you can download the papers that set out all the fundamental work behind damn near every concept contained in general information texts on acoustic subjects, and generally the early AES articles are more detailed - and often MORE accessible/useful than thinner treatments in generalized texts and includes much more extensive detail of what works and what doesn't and why [in addition to the math]. So, if you are interested in a broad range of acoustic studies the AES library pays big dividends [though you'll end up buying books as well].

That said... older AES articles should be available IMO for much less than AES charges [if not for free] as the cost of production was covered long ago and science would be best served with broader distribution.

People of the same trade seldom meet together, even for merriment and diversion, but the conversation ends in a conspiracy against the public, or in some contrivance to raise prices.

George Adam Smith

 

[Foz]

lol

I was checking the tuning freq of a cab in my classroom after hours and I guess the swept sine signals caught someones attention. One of the physics teachers walked by, shook his head, and mumbled something about digging holes in the courtyard.

I get the reference now.

Try the ground plane method in the Gym instead. No need to dig holes.

 

[bebass]

Polypro is also 1/3 the weight, and with a 1" thickness compared .5" thickness, the polypro will be 4/3's the strength for the same weight of laminate.



In practice it is not a problem.



You need to pleat or cut it. It is not that hard to do. If you are going to cover it with carpet, it's not a problem at all. If you are painting, you need to do a neat job.




Yes, definitely. I agree. Luckily the film is not really that heavy.



I can tell that just one layer is stiffer....it's just not as strong. I think 2 or 3 layers will be better although 1 would do if you used carpet and were a little bit careful handling it.

How did your version turn out?

 

[zac2944]

How did your version turn out?

+1

I'd love to know if anyone else has been working on similar techniques.

FWIW, I'm still rocking the ZL210 and both the ZL1263s. The ZL210 has probably been out on 20-30 gigs without any issues and I'm just now getting to take the two ZL1263 cabs out live.

 

[Rafael]

You say you are currently playing out with both versions....can you comment on the types of shows/venues/reinforcement/style/etc to contrast and compare the response of the two designs? I'd love to have two of each, but economics and storage space probably precludes that in my case, so I'm trying to figure out which way to go for my own personal setup and would appreciate your impressions...fyi I play in a rock band, most often with some sort of house reinforcement, with two guitar players each with a Marshall 1/2 stack at moderate volumes, with a live drummer. As a comparison I normally play w/ a 4x10 + 1x15 for larger/non reinforced shows and the 4x10 when reinforced...all this w/ my Seymour Duncan 400w amp which can produce I think 600 at 2ohms...thanks for any advice you may have. And thanks for your seminal work in composite bass cabinetry.

 

[Petebass]

+1

I'd love to know if anyone else has been working on similar techniques..

Zac, I was inspired by your design, and by some musician friends who are also into boats and therefore were very keen to see me build a composite cab.

I started work today on a composite 1x12 which will be an exact replica of the cab I just built out of wood. Should make for some pretty interesting A/B comparisons

The wood cab has a Delatlite11 2512 speaker in it and came in at 12.45kg (27.44lb). Hardly heavy, in fact it feels so darn light already I'm wondering if reducing weight should even be worth the effort. But darn it, I'm planning to have some fun building the composite cab

I also had one of those friends build a replica of a previous 1x12 design from Carbon Fibre (see pic). This speaker has a Beyma 112ndW in it so it was never going to be a flyweight cab, not with that driver in it. But his CF cab weighs 3kg (6.6lbs) less than my wooden one, 12kg Vs 15kg (26.5lbs Vs 33.1lbs).... and it looks much sexier don't ya think? This cab was made for an Olympic sailor by the people who made his medal winning boats, so as you can imagine the materials used and the build technique were very different to your cabs Zac. This one has divinycell foam, a mould, vacuum bagging, the works. If I had access to world class composites experts who'd do it for free, I would have went all out as well

 

[basscooker]

hmmm, lightweight, non-wood. good idea. best of luck.

 

[mothra2]

Zac, I was inspired by your design, and by some musician friends who are also into boats and therefore were very keen to see me build a composite cab.

I started work today on a composite 1x12 which will be an exact replica of the cab I just built out of wood. Should make for some pretty interesting A/B comparisons

The wood cab has a Delatlite11 2512 speaker in it and came in at 12.45kg (27.44lb). Hardly heavy, in fact it feels so darn light already I'm wondering if reducing weight should even be worth the effort. But darn it, I'm planning to have some fun building the composite cab

I also had one of those friends build a replica of a previous 1x12 design from Carbon Fibre (see pic). This speaker has a Beyma 112ndW in it so it was never going to be a flyweight cab, not with that driver in it. But his CF cab weighs 3kg (6.6lbs) less than my wooden one, 12kg Vs 15kg (26.5lbs Vs 33.1lbs).... and it looks much sexier don't ya think? This cab was made for an Olympic sailor by the people who made his medal winning boats, so as you can imagine the materials used and the build technique were very different to your cabs Zac. This one has divinycell foam, a mould, vacuum bagging, the works. If I had access to world class composites experts who'd do it for free, I would have went all out as well

WOW!!!...Quite the build there.