New Light weight Vs Heavy Cabs

[stevie]

[quote name='JTUK' timestamp='1377721073' post='2190953']
We looked into this very carefully when buying P.A ...and there was no doubt that a wooden cab beat the composite cab hands down on sound.
Try the QSC K12 and K12W. for example.
[/quote]

Indeed. If you actually use your ears rather than swallowing every marketing claim on the web, the benefits of a stiff, non-resonant cabinet are plain to hear. Given the amount of engineering expertise available at QSC, you'd expect them to have maximised the performance of their plastic cab. (Bracing is a doddle with moulded cabs - you can build in as much stiffening as you like.) They don't say so, but it looks like they have even used the DSP to correct a cabinet resonance. Even so, there is a broad consensus that the wooden K12 sounds better than the plastic one. Whether they are worth the difference in price and in weight is, of course, purely subjective.

I'm currently finishing off the design of a pair of passive PA speakers using the same drive units as the K12. They're working out very well indeed.

[stevie]

[quote name='alexclaber' timestamp='1377775016' post='2191573']
For someone with such strong opinions on this you're remarkably good at getting the facts wrong!
[/quote]

Always glad to back up my views with an explanation or evidence and always happy to take advice when I post incorrect information.

[quote name='alexclaber' timestamp='1377775016' post='2191573']
Some points to consider:

1. Panel stiffness is proportional to the square of the thickness, not the cube.
[/quote]

Here are some links:
[url="http://www.netcomposites.com/guide/core-materials/44"]http://www.netcompos...re-materials/44[/url]
"Engineering theory shows that the flexural stiffness of any panel is proportional to the cube of its thickness."
[url="http://www.plastemart.com/upload/literature/Core_Materials.asp"]http://www.plastemar...e_Materials.asp[/url]
"But because a plate's bending stiffness scales as its thickness cubed...."
From Experimental and Applied Mechanics by Proulx
"Stiffness of a plate or beam is proportional to the cube of thickness."
From Handbook of Troubleshooting Plastics Processes by Wagner
"Since stiffness is proportional to the cube of thickness..."
From Specialized Molding Techniques by Heim
"The overall stiffness of a box can be quantified by its "EI" product. The higher this product the stiffer the housing. Thinning the housing wall dramatically decreases its moment of inertia which is proportional to the cube of wall thickness."

[quote name='alexclaber' timestamp='1377775016' post='2191573']
2. The resonant frequency of a panel is proportional to its stiffness divided by its mass - halve the mass and you double the resonant frequency
[/quote]

Well, physics really isn't my thing but I always thought the ratio wasn't direct and that there was a square root ratio involved here. You know, if you halve the mass, the resonant frequency doesn't double - it increases by 1.4 times.

I checked this one out in the literature too.
In the Handbook of Adhesion Technology (da Silva) I read: "In vibrating systems, the resonant frequency is proportional to the square root of the ratio of the stiffness to the mass"
Mechanics of Poroelastic Media by Selvadurai
"The shifting is due to the fact that the frequency is in general proportional to the square root of the stiffness to mass ratio..."
Electromechanical Design
"The resonant frequency of a vibrating member is proportional to the square root of the quotient of the spring constant (stiffness) divided by the mass."

[quote name='alexclaber' timestamp='1377775016' post='2191573']
Here's an example of how we do bracing:
[/quote]

Credit where credit's due, that's very good - certainly far ahead of anything your competition has done. You should have a word with Mr Foxen - he thinks a cross brace is all you need.

Nevertheless, if you're using 9mm ply for that cab, elegant though it is, it will not be as inert as a cab made of 18mm birch with a circular brace and a back brace. I am assuming, as is everyone else, that this is a Sketchup of a production cab.

Edited August 29, 2013 by stevie

[Mr. Foxen]

[quote name='stevie' timestamp='1377805436' post='2192216']
If it's common knowledge, then do tell us what this material is and who is using it.
[/quote]

The variety thing is there is lots of materials. That is what 'variety' means. Two such woods are birch, and poplar, you can get ply of either, each with differing properties. For more esoteric examples, actually go read the thread where I already linked a bunch. Oh yeah, and guess what, not only have I braced a cab, but, drum roll, so has Alex Claber, and guess what they are telling me? That you are wrong. Also, know what is easier than making a braced cab? Making a not braced cab. And idiot's money spends just as well as smart people's.

Edit: Also, know what increases stiffness? Bracing.

Edited August 30, 2013 by Mr. Foxen

[Phil Starr]

Hey chaps calm down. This is a really interesting debate which I'm sure a lot of people are finding quite interesting. No need to be personal.

Here's my two pennyworth. There's merit in both sides of the argument and some truth in both the argument for thicker and thin braced panels. A lot depends upon the design criteria and there is some muddling of two criteria here. Because of Barefaced and Alex's pre-eminent position here people have become muddled. I hope if i have this wrong Alex will correct me.

Barefaced seem to me to attempt two things. To make lightweight cabs but also to engineer cabs that control spurious resonances. To an extent these two criteria conflict. To reduce the weight of the driver will save weight however you construct the cab. Using big magnets and long throw drivers means you can reduce the size of the cab due to better damping by the magnet and reduce the number/size of the drivers for a given sound output. Using neodymium means your powerful magnet doesn't have to mean heavy. Again this is all independent of the cab construction.

To reduce resonances you need to add stiffness, mass and internal damping. In one of my hi-fi designs I used lead to make the cab, a great material for cabs but not appropriate for a bass cab. You can add thickness to the panels or brace them or a bit of both. this all increases mass. If you look at Alex's diagrams the bracing constitutes nearly half the material used. If he uses the same thickness for the bracing this will double the weight of the cab. Obviously this is about resonance and not weight saving. Build the same cab out of 18mm MDF and it would sound better but be too heavy to lift. If you want bracing this extensive you have to use thinner material. Alex has come up with a compromise of weight and rigidity which he has optimised to meet his own criteria of neutral sound and practicality as a portable cab.

Stevie is correct in his Physics, All he says about thicker panels is true. Build a cab out of conventional 3/4" materials, add minimal bracing and you can have a cab almost as non-resonant as a braced cab for very little additional weight and a huge saving in costs. In addition you have to question whether you can hear the difference when you are talking about a bass being played in a live situation on stage. I've recently heard both a Barefaced cab and a 'thick walled' cab with the same driver at pub gigs, both bassists had a great tone.

Equally Alex is right in all he asserts. as far as stiffness goes his cabs are the equal of a wall the same thickness of the panel plus the brace at the point they attach. This is how an I beam works. All that bracing will work fantastically well as Stevie has acknowledged. There will be resonances but they will be raised in frequency and reduced in volume, more importantly they can be controlled by where exactly the bracing is placed. There is nothing new in this, It was used in 1930's designs and more recently too. Celestion used it extensively in a lot of high end 1980's hi fi speakers.

As to materials Stevie has a point, the commercial availability of panels in a wide range of materials is fairly limited and even fairly big manufacturers don't tend to design their own plies. For the rest of us the choice is limited to three or four types of ply, MDF and high density Chipboards.

Edited August 30, 2013 by Phil Starr

[Happy Jack]

Nice post Phil.

Can we all leave this topic alone for a few days (and any other topics involving Barefaced cabs)?

Alex is really very busy at the moment, and I'm still hoping to get my 69er finished in time for my gig next Saturday ...

[redstriper]

I still don't understand why foam core panels are not used by any commercial cab manufacturers other than Flite.

[Mr. Foxen]

[quote name='redstriper' timestamp='1377859963' post='2192834']
I still don't understand why foam core panels are not used by any commercial cab manufacturers other than Flite.
[/quote]

Think you can poke holes in the pretty easily. When it comes to touring even light stuff gets treated the same as heavy stuff. Plus obviously the vocal sorts that demand everything is wood. SVT 8x10 is still an industry standard even though massively obsolete, so stuff just doesn't catch up.

[alexclaber]

That's a sketch-up of a pre-production model, we use it to check all the panel & brace dimensions are correct before cutting the first example. The final version then has a little more material taken out where it isn't doing anything useful. That large cab weighed about 20lbs empty - an 18mm baltic birch cab that size with no bracing would weigh about 50lbs. I see I have got some of my numbers wrong - it's hard to keep track of everything when you're doing this much multitasking! By the way, when I was messing around with DIY stuff some years ago I spent quite a while looking into foam-core ply and other composite methods - Flite have used quite a few different methods and also gone out of business and changed hands quite a few times, which isn't terribly reassuring... I like composites very much - my mech eng final year thesis was in them. But increasing panel stiffness through added thickness still leaves you with a single vibrating membrane with a fundamental frequency and a series of overtones - adding braces breaks that panel up into multiple segments. Spacing the bracing cleverly can make all the fundamentals occur at different frequencies. That makes a big difference. Now in an ideal world we don't want any panel resonances but I've yet to come across any PA or bass cab which has panels so rigid they have absolutely zero vibration at high SPL.

Something that's been missed in this discussion, which makes a huge and under-appreciated difference to tone, is that complex internal bracing like this gives the backwave lots of different surfaces to to reflect off, of varying sizes, spacings and angles from the source - not a million miles dissimilar to how a Stealth F117 reduces its radar signature. The bracing also makes it easy to suspend the damping material away from the walls of the cab, which makes it much more effective at damping mids by catching the wave where the velocity is higher and pressure lower (like how you damp the right harmonics in a transmission line). The reflected backwaves that do return to the cone are thus much lower in amplitude and much more widely distributed in frequency so you don't suffer unwanted peaks and notches in the mids.

For me it's never been about the weight - I'm fairly young and relatively fit as I ride bikes fast down steep muddy hills in my spare time so I don't really care what cabs weigh. It's always been about the tone and performance. If I felt that going light was compromising the tone and performance of cabs then we wouldn't do it. It's not like they'd be heavy for their output if we used traditional construction! Our cabs have always had extensive bracing but getting our own CNC machine really increased the possibilities and I'm glad that some of you now appreciate that we're walking the walk, not just talking the talk!

Edited August 30, 2013 by alexclaber

[redstriper]

[quote name='alexclaber' timestamp='1377861910' post='2192870']
I spent quite a while looking into foam-core ply and other composite methods. But increasing panel stiffness through added thickness still leaves you with a single vibrating membrane with a fundamental frequency and a series of overtones - adding braces breaks that panel up into multiple segments. Spacing the bracing cleverly can make all the fundamentals occur at different frequencies.
[/quote]

Thanks for the explanation Alex, which makes sense even to me!
It would be interesting to compare the Flite cabs to the BFs loaded with the same drivers.

[JTUK]

I think the industry standard is still an 810 sealed cab as that is what does the job best in most cases.
The weight issue is a non-issue to them as they have crew so they can concentrate of getting the best that suits them.

Bass players will have likely done pretty entensive tests and are attuned to the nuances of sound that appeals to them.
I know one top player who can really dissect what he wants to hear and how he wants to achieve it.. so spending large amount
of time attending to the whole process of sound does actually add up to something.
These are mostly people who can use what they like....and tiem and time again they come back to multiples of 10's.

Traditionally, the 810 would have been about power in a box... in an era when sound was pretty basic, but now it still prooves to be the
tool for the job for so many who should know.
The 810 sealed cab isn't traditionally bass heavy so altho the volume can work the stage, it will not flood it..or shouldn't do.
This makes it mon mix friendly..or friendier,

You try putting too much bass on the stage and see where that gets you with the crew/soundmen.
Pre-production meetings are as much about this ..and your rig and how you use it as they would be about what effects you
might run...etc etc.

It is too glib to say these proferesionals don't all know what they are doing and aren't abreast of new technolgy and its thinking
when their whole remit is about best sound and how to achieve it for the particular job.

Some kit will stay in the pub and some will never get anywhere near a discerning stage..and some will be totally unsuitable ( relatively..) anywhere but..!!

[Happy Jack]

[quote name='alexclaber' timestamp='1377861910' post='2192870']
... I don't really care what cabs weigh ...
[/quote]

I now feel that I'm stumbling along the Boulevard Of Broken Dreams, my eyes blinded by my tears.

[Happy Jack]

[quote name='JTUK' timestamp='1377866199' post='2192963']

Some kit will stay in the pub and some will never get anywhere near a discerning stage..and some will be totally unsuitable ( relatively..) anywhere but..!!
[/quote]

And sales of bass cabs for use in pubs will always massively out-weigh (see what I did there?) sales of bass cabs for use on huge stages by high-quality professional bass players.

I wonder why that might be ...

[redstriper]

[quote name='alexclaber' timestamp='1377861910' post='2192870']

For me it's never been about the weight

[/quote]

On that bombshell...

[redstriper]

[quote name='alexclaber' timestamp='1377861910' post='2192870']
I like composites very much - my mech eng final year thesis was in them.
[/quote]

Did you try making any bass cabs with them, braced or otherwise and if so, what were your conclusions?

I know Flite have not been successful as a business, but I am so pleased with mine, I can't help wondering why the idea hasn't taken off.

[Salt on your Bass?]

[quote]
I know Flite have not been successful as a business, but I am so pleased with mine, I can't help wondering why the idea hasn't taken off.
[/quote]

.......because they're too heavy?.......

......coat.......grab......gone.....

[Salt on your Bass?]

Double post.

Edited August 30, 2013 by Salt on your Bass?

[gsgbass]

The Markbass Mini CMD 121P Combo / Markbass NY 121 cab. 300 Watts through the Mini CMD 121P Combo, 500 watts with the NY 121 cab. The Combo weighs, 29 pounds, the cab weighs 28 pounds. Markbass, solid well made gear.

[IMG]http://i.imgur.com/Imvq81f.jpg[/IMG]

Edited September 3, 2013 by gsgbass

[Conan]

[quote name='Phil Starr' timestamp='1377403675' post='2187129']
Different speakers sound different, that's as true of speakers today as it was in the 1070's [/quote]

Yep. That William the Conqueror made some really great drivers in his day. That Norman can deny.

[Happy Jack]

[RandomBass]

Lol

[stevie]

[quote name='alexclaber' timestamp='1377861910' post='2192870']
That's a sketch-up of a pre-production model, we use it to check all the panel & brace dimensions are correct before cutting the first example.
[/quote]

Well it's a good job I asked. I thought you said "Here's an example of how we do bracing".

[quote name='alexclaber' timestamp='1377861910' post='2192870']
But increasing panel stiffness through added thickness still leaves you with a single vibrating membrane with a fundamental frequency and a series of overtones - adding braces breaks that panel up into multiple segments. Spacing the bracing cleverly can make all the fundamentals occur at different frequencies. That makes a big difference. Now in an ideal world we don't want any panel resonances but I've yet to come across any PA or bass cab which has panels so rigid they have absolutely zero vibration at high SPL.
[/quote]

Yes, agreed. Bracing is good and should be a feature of all properly built cabinets - but bracing is not unique to lightweight cabinets. Offet bracing is something every amateur speaker builder knows about and hardly worth mentioning.

[quote name='alexclaber' timestamp='1377861910' post='2192870']
Something that's been missed in this discussion, which makes a huge and under-appreciated difference to tone, is that complex internal bracing like this gives the backwave lots of different surfaces to to reflect off, of varying sizes, spacings and angles from the source - not a million miles dissimilar to how a Stealth F117 reduces its radar signature. The bracing also makes it easy to suspend the damping material away from the walls of the cab, which makes it much more effective at damping mids by catching the wave where the velocity is higher and pressure lower (like how you damp the right harmonics in a transmission line). The reflected backwaves that do return to the cone are thus much lower in amplitude and much more widely distributed in frequency so you don't suffer unwanted peaks and notches in the mids.
[/quote]

Firstly, you can suspend damping material away from the walls of any cab that has a front-to-back brace. There's nothing unusual in that. Secondly, I find it very difficult to believe that a few extra braces will have any affect on the backwave, never mind make a "huge and under-appreciated difference in tone".

While we're discussing the backwave, the biggest problem with a thinwall/lightweight cabinet is transmission through the cabinet walls because the mass law equation says that 6dB more of the backwave will escape through a cabinet with 9mm walls than one with 18mm walls - even more with a lightweight panel. So, if the goal is to contain the backwave, reducing wall thickness is exactly the wrong thing to do.

[BassBod]

On the composite discussion - I have one of Mike Arnopol's Crazy 8's - a 1x8" with composite cab. Weighs nothing, works very well in small/quiet settings, but it would have to live in a hard road case for any serious touring - the walls could easily be punctured or damaged, and once the outside skin is broken there is only hollow foam/plastic. Its fine in the car in a padded bag, but not for a rock'n'roll lifestyle.

[Mr. Foxen]

[quote name='BassBod' timestamp='1378376100' post='2199252']
a 1x8" : not for a rock'n'roll lifestyle.
[/quote]

Abbreviated for you.

[alexclaber]

[quote name='stevie' timestamp='1378318103' post='2198597']While we're discussing the backwave, the biggest problem with a thinwall/lightweight cabinet is transmission through the cabinet walls because the mass law equation says that 6dB more of the backwave will escape through a cabinet with 9mm walls than one with 18mm walls - even more with a lightweight panel. So, if the goal is to contain the backwave, reducing wall thickness is exactly the wrong thing to do.[/quote]

The main problem with the backwave is not it escaping through the enclosure walls but it escaping through the cone after it has reflected off the innards of the cab - 9mm of plywood stops far more sound than a fraction of a mm of paper can. Thicker walls don't help with that at all, in fact they make the problem worse.

[alexclaber]

[quote name='stevie' timestamp='1378318103' post='2198597']Well it's a good job I asked. I thought you said "Here's an example of how we do bracing".[/quote]

Yes, that is how we do bracing. That is a sketch-up of a pre-production model which is why some of the and panels braces don't align correctly with each other and the grooves and rebates. That model is now in production but obviously the mistakes from that 3D model have been corrected.

[quote name='stevie' timestamp='1378318103' post='2198597']Yes, agreed. Bracing is good and should be a feature of all properly built cabinets - but bracing is not unique to lightweight cabinets. Offet bracing is something every amateur speaker builder knows about and hardly worth mentioning.[/quote]

Maybe those amateur speaker builders should go and educate lots of professional speaker manufacturers then because properly braced cabs seem to be few and far between regardless of mass.