Guitar Cabinet Design

Manfred-Klose

Has anyone ever built there own guitar cabinet?

I'm thinking of building my own guitar cab(since they aren't cheap and would like to learn how to do it), How does one go about doing the acoustics calculations for designing a speaker cabinet?

Is there any other links i can go read up on.
I found some great software, but the page expired a few days ago..........DAMN!!!!!

I'm plannig to use 2x12'' speakers, and the amp has a 16 OHM output.
(Peavey Delta Blues)

I know celestion 30's are expensive, but i'll settle for something a bit cheaper, as i am only going to use it in live situations.

Is there some ratio i should follow designing the cab?

Loves this page, the guy has a really good sense of humour:
http://www.colomar.com/Shavano/speaker_design.html

And some more links:
http://www.angelfire.com/electronic/funwithtubes/Speaker_Design.html

MoJo-JoJoe

Manfred-Klose

I planning on making a closed back cab, and i'm afraid it could cause phase problems, because the cab i want to build is not of a normal size.

deanBailey

I don't think there will be a hectic amount of phase problem (if any at all) unless you're hooking up the speakers weird?

What kind of wood and grill are you going to use?
I'd suggest choosing a cab you're most fond of and try an sort of 'clone' it ?

I think my cab is birch wood but I really have no clue on the amount of ply. (I'm gonna guess 14)
Orange cabs (Vintage 30's of course) are more 'ballsier' and they're 13 ply super dense Birch.
Engl use Birch for their cabs too so I would assume that that is the desired wood when it comes to great sounding cabs ?

Also stay away from chipboard unless you really don't care about the wood hehe.

For the Grill I'd suggest choosing a tough but visually penetrable one lol
It gets quite irritating when you're trying to mike up a cab and you need to whip out your torch brighter than the halo of Jesus to see the speaker!

Most musicians really do neglect live sound in SA, hence the sound quality of most bands always being less than the desired level.

I'd suggest spending money on one GREAT speaker and 3 poop ones (or even fakes) seeing that you only mic up one really ?
Then decide on what mounting you're gonna have, Front or rear mounted speakers?

I wanted to make clones of my cab but unloaded just for that awesome look of the abundance of cabs behind you ?

Dunno if any of this helps
Peace

Manfred-Klose

well like i said the cabs main purpose is to just look cool and have a punchy sound on stage, as i am micing up the 15'' speaker in live situation

Gearhead

Whether you go for open back or for closed makes a big difference. For open backs (or 50% open or similar) the size is not so important. For closed backs it's a little different, depending on what 'tone' you're looking for.
Either list the Thiele-Small parameters, the speaker type, frequency response etc. so we can have a look or go read the infamous Vance Dickason 'The loudspeaker design cookbook' - one of the best books on the topic. Alternatively as posted before, go find a professional cabinet that uses the same driver, test its tone and if you like it, copy the dimensions. Just a couple of centimetres out will not cause a big change in response.

Manfred-Klose

Found this book at yebo, looks good:

http://www.fort777.co.za/index.php?main_page=product_info&cPath=210_914&products_id=4975

Gearhead

dunno 'bout this book but b4 u buy just make sure it discusses enough theory to understand or includes the modeling software so you can go trial and error.
BTW I would go for open backed with a single driver and for a closed back with for instance a 4x12" because of the difference in efficiency. The four drivers sound so much louder that you can afford to dampen some of it to get that 'tighter', more focused sound. The enclosed air acts as a spring on top of the driver's own suspension, the air volume determining the resonance frequency and cone amplitude. Open backed guitar speakers are usually underdamped which makes the driver move long after the amp has stopped driving it (microseconds). Audiophiles dislike this loose and coloured sound but that has never stopped guitarists of exciting millions with it.

Manfred-Klose

What speakers would you recommend that are not as expensive as Celestion's?

Gearhead

Second hand Celestions ? but that's just my approach. Rather have something you know is good than ever thinking what might have been. I recently bought second hand Vintage 10s to put in floor-based 50% open back monitor speakers.

Anyway, when you go shopping you might want to note the efficiency of the driver plus some values called fs (resonance frequency), Qts (Thiele-Small quality factor) and Vas (equivalent volume). They might also give Xmax (maximum amplitude) but that is not as dominant and can be estimated. If you have those, we can predict the behaviour of the speaker in a closed box. In an open back system just note that Qts should be somewhere between 0.7 and 1.2 (which most of them will). Lower will be more controlled, higher more punch but also more boo-woo-woom.

deanBailey

Awesome ? thanks for the info.

Gearhead

deanBailey wrote: Engl use Birch for their cabs too so I would assume that that is the desired wood when it comes to great sounding cabs ?

To add to this: the thing you're looking for in a cab is that the wood does not 'sound'. Plain wood, having grain and therefore different properties in different directions and non-uniform strength, is not a good material. Plywood is better (but not necessarily just birch) and supawood (medium density fibreboard) is best. Well, actually HDF is better for being more dense but it's impossible to come by. I would say the reason they go for birch is the density and strength versus local material price wherever it is they're built. If I lived in Indonesia, I would prefer teak plywood over birch for price reasons. I build from supawood here since it is easy to get, easy to work with and easy to finish. Just don't screw or nail but glue. Rout all surfaces to be joined perfectly straight, make a clamping plan before applying any glue and you'l be okay.

The things you don't see from the outside of a cab can make a lot of difference: stiffeners to the baffle (and in the case of a closed back, the other panels as well) are as important as getting the air volume right. There's a few photos of the inside of a Mesa bass cabinet in their website or folder if I recall correctly, that nicely shows the massive panel stiffeners. Again, the best cab is a 'dead' cab.

Nicholas-L

I've read in quite a few places a dead cab is what is sought after, but now my question is what if you want your cab to have some flavor. I'm in the planning stages of building a 2 x 12 cab with Vintage 30's (already have them). Now I know Karel once spoke to me about him using pine wood on some cabs, but now what I'd like to know is how do you know what kinds of solid wood will give you what kinds of flavor? any ideas?

Attila

Mmmmm This is quite a consuming subject, with many opinion on various aspects of the build, consensus seems to be to use "void free" timber and to stay away from chip board.

I looked at this for my own 112 build a few days ago and decided to go with a ported cab, main reason is that with minor adjustments to the lengths of the port (plastic tube insert), I could control bass, to a degree, (the lower the tuned freq = more base) Also keeping the Golden ratio of length, width, and depth for optimal performance. (0.618 : 1 : 1.618)

Anyway long story short, after decided on specs which I got from an AX84 forum member, I asked the local car sound fitment centre to knock one up for me to experiment with for around 250 bucks, I can honestly say I am quite impressed, but of course this is subjective to my own references........

TomCat

The requirements for guitar cabinets is quite different to that of either PA, HiFi or Bass Cabinets. Guitars only go down to about 80Hz at most and to try and do any porting IMO could be a waste of time.
The purpose of cabinet ports is to provide additional loudspeaker damping at and just below the resonant frequency of the loudspeaker. To me thiele/small parameters are secondary in the application of guitar loudspeaker cabinets.

A second aspect is that the cabinet itself becomes part of the overall tone of the loudspeaker so using materials such as pine and plywood are quite acceptable. My first cab is made out of pine shelving board with a 12mm plywood baffle. Tone-wise the cab sounds great (To me anyway), and the liveness of the cabinet adds to the overall sound of the loudspeaker in giving it a nice open sound when cranked.

The advantage of plywood over any other material is that the cabinet will be strong for road use and unlikely to come apart if constructed properly.

For me personally a 2x12 open back cab would be optimum with about 30% - 40% of the back open.

Attila

@ Tom ... Just read about thiele/small parameters .... you are right I see the low E string of an electric is only 82.407hz which is above the tunning freq which means the port will have no real effect :sorry:

KVG labs White paper : http://www.kvglabs.com/PDF/guitarcabs.pdf

TomCat

Attila wrote: @ Tom ... Just read about thiele/small parameters .... you are right I see the low E string of an electric is only 82.407hz which is above the tunning freq which means the port will have no real effect :sorry:

KVG labs White paper : http://www.kvglabs.com/PDF/guitarcabs.pdf

Hey Atilla

Nice little article you found there.....There is an exception to the normal guitar cab and it is for 7 string guitars that have the lower B string that produces a lower bass frequency and there the use of a properly ported cab (based on the Fr of the guitar loudspeaker - somewhere in the region of about 60Hz)) may be very beneficial in tightening up the low end of the cab. I think we may see some specialized designs coming out in the future for this particular application. The risk with ported designs is that once you go below the resonant frequency of the port you risk damage to the loudspeaker from over-excursion (exceeding the displacement limits of the loudspeaker).

At the risk of rambling on a bit here... ? (I've been away from the forum for a while so I need to catch up.... ? ?), the design of ported cabinets is a fine balancing act between cabinet size (Volume), lowest resonant frequency, overall efficiency, linearity and port size limitations (too small causing whistling and too large becoming too deep for the cabinet. Very often a cabinet tuned to a higher Fr of the port sounds better than that of a lower Fr due to the higher Fr making the cabinet more efficient and punchier sounding.

A few years ago I designed some custom 18" subs for the first Coca-Cola Pop Stars winners(who remembers that.... ???). I had some nice juicy 18" JBL drivers to work with and had the cabinets built but they turned out less than impressive. What I had done was tune the ports too low (Somewhere about 37Hz, making the cabinets nice and low in terms of frequency response but sacrificing something like 6dB of efficiency. After a quick recalc, I retuned the ports up to about 44Hz which if I remember was fairly Close to the Fr of the drivers. I think the recalculation required something like about 4mm or so being cut off the ports to retune to the new Fr and suddenly these babies came to life..... 8) 8)). I went from deep bass mush to punchy lows......so the margin for error is small in these designs.

Gearhead

The way I have gotten ported cabs right in the past is by a three step approach: first you measure the parameters fo the driver itself (they are usually not very close to design spec), then you simulate the cab/ports/driver/damping combination and finally you assemble and measure again. From there it is trial and error by measuring and listening.

My conclusion after two hifi speaker designs was that the sound of ported cabs is not worth the design effort. They are heavily underdamped in the lower region, so your boost comes at the expense of sounding less tight. Rather get a better driver and put it in a closed cab, there is no substitute for quality.

A closed cab has a natural rolloff of lows at a frequency depending on TS parms and cab size. In general it is not that hard to build a cab big enough to extend the rolloff down to underneath the guitar frequencies, drop tuning or seven string or whatever. Just build it a little bigger and you're home free. Guitar speakers do well in either a closed cab or (partially) open back, the manufacturer will tell you straight which one it is.

Attila

Thanks TC and GH,

Technically your arguments make perfect sense. Conversely there are many big brands which have ported cabs ... Roland, Messa, Genz, Bogner etc. ... and a gazillion smaller brands, such as EarCandy etc. .... is this all about trying to create a market differentiator or it there more to it …. …

GH by "less tight" do you mean the bass frequencies tend to over ride everything else ? thereby becoming less defined

Extract from another article which supports your views:

"PORTS:

When blowing into the mouth of a ceramic jug, the sound of tubas and trombones could be imitated. The highfalutin term for this is a Helmholtz Resonator. The loudest tone occurs when the air suspended in the neck resonates. When a tube or port is placed in a loudspeaker enclosure, it acts like the jug and becomes a "vented" enclosure. This vent tunes the resonant frequency of the box such that the port vibrates in phase with the speaker cone. The cone driver becomes almost motionless and the sound comes mostly from the port.

It should amaze us all that the first vented enclosure designs were developed in the 1930s and were empirically derived. It wasn't until 1971 the Australian engineer Nevelle Thiele published his works in the Journal of Acoustic Engineering Society that the world had a useable mathematical tool for designing vented enclosures. Later in 1973, Richard Small added to his works. Their papers were a plea for all speaker manufacturers at that point to provide electrical and acoustic parameters with their speaker products that would be compliant with the world standard Thiele/Small parameters.

The vented enclosure is not a perfect solution. It has its problems as well as advantages.

ADVANTAGES

1. A vented enclosure can be 3dB more efficient that a closed cabinet of the same size.
2. The bass response of a speaker driver can be extended to one third of an octave lower.
3. Decreased cone movement at the resonance results in lower distortion.

DISADVANTAGES

1. The vented box is very sensitive to parameter variations. You must know the parameters of the speaker. Installing another speaker in the same hole can result in a dramatic difference in response.
2. The vented box falls off at 24dB/octave whereas a closed box falls off at 12dB/octave. This reduces transient response.
3. They have a more complex impedance curve, but that really doesn't matter too much with today's amplifiers with stellar damping factors.
4. They have more phase shift, group delay, and a more complex excursion response.
5. Last but not least is vent leakage. Some midrange frequencies come right through the vent out-of-phase with the driver radiation. This reduces the midrange output. Insulation of the cabinet with damping material will reduce this effect. This can also be eliminated by adding a 90-degree bend to the port tube. "

Peace

Gearhead

By less tight I mean that the amp has less control over the bass produced. The resonance does not occur instantly and it does not go away instantly. This makes the bass more flabby or, when overemphasized, boomy and less punchy.
I do not have any data on the enclosures you mention. I am too lazy to go and look them up, sorry :-[

The 'stellar' damping factors of todays amplifiers (meaning hifi) also do not have any influence over the much less than stellar damping factor of the speakers, and usually comes at the expense of an even worse transient behaviour of the amp itself. This fortunately does not apply to most tube guitar amplifiers, that have far less negative feedback.