questions on building a cabinet

[hotrod128z]

I was just thinking. When building a 2x12 or a 4x12 isn't it best to divide each of the speakers? In other words so that the 2 or 4 speakers are not sharing the same air space. Is it also best when building a closed back cabinet to make sure that the air space is sealed air tight? I know back in the day when we did custom cabinet builds for car stereos that the sound was a lot better when the speakers did not share the same air space in the cabinet (box) and also had a lot better low end with the enclosure totally sealed air tight

inquiring minds want to know


hotrod

 

[SteveGangi]

You could isolate them, but it is not necessary and the interaction between them can work pretty damn good (make sure they are in phase). You can get a more complex and a possibly more pleasing, fuller sound.

 

[Maxwell]

Steve is on the money.

Also, experiment with different size baffles for the back.
Yes, generally closed back is going to give a bigger tighter bass but semi open can be awesome. Especially if you don't want the bass to be boomy at all and the spill you get from a semi open cab can be really cool too.

 

[rabidhamster]

I tried a 4x12 cab someone locally built with individual closed sections around each speaker and didn't like it.
The thing sounded boxy like a pile of small cabinet 1x12s

 

[SteveGangi]

I almost forgot... your experience with stereos will not really help much here... Stereos are supposed to faithfully reproduce what has already been recorded (hi-fi).

With instrument speakers the cab and speakers are part of the instrument and are supposed to color the sound. So, forget all that science about Thiele Small, Fs, F3, Vas etc. "Our" speaker cabs were originally designed to be tough and small. There were no exhaustive calculations and no computer simulations (no one had 'puters back then). The sizes, shapes, and materials were picked by trial and error, with an eye on size and cost.

To prove the point, look up the popular cabinets now. They all vary wildly. They do NOT match any calculated parameters from Thiele Small. They are copies of pre-existing wildly varying cabs from the past.

In fact, a "properly" designed cab sounds sterile and lifeless and boring.

 

[The_Nuge]

Hi!

All the guitar cabinets i know of let the speakers share the same volume. For hi-fi different rules apply - after all, we want our amplifiers to distort!

Cheers

Es

 

[studio1087]

This isn't like me; I don't like to be Johnny-Downer.

Do you have cabinetry skills or really good wood working skills? If not you're stepping into a money sucking pit.

Every 5 or 6 years I decide to build a cabinet. Last time I bought a Roto-Zip saw so that I could cut perfect 12" circles in the sound baffle. I made trips to a fabric store for vinyl for covering and I ordered hardware online. I blew through a lot of cash.

You can order a Carvin G212 cab with your choice of Tolex covering loaded with two Carvin British style speakers for $229. Whenever I build a cab I blow through $229 before anything is complete.

Really man I don't mean to be a bummer - it's always an educational process which can be a good thing but I just ordered another G212 in red......$229.....I'm just saying.....

And you have my sincere apologies if I'm being a total drag. That's not my usual style. I usually hit the point of no return after the 6th trip to Home Depot or the Lumber Yard. Ooof.

 

[dspelman]

In fact, a "properly" designed cab sounds sterile and lifeless and boring.

You were doing so well right up to there.

Traditional guitar cabinets have never been "designed". Many cabinets were designed when a manufacturer decided how many speakers he needed to work with his amplifier, tossed them face down on the factory floor and then chalked an outline around them. No one really considered Xmax or any of that back then.

As for cabinet resonances? They're random. And generally to be avoided unless they're in the dog-ear range. There have been happy accidents and unhappy ones. The big flat back of a 4x12 will oilcan and resonate at a particularly nasty audible wavelength associated with the measurement of the diagonal of that panel. Thus we have the chunk of 2x2 or 2x4 add-on kludge that connects the front baffle with the center of that panel. It shoves that resonance up an octave or two, reduces its volume significantly and mostly takes it out of the audible guitar range. It also keeps the oilcanning from stealing the speakers' air-moving power.

A well-designed speaker cabinet maintains the power of the speaker, eliminates unwanted resonances, reduces the overall weight of the cabinet while increasing stiffness and impact resistance and allows the rest of the signal chain (guitar, pedals, EQ, preamp, etc.) to do its job without fighting or masking the input from those devices. It allows you to reproduce exactly what you've paid the big bucks for on the front end without offering its own opinion.

 

[JCM900MkIII]

Results may vary, using closed, open or even ported (usually bass) cabs...

If you have a boxy sounding cab or other resonance related issues, try moving the cab in the room.
Boxy sounding is more likely a matter of the room in which the cab is situated being too small for the lower frequencies to be heard even.
Another issue could be that the room has dimensions which are the same as (or halves/doubles of) the wavelenght of the resonant frequency of the speaker or the resonant frequency of the cab.
Just changing your own position (relative to the cab) can give a different perception of sound as well.

For a speaker with a 75Hz resonance, a room of ~4.5m is going to give problems.

Wavelength = speed of sound/frequency

4.5m= 340m/s / 75Hz

For 55Hz speakers it is ~6.1m = 340m/s / 55Hz

1/2, 1/4, 1/8, 1/16 (or 2x, 4x, 8x etc.) of said distances will cause the same issues.


One other thing about closed cabs.
You don't want them to small because of "heat build up" in the speakers. (heat destroys magnets)
If you want to "flap your pants" you better give enough room on the inside.
Oh right, that's the most important reason for ports in bass cabinets. Heat dissipation
Keep the fractions of the wavelength in mind and you should be ok.
Oh, and too big makes them expensive, heavy and unwieldy.

 

[KelvinS1965]

This isn't like me; I don't like to be Johnny-Downer.

Do you have cabinetry skills or really good wood working skills? If not you're stepping into a money sucking pit.

Every 5 or 6 years I decide to build a cabinet. Last time I bought a Roto-Zip saw so that I could cut perfect 12" circles in the sound baffle. I made trips to a fabric store for vinyl for covering and I ordered hardware online. I blew through a lot of cash.

You can order a Carvin G212 cab with your choice of Tolex covering loaded with two Carvin British style speakers for $229. Whenever I build a cab I blow through $229 before anything is complete.

Really man I don't mean to be a bummer - it's always an educational process which can be a good thing but I just ordered another G212 in red......$229.....I'm just saying.....


And you have my sincere apologies if I'm being a total drag. That's not my usual style. I usually hit the point of no return after the 6th trip to Home Depot or the Lumber Yard. Ooof.

I keep coming back to a similar decision, I'd love to build something unique, but cheaper than buying off the shelf, but I don't have the quantities of scale, so it always seems to work out more expensive to build

I can buy a ready made cabinet covered in the material/grill of my choice for less than me making one (badly). I can then put in the speaker of my choice, so this is a second option for a truly custom result. Either that or buy a ready made and swap the speakers out, but then there is the hassle of selling the unused speakers if they don't sell a version with the speakers I want.

I did similar when I built some Home Theatre subwoofers which were cheaper to have the cabinets made (1" thick MDF) than me even buying the raw materials. All I had to do was paint them and put the speaker/connector in and they were really solid too.

When I built these I used a program called WinISD which helps calculate the response of a speaker and cabinet. One of the figures was to do with 'leakage' (I built sealed subs) and it was only at the very low end that this seemed to make a difference to the computed response. In practice the leakage was important more due to noise from the escaping air, but I only noticed this at 10Hz.

I know some subwoofers combine 2 x the same driver in a push-pull arrangement, but I don't recall coming across any that have two drivers in separate compartments. Knowing the hard core DIY subwoofer builders if there was any advantage to do this I think it would be common, but it isn't.

I know guitars work at higher frequencies than subs, but similar principles.

 

[SteveGangi]

You were doing so well right up to there.

Traditional guitar cabinets have never been "designed". Many cabinets were designed when a manufacturer decided how many speakers he needed to work with his amplifier, tossed them face down on the factory floor and then chalked an outline around them. No one really considered Xmax or any of that back then.

As for cabinet resonances? They're random. And generally to be avoided unless they're in the dog-ear range. There have been happy accidents and unhappy ones. The big flat back of a 4x12 will oilcan and resonate at a particularly nasty audible wavelength associated with the measurement of the diagonal of that panel. Thus we have the chunk of 2x2 or 2x4 add-on kludge that connects the front baffle with the center of that panel. It shoves that resonance up an octave or two, reduces its volume significantly and mostly takes it out of the audible guitar range. It also keeps the oilcanning from stealing the speakers' air-moving power.

A well-designed speaker cabinet maintains the power of the speaker, eliminates unwanted resonances, reduces the overall weight of the cabinet while increasing stiffness and impact resistance and allows the rest of the signal chain (guitar, pedals, EQ, preamp, etc.) to do its job without fighting or masking the input from those devices. It allows you to reproduce exactly what you've paid the big bucks for on the front end without offering its own opinion.

You're right, I was simplifying, to make the point that the "numbers" used for hi-fi / stereo are not relevant for guitars (though they will be for bass to avoid that awful boomy woofy sound).

 

[SteveGangi]

Results may vary, using closed, open or even ported (usually bass) cabs...

If you have a boxy sounding cab or other resonance related issues, try moving the cab in the room.
Boxy sounding is more likely a matter of the room in which the cab is situated being too small for the lower frequencies to be heard even.
Another issue could be that the room has dimensions which are the same as (or halves/doubles of) the wavelenght of the resonant frequency of the speaker or the resonant frequency of the cab.
Just changing your own position (relative to the cab) can give a different perception of sound as well.

For a speaker with a 75Hz resonance, a room of ~4.5m is going to give problems.

Wavelength = speed of sound/frequency

4.5m= 340m/s / 75Hz

For 55Hz speakers it is ~6.1m = 340m/s / 55Hz

1/2, 1/4, 1/8, 1/16 (or 2x, 4x, 8x etc.) of said distances will cause the same issues.


One other thing about closed cabs.
You don't want them to small because of "heat build up" in the speakers. (heat destroys magnets)
If you want to "flap your pants" you better give enough room on the inside.
Oh right, that's the most important reason for ports in bass cabinets. Heat dissipation
Keep the fractions of the wavelength in mind and you should be ok.
Oh, and too big makes them expensive, heavy and unwieldy.

The other and most common reason for going biggger and/or using ports is to move the resonant peak down out of your instrument's range.