(Silly) question about physical volume of a cab.

[Toober]

Hello chaps,

Awfully sorry to bother you with a question that's probably very silly to you experienced cab designers and builders.

Just the other day, I played my Super Lead on a really nice sounding (closed back) cab. I would like to get one myself, if it didn't have such a bizarre shape. Not very wide, so the amp hangs over the sides. Not very tall either, perhaps just a hair taller than two Marshall heads on top of each other. It's quite deep, though. I think I can fit two Super Leads on there and neither would be hanging over the front or back.

So what if I had a cab made with exactly the same physical volume, just wider, taller and less deep. Will it still sound the same or is the way the volume is distributed around the speakers important as well ?

Thank you for your help and try not to laugh too hard. !

[Cantplay]

Volume, and stiffness of the speaker baffle are the major influences of sound in a sealed box speaker.

This assumes you are using the same speaker of course.

John

[Toober]

Hi John,

Thank you for responding.

I spoke with the bloke who owns it again and as it turns out, it's not an entirely sealed cab after all. I just assumed it because of the closed back and couldn't see the two ports in the front baffle through the grill cloth.
He told me he had it made to the specs of the Ear Candy Buzz Bomb. Looks like I estimated the size just about right, even if a Super Lead is a terrible unit of measurement.
http://earcandy.com/buzzbomb-2x12/

There are Celestion Vintage 30 speakers in his, but I might have to get a pair of Neodymium Century Vintage for my poor back.

[Cantplay]

Total port area should be combined.and length should be the same if its one port. It can be one or two ports, round, or slot that doesn't matter.

The outlet of the port should face the same direction.

I make ports a little long, then cut them back if I feel it needs it.

John

[Toober]

Thanks again, John, very interesting. I never really looked into porting before as I'm not that big a fan of open back cabs. Might be worth some further investigation.

But first, back to physical volume. The BuzzBomb's outside measurements are 18 x 28 x 16 Inch. What if I had a Cab made with the same physical volume on the inside, just different outside measurements so it'll look better with a Super Lead on top. Let's say 23,5 x 30,5 x 11,25 Inch.

Two cabs with the same physical volume inside, just distibuted differently around the speakers. Would the tone be any different ?

[Phil_S]

From the reading I've done (includes what John posts here at TAG), the only constraint on shape is that you've got to have enough depth and baffle space to accommodate the speakers and the length of the port. I'm thinking 11.25" deep (interior ~9.75" depending on the baffle) is going to work out just fine.

I think the biggest challenge with a ported cab (speaking from limited experience) is making the port right. This requires the right tools and know-how. I suppose anyone can make a proper port with a bit of experience. Figuring out the port dimensions is a whole other science. Since you have a model cab, you can and should measure the port(s). Then you get to bypass the whole business of figuring out the sizing.

You might get by with changing the port configuration. Since you've enlarged the baffle area considerably, I believe you can shorten the port and increase the area of the opening. You might be able to reconfigure the port so that it is a simple slot cut into the baffle. (I'm not totally sure about this. I hope John will comment.) If this is correct, you can simplify the construction. I'm thinking you can eliminate the need for the tube.

[Cantplay]

http://www.bcae1.com/spboxnew2.htm

I would not use MDF. I like real wood, or baltic birch ply

John

[Geeze]

IF weight is an issue I also recommend not using MDF - clear pine, poplar aspen are light solid woods and all available at Lowes. Only issue with these is they will mar more than a harder/heavier wood.

Before you jump off the neo magnet cliff I would make the effort to play through some with your equipment as they tend to be bright and [at least with the Celestions] are very efficient. The C rep I spoke with said Jazz guys tended to like them better than the rock/blues guys.

If you are handy with wood plan on making 2-3 on your way to your 'perfect' cab.

Russ

[Structo]

If weight is not a concern, there are many 2X 12 cab plans out there.

I like you like to put the amp head on top of the speaker cab.

I find some of the diagonal 2x 12 cabs intriguing that are wide enough for a amp head.

I use an old 60's Vox cab with two EV 12L's in it.
Semi open back.

Just by chance it was the same width as my Dumble clone head with the cab set on it's end.
I think it sounds great!

[Meat&Beer]

I used this port calculator when designing a sub box for my truck. Maybe it could be of some use here?

http://www.the12volt.com/caraudio/boxcalcs.asp#por

[Toober]

Thanks for all your help ! I knew there would be a lot more to a good sounding cab than just building a box with two holes, but not that it would be this much. I'm learning a lot here, thanks to you.

I spoke with the owner/builder again and asked more about how he built it. He really doesn't understand what the fuss is all about. He just googled around a bit for people reviewing 2x12" cabs, liked what he read about the Buzz Bomb and then made his own, using the outside dimensions mentioned on the Ear Candy site.

Then he estimated that 2" ports would look close to the snapshots of finished Buzz Bombs and went to the local car audio shop where all the boy racers go with their Saxos and Civics. He couldn't remember the length of these pipes, just that they were about two or three times longer than the diameter.

So what I heard was probably not as precisely tuned as the original Buzz Bomb, or how you chaps would build it.

[Phil_S]

So, this is an accident with good results. It should be blueprinted so it can be accurately reproduced! See if you can get a measure on the ports.

[Aurora]

I've probably said this before, but modern loudspeaker design relies on electrical and acoustical response models represented by the socalled Thiele / Small parameters published for almost all modern speaker elements - except most of the popular guitar elements, like Celestions....
There are several free design and simulation programs available, based on the T/S parameters, which gives very predictable results. Without a proper parameter set, one has to rely on empirical data, - or Lady Luck.
Off the top of my head, I can't see what the last referenced calculator is based on, - it may give reasonable results, but there is no input for the most dominating parameters, like the Q, which to a very large degree is responsible for setting the low F response of any cab, - closed or vented.
There are also several vented 'alignments' and ways to make a vented cab, - with different frequency responses.
EDIT: Maybe a 'stickie' or a small library of known good performers is good idea , - much like the amps designs here...

[Toober]

Back again, chaps, with more information ! I'm starting to get the feeling he's getting a bit fed up with me asking so many questions about his simple DIY project, so I promised this would be the last time I bothered him about it.

There was a sale on three layer hardwood plywood at the local hardware store, so that's what he got. FSC certified and 3/4" thick, but I don;t think it's void free. Glued and screwed butt joints, reinforced with square 3/4" slates of European (Norwegian) spruce.

The Celestion Vintage 30 speakers are front loaded and the ports are 2" in diameter, 4" long. He put the baffle 1 1/2" inwards so there would be room for the spruce frame to hold the black cloth, also from the boy racer store.

Lastly, the mono wiring (parallel) was done with some bits of solid core he had left after putting up a dry wall in the attic.

Aurora's idea of a library of good sounding cab plans is brilliant, but I don't know if this should go in there.
I think it sounds really good, but the original Buzz Bomb is probably constructed in a more sophisticated manner with better materials and ports cut to carefully calculated lengths.