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View Full Version : What does an extension cabinet do....really?


jimmyohio75
03-13-2009, 04:22 PM
Tell me if I'm wrong but an extension cabinet is simply a wooden box with some speakers in it?

Call me ignorant but what does an extension cabinet add to your live sound?

I assume words like "dispersion" and "projection" will surface but if you are already using a powerful, high wattage amp (say a 2x12) what exactly is there to gain from using an extension cabinet?

Let me give you a scenario and you tell me if my way of thinking is correct.

Real life scenario:

My band is playing an outddor gig and I am not being mic'd. Because I love the tone I am going to use a 15 watt Fender Blues Jr with a Crunch Box for my dirt. 90% of our music is harder edged blues and I don't need much if any clean headroom.
Would an extension cab (1x12 or 2x12) help make the Blues Jr. sound "bigger" and help project the sound? Or do I need more watts to make it sound "bigger"

jimmyohio75
03-13-2009, 05:41 PM
Nobody using ext cabinets?

I guess they don't work real good then.

plato67
03-13-2009, 05:44 PM
I use an old floor wedge pointed at my head like this:
http://i117.photobucket.com/albums/o48/plato67/rig1-1.jpg

works great!

Jahn
03-13-2009, 05:46 PM
If you have a tiny vibro champ, plugging it into a 4X12 cab can be a revelation. plus, you avoid the tube rattle from the original cab.

m@2
03-13-2009, 05:49 PM
I use them more for stage dispersion when the monitor situation/mix sux (which is most of the clubs/bars I play). I also just like the "bigness" in tone I get with the second cab.

DEMENTED
03-13-2009, 05:52 PM
More speakers=more sound, it's gonna sound bigger.

candid_x
03-13-2009, 05:55 PM
I use them more for stage dispersion when the monitor situation/mix sux (which is most of the clubs/bars I play). I also just like the "bigness" in tone I get with the second cab.

Well said. It expands the narrow focus of a 1x12. It also "sounds" louder, though I suppose that's technically debatable. It's about dispersion for me.

billm408
03-13-2009, 05:57 PM
On wider stages, since we only run vocals through the monitors, me & the other guitarist will criss cross 2x12's so that we're running on both sides of the stage. That way we can hear each other and it helps eliminate the volume wars.

As for running more cabs, like a full stack or more, more speakers= bigger sound and you can push your amp a little harder.

edward
03-13-2009, 05:58 PM
Well, you said it: dispersion (and "tone" if you add speakers to compliment your amp's combo).

Regarding your "real world scenario," I definitely think you will benefit from an add'l cab. Any outdoor gig is sans walls which would normally "enclose" your sound, adding depth and enhancing bottom (generally speaking, of course). With outdoors, your tone sails out into space, tends to sound thinner, lacking bottom-end punch, less volume for the same setting, and more beamy. You can help counter these detriments by adding a cab. Much depends on size of your "outdoors" of course.

Edward

jimmyohio75
03-13-2009, 06:02 PM
Well, you said it: dispersion (and "tone" if you add speakers to compliment your amp's combo).

Regarding your "real world scenario," I definitely think you will benefit from an add'l cab. Any outdoor gig is sans walls which would normally "enclose" your sound, adding depth and enhancing bottom (generally speaking, of course). With outdoors, your tone sails out into space, tends to sound thinner, lacking bottom-end punch, less volume for the same setting, and more beamy. You can help counter these detriments by adding a cab. Much depends on size of your "outdoors" of course.

Edward
Very helpful..thanks Ed!!

FenderBigot
03-13-2009, 07:45 PM
Outdoor gig and you're not mic'ing a 15 watt BJr??? Seems like you may not be heard. Well, an extension cabinet is another vehicle to make yourself heard for sure... BUT, there's other variables to changing tone. Say your amp has 12" speakers, and you want to have an extension cabinet with 4 - 10" in it... OR... you're combo is open backed and you want your extension cabinet to be closed. This gives you different sounds from the same amp source. Believe me, it matters.

GenoBluzGtr
03-13-2009, 08:48 PM
There are a couple of additional things to think about.

First of all, the sound we hear is simply a pressure wave moving through the room (or whatever the medium... air, etc..). That pressure wave has certain properties: Level, Frequency (including mixed or heterodyned multi-frequencies), etc....

One thing that affects some of those properties is the speaker or speakers and it's interaction with the cabinet (resonance) and the reflective properties of the room itself and the items / people in it. Hard floors, low ceilings, wooden beams, paneling, etc... all reflect very well, causing 'stray' pressure waves to retain more of their original levels than, say... carpet, cathedral ceilings, crowds of people, etc... That's were natural echo and reverb come from.

So if you generate the pressure wave, in phase from multiple points of reference or if that pressure generator (speaker cab) is more or less efficient or, more importantly, causes you to use larger or more speakers, you will generate that pressure wave more effectively with more reinforcement than simply using a single on-board (or even a 2X12) speaker. In essence, "moving more air" has some truth to it... you really are creating a larger wavefront with more or larger speakers.

The second thing to consider is impedance. If a combo is set up for 16 ohm output transformer impedance and there is a single 12" 16 ohm speaker in the combo, that has a certain tone. if you plug in a speaker cab that is also 16 ohms (or more drastic, a 8 ohm cab!) you are lowering by a large factor the 'resistance' or impedance that the OT will see and interact with. A good example is when I plug a cab into the external jack on my DRRI. Onboard is 8Ohms, ext is 8Ohms, so I am now "showing" the OT a 4 ohm load. It makes the amp sound different (irrespective of the speaker size/number/amount of air moved), by altering the resistance properties of the power sections of the amplifier. By lowering (or raising) the output impedance, you are causing a different reaction to the magnetic field and therefore the current in the output section of the amp circuit. That's why some amps that allow different tubes and have a selectable OT impedance switch tell you to "use 8ohms when using 6L6s and 4 ohms when using 6V6s"... because the different current flow/resistance will make the output impedance react differently through the OT and the the speaker load. Changing the load by using an ext cab is the same thing on the other side of the transformer.

When I use a cab with my DRRI, I don't like it. It does sound a bit louder, and the sound seems 'bigger' and fills the room better, but the change in impedance causes more highs to get through the OT and into the speaker. I lose low end and gain more 'ice pick'.

So it's more than just having more speakers and different cab material/location.

jchan
03-14-2009, 03:36 PM
The Blues Jr will sound very different outside than it does inside. IMO, you need closed back cabs when playing outside. I think you should add a closed back extension cabinet and mic it.

dk123123dk
03-14-2009, 03:44 PM
It will also lift the amp off the floor, and get the speaker aimed at your head a bit more.

dk

jimmyohio75
03-14-2009, 03:58 PM
Outdoor gig and you're not mic'ing a 15 watt BJr??? Seems like you may not be heard. Well, an extension cabinet is another vehicle to make yourself heard for sure... BUT, there's other variables to changing tone. Say your amp has 12" speakers, and you want to have an extension cabinet with 4 - 10" in it... OR... you're combo is open backed and you want your extension cabinet to be closed. This gives you different sounds from the same amp source. Believe me, it matters.
Actually my main gigging amp is a '59 Bassman which is plenty for outdoor gigs. I was just GASsing for a BLues Jr. and was trying to justify why I need it. I thought if I could get more oooomph out of one with an extension cab it might make a nice backup for larger gigs. (especially when I'm too lazy to drag the Bassman around)

shark_bite
03-14-2009, 05:08 PM
I'd use the Bassman.

dk123123dk
03-15-2009, 03:14 AM
I think the blues jr would make a great club rig, esp with an extention speaker. But I would stick with the bassman for outdoor gigs. I would mic the amp in both situations if possible, but at least for the outdoor gig.

dk

kimock
03-15-2009, 03:55 AM
When I use a cab with my DRRI, I don't like it. It does sound a bit louder, and the sound seems 'bigger' and fills the room better, but the change in impedance causes more highs to get through the OT and into the speaker. I lose low end and gain more 'ice pick'.

So it's more than just having more speakers and different cab material/location.

How about a 2x12? You could put an 8 and a 16 ohm speaker in the ext cab, wire the two 8's in series and put 'em in parallel with the 16 and you're back in business at the right impedance.

Gizmo123
03-15-2009, 07:31 AM
I think the blues jr would make a great club rig, esp with an extention speaker. But I would stick with the bassman for outdoor gigs. I would mic the amp in both situations if possible, but at least for the outdoor gig.

dk

Speaking from experience, the Blues Jr. will not work well for a large outside gig. If I understand your original question, it was about the extension cab not specifically the Blues Jr. Extension cab can make it a bit louder and spread the sound around better, but is still not adequate for outdoor gig if something like the Blues Jr is driving it. Of course, this depends on how loud the rest of your band is. What's wrong with just micing the amp?