cab dimensions and frequency response - open back

[diddymix]

Hi Folks,

Was hoping some heads could chime in on their thoughts/experiences on cab dimensions and response. I basically have had a new cab built for me and I just threw out some dimensions to a guy that made it for me. I went with an oversize 1x12, I am pretty pleased with the results sonically and the tone is very nice indeed and sounds very open and dimensional.. its loaded with an EVM12L. The only thing is.. it's quite 'tubby' and almost 'bloated' in the high bass/low mids... like that portion of the response is way fatter than the higher mids. I can only think of the dimensions as the culprit.. the dimensions are

L - 26"
H - 21"
D - 10"

What do you guys think?? Could this be because of the internal volume? Is there any way I could perhaps adjust this by maybe say fixing a plank of wood to the bottom of the cab internally to slighly reduce the volume?
Also worth noting, the builder used 1/2" plywood for the baffle and I asked for 1" as the EVM12L is very heavy so I thought I could use extra stiffness... he told me that 1/2" was easily strong enough and that it would sound better because it could move a little like the top of an acoustic guitar...
Im not sure but I would like to adjust this if possible, perhaps if I cant it might be worth adjusting the slope resistor in my amp head...

Look forwad to your thoughts on what Ive described! Thanks

[Craig B]

The sound of a cabinet is hugely subjective and related to room acoustics. If you haven't already experimented with this, try moving the cab and your ears around the room. Lower mids and bass are strengthened by reflecting off nearby walls or floor. Upper mids and treble are very directional. They lose volume if the speaker is not pointed directly at your ears. So tilting the cabinet or raising it off the floor can boost those sounds.
If you aren't happy with those results then try partially closing the open back of the cabinet...or remove the back completely. I love the three dimensional sound of an open back but find they interact with room placement and listener position in unpredictable ways. That's the fun!
I prefer decent quality half inch plywood for guitar cabinets. 3/4 inch for bass cabinets.

[norburybrook]

In my experience of building cabs for amps over the last 4 years, I 've come to the conclusion guitar cabs are pretty forgiving regarding dimensions , certainly open back ones. I mean look at all the classic fender combo's, there's no 'design' from an acoustic point of view, same as the Marshall 4x12, it was designed so it could be made from a single sheet of 8ftx4ft plywood and it's dimensions were based on the aesthetics of the head cab dimensions. They were the criteria, not acoustic properties

As Craig B said above, an open back cab will sound different wherever you put it. If it's near a wall or a corner then you'll get bass boost. To properly 'hear' you need to put your rig in the center of a room, or on a decent size stage , then you'll hear what the cab/amp sounds like as opposed to the room/cab interactions.

I find the EVM to be a very neutral speaker and personally I like it in a sealed ported cab for my 'Dumble ODS' amps , but it sounds great with open back cabs too.


What is the rear of the cab like? The 'Dumble' open 1x12 cabs only have a small oval cutout, however if it's more open than this you should have less bass than the Dumble design which I think of as 'semi open'


I doubt altering the 1/2 to 3/4 baffle or putting a plank on the bottom would make any significant difference. Can you turn the bass down on your amp? On my oversize Princeton reverb I have to roll the bass off to 3 because I'm using a 12 inch speaker in a bigger cabinet than the original 1x10 the circuit was designed for.

just my morning coffee top of the head thoughts.

M

[bmx]

My feeling is that a EVM12L should be mounted on something more than 1/2" plywood. Yes, it will resonate like a guitar top, but will you like the frequency it resonates at?