Originally Posted by Tim1
This goes against the advice I would give to others and against my natural instincts, but has anyone tried blocking the ports on a GK neo115iii cabinet? I have one but just do not like it with my either of my tube heads, too loose and lacking in definition at small gig level for my tastes. Before doing the obvious and getting one of the new Berg 115s I am tempted to try converting the GK to a sealed cab, probably by rolling up some tight sponge into the ports. It is a cab I just have not got on with, I bought it for the odd duo or acoustic style gig but it is just not for me I fear.
Something isn't right here. The sound of this cab is actually pretty articulate, with the upper and middle bass inherently tight and a little reticent (it has diminished, but useful fundamental energy to around F#). If you are getting sound that is loose and lacking definition you may be having problems trying to EQ out the baked in sound of the amps (tone stack). Some tube amps (especially older ones) don't have very flexible EQ. Otherwise, try the things outlined below. If none of that works, and you like the amps, it may be time to consider a different cab. One that allows you to get the tone you are after without having to modify the cab.
To try the GK Neo 115III sealed, just stuff the ports tightly with hand towels or similar material. This isn't perfect, but it's close enough to see if actually closing off the ports with wood panels would be worth doing.
You may also want to try lightly stuffing some dacron fiber (pillow stuffing) into the ports. This damps the reflex action, turning the cab into an aperiodic enclosure (resistive reflex). This may tighten up the sound, but you will likely loose some mid and low bass. The effect is very sensitive to the amount of material in the ports. You can increase the damping effect by adding material up to a point after which the cab starts acting more as a leaky sealed cab.
Check your speaker cable inside the connectors. Sometimes not all of the strands are connected (some strands may have broken off the connection). The easiest way to check for this is to use a different (known to be good) cable. Along the same lines, check the connections for the internal wires going to the 15 inch. If even one of these is corroded it will cause increased resistance and poor damping. If the cab was used or stored in a warm, humid environment some of the internal connections could be corroded. Use 'Deoxit' (available at Radio Shack, Parts Express and similar places) to clean them.
Lastly, consider connecting the cab to the 4 ohm tap. You will loose a little power, but will increase the amps damping factor (same load but lower secondary winding resistance). That should tighten up the bass some.