Ruby Amp - What size hole do I cut out of the back of the speaker mount?

[LucifersTrip]

I just blew thru the Ruby:


..and am using it to drive an 8" 8 ohm speaker mounted in a 9" x 9" x 3.5" wooden box.

I know nothing of acoustics, but I know all my amps have some type of cutout in the back.

What size hole do I cut out of the back of the wooden speaker box for proper sound?


thanx

[petemoore]

  Ported cabinets have the ability to extend bass response, but it's a tricky wicket compared to sealed enclosure design.
  See Elliot Sound projects, articles, pages.
  imagine a water wave:
  The 386 doesn't produce enough current to get a ported cabinet 'puffing'.
  2w might start a cone pressure wave at a low enough frequency to, I'd start with 10w though, then probably move to infinite baffle [sealed enclosure] or open back design.
  Rolling back and forth in a rectangle, instead of going foreward like it wants to, if the distance between the two wave peaks is longer than the rectangle [say, thin-long speaker cabinet shaped rectangle] the wave can't assume it's form in the enclosure, it's too long.
  The wave the cone excites wants to move from in front to behind the cone in the least restrictive manner = right around the speaker frame.
  Huge board [like in the wall speaker] is also infinite baffle, the wave [distance between peaks] is shorter than the 'breakwall' [baffle dimension measured in all directions from the cone]. This 'can' get you super low frequency response, stiffer the baffle the better.
  But we can get the wall up the stairs...
  So we wrap it back around, think open back cabinet.
  Then we close it off entirely, creating a fixed size chamber behind the cone-diaphram, the diaphram changing the size of the object [cabinet]. If the volume-size of the cabinet is large enough compared to the low frequency, the wave formation isn't impeded by cabinet size and LF response is accurate, no 'wrap around' waves mixing with the waves produced by the front of the diaphram-cone, to the space around and especially in front of the 'chamber that changes size], even the LF waves [with their long distances between peaks] are formed cleanly.
  Think of water wave stillshot, high pressure here and there [peaks], low pressure here and there [troughs], peak, peak, trough, peak, trough...waves.
  A high frequncy wave works in shallow water, a low frequency wave can't even form 1 cycle.
  So...the water has to be certain depth...harder to move increasing amounts of water [or air], and requires larger motor device. The 386 is a chip with capacity to drive only small motors a little bit,
  door is knocking...to be continued?
   
 

[PRR]

> all my amps have some type of cutout in the back.

Odd. A LOT of amps today use closed enclosures.

Combo tube amps "must" have an opening to release the heat. (LM386 in an 8" box does not face this problem.)

_Large_ baffles such as Two-12" may gain efficiency and bass-throw by exposing the rear-wave.

There is the "ported box". Calculations are tricky. You can NOT pick an arbitrary cone and an arbitrary box and find a vent-size as an afterthought. And in most cases, the box is "much larger" than the cone diameter cubed; your box is small.

Without knowing your driver parameters, I'd suggest an Eight in 283 cubic inches is an acceptable bit-boomy sealed box design. Since an Eight is "too small" for guitar, the bit-boomy is probably the right way to lean.

If you don't accept that: cut your 9x9 back into 1", 2", and 6" slices. Try all combinations. Wide-open will cancel the bass (below 500Hz!) but throw sound front and back with little to the sides. Smaller openings are liable to cancel other lower parts of the bass without much throw. Since an Eight is rarely boomy, I suspect none of these is generally "better". However you may find something "better for a specific sound".

The swappable-slat test-rig will be prone to buzzes. If you do find a useful hole, re-figure it as a rounded rectangle in a one-piece back.

[LucifersTrip]

Hello,

Thanx much for the info (and sorry for the late reply...went on vacation with a laptop with wrong adapter & dead battery)

I really didn't expect that much of a detailed response, but it's definitely good info to try to understand. This little amp was just a diversion from all the pedals...I don't know how serious I'll get into the acoustics.

I should've realized the best answer is the same as for: "Which transistor sounds best on this fuzz pedal?" ...Just try all variations...experiment...and stop when it sounds good to your ear.

I will try various size openings and see which sounds best.

thanx again for the info