Speaker Box Suggestions Request

[walpurgis]

Well it's a nominal 6.5 inch unit then. A Hi-Fi one would likely have a resonance of say 50Hz, but car speakers usually have slightly stiffer suspension to avoid cone sag when mounted vertically and to avoid damage from bumps and vibration, so add maybe another 10Hz, so call it 60 Hz.

What are the cabinet dimensions and how thick are the walls?

[M6NTL]

Well it's a nominal 6.5 inch unit then. A Hi-Fi one would likely have a resonance of say 50Hz, but car speakers usually have slightly stiffer suspension to avoid cone sag when mounted vertically and to avoid damage from bumps and vibration, so add maybe another 10Hz, so call it 60 Hz.

What are the cabinet dimensions and how thick are the walls?

Inches, or millimeters?

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[walpurgis]

Doesn't matter.

[M6NTL]

Doesn't matter.

Inches then - being British from the '60s, seems appropriate!
18" × 10 3/4" x 7 ". Wall thickness 3/4" plywood.

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[M6NTL]

The original Kef label showed the LF resonance as 29 Hz - it was a big oval driver!

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[walpurgis]

The original Kef label showed the LF resonance as 29 Hz - it was a big oval driver

That was an early B139 bass driver. The 29Hz relates to its free air resonance and has no bearing on the volume of these cabinets.

[M6NTL]

That was an early B139 bass driver. The 29Hz relates to its free air resonance and has no bearing on the volume of these cabinets.

Ah, right!

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[walpurgis]

Inches then - being British from the '60s, seems appropriate!
18" × 10 3/4" x 7 ". Wall thickness 3/4" plywood

Right.

Done a bit of research and working out. The cabinet volume is just under 18 litre. Taking the bass driver resonance as 60 Hz, it may be wise to tune the port slightly below that to avoid the box resonance overlapping that too much and creating larger than desirable 'hump' (there wiil be a slight one), so I'd aim for 50Hz, that will also allow the bass to extend down a bit further, there will certainly be sufficient output from the driver at that frequency to excite the reflex action. This will require a tubular bass port of 6 inches length and 2 inches inside diameter. There will be roll off below 50 Hz, but you should still get some output at 40Hz, maybe even lower if you're lucky.

I use usually use cheap plastic waste piping from places like B&Q for ports, but as Grant says, there are custom ports available that can be adjusted for length, allowing cabinet tuning to be played with.

[M6NTL]

Right.

Done a bit of research and working out. The cabinet volume is just under 18 litre. Taking the bass driver resonance as 60 Hz, it may be wise to tune the port slightly below that to avoid the box resonance overlapping that too much and creating larger than desirable 'hump' (there wiil be a slight one), so I'd aim for 50Hz, that will also allow the bass to extend down a bit further, there will certainly be sufficient output from the driver at that frequency to excite the reflex action. This will require a tubular bass port of 6 inches length and 2 inches inside diameter. There will be roll off below 50 Hz, but you should still get some output at 40Hz, maybe even lower if you're lucky.

I use usually use cheap plastic waste piping from places like B&Q for ports, but as Grant says, there are custom ports available that can be adjusted for length, allowing cabinet tuning to be played with.

Thank you for the effort!
I won't have 6" front to back - the box is 7" deep outside, minus 2 × 3/4" only leaves 5 1/2" inside. How much gap to the inside of the back is required?
Could I run the pipe in at an angle?
Should I still use wadding?
Thanks for your knowledge!

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[walpurgis]

The port can go anywhere, as long as the internal end is not right by the back of the driver. It does not need to be at the front, you can bung it in the side if that suits.

Yes, you still use wadding, but probably less and around the walls of the cabinet leaving space in the middle. You can experiment with quantity.