Lockwoods in da house! - advice please

[JohnJo]

Thanks Ken. I'd seen those drawings but didn't realise they were for kits. I will mess about a bit later using the crossover opening to test a few port possibilities hopefully. Entertaining a toothache at the mo and I've had better company, still blasting a bit of Albert Collins out though

My amp was comfortably hitting peaks of 96db at about 2.5m without obvious clipping so I reckon sensitivity in the low 90s, as expected I suppose.

[Qwin]

Just remember it's a combination of diameter and length for the port tuning, opening the crossover panel is zero length, just the panel thickness.

What is the net volume of your cabinet?

[JohnJo]

68l net volume. Was thinking of dropping the crossovers inside the cabs and blanking the opening with a bit of plywood with holes and a couple of bits of plastic pipe in them.

[Qwin]

In that 68L cabinet you are never going to get gut wrenching bass, but ported will be deeper than sealed. It really deserves a bigger box, 150 L ported will get you down to an F3 of 39Hz.

I ran my 12" Scanspeak driver details through the same program and got a 112 L net cabinet with a 3" x 23.75cm port giving an F3 of 22.5Hz. This shows its true colours as a sub bass drive unit and reflects what it is capable of in a ported enclosure. This also indicates the program is reasonably accurate in its predictions, if maybe a little optimistic.

[JohnJo]

Yeah, opened the speakers today and when you see the size of the cainet internal versus the driver basket it looks far too small. I'm seriously considering getting some cabs built.

Went ahead with the temporary porting as a trial, just finished, using the crossover opening to hold the port(s). The opening is 12 x 7 cm so no chance of fitting a 100mm port as recommended by the simulator.

I had a poke around the garage to see what I had that I could pressgang into service. Found some 40mm OD drain pipe, 35mm ID. Quick run through the simulator shows two of these 50mm long is OK. Time for some RAF style joinery
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[struth]

aye, its a big speaker that. might as you say prefer a bigger box

[Qwin]

Those ports should give you an F3 of 58.6Hz, which is a good bit lower than your sealed cabinet (94Hz).

If you do decide to go bigger, follow one of the plans I linked to previously, no need to reinvent the wheel when Tannoy have done the work for you.

[walpurgis]

Those ports should give you an F3 of 58.6Hz

That's likely to be OK I reckon. Bass output will extend well below that. Might be an idea to experiment with extra loose fibre wadding if the cabinet seems a bit 'lively' after porting.

[Macca]

Get some built John, the 160 litre or whatever, get the bass response flat down to the thirties. It has to be done.

[Qwin]

Yes, if you have the space in your listening room, they deserve a larger cabinet, otherwise you will always wonder what your missing.

The point about extra stuffing when porting your cabinet is valid, so bear it in mind if you feel the results are a bit lively with your experiment.

The main issue with a pair of ports so small is port velocity, you will probably suffer from some chuffing noise from the ports.
Good practice is to have the port diameter at least one third of the driver piston diameter for a single port, in this instance (33.5cm = 11.17cm dia) that equates to an area of 392sq cm. The two small ports your using will give a combined area of just 77cm sq which is far to small. I'm guessing as to the exact driver piston diameter based on the 385 size. Measure across the middle of the surround domes to determine the exact figure, but my estimate is close enough to suggest there is a significant problem. It will do for a quick look see, to find if you like the overall result though.

Adding a flared mouth/inner to the ports helps reduce chuffing, but it won't compensate for such a large discrepancy.

If you want to use a flare in the future, you have to take the flare depth into account for the total effective length.
You add the length of the straight section to half the radius of the flare, for the total effective length.
So if you want a calculated 100mm port length and are using a 20mm radius flare, you want 90 straight plus 10 for the flare to give you the required 100mm effective length. It will actually measure 110mm in total. If you put a flare on the inside lip, make the same allowance (half the radius used) in your calculation.