Front Firing 18" Subwoofer Design

[emersiveav]

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Hey what do you guys think of this design idea using some internal chambering to help excellerate bass out of the box.

Im not sure if its ever been done in passive front firing boxes as its used quite a bit in folded horns and is very much essential for a folded horn to work properly. But what if its used inside a bass reflex box? Will it help or will it ruin the project? I started with just the 45's in the corners to add a bit of "scoop" to the port but then added the "point" in the center and from the looks on paper it would seem to work well. But before I start cutting extra wood I figured I see what some of you guys think.

Ive been using the slot port quite a bit and like the results Ive gotten with the design but have never tried adding the 45 behind it.

I have not included the dimentions as this is a proto type design for a singl 18" woofer.
I had built a pair of single 18" subs quite a few years ago for a nightclub but Im re doing my design as I feel the old boxes were a little to big for a single 18" woofer. They pounded pretty good but I think they could have been better so I started redesigning for a single woofer I was going to be utilizing quite a bit until they disscontinued it and I wont be able to get any more so I want to build this one and try out the design.
If the results are good I will be producing this subwoofer with the new Goldwood Pro 18's and offer them in in two power sizes as needed.

[diy speaker guy]

Re: Front Firing 18" Subwoofer Design

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Hey what do you guys think of this design idea using some internal chambering to help excellerate bass out of the box.

I don't think this is a good idea. It wastes a lot of box space and doesn't have any benefit whatsoever except as a bit of extra bracing, which isn't all that effective anyway since the corners don't need to be braced. If built as drawn, it would tune the box a bit lower than expected due to the corner reflector being so close to the end of the port (unless that's what you had in mind and are already compensating for this effect).

This type of corner reflector is commonly used in folded horns, that much is true, but they are not required for proper operation if designed not to have them. Lots of folded horns don't use them.

[Taterworks]

Re: Front Firing 18" Subwoofer Design

Those corner reflectors are usually used in wide-bandwidth folded horns and transmission lines to prevent each section of the line from developing its own destructive cancellation frequency (where at a 90 degree turn, part of the wave gets reflected back toward the driver end of the line, canceling the advancing wavefront at a particular frequency). In a bass-reflex design these reflectors are not necessary. In folded horns they are not always necessary but are recommended to smooth the response near the upper end of the horn's range. You'll gain more output by incorporating a 30 to 45 degree flare in each end of the vent wall (the one that divides the vent volume from the enclosure volume), ideally so that the vent approaches an inverse elliptical cross section. This will reduce vent compression and 'chuffing' (turbulence), though if your vents are large enough then the air velocity in them isn't great enough to see much of an improvement using this method.

Like this: \____/

Best Regards,


Rory Buszka

[billfitzmaurice]

Re: Front Firing 18" Subwoofer Design

its used quite a bit in folded horns and is very much essential for a folded horn to work properly.

It's not essential at all unless the bend to bend distance measures at least 1/4 wavelength, and in that instance they prevent phase cancellation issues. In a reflex box they'd serve no purpose.

[emersiveav]

Re: Front Firing 18" Subwoofer Design

COOl

thanks for the advise on the internals....I was just drawing this and thought it was worth trying but this is what I expected for answers.

The ports are big enough so there wont be any port turbulance. Ive used this design before and non of the ports ever made any chuffing noise, one of the reasons I like this port design. Its simple, cheep and works!