Did I invent a new speaker enclosure ?

[Bigun]

I have always noticed that the double reflex design is a rarity, perhaps because it's more work for not enough gain. But as far as I can see it's always implemented in a series format, i.e. two boxes coupled with a common port and one port to the 'outside'. Having more than one reflex resonance creates twice as many impedance bumps to take care of, which sounds nasty for cross-over design ?

I recently looked at Martin Kings website and the notes on TL design. These boxes produce lots of resonances. But through suitable damping this can be ameliorated and the impedance humps can be smoothed out. Unfortunately, these harmonics don't help in extending the bass loading to lower frequencies, they just complicate the response where you don't want it.

So I thought, why not have multiple bass reflex ports tuned to different frequencies (let's call it the MULTI-PORT), using damping to smooth out the impedance humps and yet tune the ports to assist with bass loading extension. The ports would be in parallel not in series, only one enclosure box would be needed. The air inside the box can resonate at as many frequencies as it wants, so each port can 'share' the same box. It is the mass of air in each port that will vary. The multi-ports will act like coupled oscillators.

I haven't seen such an approach before - did I miss something, is my thinking simply flawed or has it been tried and found unworkable ?

[rjb]

I have seen such a design in both an Australian and British magazine. I think the British one was HIFi World, but cannot be sure. I know nothing more

[gtforme00]

I feel pretty sure that you will just end up with one resonance frequency that is higher than either port would have been by itself. The masses in the ports will sum to present one equivalent mass to the box. What will improve however is that the ports will have different organ pipe resonances and they will be at different frequencies, reducing the coloration if they are in the pass band of the speaker.

-David

[Bigun]

Originally posted by gtforme00
The masses in the ports will sum to present one equivalent mass to the box

I've heard this somewhere before - can't get my head around why this should be the case.

[gtforme00]

Well if you think about it, the thing resonating isn't really the port, it's the whole air spring of the enclosure acting against the mass in the port.

It's like attaching two blocks of mass of different size to the same big spring. The spring isn't going to resonate at two frequencies, just at the frequency which is determined by the sum of the masses.

-David

[MJL21193]

As David says, the ports would equalize I think.

What could work in this way is a TL of a few different lengths and cross section/tapers, although I don't see any advantage to doing this.

[badman]

Which has been done (multiple TLs), via some H-name IIRC.

[pinkmouse]

We discussed this, ooh, about five years ago?

edit: Here you go, six years ago!

[PeteMcK]

the Karlson slot is a (partly successful) method of smoothing out the resonance peaks...

[Bigun]

Interesting thread - from reading it I lean towards believing that you can have two ports that don't behave like a single port.

I don't see the box as acting like a single spring in this case, which if you use this as the basis for the math you may not get the right answer. After all, the driver can modulate the pressure inside the box at several frequencies at the same time (with music !!!) so the air in the box can be moving at different frequencies and can resonate with different ports.

It seems to me that Pinkmouse has proven this out already back in 2003....

but doesn't seem that it produced any breakthrough's to get people excited ? - so I guess I will go back to figuring out how to make a TL (clone of DB1+) ?

wait ! - this Karlson slot looks interesting...