Damped (lossy) BR ports

[planet10]

A damped prt gives you an aperiodic design. The classic example is the Dynaco A25 & A10.

I think of them as the missing link between BR enclosures & TLines. The 1st analytic work on this was by EJ Jordan when he woorked at Goodmans where they produced speakers with ARUs (acoustic resistance units).

I have often stuffed the port of a BR to make it aperiodic and better behaved (to my ear) and have built a couple successful designs. The most evolved design i have heard is the PEARL PR-2 (i think i've posted a picture here somewhere).

A TL with sufficient stuffing becomes aperiodic (a TLs roll-off can be between 2nd & 4th order depending on stuffing -- the ones tuned for maximum bass efficiency typically have 4th order roll-off).

dave

[roddyama]

OK Pjotr, Navin, Dave, and Al,

I apologize, but I guess I’m can be a little slow on the upshot sometimes. I have always tended to learn by osmosis. I now see the relevance of this thread referred to by Pjotr. Please forgive me if I’m rehashing old news, but I’m beginning to see the light about the aperiodic design.
TL's vs. Closed Box or Ported

By increasing only the resistive component of the port circuit and leaving the reactive component “untouched”, you may be able to get some of the benefits of a TL, BR, and closed box all at the same time. The small (SAF) size of a BR, the transient response and cone control of a TL, some of the bass extension of both, plus the added isolation of the internal noise you get in a closed box design.

If you take that one step further, as Navin suggest here: Subwoofer Qtc and 'tightness'
and above in this thread, and add a second box with the port between the two, then I have a truly sealed system in a “small” box with good transient response and bass extension.

So where’s the downside, or is there a downside?

What a great forum!
Rodd Yamashita

[navin]

before someone misunderstands i will try and offer a more clear explanation...

take a box. fill with damping material . i use 1 lb per cu. ft. of glasswool but you can add more.

divide it into 2 (usaually 60-40 or 66-33). The 60% contains the woofer. the smaller part does not.

make a hole as big as reasonable in the partition between the 2 "halves". They are not exact "halves" but you get the idea.

fill the hole with some substace that resists but does not block the flow of air like open cell foam.

voila.

now if you do this twice you can make a 2 woofer 3 box design.

in my case:
Took 2 12" woofers.

Box was 30" W x 24"D x 18"H external woofer side by side. 1" MDF. filled box with about 6lbs of glass wool (3kgs).
divided the box into 3. using 1" MDF at an angle. this also acted as bracing. cut holes in the dividers. filled hole with 50mm open cell foam.

object replicate bass of JBL 2245 using 2 12" in 25% smaller box due to WAF.

[Pjotr]

Hi Navin,

What you are describing is a closed box with extra high losses. That can be useful to tame a too high combined Qt of the ls + box if the box is too small for a given speaker unit. It looks somewhat to the old designs of Gilbert Briggs (founder of Wharfedale) that used a “Briggs filter” or "Briggs plate". However the Briggs designs were BR designs and were commercially sold by Wharfedale. These designs used also a hole in the second compartment to the outside that acted as a BR port.

Your description does neither limit cone excursion nor does it support bass output at low frequencies. It just tames cone excursion at the box resonant frequency. But yes it is a way to make small bass boxes.

What I am up to is to mimic the response of a TML. Not by lowering the Q of the box + speaker combination (that is already low due to the speaker unit itself) but by lowering the Q of the box + port combination. Although this lowers the Q of the box + speaker combination also a little bit.

Cheers

[phase_accurate]

I have once seen a picture of a reflex-port which I assume was some kind of lossy port. As far as I remember it was from a German high-end manufacturer. If I stumble over the article I will tell you which one.

The port was made of an ordinary tube which had an extension made out of fine metallic mesh that was filled with fibrous material.

I attached a simple drawing.

Regards

Charles

[navin]

true. i just wanted to sure guys were clear. i have used the lossy port method too. there again it was used for a box that was too smal.

[kelticwizard]

I have done some simulations with a stuffed port, got some interesting results. Will post later.

I would just like to point out that I kind of invited Navin into this thread when the conversation turned to aperiodic enclosures, and I remembered he had posted on the subject previously. At no time did Navin ever say or imply that the aperiodic enclosure gave the woofer excursion relief. He only posted his knowledge of aperiodic enclosures when the subject came up.

[roddyama]

Originally posted by kelticwizard
I would just like to point out that I kind of invited Navin into this thread when the conversation turned to aperiodic enclosures, and I remembered he had posted on the subject previously. At no time did Navin ever say or imply that the aperiodic enclosure gave the woofer excursion relief. He only posted his knowledge of aperiodic enclosures when the subject came up.

It was I who made this implication. My appologies. I should have known that in speaker design, nothing is gained without a price.

Rodd Yamashita

[pinkmouse]

Just a quick thought...

If you are changing the compliance of a port by stuffing it, it is equivalent to just changing the volume of an unstuffed port, isn't it ?

[kelticwizard]

Pinkmouse: No, though you would be tempted to think so.

Simulations coming up.