I theorize: "Convergence".....

[dustinbagby]

This will be cool Wolf. Logitech did a very nice job on the sub for their Z4 system which is a crappy 4" driver loaded as you're doing with a cheap 8" PR. They also ported in between the 2 chambers. I'm not sure exactly what alignment that even turned out to be but it sounded great for a 4". Looking forward to your listening impressions.

Dan

I actually used this subwoofer for a small system I had in my workspace (I got it for $5 at Goodwill). I took the amp and stuff out and drove it with the little 2.1 Lepai.

It certainly was a nice design. This one should be too.

[tomzarbo]

I actually remember reading about someone doing this a long time ago in an issue of Speaker Builder Magazine. I obviously can't remember the details, but he was very happy with the performance at the time.

TomZ

[DanP]

This will be cool Wolf. Logitech did a very nice job on the sub for their Z4 system which is a crappy 4" driver loaded as you're doing with a cheap 8" PR. They also ported in between the 2 chambers. I'm not sure exactly what alignment that even turned out to be but it sounded great for a 4". Looking forward to your listening impressions.

Dan

[Kevin K.]

This looks cool! Subscribed.

A few dumb questions, indulge me. You mount the subwoofer thru the PR hole, right? How do you get a screw gun in there? Or do you just use a really long extension?

[Millstonemike]

I would prefer a 4" port to do as you modeled for that driver, and then it gets crazy long. (I assume you mean 20 Hz HP filter, not LP.) The vent mach is just too high with a 3" port.

Reasons:
-I want to try a PR loaded bandpass as I've never done one. That's the major factor. That and to use up 2 drivers I've had for awhile along with the new plate amp.
-In a vented box, drivers unload below Fb, and also do to some extent below in a PR based similar system. The sealed cavity in the BP keeps this from happening. No HP required (for the 1445 anyway.)
-Port velocity gets too high with a reasonable port size and diameter for both vented and BP style boxes.
-No port volume to add.
-Slight output gain for an already ~84dB driver, so less amplifier power is required.
-Room gain will still allow good extension.

It's just another method to skin a cat, shake a stick at, or crank your cheese wheel,
Wolf

Aaah ...

All good reasons (I guessed a couple, see I'm learning). I did mean and model HP filter. All I know about bandpass is the sound of the "one-note-wonders" next to my car at stop lights. So I had to ask.

[Wolf]

I would prefer a 4" port to do as you modeled for that driver, and then it gets crazy long. (I assume you mean 20 Hz HP filter, not LP.) The vent mach is just too high with a 3" port.

Reasons:
-I want to try a PR loaded bandpass as I've never done one. That's the major factor. That and to use up 2 drivers I've had for awhile along with the new plate amp.
-In a vented box, drivers unload below Fb, and also do to some extent below in a PR based similar system. The sealed cavity in the BP keeps this from happening. No HP required (for the 1445 anyway.)
-Port velocity gets too high with a reasonable port size and diameter for both vented and BP style boxes.
-No port volume to add.
-Slight output gain for an already ~84dB driver, so less amplifier power is required.
-Room gain will still allow good extension.

It's just another method to skin a cat, shake a stick at, or crank your cheese wheel,
Wolf

[Millstonemike]

Trying to understand ...

I quickly modeled the W-8 in WinISD given the spec.'s you listed in a 1ft³ box tuned to 33hz using a 3in port. It has a fairly flat curve through 200hz with an F3 at ~28hz. at 200W with a 20hz 2nd order LP filter, xmax peaks at 14. Port velocity has a sharp peak at 30 hz and hits 36m/s and the port length is 15 1/4" (volume would need to added to the box size.

So other than the ~3dB higher SPL and port issues, why would you do a bandpass type implementation with a PR given what would seem like a very nice ported sub? To really hit the 20hz to 25hz region?

[Wolf]

I've been wanting to do something with these drivers since I acquired them. Both of them are Tent Sale finds- but not found by me- at the first Tent Sale in 2005. I acquired them much later from members Nick12344545353442 (or whatever the number he used was; most knew him as Marmottman), and ChrisM. Respectively, the TB W8-1445A (ser#1) is an aluminum coned concave subwoofer very much like the W8-740P and W8-1363SBF (I modeled for the Neo 1363). The Passive Radiator is an Eminence sample 12". (I recall there also being an aluminum cone version of the W6-1139, and I still regret not buying that unit.) I got them around 2009, I believe. I won a 200W YUNG plate amp at MWAF 2016 this summer, and that got the ball rolling....

I picked a name I was going to use earlier with the PR in a different project, as it still applies. Convergence applies to the units working in tandem to produce the result, and in this case- in a string or succession.
I modeled a single reflex (4th order) bandpass using the PR as the output unit instead of the port. In a total volume of 26 ltrs (18 ltrs sealed/8 ltrs vented through PR), the F3 on both ends of the response are about 35Hz and 55Hz respectively. PR will be tuned to 48-50Hz, and you can model the PR mass required for a given set of PR specs in Unibox using the 8 ltr volume requirement. Room loaded, I'm pretty certain it'll play lower, and the upper end rolls off before most room-boom occurs to be relatively flat to about 70Hz in theory. The peaking that occurs with most bandpass designs via port resonance will be effectively reduced by using the PR, so that is less of a concern.

This will be a quick and easy basic box with inside dims relating to the 11.25" wide/high, by lengths of 4" and 7" internally. I'll double the inner driver baffle to keep distance to the PR at a reasonable length by mounting to the inner board. That leaves 3" of the box behind the driver without walls to mount the amp that is roughly 2.75" deep itself. Add in a couple u-braces or dowels inside the woofer volume for bracing, and I'll call it good.

With/without the average 20Hz rumble filter, and the average 100Hz lowpass filter added to the response and plots in Unibox, the Xmax is in check for the woofer up to full power for the 1445. If one were to use the 740 or 1363, the Xmax does exceed 12mm+15% below 25Hz without the rumble filter of the amp. I am using a 12" PR, but this would certainly be scalable for use with either the 10" or 12" PR's from a certain Canadian vendor. You have to make sure the active driver can drop through the through-hole of the PR you will use. The high-Xmax of these TB woofers require an extremely long throw PR; using either a 10" with about 30mm of Xmax, or a 12" with about 15-20mm of Xmax. With the 1445, there is a net gain of 0 for the alignment. The gain for the 740 is about half a decibel, and the 1363 is about 1.6dB gain over nominal sensitivity. I tried to keep this a broader bandwidth design since BP's can get rather one-note boomy.

Here's the grit:

1445:

Box model with port:

Without rumble:

With:


Photos:





Plots for the other 2 drivers I modeled:
1363 Neo:



740 (you might either need to reduce the box to 15/8 or use a higher freq rumble filter if you intend to use the full 200W of power.):



Later,
Wolf