Home subwoofer - bandpass front, open back, 18" woofer.

[pelanj]

I have a pair of relatively cheap 18" woofers. I have used one in a MEH as the bass part for quite a while with open back and I liked it. The new round MEH will not play as low, but I thought I might use these in a sort of bandpass sub, but with open back - like on the large MEH. The Hornresp record is attached. It needs some eq, but compared to a simple H baffle or a bass reflex box of the same dimensions, I get more efficiency and acoustic bandpass filtering as a bonus. It comes with the cost of boosting the low end need and needing more amplifier power and not much output below some 35 Hz. Amplifier is not a problem and it did not play lower in the MEH anyway, so this seems like a good compromise.

The plan is to have a simple 60 x 60 x 66 cm (OD) box serving as a stand for the round MEH. Would any other enclosure style in this volume have some advantages?

 

[GM]

Following in the pioneer's footsteps again I see.

 

[pelanj]

I came to this from available space and then I tried various tunings until it started looking reasonable. And then some EQ. I will try to sketch a model how I imagine it could look like.

 

[Booger weldz]

wow, that open back/resonator sure makes a difference!

 

[L.rivera92172]

Pics of it please 🙏

 

[GM]

The pioneers 'had a clue'. They used it with a matching impedance tube amp and adjusted it by varying the driver's field coil voltage to get the desired Q response.

 

[pelanj]

This is how I imagine it:

The woofer will be mounted from the back.

 

[pelanj]

By moving the baffle backwards a bit, I can get some really low tones, still within safe limits of the driver and with a little gain compared to a standard BR, not even mentioning H-baffle.

The only thing I am afraid of is the port noise, the area is a bit too small I think.

 

[Booger weldz]

What happens if you do it like this? Too long and pipe resonances, etc?

 

[freddi]

gee - its pretty good w/o EQ

 

[Booger weldz]

too big with the larger/longer port??

 

[freddi]

that reminds me - many years ago - maybe in Speaker Builder Magazine there was a crawlspace BP4 mentioned - no back chamber - just a front chamber which vented up through a floor vent.

 

[GM]

Yeah, I remember us talking about it (or something very similar) back when we were (politely) 'harassing' Tom's claim of inventing the TH; seems it had a JBL woofer IIRC.

 

[L.rivera92172]

Couldn't you put a passive radiator and tune it and make a box in a box so you can slide it forward and backwards

 

[pelanj]

View attachment 1267171
too big with the larger/longer port??

This looks almost like moving to Paraflex territory. The folding is smart - I could also make a side firing port like I did with my 15OB350 box.

@L.rivera92172 A PR of this size is pretty expensive. But it is definitely a good idea to make the prototype tuneable.

 

[L.rivera92172]

How about a flared port or a lascala style front horn loading

 

[Booger weldz]

This looks almost like moving to Paraflex territory. The folding is smart - I could also make a side firing port like I did with my 15OB350 box.

@L.rivera92172 A PR of this size is pretty expensive. But it is definitely a good idea to make the prototype tuneable.

Got pics of the 150b350? 🙏🏻

 

[pelanj]

The port is parallel to the back wall and side firing.

 

[pelanj]

I have found out that I have pre-cut some 18 mm chipboard while preparing another project for a 12" DVC woofer (inspired by PPD subwoofer). So I actually changed the plan and will try to build a test box with the 12". Inspired by @Booger weldz , I changed the layout of the front port. The woofer will be mouted facing the "horn" part. The "horn" part should add a bit of output compared to a bass reflex of the same volume. The low end will be equalized based on in room measurement of the box built. It is smaller, the output is at 200 W.

This is the layout of the front port

 

[freddi]

that is really potent for such a small box !