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Precision Port Selection . . . Project Updates (pics)!
Guys I am confused by the Precision Port selection and tuning instructions.
I have a box of 1.1 cu ft tuned to 42 Hz using the SB20PFC30-4 and had selected the 2" Precision Port with power applied of 30W using a 3" port dia in WinISD and now that I am actually working on finishing up this long languishing build am second guessing myself.
The SB20PFC30-4 (attached Data Sheet) will be XO'd to a subwoofer below around 150 Hz.
Can I get away with the 2" Precision Port (Front Firing)?
Thanks, dudes!
Comments
For that tune a 2" port only needs to be 2.88" long. That isn't long enough for coupling the inner and outer flare directly (adds up to 4" length) so would need to just add .88" of the tube to the outer flare. WinISD says the first port resonance is ~2350hz so should be reasonably OK if you are crossing below that. I don't know how/if the flare might mess with the resonance.
But, for your specified use, I was curious how a sealed config would do. It looks like the same driver would work in .5cf. Could cross to the sub down ~60hz and a highpass wouldn't be explicitly necessary as it wouldn't breach xmax unless you are getting in the single digits frequency or pumping more than 30watts into it. Could still highpass it higher if you want though. I took some snips of my WinISD results if you'd want to see them. Otherwise I feel I'm already too far over the line on giving information that wasn't asked for
I'm kinda commited to this config and your 2.88" is what I was targeting originally and it could work I guess but just checking with more experienced folks . . . [was gonna just leave the internal flare-off].
It'll be XO'd to a sub using that Musway DSP unit initially [for testing] but eventually want this thing to become the mains flanking my TV screen and develop passive XO's for them once I establish target FR data. (So, they could be able to play much lower FR than 150 - like 80 Hz).
They are 32" tall and the boxes are 8" wide and 11.75" deep with a winged baffle rounded-over at 10" wide due to space constraints.
Tweeters are HiVi RT1.3WE IsoDynamics and mids are HiVi DMB-A 2" and have followed Charlies write-up a bit for inspiration, BTW . . .
I found some foam-backed automotive headliner cloth/suede material I will probably cover these baffles with as the Advantech underlayment panel is wonderful to work with tools but doesn't finish well using coatings.
https://www.walmart.com/ip/Car-Headlining-Fabric-Foam-Backed-Material-Roof-Ceiling-Seat-Ornament-Anti-dust-60-W/787745400
Question: what do you mean by modeling the 2" PP with a diameter of 3" in WinISD? You model them as a 2", and add a bit of length to the calculated to account for the flares.
I wouldn't port them if you're crossing to a sub, especially if you're crossing that high.
I originally modeled them in WinISD using straight 3" ports and the info I read concerning the PP's indicated I could push them a lot harder than a straight 3" port tube and just went ahead and designed around that assumption.
These are not PA speakers and I won't be pushing them all that hard . . . Learning as I go and these speaker cabs are something I have let languish for about 3 years now - just want something put together to test out this Musway DSP controller - if it works I'll try for some passive XO's later . . .
Gotcha.
2" ID port is a bit small for an 8" woofer. I would use at least 2.5" ID.
I would probably still use the internal port flare, it may reduce the overall noise (if there is any).
I was about to say this too, looking back at the data. A 2" port at 30watts would be bringing the vent air speed up about 2x what I typically hear is safe to prevent chuffing without double flares. However that air speed peak is down around 35hz. Initially I didn't mention this because it would probably be a non issue if highpassed over ~60hz. Going passive starts requiring some BIG values highpassing that low though.
Butting up an inner and outer 2" PP flare (just using one coupling ring with no extra tube) would drop the tune down to around 37hz. first port resonance would drop to 1600hz, but in a 3 way I imagine you are crossing at half that, if not lower. Any actual changes to F3 and such seem minimal. Drops overexcursion point to under 30hz at 30watts. Seems to me it would make it a more capable speaker that would have more headroom to handle "full range" without chuffing if you ever wanted to try it... Such as bringing it to one of the gatherings. And I don't see where it would have a negative effect on your planned usage either.
Thanks Drew - this just reaffirms my original choices (from years ago).
IOW - It should work [fullrange] within the constraints mentioned ^
while XO'd to a sub @ 80Hz, I can stuff a sock in the port for an F3 of 75Hz in a closed box vol of 1 cu ft with a Qtc of 0.615 - nice tight midbass
Thanks guys - now for some three-way/6-pole banana jacks . . . .
I've cut the little flanges of each flare and epoxied them together to make a really short aeroport.
Yeah in the past I had theorized chopping off the thinner portion of each flare that the coupling ring fits around, butting them together and supergluing. Then split the coupling ring in half and glue the pieces around the butt joint to reinforce it. Have yet to try though. Probably be able to shrink it an inch or so in length.
3" flared port, bendable/extendable to 1 meter in length with mounting hardware for $20 USD --> https://www.amazon.com/3inch-Universal-Intake-Inlet-Flexible/dp/B0C1D11LHX/ref=pd_rhf_d_dp_s_pop_multi_srecs_sabr_cn_sccl_1_2/143-1354853-8797731?content-id=amzn1.sym.3691afbf-8e16-459d-afed-a0e67e4d7158&pd_rd_i=B0C1D11LHX&psc=1
That could solve a lot of problems.
And likely create new and interesting ones!
I now challenge everyone to come up with an external port design with flexible duct that sits atop/aside of a matching pair of bass cabinets which looks like two [mouth agape] counter coiled [mirrored] Indian Cobra snakes ready to strike.
(Ugly Woofer & 6thplantet) - I'm looking at you guys . . .
EXTRA POINTS if you can get a stuffed parrot in a cage into the MT box that goes with the bass bins [Charlie???]
Beers (virtual) if the snakes fangs look like tuning forks.
That would work fine, maybe set it with some epoxy so it doesn't flop around in the enclosure.
I'd rather just hook my dryer up with it. No more ugly white hose!😀👍🏼
Printed a pair of port flanges for schedule 40 pvc.
Had to sand the pvc a little to make it fit.
STL file if someone is interested.
Nice they look similar to my mdf ones.
Can you make them with more flare?
Should be doable, but would need supports.
Try not to make them too flamboyant as you add more flair . . .
This is a 12mm radius roundover. 1mm thick wall.
Added holes and light chamfer.
You can in fact push these 2" ports really hard and they don't make any chuffing sounds with the 8" woofer in the subject thread - they sound fantastic, BTW . . .
Changed the 2" PP's out for a B52 3" X 5" flare ports for a box tuning of 52Hz and pushed the speakers up to the front wall and the bass these SB20PFC's produce is astounding.