You have missed something
Even of you achieve the same F3 and efficiency with a vented alignment compared to a TH or other 1/4 wave-based design with the same driver, what those SMALL-SIGNAL based models are not telling you is what happens to that response curve when you start applying more power to your vented alignment. With a vented alignment, you can expect compression at lower frequencies to affect the response, unless you make the vents VERY large. You won't or shouldn't run into this problem with a TH.
You have missed something
Even of you achieve the same F3 and efficiency with a vented alignment compared to a TH or other 1/4 wave-based design with the same driver, what those SMALL-SIGNAL based models are not telling you is what happens to that response curve when you start applying more power to your vented alignment. With a vented alignment, you can expect compression at lower frequencies to affect the response, unless you make the vents VERY large. You won't or shouldn't run into this problem with a TH.
I'm modeling with a pair of 4" round vents, that's more than enough for a low excursion 12" tuned to around 40hz. I don't think port compression will be an issue.
Hmm... My vented spreadsheet says that a 2512 in about a 56 liter box tuned to 41 Hz will give an F3 around 39 Hz. Sensitivity will be about 94.6 Hz
HornResp says that if I put that driver in a 110.6 liter (net) tapped horn with a resonance frequency around 35.75 Hz, it will get down to 36.75 Hz. Sensitivity will be 98 Hz, or 3.4 dB more sensitive than the vented alignment.
So, the TH works out to be over 3dB more sensitive than the vented alignment, and goes a bit lower too, the tradeoff being the larger box requirement.
HornResp says that if I put that driver in a 110.6 liter (net) tapped horn with a resonance frequency around 35.75 Hz, it will get down to 36.75 Hz. Sensitivity will be 98 Hz, or 3.4 dB more sensitive than the vented alignment.
So, the TH works out to be over 3dB more sensitive than the vented alignment, and goes a bit lower too, the tradeoff being the larger box requirement.
Good luck trying to fit a 40 Hz TH for a 12" driver into an enclosure that small. Even if the HornResp predictions look decent, folding a TH into a volume that small with enough space to fit the driver will be near impossible.
With THs, the emphasis is on finding the best combination of efficiency and low frequency capability, not on minimizing box size. If your main concern is box size, then it's best to stick to one of the simpler sealed or vented alignments.
.. but I like a challenge, so
S1=S2=S3=S4 = 270 cm^2
L12=20 cm
L23=168.4 cm
L34=22cm
Gives response down to 40 Hz, sensitivity just over 96dB/2.83V/1M
Net volume works out to just over 57 liters
Good luck translating those parameters into an actual box though, particularly one that can hold a 12" driver.
S1=S2=S3=S4 = 270 cm^2
L12=20 cm
L23=168.4 cm
L34=22cm
Gives response down to 40 Hz, sensitivity just over 96dB/2.83V/1M
Net volume works out to just over 57 liters
Good luck translating those parameters into an actual box though, particularly one that can hold a 12" driver.
That's pretty similar to what I came up with for a TQWT for the 12" eminator, which turned out to be the same as a the vented box. But I had a ~400cm2 area, which seemed like it would work in a simple fold, roughly 20x20x15 overall.
That sounds kind of weird for a TQWT. Mouth size usually decreases as you go from TH->TP->TQWT. What are the rest of the HornResp parameters in your model?
Trying to shoe-horn the driver into the smallest 1/4L model though kinda negates some of the advantages of using this type of alignment. Do you know you can probably get down to 30 Hz at around 96dB/2.83V/1M with this driver? You'll need to use a 200L box though
Here you go.....I adjusted my voltage to 2v for the nominal 1w on 4 ohms and get about 94 db. It was actually 360cm2 that I was working with, or 14x4". The s4 is reduced to compensate for the approximate cross section of the woofer at the mouth. A ported box of the same size sim's almost identical.
Attachments
Unless the program you're using for box modelling allows you to do the same adjustment for the vented alignment you're looking at, I suggest not doing this. Alternatively, use HornResp to model the vented alignment as well, so you can compare them directly in the same program.
Interesting idea though, putting in a "pinch" at S3 to reflect the effect of the driver on the cross-sectional area around there.
The mounting depth for the 2512 is 5.6", so that's not probably going to work out too well if you're planning to just bolt the driver to one side of the mouth. However, with 360 cm^2 available at S2, it might be possible to come up with a creative way of squeezing the driver in (e.g. magnet facing into S2, and mounting rings used at S3 to raise the driver up an inch or two so the magnet stands clear of the wall).
I took the volume of the driver and used the equation for a volume of a cone to back calculate the approximate cross section of the driver, then subtracted from s4 in the sims. I think it's about as accurate as you can get.
I used hornresp to sim the BR also at 2pi and same voltage, and got shockingly similar results.
HornResp croaked when I did that. And when I tried inputting the figures manually, it complained about S1, showing a "Cir < 1" (or something like that) warning.
I've used the PA310 (still using it in fact) in a TH. See The Subwoofer DIY Page v1.1 - Projects : "Proof of Concept #2"
If I was to build it over again, I'd use better cross-bracing in the top and bottom sections and make S4 a bit larger. This is a pretty big box for a 12" though, certainly much larger than the 56 liter vented box for the 2512 being considered earlier in this thread.
This also looks interesting:
ID=28.00
Ang=2.0 x Pi
Eg=2.80
Rg=0.00
Fta=-0.32
S1=370.00
S2=364.21
Par=17.10
F12=0.00
S2=364.21
S3=307.01
Par=169.00
F23=0.00
S3=307.01
S4=300.00
Par=20.70
F34=0.00
S4=0.00
S5=0.00
L45=0.00
F45=0.00
Sd=530.90
Bl=16.65
Cms=2.47E-04
Rms=2.20
Mmd=60.38
Le=0.40
Re=5.20
TH=1
Vrc=0.00
Lrc=0.00
Ap1=0.00
Lpt=0.00
Vtc=661.30
Atc=540.00
Pmax=100
Xmax=5.0
Comment=Dayton PA310-8 (WT3) 39 Hz
Much smaller box, but a bit of efficiency is given up and the response seems a bit worse above 100 Hz.
No clue why, I just downloaded it to the import file and loaded it from there with no problems. Ignore the caution, it's due to the first segment terminating to a point. Do you have the latest HR? V29.10 -120519
FWIW, compared it at 250 W to a BR of the same net Vb using a sufficiently large 6" dia. vent:
GM
FWIW, compared it at 250 W to a BR of the same net Vb using a sufficiently large 6" dia. vent:
GM
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Duh, forgot about "par" being the length. That was the first time I've looked at the parameters in text file format.
I'm amazed that I haven't seen that before, it didn't show up in google search. Looks good, thanks for posting it up!
Hi GM,
Just to clarify - the latest release of Hornresp is actually Product Number 2910-120829
Kind regards,
David
Greets!
Thanks, so much for relying on DIYaudio's email posting updates.
GM
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