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Discussion Starter · #1 ·
Hi guys - my first try at this. Home theater setup for a fair sized room - about 400 ft^2 with 10" ceiling and an open staircase.

Driver is 15" Dayton Reference HF (RSS390HF-4), 300W Bash plate amp.
Box volume from WinISD is 336.4 liters, with two 3" ports.

All the pieces are cut out and about ready for glue & screws.

Here are some cell phone pics and a WinISD screen capture - any advice is appreciated.
 

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I second the recommendayion on going larger on the ports...I have (2) 3' round ports in a single 12" sub box and at really low freq and when its quiet ( just low bass freq and they are really moving alot) I can hear them huffing (or hear port noise) and u have a 15"!!!! ....but its only every now and then most dont hear it, but I do...just a thought while you are still under construction.
 

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Discussion Starter · #4 ·
Thanks guys - so what's a good target for the peak port velocity. WinISD is showing 3 m/s right now. I thought it was lower - must have gotten my models crossed up :/

Going to 4" ports would bring it down to 1.7 m/s - but I'm not sure how to cleanly and accurately enlarge those holes in the back panel. Did the initial ones with a router & circle cutting jig but that only works with the center still present. Maybe I could cut a plug with that jig to give me an accurate center again. I'd also have to go get a piece of 4" pipe.

Another option could be to add additional 3" ports:

2 ports: 3.0 m/s (9.6" vent length)
3 ports: 2.0 m/s (14.8" vent length)
4 ports: 1.5 m/s (20.4" vent length)
5 ports: 1.2 m/s (26.1" vent length)

5 ports looks to be diminishing returns, and is also to long - outside depth of the box is 25" I could easily add 2 more ports in the bay next to the one where I have them now.

Another question about ports in general - they are just to control the rate of air flow into the cabinet right? You're not getting sound out of them right? I ask because I see many builds with the ports on the front. I don't care to see them so put them in the back, where they'll be inside built-in space for the HT setup.
 

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I second the recommendayion on going larger on the ports...I have (2) 3' round ports in a single 12" sub box and at really low freq and when its quiet ( just low bass freq and they are really moving alot) I can hear them huffing (or hear port noise)
You have two 3 foot ports and you're still hearing noise? That thing must move a lot of air... :rofl:
 

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Discussion Starter · #9 ·
If I add two additional 3" vents, it's going to reduce my cabinet volume to 273.8 liters. I can get a little of that back by getting more aggressive in cutting out the braces, but not much.

Green line in these captures is the 4 port model, yellow is the current 2 port model.
 

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I'm not seeing the "system input power" setting on WinISD - or any tabs at all. Maybe my version is out of date? I have WinISD 0.50a7
Your version of WinISD is fine.

I agree, it sounds like you haven't entered any system power (to match the maximum output of your amplifier, entered in the System Input Power field under the Signal tab).

The air speed numbers you provided are way low for such small and short ports. Unfortunately, you will find to keep the air speed reasonable with the appropriate power applied, the ports will be significantly larger than you've designed.

Edit: By the way, I'm looking at the WinISD tabs in your screen capture; Driver, Box, Vents, Plot, Signal, EQ/Filter, and Project.
 

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Discussion Starter · #12 ·
Your version of WinISD is fine.

I agree, it sounds like you haven't entered any system power (to match the maximum output of your amplifier, entered in the System Input Power field under the Signal tab).
Ok, I get it - sorry, I'm a little slow today :blink:

The air speed numbers you provided are way low for such small and short ports. Unfortunately, you will find to keep the air speed reasonable with the appropriate power applied, the ports will be significantly larger than you've designed.

Edit: By the way, I'm looking at the WinISD tabs in your screen capture; Driver, Box, Vents, Plot, Signal, EQ/Filter, and Project.
I also found an error in my spreadsheet which significantly increased the calculated vent volumes. The Transfer Function Magnitude plots are now pretty much on top of each other for the different vent configs, now that I've corrected my total box volumes.

So here's what I have now with the corrected volume and 300 watts in the signal power System Input Power field:

Two 3" diameter vents, 9" long:
53.8 m/s, total volume: 353.7L

Four 3" diameter vents, 19.7" long:
26.5 m/s, total volume: 344.1L

One 3" x 10.25" rectangular vent, 19.7" long:
24.1 m/s, total volume: 339.5L

One 3.5" x 10.75" rectangular vent, 25.4" long (this would have to stick out the back a bit)
19.4 m/s, total volume: 332.0L

The rectangular vents would be pretty easy to do - those sizes circumscribe the cutouts I already have for the circular vents.

So, I'm sure 19.4 or 24.1 m/s is much better then 53.8 m/s :rolleyesno: But what is a good number to aim for?

Thanks for saving my butt guys!
 

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Discussion Starter · #14 ·
Ok, so now that I've figured out the input power setting, talk to me about cone excursion! The capture below shows 300w input power to the first 3 vent configs, and 240w to the bigger rectangular vent. Thye only ohter way I'm seeing to bring this down is a much smaller box - about 200L

Is there a solution here besides the obvious one of going easy with the volume knob? Do I need a high pass filter on the bottom end?
 

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Ok, so now that I've figured out the input power setting, talk to me about cone excursion! The capture below shows 300w input power to the first 3 vent configs, and 240w to the bigger rectangular vent. Thye only ohter way I'm seeing to bring this down is a much smaller box - about 200L

Is there a solution here besides the obvious one of going easy with the volume knob? Do I need a high pass filter on the bottom end?
It looks like you have the BASH 300 from PE. If so, according to some comments on the site, the amp comes default with a 1db boost between 25-30 and a high-pass filter (HPF) at 17.7 Hz.

You can enter these settings under the EQ/Filter tab in WinISD (Boost as Parametric EQ at 27.5 and HPF as Highpass at 17.7) to see the effect on the cone excursion. The HPF will reduce the cone excursion and port air velocity from what you are currently seeing. If the excursion still exceeds Xmax (red line), the HPF can be adusted per the PDF available on the PE site via resistor changes.
 

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You are getting on the right track with your simulations. This driver cannot do more than a couple hundred watts at a sub 20Hz tune. Can do more with a higher tune and a filter for low freqs. This is a well regarded driver for low distortion so I suggest if you need more SPL go with multiple subwoofers. There are more than a few builds with these in the subwoofer database....
 

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With 300 watts the driver will be over Xmax by under 2 mm which isn't a problem. Using four 3" ports the maximum port air speed is under 18 m/s at 17 hz due to the HPF on the Bash amp. You're good to go. Here's the Project file if you want to have a look, save it to the Projects folder in WinISD:

View attachment The CoAstroGeek Project.wpr
 

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Discussion Starter · #19 ·
I reworked the vent design - went to a rectangular design with a 3" x 10.25" cross section and a 19.67" length. Final volume is 337 liters. With the new vent and the amp stuff modeled the max vent velocity is 16 m/s, max cone excursion is 15.5 mm @ 25 hz. All of this at 300 watts.

Got some of the assembly done this weekend - here are some pics. Got the bottom plate glued & screwed as well but no pics of that yet. Thanks again for the help!
 

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