HELP WITH PORT CALCULATIONS

[dreadknot]

IV GOT ALL MY TOOLS AN SUPPLYS NEEDED FOR MY CUSTOM SUB BUILD AN IV RUN INTO AN ISSUE THAT I DONT KNOW ABOUT RIGHT AWAY

IS THIS MY BOX INTERNAL DIMS ARE 16.3IN WIDE BY 9.25IN DEEP BY 72IN HIGH WITH THE DRIVERS DISPLACMENT OF 4.56LT FACTORED IN GIVES ME 6.121 FT3

WITH A PORT THATS TUNED FOR 19.85HZ AN THE PORT DIMS ARE 16.3IN WIDE BY 1IN DEEP BY 40IN HIGH AN MY DESIGN CONCEPT IS TO PRODUCE THE PORT

BY USING A SHEET OF .25IN THICK COLD ROLLED STEEL AN(correction meant to be 2.5in from the rear wall not) 1IN FROM THE BACK WALL OF THE SUB FOR THE MOST minimal AMOUNT OF SPACE TO BE

CONSUMED BY THE PORT LIKE IN MY DISIGN CONCEPT HERE

DOES DOING THE PORT THIS WAY COUNT AGAINST THE OVERALL AIR SPACE AN IN DOES IT REDUCE IT AT ALL FROM
6.121 FT3 TO LESS OR DOES THIS NOT MATTER TORWARDS THE TOTAL VOLUME

 

[pozz]

You'd likely get a better response with less CAPS.

 

[Wombat]

One port, square or circular, tends to give the best results. End flange/flare profiles can make a difference.

Port volume is added to calculated internal enclosure volume for overall enclosure size determination.

 

[witwald]

I believe that the volume of air contained in the port does not add to the enclosure volume for the purposes of computing the resonance frequency of the port. The "plug" of air in the port forms a mass that interacts with the stiffness of the air in the enclosure. Note that the volume taken up by your 0.25-inch steel plate needs to be subtracted from your enclosure volume.

There is also the concept of an "effective port length", which you may wish to consider, in order to better estimate the port tuning frequency.

 

[Prana Ferox]

I'm not sure the port needs to be square but you probably want a squarer aspect ratio. Air does weird things with very long and thin ports. Make sure to model port velocity as well, I bet for a 1" port it may be a problem. I also wouldn't bother with the steel plate unless you really like that kind of thing; plywood will work fine.

Take a look at this design for a similar layout that's been tested and built. Your dimensions will be different but I recommend that general construction method. You will absolutely, absolutely need more bracing than your drawing has. That's a good forum for getting custom sub assistance, by the way.

As above posters said, neither the port air volume nor the board creating the port (or any bracing) should be counted towards internal cabinet volume. Is there some constraint on the height? Is this going to be a coffee table?

I do give props for the Hot Dog Stand color scheme but I spent several irritating moments trying to clean the arc in your drawing upper right off of my screen.

 

[tomtoo]

I wonder if Horizontal woofers not couple special "nicely" to the floor?

 

[DubbyMcDubs]

Try using WinISD and it will calculate it for you, taking all things into consideration.

I am in the process of building two "Full Marty" boxes for my HT and found the app to be incredibly valuable. Mine are tuned for 17hz with Dayton Audio UM18-22's.

 

[dreadknot]

I wonder if Horizontal woofers not couple special "nicely" to the floor?

my design concept was for a car to begain with but now for use in my ht room place verticly against the wall one on either side of my room with the port aiming down

 

[dreadknot]

I'm not sure the port needs to be square but you probably want a squarer aspect ratio. Air does weird things with very long and thin ports. Make sure to model port velocity as well, I bet for a 1" port it may be a problem. I also wouldn't bother with the steel plate unless you really like that kind of thing; plywood will work fine.

Take a look at this design for a similar layout that's been tested and built. Your dimensions will be different but I recommend that general construction method. You will absolutely, absolutely need more bracing than your drawing has. That's a good forum for getting custom sub assistance, by the way.

As above posters said, neither the port air volume nor the board creating the port (or any bracing) should be counted towards internal cabinet volume. Is there some constraint on the height? Is this going to be a coffee table?

I do give props for the Hot Dog Stand color scheme but I spent several irritating moments trying to clean the arc in your drawing upper right off of my screen.

hey Prana Ferox in responce to your reply my design is 1.5in thick for the entire shell with the bottom top an sides made from

2 in (actually 1.5in ). x 10 in (actually 9.25 in ). x 8 ft. #2 Prime or Better Ground Contact Pressure-Treated Lumberany bracing

https://www.homedepot.com/p/2-in-x-...tact-Pressure-Treated-Lumber-166298/206964278

an double layer of .75mdf front an back

an the whole cab secured with titebond 3 an 4in screws through out the shell an my port is cut at 16.8 so .25in is secured in either side of the frame via a cut groove on the
inside panels so i dont need any bracing

constraint on the height? - my resone is just for the space an layout of my ht room it suiits me ,its easyer to move like a table ,but also for the cost for

of 170$ to build two 6 cubic ft cabs is good

my cut dims are

4 - cuts at 75in an 4 - cuts at 16.3in (all from 4- 96in boards)
4 mdf 4x8 (8 cuts at 19.3in by 75in )

the steel was some scrap that i had cut to form

model port velocity - how do i read that in winisd ( i just dont know how an what reading is considered bad

 

[Prana Ferox]

In WinISD you make sure to click on 'signal' in the bottom left, and then put your expected amp wattage in 'system input power'.

Then in filters you put in whatever high-pass filter you have or want to use. The other numbers won't be right without this set.

Then at the top of the window where it usually says 'transfer function magnitude', click on it and select 'rear port - air velocity'. (It's always a 'rear port' for WinISD regardless of where the port is, for basic ported subs like this.) Ideally you want <17m/s at the peak, sometimes you can get away with more (with big roundovers on the port, for instance) but 17 m/s is the common thumbrule. Go beyond that and you may get port chuffing - literally sounds like chuff, chuff noises at high output.

Also make sure you're checking cone excursion for your power and high-pass filter setting. Different drivers do different things at different excursions, but if you overdrive your sub it generally sounds bad and can break the driver.

You also want 1st port resonance to be well above whatever you'll be sending to the sub - double crossover frequency or more if possible. You see that in the 'vents' section where you define the port size. This is usually the balancing act, getting the port big enough to bring velocity down but not so big that the port resonance may be audible (and not so big it eats up all the box space.)

It sounds like you already have the materials, I would recommend a good hard knock test after building but before putting the driver in, you can always brace with dowel rods or scrap lumber after the fact through the driver hole. I think you'll be surprised how much an unbraced sheet of any thickness moves when you put hundreds or more of kW on a big heavy speaker. Even just dowels connecting front to back, right behind the speaker mount points, will make a big difference - remember it's not the panel edges that are the weak points, it's the panel centers. Also I would suspect a 16"x40" sheet of plate steel is going to ring like a gong, but I've never tried it like this.

 

[dreadknot]

thanks ill check on all that

 

[Prana Ferox]

I'd also check your WinISD model in general. I threw together a quick model (the box doesn't depend on the driver) and a 6.1cf box tuned to 19.85hz with a 16" wide x 40" port works if the port is 2.5" high, not 1". Even then, WinISD tends to be pessimistic so the actual tune is likely a touch lower.

 

[dreadknot]

damn iv got a peak of 55 according to winisd an without the para eq boost at 20hz with a q=2 at 10db gain its 17.7

but fq roll off without it has my fq response output drop off at 20hz by -11db for a 106db spl but with the boost its 116db

should i take the -11db hit at 20hz or play around with the port design to get a lower air velocity m/s

this is for ht use

 

[Prana Ferox]

I suspect if you're putting 10db of boost at 20hz you're going to run out of excursion in a hurry. What driver and amp are you planning on?

 

[dreadknot]

my setup spec are for ref

per cab a txxbd1 15in audiopipe dual 4ohm wired to 2 ohm an feed 775watts from my crown xls 1502 with one cab per channel

an highpass an para eq filters from my outlaw audio 976 balanced receiver

chosen settings para eq boost at 20hz with a q=2 for 10db(they only go up to 3+db but they can be stacked
an a highpass of 17hz

according to winisd with the highpass at 17 im under the excursion limit

 

[Prana Ferox]

T-S Parameters from manufacturer for this driver are here but something's wrong with them (the Cms number has the wrong units, at least.) According to this, this driver has an 8mm Xmax and a 30hz FS. I don't think it's getting to 116db @ 20hz. My model shows it blowing past Xmax in this box at 100 watts but again I'm not sure the T-S aren't messed up.

If you're using the 'Audiopipe TXX-15' model that came with WinISD, that's a different (single voice coil etc) speaker with different parameters.

Also I see you updated the OP, be aware if your port outputs straight down into the floor, then the gap between the bottom and the floor becomes part of the port and goofs with the model. I.e. it will force your port tune down and your velocity up. I'd say to put a 90 in and come out the front but that doesn't work with your plate, so you may just want the port coming out the top instead.

 

[dreadknot]

the one iv got is the audiopipe txxbd1 - 15in

its ts are 30hz FS with a linar xmax of 25mm an a max of 50mm

 

[dreadknot]

hey any thoughts on the ( fi audio IB315 v2 2ohm version ) for home theater use , an wheither or not using one ( 2ohm version ) per cab or two 4ohm
versions per cab wired to 2ohms would be better then my audiopipe txxbd1 - 15in one per cab

 

[Prana Ferox]

That's listed as an infinite baffle driver. Not sure what that really translates to in car audio but for home use you'd have to model how it does in a ported box. I doubt two per 6ft3 cab would work well at all. FI does make the HT1 and HT3 for HT use but they're both 18's.

I'm not sure if you're looking specifically for 2 ohm drivers. I would not get hung up on this for HT use. It's all how the drivers model at the amp power.

If you're looking at different drivers I would just go with the Dayton Ultimax. A UM15-22 will do well in this box at this tune (it'd actually work better tuned a little lower) and two of these, run together off a bridged XLS1502, get you 116db@20hz with zero boost or room gain. (You can boost at 20hz but a 6db boost will get you port chuffing.) If you want more than that I'd recommend stepping up to an 18" driver.

 

[dreadknot]

im going to go ahead with my current txxbd1 15in build an see how it goes.

for future concept i had a planned build that was bigger an cost more

but i was unsure about the port design on wheither it would work or not this is the spec like me know if this would be better an doable

an ill build for later when i have the supplys

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my revised concept is this


two cabs each with an outer dim of 19.3in wide by 49in high by 30.75in deep with inturnals 16.3in by 46in by 27.75in


with a 16.3in wide by 6in deep by 80.75in long wrapped around the outside from back to front also with a matching 1.5in thick wall

according to winisd with the para eq boost at 20hz with a q=2 at 10db gain an highpass of 20hz an a tuning of 20hz

i get a port air velocity of 20.876 m/s at 20.67hz reading of at peak an a spl of 115db at 20hz
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the build of each is 7.38cubic ft ( thats with owens acoustic fiberglass fill ) without is 11.88cft