# Guidance for building a slot ported box?



## billbillw (Aug 25, 2009)

Hi,
I've built several ported boxes in the past, but always used round PVC pipe for the ports. For my current build, I would like to use a slotted port since the port length needs to be so long (~30Hz on a .7 ft^3 box, can you guess what sub?). 

I've searched around, but haven't found much guidance. I've seen some mention of the ports actually tuning to a lower frequency than their length would dictate (port correction?), but I don't know how to compensate for that. Also, does it matter if the slot opening faces the same direction as the sub driver? My design was for a shallow (6" inside depth) box with the sub on the large side and the port coming out of one of the shallow edges. So it would be a 6"x 1.25" slot running down and around the inside. In the car, the slot would be facing up and the sub would be sideways near the rear corner of my hatch.

Any guidance would be appreciated. I've used WinISDpro for all the calculations so far. I also have access to bass box pro, but I have a hard time using that software.


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## chad (Jun 30, 2005)

There is an excellent tutorial on JL's website on vented boxes, including slots.


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## Oliver (Jun 25, 2007)

http://www.mecp.com/downloads/Subwoofer Box Building 101.pdf

Tube vs Slot Port and Box Building - 8th Generation Honda Civic Forum


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## billbillw (Aug 25, 2009)

chad said:


> There is an excellent tutorial on JL's website on vented boxes, including slots.


Thanks. There is some good stuff there. I'm actually following in your footsteps with the Dayton HO 10.


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## MyEmpireOfDirt (Aug 27, 2009)

Sorry for the high-jack, but my question is in the same vein.

I am curious about building a slot ported box as well, will I have problems with my sub if I tune the sub box higher than the mfgr suggests for more SPL? For example the mfgr suggests 28Hz and I want to tune the box to 33-35Hz.....what do you think? Either way I would be leaving the volume of airspace available to the woofer the same as suggested by the mfgr.


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## billbillw (Aug 25, 2009)

MyEmpireOfDirt said:


> Sorry for the high-jack, but my question is in the same vein.
> 
> I am curious about building a slot ported box as well, will I have problems with my sub if I tune the sub box higher than the mfgr suggests for more SPL? For example the mfgr suggests 28Hz and I want to tune the box to 33-35Hz.....what do you think? Either way I would be leaving the volume of airspace available to the woofer the same as suggested by the mfgr.


Your best bet is to download WinISDpro, enter the sub's parameters, then model the box and tuning frequency to see how it looks. Most of the time, when you tune the box higher, you give up low end and the freq response gets peaky.


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## MyEmpireOfDirt (Aug 27, 2009)

Thanks bill.


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## TJ Mobile Audio (May 6, 2009)

billbillw said:


> Hi,
> I've built several ported boxes in the past, but always used round PVC pipe for the ports. For my current build, I would like to use a slotted port since the port length needs to be so long (~30Hz on a .7 ft^3 box, can you guess what sub?).
> 
> I've searched around, but haven't found much guidance. I've seen some mention of the ports actually tuning to a lower frequency than their length would dictate (port correction?), but I don't know how to compensate for that. Also, does it matter if the slot opening faces the same direction as the sub driver? My design was for a shallow (6" inside depth) box with the sub on the large side and the port coming out of one of the shallow edges. So it would be a 6"x 1.25" slot running down and around the inside. In the car, the slot would be facing up and the sub would be sideways near the rear corner of my hatch.
> ...


What subwoofer will you be using? That seems like a tiny port. Also, what's the internal volume of your enclosure?

You can fire the port a different direction from the sub. Generally speaking, as long as the port opening is within 4 to 5 feet of the subwoofer with no major barriers in between (generally not an issue in car audio) you'll be fine.



MyEmpireOfDirt said:


> Sorry for the high-jack, but my question is in the same vein.
> 
> I am curious about building a slot ported box as well, will I have problems with my sub if I tune the sub box higher than the mfgr suggests for more SPL? For example the mfgr suggests 28Hz and I want to tune the box to 33-35Hz.....what do you think? Either way I would be leaving the volume of airspace available to the woofer the same as suggested by the mfgr.


If you do tune higher, be sure to get an amp with a sub-sonic filter and set it high enough that your sub doesn't unload (that's when it starts moving in an uncontrolled way). Either that or get a sub with ridiculous power handling and a very high X-max and have some fun with excursion! Tuning higher can drastically reduce power handling if you don't compensate with a SSF. (Someone will now correct me and say it's an infra-sonic filter, I'm just using the vernacular.)


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## billbillw (Aug 25, 2009)

TJ Mobile Audio said:


> What subwoofer will you be using? That seems like a tiny port. Also, what's the internal volume of your enclosure?
> 
> You can fire the port a different direction from the sub. Generally speaking, as long as the port opening is within 4 to 5 feet of the subwoofer with no major barriers in between (generally not an issue in car audio) you'll be fine.


It will be the Dayton Reference HO 10". That port size is 7.5 sq inches, which is slightly larger than 3" ID pipe. That is about the largest that will fit in the box. We are talking about a .7 cu ft box tuned to ~31hz. Even at that 'small' size, it needs 28" of length.


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## Patrick Bateman (Sep 11, 2006)

Every box that I've ever built with a port didn't agree with the simulations. The length of the port always had to be adjusted. Especially if the port is close to a sidewall, and you can't get much closer to the sidewall than with a slot port, where one side of the port IS the wall.

$99 on a woofer tester from parts express is money well spent. And if you don't need it for long, they fetch $75 or so on Ebay. (I sold my WT2 on Ebay for that much.)


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## billbillw (Aug 25, 2009)

I'm starting to think I might just use pipe again. That way, I can make adjustments. I would just have to make a bend with an elbow which is something I haven't had to do before.


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## TJ Mobile Audio (May 6, 2009)

billbillw said:


> It will be the Dayton Reference HO 10". That port size is 7.5 sq inches, which is slightly larger than 3" ID pipe. That is about the largest that will fit in the box. We are talking about a .7 cu ft box tuned to ~31hz. Even at that 'small' size, it needs 28" of length.


Perhaps you could try a 1.0 to 1.2 CF box, tuned more like 33 to 35 Hz. That will shorten port length considerably, and it sounds like the final enclosure volume will be about the same. Or simply go sealed and run a bit more power to compensate. 

Just my $0.02.


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## billbillw (Aug 25, 2009)

TJ Mobile Audio said:


> Perhaps you could try a 1.0 to 1.2 CF box, tuned more like 33 to 35 Hz. That will shorten port length considerably, and it sounds like the final enclosure volume will be about the same. Or simply go sealed and run a bit more power to compensate.
> 
> Just my $0.02.


Take a look at the modeling and you will see why. It gets very sloppy and peaky with that kind of enclosure. In a sealed box, it is just too soft down low for my taste. WinISD actually recommends a box of .587 cu ft with a port tuned to ~32Hz for quasi Butterworth alignment. I bumped it up to around .7 to shorten the port and get it looking a little flatter.

Green is the .7 box tuned to 32hz, red is 1.1 tuned to 34hz, blue is sealed box at .707 Qtc


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## Oliver (Jun 25, 2007)

Build the red one [line] and then EQ it down 

G'luck

PS tell us how it sounds


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## TJ Mobile Audio (May 6, 2009)

a$$hole said:


> Build the red one [line] and then EQ it down
> 
> G'luck
> 
> PS tell us how it sounds


You beat me to it!


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## billbillw (Aug 25, 2009)

Not going to be able to eq. This will be fed by my OEM HU. Going for a simple system


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## TREETOP (Feb 11, 2009)

I've used RE's slot port box calculator for quite a few builds, it has some flaws but it's very straightforward once you get used to it. It compensates for port displacement and it gives you a cut sheet.
RE Enclosure Calculator

I used it just yesterday, to build this:









For these:









8.2 cubes, tuned to 31.5 cycles.


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## Oliver (Jun 25, 2007)

TREETOP said:


> I've used RE's slot port box calculator for quite a few builds, it has some flaws but it's very straightforward once you get used to it. It compensates for port displacement and it gives you a cut sheet.
> RE Enclosure Calculator
> 
> I used it just yesterday, to build this:
> ...


VERY NICE !!

which subs are those ?


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## TREETOP (Feb 11, 2009)

a$$hole said:


> VERY NICE !!
> 
> which subs are those ?


Thanks!
They're Orion HCCA 12.2s. 2000w RMS, 4000w peak, EACH. 76 pounds each.
User replaceable recone kits are available too. Pretty gnarly subs for a reasonably mainstream brand.


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## TJ Mobile Audio (May 6, 2009)

TREETOP said:


> Thanks!
> They're Orion HCCA 12.2s. 2000w RMS, 4000w peak, EACH. 76 pounds each.
> User replaceable recone kits are available too. Pretty gnarly subs for a reasonably mainstream brand.


Around 84 dB on the efficiency as well, right? How much power are you planning to run? Regardless, that looks like it should play loud and low.


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## TREETOP (Feb 11, 2009)

TJ Mobile Audio said:


> Around 84 dB on the efficiency as well, right? How much power are you planning to run? Regardless, that looks like it should play loud and low.


The guy I built it for only has a single Orion HCCA-D5000 for bass, it's rated 2500w RMS at 1 ohm. I'm hoping to talk him into 3 more but his electrical won't support that yet. Baby steps. LOL.


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## TJ Mobile Audio (May 6, 2009)

TREETOP said:


> The guy I built it for only has a single Orion HCCA-D5000 for bass, it's rated 2500w RMS at 1 ohm. I'm hoping to talk him into 3 more but his electrical won't support that yet. Baby steps. LOL.


I understand... "Planning ahead" is what I call it. I have one customer who is now planning to add four more subs (the box is conveniently big enough ) and upgrading from 1.6 to 5 kW. This upgrade will include new battery and alt of course. These subs are a bit more efficient, though, and the box is 12.8 CF.

I agree though, the RE calculator can be quite useful, and I've used it a number of times.


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## Oliver (Jun 25, 2007)

Nice !

quote>
4" Copper Wound Voice Coil on an Aluminum Former.
High Temperature PAARC (Polyester Amide, Amide Resin Coated).
Continuous Power Handling will be 2000 Watts (under rated).
Peak Power Handling 4000 Watts.

X-Max Estimated at 30mm (total travel 4" peak to peak).
Field Replaceable Cone/ Voice Coil/ Spider Assembly.
Dual Flat Conex Spiders with Loop/Stitched Tinsel Leads.
Tall, Wide, Balanced, Foam (high density expanded polyester foam) Surround for Linear Controlled
- Long Excursion using a Tri-Radius Symmetrical Edge Design Optimized on Non-Linear FEA.
Enhanced Voice Coil Cooling System
- (forced convection - aluminum heat sinking - shorting rings to reduce inductive heating).
Factory Sealed Packaging.
quote>


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## Patrick Bateman (Sep 11, 2006)

TREETOP said:


> Thanks!
> They're Orion HCCA 12.2s. 2000w RMS, 4000w peak, EACH. 76 pounds each.
> User replaceable recone kits are available too. Pretty gnarly subs for a reasonably mainstream brand.


Reminds me of the audiopulse 12". Same price too. I wonder if Thilo is consulting for Orion now that TC Sounds is g-o-n-e?


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## Patrick Bateman (Sep 11, 2006)

You know you're serious about bass when 15% of your gross vehicular weight is your sub box :O


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## T3mpest (Dec 25, 2005)

Patrick Bateman said:


> Reminds me of the audiopulse 12". Same price too. I wonder if Thilo is consulting for Orion now that TC Sounds is g-o-n-e?


That was my first thought as well. It looks very similar and even has faraday rings.


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## billbillw (Aug 25, 2009)

TREETOP said:


> I've used RE's slot port box calculator for quite a few builds, it has some flaws but it's very straightforward once you get used to it. It compensates for port displacement and it gives you a cut sheet.
> RE Enclosure Calculator


Thanks for the link. That will certainly make things easier, especially with the cut sheet and verifying my calculations.

Poking around, I actually found an .exe program that RE has hidden on the website. It has a couple extra features that the web based version doesn't have, namely, it asks for speaker parameters (in english units) and tells you the optimum box size and port tuning for that speaker.
http://reaudio.com/speaker_box/LPort_Box_Calc.exe


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