# Port question on a TMWW setup



## bumpnzx3 (Apr 6, 2007)

The "WW" part of my setup is two RS180's in a combined chamber. I am looking to tune around 33hz with a volume of about 1.75cu. I can do that with a 5.1" long port and a diameter of 2.5" or a 7.8" long port that has a diameter of 3" (or so says a calculator I found).

Naturally it will be a flaired port- but I didn't know if one size would be better than another. Ported is not my usual route. All of my subs in car audio have always been sealed.


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## tyroneshoes (Mar 21, 2006)

bumpnzx3 said:


> The "WW" part of my setup is two RS180's in a combined chamber. I am looking to tune around 33hz with a volume of about 1.75cu. I can do that with a 5.1" long port and a diameter of 2.5" or a 7.8" long port that has a diameter of 3" (or so says a calculator I found).
> 
> Naturally it will be a flaired port- but I didn't know if one size would be better than another. Ported is not my usual route. All of my subs in car audio have always been sealed.


a single 2" precision port will do.


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## bumpnzx3 (Apr 6, 2007)

ok- but what length. 

i know what i am after is a certain port area- does it matter how i get there?


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## MiniVanMan (Jun 28, 2005)

1.75 cubes tuned to 33 hz probably isn't the best idea unless you're not planning on giving them much power. 

At rated power, I come up with 21 liters (.75 cubes), tuned to 42 hz. That would require a 3" flared end port of exactly 12". That would yield a F3 of 46 hz, and a power handling of 120 watts. You can actually tune to 40 hz with that volume, but I figured a 12" long port is very easy to accomplish. 

You can go bigger and tune lower, but your power handling will go down significantly. You just run out of Xmax pretty quickly with this driver. This design will allow those drivers to really sing.


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## bumpnzx3 (Apr 6, 2007)

really? that small and tune that high for a pair sharing airspace in a floor standing tower? most everyone in the PE showcase, as well as people on the HT forums I have been reading on, all tune to between 30-38 and about double the airspace you mentioned. unless of course they are doing an MTM or center channel setup- in which case they are more or less on with what you suggested.

each complete tower will see around 100 watts. not sure how much of that will actually make it to the woofer though.


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## MiniVanMan (Jun 28, 2005)

Just because it's a floor stander, doesn't mean you shouldn't still try for optimal enclosure size and tuning. Like I said, you can go lower and bigger, but with the Xmax limitations of the driver, power handling lowers.

MTM, bookshelf, floor stander, etc, etc, etc, are styles. Just because you see a tall tower doesn't mean the entire volume is used for the drivers. 

Also, understand that while you may not be using all of your 100 watts, all of the time, when you crank these things up, you want them to be able to handle what your amp gives them, ESPECIALLY on the low end. I don't know what amplifier you're using, and what kind of ripple you'll see, or clipping, etc. 

When people run extended bass shelfs (like you're proposing), it's usually with low power, and good amps. Not every amp is capable of producing 30 hz with minimal ripple, especially low to mid level HT receivers. So take that into consideration. Oh, and you'd better have a very good subsonic filter. 

Also, tuning below the Fs of the driver for the sake of extra bass extension is counterproductive to me when talking about a hi fidelity design. If you want to tune that low, pick different drivers. The lowest you should tune the 8 ohm version is 38 hz, and 40 hz for the 4 ohm. It causes more problems for an amplifiers already struggling on the low end, unless of course you design your crossover with the extra components needed to tame the resonance peaks. At that point though, with the costs rising, just pick different drivers, and trust me the Dayton RS180 will rape you when it comes to the cost of crossover components. 

25 liters tuned to 38 hz is about as much as I'd do with those drivers.

I'm doing my entire HT with the Dayton RS series stuff as well.


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## bumpnzx3 (Apr 6, 2007)

i know that a large tower isn't all airspace for the driver. i'm not at all saying you are wrong- i just wonder why others tune so much lower with the same speaker. what you are saying makes complete sense- why would you want to run an undersized 7" driver that low?

from Roman:
Actually, for a pair of drivers all you really need to do is build an enclosure that is twice as large as the one for a single driver and use 2 ports instead of 1. I’ve used single RS180 drivers in cabinets in the 22L to 28L range. The larger the cabinet, the deeper the bass will be to some degree but if the cabinet is too large then the bass begins to roll off gradually higher in frequency. I think that the optimal size for a single RS180 is about 24L with a port tuning of about 38Hz (I think that one of PE’s 2.5” diameter flared port tubes cut to about 7-8” should provide the right tuning). So for a dual setup then about 48L with dual 2.5” x 8” flared ports should work. This is just my suggestion but you can do this trick with any single driver design that you find. Actually the RS180 MTM design is a dual woofer format but I think that they only use about 14L per driver which I think is too small for a vented box. Let me know if you have any questions.

he seems to agree with your tuning freq- but roughly double the airspace.


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## MiniVanMan (Jun 28, 2005)

Actually modeling up 22 liters at 38 hz isn't too bad (for a single driver). It puts your power handling at about 35 watts per driver, as opposed to 60. In your scenario that may not be too bad. Not much room for error though, and like I said, you'd better have a very stable amp down low.

You gain quite a bit of low end extension, but you will need the extra crossover components to tame the resonance peak as your F3 will be around 34 hz.

One of the things I've always liked about the RS series drivers from Dayton are the ability to operate in very small enclosures. The subwoofers are no different. That's the one great advantage to them. The disadvantage is the cost of crossover components. Take a look at this thread and the final crossover schematic. It's a bookshelf using the RS180. http://www.diymobileaudio.com/forum/showthread.php?t=17429 Go ahead and calculate the costs of the crossover components. You'll be surprised. Don't go cheap on inductors either. Look at decent quality air core inductors (lower the DCR the better).


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## bumpnzx3 (Apr 6, 2007)

a reply in a thread i am taking part in, in a HT forum- reguarding volume/port/etc...

The dual RS180's in 48L tuned to 38Hz doesn't look too bad. I would prefer a tuning between 30-35Hz. This will give you a more gradual rolloff down low and probably give you smoother in room response. The higher tuning could potentially give you a boomier sounding bass, but if the speakers aren't pushed up against the wall you will probably be ok. Although, with no BSC they'll probably sound better up against the wall.


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## MiniVanMan (Jun 28, 2005)

I don't know where they're getting a smoother roll off with larger volume with this speaker. 48 liters tuned to 38 hz has a 4 db peak at the tuning frequency, and a 3 db peak if tuned to 35 hz. Power handling jumps down to between 25-30 watts per driver. 

It's not a question of whether it will work or not, it's a question of having enough Xmax. Unless I'm mistaken and the Xmax of the driver is greater than the spec of 6 mm. Power handling goes down because you don't want the driver bottoming out. The more volume you have the higher the Xmax requirement. 

I really need to know how you plan to implement these towers. Somebody keyed in on an important note, BSC. Where are you going to be placing these towers? Also, what kind of room is it?

What these people are saying is that in an MTM with half the volume the bass sounds really boomy, where others are saying that they sound amazing with that volume and tuning????? 

I'm not saying don't do it. I just don't quite understand completely what they're saying. Rather, I know what they're saying, I just don't know how they're coming up with it. Yeah, in a simple modeling program, 48 liters at 35 hz looks fine. A small 3 db hump at the tuning frequency, and a more gradual rolloff (not much more), but at what expense. That's what these people aren't taking into consideration.


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