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Discussion Starter #1
Monday there will be a brand new Ftw21 sitting on my door step and this seems like a good time to ask a few thing's.

First is at what point have you just ported a subwoofer just too low? I don't want to run a high pass filter if it can be avoided and I understand that there is a trade off of output for going low but is there anything else that you lose in the deal?

I looked at 30cf sonotube ported to 12HZ will that allow me to avoid the hpf or at that tune am I still going to be stuck with one. The amp I have is a cv-5000 which if I recall will do around 1800 watts into 4 ohms and not too sure but maybe fairly flat to 10hz maybe lower.

My wife told me I can place 2 of these subs into our front room and I have tried to tell her how large they will be but she said she does not care about that as she will be using them as well and they will be behind the couch until the basement room that is built some day.

Anything else I need to know before I start this quest or will this work fairly well and with gain from a second driver down the road make up from the loss of 12HZ.

Thanks.
 

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I think you should be fine. 12hz port and electronic roll off will net you a some what safe driver. Not 100% but it is very possible depending how hard your going to max out the FTW. Why do you noy want to use a Hpass?

I will be doing a sealed build with my subwoofers and while a Hpass is not needed I like having an external EQ to dial in rthe sub in my room.
 

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Discussion Starter #3
I want to avoid the hpf because of what it does to the signal phase plus the extra delay.

I am using a Onkyo prsc5508 so I should not need a extra eq.
 

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Discussion Starter #4
As of now I don't have anything to use for hpf I could buy or build something but I would like to try it first without.

The issue comes when I find that one movie that drops to 3hz and eats my driver. I normally watch at -10 from reference but boost the bass. With this setup going from sealed to ported I may not feel the need to run boost.
 

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The issue comes when I find that one movie that drops to 3hz and eats my driver. I normally watch at -10 from reference but boost the bass. With this setup going from sealed to ported I may not feel the need to run boost.
In this day and age? You will find that movie, and chances are it will eat your driver sooner than later. Running a sub without a HPF is a recipe for a short life - especially in a bass reflex alignment - so you might want to reconsider that strategy. Have you ever encountered a manufactured subwoofer that wasn't designed to protect itself? I don't recall seeing one myself, but perhaps there are some out there.
 

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Adding an HPF at 10~12 HZ depending on what is required would indeed increase group delay. But correct me if I'm wrong you can hear the difference between higher and lower group delay but since the filter will be below 20hz this is the feel the bass zone and you don't hear it anyway. Even if it increased group delay 1 octave higher it would still be 20-24 hz and this is still a sort of unheard bass zone.

Personally i don't hear much at all below 22~25 hz I tested it with test tone. Maybe my subwoofer don't play loud enough or I have bad hear. I do feel the bass in this zone though.

This is one of the reason to tune LLT low. You don't hear the added group delay from the port so I guess it's the same for the HPF.
 

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The chances of infrasonic content below 12-16 Hz is extremely low I would think. There is a short list of movies with 10 Hz content, but a huge list of movies with good bass! Your reasoning is sound, though, for example there are thousands of subs tuned in the 30s for music-only environments that last a long time because they don't see anything below tuning although they usually also have an HPF.

I have to agree, no HPF on a ported sub seems like a bad idea especially for HT. If you want low without the delay of the HPF, go sealed and add EQ. I also went that route and couldn't be happier. The only catch is the extra amp power for the sealed config, plus additional amp power for the EQ. The other bonus is a smaller box size.
 

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Discussion Starter #9
Well HPF it is then. On a other note however how low to port this baby as my wife said do what I want.

With the amount of content below 20hz where is a good compromise between spl and that low port number?

My current setup is a pair of Craig sub 18.1ss that wile I like have never really gave me what I wanted out of them.

With a 12HZ tune and 1200 watts the Ftw will output more below 40HZ then the pair of Craig subs and if I do add a second one it should be able to kill the old setup. On the other hand if I raise the port tune I will get more output from one this is hard.

Does anyone think the content I will be cutting out by going higher will be missed?
 

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Your best bet is to run it through winisd and see what you like. There will be trade offs in size, tune, ect
 

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Discussion Starter #11
I have and can't decide. I don't really care about size I am more likely going to be at 30cf tube that if my wife complains can be used to hide inside from her. The output is what I am thinking about and I do know there is content below even 15HZ it's just how much can I get too with a reasonable amount of drivers and avoid my wife filing paperwork to leave at the same time.

I know 2 will be fine and the cost is not too great overall at 3M distance it will give me 115db output at 12HZ and above and that is without any room gain. My current setup at 12HZ is around 90db so if get a pair of the Ftw I should be very happy.
 

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LLT Explained

The main advantage to tune lower than 20hz it to have the group delay of the port as low as possible and usually in the zone where you don't hear the sound but rather feel it only. Tuning to 12hz will indeed allow you to have the great output of ported subwoofer, you will also be able to go almost as low as best sealed subwoofer and you will have the same sound quality (often qualified by thight sounding bass). Tuning to 20hz would yield a little more output but you would also start hearing the added group delay of the port. Essentially the main advantage of LLT is not to hit 12hz because anyway there is rarely any content down there and anyway most of the bass that is felt is 40-60hz range. The advantage of tuning to 12hz is the added SQ while still gaining the extra output of the port. The disadvantage here would be the size. LLT are huge like horn subwoofer.

I would tune to 12hz like you planned and add an HPF just to be safe and don't have to bother with bottoming the subwoofer unless you have a really large room, then you might have to sacrifice some SQ and tune higher to get the extra output.
 

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Discussion Starter #13
That was kind of my thoughts as well. I so want to get this started but I still need to get some 30" diameter sonotube and we'll the wood but the sub is oh so close.

This is my first build ever at least as far as speaker type of project. I know it needs to be air tight. The port is going to be somewhere between 8 to 10 inches which should keep the port speed down. For the port it's self I am going to use sonotube as well.

Anything else I need to think about?
 

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Anything else I need to think about?
Im not going against anybody's advice, cause I don't really have extensive knowledge here, so I'm kinda asking in a way. It seems to me that an fs of 21hz, would not lend itself to a 12hz tune. I know there's way more to it than fs, but I'm wondering what T/S parameters lend to an LLT. This is from their site.
http://www.istonline.ca/mach5_ftw_21.html
Parameters are at the bottom of the page.
 

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Discussion Starter #15
I have seen this driver used in this way so it will work but I understand where your coming from with that. It models ok down to that point but if I understand correctly the lower you drop below fs the more over all spl you lose.

From a 16HZ tune to a 12HZ you lose like 6 db so the cost is great but I have around 6 dB of room gain starting around 25HZ so it would work out nicely.

And we'll if it does not I can cut it down and go sealed.
 

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Discussion Starter #18
It will be some time until I get a box built but here is the sub.

ForumRunner_20141215_200212.png

That is a 2 L bottle to give you a idea on scale.
 

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Good things come to those with patience. :D I have been very slowly gathering parts for my builds and that has been about 1 year now. Still not ready to start building yet. So keep us updated when your ready.

Come to think of it there is another very slow build thread using a FTW and about 25cuft ported. Will have to find that thread. He is from Perth Australia I believe. There were some nice renders of the design also.
 

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Discussion Starter #20
I seen that thread a wile ago it did look nice. The sonotube is the thing I am having issue finding. Once I find that I can finish this in a few days.
 
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