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Discussion Starter · #1 ·
Hi,

I'm planning on building two LLT subs with 2 dayton titanic mk3 drivers I got for a great price.

I want to stick to Mr Steve Callas' specifications as much as possible but have run into an issue:

With a 6" port I have a peak airspeed of 28m/s and a port resonance of close to 250Hz. This air speed seems a bit high according to Collo's flare-it program. Will it be unacceptably noisy at max power?

With an 8" port I get a peak airspeed of 17m/s which should be noise free. The downside is the port resonance is close to 140Hz which is not a good thing according to the LLT spec.

Any advice on which of these 2 options I should go for would be appreciated.
 

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Hi,

I'm planning on building two LLT subs with 2 dayton titanic mk3 drivers I got for a great price.

I want to stick to Mr Steve Callas' specifications as much as possible but have run into an issue:

With a 6" port I have a peak airspeed of 28m/s and a port resonance of close to 250Hz. This air speed seems a bit high according to Collo's flare-it program. Will it be unacceptably noisy at max power?

With an 8" port I get a peak airspeed of 17m/s which should be noise free. The downside is the port resonance is close to 140Hz which is not a good thing according to the LLT spec.

Any advice on which of these 2 options I should go for would be appreciated.
28 m/s would be above any of the max air speeds I've seen suggested for any build.

140hz is well above the 80hz crossover point most folks use. I don't think you'd hear the resonance if you use the standard subwoofer crossover point. However 8" pipe can be tough to handle. You might try a square port instead.
 

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The port resonance will be there at any magnitude level whereas port chuffing and compression can only potentially happen at very high power levels, so under that logic, the higher air speed is the lesser of two evils.

That said, if you go to a hardware store that carries 6" diameter tube, you can typically find some that are larger in diameter, say 6.5" or 6.75" still labeled as 6". That would be your best bet.

What type of amplifier will you be using?
 

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Discussion Starter · #6 ·
Thank you for responding Steve!

I've already bought a Behringer EP4000. Just waiting for my 'sonotube'-equivalent to be made up before I start with the build.
 

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Ok, and how much power were you modeling with in the attached pictures? I ask because while the Titanics are nice drivers, they probably won't be able to utilize all of the power you will have on tap, so the port air speeds may be even less of an issue.
 

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Discussion Starter · #9 ·
Actually those specific air speed graphs where taken with these settings. 545Watts and a high pass filter.

 

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The port resonance will be there at any magnitude level whereas port chuffing and compression can only potentially happen at very high power levels, so under that logic, the higher air speed is the lesser of two evils.
+1.

Also one thing that is forgotten about Collo's and other port tests like the ones by Harman is that they show that a larger diameter vent can support a higher airspeed than a smaller one pior to reaching the core speed and becoming turbulence saturated.

Note #2 is that 28ms figure is for the sub being driven near max output right at the tuning. This virtually never happens at 13-17hz in real world use and if it did I'd bet on you not noticing any change in the sound with all of the other sounds going on. How often do you expect to be running a pair of large 15" ported subs ragged?
 

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If it were me I'd increase the tune slightly from 14hz to 16 or 17hz. You'd be surprised what this increase of just a few hz in tuning can do. This will give you a bit more power handling prior to bottoming out in the 20-25hz area, it'll shorten your port quite a bit, possibly allowing you to get that 8" one in there with an acceptable length and primary resonance and you can decrease the external size of the cabs some too. The Titanics are a good driver but I think tuning to 14hz is getting a little out of their best range.

315L tuned to 17hz with an 8" port looks good to me. This would have a 187hz resonance with the 8" port.
 

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Discussion Starter · #14 ·
Thank you Ricci and duly noted. I think I'm just greedy for low extension since my two current subs measure flat down to about 15hz in my room.

My reasoning for tuning that low was hoping that taking into account room and corner gain and the fact that there will be 2 subs, they might be able reach about 120dB down to 14Hz.

The only time I'll reach those levels will be when demoing at or near reference level.

I'll play with the tuning some more and see what I can come up with.
 

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At even moderately high levels in my setup, vibrations of other things in the room (walls) and higher frequency content of the soundtrack all seem to effectively mask any port chuffing noises that may exist.

My personal opinion is that many of the great subwoofer designers here at the shack tend to be overly conservative in regard to port velocity - which is not a bad thing. However, this may prevent us from implementing certain designs that, in practice, are perfectly acceptable.
 

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Ricci said:
If it were me I'd increase the tune slightly from 14hz to 16 or 17hz. You'd be surprised what this increase of just a few hz in tuning can do.
Unfortunately, one of the things it will likely require him to do is use a highpass filter. With the dual Titanics and 14hz tunes, he would be fine without one. For that reason alone, I like the 14hz tunes.

vann_d said:
My personal opinion is that many of the great subwoofer designers here at the shack tend to be overly conservative in regard to port velocity - which is not a bad thing. However, this may prevent us from implementing certain designs that, in practice, are perfectly acceptable.
Perhaps, but you must consider that if you can reach port compression before completely maxing out the driver, you aren't getting what you models predicted you will, as compression will actually limit output. So why go with a larger ported subwoofer that tends to have more design and construction work if in the end it will only give a couple db more than a sealed sub in the infrasonic range? To get your full, clean 6db advantage, you need a port that can handle all of the required air movement without too much turbulent air flow.

My opinion is that when you spend the time and money these projects require, and when you plan to use these subwoofers for many years, you may as well do it right the first time and not go half way.
 

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Perhaps, but you must consider that if you can reach port compression before completely maxing out the driver, you aren't getting what you models predicted you will, as compression will actually limit output.
The problem is not knowing at what air speed does the compression start to make a noticeable difference, measurable and noticeable are two different things.

Output can also be limited by power compression of the sub driver, another issue that is not accounted for in modeling.
 

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Unfortunately, one of the things it will likely require him to do is use a highpass filter. With the dual Titanics and 14hz tunes, he would be fine without one. For that reason alone, I like the 14hz tunes..
I disagree. I don't see the extra little bit of extension preventing the need for a highpass at all. Actually the subs are IMHO more prone to bottoming in the 20-25hz range than somewhere below 14hz, especially with the 14hz tune and larger enclosure, because that area almost always has very high level signals whereas the amount of sub 14hz signals that are that LOUD is very rare. This is the area that most sub 20hz tuned long excursion drivers run into trouble NOT below tuning IMO, FWIW, etc...
 

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Discussion Starter · #19 ·
Thank you all for the help.

I think with these drivers I'll not follow the LLT spec completely. However, this is my first build and I learnt a lot just from Steve's explanation of it. One thing I don't understand is why a highpass is not necessary when I tune to 14Hz and it is when tuned higher. Why if there is content way below that on certain scenes in movies would the driver be protected by the LLT design?

I think I like the response with 315L and 17Hz. I know these Dayton drivers aren't the best(*go the lowest) around but they don't look bad either. All I want to do now is see if I can at least match the extension of the SVS PC12-NSD and MFW-15 I currently have. Both of these extend to 15Hz flat in my room (measured) and both of them are tuned somewhere around ~17Hz I think. I don't know what the peak spl capabilities of the MFW is but I'm guessing the Dayton 15" might actually be slightly more capable. If only because I can give it more power in a larger cabinet but that's just me speculating.

17Hz tune is definitely better since I lose a lot of headroom tuning lower. Which gives me some room to implement a house curve.

Hopefully if all goes well I can start building next weekend :bigsmile:
 

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Ricci said:
Actually the subs are IMHO more prone to bottoming in the 20-25hz range than somewhere below 14hz, especially with the 14hz tune and larger enclosure, because that area almost always has very high level signals whereas the amount of sub 14hz signals that are that LOUD is very rare. This is the area that most sub 20hz tuned long excursion drivers run into trouble NOT below tuning IMO, FWIW, etc...
I'm showing reference level capability. If he corner loads both subs, then he will have headroom on top of reference level capability. There shouldn't be any trouble in the 25hz range unless he starts acting like a fool (no offense Robert :R).

Robert said:
One thing I don't understand is why a highpass is not necessary when I tune to 14Hz and it is when tuned higher. Why if there is content way below that on certain scenes in movies would the driver be protected by the LLT design?
Check the LLT Explained, it's all in there. A <15hz tune with reference level capability will keep you quite safe.

What are you going to do for a highpass now that you have opted for a 17hz tune?
 
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