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I am working on modeling some subs with the intent of building a 24" Sonotube LLT with a 15" driver. I have looked at Dayton, Bravox (on buyout right now at Parts-Express.com), Soundsplinter, etc. I think I have settled on the Dayton Ultimax UM15-22, about 300L volume and a tune around 18hz. At full rated RMS of 800w my excursion is 1.2 x the rated xmax of 19mm at 25hz, or about 23mm. I have modeled in both WinISD and Sonosub and gotten into the area I am comfortable with, but I am always over xmax at rated power.

Ok details out of the way... Heres my question.

I drive my stuff hard and I know there will be plenty of times I will ask this thing to work hard. Am I trying to find the nirvana of subwoofer designs? I like the curve I have, I like the size I will need to build it, but the xmax issue seems to be one people are building for, and I am always over the xmax, some times by 50%. I have read that 15% over xmax is an accepted amount, and to expect distortion to increase greatly past that. So... should I just accept the limitations? Am I doing something wrong? Quit with the simulations and build the thing already? I know it will outperform (by an order of magnitude) the two automotive 10" drivers I am using now in a sealed slant (truck behind the seat thing) cabinet driven with 200w!

This is the transfer plot and xmax plots below. How does it look. I could spend a lot more time modeling this thing, as it will be a while before the build begins, but do I need to? Is this going to rattle the (neighbors) windows or just go up in smoke? :huh:
 

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For what you have modelled, at the very least you need to employ a high pass filter below port tuning. If it were me I'd reduce amp power until xmax isn't exceeded at all above 20 Hz, and use the 10-15% margin as the design limit below 20 Hz. YMMV, as specifics in a sub's suspension and backplate will determine its physical travel passed xmax. IMO, what you have is way too far passed xmax for a safe design. Designing at 120% xmax is a little asinine to me. It's nothing but a recipe for oil-canning (leading to short woofer lifespan) and/or distortion. If you need louder you need a more capable sub with more power and/or multiple subs.

The response of your model doesn't really look like an LLT, is it <20 Hz performance that you are after?

Oh, and needless to say, yes a ported 300L sonotube with a 15 will outperform two sealed 10" car subs :yes:
 

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Backing up a little bit -- are you going for SPL or the lowest octave?

I'm a big fan of LLT, but it's application and workable drivers is somewhat narrow. You need a very robust driver, tons of space, and a real desire for the lowest frequencies.

I guess what I'm trying to ask is whether you'd be better served with a good ported box.
 

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For what you have modelled, at the very least you need to employ a high pass filter below port tuning. If it were me I'd reduce amp power until xmax isn't exceeded at all above 20 Hz, and use the 10-15% margin as the design limit below 20 Hz. YMMV, as specifics in a sub's suspension and backplate will determine its physical travel passed xmax. IMO, what you have is way too far passed xmax for a safe design. Designing at 120% xmax is a little asinine to me. It's nothing but a recipe for oil-canning (leading to short woofer lifespan) and/or distortion. If you need louder you need a more capable sub with more power and/or multiple subs.

The response of your model doesn't really look like an LLT, is it <20 Hz performance that you are after?

Oh, and needless to say, yes a ported 300L sonotube with a 15 will outperform two sealed 10" car subs :yes:
The response was what I could come up with as a compromise knowing that it was not a "safe" design surpassing the xmax like that. I am not really trying to model in a fashion that already puts me past the design limits and leaves no headroom. I am curious why the 25hz range is needing so much excursion. Is that just the "tough" spot of the system to build SPL? Kinda where everything stacks against me?

I included what I had so far to get more info. And I used the rated RMS of the driver as the system input power, knowing my tendency to push equipment hard. I know I am sliding out of the range of a true LLT sub design and am ok with that. I am 60/20/20 in usage. 60% regular TV viewing, 20% Home Theater and 20% strictly music. So <20hz and that last octave is not my true goal. Smooth powerful response with the ability to extend deep when called on is.

I do listen at reference levels when permitted (i.e. no one else home, certain company) so 115db would be my goal. I know I won't get that down to 15hz with this setup.

Other than better/more subs... is there any light at the end of the tube for me?
 

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Discussion Starter #5
Backing up a little bit -- are you going for SPL or the lowest octave?

I'm a big fan of LLT, but it's application and workable drivers is somewhat narrow. You need a very robust driver, tons of space, and a real desire for the lowest frequencies.

I guess what I'm trying to ask is whether you'd be better served with a good ported box.
Well, Zeitgeist, I would love both, but in reality, I am looking for more SPL, with improved distortion characteristics over what I have now. That should not be a problem as the current stuff is marginal. The problem is getting the most out of what I can afford. I have the DSP1124p in place and it really helped tame the pair of 10"s and the room. I want more. EP2500/4000 will probably be in there. Upgradeitis if you will. I love DIY projects and the simplicity, look and performance of the sonotube build, so it seems like a great way to go. I guess my desire for the lowest Hz isn't really there. <20Hz would be great, but even if it rolled off past -10db at 14-15Hz. Still don't get the 25Hz spike in excursion. :scratch: Any input? That seems to be my problem area when I apply anywhere near max power. The excursion below 20Hz isn't a problem as I will highpass that out for the most part.

In truth a good ported box is what I need, just would like to do it in the sonotube config.
 

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Try not to think of the spike around 25Hz as a spike for a moment. Open What ever modeling program you use and model the same set up as before. Then model a sealed cabinet of the same size. Look at the cone excursion. They are nearly the same until the you get near the port tuning. Here the air inside the port starts to act as a spring reducing the excursion of the speaker at the same time as producing output itself. Once you get below the tuning frequency the cone excursion quickly returns to where it would be in a free air environment because the port can no longer control it.
Now move the tuning frequency up. You will notice that the port starts to control the speaker at a higher frequency where not as much excursion is needed for the same volume. This may be the way you want to go considering you are not trying for sub 20Hz output. Your trade offs can be better understood by reading Steve Callas' LLT explained article on this site. By raising the port tuning frequency you bring the effect of the port, which some people do not like the sound of, higher into the more audible frequency range. Remember even though it is stated that humans can hear down to 20Hz our response is not a light switch. Our ability to hear sounds is well diminished even higher than 20Hz and becomes more and more of a feel as the frequency drops.
Zach
 

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Also you may want to change drivers if your looking for an LLT design. I've read that the new ultimax drivers were geared more towards using them in a sealed enclosure. Not to say they don't work well I. Ported designs but I think the suspension is just set up in a way that LLT's probably won't model well. On PE website they give you a ported sub enclosure size with port tuning to 20hz.

Note I have no personal experience with this drive. It is all from what I've read.
 
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