I am aiming for a Qtc between 0.707 and 0.8 and an F3 around 40 Hz. For the Rl-p 15" I got the following results, using a web based box calculating program:

1.

Qtc = 0.7071

Vb = 3.5

F3 = 43.48

2.

Qtc = 0.8008

Vb = 2,38

F3 = 44.14

I was just wandering if you seasoned guys know of a way to reduce the F3 a bit further without changing the Qtc too much?

For a SQ application, do you reckon that Qtc 0.8 will sound better than the standard flat Qtc 0.707?

Or maybe, the F3s above will be low enough in a VW Passat Variant?

How low do you want it to go, at the lowest in a car, sealed F3 wise?

They are pretty related, although you could go a little bigger on the box. Sealed enclosures roll off at -12dB and not -24dB per octave so a F3 in the 40's isn't all that bad. Add a little cabin gain and you are fine.

I agree with Sean ^^. I personally prefer a slightly larger sealed box that will lower the Qtc. a tad. But the driver can react differently than your ears like. Some drivers can be lifeless at a with a Qtc. of .707, and some can get a little sloppy lower then that. I know some people prefer to build as close to .707 then add polyfill or decrease interior air volume from there.

On a side note, you can always make a bigger box smaller but you can't make a box that is too small bigger. I'd oversize it some and if you need just put some volume compensating 2x4's or something on the inside to experiment.

What about lower still F3s, in the 35Hz neighborhood, isn't there a risk for boominess at those levels? And how high can one go? Would you say you are safe with F3s between 35-45Hz? As you can see, I am quite number fixated at the moment.

And yes, it's a good suggestion to start out with a larger box to go smaller if needed, I will have that in mind when the time comes.

I think at this point you are getting too worried about something you might not hear much of any difference. I would suggest building an enclosure like Sean said and let your ears tell you what sounds best in your install.

Indeed. Worrying about the numbers of the enclosure without understanding what the environment of the vehicle will do to it is a bit pointless. Build big and be ready to make it smaller

Yes you both, you hit it right, I am worrying far too much, my dilemma, always. I am just trying to figure out how to approach "car audio nirvana" as close as possible, without the slightest hope of even coming close, but still, trying. Considering subs, I just wanted to try to figure out what range of F3 values that would give a reasonable bass response in my car. My largest worry concerning subs, is where can I start to get to expect boominess, and where does bass start to disappear? There are so many drivers now to choose from, so I tried to limit the number of prospects. To take the Rl-p 15" as an example, with the box calc software I use, I cannot get it to go lower than 43.5 Hz sealed, will that suffice? But I will stop worrying now, I guess it is time for descision instead.

I wouldn't expect the Rlp to model very well, but it is an outstanding driver. Buy one, build a slightly too large box and make it smaller until it does what you want it to

I wouldn't expect the Rlp to model very well, but it is an outstanding driver. Buy one, build a slightly too large box and make it smaller until it does what you want it to

Why is it that you don't think it would model well? I know it says something similar about the RL-s 15" drivers on their home page, but for this I wouldn't know?

And yes, I might just heed your advice. It is surely very high on my "want one" list.

I forgot to ask, what size would you recommend then, to start with?

Edited October 20, 200816 yr by buggsson

The SoundSplinter drivers, from what I have tried, do not model well in software. Heck, the SSA drivers model much smaller then they really should be. But once again, it is a thing of software results compared to real world testing in a vehicle.

I think everything models exactly how it should, you just have to be able to look a little deeper into the results...

Don't pay so much attention to F3 in modeling programs if you shoot for a Qtc less than .7, this is because the F3 actually goes up, even though you have increased low end extension, it just has a shallower roll-off. The lowest F3 a modeling program will give is always near .7 for a total system Q.

Be cautious in going a ton lower than .7 with sealed alignments. They get flatter and flatter in response, but to most of us, they start sounding a little lifeless... I have built tons of low Q subs for the home environment, Qs as low as .5.... I liked the results sometimes, many that heard them didn't so much....

One thing I never pay attention to is the recomended box alignements alot of programs give, alot of time they really aren't waht you are looking for and you can do much better by tweaking the volume (and tuning if vented) to get what you think is the target you are looking for, alot of times this is drastically different than what is suggested by the program. Just keep your eye on parameters such as group delay, xmax and vent velocities...

It's funny, I hear all the time how subwoofers like the BTL doesn't model at all, I have plugged in the T/S parameters several times (the ones on Bladeice) and with Bassbox Pro, I end up with pretty much exactly what is reccomended by FI.... You just have to interpret the results the best you can...

If I were you, assuming what you have said so far, I would shoot for a Q at little lower than .7, and then make it smaller as suggested which has been really good advice BTW...

Also, don't forget that the total Q of the system will never been anywhere near as low as the driver Qts. So if you have say a high Q driver (like some of the LMS subs) you will never get a low Q system alignment. This isn't a bad thing, it just may mean that you need some additional Eq for the bottom end and LP filter set right to get rid of the ripple above Fc.

Edited October 20, 200816 yr by 95Honda

But once again, it is a thing of software results compared to real world testing in a vehicle.

Yes, that much I understand. I just want some help to get a bit farther in the correct direction regarding sub driver choice, and for that will try some software. Most of the drivers that I am interested in seem to be very highly regarded in various places, so I hope that I won't get that far off any correct track.

95Honda, I think that your advice will be of great help when I start using "more sophisticated" software in the near future. I learn so much by being a member on a forum as this, what if one had to invent the weel once again and again?

Not to steal the thread, but there has been some discussion here about lower qtc alignments, how about higher qtc? Take, for example, the new SI Mag (ok i give in, I'm getting one), which they recommend 1.0 cube for. This, however, gives a q of .834 and f3 at 48 hz. Going up to 1.5 cubes gives a qtc of .737, but the f3 only drops to 46 hz.

so in this situation it seems that the f3 really can't be changed that much, but the system q obviously can fairly easily. What would you guys do? yes I did read your post about building big and going smaller, Sean. I just wanted to understand it more as well.

(this can also give you some comparison, buggsson, so maybe/hopefully it wasn't a total invasion )

To be honest, most reccomended sealed boxes (and a majority of all home audio mass-market sealed subwoofers) have a Q higher than .7. Alot of car audio alignments push Q near 1. There isn't anything wrong with this, besides the fact that you can get a small box, the ripple in response above Fc with a Q of .7+ is what most people prefer to hear. It also sounds louder most of the time.

F3 doesn't change drastically with Q in sealed alignments like it does with ported. In fact, F3 isn't the primary goal when adjusting Q. The goal is a smooth response (or not smooth) and .7 is the where ripple must be less than +/- 3db and is kind of a standard. By manipulating Q you are really changing the sound by changing the overall response (high and low) not just the low-end cut-off.

The biggest factor in getting a low Fc in sealed alignment is a driver with a low Fs..... And a medium to high total Qts. If you don't have these two things to start with, you'll never get a low Fc in a sealed alignment without Eq.

Also, don't get hung up on Fc/F3 alone. Because a sealed alignment has a much shallower roll-off than a ported one, the F3 can be much higher than a ported F3 and still acheive similar low-end output.

One thing I never pay attention to is the recomended box alignements alot of programs give, alot of time they really aren't waht you are looking for and you can do much better by tweaking the volume (and tuning if vented) to get what you think is the target you are looking for, alot of times this is drastically different than what is suggested by the program. Just keep your eye on parameters such as group delay, xmax and vent velocities...

Thanks for clarifying. When I said they don't model well, I should have made it more clear. Most people hit the "recommended enclosure" button and roll with the enclosure, when you do this with the Rlp you will get funny results.

Also, don't get hung up on Fc/F3 alone. Because a sealed alignment has a much shallower roll-off than a ported one, the F3 can be much higher than a ported F3 and still acheive similar low-end output.

So could you, or someone else, please tell me how much higher are we talking about? I would like to learn how high you might be able to go with a sealed and still have sufficient lowend output. I have a WV Passat Variant, (station wagon), would an F3 of around 45Hz still do in your opinion?

45Hz probably would sound fine. A majority of car audio 10-12" drivers will have an F3 around 40Hz when put in a sealed box with a .7ish Q.

Here are some predicted responses of that sub.

The orange line is a 1ft sealed box, with a Q a little under .7

The purple line is a 2.5ft low Q sealed box

The red line is a vented 2.5ft box

You can see the vented and sealed 2.5ft boxes have equal response at 20Hz, with the sealed box having increased output below 20Hz. From about 35-50Hz the ported box has around 3-4db more output.

The 1ft sealed box has a little more output 60-80Hz region than the larger sealed box, but this is pretty trivial with a subwoofer.

This driver can have a real flat response ported in a small box, this may make the bottom end sound a little bloated to some people when you factor in cabin gain of the vehicle. This may also make it tough to blend if ported with the rest of your system. Additionally, a ported box this small and tuned this low will have vent issues with a driver with this much stroke. To keep vent velocity low you would need a big port, big enough that it may increase the physical size of your box 50%+

The choice is really up to you...

45hz should be fine, but if you are concerned just make the box larger as it is really easy to make it smaller later if you like.