Will this sub survive this environment? (simple question / 4th Order)

[Mike Gann]

That's actually something I've been wanting to ask about 4th orders. Shouldn't the sub be protected from over excursion since one chamber is sealed, or protected as much as a sealed enclosure could offer? I've been theorizing that the woofer might receive abuse from having resistance on both sides of the cone, which is where my original post question came from. Having the sealed pull on it while the ported side pushes against it seems like twice the forces acting on the weak construction of a woofer.

[Mike Gann]

Distortion kills. Maybe he will get something better after it dies. He will still need to watch out for distortion.

Of course, I will be sure there that there is no distortion if I build one for him.

[Triticum Agricolam]

The sealed chamber can offer some excursion protection for subs in 4th order bandpass boxes. However, in this case since the Xmax of that sub is so low and the rear chamber is so large its NOT going to offer ANY protection from over excursion.

[Mike Gann]

Yeah I noticed the size of the sealed side is much larger then a recommended sealed. I guess the best choice would be to build a size that would offer the protection, at the expense of output

[Mike Gann]

To test this idea, I turned the sealed side down to a more reasonable 1.5cu ft and raised the ported side's tune up to near the same as the other side and we get a pretty similar graph with woofer protection [Teal line]. The first setup was what the program "suggested" that's where the large first chamber came from.

I guess the first enclosure didnt make sense in a lot of ways, the sealed size for one but also the low end tuning was way below 30hz which isn't really needed. I didn't think we'd get into the enclosure so I just posted the suggested size. This one seems a lot more reasonable. Is there any trick to flatten out the middle dips?

[Mike Gann]

I just looked up the amp, the bass boost is built to boost at 45hz which seems to be where the middle dip is at. Would setting the boost to maybe 6db flatten out the middle dip or is it just going to raise the peaks as well?

[ShadeTreeMechanic]

Distortion will happen and the only one that can stop it is the one with the volume control. Different sources and different songs from the same source can be recorded at all different levels. I don't care what you set it up with, o-scope, dd1 or any other method. If the head unit will go to its highest number you can get distortion.

We have beat this horse to death.

Simple answer to simple question: NO.

[Triticum Agricolam]

I just looked up the amp, the bass boost is built to boost at 45hz which seems to be where the middle dip is at. Would setting the boost to maybe 6db flatten out the middle dip or is it just going to raise the peaks as well?

It would depend on how broadly the bass boost changes things (this is referred to as the Q of the boost). Most likely the boost is going to be broad enough to just make the peaks raise as well. Even if it was a fairly narrow boost, bass boost is just a form of EQ and as such it cannot get you any additional output. All it can do is make certainly frequencies sound louder relative to everything else and it does this by turning everything else down.

Now with that being said, I modeled the box in WinISD and I didn't get the big peaks in output its showing in BassBoxPro. Who knows which software is more accurate.

[Mike Gann]

Distortion will happen and the only one that can stop it is the one with the volume control. Different sources and different songs from the same source can be recorded at all different levels. I don't care what you set it up with, o-scope, dd1 or any other method. If the head unit will go to its highest number you can get distortion.

We have beat this horse to death.

Simple answer to simple question: NO.

Very true. He has a kenwood headunit so the signal is probably fairly clean, I've never rode with him in the car so I dunno how crazy he gets with the volume but I do know that if you turn the volume past 65% or so the highs from the door speakers are piercingly loud. I don't think he goes up that high with that.

I just looked up the amp, the bass boost is built to boost at 45hz which seems to be where the middle dip is at. Would setting the boost to maybe 6db flatten out the middle dip or is it just going to raise the peaks as well?

It would depend on how broadly the bass boost changes things (this is referred to as the Q of the boost). Most likely the boost is going to be broad enough to just make the peaks raise as well. Even if it was a fairly narrow boost, bass boost is just a form of EQ and as such it cannot get you any additional output. All it can do is make certainly frequencies sound louder relative to everything else and it does this by turning everything else down.

Now with that being said, I modeled the box in WinISD and I didn't get the big peaks in output its showing in BassBoxPro. Who knows which software is more accurate.

It's funny you mention that, I'm having the same experience with it. This is my first time using the program, and I'm doing some dummy models with different woofers I have laying around in the garage and I'm getting some weird numbers from them too. First time using WinISD as well, I've never modeled a box this way I've only done it on paper and used the online calculators from carstereo.com.

So using these parameters -

fs: 24.2

Qts: .4

Vas: 2.45 cuft

Qtc: .707

This is a JL Audio 10W0-4 if you want to use a driver database

The calculator here calculator http://www.carstereo.com/help/Articles.cfm?id=26 says recommended box is 1.153 cu ft of volume.

WinISD says 1.228 cu ft, probably adding in the driver displacement.

But BassBoxPro says (using classic stuffing method or empty) is around .85 cu ft and I think that's with the driver displacement.

I did some research and every forum I come across everyone swears that you should trust BassBox over all others. It just seems weird that it's the only one with the off numbers. I dunno if everyones wrong or maybe I'm doing something wrong over here.

[Triticum Agricolam]

So the formulas for sealed box design are pretty simple. I calculated the sealed box size by hand for the JL sub you listed and came up with 1.153 cu ft as well.

While WinISD does not compensate for driver displacement, it does have correction for box leaks and absorption losses (box stuffing). The default values may be why it gives a slightly higher size.

The .85 cu ft size BBP recommends is definitely suspect though. There has to be some reason its so far off.