A little Soundsplinter and Fi sub comparison

[Geezerpoop 10+ year member]

I declare everyone's point irrelevent!

 

[Kfra315 10+ year member]

Either way you go you have a nice set of subs.

//content.invisioncic.com/y282845/emoticons/word.gif.64b12e39f936af3b4fff38a1c0bd0244.gif

 

[Immacomputer 10+ year member]

Good god. The transfer function that is specific to each car will not change no matter what alignment, sub or box you use. Its a scalar that is applied to whatever sub you decide to put in your car.
The anechoic response of any alignment is a good place to start looking for your perfect setup. Once you have them, you can apply said transfer function to your anechoic response and get a somewhat realistic frequency plot for your in car subwoofer.

NOT ONCE did I ever say these graphs were representative of how a sub would perform in car. EVER! These graphs are just a starting point from where a person can apply conditions specific to their application. Again, it is just a starting point comparing different subs.

Edit: This how I have been instructed to go about designing an alignment buy some people much smarter than myself. I am not providing a thread with the end results of any of these alignments in car.

The transfer function is only a scaler when all other things remain constant. You're going to be off when the enclosures take up different amounts of space in the vehicle. The transfer function of the vehicle is also dependent one the mass of air in the environment and not just the interior dimensions of the vehicle. Also, where you place the port, sub, and enclosure will all have a large effect on the actual FR. Another big factor in the transfer function is the natural resonance of the chassis and body of the car. This will also change when the different subs and enclosures are weighing down the car differently.

Theoretical graphs are useful but are to be taken with a grain of salt. They're also small signal parameters that will shift greatly when high power is applied. Just because there is a power input section does not mean it's adjusting for those parameter shifts due to losses in the EMF, suspension, or the coil heating up.

One of the most useful of the graphs is group delay and I didn't see you taking that into consideration at all.

I do believe in modeling subs before randomly designing an enclosure for them but you really need to be careful. At low volumes my IDQ in my room sounds exactly how it models up. When I crank the volume though, the low end begins to fade and the upper frequencies get boosted. My av12 in my car is the exact opposite. At high volumes, higher bass frequencies get a cut while the low end gets exaggerated. This is something that modeling programs cannot tell you.

 

[JonJT 10+ year member]

here is a tip.
people in the high ups of competition use math and what not to make ideas on how to begin a box design. once they make it and test it, and sadly hit lower numbers than they had before, they start to modify or rebuild.

i dont know about you, but i know people who have built 20+ enclosures until they were happy. car audio is not all about doing all the math possible until it works, its also about trial and error, because all this crap is speaker\enclosure\car specific, and i dont think you will find many people using all 3 that are the same.

so just go build something that sounds promising, and then, build another one, and then try another one. its not like you will be able to tell with the first box if it boasts the best sound and performance unless you have a basis to compare it to.

so unless you build mutiple enclosures - you dont know what is the best with that speaker anyway.

thats just my 2 cents. i say build it, and it will come.

The discrepancy between application and theory in engineering is something I've very aware of. I know empirical data is far more valuable, but as I have been trying to tell the first few responders; you must start somewhere.

You and I are saying the exact same thing, I know. Its just a matter of semantics.

I'm an engineering student and have quite a bit of experience applying theory (as far as engineering students go) and how the initial design usually isn't want you end up actually applying.

 

[SkatinBassPLaya]

wow an intellectually inclined discussion on caraudio.com.lol

 

[JonJT 10+ year member]

The transfer function is only a scaler when all other things remain constant. You're going to be off when the enclosures take up different amounts of space in the vehicle. The transfer function of the vehicle is also dependent one the mass of air in the environment and not just the interior dimensions of the vehicle. Also, where you place the port, sub, and enclosure will all have a large effect on the actual FR. Another big factor in the transfer function is the natural resonance of the chassis and body of the car. This will also change when the different subs and enclosures are weighing down the car differently.
Theoretical graphs are useful but are to be taken with a grain of salt. They're also small signal parameters that will shift greatly when high power is applied. Just because there is a power input section does not mean it's adjusting for those parameter shifts due to losses in the EMF, suspension, or the coil heating up.

One of the most useful of the graphs is group delay and I didn't see you taking that into consideration at all.

I do believe in modeling subs before randomly designing an enclosure for them but you really need to be careful. At low volumes my IDQ in my room sounds exactly how it models up. When I crank the volume though, the low end begins to fade and the upper frequencies get boosted. My av12 in my car is the exact opposite. At high volumes, higher bass frequencies get a cut while the low end gets exaggerated. This is something that modeling programs cannot tell you.

To my knowledge, Unibox does not plot group delay for ported or sealed enclosures. I am not yet sure what kind of alignment I will even be using. And quite honestly I don't even know if group delay is something I'm going to even worry about. I assuming but I do think that the final group delay of the system (especially at low frequency) is going to be influenced far more by the cabin of my car than the theoretical group delay of the alignment and woofer I use. Furthermore, there is no guarantee that a sub with lower or lesser theoretical group delay will have lower or lesser final group delay once the system is installed in my car. And unlike cabin gain, group delay is not something I can measure with the equipment I have at this time. Since I can't measure it, I just assume it to be a constant because I cannot gauge or control it in any practical way.

The variations in parameters you speak of are complicated phenomenon and are very difficult or even impossible for even engineers with proper equipment to quantify (in an environment as complicated and changing as a car). Such a level of detail in my experiments will never occur, nor do I feel will ever be necessary. I am going to assume things like air mass (which depends on temperature, humidity and other factors), resonance frequency of the car, coil temperature, etc to be constant for the sake of simplicity. And also because even after I have finished my sub (and this goes for ANYONE who ever puts a sub in a car) these parameters will still be changing and I have NO control over it. Therefore, I will assume the transfer function to be a scalar and I am going to do my absolute best to make sure my tests are as true to the proper scientific method as possible.

Again, not once did I ever proclaim these graphs to be actual in car performance, like I said before they are simply starting points. I'm VERY well aware of the differences between theory and application and I'm equally well aware of the extra complications that come about in applications (things that you have mentioned). But I also know when and where to draw the line between parameters that will greatly effect performance and ones that I can ignore. Most of the parameters you have brought to my attention can be ignored simply because the difference they would make in final subwoofer performance is negligible to my ears OR because I cannot keep them constant in actual application. When you are driving your car and using your system, coil temp, car resonance, air mass, etc will all change as a function of simple and normally arbitrary things like window position, engine speed, gas tank level, average car temperature, ambient temperature pressure and humidity, road elevation or slope, passenger compliment, trunk utilization, etc. Hopefully you see the absurdity of even trying to consider such parameters when your experiment's purpose is to create a system for everyday use. You cannot take said parameters into account without creating completely unreasonable initial conditions and making for an experiment that cannot be carried out.

Also, at the very end of the day the system by which the success of our hobby is measured is completely subjective, differs from person to person and is impossible to quantify with numbers, arguments or theory. And it probably is not sensitive enough to discern the effect on your subwoofer when one of these parameters changes, nor is it consistent enough to do it on a regular basis. Hell, your first priority when in the car is concentrating on the road, not listening to music! And you know humans can't commit full attention to more than one task at a time!

Let me state this once more because I feel as though everyone is taking this the wrong way.

This thread was created ONLY as a medium to share my research into my car audio system. Many people don't seem to understand that this is JUST research and is NOT a proclamation of the performance of the (my) final product. I'm probably more aware of the fact that theory just about NEVER equals application in the real world than most people on this forum. The graphs and other information I presented in this thread are to be taken at face value and NOTHING ELSE. If you use them, use them simply as a guide or a starting point. That is it and nothing else!

Edit: If your going to bring car transfer functions into consideration when designing a car system, the ONLY thing you can do is assume it is scalar. Doing otherwise is impossible due to the complexity's of the variables that effect it. You need not worry about variables that you cant gauge, cant keep constant or will be continuously changing when under actual application. The best you can do is approximate average values for these values under operating conditions and go from there. The very, static, nature of a sub install also dictates that the transfer function be a scalar as well. There is little ability for you to compensate for a change in the transfer function after the sub is installed. Worrying about it as you seem to have done is not a reasonable thing to do under normal circumstances.

 

[newusername 10+ year member]

Just out of curiosity...

Are you including port resonance and inductance in the frequency response? IIRC, these options are not "turned on" by default in UniBox and must be chosen manually.

Also, group delay can easily be derived via FFT, though I imagine as an engineer you are already aware of that.

And I, too, agree that it's not totally useless. Post-transfer function frequency response is more and more understood (and actually very well simulated by some higher end programs) and simply saying "well, that doesn't matter" doesn't help anyone learn where the discrepancies lie and how to predict them in advance.

I think most people could care less and would find little advantage in doing so (honestly, most subs work reasonably well in the same enclosures, for a given speaker size), but let's not discredit efforts to gain a better understanding here.

 

[JonJT 10+ year member]

Just out of curiosity...
Are you including port resonance and inductance in the frequency response? IIRC, these options are not "turned on" by default in UniBox and must be chosen manually.

Also, group delay can easily be derived via FFT, though I imagine as an engineer you are already aware of that.

And I, too, agree that it's not totally useless. Post-transfer function frequency response is more and more understood (and actually very well simulated by some higher end programs) and simply saying "well, that doesn't matter" doesn't help anyone learn where the discrepancies lie and how to predict them in advance.

I think most people could care less and would find little advantage in doing so (honestly, most subs work reasonably well in the same enclosures, for a given speaker size), but let's not discredit efforts to gain a better understanding here.

Yes, I enabled those options in unibox.

Please do not take my words in condescension. Eventhough I am an engineering STUDENT (far different from a practicing engineer) I surely do not know all there is to know about any enclave within the broad spectrum of engineering. I don't know a thing about FFT, nor do I know how to derive group delay from it. Declaring the fact that I am an engineering student was only used to prove the fact that I know there is a distinct difference between theory and application, and that is it. I didn't even state what specific discipline within engineering I am studying, so why would you make the assumption that I am familiar with control theory? Hell, I know there are a good number of engineers out there that know nothing about control theory and never will, as its not necessary for them to do their job. Everything I know about audio, and the physics of sound I have taught myself. Up until this point in my education, I have only taken 1 class specific to my major, Mechanical engineering. Classes dealing with systems and control theory will come later. //content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif I'm still young and have a lot to learn before I can even practice what I know.

Now, not once did I ever attempt to nullify anyones attempt to gain a better understand at all. I would love to gain a full understanding all the physical principals at work within a car. But what I need for you to understand is that there is a distinct line between what practically applicable and whats not for me and me only. I am not making a thread about the merits of researching obscure phenomenon for the sake of better understanding. If I was, I'd be agreeing with every point that Immacomputer brought up. Because this thread was created for the purpose of a single custom application tailored to my own world, I think I have a good understanding of what variables and theories to take into account and what to ignore. I do not have the hardware or software needed to simulate effects like in car group delay. Nor do I have the patience or impetus to take the time to educate myself at such a level. Although, if you know if a good way to actually simulate said parameters within my car (02 Nissan Maxima SE 6 speed) without expensive programs or hardware, please let me know. I'd love to mess around with said methods.

Car audio is just one of many hobbies I have and one that I do not want to devote too much time to. I enjoy doing other things more than car audio. I also know my ears very well and I'm fairly confident that the effects of such obscure phenomenon will go unnoticed by me. As you even said, most subwoofers perform very well in a box that is close in size to the recommended.

Remember, I am all in favor in investigating lesser known parameters that effect the performance of an audio system for the sake of increasing knowledge and wisdom. But when I want to apply theory in order to produce a working product specifically for myself, I am not going to apply all of the knowledge gained for reasons I already outlined. The effort needed and net result gained from taking into account the great number of parameters we are speaking of is not necessary because I'm not looking for such resolution, accuracy or precision withing my system. Even without such level of detail, one can still create a great sounding system.