Lets talk about

[///M5 2,833]

Why would I bother?

Here is something for you to think about, how does your calculation work if all of sudden TL is placed in the rear of your SUV.

[helotaxi 46]

how are you doing it ?

He's not. He, like a lot of us, doesn't care about SPL . He does understand acoustics though and knows that what you're doing, while better than totally uneducated trial and error, is still far from the total picture. Taking measurements with a tape measure doesn't give you the peak frequency of the vehicle. It might give you an idea where you can create a standing wave, but it won't account for the rest of the interactions that occur and that can have an even larger influence on the total SPL potnetial of the system.

[DevilDriver 28]

What's really bizarre....to me...is that when someone is trying to turn a corner, we don't help them do that....

Calculating the 1/4 wave frequency with a distance equal to the distance between your enclosure and the mic only tells you that...the 1/4 wave frequency. It doesn't tell you where your vehicle peaks, though. The best way to approximate this concept is to measure your subwoofer in the enclosure you will be using in an anechoic chamber (although groundplane measurements are more appropriate for a subwoofer), then subtract this from the measured response with the enclosure in your vehicle. This will give you some insight to your transfer function and where peaks and dips are created by your vehicle. Of course, these peaks and dips are changed if you use a different enclosure, a different firing orientation, or different obstacles in different positions within the vehicle.

Flat axial response (ie. flat measurement on an RTA) is a good start if you wish to accurately reproduce an input signal. The question is: how do you get flat axial response? Is summing a pair of drivers to achieve flat axial response but with high(er) distortion really a solution? The reality is that there is no one aspect that you can check off and say "Ok, that's perfect". It's a sum of the parts kinda thing...and something that an extremely small number of people understand well enough to correlate what their ears hear and what is actually occurring.

Can a ported enclosure be flat in a vehicle? Pretty debatable and, dare I say, unlikely. Ryan cited an EBS alignment as a relatively flat ported alignment and it undoubtedly is....but not in a vehicle. The transfer function of your vehicle throws that for a real loop. Thus, I believe a sealed enclosure is often the best solution if flat response is your goal. That doesn't mean that any of the ported enclosures will be less preferable listening to music....just that they are less likely to measure flat in what I would consider to be usable bandwidth.

[Tirefryr 1,742]

What's really bizarre....to me...is that when someone is trying to turn a corner, we don't help them do that....

Calculating the 1/4 wave frequency with a distance equal to the distance between your enclosure and the mic only tells you that...the 1/4 wave frequency. It doesn't tell you where your vehicle peaks, though. The best way to approximate this concept is to measure your subwoofer in the enclosure you will be using in an anechoic chamber (although groundplane measurements are more appropriate for a subwoofer), then subtract this from the measured response with the enclosure in your vehicle. This will give you some insight to your transfer function and where peaks and dips are created by your vehicle. Of course, these peaks and dips are changed if you use a different enclosure, a different firing orientation, or different obstacles in different positions within the vehicle.

Flat axial response (ie. flat measurement on an RTA) is a good start if you wish to accurately reproduce an input signal. The question is: how do you get flat axial response? Is summing a pair of drivers to achieve flat axial response but with high(er) distortion really a solution? The reality is that there is no one aspect that you can check off and say "Ok, that's perfect". It's a sum of the parts kinda thing...and something that an extremely small number of people understand well enough to correlate what their ears hear and what is actually occurring.

Can a ported enclosure be flat in a vehicle? Pretty debatable and, dare I say, unlikely. Ryan cited an EBS alignment as a relatively flat ported alignment and it undoubtedly is....but not in a vehicle. The transfer function of your vehicle throws that for a real loop. Thus, I believe a sealed enclosure is often the best solution if flat response is your goal. That doesn't mean that any of the ported enclosures will be less preferable listening to music....just that they are less likely to measure flat in what I would consider to be usable bandwidth.

That's what I was going to say.

[///M5 2,833]

What's really bizarre....to me...is that when someone is trying to turn a corner, we don't help them do that....

Getting there. You tell someone an answer and they read, you make them think about it and they remember it.

[Lord Baccus 1]

the reasoning behind the 1/4 & 1/2 wave mesurement, is to avoid cancellation /

i have figured out how to get the most out of 1 sub by avoiding overlapping waves that kill an spl score...

DD : Awsome answer...

we use a 12" sub in a sealed box / do a sweep track to find the freq as well. but it comes out extreamlly colse to the math im using...

Edited April 4, 2008 by Lord Baccus

[helotaxi 46]

we use a 12" sub in a sealed box / do a sweep track to find the freq as well. but it comes out extreamlly colse to the math im using...

Unless the sub is in the same position with the same volume displaced by the enclosure and with a PORT in the same place as your comp enclosure, you're still missing a lot. You've got the right ideas, they're just imcomplete in their application.

[mrray13 30]

we use a 12" sub in a sealed box / do a sweep track to find the freq as well. but it comes out extreamlly colse to the math im using...

Unless the sub is in the same position with the same volume displaced by the enclosure and with a PORT in the same place as your comp enclosure, you're still missing a lot. You've got the right ideas, they're just imcomplete in their application.

this is similiar to the way i now do that, only i simply plug the port. this way i'm using the exact subs, enclosure, power and placement to help determine peak frequency. if tuning is wrong, anotehr box is built. of course, typically a sealed box like LB uses is the first step to find an initial peak.

maybe not perfect, but it does get one in the ball park and it's easy to build/tune one way or another. it's also a good way to test placement as you can slide enclosure around to find the highest peak reading/frequency.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee