Strange enclosure peak frequencies - DC Audio Level 5 M1 18"

[the_garynator]

One you test for your car peak freq with a 10 sealled in a 1 cube box not a 12

2 testing the box outside the car WILL not tell you where the box will peak inside the car nor will it tell you if it will be louder

Again you outside test is pointless and will tell you nothing about what it will do in your car

Sorry I didn't test with a 10 sealed in 1 cube...I didn't have one handy at the time, but my guess is the results would be similar. if there is a reason for this, please explain why.

I'm not saying that testing the box outside of the car will tell me where it peaks inside of the car. However, if I wanted to duplicate the setup I had with the 15, except scaled up to an 18, the box peak would need to be about the same. the small amount of difference between a 4ft3 box and a 6ft3 box both supposibly tuned to the same frequency wouldn't cause my peak in car frequency to shift from 36hz to 43hz or higher. and since the driver is similar (18" basket and cone but same motor and coil), that would leave the difference up to the box (unless it is due to the FS of the driver, which as stated above could be different). How do you test for box differences? test in a controlled situation where you limit the million factors and see what just the sub and box peak at, removing the car from the equation.

If measuring the peak of the box with the car out of the equation doesn't matter in the least bit, that would mean I could have a box tuned at 30hz and hit a (just throwing out numbers) 150db at 45hz, then swap it for a box tuned at 45hz and it would still hit a 150db.

If I'm completely off base, then I should probably give up on car audio because I obviously don't know anything after years of being in the hobby. If this is the case, please inform me with why box tuning has nothing to do with what it peaks in my car.

EDIT: and by no means do I want to start shit with you, I have a lot of respect for you based on your posts on this forum, it's just that your posts lack reasoning other than this is the way it is and always has been. If I'm wrong, please elaborate as to why. I've elaborated why I am thinking the way I am, and have enough experience to require that I understand something before disregarding my incorrect understanding of something. i.e. if logic dictates that 2 + 2 = 4, but 2+2 actually = 3, I'm going to need to understand why. I'm not closed minded, but I'm not going to blindly accept something as fact just because someone said so.

[the_garynator]

Also, I'm not trying to find out what it will do in my car, I'm trying to find out why it's doing what it's doing in my car.

[ALPINE408]

When I get home and off mobile I can explain things better (if I remebber when home lol) ii will say this it is perfectly normal for a box and car to have more than 1 peak

[mrd6]

Didn't realize this was done outside of the car.

If you said this already and I missed it I am sorry but: how were the external measurements done? what orientation was the box compared to the mic and ground and other objects etc?

[the_garynator]

When I get home and off mobile I can explain things better (if I remebber when home lol) ii will say this it is perfectly normal for a box and car to have more than 1 peak

I think I've figured out where the disconnect here is. I know they will have multiple peaks and it is normal. What I am looking for is reasons why my box and sub are peaking higher at a much different frequency than the box is designed to be tuned to.

I.e. my box is designed to be tuned to a 36hz, but it peaks almost 10hz higher at 44-45hz. There is a peak at 36hz, but it is quite a bit lower than what it peaks at at 44-45hz.

I don't beleive this is normal.

[the_garynator]

Didn't realize this was done outside of the car.

If you said this already and I missed it I am sorry but: how were the external measurements done? what orientation was the box compared to the mic and ground and other objects etc?

it was in different locations in my shop (1500sq ft), different objects compared to the time I metered the 15. figured any difference it would make would be minimal but who knows at this point.

Sub up, port facing meter. Meter about 7ft away from the port laying on the ground. sub sitting on the ground.

I can redo the tests since I still have my 15" in the old box. I can test them both in the same place, same objects back to back to see if the results change. if need be.

[mrd6]

Double check your numbers to make sure that the tuning is like you meant it to be.

If that is still correct, try screwing a piece of wood over the port area here so that it is sealed off. Then re-meter and see where your sealed box peak is, that may be the reason for your higher peak if it is near that mid low 40hz area

Essentially you may be getting more gain from the box resonance than you are getting form the port tuning resonance. Every ported box has both of these peaks, one for box resonance and one for ported...I am probably not using the correct terminology but you get the idea lol

[ear2ear]

.......I think I've figured out where the disconnect here is. I know they will have multiple peaks and it is normal. What I am looking for is reasons why my box and sub are peaking higher at a much different frequency than the box is designed to be tuned to.....

Then let's rule out the box first. What are the actual box & port dimensions?

[mrd6]

Didn't realize this was done outside of the car.

If you said this already and I missed it I am sorry but: how were the external measurements done? what orientation was the box compared to the mic and ground and other objects etc?

it was in different locations in my shop (1500sq ft), different objects compared to the time I metered the 15. figured any difference it would make would be minimal but who knows at this point.

Sub up, port facing meter. Meter about 7ft away from the port laying on the ground. sub sitting on the ground.

I can redo the tests since I still have my 15" in the old box. I can test them both in the same place, same objects back to back to see if the results change. if need be.

So because of this, keep in mind that you are going to be getting strange results from this measuring method with the port and sub on separate planes in your shop with nothing for the sub to load off of and redirect the front wave to the mic as would happen in the vehicle. This means you will be measuring port output / the subs rear wave but not really combining it well with the front wave. In the car ideally these waves will constructively interfere at the port or ear, this would change your results dramatically but it also means the results from this measuring method are not particularly helpful :/ I think that is what Alpine was saying earlier as well

[the_garynator]

Double check your numbers to make sure that the tuning is like you meant it to be.

If that is still correct, try screwing a piece of wood over the port area here so that it is sealed off. Then re-meter and see where your sealed box peak is, that may be the reason for your higher peak if it is near that mid low 40hz area

Essentially you may be getting more gain from the box resonance than you are getting form the port tuning resonance. Every ported box has both of these peaks, one for box resonance and one for ported...I am probably not using the correct terminology but you get the idea lol

I was kind of curious as to box resonant frequency vs port resonant frequency...If we rule out other possibilities this may be something to look at.

.......I think I've figured out where the disconnect here is. I know they will have multiple peaks and it is normal. What I am looking for is reasons why my box and sub are peaking higher at a much different frequency than the box is designed to be tuned to.....

Then let's rule out the box first. What are the actual box & port dimensions?

my thoughts exactly.

Box Dimensions

External:

Width: 32" x Height: 18.5" x Depth: 23"

Internal:

Width: 30.5" x Height: 16.25" x Depth: 21.5"

Volume = 6.16ft3 - 0.26f3 = 5.9ft3

Port Dimensions (external port, does not figure into overall box volume):

External:

Width: 21.5" x Height: 6.5"

Internal:

Width: 20" x Height: 5"

Port Length: 18" including 3/4 for box opening

Port Area: 100in2

Didn't realize this was done outside of the car.

If you said this already and I missed it I am sorry but: how were the external measurements done? what orientation was the box compared to the mic and ground and other objects etc?

it was in different locations in my shop (1500sq ft), different objects compared to the time I metered the 15. figured any difference it would make would be minimal but who knows at this point.

Sub up, port facing meter. Meter about 7ft away from the port laying on the ground. sub sitting on the ground.

I can redo the tests since I still have my 15" in the old box. I can test them both in the same place, same objects back to back to see if the results change. if need be.

So because of this, keep in mind that you are going to be getting strange results from this measuring method with the port and sub on separate planes in your shop with nothing for the sub to load off of and redirect the front wave to the mic as would happen in the vehicle. This means you will be measuring port output / the subs rear wave but not really combining it well with the front wave. In the car ideally these waves will constructively interfere at the port or ear, this would change your results dramatically but it also means the results from this measuring method are not particularly helpful :/ I think that is what Alpine was saying earlier as well

I agree, I thought of that as well, but I wouldn't think it would make that big of a difference. I'm going to head out to my shop in a bit and retest under the same conditions and see what results I have.

Just a note, I have changed my box since the initial testing, so maybe it fixed it, but that's a long shot...we'll see what happens.