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

[the_garynator]

So I recently reconed one of my Level 5s to an 18" and built a new box. The box is 3/4" baltic birch, 6 cubes after displacement, with a 18.25" external slot port (should be tuned at 36hz). Up firing, rear port. I metered it outside of the car the other day to see what the peak frequency was and it peaked at around 36hz, dropped off a bit, then peaked higher starting at about 42hz and kept climbing to around 44-45hz, then dropped off again.

I'm trying to figure out why it has multiple peaks. I did this same test with my other level 5 15 in a 3.8 cube box after displacement with 3 4" external precision ports. Calculations had tuning frequency at 38hz, but it peaked at 36hz.

Pictures of the box:

I've since made some slight changes to the box, but didn't have a chance to retest to see if they made a difference. added a roundover panel on the interior of the box, Shortened the port to 16.5" including the roundover section:

The only thing I can think of is maybe my subsonic filter is cranked, but it should be off (I'll verify after I'm done with work), but assuming it is off, I have an AP30001D, gain set with DD1, Sony head unit, LPF set at 50hz. Same settings as when I tested my 15 box.

Any ideas?

[mrd6]

This is not an abnormal result, there are lots of variables that could cause this from vehicle resonance/peak to the enclosure having different sealed resonance than it is tuned.

What is your goal from creating this thread?

[the_garynator]

these peaks were measured with the box outside of the car, box on the ground, termlab sensor about 5-10ft from the port exit...should only be measuring box frequency.

[ALPINE408]

Test out side the car??? Who cares what it did that's a pointless test

[scoobywrx05]

There's probably bout 30 sum different variables that will cause it to do that. More importantly what does it do when it's in the vehicle.

[the_garynator]

Test out side the car??? Who cares what it did that's a pointless test

because I lost .5 to 1db after reconing my 15" lvl 5 2 dead coils in a box with lower than optimal port area, as well as losing even more compared to my other level 5 15" with only 1/3rd of my dd-1 set gain at 36hz.

There's probably bout 30 sum different variables that will cause it to do that. More importantly what does it do when it's in the vehicle.

It seems to meter about the same type of peaks.

I tested for resonant frequency in car with a sealed 12 a while back and it has a peak at 36hz, drops off, then another peak at 43hz (it peaks even higher when I get up into the high 50hz frequencies but i'm not concerned about those frequencies).

I metered at 36hz with the 18 in the car and it hit around a 149, then did a 150.0 at 43hz, didn't test any other frequencies in the car yet.

[the_garynator]

I wasn't expecting any huge gains going to an 18, but considering my other 15" lvl 5 hit a 150.4 on half dead batteries with gain set to 1/3rd of what my max gain on the dd1 was at (tinsel leads were short so full tilt would snap them), I would expect at least to hit that if not a bit higher, even though the new box isn't as efficient (old box had about 100hrs into it rounding inside 90's, etc.). After testing with it outside of the car, it seems to me that if it's peaking differently, that would imply that it's not getting the full output where it should be tuned at because of some reason or another.

my other thought is that if it's not broken in fully yet, but i've been playing it a lot since I reconed it, probably like 4-5hrs so far (conservative estimate)

[Sergeant_Skyrim]

I tested for resonant frequency in car with a sealed 12 a while back and it has a peak at 36hz, drops off, then another peak at 43hz (it peaks even higher when I get up into the high 50hz frequencies but i'm not concerned about those frequencies).

I don't know much about acoustics and may be dead wrong about this, but if you peaked at 36hz and 43hz with a sealed 12 to find car's resonant frequency then maybe that's what it is. Just that your car peaks at ~36 and ~43 and kinda overpowers other factors. Just throwing my guess out there, again I don't know much about acoustics

[the_garynator]

I tested for resonant frequency in car with a sealed 12 a while back and it has a peak at 36hz, drops off, then another peak at 43hz (it peaks even higher when I get up into the high 50hz frequencies but i'm not concerned about those frequencies).

I don't know much about acoustics and may be dead wrong about this, but if you peaked at 36hz and 43hz with a sealed 12 to find car's resonant frequency then maybe that's what it is. Just that your car peaks at ~36 and ~43 and kinda overpowers other factors. Just throwing my guess out there, again I don't know much about acoustics

I know what you're saying but when I meter this box outside of the car (box physically out of the car, meter physically out of the car), it is metering with 2 peaks.

When I metered my old box and sub outside of the car it peaked at 36hz and nothing else. it also peaked in car at 36hz. it had another peak at around 43hz as well, but lower than the 36, and was likely just cabin gain (as the car has a peak at 43hz).

The only thing idea I've gotten from anyone so far was from a friend who said it's probably due to the added stiff spider I have as well as not being fully broken in yet. Generally a stiffer suspension raises the FS of the sub, but I guess I didn't realize that it could have this much effect.

[ALPINE408]

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