Crazy Overexcursion on high notes....

[antonmiller 8]

Hi all,

I have 2 boxes that ive built and i am in the process of testing. ->build log here<-

they both have the same interior volume and tuning and all that good stuff. so the internal volume is about 2.45 cuft with a tuning of ~34 hz with about 40 sq inches of port each. now i had a box that was 2.5 cu ft tuned to 34 hz with 39 sq inches of port and didnt get much overexcursion.

so heres my problem. on low notes like 28-34 hz the sub barely moves and creates ALOT of sound, im very shocked by this. but when you get to like 36-40 hz the sub reaches its limits of excursion and anything above 40 its just bottom out city! im very scared about this because in the original box i built for the sub (when i dint know much about boxes) never did this! and bassically the only difference is that there is a little more port area and that its a kerfed port. i first thought, well maybe the suspension is just toast, but all the spiders seem to be in tacked, there is no coil rub, the sub is in very good condition, just very VERY loose when you push on it. just kind of need some ideas.

the sub is the Fi BL and the amp is the Rockford Fosgate T1500-1BD rated for 1800 wrms at 1 ohm and im giving the sub a clean signal from the amp set with an oscope plenty of times, and yes i checked the signal and it is still clean. and the amp is set with 0db tones and set right before clipping all the way up the hz range. just not sure what is causing this over excursion.... maybe i should just buy a BTL and see if it does the same thing...

Basically just looking for any insight into how or why it would be doing this. thanks for reading it as i know i went a little long on the explination. but more info is better than none.

oh and the reason why im confused is that i thought if you played frequencies below tuning hat you would get crazy excursion, my case is that if you play anything above tuning you get crazy excursion. just dont get it...

Thanks,

Anton Miller

[KU40 173]

You are overpowering the sub. Just because you set the gains with an oscope doesn't mean you aren't still sending the sub too much power. You're sending a 1000 watt RMS sub between 1500 and 1800 watts. A ported box will have the most control of the cone from probably 2hz below tuning to about 10 hz above tuning. If you download winISD and take a look at an excursion plot you'll see what I mean. Excursion dips around tuning then raises quite a bit above there.

[antonmiller 8]

well i know im overpowering it. the thing is it never had these excursion issues with the previous box. it was just fine before, but now its happening with both of the new boxes.... maybe the overpowering finally caught up with it. we will see if it happens with the BTL.

If any one else has any idea why it would do this please let me know.

[KU40 173]

My guess is that your percieved tuning frequency on either the new boxes or the old one was off from the reality, hence the different responses.

[///M5 2,833]

My guess is that your percieved tuning frequency on either the new boxes or the old one was off from the reality, hence the different responses.

YES

Definitely a box concern and related to the power you are throwing at it. Exactly why it isn't trivial to just "build a box" and use it. The design must take into account, the drivers parameters, the enclosure parameters, and also the vehicle or space it is going into.

[antonmiller 8]

when i get home ill post dwgs of all three boxes. but im pretty sure they are correct. but we will see.

[antonmiller 8]

ok for some odd reason my pdf hosting site isnt working. ill try again tomorrow.

[masterofallbass 0]

Yeah I can back up what anton is saying cuz Iv seen this system and it loves to bottom out above 37hz

I know the subwoofer suspension is very loose.

[tejcurrent 13]

Most likely a box issue, but there are so many variables. This may sounds oversimplified but I would try turning down the gain.