sonotube sub problems

[darren700]

ok, this weekend i started building my sonotube sub. the plans i came up with were 8 cu ft @ 17hz, using a 20" dia sonotube and 6" precision port. the driver i used is the stereo integrity magnum 15" magnum
so i cut and screwed everything together for a test run (no gluing involved) i still have yet to put the sound deadner in. so i lugged it down to my room and plugged it into the buttkicker amp (1000rms @ 4ohm) soundded great, except at 25hz (i tried a 25 hz tone to very this) it bottoms out like nuts, even though lower and higher frequencies are fine. i am lost as to what would be causing this and need some help.

[---k---]

Can you post some graphs of your model.

[darren700]

i havent had a chance to make any yet as it is just the testing phase, some on avs suggested that maybe the subs impediance was dropping at 25hz and causing the amp to clip. im thinking it could be that, or the fact that the amp is sharing a 15a circuit with a computer, 50" dlp, and receiver driving speakers. i will put it on a seperate 15a circuit asap

[ThomasW]

Not knowing the port length makes it problematic to comment in the design. But....

All designs sealed, ported, whatever must be airtight to function properly.

With that driver, a 17Hz Fb should work fine if the tube is properly designed and sealed up.

It would also be handy to know what the SPL was when this bottoming occurred.

[darren700]

i used a 6" precision port from thrilleraudio.com, with one 12" tube added, so the length is 24" before the flares, and after you add the lengh of the flares it around 29" which is 17hz. i didnt measure spl when it was bottoming out, but on some songs (that dont have 25hz notes) i was getting into the 117db range from my seating posistion, with no bottoming out. i will run some tests when i get home, but it was bottoming out at a fairly moderate volume, my guess is 90db

[ThomasW]

117db at the listening position, but bottoming at 90dB with 25Hz? That's illogical unless every thing else being played was much higher than 25Hz.

Also 117db at the listening position is almost beyond belief, unless the listening position has your ear placed 2" from the cone.

How far is the listening postion from the sub, and what are you using to make these measurement?

[darren700]

im positive it was 117db, and that was using the rat shack spl meter. listening position is 10 ft away from sub
i know it seems illogical, but im not having problems with lower frequencies than 25 hz... i will run more tests when i get home, but i am considering cutting another peice of sonotube for a 5.0 cu ft encloser and testing that

edit, just ran through sonosub.exe and 5.0cu ft @ 25.5hz would be do-able, ill give it a try tonight

[ThomasW]

Here's your box this is an anechoic nearfield sim with 950 watts input......

[WillyD]

You shouldn't be anywhere near bottoming this driver out above 16Hz even with 960W so something is definitely wrong, and it isn't the size or Fb you have chosen.

[darren700]

well looking at driver excusion in winisd, it looks like it actually does reach full excursion at 25hz, so maybe thats it... well c how the smaller 5 cu ft sounds

[WillyD]

well looking at driver excusion in winisd, it looks like it actually does reach full excursion at 25hz

Not for me it doesn't, it gets to ~22mm at the max (above tuning) with 960W.

[darren700]

here is what the person who designed this sub has to say:

Two things mainly: The box is way too big and the tuning is too low. In that size enclosure the sub is pretty much infinite baffle with an attempt at tuning involved. Wtih 1000 watts in 8 cubes, it will bottom out prematurely...as compared to the other frequencies that you listed. You might want to go back and look at what I suggested in your earlier threads such as this one:

http://www.soundsolutionsaudio.com/forum/index.php?showtopic=7635&hl=

[ThomasW]

Yep you ran out of headroom because the amp can deliver more than the 950 Pmax of the driver. And Pmax numbers are usually rated on the low side to protect the drivers.

So raise the tuning point a bunch or better yet buy more drivers...

[darren700]

Yep you ran out of headroom because the amp can deliver more than the 950 Pmax of the driver. And Pmax numbers are usually rated on the low side to protect the drivers.

So raise the tuning point a bunch or better yet buy more drivers...

should i just raise the tuning, and leave it at 8cu ft, or make the enclosure 5 cu ft with a tuning of 25.5 hz?

[ThomasW]

should i just raise the tuning, and leave it at 8cu ft, or make the enclosure 5 cu ft with a tuning of 25.5 hz?

It won't matter at all. Because if you expect 117dB at the listening position with a single driver, the driver and amp will be destroyed in less than a week.

This isn't the world of car audio with massive levels of cabin gain. If you want 117 dB at the listening position, you need 4 of more of those drivers.

[darren700]

ok, thanks for the insight, i guess i was expecting too much (this sub did close to 150db in my car)

[ThomasW]

(this sub did close to 150db in my car)

Correct and that's nearfield with cabin gain.

Everytime you double the distance away from the speaker you lose 6dB of output.

3' to 6'=-6dB, moving from 6' to 12'= another -6dB loss.

Now figure how loud your speaker was playing nearfield if you were measuring 117dB at 10'...

[Ilkka]

Correct and that's nearfield with cabin gain.

Everytime you double the distance away from the speaker you lose 6dB of output.

3' to 6'=-6dB, moving from 6' to 12'= another -6dB loss.

Now figure how loud your speaker was playing nearfield if you were measuring 117dB at 10'...

That would be the case in an anechoic or in 2pi environment. In-room it's much less than that due reflections.