sub bottoming out
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=31364
Printed Date: July 02, 2025 at 5:39 AM
Topic: sub bottoming out
Posted By: dudek38
Subject: sub bottoming out
Date Posted: April 30, 2004 at 10:24 PM
what causes a sub to bottom out? to describe, its at high volume and the sub either distorts or breaks up at certain levels. i've had this happen on a few systems and am wondering if its not enough airspace or just if its the sub itself.
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owner of
Motion Marine & Car Audio
the florida keys
Replies:
Posted By: stevdart
Date Posted: April 30, 2004 at 10:40 PM
In a ported box, the wrong port size or box volume too large. Another reason is amp clipping. Were these in systems you built?
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: forbidden
Date Posted: April 30, 2004 at 11:07 PM
The gain on an amp set too high (90% of the time). Too much power causing the coil to leave the magnetic gap. Straight DC mind you that will fry the voice coils. Wrong size box and or port as the good advice above mentioned.
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Top Secret, I can tell you but then my wife will kill me.
Posted By: dudek38
Date Posted: April 30, 2004 at 11:26 PM
its a single infinity perfect 12" in a sealed .88cu box with polyfill down fire. the air space is close to specs. im thinking the gain might be to high. its only on high volume and deep bass notes.
-------------
owner of
Motion Marine & Car Audio
the florida keys
Posted By: forbidden
Date Posted: April 30, 2004 at 11:29 PM
Gain is too high or bass boost is too high. Turn both or either down and see what happens.
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Top Secret, I can tell you but then my wife will kill me.
Posted By: DYohn
Date Posted: May 01, 2004 at 10:04 AM
Plus that sub is not designed for down firing installation. That could be part of the problem... although I agree with Rob's diagnosis as the most likely. ------------- Support the12volt.com
Posted By: Beerman354
Date Posted: May 01, 2004 at 1:00 PM
What are some good firing down subs.Will the polk mm104 work in this application?
Posted By: dudek38
Date Posted: May 01, 2004 at 1:19 PM
dyohn, how did you come across the info on the perfect not being designed for down fire? why would that affect the sub? im interested
-------------
owner of
Motion Marine & Car Audio
the florida keys
Posted By: DYohn
Date Posted: May 01, 2004 at 3:44 PM
Here's a post from before with down firing info. https://www.the12volt.com/installbay/forum_posts.asp?tid=30658&KW=down+firing. It actually depends on which Perfect you have. The SVC 12.1 calcuilates to about 3.5% sag, so it could theoretically be used down-firing, although it has more sag than I'd like to use. I say max is actually around 3%. The more sag a woofer has, the less power it can handle if mounted down (or up) firing, since gravity reduces Xmax. ------------- Support the12volt.com
Posted By: f150on22s
Date Posted: May 01, 2004 at 6:14 PM
For down firing subs...I would go with Audiobahn. I see them down fired all the time at shows and in magazines.
Posted By: southside
Date Posted: May 01, 2004 at 6:29 PM
what is downfiring? when the subs are tword the sky, or the ground or what. i'm confused?
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southsider
Posted By: f150on22s
Date Posted: May 01, 2004 at 6:34 PM
Down firing is when the magnet is outside of the box, and the face of the speaker is in the box. So its really just when you can only see the magnet.
Posted By: southside
Date Posted: May 01, 2004 at 6:39 PM
thanks
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southsider
Posted By: DYohn
Date Posted: May 01, 2004 at 6:44 PM
Downfiring is anytime the speaker cone is aiming down, whether the magnet is inside or outside the enclosure. Upfiring is anytime the speaker points up. Proper orientation for most drivers is with the speaker cone perpendicular to the ground. JBL woofers are some of the best suited for down-firing. Any speaker with a large Xmax. ------------- Support the12volt.com
Posted By: southside
Date Posted: May 01, 2004 at 6:47 PM
thank u
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southsider
Posted By: f150on22s
Date Posted: May 01, 2004 at 7:13 PM
Yeah....dyohn is smart. Dyohn...Did you go to school for this stuff?
Posted By: DYohn
Date Posted: May 01, 2004 at 10:28 PM
f150on22s wrote:
Dyohn...Did you go to school for this stuff?
Well, not to school for car audio per se, but I am an acoustical engineer and sound system designer and I've been working in professional sound, radio, television and film since 1973. So you see, I'm just an old dude who's learned a lot from being around for ever. :) ------------- Support the12volt.com
Posted By: southside
Date Posted: May 01, 2004 at 10:30 PM
dyohn is the shiznit.  ------------- southsider
Posted By: dudek38
Date Posted: May 02, 2004 at 6:48 PM
dyohn, my infinity perfect dvc 12.1d has (fs)23.32 and (xmax) 14.15mm. i did your calculation for sag and got some crazy number. i multiplied both and divided it by 24,849. im trying to find the sag percentage. thanks for the advice. i had no clue about sag and im sure thats why im experiencing problems, because the excursion distance is too great, right? theoretically, would a stiffer surround help the situation?
-------------
owner of
Motion Marine & Car Audio
the florida keys
Posted By: dudek38
Date Posted: May 02, 2004 at 6:51 PM
actually the sub must be designed for mass excursion. the surround doesnt matter? i think i understand the theory.
-------------
owner of
Motion Marine & Car Audio
the florida keys
Posted By: DYohn
Date Posted: May 02, 2004 at 6:58 PM
The theory is that more exrursion capability = better downfiring performance, since the effect of gravity on the cone will not use up too much of the Xmax (excursion) capability. Longer throw woofers with extended 'bump plates" work best in downfiring installations. Woofer with the specs you list = sag percentage of about 5.32%. WAY too much for downfiring, it could easily be "bottomed out" and the voice coil will eventually fry. ------------- Support the12volt.com
Posted By: dudek38
Date Posted: May 02, 2004 at 7:19 PM
can u tell me the formula for sag using my numbers. i looked up the other post but cant get it.
-------------
owner of
Motion Marine & Car Audio
the florida keys
Posted By: stevdart
Date Posted: May 02, 2004 at 7:49 PM
"The following is the same formula, including the relationship of acceleration and Pi in this case: Percentage of Sag = 981,000 / (Xmax * (2 * Pi * Fs)˛) where - 981,000 is acceleration due to gravity (mm/S˛) * 100 (for the percentage).
- Xmax is the maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field (mm). - Fs is the free-air resonant frequency of the woofer (Hz)
- Pi is the ratio of a circle's circumference and diameter, usually rounded to 3.14. As a general rule of thumb, any time the sag exceeds 5% of the driver's Xmax, it's not recommended for a down-firing subwoofer application." I wanted to see if I understood this too. Above is from the post DYohn made about downfiring. Now when I use your numbers, 14.15 mm XMAX and 23.32 Fs, I come up with 3.23% sag. But I'm no mathmatician. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: Beerman354
Date Posted: May 02, 2004 at 8:31 PM
What if the sub has 25 xmax and 0 fs? Does it have 0 % sag?
Posted By: stevdart
Date Posted: May 02, 2004 at 8:34 PM
Try some real numbers. 0 Hz Fs, sheeeesh.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: Beerman354
Date Posted: May 02, 2004 at 8:37 PM
Posted By: stevdart
Date Posted: May 02, 2004 at 8:51 PM
Dude, I thought you were pulling some legs here. But it is a typo anyway. It should be 32 Hz.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: Beerman354
Date Posted: May 02, 2004 at 8:56 PM
If my calc's are correct thats .97% of sag. So this sub should work great downfiring correct?
Posted By: dudek38
Date Posted: May 02, 2004 at 8:58 PM
i got 3.23 too.
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owner of
Motion Marine & Car Audio
the florida keys
Posted By: stevdart
Date Posted: May 02, 2004 at 8:59 PM
Yeah, can't go wrong with an inch of XMAX.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: Beerman354
Date Posted: May 02, 2004 at 9:01 PM
Posted By: stevdart
Date Posted: May 02, 2004 at 9:08 PM
Dudek, so it's back to the beginning eh? But I wouldn't have a clue if there was a typo in that formula or something. But it sounds about right. I get 3.02 % with my CV sub at 17 mm and 22 Fs. And I know CV makes all their home subs down-firing.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: DYohn
Date Posted: May 02, 2004 at 10:46 PM
Oops, my mistake. The Infinity should be 3.32% like I posted in the early part of this thread. Sorry. ------------- Support the12volt.com
Posted By: dudek38
Date Posted: May 03, 2004 at 7:45 AM
ok, i've looked around at jbl,jl,pioneer and infinity (xmax) specs. it seems that infinity's perfect line are the highest. i still think my sub is operating outside of it's magnetic zone at high volume. am i just putting too much power to it? also, i've lined the box with polyfill. should i stuff the rest of the box to get the full potential of "polyfill"?
-------------
owner of
Motion Marine & Car Audio
the florida keys
Posted By: DYohn
Date Posted: May 03, 2004 at 8:34 AM
Back to the original suggestions. Gain is too high, bass boost is too high, or amplifier is too large. Infinity Perfect 12.1 handles 350 watts RMS. ------------- Support the12volt.com
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