can clipping ruin a subwoofer?

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Mike
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can clipping ruin a subwoofer?

Post by Mike » Thu Nov 06, 2003 7:34 pm

I am, as most of you know, working on building a subwoofer for my audio system, since I figure if I can build one for $50 it is better than buying one for $500 to $1500. But anyway, since my LM3886 is not putting out it's max power due to the transformer, it distorts pretty easily. As it only does one thing - boom, I can't really hear the clipping until it gets pretty bad. With my wattage output of somewhere between 4 and 15W, can clipping destroy my subwoofer speaker? I know it can destroy tweeters and woofers, but can it destroy a much larger subwoofer? <p>Second, I can't figure out what makes the speaker itself make a rattleing sound and a whistling sound out of the hole in the back of it. Is that just since it is a cheap speaker, or is that the amp clipping, or is the speaker not functioning properly? Or could it also be caused by midrange frequencies coming into it?<p>Oh, also, the speaker is a Lightning Audio P1.10.4 car subwoofer (10 inch, 4-ohm)<p>
Thanks, Mike

Dean Huster
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Re: can clipping ruin a subwoofer?

Post by Dean Huster » Thu Nov 06, 2003 8:24 pm

Clipping is simply the amplifier putting out the maximum power that it can. If you turn up the volume control, the output amplitude will remain the same. As long as the maximum power output of the amplifer doesn't exceed that maximum rating of the speaker, there should be no problem. There isn't that much difference between a severely-clipped sine wave and a square wave.<p>Dean<p>[ November 08, 2003: Message edited by: Dean Huster ]</p>
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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Mike
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Re: can clipping ruin a subwoofer?

Post by Mike » Fri Nov 07, 2003 6:14 pm

Thanks, Dean. I have just read in the manuals for home audio speakers that clipping can, over time, ruin the speaker. I wasn't sure if this was the same for a subwoofer and a low power amp. <p>also, any ideas on the odd sounds out of the speaker?

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Edd
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Re: can clipping ruin a subwoofer?

Post by Edd » Fri Nov 07, 2003 10:07 pm

Mike:
A thought on your para 2:
You didn’t say if your subwoofer speaker was new from day one , or if it could be of suspect by virtue of being a used one, and you not knowing its past history of potentially being subject to high power usage / damage. Don't worry, there is no abnormality in the vents outrush of air current on a big bass excursion by by virtue of it being sourced from a somewhat larger chamber. Healthy sub-woofers voice coil diameters tend to be a median of ~2 in. To enact a test in the manner which I am prescribing, will require the spkr to be out of any mounting and to have its VC wires disconnected. You take the bare speaker and orient its cone at top and grip the outer skirt of the speaker frame in your left hand while pressing its 180 deg opposite skirt into your gut with the top of your belt affording some degree of vert support. Your right hand has been clad with a leather glove (the bone infrastructure in your palm will thank you for that). Then, you come up …square on… with the bottom of the palm, up, onto the back center of the speakers back magnet/pole piece assembly, enacting a moderate blow unto it. The cone should react with a very clean low thump, quite close to its free air resonance frequency. Any variance from that exact type of sound could signify:
A scraping noise= voice coil bobbin distorted/VC wire layer distorted/bobbin form fractured/ any of which can cause a skewing into the magnets center pole piece…producing a dragging.noise
A clattering noise=partial unbonding of cone to voice coil. /or/ loose, ferrous foreign materiel has found its way up to the cones spider around its inside front periphery and is being held in that proximity by magnetic field. That is, until some acoustic activity, and then it vibrates/clatters.
Examples :
Small washer , lockwasher, screw, spiral shaving from a drilling operation, etc..*Wire clipping from a res,cap,xstr from your workbench if the speaker was in that proximity.
*With the large spread utilization of components for auto board insertion manufacturing operations, lately, leads tend to be of Kovar. Seems like the last holdouts are the leads of power diodes , where that heavier thermal outsinking of the semi die is still needed.<p>73's de Edd
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Mike
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Re: can clipping ruin a subwoofer?

Post by Mike » Sat Nov 08, 2003 5:43 am

Thanks, Edd, but I had used this foam with double sided tape to seal it is weeks before, and the speaker doesn't budge no matter how much pressure I put on it. Its almost as if the tape worked too well. I guess you were right, especially since it is from Best Buy, and you probably know how loud people crank that stuff. <p>Thanks, though, Mike

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Re: can clipping ruin a subwoofer?

Post by CeaSaR » Sat Nov 08, 2003 9:14 am

Mike,<p>Speakers are NOT supposed to rattle when they are in use. Rattling usually signifies either a bad speaker, something caught in the spider or surround (as Edd explained), or a problem with the enclosure.<p>If you can hear rattling/scraping when you move the cone, then replace the driver if there are no visible signs of debris or contamination.<p>If the speaker is dirty, clean it as per manufacturers instructions and recheck. If it clears up then try it on another amp and see if the rattling goes away. If that clears it up, most likely your homebrew amp is probably the cause, unless...<p>Your SubWoofer enclosure really makes the the whole project work. If your enclosure doesn't
"fit" the woofer, you won't get the bass you want or you may even get unwanted vibrations from the cabinet. As you have stated, you are using an automotive speaker with a 4 ohm impedance. The last time I looked at a Lightning Audio 10" speaker, it was rated around 200w and the spec for a compatible box was approx. 1.5 to 2 c.f. "sealed ". Sound close? If you don't use a sealed box or a properly ported box, the cone will have free reign on travel and possibly overextend itself. Too much travel will kill a speaker quickly. Look over your enclosure and see if it conforms to manufacturers specs and is built solidly and completely.<p>If you need help with box sizes and types, I have a number of design programs (as published in Popular Electronics - RIP) and would be glad to help out. Just post the pertinent info: Qts, Fs, Vas and thickness of wood used in the box and I'll post back the design info.<p>As to the amp, clipping and speakers are not soulmates. Severe clipping (even at lower than rated power) has been known to damage speakers. If I were you, I'd bolster the power supply to keep up with the demands of the amp. While Dean is correct about clipping, that really doesn't apply to electromechanical speakers. They are designed to "see" sinewaves and multiples thereof, not squarewaves. Clipping in this case is "bad" distortion - OK in creating music, but not in reproducing it.<p>Good luck,
CeaSaR<p>Dean - glad to see you "post-Gernsback".
Hey, what do I know?

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Edd
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Re: can clipping ruin a subwoofer?

Post by Edd » Sat Nov 08, 2003 1:04 pm

Mike:
Oh-taay…then another….yet less exacting…technique. Considering that the front cone access is permissible. You take all 4 fingers and thumb of a hand ..spaced out equally around the cones center dust cover, (affronting the voice coil) then impart a straight on linear push and see what you hear. This method has somewhat of a shortcoming due to the dampening afforded by the fingers presence….but it does have one upside, the sense of touch by the fingertips on feeling a drag.
You can do that foam in with a flexible bread knife or even a serrated grape fruit peeler.
They just zip thru the center foam filler. Adhesive cleanoff can then be effected with paint thiner / denatured alcohol / lighter fluid (naptha)/etc. On my speakergasket faces,
the last 20 yrs or so, I have been using that special grey rope caulk (~1/4 in dia) of Home Depot/Lowes, etc that seems to have drifted down to us from the refrigeration industry, where I’ve seen some of it in use for 50 years and yet, still be soft and pliable.
Also, as mentioned by Ceasar, I’m wondering if your enclosure is over ported (unless U’re using an infinite ) with a resultant/potential cone overexcursion by virtue of inadequate cone dampening by that internal air cushion. Sounds like he can certainly help you out on that, if that is the case.<p>73's de Edd
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