Consequences of replacing 8 ohm woofer with 4 ohm woofer in home theater sub?

You're on the right track here - the 4 ohm sub will draw more current and thus output more power, so all you need to do is make sure that the amp that is driving it is capable of driving a 4 ohm load safely. You should be able to find this out from the owner's manual, or maybe even the back of the amp.

speaker

watts

around

500

it

Closed box and powered == you can replace bass unit without loosing too much sleep over impedance concerns.

I am tired of googling for its Qt and Fs, all I got was the vague impression that 1.5 to 3 cubic feet is a suitable size range for a closed box for it and that its power handling is adequate.

This is not an issue, at least not in terms of frequency response.

Yerp, this means that if you play it so loud that the amplifier clips the amp could blow a fuse and that you should check just how hot the amps assumed cooling fins get if you play it very loud for extended time.

Is there any wadding of any kind in the box? - no? - thought so. Try this: take the embroidered pillow on the couch, the one you got as a gift and hate, and toss it into the box and listen again. If you want to purchase dedicated acoustic damping material, then feel free to so do. Even if it does contain damping material on the walls of the box, do this or something similar that addes damping material to the box center. Doing that will reduce the acoustic Q and make the bass tighter and more precise. Just toossing loosely fluffed acoustilux or similar acoustic wadding into the box will have a similar effect. The embroided pillow on the couch that you got as a gift and hate may not be uniquely the best material for this, but it is a fast and easy way to test if that damping approach is likely to improve the sound.

In a closed box, the answer is that you will probably get a change of bass tonal balance. The impedance is not at all an acoustic issue with a powered box, it may or may not be an issue to the amp, which may become too hot or blow a fuse or clip at unexpected low level if made "too tightly" for driving the original 8 Ohm unit, my guess is that it is unlikely to be any kind of issue at all.

Enjoy. If you can find the Thiele-Small specs for the unit you could try asking again and someone here may be able to suggest an optimum box for that C-12, I have used fairly much time googling for them and not found them.

Kind regards

Peter Larsen

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     * My site is at: http://www.muyiovatki.dk *
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For the same applied voltage the 4 Ohm speaker will draw 2 twice as much current, which will put double the electrical power into it.

To put the same electrical power into it, you will have to reduce the voltage by the square root of 2, which will still mean that the current draw will be up by the same factor.

So it all depends on whether your amp can deliver the extra current or not. If this was a unified system (sub-woofer with amp built in) then it is unlikely that the amp is going to be happy with this. The most likely outcome is that the output transistors will blow the next time you turn the volume up.

I'm guessing that high volume is what blew the original speaker, so it seems likely that you will do this again, with slightly different results.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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The box does have factory "wadding" inside. The amp's cooling fins (heatsink) get warm, never "hot". I have no idea if they got this warm before or not- I know I never touched them or ever payed attention :(

I've been on the hunt this weekend for an 8 ohm 12" sub woofer, which is hard if not impossible to find. I may have to order it directly from A.T. if they'll sell it to me?

The box sounds ok with the C12 installed, its just quite "bassey"

ohm

They make a transformer thingy that allows you to adjust the ohm rating to match the recommended load rating of your amp. They used to sell them over at madisound.

Don't know if it'll change the acoustics of the driver itself though.

Yes, he may blow the fuse in the amp. From the test of the C12 I did find when googling for its Thiele-Small data the powerhandling of the unit is substantial.

Kind regards

Peter Larsen

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     * My site is at: http://www.muyiovatki.dk *
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[fixing microserf style topposting]

Read the above again, try it or not as you please, but do understand that wadding along the walls addresses midrange issues. It is also the only damping that should be deployed for bass reflex bins, generally line of sight should exist between either side of the unit and the corresponding end of the bass reflex port(s). You can only, generally at least - there are non-ideal bass reflex designs that rely on an acoustic resistor, ie. damping, between loudspeaker and port to reduce the coupling, deploy damping to the cabinent center in a closed box and you should only do it if you need to reduce the system overall Q to linearise the bass response. From your description just that appears to be relevant.

Oversimplified there is not likely to be an issue then.

Monacor, Seas, Dynaudio, JBL, Scanspeak, Peerless ... just to mention the first 6 product lines that are likely to contain something useful.

I can't comment on this other than saying: Yees, getting the original item is what will get your the original ssound.

Welcome to the wonderful not so simple world of the simple closed box. Just how large is the box?- do you have a spec sheete that perhaps came with that C12?

Kind regards

Peter Larsen

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     * My site is at: http://www.muyiovatki.dk *
     *******************************************

Try the NHT1248 available from

or at least it was the last time I checked. Also Parts Express has a couple of 12" woofers made for a dealed box.

The Kicker C12 is a good woofer, but they (Stillwater) give enclosure recomendations that are IMO to small for home subs. A box of around 3

- 4 cubic feet is about right for this driver IMO.

The NHT 1248 works to 30 Hz before room loading in 3 cubic feet.

If you have an SPL meter and a test disk you can find out what the sub is doing and make adjustments to see if it's OK. Perhaps some judicious tweaking of level and xover can get it to perform the way you like.