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Old 11th July 2006, 13:52   #1
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Default Impedance of Subwoofers

We see subs with the same RMS rating with usually 2 different Impedances, like a 500 RMS sub can be either dual 2 ohms or Dual 4 Ohms, now how do they differ in construction ?

Is it the coil meterial or guage makes the difference ? what makes them 2 or 4 ohms

Experts please throw some light !
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Old 11th July 2006, 14:09   #2
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I think the gauge and lenght does the trick. In a 2 ohms sub the lenght of the wire used would be less and in the 4 ohms version it will more. this is like a basic concept. there are some woofer for example jbl gti sub in which is a dvc both the vc are made seprately, but in the normal case both the coils are wounded together. not like first one coil is made then the other coil is wounded on the first coil. doing this will change the behavoiur of both the coils so they are wounded simultaneously.

for the coil material for a same series of sub it will be the same.

rest there are more experts here to clear ur doubts.

B&T where are u man this thread will surely attract u. and you are make ur sub youself , u must add a some thing to it
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Old 11th July 2006, 18:26   #3
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Hi LBM, someone told me you were beckoning

It's great fun to build speakers/ subwoofer, and the brighter side is that even if it turns out sounding bad, you atleast know who to blame. (ok, 2 smileys up)

You are right about the gauge and length part LBM, those are the only 2 easily variable factors affecting the end-impedance of the driver. There is a third, which is resistivity, a property of the material being used to make the voice-coil, and commercially available voice coil copper is mostly standard, so we dont need to worry much about that.

So either you use voice coil wire of a greater length, or you decrease the cross-sectional area of the wire used, to increase impedance, or the converse to decrease impedance.

The other approach is to use 2 or more different windings and internally parallel or serial it to get the desired impedance. This would make the voice-coil multi-layered. So it's like having ....

hang in there lbm, more later. gotta rush now. sorry
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Old 11th July 2006, 18:43   #4
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Ya I missed the vc material it is mainly copper so i assummed to be a fixed. But i remember aluminium is also used these days. or any exotic stuff is not used .....lol

hey thanks man will be hearing soon from u ..............
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Old 12th July 2006, 02:59   #5
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Even I will be waiting for the concuding part............
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Old 12th July 2006, 10:14   #6
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Usually parallel wires are used. imprdance is a factor of length, "effective cross-section", and conductivity/resistivity of wire. The resistivity of Aluminum is 2.655 while that of Copper is 1.678. For the audiophiles the resistivity of Silver is 1.586.

Hence a copper wire is about 60% more conductive than an Aluminum wire. However copper is also over 3 times are dense as alumimum. Hence for voice coils aluminum is often the best choice. In addition since aluminum is a softer material than copper one can draw it into rectangular crosssections quit easily and wind the aluminum wire edge wise. This allows for faster dissapation of heat generated as the adjacent coils have full sruface contact vs point contact if round wire was used. Some companies use a hexagonal wire to ensure better thermal dissapation.

Another reason to favour aluminum is that al2o3 (anodised aluminum) is a very good thermal conductor while being a very poor electrical conductor so if one were to use anodised rectangular alumiun wire and find a way to edge wind it without damaging the anodising layer one could get a light, thernally and electrically voice coil.

Copper is better used where the ductility of copper and mechanical strength of copper is required.
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Old 12th July 2006, 16:36   #7
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Damn...I can hardly believe I spent some extra time at office rather than heading to Churchgate station to head back home, just to write out the reply to this thread yesterday. If not, I could well have been picked off the tracks in pieces somewhere along the western train lines. Maybe I should have listened to Navin and headed to the 'burbs with him. Nevertheless, I'm glad to be here...glad to be anywhere for that matter. .. I signed off abruptly cos that's when news first came in about the blasts.

Yeah, so... a multi-layered voice coil gives you the advantage of arriving at the same impedance desired. But since the current is made to flow through a larger amount of winding material, this is viewed as a technique to increase your power handling. Before, Navin points this out, there is a side effect of the moving mass increasing and this is more profound in smaller drivers and ones that use lighter cones, formers etc. Voice coils wound in series are rare, because it is essentially the same as winding a longer length (more turns) of the same wire rather than breaking and re-joining. Parallel is very common. Also, multi-layer voice coils have to be usually applied so that the required effective length of the coil is achieved without having to increase the winding width and induce unnecessarily large and inefficient overhangs.

A DVC sub would not parallel the two discrete coils internally, and would connect the 2 taps of the voice coil to different external terminal tags to allow the user to alter the impedance in a manner suitable. Although I have been saying impedance, the real notable variation in all these instances is the DC resistance of the voice-coil. So please treat impedance as nominal impedance and not operational impedance which would swing vastly based on the frequency of the input alternating current.

When a manufacturer makes two variants of the same sub, and offers two different impedance options without drastically changing the subwoofer's operational parameters, the two subs are made with exactly the same voice coil diameter, winding width and magnet system, but using different no. of voice coil layers and/ or wire gauge to achieve the exact same thermal power handling.

Tool style... Hope this helped.
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Old 12th July 2006, 21:55   #8
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B&T between you and me we are gonna scare everyone away.
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Old 13th July 2006, 00:20   #9
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just when searching about this vc funda I can across some related to senstivity and xmax and Mms .... here it is

You have to be careful when looking at reference efficiency (sensitivity). You can make a speaker really efficient by designing the voice coil to fit entirely in the magnetic gap. This would likely yield a sensitivity of 104 or so. This speaker may work very well if powered by a low powered amplifier because of the high efficiency but would not be able to produce high SPL at low frequencies because it would have a very small xmax. Actually, if the voice coil length was the same as the height of the magnetic gap, it would have no (zero) xmax.
You can also design speakers for very high power handling and high SPL but those speakers would likely have a very low reference efficiency. Speakers designed for high SPL in cars generally have a larger xmax and therefore lower reference efficiency but would easily out perform the speaker (in the previous example) with the higher reference efficiency at low frequencies.
Speakers that are designed to operate in very small enclosures are usually less efficient than speakers designed for larger enclosures. To make the speaker perform in a small enclosure, the suspension has to be stiff. This will raise the resonant frequency. To get a lower resonant frequency, they must add mass to the cone of the speaker. This added mass and the stiff suspension kill the efficiency.

acording to the person say that a high power handiling speaker with less senstivity would outperform a high sentivity in low frequency.......

above stuff was taken from ->http://www.bcae1.com/speaker.htm
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Old 13th July 2006, 01:00   #10
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is there any way one can calculate the senstivity of a driver from it theile parameters ??????????????
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Old 13th July 2006, 01:11   #11
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Quote:
Originally Posted by navin
B&T between you and me we are gonna scare everyone away.
Well it did not scare me , this was exactly the kind of info I was looking for, thanks for the Invaluable Gyaan people, much appreciated.

And hey I think I saved someones life too with the post ,
as long as its all for the good ! I will keep troubling you with posts with questions.

Peace
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Old 13th July 2006, 01:15   #12
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HEY B&T ... great to hear you're okay man... We wouldnt want a B-in-T!!...lol

Yes I agree Navin,,.. that was a frightening post!
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Old 13th July 2006, 13:32   #13
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Quote:
Originally Posted by low_bass_makker
is there any way one can calculate the senstivity of a driver from it theile parameters ??????????????
Yes if you have complete set of T/S parameters not just the famous 3 (Fs, Qts, Vas). If you know Cms, Bl, etc.. you can calculate No (efficiency).
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Old 13th July 2006, 13:41   #14
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which other parameter are we taking about except the famous 3

Like u have added Cms, Bl and which others???????
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Old 13th July 2006, 15:41   #15
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LBM this is a topic for diyaudio.com not ICE. Transducer design is a long topic. If we went into it here we'd loose the rest of the audience (excpet for a few hardened souls - they know who they are!) :-)

i'd suggest reading books by Weems and Dickanson, and mags like Speaker Builder and Voice Coil.

Last edited by navin : 13th July 2006 at 15:43.
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