DCR Resistance

[kingjames]

I have learned here to always check dcr resistance on speakers and I see people including myself state these numbers when selling loose speakers. If the dcr is within specs of a certain speaker does that guarantee that that speaker will sound the way it should,is the voice coil good if dcr shows within specs? Can someone explain in simple English why this is a good measurement and exactly what I am measuring. Thanks,just trying to learn.

[Mr. Widget]

It is not a particularly useful measurement... it is simply the easiest measurement for most people to make. Obviously if the DCR shows a shorted or an open coil that is good to know, but beyond that a coil measuring within tolerance doesn't tell you much.

It is quick and it is easy, but it is no substitute for an impedance curve.


Widget

[Zilch]

It indicates that the voice coil is intact, and that there are no shorted turns, if within spec. I shouldn't say "no" shorted turns, probably, because the tolerance is pretty wide, however, when turns are shorted, it's usually many at once. So, basically, it's just saying that the voice coil is not blown or severely damaged, from an electrical perspective.

It is not specifically indicative of how the speaker will play; there's plenty of other potential problem sources. Even with something as severe as a frozen voice coil due to a slipped magnet, for example, the voice coil DCR could easily read within spec, even though the speaker will not actually play worth a whit.

DCR will distinguish between speakers of different impedances, when there's some reason to question it, as, for example, when the actual impedance of a reconed driver is unknown. DCR is not a direct measure of actual impedance, but it is indicative.

I like it if DCRs of a pair are close to each other, i.e., matched, but that's no big whoop, either....

[Mr. Widget]

Can someone explain in simple English... exactly what I am measuring.

A DCR measurement places a direct current through a circuit... in this case a round coil of wire. The meter then measures the current running through the wire and calculates the simple DC resistance based on the known DC voltage the meter supplied.

An impedance curve on the other hand sweeps a range of audio band AC frequencies through the coil and measures the "AC resistance" through the coil at those various frequencies... "AC resistance" is an inaccurate "simple English" term for impedance which due the the nature of alternating current is made up of "complex numbers" (vectors) you must consider the phase of the voltage and current running through the circuit.


Widget

[kingjames]

Thanks for your info here.

[Guy in WNY]

From the Loudspeaker Enclosure guide, Circa 1979

Link: http://www.lansingheritage.org/image...ual/page30.jpg

This shows you how to hook up a meter and then you do a "Sweep" with your audio frequency generator and plot the readings on the log graph paper provided. That will give you a "baseline" reading and as you make changes (to your cabinets, etc.) you can replot the curves.

I haven't done one in a long, long, time, but will be soon just to get started again.

PS: I actually have a copy of that guide, it's still in prety good shape. I also have the Pro specs for the E series loudspeaker - I don't see a scan of it in the Library. If anyone wants a scan of that, just let me know.

[ratitifb]

My recent experiences show that matched DRC do not guarantee the correct sounding of two speakers as too much ebayers let it thinking. I bought recently "a gorgeous matched pair of LE25 with DCR 4.5/4.5ohms" and as final result these two speakers gone directly to my trash (voice coil rubbing in the magnet gap, for one at low level, for the other at loud level)! However they were very beautiful on closeup pictures :thanks ebay.

DCR garantees only that voice coil is ok from static electronic point of view. It's important but not sufficient. Regarding electrodynamic speakers, DCR compared to Zmax at resonant frequency gives some idea of its efficiency (it's not the only one parameter involved in efficiency).

Be careful, DCR is important without guaranteeing speaker is "sounding perfectly fine" (even in your trash ).

[Zilch]

let it thinking. I bought recently "a gorgeous matched pair of LE25 with DCR 4.5/4.5ohms" and as final result these two speakers gone directly to my trash

Go get those outta the trash. Diaphragm kits are $76 apiece....

[Thom]

Dcr will find some drastic problems. if one turn is shorted to the turn next to it only you probably wont pick that up with dcr but with the ac of music or even a tone it's a short and a big problem. Fortunately this doesn't happen often if you short one unless you stop right now you will usually short more and that you will pick up. The rubbing voice coil you can usually find by manually manipulating the cone (straight in and out) if you don't freak out the owner two badly but any uneven pressure can sound like a rubbing voice coil (because the voice coil will rub)

[ratitifb]

Don't worry my trash is virtual and 2 LE25 are still in the box ! but i don't know today if i want spend money for (in France costs are higher and I twisted one 2402 dia last weekend ... and need money).

Sorry for english mistake but when I wrotte "rubbing" I was thinking "dry frictions" in the gap generating non-linearities so during listenning test at low level (mainly) your can hear large change in output (by step) for the same power level of amplifier (obviously sound test was music and or voice).

[ratitifb]

Manually manipulating the cone (straight in and out) is for me prohibited, on HF transducers mainly. On bass or mid you can with extrem care by applying 4 fingers (twice by hand) to keep centered voice coil ...