2 ohm speakers

I was attending a seminar /dinner last night and there were several manufacturers in attendance..one of them being Infinity.

I won't mention names but the person representing Infinity has been in the biz for 20 years...and worked as an installer for 10 years.

He started discussing the Reference series speakers (not subs) and the advantages of having 2 ohm voice coils...such as extracting full power from any amplifier.

Some of us asked about running these speakers from factory and aftermarket deck power....we are concerned about heat causing problems running them at 2 ohm..even though it is stereo. He stated that if you measure the DCR with a meter...it is around 3 ohms..perhaps a drop more. He also stated that this DCR is the lowest the impedance will drop since the dcr is measured at 0 hz. He stated when you add to that the length of the factory speaker wire..which of course is typically used when doing a deck swap with no external amp....and the fact that after about 10 minutes the voice coil heats up..adding more resistance..you get close to 4 ohms ..but will have more output since vs. a 4ohm speaker..with the added resistance of the wire and heat..will be over 4 ohms.

From a logical standpoint this makes sense..but you hear stories. I even pulled him aside during a break to ask if these 2 ohm speakers can really run with deck power without heat becoming a problem. He claims "we ran these speakers on deck power for 100's of hours at full volume with no problems at all..period. He did say there was a problem with a specific Alpine deck but that unit was recalled...so it wasn't the speakers fault.

I once used deck power on factory bose speakers and did have clipping problems at high volumes..but the DCR on those were 2ohm..not higher as with the Infinities.

I guess what I would ask is if anyone has had experience using these "2 ohm" speakers to deck power...factory or aftermarket..and what were the results...any problems, or flawless operation?

Note to the "techies"...I do not want a lesson in physics here..I understand impedance and how it effects output. What I am concerned about is that Infinity would BS me to sell a product. (not that it would be any great surprise).or if there is real world testing with these speakers out in the field. I would like to know before I consider placing an order. I can totally see an advantage to these if using a clean 2 ohm rated external amp..but I have concern about damaging a decks output(s) due to excessive heat.

I ask that replies be dealing with hands on experience with this product..not what should or could happen..although I am glad to read anyones opinions as well..I just don't want this to become a back and forth topic and never get the answer I need...do these speakers work on deck power without problems? OR..is the 2ohm rating a crock and these are more like 3 to 3.5ohm speakers..I am leaning towards that.

Thanks

Thanks for the quick response.

Also good to know Infinity wasn't pulling my leg. As far as the issues I had with the bose..I believe some of those are closer to 1.5 ohms..I have even measured quite close to 1 ohm on some of the really old ones. wouldn't even consider running a deck to that.

But since I have not actually tested a deck with the 2ohm rated reference Infinities I figured it couldn't hurt to ask..better safe then sorry..thanks a bunch guys.

I have to agree there as well stevdart..so i'm still a bit confused.

I think what I will do is this. Purchase a pair and take a DCR reading for myself.

Has far as you or anyone else knows..is there a general "rule" or guideline as to how far off the DCR is from impedance? I have found the DCR is usually higher or lower by a few tenths then the "rating". If that is the general rule then these referance speakers (if the DCR is what I was told) are actually 3ohm impedance, not a 2ohm or 4ohm. And since impeadance can't be measured physically..we need to depend on this "average"..or wait to see if something cuts out and/or overheats. Can't ANYONE give an honest rating anymore?? or is this all a conspiracy to confuse us?

And if that is the case..someones trying to pull someones leg. There is a leg pulling amoungst us.

2 is NOT 3..or 4..and I do know what "is" is.

Thanks again all..I can always depend on a learning experince here. As well as some fun.

Well, you could always go the guinea pig route. Try it out on a sound board or a unsuspecting friends car.

I recently pulled the old soundstream SPL 60's out my boss's car which was using a head unit for power. It had been doing just fine for years.

But some thing that dawned on me here is how much of an audible difference are you gonna get out of using a 2 ohm load on a deck?

According to what Infinity told me(and they actually used a powerpoint demonstation showing the DCR displayed on a DMM...and an SPL meter display as well) is a dB or 2 louder...The Stock 4ohm measured about 111dB..with the same power the "2 OHM" Infinity was measuring 112.6 or there abouts. Not really that much different..but I am sure this was simply about proving a point.

But realistically no one with an ounce of experience in this industry can expect massive dB gains from a 6.5'' speaker swap using a stock deck for power.

Then again, Infinity is telling me that a 4ohm speaker is a 2ohm speaker.  At least it seems that way.

I would like to measure the DCR of one for myself before I think the worst..but it seems to me a bit misleading to say the least.

What else can be said? I await...

When I worked at Car Toys, I noticed the DCR being up that high and made the same comment.  I figured these "2 ohms" speakers could be run just fine off deck power because of this.

It helps to know what the definitions are.  Although simplified, impedance is the total resistance produced by resistance, inductance and capacitance in an AC circuit.  So you have the base resistance (DCR), resistive elements from inductance from the voice coil and other elements, and a little capacitance induced resistance; the latter two changing with frequency and is the reason why the impedance will always be higher than the DCR.  Nominal impedance should be the lowest impedance produced within the intended bandwidth of the speaker, but is usually rounded up to a more standard nominal impedance rating.  Now Dan Wiggins once told me that you usually want to design your speaker to have a DCR that is around .707 of the rated impedance.  Impedance can be measured physically.  It is usually graphed as an impedance curve.

Differences in DCR's between speakers generally have to do with the design compromises and final goals.  Sometimes higher/lower impedances are allowed as a compromise to gain higher power handling, lower moving mass, etc.  Or sometime it is done as a goal to draw more or less power from an amplifier.  For example, having a higher DCR allows them to rate the speakers power handling at 4 ohms higher because in actuality, there is less power going to the speaker.  It's a way to fudge the number without risking damage.

I think that's a misleading demonstration.  For one thing, if the power truely is the exact same going into the speaker, then the differences are due to added efficiency, not because of the impedance.  Second, although the lower impedance speaker may be louder at a given volume control setting, the internal amplifier will run out of power sooner, so no output was gained beyond what was produced due to higher efficiency.