Question Regarding Resistor On My Speakers

[juggernaut]

I had all of my speakers replaced along with a new JVC (KD-SH55) 200w head unit. The shop put in resitors on the rear door speakers, saying that they may draw two much and overheat the head unit. You can hardly hear them now, so I am curious if I need the resistor or not?

[Bing_0]

waht they probably did is put in bass blockers, whcih are baislly little resisters that filters out the low low frequencies so the rear speakres dont blow, the down side of this is that they really make the efficiency go down, whcih is probaly why you cant hear the rear speakres, so in short, you dont NEED them on there, but there are downsides to both having them and not having them...

b

[juggernaut]

All of the speakers are now Kenwood's and it was not the cheapest investment I have made. This is why i am curious about the resistor on the rear door speakers, why pay for them if i cannot hear them?

So could i possible over heat the head unit if remove the resistor? blow the speakers? what would you do?

Thanks!!

[Bing_0]

well, if oyu have stock headunit, then they perhaps put resisters ot raise the impedance of the entire system...whcih means yeah, they are sorta neccessary... what i would do when people hook up aftermarket system to the stock headunit is only do front and rear doors, and disconnect the rest

[Stormin Norman]

A resistor in series with a speaker will destroy the damping factor of the speaker, a big roll off in response from the lower mid range on down, depending on the size of the speaker.

A bass blocker is a capacitor, not a resistor, and rolls off bass only.

Installing a resistor because "the speaker may draw too much power from the amp" is total stuff. Speakers don't draw, they are fed by the amp. This is why you have a fader control. If you have more than one pair of speakers on the front end of the fader, maybe they are attempting to balance the level between the two pairs. Duzn't sound like they are doing a good job of it if you can barely hear the speakers with the whatever it is in the line.

I would find out if it is a resistor or a capacitor. I can't think of any good reason at all to put a resistor in this line. Regrettably, the amount of residue from the male bovine is systemic thru-out retail audio. It is very possible these people really don't know what they are talking about.

P.S. I spent 20 years in retail a/v, some of which at the 1st Alpine dealer in Chgo.

[Bing_0]

good call on the capacitor, i myself realized thats probably not what he meant when i read over his post again...

but a resister can be used to raise the over all impedance of a system, which is why i think they did it. for example, the stock spekares are not all 4ohm so that the end impedance on the front and rear channels are around 4ohm, when you simply swap in a bunch of aftermakret speakres whcih are all 4ohm, you will probably end up with a final impedance of less than 4ohm, perhaps even 2ohm, this is usually not a good thing on a headunit...whcih is probalby why they did it...

now I am not saying our 850s must have a resister wired in, but i have heard people having issue with their headunit when they just swap in aftermakret speakers....also, i do understand why a shop may do this...not neccessarily a bad thing too, most shoips probably wont even think about this and just let a customer go...

b

[wattsat]

The shop put in resitors on the rear door speakers, saying that they may draw two much and overheat the head unit

Well, they are telling you a half truth.

Most Car audio speakers have a 4ohm Impedance. That means that your head unit is expecting a 4ohm Impedance. Volvo's however have 6 Speakers. This creates a problem when you only have 4 Channels of amplification. Such as the factory and aftermarket headunits.

I am not certain how the factory set up the wiring for the rear speakers. I don't know if they wired the Rear Speakers in Series or Parrallel.

If they wired them in Series then the Factory Speakers will be 2ohm Speakers and installing aftermarket 4ohm speakers will cause the HU to see an 8 Ohm Load. Thereby causing it to push too little power and not create enough sound.

If they are wired in Parrallel Then the factory speakers will be 8 Ohms and installing aftermarket 4ohm speakers will cause the HU to see a 2ohm load. Therby causing it to push too much power and possibly overheat the HU. Installing a Resistor could change the 4 ohm speaker to 8ohms therby making to overall load correct.

This is really only a problem if you use the Internal power of the HU. Today 99.9% of external amps (Even the Cheap ones) will be able to sustain a 2ohm load and installing 4ohm speakers in parrallel is not a problem. Assuming they can handle the power increase.

With a decrease in Resistance to an amplifier the Wattage Output it is increased. With an increase in Resistance the Wattage output is Decreased.

I will measure the Ohm load on one of the factory rear speakers and see what it says. Or, I could be completely wrong and the factory HU or Optional amp may have 6 Channels. If that is the case, all of the factory speakers will be 4ohms. Installing a aftermarket HU with only 4 channels and hooking up 4 4ohm speakers in parrallel in the rear will result in a 2ohm load to the rear channels of the HU and most likely will cause it to Over Heat if played at a loud volume for an extended period of time. Which could be only 5 Minutes.

So, did they lie to you. Probably not. Did they tell you the whole truth? Certainly not. Would you have understood what they told you if they had? Maybe.

Personally, if you want all 6 speakers in the car and want them to sound good. Don't buy a HU and use the internal amps. They are never ever ever ever any good. If you HU says it is 200 Watts that means it is 50Watts per channel. 50Watts per channel is alot of power. There are plenty of awesome competition Car Stereos that only have 50Watts Per Channel.

Think about this. A typical 50 Watt/Channel/4 amp will have an 8awg or 10awg Power wire with an equivilent ground and a 20 or 30 amp fuse. It will produce a very clean 50Watts of power and sound very good at all volume levels. It will also handle a 2ohm load without failing or distorting. Not that I like Alpine but as an example The Alpine MRV-F340 produces 55X4 and costs $399.99. Personally I really like Zapco or Lunar for amps, but they are pricey.

http://www.zapco.com/prod/ref_prods/3604Frame.htm

http://www.lunaramplifiers.com/mainindex.html

Comparing that to the JVC HU (Crutchfield $199) that produces 19x4 RMS and 50x4Max and is using the factory power wiring to the HU that is only 16awg wire and you should begin to understand that it may not be capeable of doing what you expected it to. I know that you don't think of this as a cheap investment and car audio certainly is not. I spent $600 on my last HU alone. + another $600 + on Amps and another $500 + on speakers, wiring and RCA's. And I performed all of the labor myself. I started buying those amps and HU's about 5 Years ago. I just sold the HU for $150 on ebay because I no longer needed it and I still have the Amps to use in the Volvo. And honestly I see no need to replace them for several more years if ever. However, the HU was becoming dated and unfortunately the 6 1/2's that I have will not easily fit in the Volvo.

I guess what I am trying to say is this. If you want good sound in your car. Be prepared to spend some real $$$$. Buying a good solid amp now will reward you well into the future. Even if you have to buy Used, buy something of quality. Hope you don't take offense, but there are generally much better and sometimes less expensive products than the big Name Brands (Kenwood, JVC, Alpine, Sony, etc) They have very large Marketing Budgets that cause them to increase the price of their products. Where the smaller companies don't advertise and can put more effort into making a better product.

[Stormin Norman]

My understanding from other posts is that the rear door and deck speakers are wired in parallel so the two 8 ohm factory speakers end up showing 4 ohms to the amp, which would be ok. If the two 4 ohm speakers are wired in series to show 8 ohms to the amp, the damping factor is toast, say goodbye to the bass.

A resistor is series with the speaker is a bad idea, particularly on a back (door or deck) speaker where there is some expectation of bass performance. Good crossovers will sometimes use a resistor in parallel with a driver (think tweeter) to lower the audio level of the speaker to match the others in the system (woofer and mid-range) by shunting some voltage to ground. But this will lower the impendance (like resistance but as a function of frequency) seen by the amp.

The ideal solution would be a six channel amp, so each pair has a dedicated channel driving them. This will also optimize level balancing tween the speakers. Many modern amps will stand a 2 ohm load. If this is true, wire both sets of rear speakers in parallel to the amp.

The more I think about this system the more I feel like things are not hooked up correctly at all. I left the audio biz in 1990, so it takes awhile to remember this kinda stuff. Kind of endearing to hear the same lies being bandied about that I heard in the '70s.

Perhaps you could print these posts and show them to the dealer while you politely demand that they FIX their install.

Good luck.

[Stormin Norman]

P.S. You can't measure a speaker impedance with a Ohm meter. The ohm meter reads the DC resistance not the impedance (function of frequency, remember?). You will see a reading of dozens if not hundreds of ohms as the ohm meter will be looking at the resistance of the voice coils.

The previous comments about quality amps are accurate. I used to tell people that power was like sex, it is really hard (no pun intended) to have too much.

[Bing_0]

i too agree with the fact hte resistors is not he ideal solution to the need to raise impedance on an system, but may be the only way under the budget to make sure the headunit doesn't toast. if what you say is true, and the rear two pairs of sepakrse are wired in paralle, then putting in two aftermarket speakers will drop th load to 2ohm, whcih WILL most likely give the headunit issues such as running too hot and burning up. as the result, the shop did what they could...

of course, a real amplifer with real processing ist he ideal way to go, but from an installers perspective, how would you deal with this issue, if someone came for you to isntall two speakrse, and have a budget of say $30 to do the install, surely you cant put an amp or anyhting like that in...and if htey are adament on putting in TWO sets of speakres, how would you solve the issue...so all i am saying is that though not the ideal solution and may not even sound good, i dont think the installer did anyhting wrong to add a resistor to the lineup

as for hte other post, aside from waht stormin normin pointed out, i definetly also want to echo the fact that large sums of money is NOT a critieria to get good sound. I can think of quite a few ways to put together an entire system with HU, amp(s), sub(s), two front speakers, and wiring for way under 1000 brand new and still sound great...:)

[Bing_0]

oh norman, i was a bit curious about two things you said, was hoping you can clarify.

1, are you saying the lower the impedance, the higher the damping factor? i was under hte impression that most amps is just the opposite. as when you see tests done on amps, the damping factor will drop when they take it down to 2ohm versus 4ohm...imean, if high damping factor is desired, then shouldnt we run our systems at like .1 ohm?

2. i had always believed that regardless of an amp's damping factor at what ever resistance, it is all limited by the very low damping factor of the speaker (something like under 10" so even if you have a 1000+ damping factor amp, your entire system will still exhibit an overall dampin factor of whateer the speaker is?

anyway, not saying youa re wrong, just a bit contradictory to what i have always believed...perhaps our freind CAE can clarify this issue up a bit...

b

[Stormin Norman]

Things like damping factor start to enter the black hole of loudspeaker (and enclosure) design. Relates to the Back EMF (electro motive force), which is, I think, the amount of current returned to the amp or some such thing. As of yet, I can't remember the answers to the most recent questions, but it will probably come to me. There's never an audio engineer around when you need one. You could try Googleing damping factor for some reference materials.

After replying yesterday, I spent more time thinking about this stuff last nite.

1. I doubt it is possible to have a true 200 watt head unit, there simply isn't enough room in the chassis or air flow to vent the heat. It is probably some stuff 'peak power all channels driven @ 1khz for .5 second' kinda crap. Presuming the HU has a standard power supply design, check the line fuse. For the sake of argument, lets assume it is 10 amps. 10 amps times the 12 volt power from the battery = 120 watts. So if the HU draws more than 120 watts from the car, the fuse will blow. If (not true of course) the HU didn't draw any power for the radio, cd drive and display; and the amplifier circuits were 100% efficient; there would be a maximum of 30 watts per channel (120 / 4 ). This HU probably puts out about 20 true watts per channel. JVC has been doing this for decades, no surprise.

2. I doubt there is any HU that will drive 6 4 ohm speakers properly, period. The system sold to the poster is fundamentally a unsound and a bad design. It won't work correctly and there is no way to make it correct short of using 8 ohm speakers in the back, which I doubt you will find. In lieu of a refund (which they won't wanna do unless you can threaten them with litagation) the shop should offer an accomadation price on an amp to drive the rear speakers. Maybe a 4 channel amp connected to the rear fader output, half the amp for the doors, the other half for the deck. Doesn't have to be a real good or expensive amp, cuz it just sees a 4 ohm load.

3. A resistor in series with a speaker is a bad idea, period. Simply converts your watts to heat and rapes the sound.

4. The impedance quoted for a speaker is a composite value averaged accross the audible spectrum. Impedance will vary by several orders of magnitude depending of the frequency where it is measured and (this is important) the type (vented or sealed) and volume of the enclosure. Most of the magic in loudspeaker design is the matching of drivers, crossover and enclosure. Damping factor is independent of impedance, I think. This really is some moderately arcane stuff we are getting into.

5. My old dead gray cells thank y'all for the stimulation. I'm surprised I remember this stuff. Hope it helps.

[wattsat]

I just looked on the back of the Rear door speaker I pulled from my car. It is marked as an 8ohm speaker. That tells me that the HU has a 4 Channel Amp and all 4 rear speakers are wired in Parrallel so the amp will see a 4 ohm load.

So, when you installed aftermarket speakers and since I am sure they used the factory wiring the new HU would see a 2ohm load and definately overheat / blow up, etc.

So, the resistors they put in are necessary but not the best solution.

[juggernaut]

Alright, first my thanks for all of the informed replies. I must admit that I have studied mechanical, and not electrical in university and have very little clue as to this side of the world.

As I understand your messages, I should get an amplifier to get the most out of what I have. Now here is what I have in the car.

JVC CD player JVC (KD-SH55) 200w

In The Dash I have tinny little Kewood tweaters that I cannot find specs for.

In the front doors I have Kenwood KFC-P502 (5") 150watts 4ohms.

In the rear doors Kenwood KFC-1377 (5&1/4") 120watts 4ohms (with Resitor)

Rear decks are Kenwood Excelon (5x7") 120watts 4ohms.

Now can you recomend a specific ampifier (new, used, cheap) that I can add to my system to get the most out of it. Also if I do add the amp does this mean the resistor comes out?

And one final question, when adjusting the sound level I can hear a slight bit of noise with each increment (up or down) of the level, sort of like a static noise. What should I make of this? I don't believe that it is a loose connection as I just added sound deading material to the car and inspected the connections.

Thanks Again!!

[JehovArob]

If the rear speakers are wired in parallel, how are the front speakers wired once you've gotten a wiring harness and installed a new headunit? They parallel, too? Or are they in series? And what are the resistances of the front speakers?