4 ohm Speaker Question

jdhdiggs

Just to add to the fun, upping the voltage is much, MUCH easier (read cheaper) in traditional amplifier designs than getting a power supply that can keep up with the amperage draw.

sousa

Okay, so given all of this, then as the OP asked why make speakers with 4 ohm impedences? If it is cheaper to make an 8 ohm amp capable of powering them then do the speaker and amp manufacturers simply want to screw us out of our money? I am sorry if my persistence or sarcastic humor are bothering anyone, this is just very different than what I have learned up to this point.

jdhdiggs

It's a design consideration and how the drivers interact with the X-over. If your schematic makes a great sounding speaker that is nominal 4Ohms and dips into 2 ohms, well, if amps can handle it, keep it there. Adding resistance to the circuit is only going to hurt the sound. It can also change the phase and othe charactoristics.

Also, your logic was traveling down the right path, you just didn't allow it to arrive. (shh, this is secret) A 2 Ohm speaker will play just fine on a receiver rated for 8 ohms, it will just be working much harder and have less overall power available to it:

Based on 8 Ohm ratings you can find the max rail voltage and at the 4Ohm rating you can find the max amperage rating and as long as you never exceed either of those limits, the amplifier should have no issue driving the speaker.

sickicw

I am still trying to figure out why they use 4 ohm speakers. i have never designed speakers before, but i am just going to assume that the lower the resistance, the more power will be transfered to the driver and less turned into heat, thus making it more dynamic and powerfull sounding. But again this is just a guess.

jakelm

jdhdiggs wrote:

It's a design consideration and how the drivers interact with the X-over. If your schematic makes a great sounding speaker that is nominal 4Ohms and dips into 2 ohms, well, if amps can handle it, keep it there. Adding resistance to the circuit is only going to hurt the sound. It can also change the phase and othe charactoristics.

LOL...I just said this.....I guess it needs to be repeated to understand

sousa

I did not realize changing the resistance of the speaker could impact the SQ. I knew the nominal impedence was determined by the circuitry used in the x-over design, but never knew changing it could have negative effects. I just always assumed 4 ohm speakers were made to get more power out of amps that were able to handle the load. Thanks to everyone, sorry if I pissed anyone off with my obvious ignorance on the topic.

jakelm

Most caps in crossovers need a certain amount of resistance to work properly (filter and store correctly). Raising or lowering the resistance changed the characteristics of the xover.

Dont be sorry..we are all here to learn..

sickicw

jakelm wrote:

LOL...I just said this.....I guess it needs to be repeated to understand

Yea, but why are all the driver's and tweeters not designed at a higher impedance?

While I'm thinking about it, i suppose the shape of the box used will also affect the speakers impedance charateristics (at least when we start talking about the lower frequencies)?

ben62670

sousa wrote:

Okay, so given all of this, then as the OP asked why make speakers with 4 ohm impedences? If it is cheaper to make an 8 ohm amp capable of powering them then do the speaker and amp manufacturers simply want to screw us out of our money? I am sorry if my persistence or sarcastic humor are bothering anyone, this is just very different than what I have learned up to this point.

I design all my home speakers to run at 4 ohms because I use quality amps. Why design a speaker to run at 8 ohms when you get less power from your amplifier? Speaker manufactures design speakers knowing that most buyers are going to use crappy receivers to run there speakers. I don't care if the receiver manufacture says a receiver is 4 ohm capable. Most 4 ohm capable receivers are just current limiting their output at 4 ohms.

ben62670

sousa wrote:

I did not realize changing the resistance of the speaker could impact the SQ. I knew the nominal impedence was determined by the circuitry used in the x-over design, but never knew changing it could have negative effects. I just always assumed 4 ohm speakers were made to get more power out of amps that were able to handle the load. Thanks to everyone, sorry if I pissed anyone off with my obvious ignorance on the topic.

The nominal impedance is determined by the drivers, and not hardly affected by the crossovers at all, unless giant inductors are used to control very low frequency drivers in sub woofer systems.

jdhdiggs

sousa wrote:

I did not realize changing the resistance of the speaker could impact the SQ. I knew the nominal impedence was determined by the circuitry used in the x-over design, but never knew changing it could have negative effects. I just always assumed 4 ohm speakers were made to get more power out of amps that were able to handle the load. Thanks to everyone, sorry if I pissed anyone off with my obvious ignorance on the topic.

Want to try this one? Get some cat 5 cable and only attach on pair of wires (there are six wires in the strand, only attach 2) and listen to how it sounds. Now connect some 14 or 16 Ga lamp chord and take a listen. All that difference is due to the resistance difference between the two cables. This will cost you about $4 in parts.

JimBRICK

ok so explain 4 ohm again LOL

jakelm

JimBRICK wrote:

ok so explain 4 ohm again LOL

More than 5 ..less than 3..lol

Gaara

Hell I always thought the speaker manufacturer tried to make the best sounding speaker possible with a set budget, and if was 4ohm or 8ohm so be it. I have never heard of a company designing their speaker to be 4ohm.

Jared

mhardy6647

I'm sorry to be snotty, but: The amount of misinformation in this thread is staggering.

The standard (well, typical) measurement of speaker sensitivity is SPL (dB) at a distance of 1 meter with an input of 2.83 VAC (typically white or pink noise). 2.83 V is one watt at 8 ohm; it's 2 watts at 4 ohm. The sensitivity of a 4 ohm speaker thus measured will be 3 dB higher than an 8 ohm speaker. That's the main reason many speakers are 4 rather than 8 ohms.

A power amplifier that can deliver unlimited current will double its continuous power output capability into a 4 ohm load relative to an 8 ohm load. If it cannot, it is indeed current-limited (as has been, correctly, noted).

A word about impedance. Impedance is NOT resistance. It's like resistance in that it obeys Ohm's law. It is unlike resistance in that it is the vector result of three quantities, resistance, capacitative reactance, and inductive reactance. The latter two (at least) are frequency dependent, so impedance varies with frequency. It is possible to build filter networks ("crossovers") which minimize the variation of impedance with frequency, but ALL speaker systems will display an impedance peak at the system resonant frequency. The nominal impedance of a fullrange speaker system is usually measured at 100 to 200 Hz, or somewhat above the HF skirt of the resonance peak impedance (whichever comes first).

http://www.polkaudio.com/forums/showpost.php?p=551400&postcount=8

Systems

ben62670 wrote:

The nominal impedance is determined by the drivers, and not hardly affected by the crossovers at all, unless giant inductors are used to control very low frequency drivers in sub woofer systems.

The crossover most certainly does affect a speaker systems impedance.:)

zingo

I believe another reason that car audio companies make car speakers at 4 ohms and below goes back to the idea of Ohm's Law. 200w at 12v equals 16.6 amps. 200w at 120v equals 1.6 amps. You can draw 16 amps from your car no problem. However, if you have an amplifier that is drawing 16 amps on your house circuit, that could pose a problem. Hope this helps.

Jim Shearer

You may not find this relevant, but FWIW, I don't think that the speaker manufacturer's are trying to make your life difficult by building 4 ohm speakers. Speaker design is a very complex task, with many competing factors. If you want some background on speakers and design, there are many sites on the internet which might help you. Here are a couple where you can hear from folks who are professionally involved. (These were previously posted by others on CP.)

The Soul of Sound page: http://www.nutshellhifi.com/library/index.html

Articles section of Elliott Sound Products page: http://sound.westhost.com/articles.htm

As to the problem of driving 4 ohm speakers, look for the thread 'Why 4 Ohm Loads Stress Your Amplifier' on the AudioKarma.org site:
http://audiokarma.org/forums/forumdisplay.php?f=13

Cheers, Jim

heiney9

Good stuff Jim, I had actually forgotten about the Audiokarma thread.