Why 4 Ohm?

MSALLA

I am looking at up grading my speakers very soon and keep asking myself about the Lsi's.
I have been listening to many bookshelf speakers from Polk, Focal, and other upper end lines. My question is why did Polk make the Lsi's 4ohm? They sound great but I have herd others that are just as good if not better and all have been 8ohm. It seems strange they would make a speaker with such high power demands if they didn't have to. What is the benefit to 4ohm?

MSALLA

Anyone have some input? It may be a stupid question but, well i need to know.

Early B.

It's a good question. I'm waiting to hear the answer myself -- not about Polks specifically, but about the pros and cons of 4 ohm vs. 8 ohm speakers , in general.

lanion

The only thing I have read about it is quite cynical -- that 4ohm speakers sound louder than equivilant 8ohm speakers on the show floor. That is, if you have an ideal amplifier and two speakers both 88db/1watt, but one is 8ohm and the other is 4ohms, the 4ohm speaker will be louder for a given volume setting. (Power = volts * amps.... decrease resistance, you get more amps). That seems really petty, but the only opinion I have heard.

Monster Jam

Not to flame, but if you've found 8 ohm speakers that sound "just as good if not better" than the 4 ohm Polks, just buy the other speakers if the impedence is a hangup for you and be done with it.

I think Polk engineers would respond by saying that they don't intentionally set out to make a 4 ohm speaker (the same would probably be said by many high-end speaker manufacturers whose speakers are ALSO 4 ohm). They design a speaker with a wide range of variables in mind (cost, asthetics, sound, etc.) and in the case of LSi's, a 4 ohm ratings was the result.

In my honest opinion, impedence is the last thing you need to worry about when buying your new speakers - I run my 4 ohm speakers (a long-term temporary solution) off of my AVR. I have little doubt that your Denon could handle the load as well.

Midnite Mick

This is a great question that I have wondered myself. I mean if you were to design a speaker why would you want to decrease your potential market. It's not as if this line is ultra high end and pricey.

One question that I ask you is this. If a speaker was to have a stronger draw, could this then lead to faster transients and greater dynamics assuming that the associated gear was not limiting this? May this be a benefit of 4 ohm? Just a thought. What do you think?

Mike

organ

Midnite Mick wrote:

This is a great question that I have wondered myself. I mean if you were to design a speaker why would you want to decrease your potential market. It's not as if this line is ultra high end and pricey.

One question that I ask you is this. If a speaker was to have a stronger draw, could this then lead to faster transients and greater dynamics assuming that the associated gear was not limiting this? May this be a benefit of 4 ohm? Just a thought. What do you think?

Mike

The greater current draw doesn't improve transient response. Most likely it would be less than a comparable 8 ohm speaker. The amp can act faster when dealing with small bursts of power. Some companies use a lot of smaller value caps in their amps because they say the caps will recharge faster than using a few big ones.

MSALLA

Monster Jam wrote:

Not to flame, but if you've found 8 ohm speakers that sound "just as good if not better" than the 4 ohm Polks, just buy the other speakers if the impedence is a hangup for you and be done with it.

I think Polk engineers would respond by saying that they don't intentionally set out to make a 4 ohm speaker (the same would probably be said by many high-end speaker manufacturers whose speakers are ALSO 4 ohm). They design a speaker with a wide range of variables in mind (cost, asthetics, sound, etc.) and in the case of LSi's, a 4 ohm ratings was the result.

In my honest opinion, impedence is the last thing you need to worry about when buying your new speakers - I run my 4 ohm speakers (a long-term temporary solution) off of my AVR. I have little doubt that your Denon could handle the load as well.

Because they are more money. I'm not knocking the Lsi's I'm really just trying to lern something about speakers. I'm tired of doing the buy-try-return or resell thing. I figure alittle tech. education could only help.
And I don't know if they have or have not intentionally set out for 4 ohms or not. Maybe they wanted that
impedence for a reason. This is what I want to know. That they didn't set out to do that sounds like a guess. I'm looking for facts.

Midnite Mick

Don't the drivers themselves have impedance ratings? I would think that when one sets out to design a speaker they select the drivers first and then optimize and tweek the other components as well as box characteristics and placement. Therefore, wouldn't one choose impedance when one chooses drivers?

I guess resisters would play a role as well but how much?

Not an expert that is for sure just throwing out some questions.

Mike

Willow

It's not a stupid question, one that I have pondered in the past and still do. I'm waiting as well for an answer. I don't undertsand it either.

MSALLA wrote:

Anyone have some input? It may be a stupid question but, well i need to know.

organ

I know Polk designed the driver. The tweeters were sourced from Vifa. Don't know if Polk tuned the speakers by ear or math (or both). They knew what they were doing and all that happened is, after using the appropriate enclosure, drivers and x-over, they ended up with a pair of 4ohm speakers. If 4 ohms is what it takes to get the sound they're looking for, then they'll build them. That's IMHO:).

Polk knew members on this forum wanted something more refined and higher end than the RT line. We were bugging them for years. Most wanted SDA back but Polk gave us the LSi. So they knew people were going to give them sufficient power.

shack

This is the best explanation I've seen...

Every speaker has a specification called the "nominal impedance". Usually, it is 8 Ohms, which means that, not including the speaker cable, the amplifier is presented with 8 Ohms of resistance (impedance) in passing its electrical signal through the speaker. The word nominal means that 8 Ohms is the average impedance. Actually, it varies depending on the frequency of the music, and may range from 3 Ohms up to 20 Ohms across the auditory spectrum. As the impedance drops, the demand for current to be delivered by the amplifier increases for a specific output level. While the current goes up, the voltage stays the same, and the power requirements at the same signal level go up. This is defined by "Ohm's Law" which states that E = I R, or Voltage (Volts) = Current (Amps) x Resistance (Ohms), and the Power Function which states that P = E I, or Power (Watts) = Voltage (Volts) x Current (Amps).

You can see from Ohm's Law that, for a specific amount of voltage, the current will go up if the resistance drops. So, if you change from an 8 Ohm speaker to a 4 Ohm speaker, the current doubles when the voltage is held constant. Then, by the power function, if you want to deliver 100 watts to the 4 Ohm speakers as you did when you had 8 Ohm speakers, the voltage would drop by a factor of Voltage/1.414, while the current would increase by a factor of Current x 1.414, in order for the power to remain at 100 watts. Therefore, if you choose a low impedance speaker (4 Ohms nominal), make sure that your amplifier can supply the current that will be necessary to drive the speaker. On a side note, a since a 4 ohm speaker will draw twice as much power as an 8 ohm speaker at the same signal (voltage) level, even if the efficiency is the same, the sensitivity increases by a factor of 3 dB, so that in a back to back comparison, the 4 ohm speaker may seem more efficient, even though it's simply just drawing more power.

Bottom line is that the lower the ohms the more power that the speaker will draw (AND USE). It is simply taking the design principal that more power is a good thing.

cmy330go

I just spent a half hour trying to type a description of different driver construction when I stumbled accross this article on Wikipedia that says it way better than I could have.

So check out this article. Especially the section entitled "Dynamic loudspeakers". It talks about driver design and how one design offers higher efficiency with less severe distortion at it's limits, while the other offers less efficiency but with greater accuracy within it's limits.

This is why many higher end speaker systems are found in the 4 ohm range. Since they are usually constructed with more accurate (and therefore less efficient) drivers, they require more power. Now what is the most cost effective way to take care of this? By matching the drivers and crossovers in such a way as to yield a lower nominal impedance. Therefore drawing more power from the amplifier. This is usually not an issue since people who spend the money on high quality speakers typically pair them with equally high quality amplifiers that can easily handle the added load.

Hope this helps.

Enjoy!

cmy330go

shack wrote:

This is the best explanation I've seen...



Bottom line is that the lower the ohms the more power that the speaker will draw (AND USE). It is simply taking the design principal that more power is a good thing.

Wow that's weird.....I just about quoted the same article in my response. We must have Googled the same thing.

Joey_V

I wondered the same thing.... I always wondered why my Summits went down to 1ohm from 13khz to 20khz.... now I know. Thanks Cmy!

sickicw

Yea, i always assumed that they are 4 ohms so that they would be drawing more current. I am pretty sure that most high end speakers have much more rigid drivers which would take more current to move them, however the tradeoff for this would be that they have much less distortion.

MSALLA

This is what I was looking for. Thanks guys. I knew someone on here would come up with some back ground. I'm at work, but I have printed out the article and will read it tonight.

okiepolkie

What speakers from the Focal line are you looking at? Also, what else are you considering?

MSALLA

I can't remember the model but they were a wood bookshelf speaker at tweeter. Also The boston VR-M 60's and B&W

Joey_V

MSALLA wrote:

I can't remember the model but they were a wood bookshelf speaker at tweeter. Also The boston VR-M 60's and B&W

You're probably looking at the Profile or Cobalt series. Did you get to hear the Logans?

[Deleted User]

Hello,
If you wanted to draw the most amount of power from an amplifier you would load it with the same load impedance as it's output impedance. In other words, if you were just interested in getting the most amount of power from an amplifier that had 1 Ohm as it's output impedance you would match that with a 1 Ohm load. This is not taking consideration of damping factor, current flow or anything else, just get the amplifier to transfer the most amount of energy into the speaker. The same thing happens when you want to transfer the tiny amount of power produced by an FM antenna (measured in FemtoWatts) into a tuner's circuits. The impedance of the antenna, 75 Ohms, is fed to a 75 Ohm input impedance for maximum power transfer.
This is why many audiophiles use thick speaker wires, to lower the series impedance between their amplifiers and the speakers. This is done to keep the total impedance as low as possible.
Regards,Ken

heiney9

Don’t try to figure out why, just understand the difference between the 2 ratings which are nominal ratings. The overall rating is an average over the whole reproduced audio spectrum. Impedance varies with amplitude and frequency so it’s always changing based on the demands presented by the audio signal and its strength, and the load it’s being driven into. It’s not constant nor is it linear in nature; it’s algorithmic. Meaning it’s constantly changing and is never ever constant. Ohms really have nothing to do with how good a speaker reproduces music outside of a guide to how difficult a load overall it will be. Only be concerned with ratings at one extreme or the other.

The rating is based on ALL the design parameters set by the engineers when developing the speaker line. I’m sure they had a target range in mind but really as long as it wasn’t an ultra difficult load to drive it’s of no consequence and shouldn’t be used to RATE a speakers subjective sound. Certainly if your electronics aren’t capable of driving the load presented by the speaker this is an issue, but there is no tried and true REASON why one manufacturer designs one way or the other with regards to the nominal ohm rating.

H9

MSALLA

Joey_V wrote:

You're probably looking at the Profile or Cobalt series. Did you get to hear the Logans?

I don't know which ones they were. The price was 1149.00 if that narrows it down. The sound was very clear with none of that slight hiss or background air noise at low volume but they were alittle bright.

Emlyn

Given that adding unecessary components to a speaker increases cost and degrades sound quality, doesn't it simply make sense to accommodate the 4 ohm Vifa ring radiator tweeter rather than trying to make the speaker an 8 ohm nominal load by tweaking the speaker to be compatible with wimpy receivers?

Holydoc

Emlyn wrote:

Given that adding unecessary components to a speaker increases cost and degrades sound quality, doesn't it simply make sense to accommodate the 4 ohm Vifa ring radiator tweeter rather than trying to make the speaker an 8 ohm nominal load by tweaking the speaker to be compatible with wimpy receivers?

Doesn't the AV123 (Rocket line) use the Vifa tweeter as well? Their speakers are rated at 8ohms. I am not sure that the tweeter makes the difference as much as how it is all put together.

Joey_V

Holydoc wrote:

Doesn't the AV123 (Rocket line) use the Vifa tweeter as well? Their speakers are rated at 8ohms. I am not sure that the tweeter makes the difference as much as how it is all put together.

The Rocket line is 8ohm, but the Reference line is 4ohm. Both use the same exact tweeter.

Holydoc

Joey_V wrote:

The Rocket line is 8ohm, but the Reference line is 4ohm. Both use the same exact tweeter.

My point exactly. I do not think it is necessarily the tweeter by itself that causes the 4 ohm rating.

Midnite Mick

May be totally stupid response but doesn't low impedance generally apply to lower frequencies because they would require more draw?

Mike

organ

Midnite Mick wrote:

May be totally stupid response but doesn't low impedance generally apply to lower frequencies because they would require more draw?

Mike

This is what I see most of the time. But some speakers have nasty impedance dips in the x-over freq area, where both the tweets and woofers use a lot of power. Makes sense since the x-over is wired in parallel.