Sensitivity?

[zumbo]

Lets say we are comparing two different sets of speakers.
89dB 1w@1m (4ohm)
89dB 1w@1m (8ohm)

And one amp that is 4ohm stable.
350w p/c into 4ohm
200w p/c into 8ohm

The 4ohm speaker will be 75% louder(generally speaking) than the 8ohm speaker at the same volume, correct?

This is what got me to thinking.

87 at 4 ohms is like 84 at 8.

 

[j_garcia]

No, they will be exactly the same. The 4 Ohm speaker requires the additional power to achieve the same SPL.

 

[jcPanny]

3dB volume increase

By the way, a 3dB volume level increase is only "slightly louder" while a full 10dB increase is required to sound "twice as loud".

 

[zumbo]

So, a 96dB 8ohm speaker will be twice as loud as a 86dB 8ohm speaker, and twice as loud as a 86dB 4ohm speaker as well?

 

[j_garcia]

3dB is a 50% difference in output, which is noticable. A 6dB increase would be a doubling of output and would be very noticable, but in general to achieve that increase of 6dB, you would need to quadruple the power with the same speaker.

Example (not exact, just to illustrate):
86dB sensitivity, impedance is not a factor.
with 100W = 100dB
with 200W = 103dB
With 400W = 106dB

 

[Jack Hammer]

No, they will be exactly the same. The 4 Ohm speaker requires the additional power to achieve the same SPL.

Does that generally make 4 Ohm speakers less desirable/efficient/sound quality? Why would manufacturers make 4 Ohm speakers as opposed to 8 Ohm? Is there any advantage, other than power required, to one over the other?

Thanks
Jack

 

[Eric Apple]

Are you sure ?

No, they will be exactly the same. The 4 Ohm speaker requires the additional power to achieve the same SPL.

I am not so sure about this statement. The specs he supplied say:
89dB 1w@1m (4-ohm)
89dB 1w@1m (8-ohm)

Both speakers need the same power to achieve the same SPL. I believe you are correct however when the mfg. states the spec as something like 2.83V@1M for both 4 & 8 ohm speakers. In the case of 8-ohm the power is 1 watt and 2 watts for 4 ohms.

In the case of comparing speakers with the above specs, the 4 ohm speaker will be supplied additional power and will play louder the the 8-ohm speaker. But, it's only 2.4 db louder 10log(350/200) and not by any stretch 75% louder. Twice as loud would be about 6db, so this maybe could be called "a little louder".

 

[zumbo]

I am not so sure about this statement. The specs he supplied say:
89dB 1w@1m (4-ohm)
89dB 1w@1m (8-ohm)

Both speakers need the same power to achieve the same SPL. I believe you are correct however when the mfg. states the spec as something like 2.83V@1M for both 4 & 8 ohm speakers. In the case of 8-ohm the power is 1 watt and 2 watts for 4 ohms.

In the case of comparing speakers with the above specs, the 4 ohm speaker will be supplied additional power and will play louder the the 8-ohm speaker. But, it's only 2.4 db louder 10log(350/200) and not by any stretch 75% louder. Twice as loud would be about 6db, so this maybe could be called "a little louder".

This is along the lines of what I have always believed, but who is right?

 

[j_garcia]

Does that generally make 4 Ohm speakers less desirable/efficient/sound quality? Why would manufacturers make 4 Ohm speakers as opposed to 8 Ohm? Is there any advantage, other than power required, to one over the other?

I wouldn't say undesirable, just that it needs to be understood that they will draw much more current than an 8 Ohm speaker with similar specs. That means you just need to be sure to have an amp that will handle the lower impedance load. The nominal impedance is a result of the drivers used and the crossover chosen, so they probably don't go into the design thinking "Let's build a 4 Ohm speaker.", it just ends up being that the combination they've chosen to give them the specific sound they are after yeilds a low nominal impedance.

Both speakers need the same power to achieve the same SPL. I believe you are correct however when the mfg. states the spec as something like 2.83V@1M for both 4 & 8 ohm speakers. In the case of 8-ohm the power is 1 watt and 2 watts for 4 ohms.

I read somewhere just the other day, here I believe, that using 1w@1m measurement was not 100% accurate for a 4 Ohm speaker.

 

[Jack Hammer]

I read somewhere just the other day, here I believe, that using 1w@1m measurement was not 100% accurate for a 4 Ohm speaker.

That would make sense, I read a review at Secrets that listed my speakers (m&k lcr851 4ohm) efficiency somewhere in the mid to upper 80's. However, I heard plenty of times that M&K makes very efficient speakers, which didn't seem to agree with Secrets measurements.

Do you remember if there was a more accurate measurement for 4 Ohm speakers mentioned?

 

[Eric Apple]

Mid to upper 80's for 1 watt at 4 ohms does sound pretty good. MLs run about 89@2.83 volts. So that's 89db with 2 watts. So the m&k's only take about half the power of the ml's to produce the same volume. That's pretty good if you consider dynamic range power - the ML's would take 400w to produce the same volume as a the M&Ks driven with 200w. But, really it doesn't make much practical difference given it's only a little louder at 3 db.

If you were to consider two speakers with a 6 db difference, it would be worth considering as criteria to help decide a purchase. The same SPL produced by the MLs at 400w would only take 100w with a 95db/1m/1w speaker. That is an audible difference and 6db more headroom with the same amp.

 

[Buckeyefan 1]

In the case of comparing speakers with the above specs, the 4 ohm speaker will be supplied additional power and will play louder the the 8-ohm speaker. But, it's only 2.4 db louder 10log(350/200) and not by any stretch 75% louder. Twice as loud would be about 6db, so this maybe could be called "a little louder".

Not entirely true. Low-impedance speakers (4 ohms nominal or less) may cause problems with amps/receivers that aren't designed to deliver large amounts of current. A speaker with a sensitivity rating that's 3 dB higher than another speaker's only needs half as much power to deliver the same amount of sound.

Mac said:

Originally Posted by MacManNM
87 at 4 ohms is like 84 at 8.

What he was trying to get across was that the 8 ohm 84dB speaker has an extremely low sensitivity, and will need quite a bit of power to play at reference levels. A 4 ohm nomimal impedance speaker of 87 masks (or mimics) the spl rating, being able to increase the spec 3dB and still maintain the same output as the lower sensitive 8 ohm speaker.

Think of a little Chevy Geo Metro 3 cylinder engine starting out in first gear. Now think of a Dodge Viper V10 starting out in 3rd gear. The Metro will get up to speed quicker with less power, but redline quicker, while the V10 may start out slowly, but have plenty of power well beyond the Metro. You may need more power with a 4 ohm impedance speaker, but may realize more potential with more power.

Impedance is simply resistance. Here's a better explanation from www.electronics-tutorials.com

A simple example of impedance
Assume you have available these 4 items on your bench:

(a) A series of eight fresh AA type 1.5 volt cells to create a total of 12 volts supply.
(b) A 12 volt heavy duty automotive battery - fully charged.
(c) a small 12v bulb (globe) of very, very low wattage. and;
(d) a very high wattage automotive high-beam headlight.
Now if we connect the extremely low wattage bulb to the series string of AA cells we would expect all to work well. Similarly if we connect the high wattage, high-beam headlight to the heavy duty automotive battery all will be well. Well for a time anyway. Both of these sets are "sort"of matched together. Light duty to light duty and heavy duty to heavy duty.

Now what do you think would happen if we connect the high beam headlightto the series AA cells and conversely the low wattage bulb to the automotive battery?.

In the first case we could imagine the high beam headlight would quickly trash our little tiny AA cells. In the second case our min-wattage bulb would glow quite happily at its rated wattage for quite a long time. Why?, therein lies my expanation of impedance. Consider it!

The heavy duty battery is capable of delivering relatively large amounts of power but the series string is capable of delivering only relatively minimal power. The first is a low impedance sourceand the other, in comparison is a relatively high impedance source.

On the other hand the high beam headlight is capable of consuming relatively large amounts of power but the minature bulb is capable of consuming only minimal amounts of power.

 

[j_garcia]

Here's what I know from my own experience: My old speakers were Paradigm Monitor 5s. 92dB sensitive, two 5 1/4" mids and a 1" tweeter 8 Ohms. Current speakers are 91.5dB sensitive, dual 5 1/4" mids and a 1" tweeter, 4 Ohms. To achieve the same percieved loudness, I had to turn my receiver up noticably (unfortunately, I didn't compare with an SPL meter) from my previous config. I'm guessing that the difference on the dial was about +2 to +3.

 

[Eric Apple]

Not entirely true. Low-impedance speakers (4 ohms nominal or less) may cause problems with amps/receivers that aren't designed to deliver large amounts of current. A speaker with a sensitivity rating that's 3 dB higher than another speaker's only needs half as much power to deliver the same amount of sound.

We agree on that!

Since the specs he gave stated a power level at 4 ohms I would guess there's no issue w/4-ohm speakers. Don't see how the amplifer output impendence matters when the mfg rates it suitable for a 4 ohm load.

Simple answer is that of the two speakers listed in the first post, the 4 ohm speakers will play a little louder with the listed amp specs as the 8 ohm speakers. Throw a different amp in the mix, and the results might be different.

 

[zumbo]

I am only speaking of a seperate amp that can handle a 4ohm load.

 

[highfihoney]

the drawback that ive found in running 4 ohm speakers is that they require much better amplification over an 8 ohm speaker,some 4 ohm speakers ive seen have impendance dips well below 2 ohms & it takes one heck of an amp to go that low.

 

[Jack Hammer]

the drawback that ive found in running 4 ohm speakers is that they require much better amplification over an 8 ohm speaker,some 4 ohm speakers ive seen have impendance dips well below 2 ohms & it takes one heck of an amp to go that low.

If I recall correctly, the same article had my speakers only dipping to a low of 3.6 Ohms. I've been running them straight off my Denon 2805 w/o any issues. But am thinking of picking up a few of the Audiosource Amp One/A's next time they're listed on Ubid to run the fronts monobriged. After a few others have posted how much of a difference that has made for them, I think It will be worth for me to try.

I know there are better amps out there, but I bought one of these for $68+sh a few months back and for that price I don't think it can be beat. I should be able to pick up three more for under $250 delivered and they'll put out around 300 watts into 4 Ohms with minimal thd.

 

[mtrycrafts]

I read somewhere just the other day, here I believe, that using 1w@1m measurement was not 100% accurate for a 4 Ohm speaker.

No it is not 2.83V into 4 ohm load gives a 2 watt input. About 2V is 1 watt.

So, if 2.83 is used, one just needs to know that the 4 ohm speaker's spl is a product of 2 watts and go from there for the calcs.

 

[j_garcia]

Thanks. I couldn't remember which thread it was in.

 

[Jack Hammer]

No it is not 2.83V into 4 ohm load gives a 2 watt input. About 2V is 1 watt.

So, if 2.83 is used, one just needs to know that the 4 ohm speaker's spl is a product of 2 watts and go from there for the calcs.

Sooo....how does one go about calculating sensitivity?