Some help again please

mr2sw21

I been reading about Efficiency now and I understand the wattage will double for each 3db. Ok what does that mean in real life like when I raise up 3db in volume it will double the wattage?
Like my amp is start from -80db to 15db and the speakers are rated at some 90db and some 89db so lets talk about the 90 db one for now. So does that mean when I playing music at -80db I am using 1watt to drive the speakers? so when I get to -77db then I am using 2 watts? so when I get to -35 (whihc is about the degree I can finally hard something normally) I am basically using 32768 watts (by math since -80db to -35 is 15 times of 3db so 1x2 watt get up to 15 times is 32768 watts) that really does make any sense to me?
But then what is the deal with the spec of the speakers for 90db or 89db? I don't really understand?

By the way if my amp can drive 4 ohm speaker but I only have 8ohm speakers am I wasting the amp? What will the sound different form 4 ohm and 8 ohm by the way?:D

[Deleted User]

Hello,
A speaker's efficiency is a way of knowing the volume output, from the speaker, when a certain amount of power is given to it. The sound pressure is measured a certain distance away from the speaker and a certain amount of power is applied to the speaker. The result is measured in dB, in order to raise this number by 3dB you would need to double the power coming into the speaker.
Regards, Ken

cnh

Thanks Ken...

That's pretty much it. You can't do the math as you're doing it. Speaker efficiency just means you need less power to reach equivalent levels with a high rated speaker. This is why, for example, horn speakers like Klipsch can run Loud (not necessarily 'good') with even a very modestlly rated AVR or amp. And a speaker rated 84db needs much more power! In general terms 3 db increases in actual sound level pressure--not speaker efficiency, is the smallest unit that will make a difference in peception, in other words where your ears will hear an audible difference...but now we're not talking about speaker efficiency any more but something else.

cnh

[Deleted User]

Hello,
That is correct to make the sound pressure raise by 3dB the power has to be doubled. The efficiency remains the same. I should have been clearer that the efficiency is an intrinsic characteristic of the speaker and that the speaker's output changes with changes in input.
I believe 1 dB is the smallest amount of sound pressure changes that most listeners can detect. My feeling is that this depends upon the frequency content. I've made changes in a tape playback at 5kHz of less than 1dB and clearly heard it. But, in general terms 1dB is usually given as the number.
Regards, Ken

cnh

Thanks again...

I stand corrected...

cnh

Ron Temple

mr2sw21 wrote: »

I been reading about Efficiency now and I understand the wattage will double for each 3db. Ok what does that mean in real life like when I raise up 3db in volume it will double the wattage?
Like my amp is start from -80db to 15db and the speakers are rated at some 90db and some 89db so lets talk about the 90 db one for now. So does that mean when I playing music at -80db I am using 1watt to drive the speakers? so when I get to -77db then I am using 2 watts? so when I get to -35 (whihc is about the degree I can finally hard something normally) I am basically using 32768 watts (by math since -80db to -35 is 15 times of 3db so 1x2 watt get up to 15 times is 32768 watts) that really does make any sense to me?
But then what is the deal with the spec of the speakers for 90db or 89db? I don't really understand?

By the way if my amp can drive 4 ohm speaker but I only have 8ohm speakers am I wasting the amp? What will the sound different form 4 ohm and 8 ohm by the way?:D

The explanations above address your question generally, but to be specific...

The gain on your MV is just a range from 0 to max output. Somewhere close to your speakers sensitivity, say 90dbs at 1 watt/1 meter, your AVR will be putting +/- 1 watt to achieve +/- 90db SPL at a meter in that channel. That could be at -40,-30, -20 or even higher on your MV gain. It varys with each AVR or pre. So until you get to that point you are outputting less than 1 watt per channel. Above that point, you start doubling for every 3db of gain. That's not all. For every additional meter to your listening position you need to subract. So if you sit 3 meters from your speakers (typical) your 90db speaker at 1 meter is 84dbs at the listening position. Bring the MV up 10dbs (10x the power) and your still only using 10w per channel. Crank it another 10dbs and you're using approx 100w. This will pretty much tap out most AVRs and doesn't account for impedence dips and dynamic peaks that can require much more juice. That's why headroom and low impedence capability for speakers that represent a heavier load are so important.

To make my point, if you don't crank your amp/avr you generally only using a small fraction of it's output capability. When you do turn it up, the output requirement goes up very quickly. This is all very general and doesn't address many factors, room/boundary gain, colocation bonus, impedence dips, etc.

Jed Leland

Hello,
All points well said. Keep in mind you have two audio channels (assuming stereo reproduction) two speakers each with a certain rate of conversion adding to the total sound pressure levels. I believe the old 3dB increase comes into play? Also this is assuming you are using point source speakers, which behave differently than line source speakers in terms of how the sound pressure reduces as distance increases.
Your question about how a 4 Ohm impedance differs from an 8 Ohm impedance is somewhat correct. Think of putting the same 200 horse power motor in two cars that weighs different amounts. Different 0 to 60 mph results, all things being equal. So, yes a lower impedance means more power can be produced by the amplifier. That's why car speakers tend to be less than 3 Ohms now, more power. If you wanted the most amount of power (all things being equal, again) the load impedance would be the same as the amplifier's output impedance, a fraction of a Watt. Of course, there are other factors at work, but the power transfer would be maximum.
Then there's the issue of the speaker generating a reverse voltage opposing the power coming into the speaker. Bigger speakers with lots of moving coils produce fairly large amounts of back EMF, swamping the incoming power. Take the grille cover off of your speakers, sometime, disconnect the power wires coming into the speaker and push on one of the woofer cones. Then put a shorting wire across the speaker's positive and negative terminals. Then push again and the movement will be stiffer. The excellent IMF speakers from Britain used to have shorting wires across their terminals to prevent the woofer cones from moving so much. That's what high damping factor amplifiers do, act like a shorting wire when there's no audio being produced. It stiffens the bass response by shorting out the woofer coils. That's why those large multi-driver SDA speakers need lots of power, high EMF swamps the power from receivers and there needs to be high damping factor to stop those coils.
Cheers, Jed

mr2sw21

Hi hi,

Thanks all of you. I think I understand a bit more about speakers now.
Since cars can have 3ohms speakers why can't we have something like that. Seem like only top of the line of polk has something like 4ohms is the max and all the rest of the lines are 8 ohms is making lower ohms a harder technology?

Sorry for being not smart, I still don't quite understand how to apply the efficiency of the speakers on real life. Let say my amp is using 140w per channel and each speakers is 90db efficiency. and the range of the amp is -80bd to 15db at normal rate of listening is about -35db so what wattage I am actually using?

By they way I just purposely buy a UPS that have LCD to show how many watt I am using but it really surprise me the AV receiver actually using about 135W consistently so I guess the AV receiver is not a really power killer at all.

Again thank you for everyone's help here.

Ron Temple

mr2sw21 wrote: »

Hi hi,

Thanks all of you. I think I understand a bit more about speakers now.
Since cars can have 3ohms speakers why can't we have something like that. Seem like only top of the line of polk has something like 4ohms is the max and all the rest of the lines are 8 ohms is making lower ohms a harder technology?

Sorry for being not smart, I still don't quite understand how to apply the efficiency of the speakers on real life. Let say my amp is using 140w per channel and each speakers is 90db efficiency. and the range of the amp is -80bd to 15db at normal rate of listening is about -35db so what wattage I am actually using?

By they way I just purposely buy a UPS that have LCD to show how many watt I am using but it really surprise me the AV receiver actually using about 135W consistently so I guess the AV receiver is not a really power killer at all.

Again thank you for everyone's help here.

I'll let someone else tackle your impedence question specifically. In general, the lower the impedence of a speaker the higher the current demand and the greater the load on the amplifier. All AVRs are rated with 8 ohm loads in their specs, some offer a 6 ohm spec and a few heftier ones are 4 ohm stable. The lower the impedence the higher the current and it generates more heat and instability in mainstream consumer products. Loud playback usually will drive an AVR into protection.

At -35 on your AVR you're watt output will be very low and will vary depending on the source demand. It might vary from less than a watt to a 10-15w peak. There's no way to know without putting a multimeter on it. That 140w rating is most likely based on running a sine wave at max output with 1 channel driven at 8 ohms, either 20hz-20khz (a true test) or at 1khz (a very weak test, which means your AVR is much less capable than spec).

For everyday at modest volume levels your AVR will never output 140w. It's capable of 140, but it's all dependent on the demand of the source material. A movie will have up to 20db peaks in the main channels, 30 in the LFE channel. Say you're watching at -35 and you AVR is outputting less than a watt average and just a few for minor peaks. Along comes a 20db major peak. Your output demand is now x 100. If your cruising at 1/4 watt, that peak is demanding 25w of output. The louder you listen to your source the greater the demand. As you get closer to -0 on your AVR MV, you're going to run into a peak that will exceed your output capability.

Hope this helps.

mr2sw21

Ron Temple wrote: »

I'll let someone else tackle your impedence question specifically. In general, the lower the impedence of a speaker the higher the current demand and the greater the load on the amplifier. All AVRs are rated with 8 ohm loads in their specs, some offer a 6 ohm spec and a few heftier ones are 4 ohm stable. The lower the impedence the higher the current and it generates more heat and instability in mainstream consumer products. Loud playback usually will drive an AVR into protection.

At -35 on your AVR you're watt output will be very low and will vary depending on the source demand. It might vary from less than a watt to a 10-15w peak. There's no way to know without putting a multimeter on it. That 140w rating is most likely based on running a sine wave at max output with 1 channel driven at 8 ohms, either 20hz-20khz (a true test) or at 1khz (a very weak test, which means your AVR is much less capable than spec).

For everyday at modest volume levels your AVR will never output 140w. It's capable of 140, but it's all dependent on the demand of the source material. A movie will have up to 20db peaks in the main channels, 30 in the LFE channel. Say you're watching at -35 and you AVR is outputting less than a watt average and just a few for minor peaks. Along comes a 20db major peak. Your output demand is now x 100. If your cruising at 1/4 watt, that peak is demanding 25w of output. The louder you listen to your source the greater the demand. As you get closer to -0 on your AVR MV, you're going to run into a peak that will exceed your output capability.

Hope this helps.

Ron, I really appricate your input. The part that I am confuse is what do you mean by power demanding? Do you mean the speakers? And sound like you mean when I am playing different stuff let say movie vs music if I play at same volume is there differece on the power?

mr2sw21

by the way is there any thing like TEST dvd or stuff like that so I can actually test if my set up is doing from 20hz-20khz?

cfrizz

He means whatever you are playing whether a movie or music. If you have the volume say at -10 and the movie you are watching has a big explosion, naturally there is going to be more demand on your receiver to increase the volume to the speakers. The same with music.

Since your receiver is already being pushed pretty hard already, it just might not have enough power left to give the speakers what they need to play that explosion. The receiver will try to do so, but not having it to do, the risk is great for the speakers clipping, and/or the receiver shutting down in protect mode from overheating. The potential for this happening increases dramatically when running speakers like the LSI's.

The tests done on receivers are really nothing even close to what happens in the real world. with 5-7 speakers being operated at the same time.

mr2sw21 wrote: »

Ron, I really appricate your input. The part that I am confuse is what do you mean by power demanding? Do you mean the speakers? And sound like you mean when I am playing different stuff let say movie vs music if I play at same volume is there differece on the power?

Hillbilly61

These are tremendous responses! In hopes of offering a summerized "cheat cheat" and not butchering facts too much along the way:

1. Efficiency represents the wattage needed to reach a certain speaker output sound pressure level at a given distance. Values are in decibles (db) and the standard distance is 1 meter;

2. A 3 db increase results in 50% more input power. 3db is most often perceived as a significant increase in loudness. To get an 84 db speaker to broadcast at 87 db, 50% more power is needed.

3. To double the perceived loudness, say 84 to 90 db, 4X the input power is needed. Doubling loudness squares the required input power.

4. Hand in hand with speaker efficiency, come the power level used for it to use its rated db level. For example, 20 watts may be required for the speaker to operate at it's rated efficiency. Read items 2 & 3 concerning additional power implications for making a speaker sound lower.

5. The output sound pressure level will drop in relation to the increase in the distance from the speaker. Theoretically, a change from one meter to four meters will drop it by 4X. A major attenuating factor that I do not have a good handle on lay with the speaker size. Speakers move air. Smaller ones move less air volume than bigger ones.

6. The dynamic range in modern digital content is very broad. If the root mean squared average db of all of the sounds being delivered via the speaker suddenly increase (explosion, etc), then the amps required to be delivered results in many more watts to achieve the required db increase. The amp may not have it available, resulting in clipping.

7. The lower the impedance the speaker is operating at, the greater the amps are required. Watts (what the amp is delivering) is measured by voltage multiplied by amps. The delivered voltage stays more or less constant. Amps required by the speaker increases if the relative resistance is disminished or if a certain loudness level is desired. Zero resistance theoretically results in infinant amps being required.

Nothing can deliver infinant amps. Therefore, wiring overheats (fries) as too much current is being delivered for the amp's wiring. The amp's internal resistance doesn't change much. Delivered high amps results in the amplifier heating up.

mr2sw21

oh so is that why some sub woofer needs to have 3000w, 4000w so to prevent clipping?
By the way sounds like 8ohms is easier to handle power then I still don't understand what is the benefit for 4ohms speakers?

cfrizz

You mean the 8ohm speakers are easier to power, which it true. However, they too benefit from more power with better dynamics, bass, & clarity.

From what I have gathered. Matt didn't set out to design 4ohm speakers, it just pretty much happened because of the parts used & the sound he wanted to achieve.

Regardless of that, it is just a fact that 4ohm speakers are harder to drive which means shelling out more money to buy more power to make sure they aren't unduly stressed.

You either want to cough up the money to buy more power or you don't.

mr2sw21 wrote: »

oh so is that why some sub woofer needs to have 3000w, 4000w so to prevent clipping?
By the way sounds like 8ohms is easier to handle power then I still don't understand what is the benefit for 4ohms speakers?

apphd

mr2sw21 wrote: »

oh so is that why some sub woofer needs to have 3000w, 4000w so to prevent clipping?
By the way sounds like 8ohms is easier to handle power then I still don't understand what is the benefit for 4ohms speakers?

Part of a reason. I would guess the subs you see with high power amps are sealed subs which would offer more resistance (physical not electrical) to the driver moving. The air inside the sealed sub, with no place to go is an opposing force to the movement of the driver. Maybe not a good comparison but a driver is an electric motor. A sealed box would be like a high compression internal combustion engine, if you were trying to start it with out a starter. It takes more force to overcome this.
Another part of this is that bass frequencies by nature take more power to generate.

Yes 8 ohm speakers are easier to power. But it's not a matter of 4 ohm speakers sounding or being better. There are many fine 8 ohm speakers and probably as many bad sounding 4 ohm speakers. Which I think is what cfrizz was referring to with the LSi. They were not designed to be 4 ohm speakers but were designed to be very good sounding speakers and after all the design and driver selection turned out to be 4 ohm speakers.

McLoki

ok - to add on to or correct a few Db facts....

3db increase - requires double the amplifier power.

10db increase - requires 10x the power and is usually considered twice as loud.

3 to 6 Db increase - when you double the number of speakers (when playing the same thing at the same volume) Vairable based on how close together the speakers are and what frequency they are playing. - Suffice it to say that if you have one speaker and add another one it gets louder. If you have 4 speakers and add another one - not so much......

6db decrease - every time you double the distance from the speaker. Efficiency is usually rated at 1 meter (39 inches) if you happen to sit 12-13' back from your speakers - the efficiency is actually 12db lower than what is advertised.

subs... It all comes down to physics. To get deep bass, you need a large box. To let your wife let the sub in the living room, you need something small no one would notice... To get around this - many manufacturers build subs in small boxes, tune them low with passive radiators (since a port will not fit in such a small box), and boost the low bass via an equalizer to get it to play flat and low. As mentioned above - if you boost by 10db it requires 10 times the amplifier power. If you boost by 10db at 20hz, your 2,000 watt amp could be replaced by a 200 watt amp in a larger enclosure that does not need the boost.

Michael

mr2sw21

thanks so much guys for those information. I think I started to understand about my system a bit more now. thanks again.

so I remember one was mentioning clipping, what cause this happen the amp has too much power and the speakers can't handle? or the other way the move require more power then the amp support? Does any has any problem with Polk speakers of clipping?

mr2sw21

so what is the deal with Tube amp why people likes them? Do they make more power?

cfrizz

No, they usually are made with less power, and are extremely expensive. What they do, is change the sound over what a solid state sounds like, which some people prefer.

They also offer the flexibility to change the sound by switching out different tubes. In other words tweeker heaven.

I'm not interested in tweeking or fiddling with my gear. I just want to sit down & listen to the music knowing that my speakers are getting all the power they need to operate to their full potential.

I also don't like the more subdued (tubers call it warmer) sound that tubes offer. If I'm listening to a live music piece, I want it to be loud & in my face like I'm right there at the concert. I don't want some tepid sound that makes me think there's a blanket over the speakers.

mr2sw21

so I recently got the Yamaha RX-Z7 and my setup is VM30 front, VM20 center and surround, and TSi200 for back surround, and (for now) PSW110 for sub. Does the Z7 has enough power to drive them or do I need extra amp?

McLoki

You should be fine, I would not worry about an external amplifier if I were you. If you have money to burn - get a better sub.

(although you can clip almost any amp by turning it up to high - similar to saying I got an accord rather than a corvette so I should not get any speeding tickets right??)