Underpowering speakers?

[gdew]

I have a pair of JBL 4412s and am currently waiting for a Yamaha P3500s amplifier to arrive in order to power them.

These speakers have an RMS rating of 150 watts and the amp I have bought is rated at 375 watts (at 8 ohms). The problem I have the speakers, but the amp is going to take two or three weeks to come into the country.

In the mean time I thought I would try powering the speakers with an old cheap amp my parents had lying around (A pioneer sx-p520, which is an integrated amp from an all in one system.). I don't know what the rating of this amp is, but the sticker on the back of the speakers that would normally be powered by this amp says max power 40 watts, so I assume the amp isn't very powerful.

Anyway, I hooked it up and the sound is there but it is quite muffled, like a wet towel has been placed over the speakers. I am being careful not to clip the signal, but still I can make the sound quite loud, although the dynamics in the amplitude do seem to be limited. Given my speakers are new and haven't been broken in, my question is this constrained sound a product of the speakers not getting enough power, or something else (like them not being broken in or quality of the amp etc) and can driving speakers without enough power be damaging to the speakers (as long as they don't clip)?

Thanks

[Swerd]

To the best of my knowledge, using a low powered amp with speakers poses no danger to the speakers, as long as you avoid driving the amp into clipping. If the amp is clipping you might damage some speakers. It depends on how ruggedly the speaker drivers were built.

The JBL 4412s (at least those made in the 1970s) had a reputation for efficiency and rugged construction. They could be easily driven by amps under 30 watts and could also handle the power of amps of greater than 150 watts. I don't know if new ones are built to the same standards.

Your description of the sound being quite muffled, like a wet towel has been placed over the speakers. suggests that the problem may be due to something other than the lower power of the old Pioneer amp, or the newness of the speakers. The amp, or your sound source may be malfunctioning. If you are using a CD player, try switching to a different sound source such as FM radio, turntable, tape recorder if any of these are available. After the switch, is the problem still there? It may also be something as simple as a poor connection between the sound source and the amp. Look at the interconnect cables and make sure they are firmly connected. The RCA jacks on the old amp may be tarnished.

If the problem is within the amp, be patient and wait until your new amp arrives. But I doubt if you will damage those speakers.

[gdew]

Ok, thanks. That puts my mind to rest.

By the way, one thing is really confusing me. The amp I am using, it would seem, is about 1/9 the power of the amp I am buying. I chose the amp because its rating was well suited to that of the speakers, but the amp I am using is still producing a lot of sound from the speakers. The fidelity isn't there, but it can still shake the room. Why is this?

How can such a low powered amp driving such high rated speakers?

[Swerd]

How can such a low powered amp drive such high rated speakers?

Don't confuse the power output of an amplifier with the power "rating" of a speaker. Consider the speaker's power rating as the manufacturer's suggested minimum and maximum amplifier power values for the speaker. They are guidelines, not requirements for the speaker.

The minimum value is a reflection of the speaker's efficiency, measured by how loud the speaker is when driven by 1 watt under standard defined conditions. Most speakers deliver about 85 to 92 decibels (db) with 1 watt, where more db is louder. Note that loudness in db is not a linear scale, 3 db more is twice as loud and 3 db less is half as loud. All decent speaker manufacturers provide efficiency values for their products. The fact that your speakers are loud with a low powered amp probably means that they can deliver 90 db or more with 1 watt. As you've noted, that is loud. Typical listening levels are lower, in the 75-85 db range. And they involve continuous power levels of less than 1 watt!

The maximum power value for a speaker is the manufacturer's estimate of the power their speaker can take without getting damaged. One hopes it is a conservative number. It is a reflection of how ruggedly constructed the woofers and tweeters are. When speakers are over driven, usually it is the tweeter that fails first.

When you get your new amp, it should make quite a potent combination with those speakers.

[_Luke1_]

Many years ago I had a similar experience. I was powering a pair of bookshelf speaks with an old Technics receiver rated around 40 wpc x2. Then I got a par of CV AT-12's. A few years later I decided to get into HT and started into upgrading it all with a Denon Pro-logic receiver rated at 70 wpc. I never did get that HT off the ground, but just the upgrade for two channel to the Denon was astounding - the single biggest upgrade I've ever heard.

Even though the CV's were fairly efficient, they sounded so much better with more juice. Based on that, my bet is your new amp will improve things.

[jbangelfish]

And should provide you with whatever you are missing. Is that power rating per channel or total for the amp? If it is per channel, you might need to worry about too much power. I'm a power nut and like to give them what they can take but worry about overdoing it. Speakers can be damaged by underpowering and driving to clipping, or so I've read. I've never done it but I won't argue that it is possible. I believe it would be easier to damage them with too much power but you might damage your eardrums first.
I'm not so sure about every 3db being twice as loud. Twice the power is required for every 3db increase. I've never heard this described as twice as loud. I can't say that this is wrong but I've never heard it explained this way. I did not think that the decibal scale was an exponential one. Seems to me that I read somewhere that 1db was what human perception could discern as a difference in volume. If this is even close to the truth, then 78db would certainly not be twice as loud as 75db, etc. Anyone, feel free to explain this in a way that we can all understand.
One thing is fairly certain. You will like what your new amp does when compared to your old one, provided that you don't have any of the other problems that were mentioned and all wiring is correct.
Bill

[Swerd]

Decibel:
A unit for measuring sound or power ratios. As originally developed, the gain or loss of power expressed in decibels was 10 times the logarithm of the power ratio. The numerical value of one decibel is approximately equal to the smallest change in volume of sound that the normal ear can detect. The scale of decibels is logarithmic, every increase of 10 dB representing an increase of about 300% in sound.

see http://composite.about.com/library/glossary/d/bldef-d1484.htm?terms=decibel

So it looks like we're both right :D

[jbangelfish]

You did show the correct spelling of the word which I missed. Always glad to learn how to spell. The rest of it loses me alittle. 10db = 300% increase in sound. SPL? If so, you are right. Not a math whiz, not an engineer but makes no sense to me how 10db increase from 0db or 90db could equal 300%. Still could be the case, not sure.
3db, needing twice the power, that one I understand.
Bill
PS, Always loved the photo you use. What company was that an ad for? Goes back a ways.

[Swerd]

…makes no sense to me how 10db increase from 0db or 90db could equal 300%…

The use of the term "300%" can be confusing depending on how you define an increase of 100%. I normally think of 300% as a 3-fold increase over some original value. But if you think of a 100% increase as a doubling of the original value, then a 300% increase is three doublings of the original value. So one doubling in sound is actually 3.3 db (10 db ÷ 3 doublings = 3.3 db). But who cares whether it is 3 or 3.3?

If my handwaving didn't explain it well enough and you really want to go back to school, try this: http://www.phys.unsw.edu.au/~jw/dB.html

The photo is from a Maxell audio tape ad from the late 70's. Its funny that you mention it because the speaker on the floor blowing the guy away was the consumer version of the same JBL 4412s that the original poster of this thread now has. gdew buddy, I hope you have everything nailed down when you try that new amp.

[gdew]

If the 1 watts can produce 85-92db, what happens when you try to produce the same amplitude with more watts.

A watt is made up of volts and amps, does this mean that volts determines amplitude and the amps determine the strength of the signal. So although 1 watt could produce that high amplitude it couldn't maintain the fidelity of the sound because there are no amps to back up the high number of volts. I am only guessing, trying to make sense of all this.

Could someone please put me straight!

I have heard the big and little brothers of my speakers in full flight (the JBL 4311s and LSR 32s) and at any volume they sing with such fidelity, clarity and force it is amazing. I can't wait to hook mine up and let them loose!

[Swerd]

If the 1 watts can produce 85-92db, what happens when you try to produce the same amplitude with more watts.


When speaker efficiency is measured, it is done under certain standard conditions that allow comparisons with other speakers, but don't resemble the way we actually listen to them at home. A signal, usually pink noise, is fed to a speaker. The amplifier output is measured and adjusted to 2.83 volts (if the speaker has a nominal impedance of 8 ohms, see below). A microphone is placed 1 meter away, directly in front of the speaker, and the loudness is measured. That is much closer than I (and I hope most of us) sit when listening. Also the room where they do this is acoustically dead so that the microphone picks up little if any sound reflected from the walls. At home wall reflections and also room dimensions play a big part in what we hear.

The bottom line is that your speakers when driven by that amp will be capable of delivering loud listening levels at less than 1% of its total potential output. It leaves plenty of power available for those very short moments in the music that call for much higher power levels from the amplifier. This is a good thing. We all wish we could pay for such power ;) .

Watts and volts are related. In practice voltage is directly measured with a meter, and wattage is calculated. Someone correct me if I'm wrong about that.

Here is some textbook stuff I cut & pasted from:
http://whatis.techtarget.com/definition/0,,sid9_gci294147,00.html

Watt: A unit of power equal to 1 joule per second; the power dissipated by 1 ampere flowing across a resistance of 1 ohm; the power produced by 1 ampere under an electromotive force of 1 volt. One horsepower is equal to 746 watts.

Volt: The unit of electromotive force. You may want to think of it as analogous to water pressure.

The watt is the standard unit of power (energy per unit time) and is defined as one joule per second. The watt specifies the rate at which electrical energy is dissipated, or the rate at which electromagnetic energy is radiated, absorbed, or dissipated.

In direct current and low-frequency alternating current electrical circuits and systems, power (P) is calculated as the product of the voltage (E) times the current (I).

P = EI

Power is also equal to the square of the voltage divided by the resistance (R)

P = E²/R

And power is also equal to the square of the current times the resistance.

P = I²R

At the top where I talk about measuring speaker efficiency, I said the amplifier was adjusted to 2.83 volts. If you use the 2nd equation, P = E²/R, and plug in 2.83 for E and 8 for R, you will get P = 1 watt. If a speaker has 4 ohm impedance, you will get 1 watt with 2 volts.

I hope all this helps.

[jbangelfish]

It tells me what I already knew and gives some technical explanations. I see that it says +3db requires twice the power, +10db requires 10x the power, this we knew.
I don't see anywhere that it says +3db anywhere in the scale is equal to twice as loud. If 1db is the difference that normal hearing can perceive, which was what I said and you verified, then going from 75db to 78db is not twice as loud. If you find this anywhere, let me know.
It did mention a 300% difference in sound which 3 db would be with each decibel being 100%. Maybe we're looking at this in different ways.
Maxell, now I remember, I think the ad was on TV too. Cool pic.
Bill

[FLZapped]

I have a pair of JBL 4412s and am currently waiting for a Yamaha P3500s amplifier to arrive in order to power them.
.....
Anyway, I hooked it up and the sound is there but it is quite muffled, like a wet towel has been placed over the speakers.

Thanks

Hmmm, the last set of speakers I listened to that sounded like that had the tweeters blown.

Did you just buy these things too????

-Bruce

[Swerd]

Bill

I kept looking for something to back me up. Instead I may have to agree that you're right. Look at this:
http://arts.ucsc.edu/ems/music/tech_background/TE-06/teces_06.html

In the 3rd paragraph it says:

The usefulness of all this becomes … … In the second place, our judgment of relative levels of loudness is somewhat logarithmic. If a sound has 10 times the power of a reference (10dB) we hear it as twice as loud. If we merely double the power (3dB), the difference will be just noticeable.

The just noticable difference level seems to be getting lower. Standard textbooks have it as 3 dB. Lately some have pushed it down to 1 dB, with claims of 0.3 dB at certain frequencies.

Maybe that is how I got 10 dB mixed up with 3 dB for the twice as loud level :confused:

Good talking with you. Your persistance is matched by your politeness. I hope we didn't lose the original poster with all this dB babble.

[jbangelfish]

I enjoyed this too. We did get off the subject of the original poster, at least off on a tangeant. This happens often here and I'm sure the original question poser is left scratching his head. I guess this is what makes an audiophile, enough interest to bore the sane people to death. Thanks again,
Bill

[gdew]

No I am enjoying this, although yeah a lot of it is going over my head.

I am nerd too, I am just not getting this notion of the makeup of any given watt and the effect that make up has on the output of the speaker.

My original query was sparked by using two low powered amps to power what I would consider to be quite powerful speakers. The amps, when turned up at the volume that would power speakers rated for their output (in this case speakers made specifically for the amp), produce a signal from the high powered speakers, the JBL 4412s, and quite a loud signal.

The quality isn't good at all, but the sound is still there loud and bolshy. On this basis there must be different properties associated with the signal output amalgamated into a determination of wattage. What I am curious about is what the different element of the current do to the speakers performance.

Swerd, you said the amp's output is adjusted to 2.83 volts. If this is also one watt, then according to my calculations (which don't nessesarily conform to any mathematical rule) the output would be about .35 amps.

Does the 2.83 volts moderate the amplitude of the speaker? Do the amperes control the fidelity of the movement of the cone (due to strength of the current)?

If this watt containing 2.83 volts can make the speaker produce a sound as loud as 85-92 dB, what would happen if you fed the speaker 100 watts with 2.83 volts? Or one watt with 5 volts? Or 100 watts with 10 volts?

The resistance is a property of the speaker, cables etc (mainly the speaker). The equation you used used the property of the resistance and the voltage to determine the power of the amplifier. I am interested in the properties of the signal emitted by the amplifier and its effect on the output of the speaker (via the internal mechanics). Anyway thanks, I am finding this thread very interesting.

[mtrycraft]

Note that loudness in db is not a linear scale, 3 db more is twice as loud and 3 db less is half as loud.


Just a small correction. While a 3dB increase in power is a doubleing in power, you need almost 10 dB spl increase to subjectively evaluate this as twice as loud. :) So, you need 10 times the power to perceive 2X loudness :)

[RGA]

Bill

I kept looking for something to back me up. Instead I may have to agree that you're right. Look at this:
http://arts.ucsc.edu/ems/music/tech_background/TE-06/teces_06.html

In the 3rd paragraph it says:

The usefulness of all this becomes … … In the second place, our judgment of relative levels of loudness is somewhat logarithmic. If a sound has 10 times the power of a reference (10dB) we hear it as twice as loud. If we merely double the power (3dB), the difference will be just noticeable.

The just noticable difference level seems to be getting lower. Standard textbooks have it as 3 dB. Lately some have pushed it down to 1 dB, with claims of 0.3 dB at certain frequencies.

Maybe that is how I got 10 dB mixed up with 3 dB for the twice as loud level :confused:

Good talking with you. Your persistance is matched by your politeness. I hope we didn't lose the original poster with all this dB babble.


The trouble is there is the math and then the perception. 3db increase require twice the amplifier power and this increase in volume is barely noticeable...ie a 100 watt amp over a 50 watt amp volume wise is hardly worth the effort and expense.

To get a "PERCEIVED" doubling of the volume level requires ten times the power. OR, a 500 watt amp will be twice as loud as a 50 watt amp to our ear. The perceived doubling of volume and the "actual" doubling of volume are not the same. ~6db is the actual doubling level or a 200 watt amp over the 50 watt amp. I always wonder because 6db may not be a perceived doubling but it is certainly very noticeable, which is why people buy 200 watt amps(assuming their speakers can take the added power).

Of course if one buys a 6db more sensitive speaker then one only needs the 50 watt amp to get the same volume level.

It's far easier to remember that doubling the amps power is not very noticeable and ten times the power is double the volume to our ear. OR a 10db higher speaker sensitivity rating will be perceived as twice as loud - 6db gain though is considerable. My 95db Wharfedale speakers take far fewer watts than say the Paradigm Studio 100...but will play significantly louder overall than the Paradigm due to a much higher sensitivity.

[Swerd]

I always like to say there is no such thing as a dumb question – only people who don't ask questions because they fear it will make them appear dumb. So in that spirit I will try to answer your questions. I think you understand more than you give yourself credit for.

If this is also one watt, then according to my calculations (which don't nessesarily conform to any mathematical rule) the output would be about 0.35 amps. Yes.

Does the 2.83 volts moderate the amplitude of the speaker? Yes.

Do the amperes control the fidelity of the movement of the cone (due to strength of the current)? My first reaction is to say no, but I’m not sure I understand what you are asking. You cannot control volts and amperes independently. Is that what you are asking? Volts and current both contribute to the amplitude response of a speaker. Fidelity is another matter altogether that is completely different from speaker efficiency.

If this watt containing 2.83 volts can make the speaker produce a sound as loud as 85-92 dB, what would happen if you fed the speaker 100 watts with 2.83 volts? Or one watt with 5 volts? Or 100 watts with 10 volts?

Remember P = E²/R. For purposes of simplicity, R is a constant 8 ohms. (In reality, speaker impedance varies some with the frequency of the tone being reproduced, but lets avoid that complexity now.)

Wattage (P) varies with the square of the voltage (E). If 2.83 volts produces 1 watt with a speaker of 8 ohms impedance, then you would need 28.3 volts to produce 100 watts. The amplifier could not produce 100 watts with an output of 2.83 volts unless the speaker had a much lower impedance of 0.08 ohms. So you cannot produce 1 watt with 5 volts or 100 watts with 10 volts as you asked. The only thing you can vary is the voltage by adjusting the volume knob. The impedance load of the speaker determines what power and current the amplifier delivers, or tries to deliver.

Your original query was sparked by using two low powered amps to power what I would consider to be quite powerful speakers. The amps, when turned up at the volume that would power speakers rated for their output (in this case speakers made specifically for the amp), produce a signal from the high powered speakers, the JBL 4412s, and quite a loud signal. The quality isn't good at all, but the sound is still there loud and bolshy. On this basis there must be different properties associated with the signal output amalgamated into a determination of wattage. What I am curious about is what the different element of the current do to the speakers performance. Now you've completely lost me. What's bolshy?

It occurs to me that you may be describing a fidelity problem and not an efficiency one. It may be that the old amplifier is not only low powered but defective. You should find out soon with the new amplifier.

It may also be that the tweeters on your new speakers are damaged. Someone already suggested that in this thread. I hope that is not the case, but they are new. Are they covered by a warranty? Do your speakers have an adjustable high frequency? Look behind the speaker or behind the grill for a knob or a switch that attenuates the tweeter output. Play with that to see if you can hear whether the tweeters are functioning at all. Let us know how it turns out.

[jbangelfish]

If my very limited knowledge of electrical current is correct, then your math is also correct. Just how an amp produces the watts, I don't know. If the voltage is steady at 2. whatever, the amperage would have to be raised accordingly to produce more watts. Either way, more volts, amps or both, more wattage would be produced.
My amps are rated at 50 amps continuous or 90 amps peak and are also rated at 750 watts continuous. By my math, this would mean 15 volts are required to produce the 750 watts. I'm not going to tell you that I know how this works or how the amps work because I don't. If they tell me that an amp has 750 watts at 8 ohm or 200 watts at 8 ohm, that's good enough for me.
Your questions about what happens if you produce 1 watt with 10 volts or with 100 volts, etc., I cannot answer. Obviously, you would be changing the amperage but how this would affect your speaker or sound, I don't know. There could be a number of ways to produce 100 watts and my guess is that with class A, AB, B, C, and many others that they have done just that.
If you understand that 3db requires twice the power, you should also understand that your new amp is not going to play tremendously louder than what you already had. What you will notice is better detail, clarity, bass and everything else that you would expect from those JBL's. You should no longer hear muddiness, clipping, distortion or any of that other nonsense that comes from not enough gas. And, it will play somewhat louder. Let us know the differences when you get your new amp.
Bill

[gdew]

Is the voltage maintained during AMPlification?

I am sorry if these question are dumb, but thanks for answering them!

[jbangelfish]

It seems to me that we are increasing both volts and amps as we increase volume. I'm not sure how it's done but we know that the wattage increases with the volume. I don't really worry about how they do it. Skeptic, Mtrycraft and others could probably give you the full answer. To me, it's not imperative to know exactly what each and every piece of an amplifier does. If I were going to build or modify an amp, I'd have to learn some more.
Bill

[skeptic]

Turn the volume down low. Turn the treble control high and the bass low. check that any high cut or hiss filter is off. set the fm tuner between stations with the interchannel muting off if possible or use program mateiral with lots of high frequencies like bells, violins, or a female voice. Put your ear right up to each tweeter. If you can't hear them, the tweeters are blown unless there are fuses protecting them which are blown. If the tweeters are not blown, listen to music with lots of high frequency content. Gradually increase increase the volume. If you hear the tweeters start to distort or crackle, they are damaged. With the bass down, this test does not require much amplifier power. Listen carefully to the mid range speakers as well. Breaking in the speakers or changing amplifiers is not likely to make a major difference in the overall tonal balance of the speaker. Check for tweeter level controls. Sometimes they are behind the grill cloth. Turn them up all the way if you have them and listen again. If you bought these new from a store, be prepared to return them for an exchange. If you bought them used, be preprared to negotiate with the seller for the cost of repair. It is entirely possible that you prefer speakers that are simply brighter sounding than these but from your description, there is the real possibility that something is wrong.

[skeptic]

From the photo on E-bay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3065254048&category=14993
it is clear that the tweeter and midrange controls are behind the grill cloth. sometimes these controls fail and need to be cleaned or replaced for their respective speakers to work.