Jump to content

How "loud" is that amp?


Phil O'Keefe

Recommended Posts

Thanks... I could have gone into a lot more depth and detail in terms of the "math", but like I said, I don't want to see eyes glazing over... :lol: if I can simplify it for the regular Joe; forgo formulas and make it fairly understandable in terms of the basic "concepts", then maybe it would be more helpful to a larger amount of guitarists. That was the intention anyway... :idk::o

 

Thanks for reading it. :):o:wave:

Link to comment
Share on other sites

  • Members

The thing that always gets me is how anyone can determine what is twice is loud. I mean really, how do you know? Sure, one amp will be louder than another, but it seems like it's almost impossible to judge what is actually twice is loud, without having an SPL meter on hand.

Link to comment
Share on other sites

are less efficient speakers more desirable for guitarists? what are the cons of a more efficient speaker? iow, why don't the amp builders use these in the first place?

 

Excellent questions!

 

Originally, less efficient speakers with relatively low power handling capability were utilized in guitar amps because that was all that was readily available. Over time, more efficient designs were made; speakers with higher sensitivity, greater power handling capacity, and wider frequency response... but they tend to cost and weigh more. Also, tonal considerations come into the equation. A more efficient speaker may - or may not - be to your liking. Guitarists are fairly finicky and conservative traditionalists in terms of their gear. AlNiCo speakers (that utilize AlNiCo magnets) are still favored by some, even though rare earth magnet materials (neodymium, samarium cobalt, etc.) are stronger and more efficient. Ceramic magnets are often utilized because of their relatively low cost... it's always a trade off in terms of weight, cost and performance... and sound. :)

 

Remember, "speaker breakup" and other tonal contributions from the speaker may be considered beneficial, even though they are the antithesis of "accurate". The E/V 12F (a 12L variant made for Fender) in my Princeton Reverb II has 200W RMS power handling capability, is highly efficient and loud as hell (~101 - 103 dB @ 1W / 1m), but it doesn't even began to strain or break up under the influence of that little 20-22W amp. It has a huge, open and big bottomed sound to it, and sounds completely different than the 15W Weber Blue Dog in my AC15, which not only has different frequency response characteristics, but also strains and distorts when pushed. It's not "better" (except in terms of power handling capacity and efficiency) or worse, just "different".

 

Sometimes we guitarists want that tonal contribution from the speaker. A Celestion Greenback breaking up has a distinctive sound to it, and it contributes positively to the sound of a wide open Marshall. A Blue is closely associated with the classic "Vox sound", just as the old Fender Jensens are the voice of old Blackface amps. Also, wide range frequency response is not always desirable in a guitar amp and speaker. We LIKE that bandpassed sound, with nothing much going on above 5-6kHz or so... run a guitar direct into a mixing board, and you hear all that high end (stuff above 6kHz) that guitar speakers naturally roll off. Bass players love it, as do keyboardists, but guitarists? We WANT low-fidelity. That's why you'll find crossovers and multiple drivers (including horns) in keyboard and bass amps, but almost never in an electric guitar amp.

Link to comment
Share on other sites

  • Members

great read phil!!!

 

couple questions

First:

With a Peavey Classic 50, is 50W the TOTAL output of the amp? Does that mean that if i get speakers that are rated around 25w each they will "break up" sooner than speakers at say 60W each? If i went under 25W speakers would they blow? If i got 300W speakers would they move at all?

 

 

Second:

Here is info from Warehouse 12" Veteran 30 - 60 watts :

 

Thielle-Small Parameters

 

Resonant Frequency (Fs) 102 Hz

DC Resistance (Re) 12.70 Ohm

Coil Inductance (Le) 0.59 mH

Mechanical Q (Qms) 12.00

Electromagnetic Q (Qes) 0.94

Total Q (Qts) 0.88

Compliance Equivalent Volume (Vas) 1.28 cu ft

Mechanical Compliance of Suspension (Cms) 0.09 mm/N

BL Product (BL) 15.23 T-M

Diaphragm Mass Inc. Airload (Mms) 26.84 grams

Surface Area of Cone (Sd) 53.24 cu cm

Sound Pressure Level (spl) 98 db

 

Is the spekaer sensitivity 98dB @ 1W / 1m?

 

Thanks

Mac

Link to comment
Share on other sites

  • Members

 

are less efficient speakers more desirable for guitarists? what are the cons of a more efficient speaker? iow, why don't the amp builders use these in the first place?

 

 

It depends on what you're going for. Speaker efficiency is only part of the equation.

 

The old Jensen speakers that came stock in vintage Fender amps often had efficiency ratings of around 93ish dB (1W/1m), while the Celestion Blues in Vox amps have always had a high efficiency rating of 100dB (1W/1m). Most stock speakers these days have sensitivity ratings that fall somewhere in between those, with 98dB (1W/1m) seeming to be the average in my experience.

Link to comment
Share on other sites

 

The thing that always gets me is how anyone can determine what is twice is loud. I mean really, how do you know? Sure, one amp will be louder than another, but it seems like it's almost impossible to judge what is actually twice is loud, without having an SPL meter on hand.

 

 

I believe I used the term "typical listener" in the article. As with many aspects of audiology and psychoacoustics, individual perceptions and capabilities vary, but on average, most people experience and perceive a 10dB increase in sound pressure level as a "doubling" of volume. Some people are more sensitive and will hear things a bit differently, just as some people can readily pick out a change of .1 dB in a mix at certain frequencies while others can't tell when such a small change is made. And yes, this stuff is frequency dependent too... you can read up on the "Fletcher Munson Curve" or "equal loudness contours" if you'd like a more in depth explanation, but the short version is that our ears are not linear in terms of their response at various frequencies and at different sound pressure levels - our hearing is most sensitive in the midrange bands; especially at low volume levels. As levels increase, the frequency response of our ears becomes "flatter".

 

Using a SPL meter for accurate measurements is a good idea, and I have one sitting on my mixing console (and one in my iPhone) at all times. Human hearing is adaptive. We tend to adapt to changes in volume levels and baseline timbres fairly readily; which means referring to a standard reference (such as a CD you know well to reference timbre, or a SPL meter in terms of "volume levels") is a good practice to get into IMO.

Link to comment
Share on other sites

  • Members

Remember, "speaker breakup" and other tonal contributions from the speaker may be considered beneficial, even though they are the antithesis of "accurate".

 

 

does kind of bring up the old "@ what THD" part of the equation. I think it was motion sound that had that electric-guit combo and the complimentary acoustic combo -- one was listed at 80 watts, the other at 100 or 110 or something -- the difference was the THD at which each was measured..IIRC it was the same power amp sectioon

Link to comment
Share on other sites

  • Members

I believe I used the term "typical listener" in the article. As with many aspects of audiology and psychoacoustics, individual perceptions and capabilities vary, but on average, most people experience and perceive a 10dB increase in sound pressure level as a "doubling" of volume. Some people are more sensitive and will hear things a bit differently, just as some people can readily pick out a change of .1 dB in a mix at certain frequencies while others can't tell when such a small change is made. And yes, this stuff is frequency dependent too... you can read up on the "Fletcher Munson Curve" or "equal loudness contours" if you'd like a more in depth explanation, but the short version is that our ears are not linear in terms of their response at various frequencies and at different sound pressure levels - our hearing is most sensitive in the midrange bands; especially at low volume levels. As levels increase, the frequency response of our ears becomes "flatter".


Using a SPL meter for accurate measurements is a good idea, and I have one sitting on my mixing console (and one in my iPhone) at all times. Human hearing is adaptive. We tend to adapt to changes in volume levels and baseline timbres fairly readily; which means referring to a standard reference (such as a CD you know well to reference timbre, or a SPL meter in terms of "volume levels") is a good practice to get into IMO.

 

 

Thanks Phil, makes sense. I have a SPL radio shack meter I get out now and then, very handy little tool. I have a "perceived" volume drop in my xo EHX Octave Multiplexer, but I'm not sure if it's really volume loss, or because the signal is going an octave lower, than it's a percevied volume loss. I'll have to use the SPL on that and see what I find. Even if it isn't a volume loss, it appears to be, because the upper mids are greatly reduced, and the bass increases, which may not sound as loud. Robo has offered to add a volume boost to the pedal, which could be a good thing.

Link to comment
Share on other sites

 

Thanks Phil, makes sense. I have a SPL radio shack meter I get out now and then, very handy little tool. I have a "perceived" volume drop in my xo EHX Octave Multiplexer, but I'm not sure if it's really volume loss, or because the signal is going an octave lower, than it's a percevied volume loss. I'll have to use the SPL on that and see what I find. Even if it isn't a volume loss, it appears to be, because the upper mids are greatly reduced, and the bass increases, which may not sound as loud. Robo has offered to add a volume boost to the pedal, which could be a good thing.

 

 

Yup, that's a good example - you're moving the sound an octave down, and your ears may be less sensitive to those frequencies - which makes it sound softer, even though it may not actually "measure" softer. With a SPL meter, various weighing techniques are utilized to help compensate for the non-linearity of human hearing; read up on A and C Weighing in your SPL meter's manual (or via Google) for more on that. But if it "feels" (sounds) softer to you, then there's nothing wrong with giving the pedal a little "goose" in level to compensate. It's all a matter of preferences and what works for you. Remember, while there are aspects of science, physics and engineering to all this stuff, for musicians, those things are in support of, and an effort to explain things that are more important to us - emotion, feel, vibe, etc. Just because something is accurate or technically "better" from an engineering standpoint, doesn't automatically make it better from a musical point of view.

Link to comment
Share on other sites

does kind of bring up the old "@ what THD" part of the equation. I think it was motion sound that had that electric-guit combo and the complimentary acoustic combo -- one was listed at 80 watts, the other at 100 or 110 or something -- the difference was the THD at which each was measured..IIRC it was the same power amp sectioon

 

Lies, damn lies, and statistics. Or in the case of gear, specifications. ;)

Link to comment
Share on other sites

  • Members

i'm really not such a math wiz and have never really learned some of the more interesting things, such as logarithms and such. so i really don't get it, but it seems like the way it would work would be that 3 dB is not always the same difference. like the difference in SPL between 50 and 53 dB would be far less significant than the difference between 100 and 103 dB. like an exponential increase. that's why it never made much sense to me when people would sort of scoff at 100 watt heads and be like, "no one needs that. it's only 3 dB louder than a 50 watt head." i know it's not twice as loud, but i've always thought that it seems like 3 dB could be a pretty big difference. i could get in over my head very easily if i keep writing. i probably already am.

anyway, thanks. that was a great little article.

Link to comment
Share on other sites

great read phil!!!


couple questions

First:

With a Peavey Classic 50, is 50W the TOTAL output of the amp?

 

I believe the output power rating of the Classic 50 is 50W RMS, yes. I don't recall if it's designed for an 8 or 4 ohm load... :idk:

 

Does that mean that if i get speakers that are rated around 25w each they will "break up" sooner than speakers at say 60W each? If i went under 25W speakers would they blow? If i got 300W speakers would they move at all?

 

It depends on how the speakers, and how they are wired. Yes, lower wattage speakers will generally tend to "break up" at lower power levels. Yes, a 300W rated speaker can be driven (and will create sound) with far less than 300W applied. Yes, if the speakers are pushed hard enough, they could blow - but that depends on how conservatively they are rated, and what you're doing to them in terms of power levels, the frequencies you're running into them and how long you are pushing them really hard...

 

There are three primary ways that speaker cabinets are wired up - series, parallel and series / parallel.

 

Series wiring increases the total resistance. For example, wire two 8 ohm speakers in series, and you wind up with a 16 ohm load for the cabinet. Series wiring also increases the power handling capability - wire two identical 25W speakers together and feed them 50W, and that power will be "shared" or "split" between the two speakers - each getting 25W.

 

Parallel wiring lowers the resistance. Wire two 8 ohm speakers in parallel and the impedance of the cabinet drops to 4 ohms. Power handling remains the same, and the work is shared by / split between the two drivers.

 

Series / parallel requires at least four speakers; with two sets of series wired speakers wired in parallel. Power is split between the four speakers (assuming they're all identical - if they have different efficiencies and impedance ratings, the math gets a lot more complicated) and the impedance stays constant - IOW, four 8 ohm speakers, when wired in series / parallel, will result in a 8 ohm cabinet.

 

Second:

Here is info from Warehouse 12" Veteran 30 - 60 watts :


(snip)

Sound Pressure Level (spl) 98 db


Is the speaker sensitivity 98dB @ 1W / 1m?

 

Maybe. Probably.

 

It's probably a reasonable assumption that the measurement is based on the industry standard practice of 1W input, measured in an anechoic chamber at a distance of 1 meter... but they don't specifically state it as such, so there's no guarantee. Please see my earlier "lies, damn lies, and specifications" comment - manufacturers sometimes use different points of reference, or just leave the specifics out of their published specs in an effort to make their product "look better" on paper.

 

Specs can give you some useful information, but when comparing two different items - such as two speakers - you need to make sure that the measurements were performed the same way, and the standards / points of reference are identical; otherwise, you're comparing apples and baseballs. And no matter what the specs say, there is NO SUBSTITUTE for hearing the item in question with the best test gear known to man - the human ears.

 

Thanks

Mac

 

You're welcome. :)

Link to comment
Share on other sites

i'm really not such a math wiz and have never really learned some of the more interesting things, such as logarithms and such. so i really don't get it, but it seems like the way it would work would be that 3 dB is not always the same difference. like the difference in SPL between 50 and 53 dB would be far less significant than the difference between 100 and 103 dB. like an exponential increase. that's why it never made much sense to me when people would sort of scoff at 100 watt heads and be like, "no one needs that. it's only 3 dB louder than a 50 watt head." i know it's not twice as loud, but i've always thought that it seems like 3 dB could be a pretty big difference. i could get in over my head very easily if i keep writing. i probably already am.


anyway, thanks. that was a great little article.

 

I pretty much hate math too. :lol::o

 

We use logarithmic scales and exponents so we can deal with huge ranges of numbers without having to write out tons of zeros. Compare a whisper in a quiet room to a guitar amp cranked, and you might be dealing with a 100dB difference in level. If we used "normal" numbers, that would represent a difference of about 1 : 10,000,000,000 in terms of power. That's a lot of zeros, and writing that stuff gets pretty tedious, so we use a logarithmic scale so we can cover the amazingly broad dynamic range of our hearing with a far more reasonable series of numbers: 0 to 140dB or so.

 

3dB is a significant amount. It represents a doubling of power, but as I said, doubling the power doesn't result in a doubling of perceived volume. 3dB is a noticeable and significant increase in volume, just not a "doubling" of volume. It's not "twice as loud" - whether we're talking about the 50-53dB range, or the 100-103dB range.

 

However, our ears are more sensitive to volume changes at different frequencies and at different levels. If we're discussing a very low frequency sound, say in the 30Hz range, it may very well be far more difficult to hear a 3dB change in level at a very soft sound than it would be to hear a 3dB increase in level of a 2kHz sound that started at 85dB. There's also issues of background noise and masking... if we walk into the tracking room of my studio (a very quiet room), you can hear a very soft sound, such as a pin drop, with no problem... if I set off a M80 firecracker at the exact same time that the pin hits the floor, the pin is still making the same amount of "sound", but it is going to be masked, or covered up by the much louder sound...

Link to comment
Share on other sites

  • Members

great article, phil--definitely learned a lot! makes me wonder, though, why aren't dB's advertised in the way wattage is with amps? something like "max dB output" or something to help lead people in the right direction in determining how loud a particular amp can get, or the relative loudness of two amps someone is comparing.

Link to comment
Share on other sites

  • Members

One thing that's missing, though is frequency response. Most players specifically choose a speaker vs. another one specifically for it's non-linear characteristics. Certain frequencies sound louder than others. To use the obvious example, if the mids are too scooped, the sound disappears -whether it's done by a graphic EQ or a speaker.

Link to comment
Share on other sites

 

great article, phil--definitely learned a lot! makes me wonder, though, why aren't dB's advertised in the way wattage is with amps? something like "max dB output" or something to help lead people in the right direction in determining how loud a particular amp can get, or the relative loudness of two amps someone is comparing.

 

 

While you can indicate the output level of an amp and speaker setup, it's relative. On a hi-fi amp, they'll indicate watts at a certain percentage of total harmonic distortion (THD); less distortion being more desirable in that kind of a system. With a guitar amp, is that still the case? Sure, the RMS power may be indicated on the specs, but sometimes you're looking for loud cleans, and other times, loud dirt, so you intentionally drive the amp into clipping. Also, it's easier to rate the potential output level for a combo amp since it has a built in speaker... but what about for a head? You can easily couple it with any speaker cabinet you want, just as long as you take impedance matching into consideration, and not all speakers are going to have the same efficiency and output... so you really can't give a "loudness rating" in terms of maximum SPL.

 

You're more likely to see figures listed for max output levels of powered PA speaker cabinets than guitar amps / speakers; again, mainly because PA speakers are designed for low levels of distortion, even at maximum volume. Maximum output of a guitar amp / speaker is going to depend on the pair - and it's just too easy to switch things up for it to mean anything - except maybe for combo amps, and again, even they are subject to speaker swaps.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...