Specs Part 1: How Much Power Do I Need? (geek/tech thread) ;)

Discussion in 'Amps, Mics & Pickups [DB]' started by macmrkt, Aug 9, 2005.

  1. macmrkt

    macmrkt Banned

    Dec 4, 2002
    There are many useful, highly informative threads in these forums about equipment and sound. But...in the midst of these discussions, I often see assumptions about power ratings that are not factual. It's understandable, as marketers use specs to sell products without explaining them making it very easy for us to latch on to incorrect concepts. So here are a few points to consider before upgrading to a more 'powerful' rig.

    1. If you have a 100 watt amplifier and you wish to double your volume, what wattage rating should you be seeking? 200 watts? 300 watts? 500 watts?
    No. 1000 watts! It takes 10 times the rated wattage to achieve a doubling of volume (all things being equal, and they never are.)
    2. Then why do amp companies make a 200 watt amp, a 350 watt amp, a 500 watt amp...when the difference in volume would be difficult if not nearly impossible to hear? Well, IMHO it depends on the company. Some are just playing the numbers and getting you to buy into a more expensive amp. Others may give you this tiny bit of extra power and throw in features to get you to jump.
    3. In my experience, more respectable manufacturers actually give you more 'current' or 'headroom' hidden in with their higher wattage rated amplifiers. This enables the amp to respond to the huge instantaneous power requirements of a low bass note or a slap tone. Your overall volume may have not changed too much, but the feeling of having power when you need it did. It's actually very difficult and costly to make an amp deliver these instantaneous low frequency sounds cleanly. However, the wattage rating will not tell you if an amp has this increased ability nor will it tell you if an amp SOUNDS BETTER. It's a measurement of power and if it's the only number you have for comparison, you don't know very much. Current and headroom use different measurments and are almost never quoted.
    4. Wattage ratings are very deceptive. You can manipulate the rating by changing the 'load' the amp drives during measuring, the time it drives it, and the input frequency. Even a slight variation in these parameters makes a huge difference in the measured rating. All of the parameters affect each other and the rating. You need to know and control the exact measuring conditions or the ratings are worthless. And you guessed it, these parameters are either not quoted or are not the same in comparing two amps from different companies. (I'm not even talking about how the three most common types of distortion play into this.)
    5. I use this analogy - if challanged to run a 1/4 mile drag race, which vehicle would you take - a 300hp Corvette or a 300hp 18 wheel tracktor/trailer. No brainer right? But if you go by the single horsepower spec, they should end in a tie. That's a way to understand how useful the wattage rating is for telling you what volume you'll get in the real world...in other words, not much. (If you think that the wattage rating of an amp is suspect, rating a speaker cabinet's handling power in wattage is a whole other can of worms.)
    6. Speaking of speakers, it's usually much less expensive to get a more efficient speaker setup to increase your volume, than to get a more powerful amplifier.

    Bottom line - you'll only know what an amp can do for you by trying it in your specific situation. Any specification, by itself, will tell you nothing about sound quality, and very little about sound quantity.
  2. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Your honor, I'm just a CAVEMAN.

    Seriously, I've studied enough of this kind of thing to sort of understand it, but in the end it all comes down to "does the amp sound good?". I've noticed that more headroom tends to sound good regardless of what the numbers indicate because there is a factor in the sound of "how hard is the rig working to get this sound?" that I've never been able to quantify with numbers. Basically, in my mind, this translates into "can the amp I'm using do what I want without sounding cranked"?

    With the live gear I've used, I find that most often the answer is to keep the gain knobs below 12 o'clock on the preamp section, which usually produces the most "natural" or "relaxed" sound. The exception seems to be the "input" section of the iAmp 800, which works differently for some reason. But beyond that, I think the most valuable aspect of a powerful amp is all of that power that stays in reserve. If someone could explain why that is, I'd be interested to listen.
  3. Freddels

    Freddels Musical Anarchist Supporting Member

    Apr 7, 2005
    Sutton, MA
    So how would you describe the Wizzy combos (200 and 500) since the speaker and everything else should be equal. I am understanding that the 500 wouldn't be that much louder but would have more headroom. That the 500 would be quicker out of the gate?
  4. Good food for thought. I have known intuitively and from many threads here that specs are just specs, but your post really sheds some light on the subject. By explaining with detailed examples of why it is so, the concept really sinks in.

    The explanation of the logorithmic scale, and the horsepower analogy were quite useful.
  5. macmrkt

    macmrkt Banned

    Dec 4, 2002
    My point exactly.

    From what I understand of conventional amplifiers (not switch mode or Class D or digital) it's the power supply - storage caps and transformer most notably, that determine reserve and the ability to be there when you need it. These are also the most expensive parts. In a switch mode amp, I don't know where this reserve comes from and I'd like to know. Once again, no single spec and certainly no commonly available one, seems to rate this ability accurately.
  6. flatback


    May 6, 2004
    Bolinas Ca
    so heres a question for you. What about bridging a 2 channel amp? I remember Walter Woods telling me that I could get 2x the power from my M100 by bridging the inputs. So what is that? 200w 400w? I think he told me that the amp was rated at 100w very conservatively and that it was really more ike 200w per channel.I want to have enough power to drive my new lds 1x8 and I am hoping that the WWM100 will be enough for most trio gigs. But I am also thinking seriously about getting a focus, cause the truth is I dont really understand all this but I do know that last week the WW (unbridged) was not doing too well firing up that EV12 in my Kolbe cab. But I dont think the EV 12 is very efficient.
  7. macmrkt

    macmrkt Banned

    Dec 4, 2002
    IMHO, I'd put that in my number 3 point above. However, the folks at EA each forget more physics and engineering in any 60 second period than I've ever learned. :help:
  8. macmrkt

    macmrkt Banned

    Dec 4, 2002
    In short, try your WW with the LDS 1x8 first - specs can't give you the answer. Since cabinet efficiency is an easier path to more output than acquiring a bigger amp, you may be OK.

    By the way...is your WW a stereo amp? Be very careful when trying any bridging connections as a wrong hookup can fry an amp. In my experience, bridging an amp often gave somewhat more volume but at a cost of sound quality. That's my experience only, but I try always to get the power I need without bridging. Of course, Mr. Woods knows an infinite more about electronics than me and since his designs are unique, who knows!

    Speaking of experience, I owned a Clarus SL and several Focus amps...and as expected, I found little volume difference between the two. I think the Focus was more powerful and sounded like it had more in reserve, but the difference was not huge. I'm a 4 string player...maybe below low 'E' there's a bigger change...
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I have been moving my DIY gear into the Class-D age, so I can share what I have learned so far. If the power supply is unregulated, then the reserve comes from the same place. But the components are smaller and more efficient, so it's easier to add reserve without adding cost and bulk. If the supply is regulated, then the current reserve is effectively infinite, until the whole thing goes up in smoke. But it is not too difficult to plan for worst-case conditions. And if the amp is pushed beyond any realistic musical situation, you've got the protection circuitry to back you up.

    In my view, the importance of having some reserve is simply the avoidance of clipping distortion.

    Just to add my opinion... the "doubling of volume" rule just adds another layer of complexity without any real benefit. In my experience, as little as 2 dB of power / headroom is both audible and beneficial.

    About the pricing of bass amps, there is no law against marketing. It is a common marketing technique to provide a range of products creating the effect of a sliding price scale with the appearance of more bang for the buck as you go up in price. This gets rid of the problem of someone coming into the store with a $400 budget, and walking away with a $200 amp.
  10. anonymous0726

    anonymous0726 Guest

    Nov 4, 2001
    The truck and corvette example is way confusing, unless that is the point that you were trying to make. You have horsepower, torque, available thrust after subtraction of inertia, and the ability to translate the available thrust -- lb per sq" on the tires and tack of the tires in this case -- the the task.

    Oh - given that the motors give even HP and torque throught their entire usable ranges (not ever) and how this is offset against the transmissions and gear selection (which gears and timing).
  11. I think that's the point. If you compare hp (or Wattage) alone, you're not getting the whole picture. Too many other variables to factor in.
  12. Phil Smith

    Phil Smith Mr Sumisu 2 U

    May 30, 2000
    Peoples Republic of Brooklyn
    Creator of: iGigBook for Android/iOS
    When you look at the power to weight ratio i.e. a corvette to a truck or a motorcycle to a corvette, you will readily know which is faster, a 300hp motorcyle and a 300hp truck, no contest off of the line, 0 to 60 and top speed.

    If you want more sound you need more cabinets or a cabinet with more drivers.
  13. anonymous0726

    anonymous0726 Guest

    Nov 4, 2001
    Although I might bet differently for with top speed in your example, PS, based on the torque specs. :)

    The old saying in the racing biz is: HP sells cars, but torque wins races.
  14. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    This is entirely incorrect. First, wattage alone does not indicate what "volume" you will achieve at all. The acoustic output in watts that is achieved by a power amplifier of a given wattage depends upon a number of factors including the sensitivity of the driver (speaker), the cabinet design, etc. These can be HUGE fators that can change the required amplifier power by orders of magnitude for the same desired acoustic output.

    Next, let's get the terms straight. Voltage, wattage, intensity, power, etc. are PHYSICAL terms. Loudness and volume are PSYCHOLOGICAL attributes.

    Neither volume nor loudness are measured in decibels. The auditory system responds, in large part, in a logarithmic fashion and operates over a large dynamic range of inputs. Thus, it is convenient to express power (wattage) in terms of decibels. When discussing power, the decibel change between two powers (P1 and P2) is expressed as:

    10*LOG(P2/P1). Decibels must always have a reference! It is meaningless to say you have an 80 dB sound. 80 dB re what reference?

    The most relevant reference for this discussion is called sound pressure level (SPL). The reference pressure is 0.0002 dynes/cm^2. When people say a sound is 80 dB, they usually really mean that it is 80 dB SPL. That is, 80 decibels above the reference pressure of 0.0002 dynes/cm^2.

    Now, if a sound is 80 dB SPL and you wish to double it's loudness, which refers to human perception, you must increase its power 10-fold, that is, by 10 dB. You would need the output to be increased to 90 dB SPL (not 83 dB!).

    That manufacturers typically offer amplifiers of 200, 250, 300 watts is a practice that has long been sucking in buyers in the hi-fi world for decades. Remember, going from 200 to 400 watts is only a 3 dB change (10*LOG(2)~= 3). That's quite small.

    It's important to keep the physical and psychological measures straight.

    I'm done now! :)
  15. anonymous0726

    anonymous0726 Guest

    Nov 4, 2001
    I only have one word after that last bit: Analgesics.
  16. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    I will have to defer to the folks in the thread who understand
    SPL's, DBs, snd Wattage ratings. You guys (and gals) have a much better handle on this stuff than I do.
    That said, IMHO the better the preamp, the better the sound.
    Wattage is important obviously, but the reason that Walter Woods
    Acoustic Image, and Euphonic Audio amps sound better is that
    their preamps are excellent. They allow you to cut or boost frequiencies and create a that's very close to the sound of your
    bass, without amplification.
    The ability to "dial in a great tone" makes it easier to hear
    the amplified sound of the bass. So, I think that the preamp
    is the real deal breaker in mix. Just my opinion though. Obviously
    you can't have a 10 watt amp these days (can you?)

  17. macmrkt

    macmrkt Banned

    Dec 4, 2002
    Thank you - I fixed the errors.
  18. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Thanks for raising a very valid and very important point. The design of the pre-amp is paramount to good sound. The pre-amp or so-called "front-end" must be capable of providing proper gain without overloading. A poorly designed pre-amp has a narrow dynamic range such that large peaks at the input will overload it leading to distortion. No amount of current capability or power output in the power-amp section can fix that! In addition, skillfully designed tone controls that affect the response in USEFUL and appropriate ways is a matter of good engineering.
  19. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I would trust amplifier power ratings before I trusted speaker sensitivity ratings. To the best of my knowledge, transient response has ceased to be a difficult design issue for power amps. Achieving high fidelity at rated power with a linear amp is no longer rocket science. The remaining frontiers are in areas of practical importance, such as size, weight, efficiency, reliability, safety, and cost.

    Of course opinions vary on the "tone" of power amps. All I can do is offer my own view, while falling back on the time honored "let your ears be the judge" disclaimer.

    Gaining 3 dB of speaker sensitivity is not as easy as one might imagine. There are some real tradeoffs between sensitivity and factors such as size and frequency response. On the other hand, it is easy to inflate the sensitivity rating by emphasizing high frequency performance. I would not believe any sensitivity rating that was not accompanied by a curve showing the crucial frequency range below 250 Hz.

    You can increase speaker sensitivity by increasing the total cone area -- not necessarily the most practical solution when portability is a concern. Suppose you have a 100-Watt amp and 1x12 speaker. Now you want to double your acoustic power. You could get a 2x12 cabinet, or a 200-Watt Class D power amp. Which one gives you better portability?

    Like DRURB said, there are still improvements to be made in preamp design. Speaker tone also continues to be a frontier. This is why I have concentrated on preamp and speaker design for my DIY amp project, up until now. And woo-hoo, I just got the last piece of the puzzle, a switching power amp kit from 41 Hz Audio (www.41hz.com). Building the kit will be my reward for finishing a business-related project that is close to its deadline.
  20. Uncletoad


    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    So the original question is "how much power do I need". A good one that has lead to much discussion that is very interesting. My take on it is I've never had "to much" power but I've certainly had "to little". I suspect everyone's answer to what they need varies quite a bit.

    I'm a big fan of headroom. I like the sound of big power amps cruising along without breathing hard. High power amps sound richer and less fatiguing to my ear than lower power amps at the same apparent volumes. I'm not a fan of clipping in solid state amps. It sounds bad to me and kills speakers.

    When playing Fender Bass at times I have used enormous amps with grotesque power ratings. SVT's or a preamp with a Crown Macrotech 1200. Double Bass can require lots of power to replicate cleanly but not really as much as those amps can generate. Perhaps that IS a case of to much power... Nonetheless when I tried those amps on DB they didn't sound as good as the EA, Walter Woods or Acoustic Image stuff even though they were way louder. Some extra support for the idea that the preamp section is king. Quality in the DB is far more important than quantity I think.

    In the same rooms that I used an SVT and an 810 with Fender Basses I'm using the Walter Woods ultra and two VL 208's with the Double Bass and they fill them darn nearly the same. (Huge rooms fwiw) The Fenders through the little rig sound anemic compared to the SVT and the Double Bass can't even work at all with the SVT.

    That all leads me to think there is a "right rig for the job".

    This year I have used the iAmp 800 and the WW Ultra for my DB gigs and they are plenty powerful to leave the headroom I prefer and sound amazing, especially considering what was available 20 years ago.

    I don't really like 100 watt amps or 200 watt amps on DB. I'd rather just get the most power I can afford with the tone I'm looking for and set the volume knob for the gig.

    Another person's requirements may vary. It is highly dependant on what style you are playing, the venue, the sound reinforcement provided, and the expectations of the leader and the others on the gig. I'd bring very different stuff to a jazz brunch gig than an outdoor rock gig without a PA.

    My job as a professional musician is to know where I'm going, what's expected, and to show up with the right stuff to do what I'm getting paid to do.

    I don't always get that right...