Amp wattage differential confusion

Discussion in 'Amp Central Station' started by BataviaJim, Oct 22, 2019.

  1. BataviaJim

    BataviaJim TDPRI Member

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    I'm evaluating compact vocal/guitar amps to perform in small venues - nursing home lounge, church social room, etc. I'm confused about watt ratings. Here's a sample:
    • Roland Cube 6.5" speaker, 30 watt
    • Fender Passport Mini 6.5" speaker, 7 watt
    • Behringer B207MP3 6.5" speaker, 150 watt
    User reviews suggest all are adequate for my intended use.
    They all have the same size speaker and are about the same price (within $30).
    So why are the watt differentials so big? How can a 7W amp compete with a 150W?

    Thanks for any explanation you can provide.
     
    Last edited: Oct 22, 2019
  2. BigDaddyLH

    BigDaddyLH Tele Axpert Ad Free Member

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    Wattage isn't a measure of loudness, sensitivity is (to some extent, since loudness is a psycho-acoustic phenomena).

    The watt rating of a speaker tells you how much wattage it can see without blowing up.
     
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  3. BataviaJim

    BataviaJim TDPRI Member

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    So it has nothing to do with output volume?
     
  4. BigDaddyLH

    BigDaddyLH Tele Axpert Ad Free Member

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    Not if you are thinking of speakers seeing the same output. Of course, if you have a lower rated speaker you may not be able to crank your amp as wide open as you could with a higher rated speaker.

    For example, on the Eminence speaker website, they list both power rating (watts) and sensitivity. https://www.eminence.com/guitar-bass/patriot-series/
     
  5. 11 Gauge

    11 Gauge Doctor of Teleocity

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    I went and looked at the particular three that you listed, and it appears that they are sort of being targeted for different uses, or for different performance criteria.

    The Behringer looks to be more of a comprehensive PA than the other two. As such, its power amp is probably capable of putting out more power. It also possibly has more of a sound reinforcement-style speaker than an instrument speaker. So 150 watts probably sound like it's common for something like that.

    The Fender Passport looks like it's a super portable grab-no-go PA, and has battery-powered capability. As such, it's not surprising that they only rate it at 7 watts. It probably has a relatively general-purpose (light duty) speaker, too.

    I'm assuming the Cube that you're talking about is the Roland Cube 30? If so, that looks like a semi-standard rating for a guitar amp.

    Since guitar amps and non-guitar (e.g. keyboard, PA, and even bass and acoustic guitar amps) amps tend to differ a bit, there's probably not much value in "translating" the actual power output between the different applications. IMO, non-guitar amplification probably has much greater demands, since you absolutely don't want any distortion for mics/keys/acoustics/mandolin/etc.
     
  6. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    Take Behringer power figures with sufficient salt to require dialysis afterwards. They rate their solid state stuff using the PMPO rating, which is less useful than sticking pins in a block of butter for determining actual, sustainable, listenable, levels. They rate that units peak power consumption to be 180W, which, given Class D efficiencies and the pre stages, MP3 player and assorted gubbins would give a transient of ~150W delivered to the speaker. If the speakers are identical in rating to the Roland, it'd be around 50% louder, but I despise the sound of a Class D amp in full on clipping mode. Ugh! Call it 50 Watts useable and be happy.
    The Roland and Fender are probably accurately rated power wise. If the Fender has a really good, efficient speaker and the Roland a less efficient speaker, there'd only be a few dB in it anyway. The first few Watts do so much heavy lifting. Be guided by your ears, not numbers. The Roland busking amps are very popular among our local buskers. They provide fantastic sound both outdoor and in the indoor market. If it were my money, it'd go Roland first, Fender and Laney in strong second place.
     
  7. BataviaJim

    BataviaJim TDPRI Member

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    Yes, the Roland I'm considering is the CM-30 Cube Monitor. It's first on my list at this point because it has 3 inputs and looks to be the most solidly built. Also the shape is best for the duffel bag of gear I stack on my amp to get to the venues.
    The Behringer also has 3 inputs, all of which are mic/instrument capable. It also has a 3-band EQ while the Roland is just 2-band.
    Neither of those has effects on either vocal or guitar channels.
    The Fender's appeal is that it has multiple effects and can be battery powered. The effects would be nice, even just reverb on the vocals. The battery power isn't important to me but could be useful in a pinch.

    BTW, I'm currently using a Block 40K amp. It's about 20 years old and crackles a little when I adjust the volume, and the pots are inaccessible for good cleaning. It's a lot bigger and heavier than the ones above, though it's got a great general-purpose sound.
     
  8. Blrfl

    Blrfl Tele-Holic

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    It has lots to do with it, but it's not the only factor in the equation. Oversimplified, the wattage figure is how much energy the amp can produce at its speaker terminals. That energy is sent to the speaker.

    The speaker's job is to convert the amp's electrical signal into moving air, which is what translates to sound pressure level (SPL). There's a figure for this called sensitivity, which is measured by driving the speaker with one watt and measuring the SPL at a distance of one meter. Speaker manufacturers like will specify sensitivity, but since speakers in cabinets are complex systems with a lot of physics that determine how much air they ultimately end up moving, so you compare entire cabinets.

    If you connect three different amps that produce 30 watts to the same cabinet, all three should produce the the same SPL if all else is equal. If you take a 30-watt amp to three different cabinets with different speakers (and, again, all other things being equal), they'll produce different SPLs depending on how efficient they are.

    Some manufacturers may play fast and loose with their wattage figures, too, but ultimately you can bust through that with measurement.
     
  9. Peegoo

    Peegoo Tele-Meister

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    Watts is the power consumed by the amp in operation. Makers use watts as an index of power rating for their amps because it simplifies comparisons.

    Wattage does not directly correlate to decibels from the speaker though; for instance, doubling the wattage does not double the volume.

    Confusing the issue even more is how each maker calculates wattage. Do they use RMS? Or PMP (among several others)? there is a whole lot of smoke and mirrors in the amp marketing world.

    Best approach is to compare amps side by side in a shop at gig volumes.
     
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  10. stormin1155

    stormin1155 Tele-Meister

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    Trying to decide what will work best for you from a spec sheet is like trying to determine which frozen pizza is going to taste best based on the picture on the box. The only way to really tell is to try them.
     
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  11. bettyseldest

    bettyseldest Friend of Leo's

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    I don't know the first two, but I have had a pair of the smaller Behringer B205D's for about eight years. Running a couple of vocal mikes and guitar pre-amps we rehearse with them along with an enthusiastic drummer and a bassist playing through a 150w 1x15" combo. We have played a couple of small gigs with them in this configuration. I have played solo gigs with just one of them and duo/trios with the pair. Before we moved to iems we have used them as monitors. I have run quiz evenings with them, used them as as stage monitors for amateur musicals, public address announcements, kids parties. Reverb would be nice, but if I need it I run everything into a small mixer first. They have been used on 250 to 300 occassions without a problem. The B207D's have an additional input compared to the B205D, so should be more versatile. All things being equal the 7" speaker will probably be louder than the 5". The B205D's sound fine and should be more than loud enough for what you are looking to use them for.

    Don't worry overly about wattage, try each of the units out, do you like how they sound? will they be loud enough? Do they have the features that you need?
     
  12. tubelectron

    tubelectron Tele-Holic

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    Specification - when it exists - of the power output has become pure fantasy today...

    I stick to the old definition of the RMS watts steady output given by an amp at the onset of clipping, under a sine wave signal of 400 to 1000Hz, measured accross a resistive power load.

    But it's me, OK ? :D

    -tbln
     
  13. schmee

    schmee Poster Extraordinaire

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    It's hard to figure. But more wattage usually means more clean headroom and a more robust product. For playing a small joint as a single or duo though, you will never get past the lower end of the volume dial much. So not a big difference in 20 watts or 100 watts. Add to that how sellers describe amps can be misleading. Some even use the rating for power input!
     
  14. BataviaJim

    BataviaJim TDPRI Member

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    I thank everyone for their responses. You've been very helpful in explaining this, and I'm much closer to deciding.
    Much appreciated!
     
  15. Corvus

    Corvus TDPRI Member

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    Rating loudness by "watts" is confusing and often marketing speak. A watt is a unit of power and you can get widely differing apparent loudness with the same output by considering the speakers efficiency. One confusion is that valve/tube amps seem to sound much louder for apparently the same rated output but a tube amp goes way beyond it's clean output loudness into a distortion that we find pleasing but a solid state amp's distortion is so nasty that they are throttled at their rated output. Loudness is also logarithmic - so a 100 watt amp isn't twice as loud as a 50 watt amp - you'd need a 500 watt amp (10x) to be twice as loud. Reversing this - a 5 watt amp is half as loud as a 50 watt amp (given the same speaker.) Try a Champ driving an efficient 4x12 cab; you'd be surprised!
     
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