Technical guide
How much sound power you really need
The most frequently asked question, and the worst phrased. Here is a table to give you a rough idea and, above all, an explanation of why that table cannot be exact.
- Type
- Practical guide
- Reading time
- 8 minutes
- Applies to
- Weddings, parties, street parties and live gigs
The short answer
The watt is a unit of power consumption, not of loudness
A 1,000 W speaker can sound quieter than a 500 W one. It is not a paradox: they are different quantities. The watt describes the electrical power the amplifier delivers to the driver. What you hear is sound pressure, and it depends on how much of that power is turned into useful sound and in which direction it is projected.
The missing piece is called sensitivity: how many decibels the speaker produces with a reference power at a reference distance. There can be a huge difference between an efficient cabinet and a mediocre one, and in decibels every step costs a great deal. To gain 3 dB you have to double the power. To gain 10 dB — roughly what the ear perceives as "twice as loud" — you have to multiply the power by ten, or change speaker.
That is why an honest comparison between two systems is not "watts against watts", but maximum SPL, dispersion and frequency response. When a serious manufacturer publishes a cabinet's maximum SPL, it is telling you far more than when it publishes its power rating.
The other concept: headroom
Headroom is the margin between the level you normally work at and the maximum the system can deliver without distorting. A system running at its limit sounds bad even if the average level is right, because the peaks — the crack of the snare drum, a hard consonant — get clipped. That is why a system is always sized above what is strictly necessary: not to turn the volume up higher, but so that the peaks fit. A system with headroom running at half throttle sounds better than a small one flat out.
The table
Ballpark figures by audience size
This is a rough guide, not a specification. It tells you whether you are talking about two speakers or a system on towers. The real quote is put together by looking at the space.
| Capacity and space | Type of event | Approximate set-up |
|---|---|---|
| Up to 50 people · indoors | Speech and background music | A pair of small active speakers on tripods. Enough for presentations, small First Communion parties and meetings. |
| Up to 50 people · with dancing | Small party | Two active speakers and a subwoofer. The sub isn't a whim: without it, dance music loses its body. |
| 50 – 150 · indoors | Wedding, birthday, corporate event | Two larger speakers plus one or two subwoofers, and separate microphones for speeches. |
| 50 – 150 · outdoors | Garden, courtyard, terrace | Go one step up from indoors: with no walls reflecting energy back, you need more system or more fill points. |
| 150 – 400 · indoors | Large hall, conference, graduation | A bigger system or several distributed points. From this size upwards, it is worth having a technician during the event. |
| 150 – 400 · outdoors | Street party, large caseta (fair marquee), big wedding | A system with dedicated subwoofers and, depending on the shape of the venue, side fills or delay speakers. |
| 400 – 1.000 | Concert, patron saint festival | A medium-format line array or ground-stacked system, stage monitoring and front-of-house control. |
| More than 1,000 | Festival, large venue | A line array sized with coverage prediction, delay towers if the distance requires it, and a full technical crew. |
The nuances
Four things that move the table up or down
1. Indoors or outdoors
This is the factor that weighs most. In an enclosed space, the surfaces reflect energy back and the level sustains itself. Outdoors, the sound goes and doesn't come back: every time you double the distance, you lose a considerable amount of level. A system that is more than enough in a hall falls short in a garden with the same number of people.
2. Type of music
Electronic music and modern pop carry a lot of energy in the low end, and bass is what consumes the most power: most of a party's amplification budget goes on the subwoofers. An acoustic set, a string quartet or a talk need a fraction of that. That is why a flamenco show and a nightclub with the same capacity call for different systems.
3. The shape of the venue
A hundred people spread out in a square space can be covered with two speakers. A hundred people in a long, narrow street cannot: you need to distribute the sound across several points. Geometry matters as much as capacity, and that is why we always ask about the venue before the numbers.
4. The background noise level
A noisy bar, a generator, traffic or a neighbouring marquee with its own music force you to turn up to keep speech intelligible. At the Seville April Fair (Feria de Abril) this is the rule, not the exception: we cover it in how to set up sound for a caseta.
Mistakes
What goes wrong when a system is sized by eye
Buying power instead of coverage
Two huge speakers at one end of the venue force you to blast the front row so that something reaches the back. Four distributed speakers do the same job with less level and a better result.
Forgetting the subwoofers
A system without bass can have plenty of level and still empty the dance floor. The party feeling lives below the range where the voice is understood.
Sizing without headroom
Matching the system exactly to the desired level guarantees it will sound compressed at the best moments. Headroom is part of the design.
Not accounting for microphones
Available power is useless if the speech can't be understood. At events with speeches, the microphones matter more than the PA.
Ignoring the legal limit
A huge system is of little use in a venue with a sound limiter or a municipal cap. Before sizing upwards, it is worth knowing where the ceiling is.
Forgetting the power supply
A large system needs a matching power supply. How to calculate it is explained in this generator guide.
Keep reading
Related equipment and pages
Frequently asked questions
Sound power FAQs
How many watts do I need for 100 people?
There is no reliable figure, because it depends on whether it is indoors or outdoors, the type of music and the shape of the space. As a ballpark, a pair of medium-sized active speakers with one or two subwoofers covers a party of that size indoors.
Is one big speaker better than two small ones?
Almost always two, spread out. They even out the level between the front row and the back far better, and produce a lower peak level at the loudest point of the venue.
Do I need subwoofers if there's only background music?
No. For background music and speech, subwoofers add nothing and do bother the neighbours. They are added when there is dancing.
Can I use the venue's sound system?
Sometimes, for PA announcements and background music. It is rarely enough for an outdoor ceremony or a dance floor. It is worth checking exactly what it covers before ruling out renting.
What happens if I don't have enough power?
The system works at its limit, distorts on the peaks and sounds harsh. Turning up the volume in that situation makes things worse rather than better.
Tell us the audience size, venue and type of music
With those three details we'll tell you exactly which system you need, without overselling.
