Sound/Audio Rental Price List

Professional Audio Reference

For FOH engineers, production managers and technical directors reviewing our inventory. If you're advancing a show or comparing our rig against a rider, this is for you.

SPL, Sensitivity and Why Watts Are Irrelevant

Sensitivity is the specification that actually tells you how loud a speaker is — measured in dB SPL at 1 metre with 1 watt of input (1W/1m). A speaker with a sensitivity of 100 dB/1W/1m will be 10 dB louder than one rated at 90 dB/1W/1m using identical amplification. That 10 dB difference means roughly twice the perceived loudness, from the same amp.

Watts determine how much headroom you have above that sensitivity baseline. More watts = more headroom before the amplifier clips. But a high-sensitivity speaker with a modest amplifier will outperform a low-sensitivity speaker with a massive one. This is why watt ratings are a marketing number and sensitivity is the engineering number.

The Inverse Square Law

In free field conditions, sound pressure level drops 6 dB every time you double the distance from the source. This is the inverse square law and it's the foundation of every throw calculation:

Free field calculations. Real environments vary due to reflections, absorption, humidity and temperature. Indoor venues typically add 3–6 dB from boundary reinforcement.

Acoustic Summing

When two identical speakers reproduce the same signal in phase and are physically coupled (close enough that their wavelengths interact), they acoustically sum. The result is a 3 dB increase in SPL — the same gain you get from doubling the amplifier power into a single speaker. Whether you double the power or double the coupled speakers, the result is 3 dB. Every time.

The key word is coupled. Two speakers that are too far apart will sum in some frequencies and cancel in others, creating comb filtering — a series of peaks and nulls across the frequency spectrum that sounds like a hollow, phasey mess. Proper coupling requires the sources to be close enough relative to the wavelengths being reproduced. As a rule, the spacing between sources should be less than half a wavelength at the highest frequency being summed.

Adding a second identical coupled speaker gives you 3 dB more SPL. Adding a second uncoupled speaker pointed at the same area gives you 3 dB of additional power on paper and a comb filtering problem in practice. Position matters as much as quantity.

Line Array vs Point Source — What You're Actually Getting

A true line array is a vertically coupled array of transducers that behaves as a line source — meaning SPL drops approximately 3 dB per doubling of distance in the near field (versus 6 dB for a point source), giving it dramatically better throw and more even coverage over long distances.

To achieve true line source behaviour, several conditions must be met:

• Elements must be closely coupled vertically — typically gap between elements of less than half wavelength at the highest reproduced frequency
• Sufficient number of elements to control the vertical pattern — a two-element "line array" is not a line array, it's a point source with a friend
• Consistent horizontal coverage pattern across all elements
• Proper J-curve splay to aim the array at the audience rather than the ceiling or floor
• Matched transducers and crossover points across all elements

Just because a manufacturer calls something a line array does not mean you are getting a line array. Many products marketed as line arrays are simply rectangular cabinets that can be stacked vertically. When advancing a show, ask the vendor specifically: how many elements, what is the vertical coverage angle per element, what is the splay range, and what is the rigging capacity. If they can't answer those questions, you're not getting a real line array.

Our Electro-Voice XLD 281 is a genuine compact line array element — engineered for true line source behaviour when properly configured, with controlled 100° horizontal dispersion and variable vertical splay for J-curve configuration.

Cardioid Subwoofer Configuration

A standard subwoofer radiates omnidirectionally — bass energy goes everywhere including behind the array, onto the stage, and into microphones. Cardioid sub configurations use physical placement and signal polarity/delay to create destructive interference behind the array and constructive interference in front, effectively directing bass energy toward the audience and away from the stage.

Common cardioid configurations include:

• End-fire — subs arranged in a line facing the audience, delayed progressively toward the rear. Simple, effective, requires depth.
• Reverse-cancel — one sub facing backward with polarity reversed and delayed. Compact, works in tight spaces, slightly less effective than end-fire.
• Gradient — two subs spaced apart with one delayed, creating a cardioid pattern. Requires precise delay calculation.

Cardioid sub configuration can reduce stage bleed by 10–15 dB depending on configuration and frequency. If your drummer is complaining about bass on stage and your monitors are fighting sub wash, talk to us about cardioid configuration before you add more wedges.

System Headroom

Headroom is the difference between your operating level and the system's maximum output before clipping. A system running at 100% output has zero headroom — any transient above the average level will clip, producing harmonic distortion that is immediately audible and potentially damaging to HF drivers.

Professional systems are typically designed to operate at 6–10 dB below maximum output during normal program material, reserving that headroom for transients. A system that sounds loud at 70% capacity is a properly sized system. A system running at 100% to get adequate level is undersized for the application.

This is another reason why raw watt ratings are misleading — a 2000W system running with 10 dB of headroom is delivering around 200W of average power. The remaining 1800W exists to handle peaks cleanly.

Impedance and Amplifier Loads

Impedance (measured in ohms) determines how much current a speaker draws from an amplifier. Lower impedance = more current draw = more power delivered (to a point).

• 8 ohm — standard single speaker load. Most amplifiers are rated at 8 ohm.
• 4 ohm — two 8 ohm speakers wired in parallel. Amplifier delivers more power but runs hotter. Most professional amplifiers handle 4 ohm loads.
• 2 ohm — four 8 ohm speakers in parallel. Only stable on amplifiers specifically rated for 2 ohm loads. Proceed with caution.

Wiring speakers in series doubles impedance and halves the power delivered. Wiring in parallel halves impedance and increases power, but check your amplifier's minimum rated impedance before connecting. An amplifier driven below its minimum impedance rating will overheat, protect, or fail.

Always verify amplifier minimum impedance ratings before building a passive system. If you're advancing a show with a passive system requirement on the rider, send us the rider and we'll confirm compatibility before the date.

Advancing Your Show

We have been providing professional audio for concerts, tours, galas and corporate events across Calgary and Alberta since 1987. If you are advancing a show or have specific rider requirements, contact us directly with the rider and we will provide a straight answer on what we can match, what we can cross-reference, and what we can't provide. We do not oversell our inventory.