Calculating line array sensitivity

[brucemck2]

How do I calculate the sensitivity of a line array?

I've got 8 c82s and 8 Founteks in a sealed cabinet, with crossover via DEQX and active amplification.

Reason for asking is that I'm trying to determine how much amplifier I'll need for the Accutons and the Founteks in a 3000 cubic foot room.

[JonMarsh]

Two considerations-

One, the driver mutual sensitivity for 1 meter response, depending on the wired configuration and net impedance.

Two, in the frequency range in which an array is a true line array, the SPL drops more slowly with distance because of the effective plane wave; in theory, a point source drops 6 dB for every doubling of distance, whereas an ideal peforming line array drops only 3 dB. The catch is "ideal"; at lower frequencies, if the line array doesn't go floor to ceiling, the array stops acting as much like a line source, and the output starts to drop at a more conventional rate. This accounts for why most "typical" size 6 foot line arrays tend to sound a bit shouty (upper mids and highs emphasized) in larger rooms with high ceilings, as the bass and very low mids drop off more.

Of course, the other matter is how loud you hope to play the system, and what power the speaker system is actually capable of handling and remaining in the linear range- I'd consider adding a larger, taller bass line array to your C82 setup, and maybe crossing in the 250 Hz area- the C82's even in a small room, say in an MTM, can be driven at moderately loud levels to early distress with full range material- they're only 5" drivers, after all.

~Jon

[brucemck2]

Bass is currently being handled by a pair of Mark Seaton's Submersives. The Accuton arrays have a measured F3 is 80hz and F6 is 65hz

Longer term I may build two "tall line bass arrays" that match. Right now I lack room in the room, unless the bass arrays goes on their side or my Wife lets me convert the bedroom!

90% of the time I listen at medium loud levels, but on occasion like to blast old 70's rock. Not to rock concert levels, but very loud.

[Piotr]

One good solution would be to use as tall midbass array as possible, preferably all the way from floor to ceiling. Then you can use 2-4 ordinary subwoofer boxes with a crossing slightly below that of the first standing wave between floor and ceiling. Subwoofer towers from floor to ceiling is overkill by a wide margin in most situations. Having uniform respons in the (aprox) 70Hz to 2kHz range is very worthwile OTOH.

The first standing wave between the floor and ceiling is about 70Hz when the height of the room is 2.4 meters. That's why it's wise to spread out the radiators from floor to ceiling to supress or totally avoid exciting this mode. Then you can safely use floor mounted subwoofers without exciting the floor-ceiling mode and you can concentrate on fighting the modes between the walls of the room by clever placement of the sub boxes.


/Peter

[brucemck2]

Appreciate help with thoughts on bass ... but what's the method to calculate the efficiency of a line of 8 c82s?

[Dennis H]

Base efficiency (1 driver, 1W, 1m) = Base sensitivity (1 driver, 2.83V, 1m) + 10*log(nominal impedance / 8 ohms)

The effective efficiency and voltage sensitivity gains from running multiple drivers can be calculated as:

Efficiency gain = 10*log(Number Drivers)

Sensitivity gain = 10*log(8 ohms / nominal impedance of series-parallel combo)

Net efficiency of system = base efficiency + efficiency gain

Net sensitivity of system = base efficiency + efficiency gain + sensitivity gain

[brucemck2]

Thanks. Exactly what I needed.

[Jim Holtz]

How do I calculate the sensitivity of a line array?

I've got 8 c82s and 8 Founteks in a sealed cabinet, with crossover via DEQX and active amplification.

Reason for asking is that I'm trying to determine how much amplifier I'll need for the Accutons and the Founteks in a 3000 cubic foot room.

Here's a spreadsheet that I ran across sometime ago. I don't remember who created it but it'll save you some pencil work if you have Excel.

Jim