SPL in a Line array

[becki200]

Hello, maybe a stupid question, but i never understood the "dB".
I have 4 speakers with a SPL of 91 dB each. How much will it be with 4 speakers in a line array? 94 ? 97 ? Please help me. Thanks and best regards Thorsten

[TeLHannos]

Hi becki200,

since your drivers are coherent sources, the system gains 6dB when the sources double. Since they double two times the total gain is 12dB.
So the system SPL is 103dB ideally. Hope that's right

Kind regards,

Hannos

PS: Schau doch mal [url=http://de.wikipedia.org/wiki/Schalldruckpegel] hier, da kannst es selber nochmal nachschauen
Kohärente Schallquellen sind z.B. zwei baugleiche Lautsprecher - inkohärente Quellen sind verschiedene Instrumente - also beispielsweise Trompete und Saxophon. Wenn der Schalldruck gleich ist lässt sich die Kette - wie oben - einfach berechnen.
Ich hoffe ich konnte dir helfen.

[Scottmoose]

It depends how they're wired (which is also going to depend on the end impedance... )

Take series wiring. If you wire four drivers in series, SPLs will remain unchanged as each driver now 'sees' 1/4 the voltage of a single unit, impedance will be 4x that of a single driver, and individual cone displacement will be 1/4 that of a single unit.

If you wire four drivers in parallel, each driver will 'see' the same voltage as a single unit. Displacement will be the same as the single unit, impedance will be 1/4 that of the single unit, and SPLs will increase by 12dB.

Both of these could result in a difficult impedance load, unless you've got drivers with a 16ohm nominal impedance (in which case parallel will be fine if your amp can take a 4ohm load; most can), so a combination of 2 parallel packs of 2 series wired drivers might be the best compromise. That would give a +6dB increase in SPLs for a 50% reduction in individual driver displacement, and a nominal load = to that of a single unit. So, if the original drivers are 91 dB, you'd get 97dB out of them for 1w of power. To put that in perspective, if you were using a single driver, you'd need 4w to make it go that loud, displacement and distortion would be far higher, while powerhandling and dynamic bandwidth far lower.

[becki200]

Thank you Hannos and Scottmoose, that was the answer i was looking for. I think i will wire them as Scottmoose suggested 2 in series and then parallel the other 2 in series. Or maybe i can get some speakers in 16 Ohm.. Well see.
Any ideas about the match on sunday?? OK thats OT

[Scottmoose]

What drivers were you thinking of originally? Or was it more of a hypothetical question (always good).

Hmm. The England v. Germany match. It'll be close, that's for sure. Assuming that our lads actually play as we know they can, then my guess is 2-1 to England. Pace and general movement has been a problem for us though; you guys have looked much more energetic in the group stages & you'll run rings around us if we don't address this. I'm hoping Joe Cole will be starting on Sunday, he can give us that bit extra. Both sides have some injury problems, so that'll cancel itself out. I'm not convinced us playing Gerrard down the left is such a good idea; it works if he stays there, but he often pulls further into the centre, leaving far too much free space, although admittedly he curbed that habit a bit against Slovenia the other night.

OK, on balance, I still reckon 2-1 to England, but it's going to be tight.

[becki200]

Hi Scottmoose, question was more hypothetical. As always i have a low budget, so i think
i have to wait until i get some pretty cheap speakers.
Yes an you are right it will be close (the match) i think it will be 8:7 or so (penalty)
But i think Germany will win, sorry

[Scottmoose]

According to the BBC website, it appears that a psychic octopus with a remarkably successful prediction-rate agrees with you about the outcome. Let's just hope it doesn't end up with penalties & whoever proves the best team on the day wins.