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anonymous 22 April 2005

ok...I'm looking at buying (4) Mackie 1521's...now each Mackie will get a max spl at around 133db...long term spl 130db...if i had four of them...what would my LONG TERM spl be?...or how do you figure that out?

thanks,
mike

Comments

anonymous Fri, 04/22/2005 - 20:31

:? 8-)

You really can't rate something like that. Actually, I don't even know where you figure those sound pressure level numbers really mean anything. Overall volume will depend on the room your in and how much clean power your amps are pushing to the speakers. Plus I assume these PA speakers really aren't going to give you all that much low end, so you might want some subs. I prefer a steak and cheese myself. :wink:

Guest Sat, 04/23/2005 - 05:22

mike_anthes wrote: long term spl 130db...if i had four of them...what would my LONG TERM spl be?...how do you figure that out???

I do believe that long term SPL is referring to the highest level of "sound pressure level" that the speaker can re-produce without distortion (for a given amount of time).
Like for instance..say your guitar player is playing through the speaker. And he always sounds great. Until he holds that one note, and the speaker starts to "max out" or "distort" or better yet "clip".
The reason for this is the "sound pressure levels" are at such a high amount that the speaker is not able to sustain that frequency for any length of time. Sometimes not at all...if it is REALLY loud. (like a mic-pre being driven to loud in the signal path, or a mic too close to a guitar cabinet, or an arena type setting where there are 1000's apon 1000's of Watts of power and sometimes 100's of thousands of people screaming to the top of their lungs.
So the only thing you really need to worry about, are how many Watts of power you need for the shows you want to do.

AudioGaff Sat, 04/23/2005 - 16:27

The SPL numbers you get from a manufacturer are rather useless as they are derived from very special test conditions that don't represent real world conditions. Why is it that you are so concerened about SPL? Since SPL changes based on room, temp, humitity, freq, eq settings, headroom of anything in the audio chain, how the speakers are placed/mounted, and how far from the speakers you measure, and likely a few more things I'm not mentioning, your barking up the wrong tree with the focus on SPL

moonbaby Sat, 04/23/2005 - 17:27

Based on the Fletcher-Munson Law, every time that you want to increase the SPL by 3dB, you will have to double the power amp's RMS output and/or the speaker coverage. In other words, if a single cab generates 130dB "long term", doubling it to 2 cabs will yield 133 dB, and doubling THAT (4 cabs) will yield 136 dB. This is figuring that (one) cab is an 8-ohm load, and that the power amp will yield to the resultant 4-ohms-per-channel enough power to keep up with that. A good quality amp shouldn't have a problem with that. Tell the venue owner to expect 135dB within the confines of their walls...

AudioGaff Sun, 04/24/2005 - 00:06

The Fletcher-Munson Law is based on all things being controlled and equal. For one thing, impeadence is not constant and differs by frequency. The other thing that most people fail to consider when they are using Watts to get vaules such SPL, is that not all Watts are available for sound. Some wattage in an amp, the speaker and the cabinet the speaker is in, are not 100% efficient in using wattage. A certain percentage of wattage for each item is wasted as heat energy. One amp, speaker and cabinet combo rated at a higher wattage values then another amp, speaker and cabinet combo may not in fact have a higher SPL as you would expect.

It is not the number of Watts as much as it is how efficient the use of the Watts is that matters and is one main thing that makes one amp. speaker and cabinet better than another.

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