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<blockquote data-quote="Scott Bolt" data-source="post: 137943" data-attributes="member: 3950">Re: dB calculationsIvan has it right.&nbsp; The problem is that most people want a simple answer to a question that really isn&#039;t that simple at all.SPL is calculated as a weighted average over a wide frequency range.&nbsp; There are several different weighting curves used for various different purposes.See the graphs here:&nbsp; &nbsp; <a href="http://en.wikipedia.org/wiki/A-weighting" target="_blank">http://en.wikipedia.org/wiki/A-weighting</a>The &quot;A&quot; weighting is the most frequently used.&nbsp; As you can see, this is how a double 15&quot; with a horn can end up with an SPL the same as a 2-way 8&quot; speaker <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f609.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=";)" title="Wink&nbsp; &nbsp; ;)"&nbsp; data-smilie="2"data-shortname=";)" />&nbsp; The lows are practically discarded in this weighting.&nbsp; The A weighting was designed for use in determining hearing damage (thus the reason LF is discarded in the weighting).If you were to cut the HF out using a cross-over then used an A weighted SPL measurement, it would be practically useless IMO.As for the original topic, I generally figure that center clustering a pair of subs will increase the output enough for it to be noticeable to anyone who was listening for it compared to having the subs far enough apart not to have any coupling.I like the +3db number to go along with my &quot;easily noticeable&quot; definition.&nbsp; Center clustering subs also has the advantage of providing a more even distribution of sub frequencies over a wider area than having the subs stage left and stage right.</blockquote>

[QUOTE="Scott Bolt, post: 137943, member: 3950"] Re: dB calculations Ivan has it right. The problem is that most people want a simple answer to a question that really isn't that simple at all. SPL is calculated as a weighted average over a wide frequency range. There are several different weighting curves used for various different purposes. See the graphs here: [url]http://en.wikipedia.org/wiki/A-weighting[/url] The "A" weighting is the most frequently used. As you can see, this is how a double 15" with a horn can end up with an SPL the same as a 2-way 8" speaker ;) The lows are practically discarded in this weighting. The A weighting was designed for use in determining hearing damage (thus the reason LF is discarded in the weighting). If you were to cut the HF out using a cross-over then used an A weighted SPL measurement, it would be practically useless IMO. As for the original topic, I generally figure that center clustering a pair of subs will increase the output enough for it to be noticeable to anyone who was listening for it compared to having the subs far enough apart not to have any coupling. I like the +3db number to go along with my "easily noticeable" definition. Center clustering subs also has the advantage of providing a more even distribution of sub frequencies over a wider area than having the subs stage left and stage right. [/QUOTE]

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