How loud is loud, What DB is actually loud?

Rayray8, 01-08-11: 135db in a car is pretty easy to do with subwoofers. i use to compete with my car about 9 years ago and only had 1 12" subwoofer and would score 136db any day. these competitions are bass only, and usually people use simple test tones to hit one frequency. there are vehicles now that score well over 170db in these competitions.

Elevick, 01-08-11: Imagine what it takes to get to 170db if you keep doubling your power to gain a measly 3db? You need to gain about 10db to double the perceived volume. Even with 102db speakers (which are rare), it takes more wattage than any amp I've seen to get 170db. I imagine that it sounds pretty crummy and distorted at those levels.

If we optimistically assume 110 db for 1 watt, 170 db would require 1,000,000 watts. Doesn't sound too likely to me. Fortunately :-)

Regards,
-- Al

What?

:-)

Best regards,
-- Al

Doesn't adding a 2nd driver add 3db if the power stays the same? Been so long I forget. But if 100w does 100db with a single 12 then that same 100w going into a pair of 12's would equal 103db?

Driving two 100db/100W subs with two separate amplifiers, each providing 100W, would result in an spl of 103db, assuming that the subs are positioned such that their outputs are in-phase at the listening position.

Connecting two 100db/100W subs in parallel to a single amplifier, that would provide 100W into one sub, would also result in 103db, IF the amplifier is capable of providing the 200W that would be drawn by the halved impedance that the paralleled speakers would present to it. And assuming also that the amplifier has negligibly small output impedance (which is the case for most solid state amps, but not for most tube amps).

Connecting the two subs in series, btw, would not make sense as it would result in a reduction to 97db spl, with only 50W being drawn from the amplifier.

Rayray8 -- truly awesome. I'd imagine that one reason for keeping the tone bursts short is to prevent the voicecoils from melting!

Regards,
-- Al

Weseixas & Viggen900, one 100db/100W speaker will put out a certain small number of acoustic watts, in response to the 100 electrical watts that are being fed into it.

A second 100db/100W speaker, also being driven with 100 electrical watts, will put out that same small number of acoustic watts.

If the two speakers are at identical distances from the listening position, the number of acoustic watts arriving at the listening position will be double what it would have been with one speaker. Twice the number of watts (acoustic or electrical) corresponds to a 3db increase.

You may be thinking of the fact that a larger driver will tend to be more efficient than a smaller driver, everything else being equal, producing more acoustic watts for a given number of electrical watts. However, that has no relevance to the question being considered.

See "Multiple Sources" near the bottom of this page:

https://ccrma.stanford.edu/CCRMA/Courses/152/SPL.html

Kijanki's post and my previous post are correct.

Regards,
-- Al

01-09-11: Weseixas
The 3 db gain is correct for free space ( anechoic) go ahead and measure your hi-fi system, with speakers l/r and with room gain it is more than 3 db, when you turn off one side from the listen position.

Weseixas, room effects are a separate issue from the contention that I was disagreeing with. The contention I was disagreeing with was that the spl resulting from two paralleled speakers would increase 3db due to doubling of the power supplied by the amplifier, and ANOTHER 3db due to doubling of total cone radiating area.

My contention in response was that total radiated acoustic power would be doubled, resulting in a 3db increase in spl (neglecting any inequalities in the effects of the room on the two speakers). The Stanford paper I cited directly supports that, based on the assumption of "no interference." The paper Frank linked to takes interference effects into account (as distinguished from room reflection effects -- as you may realize they are two different things), and states that on average there will be a 3db increase, with a range between 0 and 6db depending on the interference effects at the exact listening position and frequencies.

Your post that I quoted above refers to a 3db increase as being correct apart from room effects, so I think that we are now essentially converged on that issue.

As far as room effects are concerned, I would certainly agree that inequalities of those effects on the sound produced by the two speakers could change the 3db figure, but not always in the direction of making it larger. Consider the situation where positioning is such that one speaker receives a bass boost due to room effects that is significantly different than the bass boost on the other speaker. Turning off the speaker that is receiving the smaller of the two boosts would reduce spl at the affected frequencies by less than 3db (as averaged over the listening space to account for interference effects), while turning off the other speaker would reduce it by more than 3db (as averaged over the listening space to account for interference effects).

Regards,
-- Al