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More than 1 spkr. Why?

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  • #46
    There are situations though where the speaker and enclosure design are quite surprising and (from my perspective at least) challenge the idea of what should work well or not.

    As an example, I recently had a 350W bass-sub powered system in for repair with an 8" speaker. I thought it was going to be less than spectacular, but that thing really shook the workshop. A light and rigid glass-fibre cone with huge x-max for the size, and a super flexible suspension, but a tiny (but long) voice coil. I wondered what it would be like as a guitar speaker and it reproduced treble just fine, the limitation being the cutoff frequency of the power amp LPF.

    Increasingly, bass guitar is being handled by ever-smaller drivers. 4x6" cabs are commonplace. Maybe not the projection of larger units, but no shortage of low-end. The modern trend for emphasized bass in recorded music has probably been responsible for the adoption of improved drivers in instument amplifiers. I don't think there's been an engineering reason why this couldn't have been done years ago - just perception and fashion. When I began playing, 18" speakers were pretty common for bass. I rarely see them these days other than in PA systems.

    There are some setups that I've encountered that sound much better than they ought to; A combo with 3x7.5" eliptical TV speakers used for double-bass, a 3x10" staggered vertical guitar cab in a restricted, closed-back enclosure, and a plastic combo with 2x2.5" drivers.

    And what about those Mk1 Peavey Nashville 400 combos with the 15" pancake magnet speakers? Sweet treble and wonderful mids. Well-balanced and a delight to play.

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    • #47
      Originally posted by Mike Sulzer View Post
      I am having trouble figuring out how this works. How does it happen? Anybody have a reference?
      Have a search on 'mutual coupling'.
      My band:- http://www.youtube.com/user/RedwingBand

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      • #48
        This article seems to present a very scientific analysis (although it has not reproduced very well in html or whatever):

        Loudspeakers, Mutual Coupling and

        It states that acoustic power is doubled (with two speakers) in various circumstances, and even quadruples in some circumstances!

        Edit: The above article keeps referring to two identical loudspeakers which are 'receiving the same signal' (as a single speaker). If that means 'the same voltage', then the total electrical power input is doubled anyway!
        Last edited by Malcolm Irving; 11-24-2015, 05:34 PM.

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        • #49
          Originally posted by Malcolm Irving View Post
          This article seems to present a very scientific analysis (although it has not reproduced very well in html or whatever):

          Loudspeakers, Mutual Coupling and

          It states that acoustic power is doubled (with two speakers) in various circumstances, and even quadruples in some circumstances!

          Edit: The above article keeps referring to two identical loudspeakers which are 'receiving the same signal' (as a single speaker). If that means 'the same voltage', then the total electrical power input is doubled anyway!
          Thanks! Relevant quote:


          The influence of room boundary walls on the power output of a loudspeaker has been well researched and documented. In [1], Allison shows how the presence of a single boundary wall increases the power output of a loudspeaker by 3dB at low frequencies, and that introducing two more boundaries gives a net increase of 9dB. More recently, Ward and Angus [2] have extended the concept further to include all six boundary walls. The significance of these findings in the context of this paper is that the presence of a single boundary gives rise to the same sound field as would the introduction of a second, identical loudspeaker placed at the mirror-image position in the absence of the wall. It is therefore logical to assume that introducing a second, identical real loudspeaker - the second of a stereo pair - would also increase the power output of the first loudspeaker.


          So what the second loud speaker does is like what a wall does. (And all of this only works at low frequencies, less than 1/4 wavelength of relevant dimensions they say, but I am thinking much less than 1/4 wavelength to really work right.) So one wall doubles the power radiated. And a second speaker placed at the image point does the same thing. But the second speaker takes the same amount of power as the first one, unlike the wall, which does not take any power at all. So did we gain anything?

          Well, maybe. The speakers act as walls for each other; in effect, when we use two speakers we fill both sides of the "wall" with sound, while with a real wall there is sound only on one side.

          But I think the key point is that it only works at low frequencies and that does not do much good for electric guitars, which do not have much.

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          • #50
            Originally posted by Malcolm Irving View Post
            This article seems to present a very scientific analysis (although it has not reproduced very well in html or whatever):

            Loudspeakers, Mutual Coupling and

            It states that acoustic power is doubled (with two speakers) in various circumstances, and even quadruples in some circumstances!

            Edit: The above article keeps referring to two identical loudspeakers which are 'receiving the same signal' (as a single speaker). If that means 'the same voltage', then the total electrical power input is doubled anyway!
            Thanks Malcolm, great reference. So... instead of adding a speaker add a wall.

            One thing jumped out at me in respect of the power output and cone area.

            "Also, if you double the area of the diaphragm of a loudspeaker drive-unit, given the same diaphragm velocity, the power output will again increase by +6dB."

            If you double the area then you double the force required as there is twice as much air to push. The driving force is unchanged (or at the very least not doubled) so the acceleration must be less and therefore so must the velocity. Thus the power output is not doubled either.
            Experience is something you get, just after you really needed it.

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            • #51
              Originally posted by Mike Sulzer View Post
              ...But I think the key point is that it only works at low frequencies and that does not do much good for electric guitars, which do not have much.
              The results provided by Celestion seem to indicate that mutual coupling works pretty well over much of the guitar relevant frequency range, see link in post #19.
              My band:- http://www.youtube.com/user/RedwingBand

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              • #52
                Originally posted by pdf64 View Post
                The results provided by Celestion seem to indicate that mutual coupling works pretty well over much of the guitar relevant frequency range, see link in post #19.
                This could just be the "antenna array" effect I mentioned. More power directly in front, less power at greater angles. The have not shown that more total power was transmitted because they have not shown that the impedance the drivers looked into went up..

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                • #53
                  By the way, speaker makers are prone to the same illnesses as any other business - fudge the numbers. Just because the audio engineering community likes to list speaker efficiency by SPL generated by 1W at 1M on axis doesn't mean they like it. For instance, 1W in 8 ohms is ... um, 2.828Vrms if I punched the buttons right. Speaker makers have done tricks like reporting the SPL generated by 4 ohm speakers with 2.828Vrms drive - and just not mentioning that this is 2W into 4 ohms. They also do certain tricks like finding a cone resonance where the cone is really humping out the audio power because it's resonant there, and doing their audio testing at a single frequency - that's right, the one at the resonance, and quoting that.

                  The hideously bad efficiency gives lots of ways to cheat... er, I mean, misunderstand the proper way to report efficiency. But down at the bottom of this is Mother Nature's insistence through the laws of thermodynamics that there ain't no free lunch.
                  Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                  Oh, wait! That sounds familiar, somehow.

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                  • #54
                    I had never known the horrible efficiency numbers before I saw them in this thread (0.5%).
                    And years and years of development with no big gains.
                    Think if there were some revolutionary development in the efficiency, we could flip the speaker around (as generator) and harvest noise pollution for energy.
                    Originally posted by Enzo
                    I have a sign in my shop that says, "Never think up reasons not to check something."


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                    • #55
                      Guitar speakers are more efficient than hi-fi speakers. Here's a useful on-line calculator:

                      Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs speaker sensitivity 1 watt = 2,83 volt box chart - sengpielaudio Sengpiel Berlin

                      A 100dB sensitivity guitar speaker (which is about right for a good one) is 6.3% efficient.

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                      • #56
                        Guitar speakers are designed for efficiency; they are woofers used to a much higher frequency than they "should be", for example, if flat response is the goal. Thus the "problems" with a guitar speaker response become part of the sound of the guitar. Everyone is adapted to the sound, and so it is "right". But the details are important, and small differences in the design of the speaker make audible differences in the sound. That is why Eminence has 3,456,372 different models of guitar speaker for sale. Well, that, and good salesmanship.

                        Originally posted by Malcolm Irving View Post
                        Guitar speakers are more efficient than hi-fi speakers. Here's a useful on-line calculator:

                        Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs speaker sensitivity 1 watt = 2,83 volt box chart - sengpielaudio Sengpiel Berlin

                        A 100dB sensitivity guitar speaker (which is about right for a good one) is 6.3% efficient.

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                        • #57
                          Originally posted by Mike Sulzer View Post
                          Eminence has 3,456,372 different models of guitar speaker for sale.
                          That's why I call Eminence the "Baskin-Robbins" of speaker manufacturers. Too many to make a decision = the tyranny of choice. It was so much easier when they offered only a very few to the public, up 'til the marketing boys took over. (Many more choices than that to manufacturers with $10,000 and up orders.) Vanilla, chocolate or strawberry, whaddya want? Now customers get lost trying to decide which flavor today. Butter brickle, or peach melba? And 3 dozen others, just the 12's. The genie's not going back into the bottle; I've found a few "favorites" in the crowd I can recommend heartily to customers. But spend a lot of jaw time "I dunno about that one, never tried it," and "don't know what's so much better about the $200+ speaker over the $65 one." Who has the time? Budget? Can't really tell much with recorded samples over the interweb. What is nice though, even the cheapest Eminence sound pretty darn good.
                          This isn't the future I signed up for.

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                          • #58
                            For me the answer to thread is pretty simple: relative to a cone area the low freq. loose to much energy comparing with hights because low frequencies are not so directive like mids and hights are. As far you going back from source you will loose quick the low freq. projection compared with hights cause it simple loose quick its energy. Imagine a small portable radio in back of a stage. You still hear it well how it bark but it have not "body". So, you need to compensate this somehow. Acoustical coupling is the most eficient way to do it as I know.Put two identical speakers close enough to work in the same phase on the floor and you gain instantly +6db acoustical pressure in bass.Smart enough, isn't it ? Over that like a second benefit the dispersion in hights will improve radicaly.
                            Basically you dont need to improve the lows freq. but to compensate the loses of low freq. wich are wide dispersed everywhere (more than: selective absorbed and reflected or canceled by environment) instead to be projected straight in you face like hights are.
                            Catalin
                            Last edited by catalin gramada; 12-07-2015, 10:18 AM.
                            "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."

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                            • #59
                              Originally posted by Malcolm Irving View Post
                              Yup. A physics lesson that's gone wrong somewhere.
                              Well Ive got the two spkrs in: thankfully no discernable difference between one side or other (c10Q + p10R). Tbh I cant hear much difference in tone or much at all to my fender oxfart 12". Perhaps a bit honkier and 'voxy' which is nice I think.. but the bass farts out badly: basically they sound a bit "cheaper", the 12" sounds richer and creamier/ a better quality spkr. Just. (there's very little difference tho: the 12" farts too as the name suggests).

                              If Id have the choice.. Id have stuck with the 12". So rather an expensive side-step (for me).

                              Maybe a case of 'not broken in' I dunno.. but tried a fresh-out-box single p10R and didnt hear any similar flaky/ farty bass suggesting break in not the Q.

                              More consternation with gtr amps for me.. one day I will get an amp I can say 'hey that sounds great!' and stick with it: tried for 30 yrs now & still cant find it tho. SC

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                              • #60
                                Originally posted by catalin gramada View Post
                                For me the answer to thread is pretty simple: relative to a cone area the low freq. loose to much energy comparing with hights because low frequencies are not so directive like mids and hights are. As far you going back from source you will loose quick the low freq. projection compared with hights cause it simple loose quick its energy. Imagine a small portable radio in back of a stage. You still hear it well how it bark but it have not "body". So, you need to compensate this somehow. Acoustical coupling is the most eficient way to do it as I know.Put two identical speakers close enough to work in the same phase on the floor and you gain instantly +6db acoustical pressure in bass.Smart enough, isn't it ? Over that like a second benefit the dispersion in hights will improve radicaly.
                                Basically you dont need to improve the lows freq. but to compensate the loses of low freq. wich are wide dispersed everywhere (more than: selective absorbed and reflected or canceled by environment) instead to be projected straight in you face like hights are.
                                Catalin
                                But just multiplying the spkr according to this means more cone area = more losing of the bass. So it doesnt fit as a reason for multiplying the spkr (rather it seems counter-intuative according to your explanation if it means just mote mids and top is heard if multiplying/ bass is lost).

                                The only reason I can ascertain from the replies as an answer directly to the OP question, is power. Multiply spkrs = raising the power = making effectively the amp just louder. I cant see any other reason whatsoever. In this case, if this is the only case, then for me it was exactly the opposite of what I needed. Live & learn the loooong way for me re. gtr amps. Still an utter mystery. SC

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