Er det ok å seriekoble elmenter ?

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  1. #1
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    Er det ok å seriekoble elmenter ?

    Årsaken til at jeg spør er at jeg engang hadde en bok om PA.
    Den frarådet seriekobling av basser.
    Det som skjer er at dempiningsfaktoren blir påvirket ?

    I dette tilfellet så ønsker jeg å kjøre 4 diskanter pr side.
    2 i serie og så i parallell (pga krav til effekt). ?

  2. #2
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    Når man parallelkobler så halverer man impedansen i HT, har man 4 Ohms elementer er man nede i 2 ohm, og det kan være for tung last for mange forsterkere.
    Da kan man løse det ved å seriekoble i stedet, eller en kombinasjon av de to når man her flere elementer.

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    Tenker ikke på impedanse problematikk.
    Er meget godt kjent med å beregne dette i forhold
    til forsterkere.
    Tenker på økningen man får i reaktans
    (sving spole i serie med sving spole).
    Har lest i litteratur at man pga lyd kvailtet og dempnings faktor
    bør unngå å seriekoble (selv om impedanse er korrekt i forhold til forsterker).
    Har også lest om det i PA sammenheng (JBL ? eller Eminence)
    Men aldri fått noen forklaring på om det gjelder kun bass elmenter.

    Spurte bache (bil bygge firma i Sverige) Han mente at det ikke hadde
    noen betydning om elmenten var akustisk koblet slik som i push pull.
    Men at det burde unngås for en enhver pris om det var snakke om feks to separate kasser.

  4. #4
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    Har ikke lest nok rundt dette emnet, men jeg vet at store PA array systemer gjerne er parallell og seriekoblet, om dette har noen stor invirkning på lyden i negativ grad vet jeg ikke. Disse systemene er ofte bygd opp av 5 eller flere kasser hengende fra taket.

  5. #5
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    Var en diskusjon om dette på diyAudio nettop: diyAudio Forums - Series vs. parallel sound quality

    Konklusjonen ser ut til å være at serie-kobling ikke er et problem ift dempe-faktor og at JBL tar feil i dette tilfelle. Matematikken i dette kan jeg ikke etterprøve selv, men her to forskjellige forklaringer på hva som skjer:

    Forklaring 1:
    -----------------------------------------------
    I tend to agree with you that the JBL must have made a mistake. A simplified explanation of the problem may go more along these lines:

    Electrical Speaker Dampening is determined only by current Iemf, which is induced by voltage Vemf. The value of Iemf is determined by the total impedance in the circuit. If we assume that the output impedance of an amp is zero and that the connection cables are ideal, then the only impedance in the circuit is that of the speaker coil Ze. Iemf is then:

    Iemf=Vemf/Ze

    If two identical speakers are in series, then the total voltage VEMF is 2xVemf because these voltages are in phase. The total impedance is then ZE=2xZe and IEMF is calculated as:

    IEMF=VEMF/ZE=2*Vemf/(2*Ze)=Vemf/Ze=Iemf

    It follows that each speaker, given the same Vemf, generates the same Iemf. However, as this applies only to ideal cases, and we know speakers cannot be 100% identical, the voltages Vemf generated by the speakers cannot have the same value. Thus, it can be said that the damping factor is a bit lower for serial speaker connections but the serial connection cannot cause the factor to drop below 1, IMO.

    ------------------------------------------
    Forklaring 2:
    ------------------------------------------
    Originally posted by Richard Pierce:


    In article <kQiX5.1753$qs2.401109@dfiatx1-snr1.gtei.net>,
    Bill Whitlock <bill.whitlock@verizon.net> wrote:
    >Perhaps I confused you with my answer. To restate, I believe it is OK to
    >wire two 4-ohm speakers in series to present an 8-ohm load to the
    >amplifier, provided that the speakers are identical.
    >
    >Before reading the article by Richard Clark, I believed that doing so
    >would have a detrimental effect on damping factor (which can affect the
    >speaker's frequency response, especially at low frequencies). Others in
    >the audio field still believe this is a controversial issue.

    And it is only a belief, unfounded by any physics.

    The notion is that putting one speaker in series with another can
    adversely effect that damping. This conclusion is based on a
    highly flawed model of what the damping in the speaker REALLY
    is and what it is due to. To dispel this falsehood, it's
    necessary to do a more detailed analysis of what's really going
    on using the actual parameters involved.

    The damping of the speakers is due to very specific mechanisms,
    primarily mechanical (due to frictional losses in the
    loudspeaker suspension, and some minor absorbtion losses) and
    electrical (due priomarily to the DC resistance of the voice
    coil). The amount of damping is measured using the "Q" factors
    due to each contributing source.

    The measure of mechanical damping or Q, Qms is:

    Mms
    Qms = 2 pi Fs -----
    Rms

    where Qms is the Q factor due to mechanical losses, Fs is the
    resonant frequency, Mms is the moving mass of the system, and
    Rms is the mechanical (frictional) losses. Notice that there is
    no implicit term relating how the Qms is affected electrically,
    i.e., how it is connected to the amplifier. Now, with two
    drivers, we have double the mass, Mms, because we have two cones
    instead of one. But we have also have twice as much suspension
    and thus twice as much suspension loss, Rms. Thus the ratio of
    Mms to Rms remaines the same, and thus the mechanical Qms
    remains the same.

    The measure of electrical damping, or electrical Q, Qes is:

    Mms
    Qes = 2 pi Fs ----- Re
    2 2
    B l

    where Qes is the Q factor due to electrical losses, B is the
    flux density in the magnetic gap, l is the length of the voice
    coil wire immersed in the magnetic field, and Re is the DC
    resistance of the voice coil. Hooking two such system in series
    does three things:

    1. It doubles the moving mass Mms,

    2. It doubles the DC resistance Re,

    3. It doubles the length of wire in the magnetic field l.

    So while the intuitive leap might be to suggest that because the
    resistance Re is doubled, and therefore the Qes is similarily
    doubled, doing so completely ignores the other two effects.

    Let's look at the ENTIRE analysis. Let's double all the
    necessary quantities and plug them back into the equation and
    see what happens. For Mms, we'll substitute 2*Mms and so forth:

    2 Mms
    Qes = 2 pi Fs --------- 2 Re
    2 2
    B (2 l)

    and:

    And we can simplify by gathering the factors together. In the
    numerator, we have 3 instances of factors of 2, for a total of
    8, and there is a single factor of 4 in the denominator:

    8 Mms
    Qes = - pi Fs ----- Re
    4 2 2
    B l

    Simplifying one step further, ye factoring out the common factor
    of 4 now in both the numerator and denominator, we end up with:

    Mms
    Qes = 2 pi Fs ----- Re
    2 2
    B l

    which shows that the electrical damping for two systems in
    series is identical to the electrical damping for a single
    system alone. Q.E.D.

    This contradicts the seemingly intuitive notion that two drivers
    in series must be severely underdamped as a result of the
    additional series impedance. It's not the first time that
    intuition has failed to coincide with physical reality in audio.

    --
    | Dick Pierce |
    | Professional Audio Development |
    | 1-781/826-4953 Voice and FAX |
    | DPierce@world.std.com |

  6. #6
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    Takk afoelges for linken til denne gamle tråden.
    Ser ut som det er JBL som startet "rykte".
    Kanskje det betyde litt når avviket var stort
    på elmenter, men i praksis ingen betydning overhode.

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