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Ny kategori - aktiv deling?

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daniels View Drop Down
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  Quote daniels Quote  Post ReplyReply Direct Link To This Post Topic: Ny kategori - aktiv deling?
    Posted: 04 Dec 2014 at 23:12
Jeg arbejder meget med aktive filtre, og der er lige så mange ting man skal tilpasse i aktivt som i passivt.
Der er ingen hurtige genveje.

Man kan ikke bare sætte nogle delefrekvenser med LR filtre og tro at der er styr på fasen... Der er de samme udfordringer med aktivt som med passivt.

Den store fordel i digitalt aktivt ligger i mulighederne for at simulere filter og DSP funktioner - og det er en stor fordel ved udvikling af en højttaler. Med DSP kan man korrigere for rummet.
Man kan selvfølgelig også sætte en DSP på et passivt filter og få den effekt.

Støj er nu ikke det store problem, hvis filteret er bygget godt. Her er det vigtigt at gå metodisk frem og sikre sig man ikke har strømsløjfer i sit system. Der skal bare én enhed til, med problematisk håndtering af jord, for at højttalerne støjer. Høj pris på grejet er ikke garanti for korrekt håndtering af jord/stel i en komponent.
Jeg har oplevet at aktive filtre kan være ret følsomme overfor dette - også selvom det ikke er filteret der er ballademageren, men en anden komponent, som ellers ikke plejer at lave bøvl.

Jeg synes dog A/D - D/A delen bør have opmærksomhed. I disse HD dage, skal man være opmærksom på at f.eks. mange af miniDSP produkterne kører 24Bit/48KHz og GroundSound 24Bit/96Khz. Og valg af opamps kan være lidt af en religion for nogen.

__________________________________________
DanielS - Alkohol tager toppen af ubehagen ved livet - Der findes ikke dårlige ideer, kun mangel på vilje til at udføre dem!
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  Quote svendborg@email Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2014 at 12:38

Husk at nyde musikken også.
Jeg har været nødt til at fjerne computeren fra lytterummet, ellers sidder jeg og piller hele tiden :-)
Altså i filteret.
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  Quote Kjeldsen Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2014 at 12:09
en ting man hurtigt glemmer når man arbejder aktivt/DSP er hvilken belastning forstærkeren ser. Når man arbejder passivt, tror jeg mange tænker på at impedanskorrigere, og det er der nok ikke mange der gør ved aktiv deling. Derfor kan en forstærker godt kommer på en ekstra prøve i et aktivt set-up fremfor passiv.

Jeg bruger selv MiniDSP og Holm til målinger. Det er bestemt hurtigere at nå et godt resultat, men det tager stadig lang tid. Jeg justerer stadig efter 6 mdr.
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  Quote vincent. Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2014 at 16:03
Nej jeg har ikke prøvet at have den tilgang til aktive filter, men det kunne da være sjovt. Et er sikkert, man får ikke foræret noget ved den aktive frem for den passive løsning i forhold til hvor nemt det er at vælge det rette filter. Det er dog hurtigere at loade et nyt filter når det er digitalt det forgår, så til de hurtig lyttet test hjælper det, men så er der det næste aspekt, folks hukommelse omkring lyd indtryk ofte er meget meget kort og ikke specielt detaljeret. Så målinger er endelig det eneste valide at læne sig op af.
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  Quote syncroniq Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2014 at 13:17
Hey,

Ellers skulle vi prøve og lave nogle herinde. LspCAD kan simulere aktive filtre ved jeg. 
Har du prøvet det?

Jeg kan huske at nogen engang har snakket om at dæmpningsfaktoren ikke er super vigtig over eneller andet værdi. Jeg kan ikke huske hvor høj, eller hvem. Plus, at med en seriemodstand på måske 0.2 ohm, ryger dæmpningsfaktoren vidst ikke super langt ned.

Min bekymring er støjen fra det aktive filter. Og så at det er så nemt, at folk bare sætter det til og sjusser sig frem. Man skal igennem præcis de samme steps, for at få en god højttaler, om det er passivt eller aktivt.
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  Quote vincent. Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2014 at 12:48
Det er ikke så meget den tabte effekt jeg bekymre mig om, forstærker kraft i høj kvalitet koster jo ikke specielt mange penge nu om stunder. Det er snare tabet af dæmpnings faktoren på forstærkeren som bliver sat over styr i det passive filter. Men igen træerne vokser ikke ind i himlen, der er rigtig mange gode passive højttalere. Jeg har godt nok et sæt aktive, men de er tunge som jeg ved ikke hvad.. Men mon ikke man kunne finde nogle andre her inde der kan byde ind med et sæt mindre.
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  Quote syncroniq Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2014 at 09:42
Hey,

Vi må hellere få hørt nogle aktive højttalere så Smile
Har i en aktiv højttaler man kan tage med til f.eks. julefrokosten? 

Jeg forstår dog ikke hvordan et passivt filter kan absorbere 20% af energien uden at falde i lydtryk. Det er jo meget lidt modstand der er i spoler.
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  Quote vincent. Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2014 at 00:01
Jeg fandt denne artikel på enjoy the music.

Den er skåret lidt ud i pap. Men ikke des do mindre lære rig..




The performance benefits of active over passive loudspeakers is substantial. Even a system, which incorporates the best available stand-alone power amplifier, will never achieve the performance of a similar active system. Yet active loudspeakers are slow to be accepted for home use, when they are the only choice of the professionals who master your DVDs and CDs.

This is a strange anomaly that doesn't exist in other significant consumer markets. Take the motor industry for example. When buying a car, would you buy the chassis from Ford and the engine from General Motors. Of course not, the engine would have to be unnecessarily modified and overbuilt to be able to drive the many different transmission loads imposed upon it. Yet this is the accepted thinking in the market for residential hi-fi and home theatre installations, where the use of separately sourced amplifiers and loudspeakers, and the extra cost and inefficiency this entails, is not only tolerated, it is recommended!

Why is it then that the obvious merits of Active loudspeakers long accepted as standard in the professional arena have been slow to be accepted for home use?

Many Hi-Fi dealers pledge to sell customers the 'best system for their money', and yet they sell separates, when one of the many advantages of self powered active loudspeakers, is a considerable economy in cost, for any given performance level.

Why is this? The common complaint is one of inflexibility. Generally, you cannot upgrade an active speaker with new amplifiers, which limits consumer choice. This is a myth that relies more on the commercial sensibilities of dealers and their suppliers (the separates manufacturers) than on anything else. It is simply the fact that an active loudspeaker is an optimized coupling between amplifier and loudspeaker driver, and is the best solution, and an upgrade in the longer term is unlikely to be necessary. Thus an active system will always provide a superior result than its separate counterparts. Dollar for Dollar, in performance and value for money, there is no contest.



The Professional Approach

The demands of the recording industry were for highly accurate, ruggedly built speakers, capable of reproducing the dynamics and subtleties of the original performance, and frequently capable of being used on location as well as in the studio.

The only solution to meet this need was to design and build the amplifiers and drive units as a single close matching entity in one enclosure. Hence, Active loudspeakers are today used by virtually every recording company, every major recording studio, and every major film studio.

What then are the main advantages of Active loudspeakers and
disadvantages of Separates?
Economics

Firstly, it costs a lot less to design and build high quality amplifiers and drive units in a single enclosure than it does to build similar quality separates. Equal or better performance at lower cost is a good starting point. The advent of DVD and Home Theatre has done much to take the 'black art' out of sound reproduction in the home. Gone are the wooden blocks, and green inks but crazily priced loudspeaker cables are still prevalent. Active loudspeakers only need a low cost, good quality microphone cable, to transmit the high impedance output from today's surround processors. Another major cost saving.



Crossovers: Electronic Vs. Passive

A major source of difficulty in designing a Passive loudspeaker system lies less in selecting the drive units or enclosure, but in designing and building the passive crossover. This device with its large capacitors and resistors receives the low impedance, full frequency output from the amplifier, and divides it between the two, three or more drive units. It is hardly surprising when taking a look at the size and complexity of these unpowered components that the passive crossover can absorb up to 20% of the amplifier's power output. And that's not the only problem!

The magnitude of the frequency response of both active and passive loudspeakers can be controlled, with good design, to be within 1dB of one another. However, the phase component of the frequency response will always be better in an active system. The active filters produce better filter roll-off characteristics at crossover. Combine this with the inclusion of a variable all-pass filter at each crossover point to correct the phase response of the drive units through the crossover regions and the result is a loudspeaker with much better group delay characteristics. The benefit to the listener will be improved polar response and therefore radiated power response. Such an active loudspeaker will have a large stable sound field with stable imaging and source location. Very difficult and costly to achieve with a passive loudspeaker system.

A passive crossover will only operate correctly into the load impedance of a particular loudspeaker drive unit. However, the impedance of a loudspeaker drive unit will change with the amount of power input. This is because loudspeakers are very inefficient and most of the input power is dissipated as heat in the voice coil. As a result the temperature of the voice coil will rise and because copper has a positive temperature coefficient of resistance the impedance of the loudspeaker drive unit will rise. The result will be frequency response errors as the filters move from their designed response with increased input power. This effect does not occur in active loudspeakers where the filter response is maintained independent of input power to the loudspeaker.



Active Vs. Passive Amplifiers

The Separates amplifier manufacturer, has no idea what is going to be hung on the end of his product. Hence the need (as would be the case in the car analogy), to massively over-build to ensure that the amplifier will sound good with almost any speaker impedance and cable. It is not surprising that the massive amplifiers that typify the high end today are both costly and power consuming.

These problems of efficiency, size and cost are much reduced in the case of amplifiers designed for Active loudspeakers. Here the designer has the luxury of designing an amplifier pack containing separate mono amplifiers that only have to power one drive unit, whose every performance characteristic, bandwidth, frequency range, power handling, and shortcomings, are known to the designer.

Because the amplifiers in an active loudspeaker system are only required to operate over reduced frequency bands the intermodulation distortion products present in a passive system will be dramatically reduced, by typically 20dB, in an active system.

For a given amount of amplifier power, an active loudspeaker can be expected to produce approximately 6dB more level (twice as much) than the equivalent passive system. Furthermore, power for each drive unit may be more optimally specified in an active system. A tweeter, for example, requires much less power than a woofer to produce a balanced system performance.

A power amplifier designed specifically for the limited frequency range of an individual drive unit gains further benefits in efficiency, due to the fact that the wider the amplifier bandwidth, the less efficient it is. A well designed two or three way mono active power amp, for a given input and power rating, will always be capable of safely reaching higher peak SPL levels with less distortion than the equivalent single wide band power amp. This additional safety margin is now essential for coping with the wider dynamic range of DVD-Audio, SACD, DTS and Dolby Digital film soundtracks. In an active system the absence of both passive crossovers and long cable runs, together with a known amplifier damping factor, prevents the modification of the loudspeaker drive unit "Q" ensuring better controlled low frequency performance.
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  Quote syncroniq Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 16:40
Hey,

Jeg kan måske se en-to fordele ved aktiv. Men jeg kan også se lige så mange ulemper. 

Hvis du blander en dsp ind i billedet, kan den jo bruges i begge tilfælde. Det samme gør sig gældende med følsomheden. Du kan jo sætte en forstærker til hver enhed lige som med aktiv filter.

Delay i passive filtre gøres ved at dreje fasen, ingen problem. 

LspCAD kan simulere dit passive filter ud i højttaleren du simulere på, og du kan derved lytte til så mange passive filtre du vil.

Rummet gøres vel ikke med et aktivt filter, men en dsp. Så det kan du også gøre ved passive bi-amp.

Du får ikke mindre kabel ved aktivt filter. Du får mere da du er tvunget til at bruge flere forstærkere. Inde i højttalere kan jeg ikke se hvordan det bliver mindre kabel ved aktivt.

Ved aktive filtre skal du tage højde for det samme som ved passive. Altså frekvensulineariteter, delay, baffelstep, niveau osv. Hvis du bare vælger et 2. ordens LR filter, er det dømt til at fejle præcis som hvis man gjorde det samme ved passive filtre. 

Den eneste vej frem (om det er aktiv eller passivt) er igennem måling, simulering og trimning.

Jeg siger ikke at aktive filtre er dårlige, men bare at jeg ikke mener de er bedre. Der er ingen støj i passive komponenter som i et aktivt filter. Der er dog et lille tab (meget lille).

Skulle der komme flere der bygger med aktive filtre, så opretter vi meget gerne et subforum. 

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vincent. View Drop Down
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  Quote vincent. Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2014 at 01:26
Hver forstærker trin arbejde i et specifik område og har dermed alle de kræfter der måtte være behov for

Ingen komponenter imellem forstærker modul og enhed.

Korter kabel træk

Betydeligt hurtigere at lave forsøg med filter og ganske nemt at lave A -B - C sammenligninger imellem de forskellige filter design hvis det er en digital dsp der kan gemme flere opsætninger.

Man er ikke død og pine tvunget til at balancere følsomhed ud

Man kan nemt korrigere for delay enhederne imellem

Man kan kompensere for rummets unoder i forhold til room gain, det ændre dog ikke på at akustikken i rummet stadig skal være god da man i sagens natur ikke kan ændre på efterklangs tid, ja medmindre man da har en skov af højttaler og en stor mængde dsp til at korrigere og lave signaler i modfase. Meyer sound har et system der kan netop dette.

   

Edited by vincent. - 16 Jul 2014 at 01:28
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