سازگاری Matching بلندگو با آمپلی فایر

سازگاری Matching بلندگو با آمپلی فایر

دوشنبه 8 جولای 2013
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موضوعی که قبلا هم مطرح شد بحث مچینگ بین بلندگو و آمپلی فایر هست. بنظر آرتور سالواتوره این مچینگ بسیار بسیار مهم هست ، خیلی بیشتر از تصور عموم آئودیوفیل ها و یادمه تو سایت آئودیو پکس Audio PAX قبلا مقاله ای بود در این مورد تو سایتم بهش اشاره ای کردم و دلیما میگفت مچینگ بلندگو با آمپ خیلی مهم هست و حتی مثالی آورد از اینکه اگر بلندگو دیستورشن اش هارمونیک دوم با فاز x باشه و آمپ هارمونیک دومش با فاز x صدو هشتاد درجه اختلاف داشته باشه این دو همدیگر رو تا حدی خنثی میکنند.

میدونیم فیدبک هم تو بعضی آمپ های لامپی مثل Lamm از بیرون قابل کنترل هست تا دمپینگ فکتور بر اساس بلندگو تغییر کنه و حتی نسبت ترانس خروجی لامپ ها هم تو مچینگ موثره و برای همینه ممکنه تو تنظیم 8 اهم صدا با تنظیم 4 اهم فرق کنه.

پس جای تعجب نداره اگر ما تجربیات متفاوتی از یک بلندگو یا یک امپ در مچینگ های مختلف داشته باشیم همونجور که تو اتاق های متفاوت بلندگو صدای متفاوت داره.

در ادامه این بحث به طراحی برخوردم که مطلبی در این مورد نوشته بخونید :

http://www.6moons.com/audioreviews/tomevans/lineara_4.html

Tom Evans Audio Design

The Amplifier/Speaker Interface
Tom believes that today’s HiFi design culture has been looking at things “the wrong way ’round. First, HiFi requires a source such as vinyl, CD, radio or tape. Then we need a whole heap of voltage & current gain to drive a loudspeaker or two. After the signal leaves the source, the major factor determining a HiFi’s ultimate sound quality is the amplifier & speaker combination being used. Some might say, ‘Aha! But don’t all amplifiers sound the same? It’s the speaker that sounds different. You know: The boom & tizz, the sibilance & bass, man!’…”

Tom stresses that it’s the interaction between amplifier & speaker that determines the sound as a whole. You have to engineer with that in mind to extend the edge of the art in amplifier design. “There are more permutations of amplifier & speaker combinations than you can count. To get an optimum match between most amplifiers and speakers, you have less chance of success than winning the lottery. One of our design goals had to be that the Linear A would work equally well in all those interaction situations to ensure consistently good sound for all of our customers. Keep in mind that the laws of physics will apply to anything electrical and mechanical. We’re faced with designing for an infinite variable of customers with different room sizes, aesthetic tastes, budget, differing equipment and the often-overlooked fact of the frailty of human hearing slowly fading from constant use. The end result is that the same system in different rooms and with different ears will sound different for better or worse.”

Tom uses the following analogy to illuminate loudspeaker/amplifier interactions: “The problem that most speakers pose for an amplifier is that from an electrical standpoint, they are moving targets with respect to impedance versus frequency. Imagine you’re sitting at a piano. The furthest key to your left plays a 27Hz note, the furthest key to your right a 7000Hz note. Loudspeakers try to mimic the sound of those two notes from a recording yet each note presents a different electrical load to the amplifier due to the way loudspeakers are constructed. In the same way, a 40-watt light bulb presents a different load to the mains than would a 100-watt bulb. Just as one light bulb emits more light, one note is easier to drive from an amplifier’s point of view.”

“It’s a widely held belief in the audio community that a high damping factor is all that’s required to drive any speaker impedance curve. Actually, the truth is that the damping factor merely stops the speaker from ringing or bouncing like a spring once the music stops. As has been shown by Gilbert Briggs, founder of Wharfedale, the amplifier output impedance only needs to be half the speaker’s impedance to have this effect. I can hear you laughing and thinking we’ve lost our marbles – but how come all amplifier manufacturers quote different power outputs into 4/8/16 ohms when the magic low output impedance means it allegedly produces the same power irrespective of load? Worse even, transformer-coupled tube amplifiers use multiple impedance taps. Look at any loudspeaker. Very few are ruler flat over their frequency range and most look like the side view of a roller coaster fairground ride. A 32-ohm peak at bass resonance and crossover point requires double the voltage of an 8-ohm load as does a 16-ohm peak against a nominal 4-ohm load. Remember that amplifiers clip when supplying higher voltages and that all amplifiers have a falling power output into rising impedance. As a result, the driver has a frequency response rolloff as the impedance rises.

The rising impedance with frequency, as seen by the amplifier, produces a benign inductive load. However, the corresponding fall with frequency is capacitive and will cause the amplifier output devices to overheat. Because the Linear A uses an output transformer and operates in Class A, it is immune to any of those ills usually associated with amplifiers. Since the valves don’t see the loudspeaker (only the transformer), and because they are on all the time, they don’t draw more current at higher power. However, the major advantage of the Linear A is that we have matched the transformer and composite valve to produce over 20 watts between 5-10 ohms. The speaker output remains the same when its impedance curve fluctuates anywhere between 5 and 10 ohms. The fall in power above 10 ohms is offset by the improved output transformer efficiency. Since transformer losses are “current squared x winding resistance”, the current requirement falls off with rising impedance. In sonic terms, it means your loudspeaker presents a less peaky sound output if you are using a Linear A.”

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