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Multi-Way Conventional loudspeakers with crossovers

Beginner speaker building help
Beginner speaker building help
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Old 15th June 2009, 07:10 PM   #1
Telemin is offline Telemin  United Kingdom
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Join Date: Jun 2009
Default Beginner speaker building help

I'm setting up to build my first set of speakers to this design, and need to know a couple of things about them.

First off I have been told that these speakers will be perfectly fine and not overpowered by a 20W amp (the audiodigit class T 2020), is this correct?

And then secondly what power rating must the resistors I use have? The ones specified in the speaker design are 10W resistors but surely these won't handle the power from a 20W amp or is it not that simple? I don't want to set fire to my speakers!

I hope these questions aren't trivial or "noobish".

Thanks in advance

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Old 15th June 2009, 08:00 PM   #2
Jonathan Bright is offline Jonathan Bright  Australia
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Location: Queensland Australia
Greetings Telemin from Australia where it is currently 5.50 in the morning. The answer to both questions is "Yes, they'll be fine" . They are not stupid questions. Someone said that the only stupid question is the one you DON"T ask.

The reason that the power ratings are okay is this. (A) At reasonable listening level (actual sound in the room) the amp is only using a few watts. one or two is not uncommon, you never have all 20 going through the speakers. (B) Secondly the sound level in music is very variable. There are loud passages followed by quieter ones. Unless you listen to a sine wave at full volume there are no problems at all. (C) Thirdly there is thermal lag in both resistors and voice coils. They take a finite time to heat up and burn out. Look at your toaster this morning and see that the element doesn't become red hot for a few seconds after you switch it on. . So both speakers and resistors have a impulse or short term power rating substantially higher than the nominal ratings. okay? Hope this makes sense.
Cheers Jonathan
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
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Old 15th June 2009, 11:26 PM   #3
PeteMcK is offline PeteMcK
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Join Date: Feb 2002
Location: Western Sydney
additionally, on average, most power is at the bass end of the spectrum, the tweeter only handles a small portion of the total power
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 16th June 2009, 12:23 AM   #4
Cal Weldon is offline Cal Weldon  Canada
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Location: Near Vancouver
Beginner speaker building help
So in conclusion, the resistors are not likely to ever sustain the 10 watts you are concerned about. I use 10 watters in 50 watt speakers.
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