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Old 15th October 2006, 07:11 PM   #1
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Smile Baffle step circuit, how many watts for the resistors?

Hi Im a new to this forum, althought Ive read a lot of posts on this one! Im building a 4.1 speaker kit for my computer and because the front speakers are really far aways from any wall, I will need a baffle step circuit. Despite knowing all the component values, something really important is missing... its all good to know what are the resistor values in ohms, but go to a vendor and tell him you want a 5 ohms resistor. He won't know which one to give... how many WATTS those resistors have??? lol! This information doesnt seem so available in any webiste or forums. And how to calculate it? Im using an Aurasound NS3-193-8A in each of the 4 sats Im making and they will be powered by a Yamaha receiver which gives 75W rms x4.

THANXS for helping me out with this!
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Old 15th October 2006, 07:24 PM   #2
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I am guessing 10 watt.
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Old 15th October 2006, 07:55 PM   #3
soongsc is offline soongsc  Taiwan
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I tend to go with at least 20W so that the resistor conducting cross section is a better match with internal wiring. For large speaker I would go for the 100W flat wired ones.

5 watts would stand well with table top computer speakers if you are not so worried about sound compression.
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Old 15th October 2006, 08:09 PM   #4
Salas is offline Salas  Greece
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See from where to where (in Hz) and how much attenuation your circuit creates. Calculate the cut power by extracting the sliced bsc segment from half the RMS power of your woofer. See how much voltage it can create on the given bsc resistor. Make out power dissipation and double it for safety.

Here is a calculator to help you out.
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Old 15th October 2006, 09:06 PM   #5
owdi is offline owdi  United States
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Half the RMS rated power of the driver is a good general guideline. Keep in mind most of the current flows through the BSC resistor between 400-1500hz. With your 75wrms amp, the BSC resistor will never see more than 6-8 watts playing music. The only way you could fry it is playing test tones at ear bleeding levels.

Dan
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Old 16th October 2006, 02:13 AM   #6
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Quote:
Originally posted by salas
See from where to where (in Hz) and how much attenuation your circuit creates. Calculate the cut power by extracting the sliced bsc segment from half the RMS power of your woofer. See how much voltage it can create on the given bsc resistor. Make out power dissipation and double it for safety.

Here is a calculator to help you out.
From where to where in Hz... calculating the cut power by extracting the sliced segment... Seems to be really nice information in order to calculate accurately the power needed for the resistor however, I dont understand completely what you said, Im sorry. Maybe due to not beeing a totaly english dude? I often read it, speak it rarely... generally I understand it really well but Im missing something there I think

By the way thanks to all the other people for their answers So it seems like with a 20W resistor I should be fine, even 10W because I dont think that Im gonna fire 40 Hz test tones during one hour
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Old 16th October 2006, 09:23 AM   #7
sreten is offline sreten  United Kingdom
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Hi, see NS3 info at http://www.zaphaudio.com/ , /sreten.

P.S. 10W will be plenty high enough for your case, 5W would be OK.
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Old 16th October 2006, 12:08 PM   #8
Salas is offline Salas  Greece
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Quote:
From where to where in Hz... calculating the cut power by extracting the sliced segment... Seems to be really nice information in order to calculate accurately the power needed for the resistor however, I dont understand completely what you said, Im sorry. Maybe due to not beeing a totaly english dude? I often read it, speak it rarely... generally I understand it really well but Im missing something there I think
Example: Lets say you have a 20W RMS 3 inch driver. You apply bsc of -3dB from 500-1500Hz. 20/2=10W because you dont touch lower mid and bass, so half is a good rough approximation for music. 3dB of this 10W you kill in your bsc circuit. 3dBw of 10W =5W. You can double it for total safety and use a 10W resistor.

*This is a much generous approximation, in practice the music's cycle will heat up the resistor from time to time, giving it a lot of chance to cool off. But in DIY we can be generous.

**Sreten was spot on.
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