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Why 40 hz? What about the other frequencies?


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Hey guys,

I was talking to a friend of mine about the DD1 the other day, we stumbled upon the fact that it only measures distortion at 40 Hz, based on the following fact:

I have a RF T2500 bdcp amplifier which does come with a output meter, so I tought I could trust it to , at least, know if im near clipping

I used a 40 Hz test tone to set the thing by ear and eye (using the output needle), ok, it sounded preety loud at that frequency and didnt look distorted, so I was happy for that day, went to bed and slept

The following day, I was at a lower volume , 15 (I've set my gains with a volume of 25) listening to some low bass music (woofer cooker, decaf, etc) and I noticed the bass was extremely intense, took a look at the output needle and it was ONLY red (maximum output)

I was very confused, if I used the same principle as the DD-1 it should make that much difference between the frequencies....I was probably very near clippling at volume 15 while Ive set my gains at 25......if I did the same with the DD1, the same thing would have hapenned

Am I right or the RFs output needle cant be trusted?

So....why 40 Hz at setting gains with the DD1, and does that really work? I mean, couldnt I have a clean signal at 40 Hz and a clipped signal at 28 ?

Thanks

Edited by ReaperX
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You probably set it with a -10db tone or so, and then you're playing amplified/boosted/ music which would put you into clipping. You should set your gains with your head unit turned up to it's maximum undistorted level, not a middle of the range level that you pick. Do you have your bass boost turned off and your head unit settings flat also?

PS - To answer your question, a clean signal set with 40hz tone will also be clean when running a 20, 25, 30, etc through it as long as it is not amplified further than the 40hz that you set it with is. Example would be, setting with a 40hz -7.5 tone, any other tone you through through it will also be clean at -7.5. Now, if you put a 0db tone you can be pushed into clipping.

Edited by REH
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I guess I understand now!!!

But then there is one problem: I cant play any music ?

I mean, If my friend comes over with his pendrive and the music he wants to show me is at 0 db , if I set my gains at -5 db, i will be clipping at my maximum volume?

That looks complicated....it means I can never be 100% safe

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They use 40hz because it's the resonant frequency of the toroidal coils within the amp, creating a smooth rectified power flow going to the transistors so there aren't any artifacts within the output signal to distort your reading

.....I'm full of crap don't listen to me

But on the real: how loud was the tone you were using? And where did you set the filters on your amp when you were toying with this?

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40hz and 1000hz are used as a reference point to find distortion. They have nothing to do with what you will play later.


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I guess I understand now!!!

But then there is one problem: I cant play any music ?

I mean, If my friend comes over with his pendrive and the music he wants to show me is at 0 db , if I set my gains at -5 db, i will be clipping at my maximum volume?

That looks complicated....it means I can never be 100% safe

No Sir. Music is not made of 0db waves. Read up on gains and tuning tutorials and it'll explain things in detail for you. Here's a good link to get you started.

http://www.stevemeadedesigns.com/board/topic/96978-test-tones-and-tuning-tutorial-all-new-links-again/#entry1342541

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FYI: the output needles on a RF amp are not set to turn red at clipping. They are just output LED's that's all.


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They use 40hz because it's the resonant frequency of the toroidal coils within the amp, creating a smooth rectified power flow going to the transistors so there aren't any artifacts within the output signal to distort your reading

This comment blew my mind.

Edited by Volvo63'
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FYI: the output needles on a RF amp are not set to turn red at clipping. They are just output LED's that's all.

OH, I didnt know that....tought they were accurate

Guess Im going to coff the U$150 and get a DD1

Meade, do you guys plan to sell the used DD1s that comes from the exchanging to DD+1s?

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