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Deep End DIY - My first speaker project

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No need Matt, keep it going here.

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2 hours ago, 125dBmonster said:

:) Well I'd like to see them driven to 125db of earth shaking terror with a 4 ohm output Z.  More like something with 0.01ohms at 80 volts with 25A on tap.

Heard of Ohms Law Dave and I2R loss ?

Hold on.    We were talking about accurate drive.     ie. the  accuracy, or the "control", of the cone.    ie. like how they said in the article whether the bass is "tight" ... or whether the cone "flaps about".

 

  • You don't need a low output impedance to ensure the "cone moves accurately"
  • You don't need a feedback loop (although it IS convenient to use one) to even achieve low output impedance.
  • Your chosen example driver (low cms / high rms, in a sealed box) is about as extreme as you can get of a driver which requires no extra electrical damping  (as it is already highly damped mechanically).

 

Hence my flat "No".

 

.... but you've jumped over to something else P=I^2.R  (and sure, I've herd of it a few times before).... If you had an amplifier which such an internal impedance, a quick sim in winisd shows that once the frequency responses have been EQed to the same result .... then you get half (-3db) the SPL.    So you'd need double the drivers.

 

 

.... but remember we weren't talking about this.   We're talking about whether the cone is "under control".... "grip" .... whether it is "tight", or it "flops about uncontrollably" ..... that a completely different thing from what you've just jumped to.

Edited by davewantsmoore

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1 hour ago, 125dBmonster said:

Dave, those 2 statements don't sit well with me in my mind as they contradict a few laws of Electricity.

You may have to explain this in detail

It is very cumbersome to do on a forum like this.

 

You can kinda approach it from two angles.     Either can start from zero, and build up all the explanations, ifs and buts ... which lead to the complete picture.

 

... or can approach it from the disproving a 'fallacy' angle and ask take a flawed explanation (like in some of those articles) where they say that low amplifier output impedance supplies "grip" or "control" .... and demonstrate how it's wrong.

 

 

The "whiteboard" is important....  because it helps to actually engage with people.    "What do you mean by 'grip'?" .... How does it do that? .... What about this? 

 

Wirtting walls of text is a bit one sided, and if the other person doesn't follow, then the critical bits can easily be lost.    If you were standing right in front of me, and I said X, it is much easier for me to see if you've understood ... and if not explain slightly differently, or whatever.

Edited by davewantsmoore

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12 hours ago, 125dBmonster said:

Will concede that DF is not actually a "real" thing

 

Well, it IS a real thing ..... it just doesn't have the effect that all the "articles" out there say it does.     It's effects are a lot more complicated .... and after we look past the simple fact that replacing an amp with another (that has a different damping factor) might produce a different (and maybe undesirable) frequency response for a speaker .....   we see that the rest of what high 'damping factor' does is negative.

 

The root of the problem with the 'conventional wisdom' on damping factor is it's the story from the perspective of amplifier manufacturers ..... and it largely ignores the basics of how a speaker operates.

 

That all being said.... most people need to use an amp with 'enough' damping factor .... becuase that's the way their speaker was designed.

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Damn L-Pads.  Was a bit rainy yesterday arvo so I  thought I would have a crack at one of the amplifier jobs that I was least looking forward to...soldering up the ladder attenuators for the tweeters.  Previously, I had soldered up a pair for another channel, but this pair had some nice pcb's that made the assembly very quick and easy, maybe a couple of hours for the pair.  Those switches were unused second-handers from fleabay and Elna no longer supply the pcb's and no matter how hard I looked I could not find another pair so had to buy the current version with solder tabs.  Soldering them up was a job I was really not looking forward to so it was best to just jump in and get it done.

 

59e28f0639c32_LPad2.jpg.9ee423903c3287f798aa92829eed9d2c.jpg

 

My, oh, my...the first one (far right) is a bit ugly but it works.  The second one (middle) is in better shape but would still not win any beauty contests...lucky these are out of sight.  Anyway, that was half a day of my life I am not getting back!  How I wish I had fond some more of those nice discontinued pcb versions.

 

That is nearly 200 resistors soldered up in the two pairs of attenuators...by far the great majority of resistors in the entire project.

 

59e28f5f8618c_LPad1.jpg.7be6f9c8516a7884eb0b2f3e0fe37201.jpg

 

Edited by acg

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Damn L-Pads.  Was a bit rainy yesterday arvo so I  thought I would have a crack at one of the amplifier jobs that I was least looking forward to...soldering up the ladder attenuators for the tweeters.  Previously, I had soldered up a pair for another channel, but this pair had some nice pcb's that made the assembly very quick and easy, maybe a couple of hours for the pair.  Those switches were unused second-handers from fleabay and Elna no longer supply the pcb's and no matter how hard I looked I could not find another pair so had to buy the current version with solder tabs.  Soldering them up was a job I was really not looking forward to so it was best to just jump in and get it done.
 
59e28f0639c32_LPad2.jpg.9ee423903c3287f798aa92829eed9d2c.jpg
 
My, oh, my...the first one (far right) is a bit ugly but it works.  The second one (middle) is in better shape but would still not win any beauty contests...lucky these are out of sight.  Anyway, that was half a day of my life I am not getting back!  How I wish I had fond some more of those nice discontinued pcb versions.
 
That is nearly 200 resistors soldered up in the two pairs of attenuators...by far the great majority of resistors in the entire project.
 
59e28f5f8618c_LPad1.jpg.7be6f9c8516a7884eb0b2f3e0fe37201.jpg
 
That's a looooooottt of work mate. Well done. I can appreciate the effort in trying to get them right.

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A bit surprised that you did not enter into making new PCB's for these? :thumb:

Would have added that extra skill set?

 

I know how difficult that sort of soldering is to get right let alone something that looks good as well.

 

I think you will need a large appointment book once you have this system finished, I am sure that many of us following the thread would like to have a listen.

 

Well done, keep up the good work.

 

 

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21 minutes ago, soundbyte said:

A bit surprised that you did not enter into making new PCB's for these? :thumb:

Would have added that extra skill set?

 

I did actually look into that.  I've had pcb's made for other parts of this project (the bleeder circuits and diode bridges) but in the end it was either spend half a day soldering them up or spend half a day designing the pcb...I chose the path of least resistance.

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