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Toad
 Toad
(@toad)
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23/08/2019 9:45 pm  

@123toid

i figured out my baffle step and its 536.5 hz. so does that mean i have to bring the tweeter down 6db and the woofer so that the main frequency line is down 6 db after 536.5hz? is it possible to guess the z offset without measuring it. i know that the tweeter depth is 1.75" and the woofer is 3.17". the difference would be 1.42'. does that sound close?


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123Toid
(@123toid)
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24/08/2019 12:01 am  

@toad

That sounds about right for that driver in something like an 8.5" baffle.  You will want the response to be flat after that point and it should be about 6db down.  So 536 and above should be 6db lower than your low end. 

Remnind me again the tweeter you are using so we can see if we can estimate it.


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Toad
 Toad
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24/08/2019 12:33 pm  

@123toid

the tweeter is dayton audio rst28f-4 1-1/8

 


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123Toid
(@123toid)
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29/08/2019 3:23 am  

@toad

alright I'll look into it.


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Speaker Builder
(@speaker-builder)
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15/09/2019 2:00 pm  
Posted by: @toad

i quickly made something up in xsim and this is what i came up with. i understand that im gonna need to get some equipment to measure the devices. i feel like im getting a better understanding of designing a crossover from talking with you guys. 

Don't be discouraged by this, but I think you may want to take another look at your last crossover design. It is all well and good to get a nice frequency curve in the XSim panels, but crossovers do not operate in a vacuum, they are tail ended onto amplifiers and lead into drivers. So the whole picture, including failur modes, needs to be assessed before building...

If you bump the amplifier power up to 100 watts you get a very interesting result.  These are the current graphs for the components... 

First the high pass...

Currents 1

Now the low pass...

Currents 2

Now, a 100 watt amplifier feeding an 8 ohm speaker is expecting to deliver...

V == Sqrt(P X R) == sqrt(100  X 8) == Sqrt(800) == 28.8 volts.

I == V / R == 28.8 / 8 == 3.5 amps.

In the first image note that the high pass shunt coil is carrying some very heavy current to ground at the crossover point... about 4 amps which is in excess of the amplifier's ratings.

In the second image we see that as soon as the low pass coil tapers off, your two capacitors will begin acting in series carrying very significant currents just above the crossover point and it becomes worse as frequency increases... reaching a peak of 18 amps which is definitely a short circuit.

Moreover if the shunt coil in your high pass were to fail because of the excess current, the large series capacitor could place low frequencies (i.e bass) on your tweeter which could destroy it.

The bad news is that crossover design would likely be very inefficent and risks overheating or possibly damaging the amplifier. The good news is that we caught it before you ran into problems.

This isn't to say you should give up... Just the opposite. Think of it as a "teachable moment" in which you learned about the possible side effects of an otherwise good design and, in future, you will know what to look for.

 


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Toad
 Toad
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24/09/2019 9:54 pm  

@douglas-blake

thanks for the input, im taking everything as a teachable moment. its hard not to get discourage by this whole processes. its defiantly a lot harder than i thought it was gonna be to learn how to design a crossover. ive also been really busy lately which also doesnt help. i have made a new crossover desgin which has the baffle step and when i change the amplifier to 100 watts the low pass graph looks a lot better than my previous one but the high pass looks similar. do you know of any links or videos that go into a bit more detail about the stuff you were talking about.


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Speaker Builder
(@speaker-builder)
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25/09/2019 12:32 am  

@toad

You can't design a crossover entirely in XSim or Spice. It's not like playing a video game with building blocks. In the real world these programs are helpful only as a starting point and you do need to know electronics to get the best from them.  The final design always comes from testing, testing and even more testing and you just might be surprised how often the final result is nothing at all like what you drew up in the software.

To do a proper job you need to understand the actual workings of the individual components and their effects in a circuit. It is electronics and the best place to learn that is from All About Circuits which gives you the basics. Do be smart, don't just go there and look up what you think you need to know... give yourself the full course in basic electronics. You will be very glad you did.

Keep at it. Study up. Electronics in general and audio in particular is a fascinating and challenging field of study and there's just no way to know too much.

And FWIW ... the best "baffle step" compensation is often just to move the speakers closer to a wall and let the reflections from the wall fill in the missing low bass for you.

 


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Toad
 Toad
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25/09/2019 7:50 am  

@douglas-blake

thanks ill take a look at that. 


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nicholascjs
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13/10/2019 9:55 am  

something new for me to learn, great community cheers 


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123Toid
(@123toid)
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13/10/2019 11:22 am  

@nicholascjs

Welcome! We're glad to have you. Feel free to introduce yourself in the lounge area or ask any questions. We'll answer what we can. 


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nicholascjs
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14/10/2019 4:26 am  

@123Toid Thank you for the warm welcome!


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