First DIY 2 way stereo speakers. What am i doing ?

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Florent

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First DIY 2 way stereo speakers. What am i doing ?
« on: 10 Feb 2020, 03:16 pm »
Hello everybody,

I'm from Belgium. Always been a fan of various kinds of music, jazz is on the top shelf, but never really had good speakers. So recently, i started looking every videos i could find and forums to try to understand all of what make a good speaker.

I started designing a pair of 2 way speakers. This is a budget build but i start from SCRATCH, i don't even own an amp ! So i have to buy everything...

The first project that ended up in the dumpster was a 8ohm speaker. Then i realized an amp for 8 ohm speaker is way more expensive than those 4ohm ones. So i picked some amp module from wondom, and looked for speakers, started designing the crossover, the enclosure and here i am full of doubts !

Here below you can see all the info about the speakers i am trying to make. And one thing that bothers me is that i have no idea what the phase graph should look like.
Besides that, i can imagine some of you will comment "that is never going to work" and start pointing problems at my design. And THAT IS WHY I AM HERE, shoot ! Fire at will !

My point is to make a 2way bookshelf stereo pair that sounds decent for 350 ~ 400 euros. AMP INCLUDED.
I am very excited to press that purchase button with all the stuff i think i need to build this but i thought i needed some opinions from people with knowledge of all this.

So here is my parts list and the crossover design and some graphs.

Drivers :
Dayton audio ND25FW-4
Dayton audio RS180P-4

Amp :
Wondom T-amp Class D 2x400W 3Ohms 48V

Power supply :
Mean Well 48V 7.5A 350W

Enclosure :
24 liters
30,8*2*21cm (LxHxW) vent

I inverted polarity on the woofer. It gave better results on the frequency response graph but is it OK to do that ?


« Last Edit: 11 Feb 2020, 10:33 pm by Florent »

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #1 on: 11 Feb 2020, 06:21 am »



S Clark

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #2 on: 11 Feb 2020, 04:00 pm »
How did you measure your response?  As it is, it looks pretty good.  You might try a 4 ohm instead of the 5.6 if you'd like to lift that treble response a bit. 
But that is that an impedance graph in the lower left?  If so, you'll melt down amps with it. 

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #3 on: 11 Feb 2020, 04:28 pm »
How did you measure your response?  As it is, it looks pretty good.  You might try a 4 ohm instead of the 5.6 if you'd like to lift that treble response a bit. 
But that is that an impedance graph in the lower left?  If so, you'll melt down amps with it.

Thanks for your answer !

For the response, i downloaded the FRD and ZMA files from parts-express and loaded them into VituixCad2. Then noodled around with the crossover until this result !
And yes, it is an impedance graph in the lower left. What do you mean i will melt amps with it ? What i read about it is that it is the lowest figure that can be a problem, which is 3.3ohm. So i was thinking on buying the Wondom 2x400W 3Ohm amp, wich is super cheap btw. Would this be OK ?

wushuliu

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #4 on: 11 Feb 2020, 05:17 pm »
Thanks for your answer !

For the response, i downloaded the FRD and ZMA files from parts-express and loaded them into VituixCad2. Then noodled around with the crossover until this result !
And yes, it is an impedance graph in the lower left. What do you mean i will melt amps with it ? What i read about it is that it is the lowest figure that can be a problem, which is 3.3ohm. So i was thinking on buying the Wondom 2x400W 3Ohm amp, wich is super cheap btw. Would this be OK ?

He's looking at your rear port graph, not impedance. Your impedance looks fine. However, I think you are going to need to increase the woofer inductor. .56mh seems very low and your crossover shows a peak at 1.4k for the RS180. You will want to flatten that out, probably by increasing the inductor value. Typical 4ohm woofer would be more like 1-1.5mh.

No. You should not need to invert woofer polarity.

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #5 on: 11 Feb 2020, 05:31 pm »
He's looking at your rear port graph, not impedance. Your impedance looks fine. However, I think you are going to need to increase the woofer inductor. .56mh seems very low and your crossover shows a peak at 1.4k for the RS180. You will want to flatten that out, probably by increasing the inductor value. Typical 4ohm woofer would be more like 1-1.5mh.

No. You should not need to invert woofer polarity.



Polarity reset to normal. This is as close as i can get to flat with this crossover. But isn't it the gray line that represent the average frequency response between woofer and tweeter ? That red bump in the initial graph is going to be heard ? Because at 1400Hz with polarity inverted, that gray line is lower than the red one.

wushuliu

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #6 on: 11 Feb 2020, 05:59 pm »


Polarity reset to normal. This is as close as i can get to flat with this crossover. But isn't it the gray line that represent the average frequency response between woofer and tweeter ? That red bump in the initial graph is going to be heard ? Because at 1400Hz with polarity inverted, that gray line is lower than the red one.

Yes, the red line (woofer) and blue line (tweeter) will be heard. The gray line just shows the mix of the two.

Normal polarity is what you want for your 2-way (especially for your first time). The reverse polarity will not sound right.

Now look at the graph: see that woofer peak? You should be able to flatten that by increasing inductor value and changing capacitor value. If not, you may need to add a 'notch' filter to flatten it.

Also you are crossing that tweeter too high for this woofer. You need to crossover lower if possible - 2.5-3k.

wushuliu

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #7 on: 11 Feb 2020, 06:09 pm »
Okay, I bet your are doing this based on Kirby Does Audio tutorial on YouTube.

*sigh*

It's a bad tutorial. I am guessing you did not account for baffle step loss, nor did you account for real impedance inside a box. Correct?

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #8 on: 11 Feb 2020, 07:14 pm »
Okay, I bet your are doing this based on Kirby Does Audio tutorial on YouTube.

*sigh*

It's a bad tutorial. I am guessing you did not account for baffle step loss, nor did you account for real impedance inside a box. Correct?

Correct ! I have no idea what you are talking about, I am all ears...

wushuliu

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #9 on: 11 Feb 2020, 08:00 pm »
Correct ! I have no idea what you are talking about, I am all ears...

1. Know what the enclosure dimensions are: LxWxH

2. Use a program like Jeff bagby's Box Response Modeler to model frequency response based
on your enclosure dimensions.

3. Export the adjusted frequency response and zma/impedance files.

4. Import back into Vituicad or whatever software.

OR

Use Vituixcad Diffraction Calculator. It looks like it can do the same thing and would be easier since it's the same software, but I have never used it so I don't know for sure.

Paul Carmody has some instructions that may be helpful. Start at Step 5:
https://sites.google.com/site/undefinition/simulated-measurements

Speaker design is *not* simple. The Kirby Meets Audio video is misleading. Without modeling response based on actual box dimensions and baffle step your results will be terrible and not match real world response. That said, the Vituixcad software does look a nice tool for speaker design.

What you need as a first-timer is to have an actual microphone for measuring. Otherwise how will you know if what you design is even accurate? You will have no idea. Designing without measurements is usually suggested AFTER you know the basics.

I strongly suggest you just pay the ~$90 for a calibrated measurement microphone and start there. It will make your life much easier.

http://www.cross-spectrum.com/measurement/calibrated_dayton.html

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #10 on: 11 Feb 2020, 08:08 pm »
1. Know what the enclosure dimensions are: LxWxH

...
:thumb:

I will come back when my head is a little less empty ! =P

I have to say that i didn't think for a second that it would be easy, i am far from quitting this !! Thank you for your help. I very much appreciate it.

S Clark

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #11 on: 11 Feb 2020, 09:29 pm »
He's looking at your rear port graph, not impedance.
No, it was just that the graph was so small it looked like the impedance was just above zero.  3.3 is low, but some amps will handle it (and some won't).
Yep, it's clear that no baffle step correction is in the crossover.  Also, there may be phase issues that won't show up in that model... and they can cause wild deviations in output. 
Like Wushiliu mentioned, real time measurements are crucial to real success.  For most, the easiest (and best) answer is to build a kit. 

S Clark

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #12 on: 11 Feb 2020, 10:14 pm »
I can't find either woofer nor tweeter at the Parts Express web site.  Are these discontinued drivers?


hdspeakerman

Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #14 on: 11 Feb 2020, 11:22 pm »
Go to Parts Express Tech Talk forum for help.  Good group and lots of newbies.

wushuliu

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #15 on: 12 Feb 2020, 12:05 am »
Go to Parts Express Tech Talk forum for help.  Good group and lots of newbies.

Agreed, he should go to Parts Express Techtalk. Especially since he is using their woofer and tweeter.

Folsom

Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #16 on: 12 Feb 2020, 12:22 am »
Wush is doing a pretty good job.

But the whole point of measuring in box and going from there can't be understated. I'd save money for replacing crossover parts to fine tune anything you make. And I'd want to build/buy a box that I could replace the front plate on incase I couldn't get the woofer/tweeter to match up. It would be wise to ask someone if a tweeter and woofer would be very compatible. DIYaudio & TechTalk are the go to places in the US but there's other euroforums, too. (does Visaton have one?)

Welcome to the craziness, the difficulty, the fun, of true DIY.

P.S. I like Kirby but the way he's doing it he'll have to measure real world performance and redo the crossover again a few times perhaps. It's unlikely he'll get any true performance of a studio monitor any time within the next two videos but he'll probably be happy with them. I just enjoy that people are building anything at all from watching him.

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #17 on: 12 Feb 2020, 05:50 am »
I think i will dig a little more into all this and order the parts + microphone. Making different sized enclosure and baffle is no problem for me since i am a cabinet maker and i have my own workshop !
From the measurements i will get, i Will order some more parts for the crossover.

Thanks for the help !

wushuliu

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #18 on: 12 Feb 2020, 05:55 am »
I think i will dig a little more into all this and order the parts + microphone. Making different sized enclosure and baffle is no problem for me since i am a cabinet maker and i have my own workshop !
From the measurements i will get, i Will order some more parts for the crossover.

Thanks for the help !

Great! Making the cabinets is half the battle. Keep us posted on your developments.

Florent

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Re: First DIY 2 way stereo speakers. What am i doing ?
« Reply #19 on: 12 Feb 2020, 07:24 am »
Great! Making the cabinets is half the battle. Keep us posted on your developments.

So i read everywhere that your amp should be way more powerfull than what you need to have minimum THD so i chose 2x400W for that 2x80W build. If i am correct, at 3Ohm, 15,5V i should have 5,15A and 80W (woofer+tweeter)
Can i just add a 10A fuse (Left + Right) between amp and power supply ? I guess the amp itself will draw some power and won't transmit 100% of what the power supply gives but, let assume it does for now. Would it add noise ? It would be supper handy, if i blow up the fuse, there you are, i know how far i can push the knob on the amp before destroying my drivers...

Inner impedance has to do with excursion right ? On vituixcad i see that at 60W (the woofer), the excursion graph looks good, stays under the 6mm Xmax

About the baffe step loss, i read here and there that rounding the edges is a good idea, will it make any difference ?  What are other things that can be done here to reduce Baffle step loss ?

EDIT : For those like me who don't really understand all this, here is an interesting video about baffel step. https://www.youtube.com/watch?v=sttbT1ONP80
« Last Edit: 12 Feb 2020, 12:14 pm by Florent »