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Boominator MINI (development thread)

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Aterren View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 3:12am
I've spent a bit of time listening to my mini and I am finding the vocals fairly thin, or harsh and not nearly as natural (to my ear) as the NS6 mini.    My sources have been iPad and iPhone via Sure bluetooth and 3.5mm jack.   Amp is MaxAmp 20, of course.   And I am using Accusafe's very nice x-o boards too, On the bench they sounded the same as the ones I made on perf board.

Using Spotify's embeded eq the sound quality is quite a lot better if I reduce the output in the 1.5kHz to 3kHz range.   I expect this is the general range where the SP60 and ND16FA cross.  This leads me to question my part selection (see below).   

Questions:
1) Has anyone else notices the same thing in the mid-range?
2) Can anyone confirm these parts are appropriate?  

470uf Bi-Polar:

Ferrite Choke:

6.8uF Capacitors


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Post Options Post Options   Thanks (0) Thanks(0)   Quote lutkeveld Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 8:53am
They cross somewhere around 7kHz IIRC. Do left and right both have this issue? 
You bypassed the 470uF cap right? Do you have any shots of the filterboards or the speaker compartiment in general?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 2:28pm
lutkeveld,  

Thanks for the reply.  I can get shots of the interior however it does mean cutting the box which it looks like I will be doing.

I am quite sure both sides have the issue and based on my initial testing.

Could you clarify your question about bypassing the 470uF cap?   The crossover is wired as shown in the link below with the 470uF wired in parallel with the 6.8uF cap.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesleyK Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 4:20pm
The 6.8uF capacitor bypasses(or is connected in parallel to, same thing) the 470uF cap on the filter board, so that should be fine.

Edited by WesleyK - 16 November 2014 at 4:35pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 7:45pm
I've listened to both channels separately today (~1hr each) and they both sound the same.   

My knowledge of crossovers is limited to more standard designs and frankly just quite limited.   I have confidence that it is built as specified.   So let's assume that is the case.

Are there any suggestions on how to tune the XO to attenuate the 2k and up frequencies?   Additional series resistance to the tweeter isn't likely to have an impact if the transition is at 7kHz.

I suppose this might be a good excuse to buy a mic and play with HOLMImpulse and Jeff Bagby's PCD program but that does blow any chance I'm going to complete these before 2014 Christmas.    Certainly not ideal.  On the bright side it is a next step in my education.   :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lutkeveld Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 8:01pm
I can recommend a slightly modified Pansonic WM61A. Works like a charm with some RTA software. Best of all: it costs <10 dollars. 

But if it measures correctly but sounds wrong we still got a problem ;p.


Edited by lutkeveld - 16 November 2014 at 8:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 10:04pm
Originally posted by lutkeveld lutkeveld wrote:

But if it measures correctly but sounds wrong we still got a problem ;p.

Lutkeveld,

I like they way you think.    

As for the Panasonic mic, I will take a look but at this point I'm more interested in plug and play when it comes the the measurement equipment.  That's not where a want to spend my limited time and the time is worth more to me than the $.

You have lived with yours for a bit.  Can you draw a comparison between the mini and a decent set of bookshelf speakers? 


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Post Options Post Options   Thanks (1) Thanks(1)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 11:15pm
I can't shake the feeling that the very deep and wide chamfer might be the cause of the problem creating a horn shape. The frequencies certainly match. I'm just surprised it could have that much effect.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2014 at 11:36pm
Saturnus,  

That is an interesting thought.   Do you think play-doh (clay) would be sufficient to alter that geometry?   I could make a long string of it , wrap it around the chamfer and smooth it out.   Certainly it wouldn't be perfect from a geometry perspective but I am more concerned with proving the theory






Edited by Aterren - 16 November 2014 at 11:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2014 at 12:13am
It couldn't hurt to try on one side and see if there's a difference. Just to test it out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2014 at 3:18am
I put clay on one side and connected a wire with an alligator clip on one end and just flipped back and forth between the channels.

The difference was quite noticeable and in the right direction.  

I have mixed emotions about this discovery as I don't see a clean retrofit option *and* I have 10  other baffles ready for paint.  Cry  

I am open to creative ideas! 

For reference the hypotenuse of the chamfer is ~12.25mm long. 




Here is the other side for those who wanted pictures.  The paint was so smooth I had trouble getting the clay to stick.  







Edited by Aterren - 17 November 2014 at 12:34pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lutkeveld Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2014 at 4:24pm
Was it a blind test? Otherwise there might be a bit of placebo effect :). You can run both channels and disable one channel at the time to have a more direct comparison.

My micro sounds just fine on the vocals, just a bit shouty if listening on-axis and high female vocals are a bit dull (lack of tweeters). When I build my Micro rev2, with all the things I learned from building my rev1, I can give you a proper description (and measurements :)) 

If I find the time I will measure the Micro in various settings to confirm/deny my thoughts :) As we say in Dutch: 'meten is weten', 'measuring is knowing'.


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