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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: 17 November 2014 at 6:06pm
I am very sensitive to the placebo possibility which is why I have been slow to comment on the listening impressions. Sometimes different is not better or worse, it is just different.   In this case I have a decent set of book shelf speakers (ported, 4" tang band drivers) for comparison.   "Shouty" is a good word for the mini with chamfers.   The problem area was much improved by adding clay to simulate a round over.   I was able to do an A/B comparison as described in my post above. I also played it for my wife (not a critical listener) and she was able to clearly hear the differnce and describe the change.

That satisfies me.

As for Measuring is knowing: I havee built my career on data driven decision making.   I am a huge fan.   It is also critical to understand the capabilities of your testing process.   Is it precise, accurate, and repeatable?   In the case of speakers are you looking for absolute measurements or relative (to see what changed) . If absolute, is you mic calibrated? Can you account for effects of the test environment? Are you really able to measure what is important to enjoyable sound?   It seems like equal parts useful data and lots of complexity.   

That said , I am ordering a mic. :)
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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 7:56pm
Aterren, I wish I could point you to a product and say: "use this and it'll sort out your chamfer problem". Obviously, I can't. I'm afraid there is not much else you can do than redo them.

The "correct" round over or chamfer is 6mm round over or a 4-4.5mm 45 degree chamfer. Both are so close to the optimum flaring that the added complexity of doing the flaring would not be worth the effort.

Just to note it. The 9mm 45 degree chamfer or full 12mm round over is correct on the Boominator with HP10W (or GW1058). It serves to correct the slight dip between 600hz and 1khz.




Edited by Saturnus - 17 November 2014 at 8:03pm
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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 9:13pm
Aterren; It's difficult to measure how 'enjoyable' the sound is because flat isn't always the best and the response doesn't tell everything. But if is something is noticable it will probably show up on your measurements. But you can measure a lot more than just the FR, but that's for later.

I would start with nearfield, then open field and then room response, both on-axis and off-axis. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2014 at 9:53pm
No version of the Boominator is designed to have flat response. What I have tried to achieve is to get as close to the sound of a Fostex FE206e in back loaded horn slightly off-axis driven by a 8W Son of Zen class A amp. This to me is the ideal. It is not by any stretch the highest fidelity speaker you can get but it's probably the most engaging.

The thing is. For many years I have designed both ultra-hi-end and mid-range speakers but at the end of the day, high fidelity is a dead end road. No matter how much money you pour into a system, it will never be truly the same as being there with the band as they record it. To get as close as possible you have to eliminate the room. That's typically done by limiting dispersion which in turn means that there can only be one or max two people in the "sweet spot". And to me, music is about shared experiences. So I went the other way. Get as good a sound as possible to as many people as possible.

Sitting with your friends in a park with a few beers listening to some chill out. On a beach doing a BBQ while banging out some reggae or dance hall tracks. Sharing a spliff with your girl friend looking at the night sky in the desert listening to some Pink Floyd. That's what I think music should be about. Creating shared experiences. And that's what I design speakers for. 


Edited by Saturnus - 17 November 2014 at 9:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TIP220 Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2014 at 10:08pm
and that Saturnus is why we build your speakers Thumbs Up

Edited by TIP220 - 17 November 2014 at 10:09pm
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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 11:16pm
Originally posted by Saturnus Saturnus wrote:

Aterren, I wish I could point you to a product and say: "use this and it'll sort out your chamfer problem". Obviously, I can't. I'm afraid there is not much else you can do than redo them.
 
Yes.  I reached that conclusion too.   I was grasping at straws.   On the bright side I now have some nice material for curved corner braces for some, as yet unidentified project.
 
Anyone else who wants to play with bad baffles drop me a line.  You'll be surprised by the differences.
 
Originally posted by Saturnus Saturnus wrote:

The "correct" round over or chamfer is 6mm round over or a 4-4.5mm 45 degree chamfer. Both are so close to the optimum flaring that the added complexity of doing the flaring would not be worth the effort.
 
In measuring the 4 to 4.5 mm, is that the vertical height or the hypotenuse?
 
Originally posted by Saturnus Saturnus wrote:

Just to note it. The 9mm 45 degree chamfer or full 12mm round over is correct on the Boominator with HP10W (or GW1058). It serves to correct the slight dip between 600hz and 1khz.
 
Do you have recommendations for the Basslite or SN10B drivers?   I'll update the Word document on drop box (I sent you a link via PM on the other site).


Edited by Aterren - 17 November 2014 at 11:18pm
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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 11:25pm
Originally posted by Saturnus Saturnus wrote:

Sitting with your friends in a park with a few beers listening to some chill out. On a beach doing a BBQ while banging out some reggae or dance hall tracks. Sharing a spliff with your girl friend looking at the night sky in the desert listening to some Pink Floyd. That's what I think music should be about. Creating shared experiences. And that's what I design speakers for. 
 
Clap  You have perfectly summed up how the Boominator has contributed to my quality of life.  Thank you. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tsyphon Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2014 at 3:31am
Originally posted by Saturnus Saturnus wrote:

The "correct" round over or chamfer is 6mm round over or a 4-4.5mm 45 degree chamfer. Both are so close to the optimum flaring that the added complexity of doing the flaring would not be worth the effort.


IIRC, I think I read an earlier post on the other thread in reference to the Mini where you said the correct inner face chamfer would be 8-9mm, and I'm assuming that means 8-9 mm deep with a 45 degree angle however far it takes to get the hypotenuse to reach the back face. Wouldn't this mean that the maximum front face chamfer be about 3.5mm to prevent the thinnest part from being too thin? Or is it fine to have the angle where the 2 chamfers meet be that thin...or am I wrong with the 8-9 mm part?


And to add another question instead of making a new post, the dimensions for the "free air" speaker space is four 200x60x138mm boxes right?


Edited by Tsyphon - 18 November 2014 at 11:37pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2014 at 12:27am
@Typhon
I think there may have been some confusion on this point (there may have been a mixing of mini vs standard boominator).   I've paraphrased the relevant Q&A below and based on my experience I would use the 6mm round over on the mini v2.   There is no question in my mind that the 12mm round or 9mm chamfer will give sub-optimal results.  

DIYAUDIO - Starting at post #5097  Circa 13 May 2014
Q:  Would it be ok for me to protrude the gasket through the baffle and just put a 4mm spacer behind the driver?

A: It matters. Please mount it the way it is intended.
If it helps, it's also why the hole is deliberately too small at 96mm.
Please remember the front baffle requires a You either a 12mm round over or 8-9mm chamfer.
This linearizes the frequency response in the 3khz-3.5khz region. If you do not mount it correctly, it will have an audible dip in the frequency response due to diffraction.

Please also remember that it is the chemical metal between the driver and the center brace that holds the driver in place. The screw on the front is not needed, just the sealant but the screws help to hold it in place while it's being mounted.

Speaker Plans - Circa 17 November 2014
The "correct" round over or chamfer is 6mm round over or a 4-4.5mm 45 degree chamfer. Both are so close to the optimum flaring that the added complexity of doing the flaring would not be worth the effort.

Just to note it. The 9mm 45 degree chamfer or full 12mm round over is correct on the Boominator with HP10W (or GW1058). It serves to correct the slight dip between 600hz and 1khz.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tsyphon Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2014 at 2:35am

So like this? being a 4-4.5mm in depth chamfer at 45 degrees. That means the remaining depth of the baffle will be between 7.5-8mm. I realized after your clarification and looking at my previous post that half of it was very misinformed haha.

Anyways, if the picture above is correct, I would cut the chamfer then slightly smooth the external and internal edges by hand during the whole baffle face sanding process. Sound about right?


Edited by Tsyphon - 19 November 2014 at 2:36am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Aterren Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2014 at 6:53am
Yes that sounds about right.   I will build two, possibly next week and one will be chmafer as you note and one willbe 6mm roundover...    That should give me a good basis of comparison
of the differences.

Edited by Aterren - 21 November 2014 at 4:54am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Saturnus Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2014 at 10:54am
Ok.

The best flaring shapes that can be done easily are in order of preference:

1) Have a round over tool with twice the radius of the baffle thickness. Make the round over from the inner bottom edge. Smooth over outer edge with sand paper.

2) Use a chamfer with chamber length (hypotenuse) of half the baffle thickness. Chamfer from outer edge. Smooth over inner chamfer edge and mildly "break" the outer chamfer edge with sand paper.

3) Use a round over tool of half the baffle thickness. No additional sanding needed.

The reason why the cut out diameter is 96mm and not the about 99mm of the driver is that a tube resonance is inevitable. If it's 99mm then that tube resonance base frequency would be 1742hz which is extremely close to (within 1%) of 1760hz which is a harmonic of the note A on which most western music is based. It is important to avoid resonances that coincide with harmonics of musical notes, and especially harmonics of A should be avoided, and doubly so in the 2khz range where the ear is most sensitive. By having the cut out at 96mm the resonance is 1797hz which falls between A and B-flat which is much less of an issue. It could also have been 102mm which would see the resonance fall between A-flat and A but I choose the smaller radii. You can try 102mm cut out if you like. I have not.

Now you might think it's not that important and surely a speaker should play and treat all frequencies the same but that's completely wrong. Special care must be taken to eliminate resonances at harmonics of musical notes. Musical notes aren't arbitrarily chosen. They are those frequencies because those "sound" the best to our brains. Anyone can test this by tuning your guitar to A=452hz (right between A and A-flat). It will sound awful and give you a head ache after only a few minutes. 


Edited by Saturnus - 19 November 2014 at 11:20am
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