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Old 8th February 2013, 02:50 PM   #1
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Exclamation Building Sphere - First Time Builder Needs Help

HAY THERE

First intro - My name is jay, i wish to build a speaker and hope with fellow users i will be able to do so. i have done some research (nothing to heavy) i have been reading a few good books i have seen people speak about such as:

Audio power amplifier design handbook by Douglas self
The Design of Active crossovers by Douglas Self
The Loudspeaker design cookbook
loudspeakers for music and production.

I am wanting to build sphere shaped speaker enclosures which i know has a lot of debate surrounding them but that's what i want lol I do intend to use them as studio monitors and would like to make them compete with the SE Munro EGG, yes ambituios i know, this is for my dissatation so it has to be amazing.

I have these Drive units in mind (speakers/cones - whatever you wish to call them)

Monacor - DT-25N (pdf attached with specs)
Monacor - SPH130AL (pdf attached with specs)
This is down to frequency response and the looks it will give, i wanted to use a white woofer to get that NS10 look, and the DT-25 tweeter to mimic SE EGG.

With my enclosure for the woofer, i worked out that a 4inch needs approx 0.25 to 0.39 cubic feet of volume within the enclosure. Because the frequency response of the SPH130AL is so low at the low end i am hoping that by using a small enclosure with a port will just boost the bottom end??? i hope i am right on that one. the volume i actually require using 0.25cubic feet as a reference this comes to 432cubic inches, giving me a radius of 4.69 ices for the sphere enclosure. I plan on using GRP to Make the enclosure with support struts and a metal mesh. Like if you take a football and but the struts around that then apply the mesh round that struts then by using the paste on top if the mesh, the allowing it to dry, then by deflating the ball/object inside the casing and pulling it out where the driver unit will sit then using the paste on the inside. then when all is dry and good using a bit of elbow grease and wet and dry sandpaper sand it down to a smooth finish. I know Spheres also generate internal reflections so when i have the electronics done (hopefully with your help) i will find out what sound is making it honk or tweet and treat it accordingly.


Now with the enclouser delt with its the electronic designs i am confused and bewildered by such as a transformer,power amplifier, and crossover.

Now i wish to make it an active crossover utilizing a 6th order linkwitz riley design. I went over to 2-Way Crossover Designer / Calculator
and this is what i got

6th Order Linkwitz-Riley


2000 Hertz

8 Ohm Tweeter / 8 Ohm Woofer Click the image to open in full size. Parts List
Capacitors
C1 = 5.53 uF
C2 = 6.76 uF
C3 = 13.68 uF
C4 = 18.42 uF
C5 = 11.14 uF
C6 = 2.49 uF
Inductors
L1 = 0.34 mH
L2 = 0.57 mH
L3 = 2.55 mH
L4 = 1.15 mH
L5 = 0.94 mH
L6 = 0.46 mH


So that's telling me the right stuff, but i would also like to make this as flat as possible. so I am guessing i would also need to place a bandpass filter over the top of the crossover which is where I need help. Because i could build that simple enough, but its the Amplifier, turning this into an active crossover, adding a low filter boost with volume nob and then building the transformer so i can plug in my active crossover to a mains 240v, I don't plan on having the electronic boards in with sphere but a stand alone unit. connected like a normal studio monitor balanced jack plug or xlr I may use a newer connection system.

Please Can some one help me design this, I know its a lot to ask but a few bits are lost on me with the books and dose not say use this to get this result lol.

this as i said is my dissertation work and wish for it to over top the markers expectations and to challenge the SE EGG

btw i am still reading the books in hope i can have my light bulb moment but still think a little guidance is needed.

Thank you for reading I hope you will and can help. J
Attached Files
File Type: pdf dt-25n(1).pdf (68.1 KB, 7 views)
File Type: pdf sph-130al.pdf (67.8 KB, 10 views)
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Old 8th February 2013, 05:33 PM   #2
AllenB is offline AllenB  Australia
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If you want these to be monitors and expect them to be competitive, you may need to take several measurements of them in their final enclosure and process this data appropriately. Unfortunately, simply choosing a sixth order crossover will not guarantee exceptional sound, nor does it make a lot of sense without the data...and going active won't get around this.
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Old 8th February 2013, 05:53 PM   #3
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Try simming the response of your design with programs like this:

LinearTeam
Boxsim - Homepage
Home of the Edge
Leonard Audio - Coming Soon

I would seriously consider DSP for a project like this, Hypex DLCP & MiniDSP come to mind

Hypex Electronics BV - Home
Home | miniDSP

And when you build your design measure it with a program like this:

ARTA Home

The reason I really advice a DSP for a system like this is the freedom it gives you to tweak the response without building a lot of X-overs, passive or active..

And if you have to build your own X-over for your dissertation the DSP can help you figure out what you need to build! Just stick with IIR filters in that case.

The filter you designed is passive btw

Additional link: http://www.linkwitzlab.com/filters.htm
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Last edited by Mark.Clappers; 8th February 2013 at 06:15 PM.
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Old 8th February 2013, 08:35 PM   #4
tvrgeek is offline tvrgeek  United States
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I would really suggest starting with a far more conventional two-way box. You are taking on way too many advanced issues all at once. Even experienced builders will test one new concept at a time. BTW, it is very uncommon to use 6th order electrical networks, even active.
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Old 8th February 2013, 08:54 PM   #5
Boscoe is offline Boscoe  United Kingdom
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I find it hard to believe you write like this and completing university. Can I ask what course you are doing? Music tech? Something like that?

Designing a two way speaker is easy as long as you know a few things. If your going to go to the trouble of making a sphere (which IMHO is pointless from an audio quality perspective) you should use some better drivers. Look up Falcon Acoustics and have a look at the SB Acoustics range of drivers, they are very well priced and are some of the best only the likes of Scan speak and Seas are better.

Look up Linkwitz Riley active crossovers and 6th order is overkill, use 4th order.
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Old 8th February 2013, 10:58 PM   #6
flg is offline flg  United States
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Well I don't have your answer either. Just wondered if you've seen these thresds?
Ikea spherical speakers, first build done.
Spherical Speakers
Spherical speakers and all that jazz
And, I'm sure with a little searching you can find more
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Old 8th February 2013, 11:59 PM   #7
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Quote:
Originally Posted by Boscoe View Post
I find it hard to believe you write like this and completing university. Can I ask what course you are doing? Music tech? Something like that?
Ummm ... no comments about the speakers, but I think this is a case of the kettle calling the pot black.
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Old 9th February 2013, 12:16 AM   #8
Dissi is offline Dissi  Switzerland
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A design using the same drivers:

Ambilight Heimkino von Radioaktivman: Juni 2012
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Old 9th February 2013, 01:56 AM   #9
bjorno is offline bjorno  Sweden
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Hi,

Studio Monitors? No Way, PC speakers at a listening distance ~<= 1m is Ok.
IMO: The Visaton Driver xmax= 2.3 mm is the mayor limiting factor.

Even when (if) ported it would be a low performer...

b


Ps: Supporting calculations : Posting a quickly made Picture:
Attached Images
File Type: jpg Monacor - SPH130AL_Sphere.jpg (469.5 KB, 104 views)
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Old 9th February 2013, 12:47 PM   #10
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What would the insertion loss of a 6th order xover be?

Just looking at the low pass series inductors at 200Hz the 1.15mH inductor has an impedance of 1.45 Ohm, the 0.94mH 1.18 Ohm and the 0.46mH 0.6 Ohm (all NOT counting the inductors DCR which would have to be added).
Do they just add up being in series to about 3 Ohm at 200Hz?

The series capacitors in the high pass have impedances of 2.8 Ohm, 2.4 Ohm and 1.16 Ohm respectively at 10 000Hz.
Do they simply add up 6.36 Ohm?

I used these impedance calculators: Pronine Electronics Design - Capacitor Impedance Calculator and
Pronine Electronics Design - Inductor Impedance Calculator
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