Zigmahornet 'dualies' made with 3/4 MDF & Merrill DCA4's - diyAudio
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Old 24th April 2009, 08:00 PM   #1
Tevis is offline Tevis  United States
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Default Zigmahornet 'dualies' made with 3/4 MDF & Merrill DCA4's

*This is a copy and paste from DiyAudioProjects.com where I found the plans to build my Zigmahornets
http://diyaudioprojects.com/Forum/vi...f=11&t=728&e=0*

After visiting my audiophile friend Cris he showed me his recently made Zigmahornets with Merrill DCA4's inside. I was so impressed I had to make my own pair.

They we're used to fill out my surround setup in my home theater 'bed room'. They worked real well to bring out voices in movies and music... but I'm a big volume guy and I had to shut down the amp driving the Zigmahornets if I really wanted to crank up the volume and rattle my walls.

So.. after talking back and forth with my friend Cris we got to wondering what would a pair of DCA4's sound like in Zigmahornets.. and what if they were made of 3/4 MDF.

Well.. after 10+ hours of work my Zigma dualies we're born!

For those who say a Zigmahornet has 0 bass, these will will surely make them look again.

I kept all inside dimensions the same. I used the center line of the original and went above and bellow 2 1/4 for speaker placement.


-Tevis
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Old 24th April 2009, 08:27 PM   #2
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North Idaho!

Apparently we are neighbors!

They look great, I bet they are nice and solid. IIRC, aren't you suppose to double the cross-sectional area for TLs if you add a second driver?

Roger
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Old 24th April 2009, 09:28 PM   #3
Tevis is offline Tevis  United States
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I'm a real newbie when it comes to doing this DIY stuff, I started with a Zigmahornet with a single driver and I wondered what they would sound like with a pair per tower.

So far... the top end has really suffered, while the mid low have really come alive.

gmilitano has suggested that I turn them into a 1.5 setup
Quote:
Something you can try quickly is a 1.5-way design. That is, one speaker runs fullrange and the other has a high-pass (so it only plays the low portion). I would try a 2nd order high pass where the baffle step starts. To get them back into phase, you can reverse the polarity of one driver.
I dont know where to cut the frequency at, any suggestions?

I'm also not opposed to wacking a section out of the MDF and rebuilding part of them to make them sound proper.

any, all suggestions welcome. Please keep in mind that I'm still very new to this 'pictures for the bigger words'

-Tevis
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Old 25th April 2009, 04:49 AM   #4
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Hey, you live you learn. I think you still have plenty of options though. That is half the fun.

You can calculate the baffle step frequency simply as:
baffle step frequency = 4560 / width of cabinet in inches

If you want to go back to a single driver arrangement you could probably cover the driver holes with an over sized baffle like they use on the Cain and Cain speakers. See here .

You could also remake them as bipoles with twice the cross-sectional area. Something like these.
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Old 25th April 2009, 09:04 PM   #5
Tevis is offline Tevis  United States
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BSF is 1216 = 4560/3.75

3 3/4 is the inside width of a zigmahornet.

I've been looking around parts-express, the lowest 2nd order I can find is 2000mhz *http://www.parts-express.com/pe/show...number=260-140 is this the correct type of part to buy?

Is doing a 2nd order my best option or...

I asked my friend about a dipole setup and he said I would have 'timing issues' with half the audio bouncing off the wall. But if it does sound OK, I'll do the mods to the towers.

Either way I would have to router flat, cut out, replace, fill and sand a new piece of MDF into the front of the tower to house one speaker.

to turn it into a dipole I would put a ring around each speaker to space them further apart from each other, each back to back. or... is my cabinet already not deep enough acoustically to do a dipole?

In ending, I will do what will make the best sounding speaker with what resources I have on hand.
Suggested so far:
1. 2nd order crossover, $60 in parts.
2. Dipole setup. I would only mod the top of the cabinet to house two speakers back to back by spacing them apart. *I'm not ready to tackle rebuilding the tower wide enough to house the two inside.*
3. Build them to be a single speaker enclosure, where I would then make the other two DCA4's into bookshelf units.

-Tevis

**
roger_lew,
I'm not to far from you, I live in Sandpoint... and I'm planing on going to UOI this fall.
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Old 26th April 2009, 02:36 AM   #6
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Hey Tevis,

You would want to use the outside diameter of the cabinet to calculate BSF.

4560/5.25 = 869 Hz

You can use the crossover calculator on this page to figure out capacitor and inductor values you need to build your own crossover. It should be cheaper than buying a premade X0 since you are only buying the low pass portion and not the high pass portion of the crossover. You might also check out madisound.com as shipping might be cheaper to our neck of the woods.

If your drivers are facing back-to-back but firing in phase then you would have a bipole speaker. The bipole should have a fairly omnidirectional radiation pattern with high frequency beaming on axis with the drivers. On the other hand if your speakers are faced back-to-back but firing out-of-phase you would have a dipole. Dipoles have a figure eight radiation pattern where sound is placed in front and behind the speaker but not much sound is placed on the sides. See http://www.linkwitzlab.com/ . What you would be building is a bipole.

To do the bipole correctly you really do need to put 2 of the zigma horns back-to-back (that is a great idea actually) or build an enclosure with twice the cross sectional area. For the bipole (and dipole) you also need some space behind the speaker so the reflection with the rear wall does smear the arrival of the signal arriving from the front. You could also try doing a 1.5 way bipole where the driver facing the rear wall is low passed at BSF. That way you wouldn't have to worry as much about placement and the indirect sound coming from the back.

To try the 1.5 way with your existing enclosure you just need to add the crossover to one of the DC4s in your existing cabinet.

I'll still be here in the fall, maybe we can get together some time to talk audio.

Roger
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