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PostPosted: 06 Nov 2009, 16:36 
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Joined: 23 Apr 2009, 16:23
Posts: 26
Location: North Idaho, USA
I'm building a pair of G Chang speakers. (http://homepage.mac.com/tlinespeakers/F ... 170608.pdf)
All parts have been ordered from parts express.
I'm using Pioneer B20FU20-51FW 8" Full Range Drivers and Dayton ND16FA-6 5/8" Neodymium Dome Tweeters
http://www.parts-express.com/pe/showdet ... er=290-045
http://www.parts-express.com/pe/showdet ... er=275-025
and a few capacitors for tweeter crossover.

Unfortunately some of the pictures of the construction are no longer available from photo bucket.
I bought some of the 'Sonic barrier' foam, and have some poly fill.
I have heard that it is recommended that dampening be placed directly behind the driver, top and one side.
Is this correct? what about the use of poly fill?

I'm using 1" MDF. I know its not the best material, but I already have it on have on hand.


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PostPosted: 06 Nov 2009, 19:31 
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Joined: 28 May 2008, 21:53
Posts: 4586
Location: Winnipeg, CANADA
Hi Tevis, that design looks great. 1" MDF is pretty heavy so given the size of the enclosure that will be a pretty heavy speaker.

A few capacitors .. were you thinking of some sort a switch or just to experiment with the right size?

That is a good place to start with the damping. You may even find that lining the 45s may help. You will likely want to adjust the amount and location of the damping after the drivers are broken in and to suit your room. Given the size of the driver you will have plenty of room to get your hands in there after the box is all sealed up to experiment with the damping. So you may want to use tee-nuts for the drivers as MDF is not great for holding screws after they have been removed a couple of times.

Cheers

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PostPosted: 06 Nov 2009, 21:31 
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Joined: 23 Apr 2009, 16:23
Posts: 26
Location: North Idaho, USA
Gio wrote:
A few capacitors .. were you thinking of some sort a switch or just to experiment with the right size?
You may even find that lining the 45s may help

use the caps on the + side of the tweeter.
I have 4 2uf and 2 1uf so I can do 2, 3, 4, or 5 uF for the cross for the tweeter, the 8" goes full range. With those caps I should be able to cross between 5k-10k.? Thats what I read anyway.

I'm going to use 'Great Stuff Window and Door" to fill the inside of the 45*

This is the exact same setup gychang used in this thread I found:
http://www.diyaudio.com/forums/full-ran ... riant.html
However mine will be made of MDF :|

Perhaps if the TangBand W8-1808 or 1772's sound great I'll build a set out of birch and use them as a quadraphonic surround.

I'm considering a different amp to power these, currently its a monster over kill 5 channel 120watt RMS per channel class A amp :shock: but it sure sounds good :D


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PostPosted: 07 Nov 2009, 11:09 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Tevis, I think you will find that you need to be in the order of about 1uF for the first order crossover on the tweeter. I can't imagine you will need to go over 2uF.
Cheers.

PS - I fixed the typo.

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PostPosted: 25 Nov 2009, 02:50 
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Joined: 23 Apr 2009, 16:23
Posts: 26
Location: North Idaho, USA
After my initial hearing these in an A B test against my Zigma Dualies.. to quote a movie...
"After careful consideration I have come to the conclusion, your system sucks"

I am not an experienced audiophile and only know from what I have already built and listened to.

Voices from the Changs are muffled / flat / compressed and really lacks clarity in the top end.
Music listened to tonight, Dido, all 3 albums, Chris Isac Heart shaped world, Tracy Chapman

one of the striking differences is the clarity in ALL guitar notes when listening to Tracy Chapman's 'Give me One Reason' *! I mean every note !* the clarity difference is pitiful when compared to the Dave Merrill DCA 4's. Those little drivers are awsome.

The only advantage is the Pioneer B20's have, is thier ability to scare the cat during the Jurasic Park T-Rex sound bite.
They hit low, loud and ~clear even compared to my 12" sub (pioneer car subwoffer in sealed box)

I have even tried using VLC and WMP's equalizers to try to match the response of the DCA'4, but I cant..

They are extremely efficient, 20watts is very loud. I used a Class D 12v amp powered from a quality computer PSU with an amp meter inline. I also used a 5 channel 120watt RMS class A amp.

Before I go re-reading a lot of forum posts I want to confirm my understanding of my tweeter crossover.
Higher the uF, the lower the tweeter will go when adding capacitors to the + side?

That is the only thing I can think of to improve their sound, although I dont know how much. They seem to have trouble at about 500 hertz on up, tweeter is only good for 5k on up?

I think I have given them enough break in time. I know they played for at least a week in my dads shop 24x7 at a reasonable volume playing a classic rock station.

Pictures soon to come. Guess I'll be eagerly awaiting the Tang Band w8-1772's? wonder if they would be happy in that enclosure?

I have a pair of DCA 4's I wonder if I should put those in place of the tweeter and cross them at 100 hertz or not crossing it at all? ( I have grown to love the sound of my Zigma Dualies with no circuitry in them) One thing to note is how well my listeners thought the Changs and Zigma dualies complimented each other when played together.

I ordered a headphone tube amp, I plan on using it as a pre-amp into my Class D amp to see how its sounds.

After putting so many hours into their build, my head is spinning with doubt and wonder on where to go from here.

-Tevis


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PostPosted: 25 Nov 2009, 22:15 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Tevis, that is disappointing. The pioneer is not as good a driver compared to the similar sized Fostex drivers so that may be part of it. Comparing to the smaller units is also difficult as 4 to 5 inch drivers seems to be that perfect size for full range units provided you don't need big bass.

That is how a high pass first order XO works. About 1 uF on the tweeter should be about right with the pioneer driver. But that won't help with the issues you are describing.

A couple of things, try listening to the drivers slightly off axis. Turn them inward so if you draw straight lines out from the drivers they intersect just before the listening position. Experiment with the location.

Did you use a Baffle Step Correction (BSC) Circuit? The baffle width of G Chang's means that the frequency midpoint of the transition from 4π space to 2π space is about 500 Hz which is were you noted problems. It would be worth trying.

Those new Tang Band drivers are getting good reviews. Let us know how you make out with them.

Cheers, Gio

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PostPosted: 27 Nov 2009, 12:41 
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Joined: 23 Apr 2009, 16:23
Posts: 26
Location: North Idaho, USA
Gio, right you were about the BSC, but its the Zigmas that really need it. That article you linked sums up exactly how the Zigmas sound.

However the way my ear thought they should sound was somewhere between the stock recommended and the Zigma's..
So I.. um gave them a bigger tweeter!
Image

I'm flying by the seat of my pants here, but running the DCA'4 full range with the pioneer really improved the sound.
My initial thoughts are to cross the DCA'4 at 150-250 hrz (100-125uF of capacitor) and possibly doing a hpf on the pioneer.
At this point I have violated the nature of a full range driver :( but I need to recover my investment by making them sound better.

The crazy thing is my girlfriend convinced me to buy the makings for another set of these before doing our A-B Test. I'm thinking of getting a pair of 3" drivers to act as mid-high range for hers.
The problem is most small drivers, like the bambo cone TangBand 3" is only 86 db efficient, I guess I could put a resister inline with the pioneer to reduce its power demand to compensate for the less efficient 3" driver.
I'm going to stick with the Merrill's for my set but I really need to find a solution for my GF's.

Thanks for the input Gio
-Tevis


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