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I have been slowly replacing the cheap speakers in my 5.1 system for the past two years. My fronts are now the Zalytron Ego design using Focal 5W4252 / 5.25” Mid-Bass and an Hiquphon OWII, 20 mm (3/4”) Dome Tweeter. I don’t have wood working tools so I used the curved-sided design PE 0.38 cubic ft (11 Liters) Piano Black box for the housings (14" H x (8" Front, 4.5" Back) W x 11.8" D). All total, these were expensive for me to make (not expensive if you look at audiophile commercially available book shelf designs) but the results produced a great pair of speakers. My wife saw them and liked them but when I put them on a table stand in the front of the family room she did not like that arrangement and did not want these mounted on stands. The house I bought already had the family room wired for 5.1 and the front and rear speakers were JBLs mounted on the wall so I told there those were my too options – on stands or replace the JBLS on the wall. She opted to replace the small speakers on the walls. The Ego’s are heavy speakers weighing in at over 28 pounds a piece and I was leery of mounting them like this. I found a wall mount called a BR1 supposedly built to handle up to 44 pounds.


You can’t imagine the balancing act of trying to mount these heavy bastards but I did it and they have been there for 3 months and look good and the wall hasn’t fallen down yet. I may use these for the rears too.


My center is the Zaph ZDT3.5 – ZD3C sealed Center Channel Option built using Dayton drivers. This was a delayed project because of the multi-backordered RS52 2” dome mid-range speaker. Now that I have it, I am once again searching for someone to cut the holes and route all the surface details because my young guy in the garage joined the army and left for Iraq last month. This too is in a PE Piano Black box so it matches the front mains. The center will be laying on a shelf above my Samsung LCD TV and I think this might present diffraction problems from the shelf itself so I am going to design a small stand for under it to get it off the floor of the shelf. This stand will also point the speaker at an angle downward toward the listening area . I will post pictures of these and my setup when I get the center speaker completed.


So, now my thoughts turn toward my rear surrounds. I have been reading a lot about these and think that I will take a turn at creating the final design myself. There are certain parameters I want to use and reasons I am making this choice. These are:


1. I want to use the curved-sided design Piano Black PE Dayton TWC-0.25BK 0.28 ft³ (8 liter) 2-Way Curved Cabinets sold in pairs to match the design of my front mains.


2. There are several reasons for this selection and I know that there are trade-offs I will need to deal with based on this selection.

a. First, I just don’t want to put another pair of 28 pound speakers on the wall. These should weigh in at about 19 pounds when completed.

b. Second, I want to maintain the curved side styling which look and function well.

c. And, I am trying to keep the cost down and I can get the pair of cabinets from PE for $143.00.

3. These will be wall mounted like my fronts. For the fronts, the front baffle is about 14” from the wall and the rears will be about 12” when mounted. This is not ideal but it is a room design compromise my wife can live with. Thank God there were already speakers mounted on the wall in these locations so she could accept this option.

4. A 2-Way: With such small cabinets this limits me to a 2-way design. Essentially, these will be Mini’s. From what I read, Mini’s are a compromise design but some have been labeled as sounding pretty good so I believe I can do the same and am at least willing to try.

5. My own design including the cross-over: Unlike my previous speakers using proven designs I want to try to design this using what I have read from all the sources available on the internet and in the forums. I will ask for help for this to provide assistance so that I make the best selections form the decisions I must make.

6. Driver selection: I want these Mini’s to be able to match the fronts in frequency ranges with a similar sound. From what I have read the rear surrounds are less critical from a design perspective as the amount of time these are actually in use is reduced. The front baffle size is 12” tall x 7.5” front to back 4.5 x 11”deep. This will be my main design issue in selecting drivers. And because of the ‘large’ sound coming from my fronts and center, I want to be able to minimize the rears sounding like the small speakers they will be. For this reason I want to use the largest woofer I can fit into the cabinet and a matching Tweeter.

a. I have chosen the Tang Band W6-789S 6-1/2" Woofer



because I believe I can get it to fit though it will take up most of the bottom of the front baffle but more importantly, the SPL vs Freq map looks like this driver is very efficient (92%) with a fairly flat frequency response extending from 100 hz to 5000 hz. I think I will need efficient drivers for this Mini to come close to matching the fronts.

b. The tweeter I will be using is based upon what I already have but also because the SPL vs Frequency map is also a remarkably good match to this woofer. It is the Tang Band 25-302SH 1" Shielded Neodymium Dome Tweeter.



It is close to matching the woofer in efficiency (a little higher) at about and 95% through a relatively flat operating range from 1500 hz to 20k.

7. The cross-over will be designed using the various design programs available free on the internet. This is where I will need some assistance in some of the finer points (an art you guys have mastered) of cross-over design and I hope you will be able to review my schematics and make suggestions to optimize it for this set-up. My basic cross over will be a Linkwitz-Riley, Second Order (12db/octave) Two-Way Crossover. From what I have seen these are basically an inductor and a capacitor for each driver.


I plugged in the high and low impedance of the speakers using the listed spec DCR impedance of 6 ohms for both into the calculator. I know that the actual impedance is variable over the range so I am not sure if I should do this or use the ‘nominal’ impedance of (both 8 ohms). I chose a cross over point of 2500 hz. The values for the circuit are:


Woofer: C2 = 5.3 uf , L2 = 0.76 mh

Tweeter: C1 = 5.3 uf, L1 = 0.76 mh


The Linkwitz-Riley crossovers match attenuation slopes so that system response is flat at crossover point. I am not sure what else I need in the circuit. While the tweeter is more efficient than the woofer I am not sure that this might not be ok for a rear surround and not need adjustment. I think that the size of the speaker design and the location where it will be mounted needs to be considered but again, I am not sure and need assistance here.

8. Other parameters: In some of the cross-overs for rear speakers, I see the tweeter polarity reversed. If someone can explain why this is I would appreciate it. And I would like to add a switch to listen to the effect of a regular hookup and a dipole as I do not know what I would like best for my rears. Might as well try this and listen to see which I like the best and with a switch as I don’t want to have to take it down and rewire it.


This will be driven by an Onkyo receiver/amplifier TX-SR605. The manual says it delivers 90 watts per channel able to handle 6 to 16 ohm impedance and I don’t drive my speakers to painfully loud levels. I am not sure if these parameters figure in to the cross-over design but if they do I would appreciate hearing what I need to do.


Finally, the speaker placement on the front baffle - I am not sure how to determine this. I know there are room constraints but if there is a best placement based on what I am using, I would like to know it.


Can I design a better rear surround - sure. If I use a bigger cabinet, more expensive drivers and want to spend a lot more money I could do this but for now, the above parameters are what I have to work with and I would like to take what I have and build the best rear surrounds I can with what is given.


All comments and suggestions appreciated on this project as I don't know if I can get through all of this without your help.


If there is anyone in the Dallas Ft. Worth area that could help me with the speaker holes and routing this would be appreciated too.


Usil
 

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Discussion Starter · #2 ·
Well, I found a nice little wood shop to cut and route my speaker holes so I should have the baffle back later this week. Then a quick assembly for the Zaph ZDT3.5 – ZD3C sealed Center Channel and I can finally fire it up on the main system.


I have placed pictures of it in my Center channel thread.

http://www.avsforum.com/avs-vb/showthread.php?t=1088141


Usil
 
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