My turn to build JC's DBB

[Rudy81]

John: Sorry, for the long wait, but I have been out of town for the last two weeks. Came home to find the WT3 waiting for me. Mind you, I just followed the instruction to calibrate the system and then ran the tests. I was anxious to post these, so I have not had a chance to 'analyze' the results. I followed the software directions on how to measure a ported enclosure. I suspect, just by looking at the graphs with very little knowledge, that the results are just what JC would expect. Your interpretation is greatly appreciated. Please remember to keep it in layman's terms.

This is the Free Air test of the woofer. Looks very similar to the published plot on the Eminence site for the Kappalite 3015lf. http://eminence.com/pdf/kappalite-3015lf.pdf

[Rudy81]

The WT3 has you make two runs for the driver mounted in its enclosure. One run with the ports blocked to get a 'closed' box result. Then, one with the ports open. Those results follow. This plot is whith the ports blocked.

[Rudy81]

Here is the result with the mounted driver and the ports open. BTW, I see the entire .jpg is not visible in the forum display, but you can click on the .jpg and enlarge it to see the measued parameters on the right side.

[Rudy81]

Finally, I zoomed in on the last graph in order to get a good closeup of the DBB tuning frequency. I show it right at 40Hz.

[jwc]

Wow. You have got some cool tools.

[Rudy81]

Based on my interpretation of the graphs, I get the following:

fL is approximately: 27Hz
fH is approximately: 65Hz
fM is approximately: 40Hz

The WT3 instructions also lead me to get the following information from the runs:

Equivalent 'closed box' tuning frequency F(sc) is 57.87Hz
Equivalen closed box total Q(tc) is 0.6602
System DC resistance is 5.428 Ohms

[Rudy81]

Wow. You have got some cool tools.

One thing is having cool tools, another is knowing what the heck I'm doing with them []

I am just blindly following John's suggestions in order to get some readings on the DBB build. From a complete idiot's perspective, it looks pretty good to me. I just need to learn to interpret the results. I know one thing JC, we were shooting for a 40Hz tuning frequency, and you nailed it!

Needless to say the WT3 hardware and software is easy to use if I had it up and running in 5 minutes. It was $90 for the WT3 and maybe not worth it, but since I was going down the "learn everything I can" road for the DBB, I just went for it. Pretty cool piece of gear.

[Rudy81]

I'm still researching how to use this data and have come upon a formula to generate the box tuning frequency Fb. What I found is this: Fb = (Fh^2 + Fl^2 - Fc^2)^1/2.

Some quick calculations give me a Fb=40.06Hz. Which is very close to the vent tuning frequency of 40Hz., supposedly this is a good thing.....still researching.

[Al Klappenberger]

This is good! This software is the first I have seen that gives you the simple impedance of a woofer as well as the polar phase component of the impedance. This is exactly how I measure a woofer to get the required impedance to design a crossover network. It's the same type display I get with my HP3563a analyzer and Z bridge. All you do is covert the Polar Zo and phase to rectangular R +-jX at the frequency where you want the crossover. The "R" component is the design impedance. That also becomes the resistor value of a a series R-C Zobel. The last step is to experiment with the cap value to get Zero phase around the crossover frequency. THEN you can use any of the many crossover calculator programs to design the crossover. The "R" component of R +-jX is used for the impedance.

SUPER!

Al K.

[Rudy81]

Al, I wish I had the understanding you do. The software is more capable than what I have mentioned. It can be used to measure woofers, tweeter and mid drivers as well as resistors and inductors. It also has some feature that assists in designing Zobel networks. It apparently can also be used to diagnose driver problems.

There are a couple of reivews on the WT3 on the web that indicate it is a good buy for the money.

Now I just need to figure out what all these measurements are telling me about the technical merits of the DBB build.

[Al Klappenberger]

Rudy,

Don't let all the bells and whistles of that software bug you. Think of it as a big toolbox full of tools. You may use all of them someday, but you only use the ones you need at any given time. I only learned of that package a few days ago, so all I know of it is what you have posted. From that little glimpse, I am impressed! It's going to be your guide to learning about a lot of stuff you didn't know anything about before. Enjoy the process!

Al K.

[Rudy81]

Al, you are correct. I am enjoying the process and already have learned quite a bit from just a year ago. I keep kicking myself because I didn't pay much attention during my EE classes in college. I was more interested in Thermo of all things. I really should have taken more of an interest in EE, it would have made all this much easier to understand.

Between building the DBB and going active three way and then two way, the learning curve has been steep..... but very much worthwhile.

[John Warren]

detour

http://northreadingeng.com/Forums/index.php?topic=4.0

[pzannucci]

detour

http://northreadingeng.com/Forums/index.php?topic=4.0

Thanks John, Looks like a good place to discuss a lot of this type of stuff that really doesn't belong with a Klipsch forum.

I had Woofer Tester 2 and WT3. What a difference. WT3 is much better. The only bad part is you start seeing differences in samples. I got a pair of 220TI drivers and was amazed at how far off they were in impedance though maybe not enough to worry about since the drivers hadn't been broken in.

[Rudy81]

Detour taken...

[bigrfish]

Detour taken...

Here's another detour: Google the Phrase, "Behringer DCX 2496 Word Clock and Power Supply Modificarions"

Could be the missing puzzle piece....sorry off topic but is related...Chuck

[Rudy81]

I had looked into DCX2496 mods a while after I started using it, purely from curiosity. I know there are quite a few things that can be done to 'improve' the quality and performance of the crossover. However, I figured I would be better served to learn to use the DCX and at some point, upgrade to a better quality crossover, like an Ashly or XTA.

Frankly I have not been too disappointed with my DCX, it is very quiet and works rather well. I have not compared it with anything else, so my point of view is limited. I am in the process of looking at the Ashly Proteas and XTA options.

[PrestonTom]

I had looked into DCX2496 mods a while after I started using it, purely from curiosity. I know there are quite a few things that can be done to 'improve' the quality and performance of the crossover. However, I figured I would be better served to learn to use the DCX and at some point, upgrade to a better quality crossover, like an Ashly or XTA.

Frankly I have not been too disappointed with my DCX, it is very quiet and works rather well. I have not compared it with anything else, so my point of view is limited. I am in the process of looking at the Ashly Proteas and XTA options.

The Behringer is actaully not all that bad for home use and they are certainly quite affordable and have a number of features. For the vast majority of systems, they could be a real upgrade. When you read about the upgrade path on DCXs it can be a bit imtimadating.

My view is that the real weak link in the Behringer is the analog out section. This can be replaced by 1) a passive circuit as outlined by Didden in his Audio express article (basically and pair of RC filters and a DC blocker after the DAC outputs). Or, 2) a transformer after the DAC outputs to block the DC and convert from balanced (XLR) to unbalanced (RCA). The transformers can be expensive to inexpensive. The Jensens are about $70/channel, the Cinemags about $35 and edcors for about $15. Choice of which specific model is important.

I have done both versions and they sound fine. The other componets in the Behringer are comparable in quality to the more expensive brands (DAC, ADC, DSP). Agin, the reason to go with a Behringer is the attractive price.

If you do use the Behringer, it is best buy a new one, to feed it a digital signal, and read the instruction manual.

Good Luck,

-Tom

[Rudy81]

Figured I'd update this thread now that I'm close to being done with the whole setup.

I am still really enjoying the sound of the DBB's with the P. Audio top section. In order to get that last bit of performance out of the system, I jumped and replaced the DCX 2496 with a much better quality Ashly Protea 4.8SP. A big jump in audio 'quality'. Expensive, but well worth the investment in the improvement. This is a very nice crossover with plenty of capability. It is very quiet and no more 'hiss' from my horns.

An added improvement was to take my RSW-15 and add it to the mains from 50Hz on down via the Ashly. The DBB's and RSW are all time aligned for a seamless sound. I wish I had a second RSW in order to go 'stereo' with the subs, but for now only have one. I placed it in the center of the room and run both L and R to the sub. Sounds extremely good for 2-channel listening and lets a great sub do the heavy lifting of the lower frequencies.

Finally, I obtained a licence and the equipment to use Audyssey Pro on my system. Again, another improvement over the old setup. The nice thing about the Audyssey Pro package is that it allows me to tailor the response curve to my liking. It also allows me to graph and 'see' what Audyssey is doing.

This project turned out to be exactly what I was after.

[chrapladm]

Cant seem to find JC thread so I will ask here but is there any plans for a DBB using 12"?

I would like to build one of these but my space is limited. I just dont have the width to fit these bad boys and my subs next to each other. Dual Crites 12's maybe.