My turn to build JC's DBB

[Marvel]

Gomer Pyle: Me and Goober are goin' down to see that Cary Grant movie. Goober never misses a Cary Grant movie. He studies him. You want to hear him take off on Cary Grant? C'mon, Goober; do Cary Grant.
Goober Pyle: Well, I don't know...
Andy Taylor: Well, Gom, if he doesn't want to...
Goober Pyle: I'll do it! Judy, Judy, Judy!
Gomer Pyle: [laughing hysterically] Ain't that great, Andy? How do you do it? Let me try; Judy, Judy, I can't do it. Andy, couldn't you just swear it was Cary Grant standin' right before you in this room?
Andy Taylor: Uh, yeah, Gomer; that was real good, Goober.

[jorjen]

I'm sorry, did I do something wrong?

Nope, just the opposite. I thought everyone had seen the Notre Dame football movie "RUDY". I was chanting your name for a valiant effort.

[Marvel]

Now I should be embarrassed.

I thought you were just making a play on the Gomer Pyle episode...

Rudy, they are looking great. I can't believe how fast you have put these together.

[John Warren]

John, very nice. I am in the process of deciding how to finish my cabinets. My goal is to keep the cost and the difficulty level down. My initial idea was to finish them like JC did his, in black. Specifically, Black Lacquer to match my La Scala center. I have also been contemplating a veneer, but the issue with the DBB is that when you are looking at them from the front you don't see much of any veneer. You would have to walk around the speaker to see the grain. I'm just not sure it is worth the trouble in my situation since they will live in my HT, which is all black. At least the other speakers and the curtains.

Looks like you've finished them.

I like veneers but paint works too if done right. I've found that first priming the bare surface with a high solids latex stain blocker, then palm sanding the primer does a nice job getting it smooth for spray paint. The front baffles shown in the earlier pics are done with 3 or 4 primer coats, each sanded using 150 then 600 grit paper until smooth as a linoleum countertop. It generates alot of white dust but the results are worth it. Paint is a flat spray paint. It looks like the old school JBL factory stuff. MDF is smooth but the surface still needs this sort of treatment.

Here's a pic that shows baffle-

[Rudy81]

I very seriously considered veneer. However, from the listening position, you cannot see anything but the edges of the cabinet and a bit of the top hat. No use in spending several hundred more dollars if I was not really going to see the veneer unless I was walking around the speaker.

So, I chose the paint. It turned out rather well, although lacquer would have been much nicer had I not made a mistake with the primer coat. I will say that after sanding the primer coat, the surface was super smooth.

For all intents and purposes, they are done. I can't wait to get back and have a real listen.

[Rudy81]

Now I should be embarrassed.

I thought you were just making a play on the Gomer Pyle episode...

Rudy, they are looking great. I can't believe how fast you have put these together.

Now I get it! Rudy is one of my all time favorite movies for a good 'feel good' story. I was a bit confused with the whole Gomer thing.

[jorjen]

Now I should be embarrassed.

I thought you were just making a play on the Gomer Pyle episode...

Rudy, they are looking great. I can't believe how fast you have put these together.

Now I get it! Rudy is one of my all time favorite movies for a good 'feel good' story. I was a bit confused with the whole Gomer thing.

OK guys, glad we finally got that straightened out. []

[Rudy81]

Finally got a chance to test the DBB outside. Warning: I am a total amateur at taking measurements and barely know what I'm supposed to be doing. So, take these measurements with a grain of salt. Who knows how accurate they are. The test subject is my build of JC's DBB with Emminence Kappalite woofers. The mic is an ECM8000, software is REW with a Tascam external audio card and my laptop.

This is the best I could get with the mic at 3 feet away. The bass bin is outside, but close to the garage due to hookup limitations. Of course, the speaker is pointed away from the house.

Expert interpretations are welcome.

[Rudy81]

I also hooked up the P. Audio driver and horn and ran some plots on that. I did on axis, 30 degrees right and level, and 60 degrees right and level.

I suspect the proximity to the house is having some effect, but there is really no way for me to move further away without going to a lot of trouble to set things out in the middle of the yard. I know Chris did some tests with the same setup outside and I beleive he got better results.

In any event, here is what I got. If anyone wants the REW files to play with the results, let me know and I'll send them to you.

[Rudy81]

This was the setup for the DBB test

[Rudy81]

This was the setup for the P Audio test. I will say that at the lower frequencies, the plastic horn does tend to vibrate quite a bit. I don't know if that is normal or not, but I think a bit of rope caulk will be in order to dampen the horn a bit. What do you guys think?

[jwc]

This is great stuff. Looks like the bass bin is tuned right about where we talked about it. That slow dip after 300Hz I hope is from the proximity of the Mic, or some XO issues, or phase. Very well could be from the mic proximity.

That woofer shouldn't give out of gas that soon....

http://eminence.com/pdf/kappalite-3015lf.pdf

They look awesome.

jc

[Rudy81]

JC; Thank you for all the help. I'm not sure why it rolls off drastically after 1.5kHz. Certainly there are many factors on my build vs. whatever method Eminence used for their test. Cabinet design, my setup, mic calibration etc. Overall, I think the plot is rather respectible for something I built in my spare time based on your design.

The beuty for me is that no corners are needed, and once corner loaded, they should really crank out some lows. I started the runs at 30Hz since I did not want to push my luck with the ported design and the woofers' capabilities. I have read that if you push a woofer too much below the cabinet design you can damage the woofer.

Next will be to lug these monsters upstairs and hook everything up....then some music testing. I do have to brace the top panel of the top hat a bit. It tended to flex a little too much for my taste and I anticipate it may resonate some when things are cranking.

More tests and music impressions to follow.

[pzannucci]

This was the setup for the P Audio test. I will say that at the lower frequencies, the plastic horn does tend to vibrate quite a bit. I don't know if that is normal or not, but I think a bit of rope caulk will be in order to dampen the horn a bit. What do you guys think?

So you are getting a lot of resonance in the lower vocal range in with the horn? I was noticing a fair amount with my Selenium D305ti drivers but was thinking it was the drivers. If it isn't and there is a lot of lower end resonance then I'll stop looking at ways to correct the drivers and go back to building a new horn.

[Rudy81]

So you are getting a lot of resonance in the lower vocal range in with the horn? I was noticing a fair amount with my Selenium D305ti drivers but was thinking it was the drivers. If it isn't and there is a lot of lower end resonance then I'll stop looking at ways to correct the drivers and go back to building a new horn.

I ran a 500 Hz tone through the horn and the big 2" driver made it vibrate more than what I expected. Heck, I don't know what 'normal' is. I never really had an opportunity to run a low test tone and see how much vibration was in the horn itself. It seems reasonable to expect the horn to vibrate at the lower frequencies. Heck, a bass bin will vibrate at the low frequencies as well.

I think I will just add rope caulk for the heck of it and go from there.

[Rudy81]

Tonight I lugged these behemoths upstairs and put the woofers in. I couldn't wait to listen, so hooked them up. Gut feel, initial impression is excellent. Darn these things put out some chest pounding bass. I didn't get the same feel when I used just one (with one Khorn bass bin) to see how it sounded, but two bins pound the walls.

It is a very different sound than the Khorns. They sound much more like a La Scala or a Cornwall, and the bass is effortless and powerful.

I plan on doing some comparison listening by selecting several songs and playing them once on the DBB's and then the Khorns. The DBB's seem to play very well with the P. Audio horns. I did not even take the time to do any tweaking, level matching etc, so I hope and think it is only going to get better.

Right now the DBB bins are sitting directly in front of the Khorn bass bins. I'm not going t move the Khorns until I decide if I am going to keep the DBB's...but so far that is a very real possibility.

More impressions to follow, and some plots of the DBB set up with the P. Audio driver and horn.

I beleive the effort in building the bins is going to be well worth it.

[Rudy81]

BTW, here is the same plot in db FS y axis.

[Rudy81]

Here is the waterfall plot for the reading taken outside.

[DrWho]

Finally got a chance to test the DBB outside. Warning: I am a total amateur at taking measurements and barely know what I'm supposed to be doing. So, take these measurements with a grain of salt. Who knows how accurate they are. The test subject is my build of JC's DBB with Emminence Kappalite woofers. The mic is an ECM8000, software is REW with a Tascam external audio card and my laptop.

This is the best I could get with the mic at 3 feet away. The bass bin is outside, but close to the garage due to hookup limitations. Of course, the speaker is pointed away from the house.

Expert interpretations are welcome.

The single sharp narrow dip at ~320Hz can very likely be attributed to the mic height during the measurement, and the reason we don't see the harmonics of the floor reflection is probably because the polars are getting narrower in the vertical due to the driver spacing. This would also explain the rising frequency response above ~400Hz or so.

The soft rise in the response from about 50Hz to 200Hz is probably baffle step gain from the wide cabinet face, and also polar response related. I think if you moved your target response line from 75dB to 72dB, and called that the nominal sensitivity of the driver, then I think it would help demonstrate the behavior. In other words, I don't think I'd necessarily look at the 250Hz to 450Hz region as a dip per say. I believe the cabinet design is giving you the extra output from 50Hz to 200Hz due to baffle step or whatever you want to call it. The real way to know would be to measure the absolute SPL for a 2.83V input at a distance of 1m, but that involves all sorts of calibration that would probably end up being more misleading than informative (simply because absolute calibration in REW requires another calibrated measuring device....and a ratshack SPL meter isn't going to be accurate enough).

But ya, this is one of the reasons I like to place the microphone on the ground about 10ft away and then tilt the speaker forward a bit. Another really useful thing is to move the microphone around...and record both the height of the microphone from the ground as well as the distance from the speaker (so you know the relative angle to the speaker). Due to the polar response behavior, the frequency response isn't the same on every axis (although ideally it would be).

In the end, it really comes down to what you're trying to do with the measurements....Ultimately, I don't think taking a single sweep is very useful, because it's only one snapshot of the entire system behavior. Because of this, I usually try to use measurements to identify problems and then I can choose whether or not to remedy them once I understand what's going on.

Btw, if your horn is actually resonating at 500Hz or so, then you should see a big dip in the frequency response at that frequency. I also wouldn't mind if you sent the REW files my way so I could see what kind of reflections were showing up in the ETC. If you look at the relative phase offset of the reflected sounds, then that's another way to identify that reflections are affecting the measurement. If you send them my way, then I can go through and annotate them to show how one can calculate reflection related dips in the frequency response. There's no guarantee on when I'll get around to it as I'm barely able to read the forums anymore...

[Rudy81]

Dr. Who. Thanks for the comments. I just finished a comparisson of the DBB with the Khorn bass bin by listening to some select songs. I really like the performance of the DBB based solely on how it sounds. I have no idea what the distortion differences are or anything else. The DBB has a much more immediate sound, obviously more direct and very competitive with the Khorn bass bin. It is a different sound for sure, but pretty much what I was after.

In all fairness to my Khorns, they are not and have never been in a true room corner, because I don't have good corners. So, I always had to get by with false corners.

PM me your e-mail and I will send you the files if you are interested in playing with them.