Ricci

How's it sound in the jeep?

Delicate. Nuanced. Like a dump truck crashing into a bridge abutment.

It's all over the place. One day it's sunny and 65 and the next it's 35 and raining. We had some sub 20deg weather just 3 or 4 days ago.

But I'm getting prepared for the next available window.

I'm a little disappointed, but not surprised. Looks like a 25-40Hz rumble fest. Still like the movie though.

One cabinet has been assembled at the moment. Yes, at the moment working on measurement, waiting for nice warm weather both to measure outdoors, also to order Duratex when the risk of freezing has passed.

 

I am not against a series connection, it would increase the applied voltage and cut wire losses, increasing damping factor. A warm voice coil increases in Re, and if my math is correct, at just 50C, the VC Re would increase to 3.724 ohms.

Please post the measurements and a follow up when you do get around to the measurements.

Are these speakers intended for your home audio / HT or are they going to be used for sound reinforcement / PA?

Hello Ukko...Hell of a first set of posts. Information overload!

I like your choice of drivers for this project. The XT1464 seems to be quite popular and performs well. It seems like your cabs are built and assembled already , so you are at the point of fine tuning with DSP? Will you be finishing the cabs afterwards?

I'm curious but why parallel the woofers resulting in minimums near 2ohms? Why not run the drivers in series for a much easier load on the amplifier? The pair of Faital's in a large vented cab should be very efficient and won't require much voltage to hit very high levels even if it is an 8ohm load.

For some reason the tweeter isn't omnidirectional at and near the crossover frequency, but somehow matches the directivity of the midrange. I don't know how this is possible.

 

This type of thing is why measurements are so important. In a nutshell most of our modeling or simulations, or common knowledge are simplifications of what are much more complex issues in reality. They say bass is omni too but that's not entirely correct either.

Any other news? Are you listening to these and working on dialing them in?

I'm pretty much ready to take this out to the field and see what's what. Just waiting on weather and a good day for my schedule to line up.

Well it's definitely loud. Where are these guys from?

Nitoni,

Driver or even cabinet sensitivity specs are still important but efficiency is much more important to me. Once the efficiency starts to get very high as it is with this driver base voltage sensitivity starts to drop. Despite this the driver requires less power despite the lower sensitivity.

Equalization is a manipulation of the signal being sent to the amplification stage it does not change the voltage sensitivity of the cabinet and driver system.

I expect this driver will be around 100dB at 100Hz with 2 volts in the 4.5ft sealed cab in the GP test.

Ah... that explains it!     Sorry, I missed that part completely. There's no mentioning of a 4 ohm version on B&C's website so I hastily concluded there's only one model available...

 

So what sort of peak voltage (burst) could you safely put through the nominal 4 ohm VC from a thermal perspective you reckon and what sort of compression could one expect at that level?

You'll have to wait for the ground plane measurements to answer that. I could guess but the workup will answer that much better.

How come though that your measured Re of 2.2 ohms is so far off factory spec of 5.1 ohms? That's less than half and would rule out some amplifiers not happy driving less than 4 ohm loads (e.g. bridged Class D). I mean this is nominally an 8 ohm driver with a rated minimum impedance of 6.5 ohm.

 

On the same note, nominal power handling of 1700W is based on rated minimum impedance. Ohms law yields 105V @ 16A. Based on your own measurements, what peak voltage (Vp) would push your driver to Xvar of 16.5mm at 15Hz? Around 75V? 

Hello Nitoni,

I measured the 21DS115-4 not the 21DS115-8. See the PDF and compare with the parameters I pulled.

21DS115-4.pdf

Parameter  Value  Dim    

Fs 31.51  Hz    

Re 2.2  ohms[dc]

Qt 0.2  -    

Qes 0.2  -    

Qms 6.86  -    

Mms 379.75  grams    

Rms 10.95386  kg/s    

Cms 0.000067  m/N    

Vas 266.34  liters    

Sd 1680.02  cm^2    

Bl 28.52571  Tm    

ETA 3.94  %    

Lp(2.83V/1m) 103.67  dB              

Le 821.03  uH

L2 1930.6  uH  

R2 57.1  ohms    

L3 0  uH     R3 0  ohms    

1kHz Le 2.62mH

Whatever you want to do. I'd need 4 of either just in case.

Ordered a used firebox last night for $43 shipped. Was going to jump to a Motu UltraLite-mk4 but at $595 that's a bit more of an investment. I'm going to order another backup firebox for <$50 and take some time to look at some newer interfaces. I used to have a backup but I sold it to a buddy last year. The Motu looks nice but it is expensive and has a ton of extra functions and needless setup complexity I have zero use for.

Dave,

I tried foam a few times before on other cabs and once you start putting 20+ volts in near tuning you can feel air movement from the vents that are " blocked". Larger vent areas are worse. These are roughly 7x4" or about that.

Ti,

The wood blocks fit well but it's the vertical area where I can feel a bit of air. I'll have to cut them down to get gasket tape on those edges. They fit very tight without any gasket tape on. That's the current plan .It's not so much the middle vent using one block but when I try to block a second. The second doesn't fit as deeply due to the 6mm offset from the first since they are overlapped. It still fits well and looks ok. I'll figure something out. I hadn't planned to run them with one vent open but I do want to test them like that. Might as well.

How difficult would it be to whip up 4 more of those same vent blocks?

Went to fire up my rig and heard a loud pop. Came back to the desk and my trusty Firebox looked like a hookah lounge, releasing magic smoke everywhere. Damn it. Luckily everything else is fine. No idea what happened. Wasn't even running anything at the time.

I'm sure. I don't have much trouble with drivers in free air but once I load them into a cab I have trouble getting a completely clean LF impedance in the garage for a number of reasons.

Impedance measurements compared with the HR simulations. I often see a bit of noise in the measurements when doing impedance captures on big cabs in my garage so the measurements are a bit jagged in a couple spots. Also I am getting some leaking from my port plugs and that is affecting the 1 vent and 2 vent measurements a bit. Also there is the damping I put in the cabs. Both of those will likely reduce the peaks a bit. After I decide on a more air tight method for blocking the vents I'll probably rerun the impedance in each of the configurations.

It matches up fairly well. The centering of the  peaks is slightly off but this is expected and it's quite minor. As mentioned I think the port plugs not being entirely sealed is diminishing the bottom peak a bit. The result is a lossy vented system. I have wooden port blocks but I may have to shove a significant amount of foam in behind them to help seal.

Adding a few pics. I'm going to be working on some close mic measurements and figuring out a way to more effectively block the vents since I'm getting a bit of air leaking. Other than that it's time to do some listening and prepare for the ground plane torture. I decided to add some foam lining around the drivers to try and knock down out of bandwidth reflections from bouncing around in there a little bit. It ended up making mounting the drivers more of a challenge than it otherwise would be. It's very tight by the cabinet side walls with it in there. Depending on what I see on a bare cab versus with the lining I'll decide whether to yank it out.  

Related to the Ipal Technology, I found a test with the 18 ID driver

http://www.audioxpress.com/article/test-bench-eighteen-sound-18id-18-inch-woofer

Yes. Unfortunately VC mag tested almost every other B&C woofer but the Ipal's. For some reason the 18sound Klippel tests always seem to have a bit more variation than the B&C's. Still it's a nice driver and came in at about 13mm xmax which is only 1mm under their 14mm spec.

In other news it lives. I finally got power put to the Ipal loaded one yesterday. I only got some quick measurements before having to go out for the night. No surprises yet.

You don't want an SP amp per driver. You'll cook a coil very quickly with that last 3dB of power. Just run a 4k or 6K plate one per cab and wire drivers in parallel.

Yeahhh I scraped the extra off the corners cuz it's ugly. That'll show me.

LOL! No shit!? That's too funny.

Yeah I ran wires through the baffles. Single speakon on a single hatch. Or single amp plate as may be the case.

Similar to the other B&C drivers. Clean and quiet up till 20mm peak to peak. Takes on a bit of mechanical noise but otherwise still quite useful at 30ish mm p2p which is rated xmax. It'll go further but it's diminishing returns past that point. Distortion and noise grows quite a bit. I'd estimate I pushed it to 40mm peak to peak. Takes a lot more power to get there. Like the others it'd take some work to mechanically damage it.

I had a chance to pull the specs from these after a bit of mild 20Hz break in. I have the 4ohm versions. This is about as close as I've seen to matching factory specs. This driver is encouraging so far. It's light and $100 cheaper than the 21SW152. The only thing I was disappointed with so far is they used a smaller diameter spider than on the Ipal and 152. It has a smaller coil diameter so the bigger 6" formers need a bigger spider but the large one would've improved suspension linearity most likely. I assume they did it for mechanical protection where the smaller spiders increased stiffness will keep things under control if hit with too much power. More later.

Specs I pulled. Like I said this is really really close. They've got a pretty low DCR on this driver but it is so efficient that the impedance peak is huge so it'll likely be at or above 3 ohms min between 10-125Hz.

Parameter  Value  Dim    

Fs 31.51  Hz    

Re 2.2  ohms[dc]

Qt 0.2  -    

Qes 0.2  -    

Qms 6.86  -    

Mms 379.75  grams    

Rms 10.95386  kg/s    

Cms 0.000067  m/N    

Vas 266.34  liters    

Sd 1680.02  cm^2    

Bl 28.52571  Tm    

ETA 3.94  %    

Lp(2.83V/1m) 103.67  dB              

Le 821.03  uH

L2 1930.6  uH  

R2 57.1  ohms    

L3 0  uH     R3 0  ohms    

1kHz Le 2.62mH

Well at first I was just doing the wires because it's what I had on hand. Then I did all the baffle seams just to make double sure. From there I figured screw it I already had the gun in hand.

Did some work on these last night. Got the holes drilled for the wires and sealed those up. Went ahead and split another tube of PL between both enclosures and lined or filled in any joints that didn't already have PL squeezed out of them. So now there's 6lbs of PL in each cab? I always go back and do this any more. Probably unneeded but I think I gain a bit of woofer speed and 0.1dB from it.

I'll be putting some lining in the cabs behind the drivers and loading the drivers in Sat morning. Hopefully I get to power one up this weekend.