lilmike

10 hours ago, Ricci said:

Well I added some info and screenshots at least. 

I don't have real cabs or test data yet but it will happen this summer. Based on the results from my last couple of designs I've got a high confidence of what these are going to behave like. 

You'll most likely get this built and fully tested before I get anything done with my projects. Thanks for sharing the renderings and concept.

1 minute ago, dsl1 said:

Building the hype.

I know. I've waited like two whole days already...

Oh you tease...

I'll add a second to Ricci's post. I typically measure big drivers at about a watt applied, so 2V for a 4R driver, 2.83V for an 8R driver.  My DATS and WT2 aren't quite enough for the big drivers, the Clio Pocket does OK though. The Clio manual recommends the lowest drive level that yields a clean signal. 

The headphone out on the UCA202 is almost enough power, but the crosstalk killed it as a contender, Pity, it was widely available and only $30. I haven't tried the headphone outs on the other Behringer USB interfaces I have. Maybe one of these days...

When I need an amp, I use an old single-channel amp I got from a buddy now, it is an old TOA. Overkill for the low level stuff and it weighs WAY too much to move around, but it was free and does the job.

Be sure to use a good meter and watch voltages when using an amp, it's way too easy to send more signal than the sound card can handle. Back to back Zener diodes and/or voltage dividers are a good idea. 

Yeah - my last post was ambitious... It has been damn near 6 months and I still haven't had the time to pull final specs and design final boxes. Worse yet, I am rapidly working my way through my stash of plywood building other projects.

Without accurate driver specs and Thiele-Small parameters there is no way anyone can design or predict anything. 

I've done some rudimentary testing with other drivers and found that I could put a lot more power to them in the tapped horn than in a free-air situation. The driver I was working with (Shiva X2) would make mechanical noise (tapping) at really low frequencies at about 100 watts applied free-air. The same driver in a tapped horn was able to take 500 watts without any noises. Not totally scientific, and certainly not what I have planned for my future efforts, but at least it showed that there is some loading on the driver below the horn passband and at least some difference between the displacement predictions and actual performance in that case. 

I have also found that my tapped horns tend to measure a little flatter at higher output levels than they do at a watt. 

In the case of a ported box with an undersized port, the excursion increasing as the port compresses makes total sense to me. In the vast majority of cases the ported box is larger than a  sealed box would be for the driver in question and the port essentially becomes a large leak once compression sets in and the port is no longer functioning as a proper resonator. 

Sorry for the late reply, just getting back online after a vacation.

The 4th order recommendation was based on simulations of the performance of lower-order filters. The lower-order filters do not provide sufficient protection from overexcursion below the horn's tune. Once at 4th order, things look OK, higher than 4th looks a bit safer, but as SME mentioned, higher-order filters come with other issues, like ringing and phase issues.

That was all done in simulations, which are predictions of large-signal performance based on a set of small-signal parameters that do not scale linearly as signal increases. My experience is that excursion tends to not be as much of an issue as Hornresp predicts. Usually, there are warning signs before the bad noises happen, and so far, I've not killed any drivers in tapped horns (though, I don't set out to do so). I haven't had a chance to actually measure the excursion of a driver in a tapped horn yet, but I hope to be able to do that before too much longer. I do have most of the gear and software, just need to get it all configured. 

The highpass recommendation was my effort to try to make these cabinets as bulletproof as possible for other people. I would hate to have someone kill the driver in their newly-built sub while showing it off in a demo because I didn't recommend a highpass to protect the driver and minimize distortion. I run 20 Hz at 4th order in my system, and I definitely twist the volume knob to silly on occasion. The sub has moved itself out of the corner several times. So far, only warm voice coil aromas, no bad noises or other complaints from the sub. The rest of the system was running out of gas at that point, but I am working on that.

Thanks!  

Timing was just about perfect for my projects. I hope to get the sub designs finalized in the next couple weeks, then get some sawdust made before year end. Will drag out the measurement gear and get some impedance sweeps of my drivers as soon as I can, then see if the models still look OK. Neither driver has all that high of an inductance (Le/Re of 1.03 for the 15s and 0.47 for the 18s). 

On 5/23/2018 at 7:54 PM, Infrasonic said:

 

Mmmm...

A gear list like that makes me get a fizzy sensation somewhere behind my penis but not in my prostate.

Does anyone else get a fizzy sensation behind their penis or is it just me?

 

?

 

for reference...

https://youtu.be/hcOwz99GS4c

I'm right there with ya. Definitely have experienced the "fizz" with cars, even some proper subwoofers...

Admittedly, I oversimplified the statement regarding equal peak height above.

The relationship between the driver parameters and the box tune dictate the relative size of the two peaks. What matters most is that the peaks you're measuring are a decent match to what your simulation software is predicting. 

As far as the grille spacing? Yeah, make sure things won't hit. X-mech plus a few mm is a great start, I'd look at the thickness of nominal pieces of plywood or other scrap stock. Make sure the grille does not rattle. Foam weatherstrip and lots of screws.

Yeah, that lower peak is a bit "soft", that generally means losses or leaks (or, as I learned, a really useless port). 

With a typical reflex box, we want the peaks to be about the same height. 

3 hours ago, Samps said:

Would there be any benefit to adding a deflector to the back corner of my port?  

Currently there is a pretty big difference in volume of that corner vs the rest of the port.  

Possibly.

Looks like it is something where you could try it and see. Heck, just cut a piece and set it in place for testing. Won't be 100%, but will give you an idea.

5 hours ago, Samps said:

I built and sold two THTs that were never finished.   I figure you have to test it before you spend all that time finishing, but then it never gets done.  

My impedance jig isn't working correctly.   It will make a sweep but the level is super low and the graph doesn't look anything like what I've seen before.   Pretty sure I built the jig correctly, but not sure I'm using the correct settings in REW and or computer.  Been testing a little bookshelf for practice.   

PM me. I can help you work through it. 

They're pretty basic. Might be as simple as L and R channels swapped. 

6 hours ago, maxmercy said:

Make sure you put a finish on the cab before you install the driver.  I have had cabs that went without finish for 3 years, b/c after the driver goes in, it is so easy to just listen to it.

JSS

Three years.... Weak.... I am still rocking the OG MicroWrecker (since 2013)... No finish, not even sanded, still has big PL boogers on it. 

Well, that sucks. 

Still, for what they cost and what they do, 6 years isn't too bad, mine's actually coming up on that point too. I'll be sad when it dies, but I've gotten my mileage out of it.

Ummmm, yeah, actually I'm pretty sure I do have some power on tap.

Nowhere near that level though.

DAYUM man, that's more wattage there than some tours run....

On 11/2/2017 at 2:00 PM, Ricci said:

Puts BR in cart on the Zon...Must purchase nowz.

Sweet, this will be perfect. I can enjoy the movie without a sub and know that I am not missing a damn thing.

(No subs yet because I am still trying to scrape the cash together to buy my drivers...)

Those lifting straps? I've tried them, they're OK for some things like couches and beds, but not something I would use on a sub.

I have a little bit of experience moving big subs. We used an appliance dolly when we had to get the pair of LilWreckers down a flight of stairs and into a basement theater. Definitely took two of us, and I'm not a small guy. LilWreckers are ~32 cubic feet and about 300 lb if I recall.

Google appliance dolly images 

You should be able to rent or borrow an appliance dolly without too much trouble.

I moved the F-20, MicroWrecker, and a number of other unnamed tapped horns with my 2-wheel dolly, but I didn't have to climb too many stairs. 

No matter what,  using some straps to secure the sub to the dolly is a fundamental. A second person can be a huge help too.

Of course, if you have another stout person handy (looking at you, @Ukko Kari) , you just pick the cabinets up and carry them, like we did with the AlpineGeists. 

Yeah, the Woofer Tester 2 is pretty nice. I am pleased with mine, I have used it for years. I shared my version of the REW impedance jig that the OP's gear is based on for cases like this where that sort of an investment may not be warranted.

It might not be perfectly exact, but it is a measurement of the impedance of the drivers in the cabinet, which has a LOT of value, even with the crosstalk issue. It's pretty clear that the tune is closer to 30 than to 40, which was his target. Odds are, when he takes the tune up closer to 40, the crosstalk will be less severe and the results might look a little better. I have no direct experience with the specific gear he is using, I do have its little brother though (Xenyx 302USB). It's not used in my measurement rig due to the crosstalk. 

EDIT - my bad - OP is using a UCA202 for the USB input and source. Those definitely have the crosstalk issue we're seeing here. I have plenty of those and know the crosstalk issue very well. 

Looks like the sound card has the dreaded Behringer crosstalk issue. There's a strong rising response below 20 Hz. That may mess with phase.

Nice work man, nice work.

Very impressive results. Far better behavior in the impulse and waterfall than I expected. 

There you go, raising the damn bar again...

I'll second Ricci here, not sure that 2R load is a great idea. Sure, it is a ported cabinet, so the average impedance is much higher, but that minima at 40 Hz might cause issues.

Have you measured impedance of the actual build yet?

Want 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. Luckilyeverything else is fine. No idea what happened. Wasn't even running anything at the time.

That sucks. Glad nothing else got fried.

...

 

On a semi related note, has anyone seen the Great Wall previews with Matt Damon? Almost seems like a missing spoof trailer from the beginning of Tropic Thunder or he lost a bet with some friends and has to do a terrible movie as a dare. IDK maybe it'll be great but the previews left me scratching my head like WTF is that?

That's exactly where I am. I have no idea where they're going with this one.

Wow.  Jack Reacher 2 was even worse than I could have ever expected.  Didn't even get to appreciate any sound/bass due to the constant cringing at the writing/acting.  Sometimes when a film gets deadpan reviews, my expectations are so low that even a mediocre movie can seem OK.  Not the case here.

 

JSS

I nearly grabbed it when I saw it on the shelf the other day. Sounds like I should be glad that I passed.