Big 2-way

chris661 · Post by **chris661** » Sat Sep 13, 2014 11:05 pm

Okay, so I fired up the shiny new ECM8000, DCX2496, 2222FX, N56, UCA200, and Servo-550 (because everything needs more letters and numbers).

The compression driver was, initially, all over the place. Still, that's to be expected from a constant-directivity horn. So, I took an on-axis and a "typical maximum" off-axis. Set EQ for both, messed around a little, and got this, on-axis (see below). Off axis, the top end droops down a little as expected, but the frequency response is still remarkably flat.

Next, the woofer. After some EQ'ing and seeing how the crossover filters sit with the EQ filters, I got a rather good on-axis response.
... Then I looked at the off-axis, by moving the mic toward the woofer's surround, about 6" away.
Serious problems there: a 15" rolls off rather a lot that far out.

No problem, though, I can add some serious boost to the top end (remember, these drivers will stand 1.2kW literally all day). Did that, and then, of course, on-axis had a huge peak toward the crossover frequency.

Halved the "serious boost" to something sensible, and got these graphs:

Haven't figured out a nice way of placing the mic to check summing yet - that'll have to be outdoors to get the mic distance without room interactions.

There's 200mm of delay dialed in on the woofer for time-alignment with the compression driver diaphram. Conveniently, the compression driver's 10kHz sensitivity is the same as the woofer's in-band sensitivity. The CD has a lot of attenuating EQ to get the two drivers to line up around the crossover point.

That's all for now, I'm gonna go have a listen.

Chris

PS - just tried the saxophone track on the Sound Check CD. Wow. This is quite comfortably the best I've had from these drivers.

chris661 · Post by **chris661** » Wed Sep 17, 2014 12:57 am

Right, so.

The compression drivers I had been using have gone back to their original cabinets, so that's a nice pair of 12" two-way cabs reassembled.

The new setup is a pair of old EV Deltamax cabinets, with DH1a compression drivers in them. These are heavy-duty 2" exit drivers with plenty of power handling and silly sensitivity: they're 115dB@1w when horn-loaded. For an idea of size, the magnet is, I kid you not, 9" across. Those are mounted to 60x40 horns, with a lower cutoff of 1kHz.

Had a quick play around with REW this evening, and threw a basic EQ curve at the new compression drivers. Not a whole heap of difference at low listening levels, but 2" exit drivers can just keep getting louder where 1" ones are running out of steam.

I think I'd like these to come to Owston - going for the loudest noise award.

Chris

steve s · Post by **steve s** » Wed Sep 17, 2014 7:55 am

Will look forwards to hearing them Chris...

brig001 · Post by **brig001** » Wed Sep 17, 2014 12:19 pm

steve s wrote:Will look forwards to hearing them Chris...

If you open your window, you probably can

Dave the bass · Post by **Dave the bass** » Wed Sep 17, 2014 12:22 pm

I just did.... but I couldn't here them down here...

chris661 · Post by **chris661** » Wed Sep 17, 2014 1:16 pm

Only on quietly at the mo, guys - there's a little bit of work to do before I can produce a serious blast radius. The speaker clamps touch the woofer surround slightly, so I daren't push for much excursion as the woofers ain't cheap.
Port tuning is 50Hz at the mo, which is slightly higher than what I would've aimed for (45Hz), but a slight peak before rolloff isn't going to worry me.

Here's a shot of the new EV cabinets, but with the first set of compression drivers sat on top - at that point, I wasn't sure if the EV drivers worked.

... and here's the EV compression driver. To the right is the Das compression driver I was using, and the left is a can of Sprite.

Chris

chris661 · Post by **chris661** » Wed Sep 17, 2014 1:21 pm

Everything's installed and fired up in one of the cabinets. Really rather good, and the big compression drivers are hitting 1kHz without a bother in the world - they'll go to 500Hz if you put them on a big horn and ask nicely.

Chris

Ali Tait · Post by **Ali Tait** » Wed Sep 17, 2014 1:42 pm

You'll have to change your name to Hotblack Desiato..

Dave the bass · Post by **Dave the bass** » Wed Sep 17, 2014 1:58 pm

...and spend a year dead for 'tax reasons'?

chris661 · Post by **chris661** » Mon Sep 29, 2014 9:49 pm

So, these were used at a gig in a village hall last weekend.

They covered a 12m (opens to ~15m through the bar) by 8m space without trying. Sounded rather good, too.
The horns and large drivers meant they're rather directional until <500Hz, so there wasn't much trouble with feedback either.

It'll be difficult to get these to Owston, chaps, but I'll see what I can do.

Chris

IslandPink · Post by **IslandPink** » Tue Sep 30, 2014 5:55 pm

Would be interesting to hear, Chris, if you can .
Is the crossover(ing) all done with digital filters, then ?
Is that effectively 16-bit or 24-bit ?

chris661 · Post by **chris661** » Tue Sep 30, 2014 9:58 pm

Yep, the crossover and EQing is all done with my DCX2496.
24-bit processing, then.

This allowed me to get a high-Q notch in the woofer's stop band to kill the 1.6kHz breakup peak, I'm running Linkwitz-Riley crossovers and the midbass is delayed by around 8" distance to get the time-alignment.

The CD also requires some EQ to get it sounding right: the horn gives a lot of boost in the 1-4kHz range, so that must be reversed, or you get the "cupped hands colouration" that you hear about occasionally. To hear what it sounded like, use Foobar EQ (or similar) to boost that range by ~9dB - you should get a rough bell curve that's at unity gain at 1kHz and 6kHz.

I'm not sure I've got them Owston-worthy yet - the cabinets have large unbraced sides, so I'm going to look at those next. The plywood is pretty thick, but I know a couple of bits of wood in there will help.

To figure out the optimum brace placement, I'm going to get a cheapie piezo pickup (the ones meant for sticking on acoustic guitars), and stick that on the cabinet. Then I'll run a frequency sweep via the midbass driver, while feeding the pickup into REW. That'll give me a frequency response.

Keeping gain settings constant, I'll move the pickup and repeat.
That'll give me a map of which bits of the cabinet vibrate most at which frequencies. Using some magic, that'll tell me where to put the bracing. Sorted.

Last thing is to figure out how to get these bad boys up on stands - there's winchable ones available, so I might see if its possible to DIY a pair of those.

Chris

chris661 · Post by **chris661** » Mon Oct 06, 2014 10:39 am

So, these were used at a student house party on Saturday night.

The PV2600 amp (driving the bass drivers) was hitting its soft-clip limiter. That's somewhere around 6-900w/ch. There was some LF boost applied to get that party feel, but I reckon more power might be nice. Maybe.

Chris

chris661 · Post by **chris661** » Mon Oct 20, 2014 5:04 pm

... I'm unlikely to get more power without spending a lot of money, or adding (and bridging) more amplifiers, which means more weight.

The cabinets now have stand sockets in the base, but have proven difficult to lift on to stands. The trick is to put the speaker face-down, put the stand in and then tip the whole assembly upright. Its a 2-person job, but only one person (me!) has to do any lifting - the other just foots the stand.

A little 1U amplifier has been sorted for 100w/ch into the compression drivers (which is about their thermal rating IIRC), so the maximum output there is 135dB@1m. The bass drivers come in around 125dB@1m, so the compression driver is getting an easy time. Hopefully.

There's a few gigs coming up, so I might be able to get a photo of them in action. Of course, there'll be some kind of Hallowe'en party to put them through their paces.

Chris

chris661 · Post by **chris661** » Mon Dec 01, 2014 7:26 pm

Update: picked up a Behringer NU6000 amplifier off eBay. I was skeptical of using a Behringer power amp, but people have bench-tested a NU6000 to the ragged edge, and have found it'll do 1.2kW a side into 8ohm all day, and 1.8kW/ch into 4ohm, dropping a bit after a few seconds to avoid overheating the power supply (and, presumably, blowing the 8A breaker on the back).

Still, there's a massive pile of power there, in a shallow 2U unit. Weighs ~5kg (two and a half big lemonade bottles), which is an improvement on the 22kg Peavey amp I had been using.

Tried running everything right to the edge a little while ago - just nudging the clip/limit lights on the Behringer amp. Just over 110dB peaks at 10m (130dB @1m). The scary part is that everything was still sounding nice - it wasn't until I tried talking that I noticed that, actually, its really very loud.

If possible, these are coming to Owston. I don't know if these count as DIY or not, but I'm very pleased with how they've turned out.

Chris

PS - I might be working on a pair of subs. The itch is back.

audio-talk

Big 2-way

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