Active Adventures

[Horatio]

I have been diddling, on and off, with the exercise of active crossovers for my Speakerlab K's, which have K33E woofers in them, and for which I have been using a Type AA crossover for quite a while (in other words, they're the Klipsch sound) for a few years, now.

Like others, I have sought to improve the midrange performance, and have felt that the real answer lay in a different direction...CD horns. But not the commonly understood CD horns as most know them. I am referring to the original Keele designs from the 1970's.

There are at least two problems with this. First, the HR-series horns that provide response to 350-400 Hz are BIG. Really big. EV made another, smaller HR series, but these can't really be used below 500 Hz, and part of what I was trying to do was to get down under what I percieve to be the 400Hz raspiness of the bass horn.

I acquired a set of HR9040A's and EV DH1012 drivers for these; they sounded glorious, but were unbelievable in a livingroom. I then acquired a set of HR90's (the smaller brotheren of the Great Whites), and those sound good, could be integrated without a thought, cosmetically, but again, it's the bottom end I was after. And, those HR90's, A/B'd against the HR9040A's (both with the same driver) just couldn't keep up with the HR9040's. Those stole the show.

The solution emerged: there were three horn models in the original EV CD horn offerings: the HR9040, the HR6040 and the HR4020. the HR6040's would *just* fit the top of the bass horn cabinets. Sure, the overall stack is taller, but at least they fit in terms of width. So, I scoured around and acquired a set of HR9040's (these are the first generation production models, not the later 'A' suffix models, but that's another story). The other compelling reason for choosing these over the HR9040s had to do with the coverage angle being a bit narrower (60 vs 90 degress), and published observations on other horn tests that suggested that narrower coverage angle probably results in better overall listenability in a reasonable room, once reflections are considered.

The second problem, once the size issue is sorted, is driving these; CD horns require equalization. So, it makes no sense to even consider using these horns unless you are also willing to go active.

Toward that end, I have played with a Rane AC23 and a McClelland 4-way, both of which have CD equalization, and these showed promise, in terms of being able to dial in the crossover frequency and provide adequate equalization for the HR horns, but, I could never get the hiss and noise problems sorted to my satisfaction, this being pro-sound gear, and the rest of my stuff being consumer gear. Another thing I wanted was programmable delay, but that's not easily done with analog gear.

For a long while, I considered Behringer stuff (cost being a driver; sure, we all would like Ashleys, but there comes a point...). The problems with this path were several: there's a lot of hotrodding that goes on with Behringer DEQ, and DCX, to get the power supplies quiet, replace output capacitors, stablizing clock jitter, and on and on. It's meant for professional output level gear, and that can be an issue, although it appears to work with consumer gear, from what I have gathered (here and elsewhere). And, there's the problem of needing to have a single volume control....

Then I stumbled upon miniDSP modules. Here, I could get the main things I was after: all the crossover control, CD equalization, and, when used with REW, you can feed it the parameters to do a bit of room-based tuning. So, this looked like it would replace the DCX and DEQ need. Moreover, additional boards were available to do direct digital feed, and there was even a digital amp. The price made it a reasonable risk for me. And, it has a single volume control that acts on all outputs, once you've tarted things up the way you wish.

I acquired this stuff last fall, and have just gotten around to playing with it, and just finished an initial tuning of this system.

VERY pleased! The HR6040's sound as nice as I recalled the HR9040A's sounding. And, I could adjust the delay for the HR horn, dialing this in at 6.5ms, at least for now. A funny thing happened when I did that, though: alot of the woodiness I have disliked in the original configuration pretty much disappeared. I have the crossovers set for 350Hz, as the HR6040 will get there, and the DH1012 can easily do this (I don't have to worry about long term high power use, you know!), and so part of the improvement may be there.

But the major element of the improvement is this: with the HR6040 on top, this is a formidable 2-way system. With a time-aligned top end, it gets very nice indeed.

I am not affliated in any way with the miniDSP folks, but, if there's anyone on the fence on these lists considering one of these, you really ought to give it a try.

The next several weeks will undoubtedly include some measurements (using REW), and I will try to do some followup posts of this work, as I get time.

-M

[rjbond3rd]

Very exciting and a fascinating direction. It would be great to see a picture!

[Guest David H]

This looks like a great little setup, I have been using modified Behringers, and although really nice modified, are less than great stock

Please keep us up to date on your project.

Dave

[psg]

Wow! Sounds like you really know what you are doing and know what you want!

I use a miniDSP to EQ a sub with REW; it's great. But volume control? Which do you have? Do you stay connected via USB all the time to control it?

[Horatio]

That was one of the things that attracted me to the miniDSP: you *don't* have to stay connected by USB to control volume. The board has a three-wire jumper to which a 10K pot can be fitted which provides the volume control. Once the board is set with what you want, in terms of levels, crossovers, EQ's, etc., etc., you just disconnect the USB and power it up like any other piece of equipment. The pot is there to adjust volume (as long as you've configured the board to do volume this way, and not by USB). This pot adjusts all outputs uniformly (although each output can be level adjusted individually to trim the drive levels; the pot applies the overall adjustment to all outputs, regardless their level offsets).

Right now, I am using a set of monoblock MOSFET amps of English make to drive the bass horns, and I am using a (rediculously cheap and just as rediculously good sounding) T-amp for the top end. The T-amp has volume adjust, also, so I level adjust the top end with this, and leave everything else alone.

The main remaining problem is devising a decent way to sequence power on and power off to this whole chain so that it is quiet and transient free.

Another thing I've learned: messing around with the connections must be done very carefully with active systems, even when channels are muted. I found this out the hard way, with one side of this system issuing such a bark that it shook windows and collapsed picture frames sitting on tables (!). Powering down to make changes is the only safe way.

-M

[babadono]

Hi All,

OK I'll jump. What's a miniDSP?

babadono

[Horatio]

minidsp.com