Oris 250 Horns with Lowther DX3 Drivers

BD-Design’s Oris Horns have been on my radar for well over 10 years now. They fell off the radar after the birth of my first kid and my first foray into front loaded horns (a JBL 2445 compression driver mated with a 2385 horn). I had mixed results with the JBLs as I didn’t know as much back then as I do now.

When I recently saw Oris 250 horns being unloaded on Audiogon from a US seller, I couldn’t pass up on the chance. My dilemma was this: I enjoyed the explosiveness and lack of compression of my current Altec 511Bs horn  and 806 compression drivers, but they lacked the resolution of the better traditional dynamic driver widebanders (Fostex Sigma, Moth Cicada, Lowther, etc.). I wanted something that would offer the best of both worlds. JohnnieD’s AER drivers mounted on Oris horns on SBAF  was definitely an inspiration.

I recycled the crossover I used for the Altecs to quickly integrate the Oris 250 horns / Lowther DX3 drivers with the 12″ Beyma woofers (in a ported box). The crossover is point is 500Hz, so this isn’t ideal; but at least I could get a quick idea what the Oris horn had to offer, granted that I am very far from an optimized system (it’s always the little details, the last 5% of secret sauce and tweaking that makes something sound right).

I’ve been around the block a few times when it comes to oddball speaker projects, so I am not going to bullshit you and say that I heard the voice of angels. Here are some initial impressions:

  • Not as explosive, lacking in compression, clean, or fast as the Altec or JBL horns, but definitely better than DX3s mounted on an baffle (or anything else mounted in a box). Really not a fair expectation as compression drivers have phase plug / throat / horn interfaces that serve as a mechanical impedance transformer. For movies, I’d go Altec all the way. For music, I’d take the Oris.
  • A large degree of immunity to room interactions. The horns provide a large degree of directionality down to a few hundred cycles, so the effects of first reflections off walls, ceiling, and floor are minimized. The downside to this? Horn coloration. Told you I wasn’t going to bullshit you. The horn coloration is less noticeable when sitting farther away. Translation: you will need a large room, or at least a deep room. I should mention that I was able to acclimate to the horn coloration rather quickly (after I sort-of solved the treble problem – see below).
  • Small stage width (with the horns toed in to the DX3s are 15 degrees off-axis). This should be easy to correct by moving the speakers wider apart. I will try this and report back.
  • Mediocre sized sweet spot. Nothing at all like Altec or JBL horns which impart very even frequency responses off-axis. I’ve heard worse though.
  • Microdynamics and microdetail are superb as expected, although I get the feeling that with the Oris horns in place, even higher quality amplification and sources is necessary to get the best out of the DX3 drivers. Low power SET with simple circuits all the way, at least for the horns (solid-state might be best for the woofers). And not just any SET, but transformer output coupled with quality transformers, which means not cheap, and not any of that OTL shit, because big caps always get in the way.

 

Lowther DX3 on Oris 250 Horns and Beyma BR70. Custom 45×2 SET amp. Schiit Yggdrasil DAC.

Now let’s take a look at frequency response measurements. I took the on-axis frequency response measurement below of the Lowther DX3 in the Oris 250 horn under the same circumstances (distance to driver and gain) as the Lowther DX3 in an open baffle. Note that I left the back of the horn enclosure open – it sounds better this way. There isn’t much cancellation from the backwave because of the large horn and the small rear exit. The measurements below were taken without a crossover.

Green = Lowther DX3 in Oris 250 Horn
Gray = Lowther DX3 on 12.5″ x 17″ open baffle

Lowther DX3 Frequency Response in Oris 250 Horn vs. in Small Baffle

 

How the DX3/ Oris 250 was measured in my backyard to avoid reflections

We can see that the Oris 250 horn actually provides a gain of approximately 10db through a wide swath of the audio band (more below 300Hz, less after 5khz). This is incredible considering the DX3 is already about 97-98db efficient (which is a non BS figure BTW: I found in practice that the DX3 was about 5db more efficient than the 92-93db efficient Fostex 6″ Sigma drivers). The L-pad on the crossover was turned quite a bit down from the setting used for the Altec horns. Yes, these are actually a crazy 107db+ efficient! More efficient than the Altec compression drivers.

The unfortunate part is that the frequency response, at least on-axis, is horrible. You’d need to have hearing damage to be able to bear the highs. Perhaps a more polite way to say this is to channel Amos and say that “it sounds good with classical” (since most modern classical recordings tend to be mastered like shit with emphasis in the mids and rolled-off highs and lows). Also, since there isn’t any gain at all past the low-treble, we are now in need of a super tweeter (like the really expensive sweet sounding Fostex one that JK47 and Struggles brought to the last big SBAF meet).

OK, now take’s take a look at the off-axis response of the DX3 mounted on the Oris 250 horn.

Green = 0 degress on-axis
Yellow = 11.25 degrees off-axis
Purple = 22.5 degress off-axis

Lowther DX3 Frequency Response in Oris 250 Horn Off-Axis

At about 20 degrees off-axis is where I found the speaker to be tolerable. Still, I don’t find this an ideal situation. My kids sometimes sit a few feet in front of me when I listen to music. I don’t want their ears fried by this high frequency fuckery.

So the next logical step is maybe covering the whizzer cone with paper towels! Ideally, a large doorknob or flood light type bulb would be ideal, but I’m just exploring ideas right now and doing things on the quick and dirty. Here are the measurements with a strip of paper towel covering the whizzer cone. Note that for these measurements, I’ve added a single 80uF cap in series, so there is some minor rolloff starting at around 300Hz compared to the prior set of measurements.

Green = 0 degress on-axis
Yellow = 11.25 degrees off-axis
Purple = 22.5 degress off-axis

Lowther DX3 in Oris 250 Horn Frequency Response Measurements Off-Axis. Paper Towel Over Whizzer Cone.

 

Don’t laugh: a paper towel strip over the whizzer cone.

This yields a really good result at 11.25 degrees off-axis, but on-axis frequency response doesn’t change much at all. The 22.5 degree off-axis measurement becomes more lumpy. I’m going to stick with this for now, until I find time to make an appropriate phase plug.

Next steps:

  • Fabricate some sort of phase plug to tone down on-axis high frequency nonsense and get the off-axis response more consistent.
  • Ditch the Altec crossover (12db/octave Butterworth at 500Hz) with a single cap (6db/octave Butterworth at 300Hz) for the DX3 / Oris 250.
  • Biamp – use solid-state amplification for the woofers, maybe with a DCX2496 in the interim to model a passive low-pass crossover.
  • Listen to them using the original hires format (better than MQA): turntable / vinyl. I haven’t done this yet, but I bet this will be sweet!

3 thoughts on “Oris 250 Horns with Lowther DX3 Drivers”

  1. I’m interested in seeing what happens with this project, but I kind of doubt you’ll be able to tame those highs without causing a huge suck-out somewhere else. Although, that might be preferrable. You’ll still be left with the horn coloration though.

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