Why do I hate my omni speakers?

[mtbiker]

I have a pair of SS8530/Neo3PDR omnis I built a few years ago and have gotten essentially zero use since then. Periodically, I take another crack at a crossover for them, comparing the omnis (blue in graph) to my passive TM Vifa P17/D25 (red line). The ragged treble on both is just bad diffraction. I have the omnis running active from a DCX with each driver EQ'ed flat and crossed at 24dB L-R. I have tried 1.9kHz and 1.6kHz, both points measuring the same, sounding about the same, and nothing at all (NOT EVEN CLOSE) to my old passive speakers, which for all their faults, are subjectively well balanced FR-wise.

So I am still wondering
1. Do omnis simply factor room reverb into their sound too much for my tastes?
2. Do I need to cross MUCH lower before the midbass directivity becomes an issue?
3. Is there some non-obvious trick to measuring the response of a raw omni driver?

[mtbiker]

Re: Why do I hate my omni speakers?

Just adding that the subjective problems with the omni are mainly poor speech intelligibility when watching TV (a trait shared with some Martin Logans I also have). Listen to music on the omnis or the ML and they're both great. Setup an A/B and the Vifas beat both the omnis and ML hands down. Watch TV with the omnis or ML and you're going to strain to hear a lot of dialogue.

[Wolf]

Re: Why do I hate my omni speakers?

Well- that dip at 7k is likely the Neo3PDR's inherent anti-sssibilance dip.

FWIW- that is still one of the most creative and well thought out omni builds I've seen on the forums. I was in awe at the amount of work and detail you put into those.

BTW- if you hate those Rev's, you can just give them to me...:D
Later,
Wolf

[Deward Hastings]

Re: Why do I hate my omni speakers?

So I am still wondering
1. Do omnis simply factor room reverb into their sound too much for my tastes?
2. Do I need to cross MUCH lower before the midbass directivity becomes an issue?
3. Is there some non-obvious trick to measuring the response of a raw omni driver?

1. No way to know until you try. The speakers pictured are not "omni" by any stretch of the imagination, and worse.
2. Yes.
3. No.

You should probably reread (at the linkwitzlab site) and reconsider the explanation of the design choices that went into PLUTO.

[wlb]

Re: Why do I hate my omni speakers?

Just adding that the subjective problems with the omni are mainly poor speech intelligibility when watching TV (a trait shared with some Martin Logans I also have). Listen to music on the omnis or the ML and they're both great. Setup an A/B and the Vifas beat both the omnis and ML hands down. Watch TV with the omnis or ML and you're going to strain to hear a lot of dialogue.

I take it you don't use a center channel for HT or TV sound. Stereo and movie sound are definitely different animals. If those Omnis sound so good for music then just invest in a center channel for TV sound tracks. Unless you don't have a suround sound amp.I always adjust my system a little differently for music than I do TV or movie play back. In fact most stereo music sounds better with only two channels.
By the way nice looking cabinets on those Omni's.

[ligs]

Re: Why do I hate my omni speakers?

My personal experience is the midrange matters(muddles) intelligibility just as much as high range. In addition, direct radiated sound probably determines intelligibility more than a reflected sound even the overall loudness is the same. My 2 cents. If you can switch your Vifa woofer with the Scanspeak woofer you can find out if the omni placement of the woofer is the culprit. As far as I can see your tweeter is not omnidirectional unless it is open in the back.

[fbov]

Re: Why do I hate my omni speakers?

Just adding that the subjective problems with the omni are mainly poor speech intelligibility when watching TV (a trait shared with some Martin Logans I also have). Listen to music on the omnis or the ML and they're both great. Setup an A/B and the Vifas beat both the omnis and ML hands down. Watch TV with the omnis or ML and you're going to strain to hear a lot of dialogue.

I'll note that your results with the ML's vs. conventional Vifa's is no surprise to anyone who's read Toole. I find omni's and bipole's spatial characteristics make them a high-risk/high-reward design, leading to a lot of love/hate relationships.

I built a Pluto clone, using the same NSW2 upper mid/tweet as Linkwitz, but with a Silver Flute W1425RC and a passive XO. I designed them using the normal amateur DIY tools, measuring FR and ZMA in box (pipe?), then combining responses with filter effects in PCD. It's clear I have more BSC in mine, and my AVR gives them a 40-50Hz cut-off. Attached is my final FR results, albeit with a nice suck-out at 2.8KHz that wasn't present until I tested all-up/all-in the day before leaving for InDIYana 2010 (XO is more like 1.3KHz, and phase-reversed is worse, so...).

My basis for comparison are MTM's, one step toward the line array side of speaker dispersion, and so on the opposite side of dispersion from an MT. The imaging differences are huge; pinpoint vs. spread, localized vs everywhere. The MTM's are a much more visceral speaker, but all the instruments move when you do. That doesn't happen with the Pluto's omni geometry. The stereo image is audible nearly everythere in the room, but the FR, and thus the timbre, does change as you move out of this sweet spot due to limited HF dispersion of a 2" mid/tweet.

My conclusions were
- omni's are great for stereo listening, where the program benefits from the added spaciousness
- omni's must be located properly, well away from walls or you get very strong comb filtering from the delayed reflections.
- as hybrid omni's, the directional driver must be aimed at the listener for best results
- they make bad CC's, for all the same reasons they work so well for stereo.

I'm using them as surrounds now, but I'm even questioning that multi-channel application given that in a multichannel mix, the program contains the ambiance/spatial information.

Or is it just a reason to build more speakers???

Have fun,
Frank

[Deward Hastings]

Re: Why do I hate my omni speakers?

find out if the omni placement of the woofer is the culprit. As far as I can see your tweeter is not omnidirectional unless it is open in the back.

You're right about the tweeter, wrong about the woofer. The woofer is anything but omni in this example . . . it is beaming badly above 1100-1200 Hz. with a substantial null on the horizontal (listening) axis. The frequency response curve shown can exist as shown only if the null is "corrected" by equalization for the test axis, in which case there is a substantial peak in the off-axis (room) response. The result is two highly directional drivers aimed on different axis equalized to "look good" at one test point. An "omni" speaker that does not make . . . measure it at +30, +60 and +90 degrees on the vertical axis and it will look like scat. Doing the same on the horizontal will expose the tweeter as just as bad there too. Plus, do I see a port at the end of the "pipe" (tube, box, whatever)? There's another really bad idea . . . (if that's what it is).

The key to "fixing" this speaker is to scrap the tweeter (from which many of its other problems flow). Lower the crossover to 1000 Hz. (at which point the woofer is still reasonably "omni") and seal and stuff the pipe (adjusting low end response with a LT). Then add a reasonably omni tweeter (the NSW2 as used in PLUTO is the obvious, and proven, choice). But don't spoil it by mounting it in/on the woofer pipe . . . put it over the woofer just like Linkwitz did. The whole "fix" would cost barely $50 in drivers and pipe fittings (a couple long sweeps from the Home Depot electrical section cost under five bucks). Then we could have a discussion about what omni speakers sound like . . .

. . . which is "just fine" as a center channel (if done right). Mirage did it commercially, and it works. Once the terrible polar response (and the totally inadequate tweeter) of the speaker above is fixed one of them will, placed properly (under and in front of the screen), give clear and localized dialog over a wide listening area . . . just what a center channel should do. Used (in a pair, properly placed in the room) they will do fine for music, too. The speakers shown look nice, the workmanship and execution looks excellent. It's a shame it was wasted on such an acoustically flawed design (the proof of which is the builder's own dissatisfaction with their sound).

[mtbiker]

Re: Why do I hate my omni speakers?

Thanks for all the input, everyone. I hope to find time to digest everything and do some more measuring and testing tonight.

[ligs]

Re: Why do I hate my omni speakers?

You're right about the tweeter, wrong about the woofer. The woofer is anything but omni in this example . . . it is beaming badly above 1100-1200 Hz. with a substantial null on the horizontal (listening) axis. The frequency response curve shown can exist as shown only if the null is "corrected" by equalization for the test axis, in which case there is a substantial peak in the off-axis (room) response. The result is two highly directional drivers aimed on different axis equalized to "look good" at one test point. An "omni" speaker that does not make . . . measure it at +30, +60 and +90 degrees on the vertical axis and it will look like scat. Doing the same on the horizontal will expose the tweeter as just as bad there too. Plus, do I see a port at the end of the "pipe" (tube, box, whatever)? There's another really bad idea . . . (if that's what it is).

The key to "fixing" this speaker is to scrap the tweeter (from which many of its other problems flow). Lower the crossover to 1000 Hz. (at which point the woofer is still reasonably "omni") and seal and stuff the pipe (adjusting low end response with a LT). Then add a reasonably omni tweeter (the NSW2 as used in PLUTO is the obvious, and proven, choice). But don't spoil it by mounting it in/on the woofer pipe . . . put it over the woofer just like Linkwitz did. The whole "fix" would cost barely $50 in drivers and pipe fittings (a couple long sweeps from the Home Depot electrical section cost under five bucks). Then we could have a discussion about what omni speakers sound like . . .

. . . which is "just fine" as a center channel (if done right). Mirage did it commercially, and it works. Once the terrible polar response (and the totally inadequate tweeter) of the speaker above is fixed one of them will, placed properly (under and in front of the screen), give clear and localized dialog over a wide listening area . . . just what a center channel should do. Used (in a pair, properly placed in the room) they will do fine for music, too. The speakers shown look nice, the workmanship and execution looks excellent. It's a shame it was wasted on such an acoustically flawed design (the proof of which is the builder's own dissatisfaction with their sound).

There is typically 6 db loss at 2000 hz at 60 degrees for a 7 inch driver and I agree it is far from omnidirectional. To be truely omni you need a small driver and cross it low like you said. Maybe Bose got it right in some of their designs

[ligs]

Re: Why do I hate my omni speakers?

I never thought my K 6.5-BG Neo 8PDR as omni directional but it would be more omnidirectional than SS 6.5-BG Neo3 While the exact XO point is less certain but it would be closer to 1000 hz than 2000 hz.

http://techtalk.parts-express.com/showthread.php?t=223095

[Sydney]

Re: Why do I hate my omni speakers?

mtbiker: Curious - where is the tweeter with respect to the upward facing driver?

[Mayhem13]

Re: Why do I hate my omni speakers?

There's a few Omni designs on DIYAudio where the woofer is mounted in reverse, firing into the cabinet ala Walsh style with the rear of the cone being the primary radiating surface. One of the threads had measurements (believe Peerless Nomex 6.5's) and the rear radiation was astonishingly smooth and very close in FR to the front but also eliminating the beaming and being a true omni to the limits of cone breakup. Since the holes are already there for the frame, try reversing it for starters.....but as Deward says the tweeter is never going to work well as designed. I'm not sure why he recommends replacing ot though as i'd try simply mouniting it above the woofer OB. One of the designs above used a simple metal frame L bracket that attached to the woofers magnet via magnetism.

[Pete Schumacher]

Re: Why do I hate my omni speakers?

Plus, do I see a port at the end of the "pipe" (tube, box, whatever)? There's another really bad idea . . . (if that's what it is).
seal and stuff the pipe (adjusting low end response with a LT).

What is wrong with a vented enclosure? Vented or not has absolutely no effect on its omnidirectional performance.

LT on such a small woofer is not a good idea. Why try to squeeze low end performance from a driver that is inherently limited there anyway? Better to high pass that driver and send the lows to a sub.

[ligs]

Re: Why do I hate my omni speakers?

Bohlender Graebener Neo8-PDR Planar Transducer is on sale at PE.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-713

For about $ 120 a pair you can probably crossover a pair of them with any decent 4-10 inch woofer without too much work. You can use simple open back enclosures to house Neo8 and just seat them on top of the woofer enclosures. I often wonder the attractiveness of Econowave is partly due to the lowering the W-T crossover frequency so you have a more even dispersion of the midrange. The lowering of THD of the tweeter at the lower part of to its operating range is another virtue.

Now the question of intellegibility of speech. I can hear clearly a pair of K 6.5-Neo8 placed downstairs while I do my listening upstairs Of course Neo 8 does not give you the sparkling highs a metal dome would do but it rewards you with a very big sound and substantially more midrange details(intelligibility again) than than a typical W-T way.