Feel free to ask questions. I'll do my best to answer.


Monday, September 6, 2010

Forward Lobe







Another important aspect of speakers is their vertical polar response. Every typical two-way speaker will have lobes and nulls in the response formed by the non coincident sources playing the same frequencies. In the near field--before the reflections become a major player--these lobes/nulls are audible with fairly small head movements if the nulls are not spaced very far apart. So ideally a "near field" monitor would have a broad forward lobe. The forward lobe is dictated by the distance between the drivers, the crossover frequency and slope, phase, and driver directivity at the crossover frequency, but that can be a heavy topic. Essentially you want to forward lobe to point at your ears. Check this out for a great visual on lobing: Falstad's wave interference applet.

Let's have a look at the studio monitors we have on hand.

You can see in the top graph that there are 3 lines that are basically flat. Since the speaker is rotated in 11.25 degree steps toward the tweeter, that corresponds to a 22.5 degree forward lobe that is angled 11.25 degrees toward the tweeter. Behringer lists the crossover frequency at 2 kHz for the B2031P(the speaker graphed). Seems pretty darned accurate. This is pretty good performance for the near field, but not ideal. The graph toward the woofer is 5 dB down at 11.25 degrees off axis. I got to do a little more precise measurements in smaller increments on this at a friends house and it's actually a bit better performance than what this indicates and the lobe is centered at 10 degrees toward the tweeter. I didn't include the graph toward the woofer

The next is the Behringer 1030A--graphs 2 and 3. The 2nd is toward the tweeter and the 3rd is toward the woofer. Combining those 2 you can see four lines that are basically flat. That is impressive performance--33.75 degrees of good behavior. The wide directivity of the drivers (small mid/woofer and shallow waveguide--see horizontal polar pattern for evidence), low crossover frequency, and close driver spacing contribute to this.

Now let's check out the Mackie HR 624 mkII, the 4th and 5th graphs.

The Mackie looks to have a bit more narrow lobe than the B2031P and it seems almost perpendicular to the baffle but slightly toward the tweeter. Not necessarily a bad thing, but good to know info. Placement is critical with these speakers. To be sure, these are my favorites out of the bunch, but they are the most difficult to get right. In the near filed, small head movements can definitely alter the sound. The 1030A seems immune to them. I listen to these Mackie monitors from 6-9 ft away. That gives you a vertical window of a little over 2-3 ft respectively. Of course you are also into the reverberant field at 9 ft so you can all but totally ignore the lobe. At 6 ft in my room I can still hear it with pretty dramatic head movements unless placement of me and the monitors is just right. At 3 ft away and a 1 ft vertical window, head movements can be an issue if monitor placement is not precise.

40 comments:

  1. Not sure why I missed this page, but was referring to something like this in my earlier comment (with lot more graphs)
    Btw
    1) how did you derive 2khz crossover from 22.5 deg vertical forward lobe for 2031 ?
    2) That would be total of .8 m at 1m rt ? Thats good enough isn't it ?
    3) Why measurements at both woofer and tweeter required ? Can't one choose just one point on the baffle ?

    ReplyDelete
  2. 1) just a guesstimate based on where the notches/nulls are located.

    2) it is good enough but the 1030 is luxury at that distance.

    3) it is 1 point on the baffle for both graphs. It's just the direction I'm rotating the speaker while taking the graph. When you place all the lines overtop of one another, it becomes difficult to see what is going on. So I separate them for clarity.

    I thought you knew about this page, just wanted more speakers on it. I do want to make one with all the speakers. Can't believe I haven't yet. I have about a dozen entries I want to do. I just never seem to have the time.

    ReplyDelete
  3. No I think I missed this page..
    I can understand. It takes a lot of time, and you have already documented a lot. And to add to that answer innumerable questions from newbies like me :)
    Kudos for maintaining this blog.

    About (2) yes 1030 will really be luxury , but won't it really be a luxury ? I mean +/- 0.4 m seems quite sufficient at 1m

    And (3) For all speakers you tested, tweeter level is the ear level isn't it ?

    ReplyDelete
  4. Thank you.

    (2) that is definitely a luxury. It's what makes me say coax or short CBT is not necessary. There canes a point to where it's just not going to matter anymore. If your overpass is 5 meters high, a car 4 meters tall will fit under it just as well as a 2 meter one. The emotional/irrational part of me will feel more at ease in the 2 meter car however. Lol

    I. Usually start with the microphone right between woofer and tweeter and look for the vertical nulls first. That will show me the optimal place or the best axis the speaker has and I'll do my horizontal and vertical polars from there. Some speakers I'm more laced on than others though. The ADAM A3X for instances. It performs well at such range of angles that I didn't really pay attention to exactly where I measured it after doing the initial verticals. I learned later that it was a dumb move b/c it has a significantly broader horizontal pattern closer to the woofer(they all do).

    Hope that isn't too confusing.

    Some interesting things I've seen in regard to vertical polar patterns: the B2031A was measured by Harman and the vertical lobe was perpendicular to the baffle. ZAPU found the same thing. In all 5 I measured, it was slightly toward the tweeter~about 10 degrees.

    Not sure why that is. I think Zaph measured the passive one like I did, but Harman did the Active version. Even mine still looked good between the drivers and perpendicular to the baffle, but that discrepancy always bothered me.

    ReplyDelete
  5. (2) That analogy would apply to almost all areas of audio/hifi world... :)
    I too now don't see a need for coax. WG based 2-way , 90 x 45 pattern, and subs.. should be good enough. Though I am not able to let go of 8" woofer yet :):)
    I am reading about PI speakers. Look interesting.

    (1) Got it somewhat :)

    Its quite possible that 2031A is better. I very much like Dr Geddes's polar map for it in his software. Also its reported HF nastiness can be reduced via a switch, unlike the passive version. Though the on axis response of 1031A is much better than 2031A, based on the german site I sent earlier.

    ReplyDelete
  6. It's HF nastiness seems largely mitigated by smoothing the response FWIW. I think ragged responses have plagued a lot of speakers over the years and people have just turned down the treble to compensate. Not the best way to do it IMO. I'd prefer to fix the problem rather than hide it. Of course I have zero proof of my concept in regards to that speaker, but smoother measuring speakers have been shown to be preferred for decades. I'd bet this one would buck the trend.

    ReplyDelete
  7. And as you mentioned earlier, the port and the cabinet is responsible for ragged response, right ?
    Coming back to waveguides. I see almost no company making waveguides for their dome tweeters, but they do make for compression drivers. PE did mention low volume sale as a reason, but a 8" waveguide for RS28F/A would be amazing. PE has one for compression drivers which has been modified by some to fit dome tweeters including RS28F.
    Only Seas has a nice DXT lens tweeter although its smaller waveguide makes it bit problematic for 8" drivers as per many.

    ReplyDelete
  8. Yep. I bet if yo unified the cabinet better, you could get a better response.

    ReplyDelete
  9. Oh, what problem do they say it has?

    ReplyDelete
  10. Mark K talks about controlled directivity not extending low enough.
    I guess due to waveguide being smaller

    http://www.audioheuristics.org/projects_gallery/ER18DXT/ER18DXT.htm

    I wonder if similar to ER18DXT using 2kHz crossover , if an 8" can go upto 2 kHz like 2031, can it be matched (although a LR4 would be needed)

    I did find a 8" DXT based speaker design , but the woofer is pricey :)

    http://www.loudspeakerbuilding.com/Magazin/Loudspeakermagazine-2012/December-2012/_Excel-22-DXT_8636,en,900972,4363?detail=4363

    Seas also has a speaker with 8" and DXT though vertical directivity is even smaller (30 deg)
    http://www.seas.no/index.php?option=com_content&view=article&id=428:seas-pro-audio-av-60-sound-solutions&catid=85:all-pro-audio-products-seas-sound-solution-pro-audio-2&Itemid=416

    Btw, whats your opinion on compression drivers ? One advantage is availability of lot of off the shelf waveguides.

    ReplyDelete
  11. Did you ever check out Visaton's studio monitor kits? They might be worth looking into.

    Compression drivers can be good and can be crap. They are all over the map. I personally haven't heard any I thought were great, but the better they measure, the better they sound and some measure really well.

    ReplyDelete
  12. Thanks, will check those out.

    B&C DE250 and DE500 are supposed to be good....

    ReplyDelete
    Replies
    1. They can measure well in the right WG and the sound should match.

      Delete
  13. Just found a interesting post
    See #253
    http://www.diyaudio.com/forums/multi-way/147514-pro-vs-hifi-drivers-pros-cons-26.html

    Would that be the reason 2031 sound bright ? As they seem to have wider dispersion than 103x above 8kHz...

    I also wonder how constant directivity speakers compare to gradually narrowing directivity speakers.

    ReplyDelete
    Replies
    1. I'm not so sure about the good doctor's assertion. That frequency range is bordering on the 'ignored' region of 'audible'. I can't exclude it of course, but I'd go for the ragged response being the issue. The 1030 sound brighter to me... So who knows. Subjective opinions sure make things confusing.

      Delete
  14. Btw, my thought behind gradually narrowing directivity was if it will be better approach when there is single listener/nearfield setup and when on axis is used

    ReplyDelete
    Replies
    1. I wouldn't claim to know, but most speakers are gradually narrowing to some degree. Some stay more steady and drop while others are very gradual. Hard to say what pattern would be better for what. Actually, the more I look at them, the more I like those Visaton.

      Delete
    2. I think that can be seen in 1031A vs 2031A graphs here
      http://www.bonedo.de/artikel/einzelansicht/behringer-b1031a/2.html

      1031A goes down gradually (whereas 2031A goes steady upto 15kHz and drops abruptly.

      I wonder though if 1031A qualifies as constant directivity as one can see changes in directivity at 1 kHz, 5kHz and 9kHz unlike 2031A..

      Which Visaton are you specifically interested in ?

      I think my goal now is to build something like 2031A without any of the flaws you brought up, maybe even using pro drivers like B&C (8BG51 and DE250 in a waveguide) for higher efficiency :):)
      Its very tough to find a good waveguide for usual dome tweeters..

      Delete
    3. The good things to retain from 2031A would be its polar response ( as seen on polar map software on Dr Geddes website)

      Delete
  15. The 1030 probably doesn't qualify so much. None the less it's not bad.

    The visaton La Belle CR or the Studio 2. The visaton WG looks to do the trick down to 2kHz. Too bad they end up on the pricey side. They meet my criteria well though.

    ReplyDelete
  16. You found any measurements for Visatons ?

    ReplyDelete
    Replies
    1. Just on their website for the studio 1.

      Delete
  17. You looked at PI speakers ?

    ReplyDelete
  18. Not recently, but Wayne was certainly pushing this mentality of well controlled directivity for LONG time. He used to put together some very nice kits.

    ReplyDelete
  19. I guess your application is farfield you can go for something like
    http://www.diysoundgroup.com/waveguide-speaker-kits/fusion-15/fusion15-kit.html#

    Polar looks good, isn't it ?


    Out of question for my nearfield setup... :(

    ReplyDelete
  20. Those look as good as I've ever seen. The price is right to boot!

    ReplyDelete
  21. Btw the Behringer PA speakers should also be great for your garage usage
    And price is even cheaper than diysoundgroup

    http://www.avsforum.com/forum/89-speakers/1519940-behringer-eurolive-b215xl-15-2-way-l-r-mains.html

    There are active variants as well...

    ReplyDelete
  22. Yep. I wonder how they measure up? Thanks for the idea! It's hard to beat well designed commercially available speakers.

    ReplyDelete
  23. Its very tough to beat them esp on moulded baffles and cabinets.
    Can't do that in DIY...

    There are some measurements in that thread but no polars. If some seller has a good return policy one can get them,hear and measure them, and return if not happy :)

    ReplyDelete
  24. Oh, it can be done DIY, but it's not easy.
    Right now I really have enough speakers. More speakers are sort of redundant really. I've given up on the desire.

    ReplyDelete
    Replies
    1. "I've given up on the desire"

      That "sounds" good :)

      Delete
  25. Another nice build : http://www.diysoundgroup.com/forum/index.php?topic=9.0

    ReplyDelete
  26. Definitely looks nice. I'd love to check out those graphs sans smoothing.

    ReplyDelete
  27. Back after a long time :)
    A quick question (not sure if I asked it before ) : Do pro high sensitivity woofers (like the eminence 12" used in above project) have less smooth response than a "hifi" woofer, based on your experience ? Or the only (imp) differences are lesser sensitivity and hence a lower Fs for the hifi woofer ?

    ReplyDelete
  28. The Eminence woofer has a rougher break-up, but prior to then it is similarly smooth. I added damping compound and it smoothed it out radically(it's graphed out in detail somewhere on this blog), but it also lost efficiency... No free lunch.

    ReplyDelete
  29. I was just trying to see if woofers like Eminence delta pro or deltalite II are audibly unsmooth as compared to woofers used in studio monitors measured here...

    ReplyDelete
  30. They'll be audibly closer than they measure, and they measure near identical barring the break-up. You also need to damp the enclosure more with uncoated cones. I have measurements to back that up as well on this blog. Cone dampening should also help keep the backwave in the enclosure.

    ReplyDelete
  31. Check this out: http://dtmblabber.blogspot.com/2010/07/effects-of-stuffing-loudspeaker.html?m=1

    ReplyDelete