[JohnR]

You may be right with your last sentence. For example, me, Tyson, and Linkwitz (howzzat for name dropping?!!) seem to listen a fair bit to classical and tend to refer to it when talking about realism of reproduction. However I rather enjoy other genres of music on my system as well, where if talking about realistic reproduction one may need to simply adopt some reasonable supposition of "what it's supposed to sound like." For example, I don't find pin-point imaging to be terribly realistic, although others might and in turn call a realistic presentation "diffuse."

I've never really been much for the "you are there"/"they are here" dichotomy. I must not have read the right magazines, or perhaps I simply lack imagination, but do you have a definitive reference on the characteristics implied by the two terms?

[BPT]

David:
If two speaker systems play the same recording using the same electronics (same room, set-up as well as possible) and one presents it as "you are there" and the other presents it as "they are there", it is mainly due to differences (sometimes very small) in their deviation from reproducing a flat frequency response. To a lesser extent, their differences in phase and group delay characteristics will affect this as well.

A perfect speaker should do both.

OBs can do precise imaging (mine do) if set-up in a large room, far from walls or using lots of room treatments.

The type of music doesn't matter. It's the way it was recorded and mastered. Also the ability of your audio system to resolve low level information. A good test is how well you can hear the space between the artist/instrument and the microphone. I also like to choose chorale works (acappella) with 8-25 voices and improve upon the ability to discern individual voices.

YMMV
Chris H.

[doug s.]

I'm not sure how that can be "fact" given that e.g. Linkwitz says he prefers no room treatments, and the technical matter - I should say fact - concerning higher direct-to-room sound with dipoles.

 

i guess i should say it's a fact for my ears.    and, based on obserwations of many others, (some who have posted their accounts here), it's a "fact" for their ears, as well.     

and, regarding the "fact" concerning higher direct-to-room sound, i disagree.  dipoles certainly have a lobing effect, where they reduce sound output at the sides, but they obviously have a higher indirect-to-room sound re: their output from the rear.

David:
If two speaker systems play the same recording using the same electronics (same room, set-up as well as possible) and one presents it as "you are there" and the other presents it as "they are there", it is mainly due to differences (sometimes very small) in their deviation from reproducing a flat frequency response. To a lesser extent, their differences in phase and group delay characteristics will affect this as well.

A perfect speaker should do both.

OBs can do precise imaging (mine do) if set-up in a large room, far from walls or using lots of room treatments.

The type of music doesn't matter. It's the way it was recorded and mastered. Also the ability of your audio system to resolve low level information. A good test is how well you can hear the space between the artist/instrument and the microphone. I also like to choose chorale works (acappella) with 8-25 voices and improve upon the ability to discern individual voices.

YMMV
Chris H.

i agree that you can have "you are there" and "they are here" effects w/the same speaker.  and i agree that the recording is key.  i also agree that ob's will perform better in a large room.  but, so will all speakers, imo.  but for my ears, the ob style speakers need it more than most, and are compromised more than most if they don't have a huge room. 

when i had a 26x38x8.5 listening room, it was difficult to have any speaker not sound at least wery good.  quite a few sounded outstanding, tho i never tried dipoles.  unfortunately, i also never got a chance to try horns there either - i would love to hear the horns i have now, in that room... 

(horns, imo, are another speaker that benefit more than other types, from a large room, but, i believe their compromises in smaller rooms are "sins of omission" rather than "sins of commission", as long as you are able to sit far enough away from them...)

doug s.

[Bob in St. Louis]

Box speakers and solid state amps mimic the master tapes best.  Tubes and OB mimic actual live music best. 

I see what you did there.  

[JohnR]

and, regarding the "fact" concerning higher direct-to-room sound, i disagree.  dipoles certainly have a lobing effect, where they reduce sound output at the sides, but they obviously have a higher indirect-to-room sound re: their output from the rear.

Yes, they radiate to the rear and not to the side (or top). The net effect is that a dipole has higher direct-to-reverberant ratio than a monopole, that's not really a subjective question. For conventional speakers, which are neither dipole or monopole, I expect it would be somewhere in between. For some reason, everybody forgets that almost every speaker radiates to the rear below some frequency.

[doug s.]

Yes, they radiate to the rear and not to the side (or top). The net effect is that a dipole has higher direct-to-reverberant ratio than a monopole, that's not really a subjective question. For conventional speakers, which are neither dipole or monopole, I expect it would be somewhere in between. For some reason, everybody forgets that almost every speaker radiates to the rear below some frequency.

agreed that all speakers radiate sound to the rear.  dipoles yust radiate quite a bit more in that direction.  of course it is all subjective, but for my ears i prefer the trade off of less rear sound radiation and more at the sides.  then, if in a smaller room, the only serious room treatment needed would be first reflection points on the side walls.  and, if you are listening to wave-guide speakers, you may not even need much of that...

doug s.

[Nate Hansen]

i agree w/scotty here completely.  ob  is dipole. 

Actually, ob is not dipole, not all of them anyway. A door size ob with a 10-12 whizzer cone/coax is only dipole to a certain frequency, and is a different beast from a proper (imo) dipole such as the Nao Note, which has flat on and off axis response as high in freq as the physical limitations of the tweeter will allow. A constant directivity dipole will "throw a relatively uniform soundfield at all frequencies" (as you say), except for the null at the sides, which can be used to your advantage in reducing wall reflections when placed in the room properly.

At least, this method works for me. My cd dipoles give me a spacious presentation (when it's in the recording), while at the same time doing the 'pinpoint imaging' deal quite well. FWIW I listen mostly to heavy rock, with some acoustic recordings.

[Russell Dawkins]

The problem is radiation patterns and power response.  Live music has omnidirectional radiation patterns and even power response.  But box speakers have neither of these characteristics.  OB speakers are closer to ideal in these two areas, although even OBs are still not perfect.  Much better, but not perfect.  Because nothing is perfect.

All musical instruments I am aware of, with few exceptions, are very directional in their radiation patterns. If you are including in "live music" amplified concerts, the PA speakers are very directional - at least above the range covered by the subs, as evidenced by the sound behind the stage and in the wings.

[Russell Dawkins]

Tyson, a live performance from an acoustical instrument usually does not have an out phase wave radiating from the rear of the instrument. In this respect a dipole has a very different radiation from a live acoustical instrument.
 A closer approach, radiation pattern wise, is found in the radiation patterns of Ohm and MBL loudspeakers which are mostly phase coherent omnidirectional speakers.
Scotty
[/color]

It is worth noting that a piano, for example, is effectively a dipole with a horizontal axis - sort of a horizontal shallow H baffle with a reflector on one side. Not a perfect dipole, like a Bodran, Inuit drum or any other frame drum, but close. A kick drum, snare and floor toms could all be considered U-baffles with certain dipolar characteristics. Snare drums when double mic'd (above and below) usually have one of the two mics polarity inverted to compensate for the inverted polarity, top to bottom.
Rolf Harris's wobble board was a perfect dipole.

[puppet]

For me, instruments .. including voice .. sound most natural when reproduced with an OB driver. This aspect alone goes a long mile toward a realistic experience, for me. 

CD's, records, tapes et al are just a conveyance. They allow me to bring home the sound that the "band" intended .. their conveyance. Whether or not that is accurate is another debate.

Russell Dawkins .. I'd argue the opposite about musical instruments being directional. The whole percussion section .. including the piano, string section ... including the stand-up bass, arguably the woodwinds to a degree (don't let the big open end make you forget about all the smaller hole along their length), .. I'll give you the brass section.       

[Russell Dawkins]

All brass are directional and predictable in their directivity, just as a horn is. The least directional brass are french horn and tuba/euphonium.
The radiation patterns for strings, whether bass, cello, viola or violin are complex, with different tonality at every point surrounding them. The violin family instruments are designed to radiate mainly from the front - from the surface as well as the lower register through the f-holes - while the back and sides are purposely curved in such a way as to render them as rigid as practicable, in the same manner as a certain guitars and definitely lutes.

There is nothing like placing a microphone, monitoring the results simultaneously through in-ear monitors (Etymotic Research ER4S) covered with shooter's hearing protection for a total isolation from the ambient sound field of 60-70 dB, to get a handle on radiation patterns. I have done this a lot over the years, in the process of recording orchestras and smaller acoustic ensembles.

Very few instruments or ensembles of any size radiate omni-directionally, except at lower frequencies.

Perversely, the lower frequencies are said to benefit most from dipolar reproduction in the home

[Tyson]

I guess what I'm trying to say about live performances is that you get direct sound from the singer or instrument, but you also get delayed, reverb sound from the acoustic they are playing/singing in.  OB speakers do the same - strong direct sound from the front of the driver, and delayed reverb sound from the rear. 

[scorpion]

Ever since I bought my first OB dipole speakers in 1974 the Magnepan 1.2 speakers. I have been cougth by their sound.
I have buildt some number of OB speakers that more or less have been successful.
However for sound I have not found many loudspeakesr doing a better job than the OB speakers I have buildt for reproducing any CD-disc.

I have however found many other loudspeakers on many occasions performing exteremly bad in comparison to my OB speakers.

/Erling

[PDR]

Dont most bands/orchestras sit in a semi circle around the conductor?
Seems no matter where you sit in the audience your going to get direct sounds
from some instruments and indirect from others.....so what does it matter what the radiation pattern of the particular instrument......seems its only the conductor that
in the sweet spot..... ......betcha he gets pinpoint imaging...

[studiotech]

Lovin' the discussion guys.

The way I see, well hear it actually, is that the "they are here" -vs- "you are there" is very much a function of the production choices during the recording.  IF the mics are set-up in such a way as to record the ambiance of a nice medium sized hall for example, then if your system can reproduce those very subtle, low level cues and not add too much of it's own room sound, you have a much better chance of being virtually transported to the event.  Once again, if you speaker is spraying sound all over the room AND you are more or less in the far field and getting a low ration of direct to reflected sound, then the illusion will be weakened or destroyed completely.  Try an old RCA Living Voice recording from the 50's.  Many were done with just three mics.  They sound a little old fashioned and lack extension at both ends of the frequency spectrum, do a good job of sending you to the event.  Modern recordings from Reference Recordings do this well with better clarity and lower noise floor.

However, take a more modern production of classical music for say a soundtrack recording with multiple mics scattered all over the damn place and spot mics on sections and soloists, the engineer is going to have a very hard time creating a mix with a good amount natural, coherent "hall" sound.  You are now entering the realm of "they are here" and much more spotlight type imaging.  Not exactly natural to what one would hear if present for the original performance, but can be nice in it's own way.  Sometimes it is fun to here all of the instruments as if they are under a microscope.

These rules hold for small venues like jazz clubs and studios as well.

You all got me wanting to try some good diffusion now too.  Works wonders in smaller studio control rooms to make them sound larger. Some diffusion on the front wall(that's the one behind the speakers) might make a nice compromise of reducing in level and scattering the rear radiation rather than just sucking it all up in the acoustical black hole I've got going now.  Although, my room is not laid out symmetrically, so that is initially why I went with the heavy absorption.  Symmetry is very important for a good, stable image.  Not sure if diffusion would work best for me with this room layout.

Greg

[D OB G]

BPT, have you been able to find any particular correlations?

The Quad ESL57s I once owned did classical extremely well (apart from dynamic range of course!).  Not entirely a flat response (although pretty good), and they aren’t actually dipoles, unlike the later ones, as they have thick damping  on the rear side.
Presumably high frequency comb filtering with the size of the panels.

The JBLs from the 70s (century?) had very strong peaks at 100Hz and about 7kHz.
Not flat at all, but they did rock, and were considered good with vocals, and “immediate”, but were hopeless on classical.  (The old east/west coast type of thing?).

Can you describe the effects of differences in phase and group delay characteristics on  the presentation?

If we could have the (theoretically) flat response on axis, then presumably the polar response, the directivity, interacting with the characteristics of the room, distinguishes dipoles.
As JohnR says, monopoles still progressively radiate to the rear, and dipoles have reduced radiation directly upwards.

If we compared a speaker that is only progressively dipole down (e.g magnet shadowing) from the baffle step region of a monopole to that monopole, thus both radiating to the rear in different ways, what would be the subjective differences? 

Does the fact that dipoles roll-off at 18dB per octave below resonance (if equalized only to resonance), compared to 12 for sealed and 24 for vented, have any significance to this discussion (crossing over to subs would eliminates any differences)? 

David

[thomasjefferson]

The suggestion is that LF is radiated in all directions regardless of the design, and OB radiates HF WITH the LF where box speakers only send it forward.

This is not right.  Where is Kreskovsky when you need him?

I think the above statement confuses dipoles with omni sources.  Dipoles radiate less power to the room, relative to the direct power, than box / monopole speakers.  That's the often repeated 4.8 dB reduction in room power (4 pi total output) for the same loudness at the listening location.  This is because box speakers are omni sources for bass, whereas dipoles are not.  In effect, the dipole radiation pattern suppresses the room by 4.8 dB, at least in the bass region. 

True that monopole speakers radiate less power at high frequencies, when there's no rear-facing midrange or tweeter.  But it's important to understand that the rear output from a dipole speaker doesn't necessarily just splash sound everywhere.  It's possible to design a dipole speaker with constant directivity for pretty much the entire audible spectrum.  The best known example of this would be John K's Nao Note.  This is not possible with a box speaker, because the power response is so different above vs. below baffle step frequency.   In fact for a minimal-baffle dipole like the Note, the rear output is largely a means to control (reduce) the sound energy radiated toward the left and right, so it doesn't merely add energy to the room. 

[thomasjefferson]

... regarding the "fact" concerning higher direct-to-room sound, i disagree.  dipoles certainly have a lobing effect, where they reduce sound output at the sides, but they obviously have a higher indirect-to-room sound re: their output from the rear.

Does this comment reflect experience listening to larger size open baffles?  I think this is an important point, because as Nate Hansen mentioned, an open baffle is not necessarily a dipole, strictly speaking.  When the baffle becomes large relative to wavelength at higher frequencies, the radiation pattern starts to "bloom".  Look at the red curves in this diagram from John K's website:



What the red curve shows is when a baffle is large enough to interfere with cancellation between the front and rear output.  This results in more energy radiated toward the left and right than a true dipole figure-8 radiation pattern, which effectively boosts the power response.  If the baffle is small enough to allow cancellation to wipe out a major fraction of the total output, then the power response is reduced.  This isn't easy to do at higher frequencies, and it's something a handful of people are working on with nude drivers and minimal open baffles.  The goal is to maintain controlled directivity full range, and the result is a decidedly different presentation from an omni source that throws sound all over the place.

[Gothover]

I'm not really playing the devils advocate (ok, yes I am) But the "way of the audiophile" would suggest that the truth of the recorded event is what we are seeking to reproduce and hear at the listening position. Does not the OB presentation add a false ambiance, much like what you could add with DSP or even (gasp) equalization or tone controls?

First, this thread is a great read, alot of good info.

My take on the O-B from my limited listening experience is there may be a bit of false ambiance, not sure that is a bad thing. The sound stage I am hearing with open baffles is massive, open and crystal clear.

Dave

[jimdgoulding]

One concern I'm guessing some readers may have is that with minimaly miked live-on-location recordings, all the info- instrumental form and the decay of sound in the venue- is contained in the first wave of sound and that a second wave may be redundant and addtive.  Diffusion would better scatter the back wave rather than absorb it and possibly neutralize or obscure somewhat the benefit, it seems to me.  A question some readers may have is that if all the info is available in the first wave, what is the benefit of a second wave? 

Hard to quantify when we're not talking about a specific speaker as some acoustic suspension OB's may have the bass driver enclosed which doesn't make good sense to me theoretically.  The benefit as I gauge it is in space and grandeur.  But, getting the distance from the rear wall so that you have instrumental cohesion and imagery may drive a person crazy.  Is this a possible fly in the ointment?  Comments are appreciated.