Horn beaming

[Ian Mackenzie]

I wonder about the contribution of beaming with regards toward imaging. I am not suggesting you are wrong, however I have never heard anyone else suggest that it is an aspect of better imaging.

An off topic but interesting side note is that when Bo and I swapped out his 2421s in his 4345s with a pair of TAD 2002s, the image depth changed. The 2002 and the 2421 have virtually identical geometry so it certainly wasn't a throat change... I was quite surprised.


Widget

I realise this is OT but it is something to weigh in on the subject.

When I went to acquaplas the front/back depth thing expanded somewhat.

I put it down to control of resonances and damping of them.

From my own fiddling over the eons I think slight eq in the 1-4 kherts area can bring forward and push back vocals but this is an entirely different aspect of depth and apparent dynamic scale where very low level details of natural decay and spacial cues provide subjective depth and rendering of an image (as opposed to a flat planar sound). There is a similar correlation to using class A amplification.

I also agree with Rob's comments on recordings and perhaps being able to pick that means your system is in the Zone!

[Earl K]

- That was not the intent.
- It was a try for more conversation on what I feel is a very interesting topic for a number of reasons.
- If I offended you I apologize.

- You didn't offend or irk me or anything related.

- I'm just really busy and can't respond in depth .

- I return from a 3 week vacation and will be able to start posting in the last week of July / perhaps I'll feel like talking about imaging at that point ( though more likely golf, etc. )

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[Steve Schell]

This is a great thread and a huge subject. I'll add a couple of random thoughts.

My friend Bill Woods, retired chief speaker engineer at Yorkville Sound in Canada, used to frequently mention the positive attributes of conical (straight sided) horns in his emails. One thing he would mention is that they sound "...the least like horns." After about a year of this I finally decided to see what all the fuss was about.

I had been using a huge pair of 1930s RCA 12 cell horns in my main system. Not knowing how else to proceed, I built a rectangular conical horn with the same throat size, mouth size and length as the RCAs. When I put it in one channel of the system, the sound on that side was a bit lightweight in the lower mids, but the clarity and overall lifelike quality of the sound was startling! The sensation was that a bunch of obstructions had been removed between me and the driver on that side. I was up half the night building a second conical horn for the other side, and I have used conicals more or less exclusively since then.

With a conical horn the pattern is pretty much set by the angles of the horn walls. Want a 90 degree horizontal pattern? Use side walls that have an included angle of 90 degrees. The directivity vs. frequency is excellent, the best of any horn type. Nothing is perfect, though. There can still be some h.f. beaming, as often some beaming is often established before the sound leaves the driver's throat. The pattern will also lose control and go wide below cutoff, as with any horn.

Part of the reason that conicals tend to not sound "horny" is that there are no abrupt changes in cross section or shape to cause diffraction, or points of secondary radiation of sound. I was bobbing my head at Widget's comments about biradial horns, which have always sound confused and messed up to me when used in a hi fi context. Those sharp edges become secondary sources of sound, like a clusters of drivers at different distances from the listener all squawking at once.

[Titan100]

One thing that should not be neglected when discussing sound stage, depth and positioning of instruments in the sound field is the phase response of a speaker or the phase response of the complete system. Our brain extrapolates the position of a sound source by the minute phase differences of the sound heard by each ear. (Power differences in each ear is another clue of positioning sound sources in our perception of sound). Given the fact that there is practically no full range transducer, we have to rely on several transducers (woofer, mid, tweeter) to accomplish a full range reproduction. As it is known, transducers do not have linear phase response within their full usable frequency range. Most importantly, crossover networks thrive on phase alteration to filter the necessary frequencies. Even when having a linear frequency response in a given speaker, phase response is never linear. (The best test to check the phase response of a speaker is to try to reproduce square waves). Speakers with offset transducers in the vertical plane are attempts to correct or linearize as much as possible the phase response of the complete speaker. Several examples of such design are made by different manufacturers. Speakers having better phase responses tend to have better localization of instruments within the sound stage, while other non so linear phase response speakers can have a better frequency response but not so good of instrument localization. To complicate matters further, your amp, preamp and cd player alter the phase of the original sound in different ways. In conclusion, to have a good localization of instruments in the sound stage, phase response should be respected as much as possible not only in the speakers but also in the electronics driving them.

[Maron Horonzakz]

Your all forgetting the most important thing about sound stage & image...The microphone placement....In most cases in large orchestral works the mics are on tall stands looking down on the bald heads....In small groups the mics are shoved up the musician,s nose. So true soundstage is a falicy....I have hundreds of photos to prove that. When some of the reviewers claim soundstage placement and image....I wonder what they,v been smokeing

[Robh3606]

The microphone placement....In most cases in large orchestral works the mics are on tall stands looking down on the bald heads....In small groups the mics are shoved up the musician,s nose.

Typically I find that real easy to hear, not the over the head part but the minimal vs. the up you nose vs. multitract. I think the most realistic representation and most natural sounding sense of space are from the minimally mic that are done in the actual acoustic space. The whole mulitract thing I find distracting sometimes depending on the effects used. I have heard that they try to give each instrument it's space using level and effects but there are no naturally occuring reverberations that tie it all together like in some of the larger orchestral works. Without all the instruments being in the "same acoustic space" it just doesn't sound natural especially where they mix microphone techniques with some close mic and others not. It can sound really good but there simply is no sense of depth and space that really sounds right, to me at least.

JMHO Rob

[Steve Schell]

Maron I don't think that any of us have forgotten about the importance of microphone technique, it is just that you were the first to broaden the thread to include this topic.

I prefer to use the Blumlein technique of conincident figure eight ribbons when I record, as other techniques inevitably capture sounds with multiple microphones with varying path lengths. This presents our brains with conflicting information on playback, leading to ambiguous localization of sound sources.

To return to the subject of horn beaming, I think it is important that the reverberant field in the room have a similar spectrum to the direct sound. Our brains can tell that something is not right if the direct sound from the speakers is bright and the reverberant field is dull. Sounds tend to expand spherically in nature, so the reverberant field of an enclosed space will usually resemble the direct sound. So, a horn that does not beam high frequencies will sound more natural in this aspect.

One reason we have so many beaming horns is that in the past this characteristic has been exploited to try and correct for the falling power response of compression drivers. The power response of compression drivers begins to die at 6dB/oct. above 3kHz. or so. A curved throat horn will naturally channel high frequencies into a progressively more narrow beam, making an on axis measurement look much richer in high frequencies than the driver's power response. Of course the off axis response will be dreadful, as most highs have been steered to the center. This creates the situation mentioned above where the direct sound and reverberant field are very different.

Another (I think better) approach is to use a horn that doesn't beam, and use equalization to correct for the falling high frequency power response of the driver. This EQ can usually be pretty mild and incorporated into the crossover, as most people prefer a gently falling high frequency response anyway.

[Maron Horonzakz]

Right on....for twenty years i used only three mics on larg orchestral works...very rarely did i need any sweetining mics...Too many mics spoil the soundstage....Tell that to the master engineers at Duetch Grammerphon.....The worst i ever heard was from RCA useing 32 mics ...Somebody forgot to shoot the engineer after installing at least 4 mics.

[Titan100]

As a sound engineer, I can confirm with you that recordings made using 2 or 3 well placed high quality microphones will give very good stereophonic image. Here again, phase relationship between the microphones which is affected by their polarity, placement, distance between them and position play a crucial role in the final stereophonic image.

For the sake of analogy with speakers, imagine having two sets of microphones to do a stereophonic recording, one set for each channel and each set consisting of 3 microphones, one for the bass frequencies, one for the mid frequencies and one for the high frequencies. It will not be difficult to imagine the range of technical difficulties that the sound engineer will have to solve in setting up and positioning the microphones, filtering, mixing their outputs and recording on two channels, to be able to achieve a good and acceptable recording quality while having at the same time a good stereophonic image. Quite an impossible task!

In analogy, that's what a speaker does, a task where a "high fidelity" end result is difficult to achieve and all depends on how careful the designer has been in solving the different inherent problems.

The majority of audiophiles, music lovers and JBL speaker lovers including us, don't have the means to change anything in the recording once it is made and put on CD, LP or broadcasted on FM. (Fortunately, there are very good recordings on the market). At this stage, the best that can be done is to try to have the best phase response of the speakers and the electronics driving them, as mentioned previously, in order to reproduce the most faithful reproduction of the stereophonic image of the recording. Non linear phase response in the reproduction system will necessarily and negatively affect the perceived stereophonic image.

[Maron Horonzakz]

Steve Schell....I guess that why I still love my Bob Smith wood DSH horns...In the horizontal plane It distributes evenly and verticly it diffracts giving its sound seems to appear at the mouth rather than at the throat. Ive preferred this horn now since the late fiftys.

[Hoerninger]

I prefer to use the Blumlein technique of conincident figure eight ribbons when I record, as ...

There is a very sorrow investigation on miking
Multichannel natural music recording based on psychoacoustic principles, Update October 2001 (PDF, 45 pages)
on sound stage imaging and room perception. It goes far beyound DECCA-tree, Blumlein, XY, AB, INA3 etc.
IMHO an interesting approach, unfortunately I do not have a mikrofon set according to the recommendations.

May be it is of interest for a future use.
__________
Peter

[Ian Mackenzie]

I like the Smth horns too but I think they need a large room to work properly.

There is an excellent discussion here on loudspeaker imaging in the link below.

Some consider Dipole loudspeakers superior for imaging.

www.linkwitzlab.com


I also think a lot of what is heard by way of imaging is effected by the source equipment. For example X brand may offer a different rendition to brand y CD player.

In my own experience a Pioneer DVD universal player had a genric holographic image that was always between the loudspeakers.

No kidding!

Using the above DVD player as a digital tansport to an outboard DAC gave a different presentation that was broader and far deeper with a lesser tendancy for a central holograph.

This may appear to contradict the notion of stereo image because we are sold on the idea of a central image with test setup cd's. In many cases the apparant image is a lot less flattering than you would expect.

I only discovered this after playing a number of familiar cd's.

I am not a digital nerd so I cannot offer an explanation.

My point is everything you hear is conditioned one way or another and we make assumptions about what we think is right or wrong based on that conditioning.

It is however useful to know and appreciate the production qualities of the original recording good or bad.

[Steve Schell]

Maron, your comments about the Bob Smith horns make sense to me. These were of course designed in the mono era, and one of his goals was to to create a wide apparent source of sound rather than the single point source effect of many horns used at the time.

[Maron Horonzakz]

Schell...You your point is true about the Smith horn. The first one in the earley 50s here in the midwest was built by George Ashworth...The scientest who worked with Paul Klipsch on chemicles to lower complience of outer surrounds on woofers and lower free air resonence...This was the first time Paul Klipsch heard a working one,,,Two version were on hand one with a 1" throat & the other with a 2" throat. George Ashworth was a mono man until his death (93) He was suspicious of the way stereo mic ing was done and insisted it was just multi mic mono for each channel...Before the DECCA tree mic placement was perfected....I worked with him recording the Philharmonic for many years....I now have those Smith horns of his...Plus many other smith designs I use in Stereo...yes you can get a sound stage & image from them,,, but i feel now the tracktrix horn is better.

[Harryup]

I'm using Tractrix horns on 2450. I have over time achived better and better sound stage by;
Switching from solid state to a 300B
lower early reflections from sidewalls and with a thick carpet from the floor
Switch from 2382->Smith horns (2397?)->disconnected the tweeters (072->2404->077)->Tractrix with some eq for the top end and some resonances around 1-2kHz -> toed in the speakers ->moved them closer to each other at about a 46° listening angle.
I now have a depth from the loudspeakers and backwards or no depth at all depending on the recording. From the begining the soundstage was more flat or in your face.
I think very low distorsion in the treble from the electronics are very important at least for me. With some distorsion added from the electronics the soundstage becomes also more left-center-right direction and the speakers does not "disapper" in front of you.
And the beaming is just of the level of noticable if you are really listening and not a problem any more.

cheers
Harry