I've always wanted to cut past the room and get to the recording within. For my purposes, less reflections is best. Headphones are OK, but the image isn't right, and you can't 'feel' the music, and your ears perspire
Didn't see this.. re first question last post.
That seems reasonable.
In addition, I recently took an in room power average at around 5 feet, going +/- 15 degrees horizontally, and +/- 60 degrees vertically using 27 point samples. I was trying to verify the power response of the crossover and I found that this quite resembled the total free-space power response.
Of course, if we are talking about a horn's bottom end ripple it is exactly because of diffraction and reflections that it exists. I'm not saying it is horrible or that it can't be overcome, just that it is always there to some degree.
True, but only coming from within the frontal 60 degrees. If we move to multichannel then I think there is an absolute arguement for narrow directivity. With 2 channels it is a trade off and people have a legitimate range of preference.
Very true that most of the power response is built up by the energy in the forward lobe. My point is that somehow optimizing power response has never been shown by anyone to be a worthwhile goal. Optimizing the axial response, and realistically dealing with the fact that people don't aim their speakers with laser precision or might want to sit and stand, or even listen with a friend (calling for a widish listening window) makes much more sense.
David S.
Member
Joined 2003
Agree. My personal preference for stereo is narrow vertical with very wide horizontal.
My preference for multichannel LCRs is narrow horizontal and very narrow vertical, very wide for the surround channels.
Headphones are OK, but the image isn't right, and you can't 'feel' the music, and your ears perspire
I always wondered what bass shakers could do in terms of "feel"?
I dont really understand what you mean and i apologies but dealing with the fact that we dont listen in anechoic chambers, that we want a larger sweet spot etc isnt actually optimizing for a better power response?
I believe the importance of power response has been demonstrated and discussed many many times.
Again i hope i didnt misunderstand you.
I keep track of the published literature on the subject and I don't see anyone arguing for a particular power response in any of the professional journals. If you are referring to discussions on these forums, then a general consensus of oppinion on a subject doesn't really count for proof.
David
The horn I use has a pure catenary profile for both horizontal and vertical flares from throat to the last inch before the mouth, where it radiuses to match the baffle.
More detail here:
There are other profiles that are very close to a catenary from visual inspection, and I suspect they would give good performance too. For example, a parabola is quite different mathematicaly, but it looks very close to a catenary. So I think the the throat transition were given a parabolic curve, it would be fine. Likewise, a quadratic or even a radius could probably work well. But mine is a catenary, which is a minimum surface curve. I think that's the best shape to use.
I think this attribute of a good wave-guide is often under-appreciated and perhaps much more important than it appears.
When comparing wave-guides to direct radiators a lot of attention is placed on the directivity characteristics of the device and its effects on the response in the room - increase in direct to reflected ratio, change of distribution of early reflections in the room etc, and whilst there is no doubt that the effects of different directivity in a given room can be very audible, it would be hard to say that one directivity or another is necessarily better or worse quality as such, just that they sound different. In other words a more directional speaker isn't necessarily better quality just because its more directional.
Some people like the drier more precise presentation of a more directional speaker (me among them) others prefer a more open diffuse sound, and different rooms require different amounts of directivity to get a certain balance leading to there being no one ideal directivity, (IMHO) although there may be a certain usable range of directivities that work well within typical rooms.
However the other major effect of wave-guide directivity other than the illumination pattern of the room is the illumination pattern of the baffle itself.
One of the major problems with small direct radiators such as dome tweeters is that whilst they could potentially be super-flat in response on an infinite baffle, they never are when placed on a typical finite flat baffle, even if the edges are rounded somewhat.
It's almost inevitable that the frequency response is going to be significantly and very audibly non-flat simply due to edge diffraction, and typically its going to be worst right in the mid treble where amplitude response flatness and balance is exceptionally critical for imaging.
Try to EQ the response in the network on one axis and you make it worse on another axis. Try to offset the driver asymmetrically on the baffle and the on axis response is a bit flatter but the off axis response may be worse, and you don't actually reduce the amplitude of the diffraction at all.
If the peaks and dips in the mid treble vary in frequency and amplitude for small shifts off the horizontal axis the stereo image will be very unstable with a narrow sweet spot because the (very critical) treble response balance between left and right is varying as we move our head slightly, which will keep pulling the image to one side or the other.
There's also some suggestion that the time delayed, physically displaced diffraction itself (especially on a larger baffle) has negative effects on imaging beyond just introducing a non flat frequency response that varies as you go off axis...including causing localisation of the depth of the sound at the depth of the speaker. (This may be controversial, but I believe it has some merit)
Yet another school of thought (Geddes etc) suggest that diffraction at high frequencies is responsible for harshness and a perception of distortion which increases with SPL. (Again, perhaps somewhat controversial)
A wave-guide, whether CD or non-CD can make a major improvement to this problem by minimising the illumination of the baffle. If you don't illuminate the baffle significantly (say 20dB down or better) over the working range of the driver then even a large baffle without rounded edges will sound good.
The speaker more closely approaches a point source within each drivers range (no unwanted contribution from the baffle edges) the frequency response of the driver on and off axis is MUCH closer to the infinite baffle response in a real world finite baffle, variation in response as you move off axis can (assuming a well designed wave-guide) be very smooth and consistent, making for much more stable imaging and sweet spot.
(Try clamping a round face plate dome tweeter in mid air and measuring the on axis response - it will be horrific, try the same thing with a round face plate wave-guide tweeter and the response will be almost usable even without a baffle)
All of these give tangible improvements in quality, so I'm beginning to believe that a large part of what makes a good wave-guide system sound good is not so much the directivity pattern which it projects into the room, but rather the drastic reduction in baffle illumination and diffraction which typically comes along with it for "free".
Maybe what we hear is the much cleaner projection of sound into the room without the mess and confusion introduced by diffraction. Not only that, but we can avoid any drastic shift in diffraction pattern when crossing between a woofer and a tweeter if the tweeter is a wave-guide and the woofer is just starting to beam below the crossover point, leading to better driver integration.
I agree completely, I don't place undue attention on the response of the speaker at very wide angles (like 60 degrees etc) or exact power response for that matter, but focus on a listening window.
If you're talking about large speakers in a living room then you can estimate a listener window within which you want the speakers to remain relatively flat, or if not perfectly flat, at least change smoothly, gradually, and monotonically (with angle) away from the on axis response. For critical listening that required angular window is surprisingly small.
You're generally not going to sit anywhere beyond about a +/- 20 degree horizontal window, (outside this range you're almost in line with one of the speakers so won't be getting a phantom image anyway) and maybe +/- 10-15 degrees vertically at most. (Not many people expect perfect imaging while standing, and not many speakers deliver it)
Whatever that window is is where the response is critical, everything outside that window just falls into the "room response" and contributes to the overall power response in the room and becomes far less fussy. Given a choice to optimise the near on axis listener window response or the very wide off axis response I'd choose the near on axis response every time.
Of course small bookshelf speakers that are listened to up close need a much wider dispersion simply because the geometry dictates a much wider listener window, but that's a different design goal than a full size living room system listened to at 2.5 - 3.5 metres, where angular listener window is narrower and desired directivity for obtaining a suitable direct/reflected ratio is probably higher.
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As much as i know JBL addressed this issue from back in 1983. Others like S. Linkwitz, Earl Geddes also wrote about it. It is true that there isnt a particular power response that we should be looking for, but a constant power response. And in a way most speaker designers do that even if they are not aware of it or maybe they call it constant directivity index.
If the loudspeaker has high directivity or not doesnt really mean much (in the sense of power response linearity)
I don't think that the issue is diffraction due to baffles or flat power response (on-axis):
Modulation Distortion in Loudspeakers
Loudspeaker FM and AM Distortion (Klippel)
Chris
"Anything that moves--distorts"
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"...it seems to follow that high-efficiency horns will display small FMD and negligible AMD compared to direct radiators, in which both forms of distortion are higher. Small direct radiators driven to output levels necessary for 'realistic reproduction of music' may display a preponderance of AMD over FMD, and at objectionably high distortion levels."
"Clearly the AM modulation is dominant at low frequencies while the frequency modulation mainly caused by the Doppler effect is about 15 dB higher at high frequencies."
"Frequency modulation [distortion] of 0.35% was found by experiment to be objectionable."
Chris
"Clearly the AM modulation is dominant at low frequencies while the frequency modulation mainly caused by the Doppler effect is about 15 dB higher at high frequencies."
"Frequency modulation [distortion] of 0.35% was found by experiment to be objectionable."
Chris
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I'm not sure what you mean about JBL in 1983. I was the primary author on the 4430 paper and made the point that the smoother power response would help for those that were EQing the steady state curve, that leans more heavily on radiated power, but that flat power response was not the goal. Flat axial response was.
A "constant" power response is a very "particular" power response. There may be no harm in keeping an eye on power response while you design but the question becomes what to do when power response and axial response are in conflict? There is plenty of evidence that optimizing power response is a poor approach. That is, putting a system in a reverberent room and adjusting to flat power (very wrong) or to a particular room curve related roll off will not result in good sound. Worse yet, many systems could have the same power response and totally different axial responses. Clearly they would all sound different.
David
What "issue" are you referring to ?
I'm not sure what you're reading into what I'm saying as the part you're quoting is talking about diffraction and changes in diffraction pattern at the crossover frequency, I wasn't talking about distortion, in fact I didn't mention it in my whole message.
It's true that wave-guides can help to reduce distortion, and thats nice, and they can also help increase dynamic range which is also helpful, but it doesn't really have much relevance to imaging, ability to achieve near point source operation, smoother frequency response on and off axis etc.
The only thing I can think of is you've jumped on my use of the word "cleaner" and assumed I must be talking about distortion, but I'm not, and I don't believe distortion explains any of what I was discussing in my post.
A lot of what we perceive as "distortion", such as harshness at high frequencies is often caused by linear phenomena like narrow band non-flatness of response such as that caused by diffraction and resonances. Non-linear distortion is a lot less audible (on music, not test tones) than is typically believed.
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Simon - thats an enlightened comment - sounds familiar.
As to power response: "flat" should be distinguished from "smooth". Smooth is very important and desirable, but flat isn't really necessary or desirable. I design for smooth with a slight rolloff at the high end. DI, power response and the listening axis response are all important and all need to be controlled. What they are controlled to be is debatable to many (but I know what I want them to be.)
Yes, in fact, that was my point, above. The "elephant on the dance foor", as Nelson Pass puts it, is modulation distortion in terms of goodness of reproduction of music, whatever units you would like to use for this subjective quantity.
Audio distortion and feedback - Nelson Pass
You do seems to have a different set of measures for system merit than I do (however, your system of measures are not atypical from many that I've seen justifying direct radiating loudspeakers from the 1970s). I guess for the time being we'll just have to agree to disagree on this point.
But I also believe the biggest single element that horn-loaded or "waveguide" speakers brings to the table (the OP's original question of this thread) IS their measured 25-35 dB(SPL) lower modulation distortion than the same cone drivers used in direct radiating applications. To wave your hand and say that this isn't important or an issue, (even though my own ears tell me otherwise) , is I think imprudent. Extremely low modulation distortion IS the major difference of horn-loaded ("waveguide") speakers over direct radiators.
Chris
If you don't mind, I'd like discuss this topic off-line with you.
Note that I have read your book and your presentation "The Perception of Distortion", ca. 2000, but I have a a few questions that would be best served out of the public eye.
Chris
Indeed , (speaker !)Dave had used the word flared to save from that misconception .
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