[JoshK]

I am not 100% clear on the advatages or the 12" over the 10".

The idea is pattern control further down in frequency.  The 10" waveguides can't hold the pattern as low as the 12", the 12" can't hold as low as the 15", etc.  The larger woofers also narrow their directivity lower in frequency so they help a little too.  The trade off is the size. 

For a small room, the 10" are probably the right fit.  Add subs and your golden.

[konut]

Anyone know the similarities between sp tech and gedlee? 
They look similar but I am not sure if it is only skin deep.  I have read accounts that they do not sound similar.  Is sp tech cd?

I have a set of the Geddes Abbeys and also a set of SP Tech Timepieces though a quite old version. I'm sure the newer ones are different. To my ears they do not sound very similar.

The SP's have a lower sensitivity and can suck up power like a sponge while the Abbeys are quite easy to drive. Obviously the wave guide is a different profile as is the use of the foam in the Geddes design. The SP's play quite a bit lower in the bass while subs are mandatory for the Abbeys if one wants any real bass.

I prefer the Abbeys but that is my preference, I am not in any way discounting the SP Tech/Aether Audio speakers. As one of the few who actually own both I'm in a position to choose.

I will say that without the foam, the Abbeys are more like what I consider a traditional horn in sound and I don't much care for them that way. One visitor who has heard them mentioned he might try some type of open cell foam in his Altecs.

Outstanding comparison. I have been working with Jim Goulding experimenting with his Diffractionbegone pads to reduce diffraction. So far its my impression is that only at higher SPLs do they make an audible improvement. Has it been your experience that at lower volumes the foam has less of an effect? Also, which would you say is the more linear speaker? One of the knocks against higher efficiency designs is that they tend to get less linear the higher the sensitivity. Of course with bi and tri amplified designs its possible to use a digital Xover, as macrojack has done, to solve THAT problem.

[JoshK]

Konut,

The dependency of diffraction audibility and SPL is documented by Geddes.  They found that to be the case in their empirical studies.

[TRADERXFAN]

I did read from Geddes that the psychoacoustic response to High Order Modes (HOM) in horns, resulting from diffraction (but not equivalent), are much worse as you go higher in SPLs. 

The foam in the waveguide is to attenuate HOMs.


What I believe lower diffraction on a speaker at any spl will do is make the speaker more intelligible, enhance clarity. Which is why the Geddes speakers also have large radius roundovers, and meticulous smoothing of sharp edges throughout the tweeter -waveguide interface.

-Tony

[sts9fan]

I would say that the foam made a huge difference at all listening levels.  Maybe at lower levels it is less obvious but still there.  I think it has also been said that while attenuating HOMs it also reduces the energy or attenuates the high frequecys.  I could be wrong though.
The speakers were a bit harsh before I put in the plugs.  Not a lot but a bit. 

I wonder what would happen if Macrojack stuffed his horns with the opencell foam?     

[konut]

I recall reading that adjustments to the crossover needed to be made to compensate for the attenuation, at the highest frequencies, by the foam. I'm trying to line the Minis' waveguide with the wool padding to decrease HOMs without attenuating the high freqs.

[macrojack]

Is there a way to talk about horns in English? What is diffraction? I know distortion and can't say I hear any until I reach an SPL that seems to overwhelm my space. Bill states that a conical horn is the only shape that permits sound waves to emerge from the horn mouth intact and undisturbed. If he's right, that would explain the need for rounded edges and cell foam implants in non-conical horns.

I spent a bit of time reading at Oswald's Mill site and I've gleaned from topics peppered here and there that there are intense differences of opinion among horn designers that sometimes have them at each others throats. If a few of those guys show up here, we will have to proclaim no religion, no politics, and no horn talk. A lot of it was apparently incited by Romy the Cat.

So, if we are talking about light, I understand diffraction. Is that the same with sound? If so, what causes it? Could it have to do with the disturbance of the pattern of sound waves as they move from the throat to the mouth and out to our ears? And what would I look for and why would I want to, stuff foam in my horns? What are High Order Modes?

By the way, I haven't mentioned this but my drivers are coax and I have never hooked up the tweeter. Bill told me he tried it and thought it was too hot so, even though I have the passive XO parts here, I haven't bothered. Someday curiosity might overcome me but for now I don't care. My upper end probably rolls off above 14Khz. I probably can't hear even that high.

[sts9fan]

If a few of those guys show up here, we will have to proclaim no religion, no politics, and no horn talk.

well as of now no horn designers and its pretty nice.

I think a HOM is sort of like a bass mode just inside the mouth of the horn.  Is this correct?

Diffraction happens with all waves

Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Similar effects are observed when light waves travel through a medium with a varying refractive index or a sound wave through one with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, x-rays and radio waves. As physical objects have wave-like properties (at the atomic level), diffraction also occurs with matter and can be studied according to the principles of quantum mechanics.

While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves where the wavelength is on the order of the size of the diffracting objects. If the obstructing object provides multiple, closely-spaced openings, a complex pattern of varying intensity can result. This is due to the superposition, or interference, of different parts of a wave that traveled to the observer by different paths (see diffraction grating).

The formalism of diffraction can also describe the way in which waves of finite extent propagate in free space. For example, the expanding profile of a laser beam, the beam shape of a radar antenna and the field of view of an ultrasonic transducer are all explained by diffraction theory.

[macrojack]

The stock horns in my JBLs have what JBL calls "diffraction lenses" velcroed onto the baffle over the horn mouths. Perhaps these reorganize the sound waves to reinstate original integrity. Previously I had assumed they were provided to create dispersion since the horns are short and narrow.

I don't pretend to understand the relationships between throat diameter, horn length, and angle of expansion. These variables do effect the loading of the horn and the integrity of the sound waves that emerge I'm told but my untrained mind starts to cramp when I speculate about what it all might mean. Maybe book-learnin is a good thing after all.

[nullspace]

Most hornies align the drivers in an attempt to match the acoustic centers for time alignment, but that results in the time alignment for only the on-axis direction.  Move off axis and they are no longer time aligned.

Not to pick nits, Josh, but isn't that the case with most all loudspeakers (conceptually, I'll except coaxial speakers), that it can only be time-aligned on one specific axis? On any other axis, you could be close to time-aligned but the trig just doesn't allow it.

Therefore the power response isn't even into the room.

My larger point, then, is that I don't think this is true. I don't think time-alignment is either necessary or sufficient to achieve a decent power response. You can achieve decent power reponse without aligning the acoustic centers, and you can get poor power response with closely aligned acoustic-centers -- think Altec 604s. I would think that it is more a matter of matching increasing directivity of one driver to the widening directivity of the other driver, and paying close attention to phase-coherence across a wide range of on- and off-axis responses.

I hope that's not an incohernet mess. Does that make sense?

Regards,
John

[macrojack]

Please define "power response".

[nullspace]

II picked up an 845 based SET a couple of weeks ago and I'm starting to see the attraction.

Mike,

Could you tell us a bit more about your 845 SET? The reson I ask is because, since it's SET I assume no-feedback and therefore a 2-3ohm output impedence, based on the Abbey's impedence plot you posted the freq. response should differ from the official plot Dr. Geddes has posted at his website. And I would like to hear your impressions on how the speakers sound with the SET.

I'm mightily curious about the Abbeys, but were I to snag a pair I'd almost certainly try putting a LCR across the speaker to smooth about the impedence bump at 1.5khz.

Regards,
John

[TRADERXFAN]

Please define "power response".

here is a decent explanation about mid way down
http://www.aeronet.com.au/concepts2.htm

Here is a link to some musings from Linkwitz on perception of sound from loudspeakers
http://www.linkwitzlab.com/speakers.htm

[TRADERXFAN]

I recall reading that adjustments to the crossover needed to be made to compensate for the attenuation, at the highest frequencies, by the foam. I'm trying to line the Minis' waveguide with the wool padding to decrease HOMs without attenuating the high freqs.

I have seen this too. And it makes a lot more intuitive sense than the more complex subjects we are getting into!

[nullspace]

Please define "power response".

"The power response of a speaker is the total of both its off-axis and on-axis amplitude response. In other words, it is the total acoustical power that is radiated into space."

The logical follow-up to that is: So what? Why would one care what a speaker's power response is? The truth is, some do and some don't, and I suspect a lot of it has to do with their respective listening habits.

There are some designers that focus only/ primarily on on-axis measurements, and they listen generally on- or slightly off-axis. The mammouth "Beyond the Ariel" thread at diyAudio, Lynn Olson has said he cares most about on-axis measurements and doesn't get very hung up about power response. Consequently, he's using horns that don't have as a goal a great power response. He's well-respected and I take him at his word on whether or not power response is important.

Others, like Earl Geddes, give no more thought to the on-axis response than they do to any one off-axis measurement -- it's about the total power radiated into the room. Generally, people who listen to these speakers do so off-axis or, in my case, frequently from another room. I often have my stereo on while I'm cooking or doing other various duties and it's important to me for the sound to be right from anywhere on the first-floor. And an even power response helps greatly with that.

Horses for courses...

Regards,
John

[mgalusha]

They are a pair of the Consonance Cyber 845's and I don't they have any feedback. I have not traced the circuit yet, so I can't be 100% certain.

I do plan on trying a Zobel to try and smooth out the impedance bumps and make life a little easier for the amp. Assuming I can find time this weekend I plan on measuring the amps, including the output impedance. I need to calculate the values for a Zobel as well along with what seems to be a ton of other things.

II picked up an 845 based SET a couple of weeks ago and I'm starting to see the attraction.

Mike,

Could you tell us a bit more about your 845 SET? The reson I ask is because, since it's SET I assume no-feedback and therefore a 2-3ohm output impedence, based on the Abbey's impedence plot you posted the freq. response should differ from the official plot Dr. Geddes has posted at his website. And I would like to hear your impressions on how the speakers sound with the SET.

I'm mightily curious about the Abbeys, but were I to snag a pair I'd almost certainly try putting a LCR across the speaker to smooth about the impedence bump at 1.5khz.

[nullspace]

Thanks Mike; I'm really interested to hear your thoughts concerning w/ and w/out impedence compensation for the Abbey. It seems to me it ought to make a difference, but who knows...

Regards,
John

[macrojack]

Please define "power response".

"The power response of a speaker is the total of both its off-axis and on-axis amplitude response. In other words, it is the total acoustical power that is radiated into space."

The logical follow-up to that is: So what? Why would one care what a speaker's power response is? The truth is, some do and some don't, and I suspect a lot of it has to do with their respective listening habits.

There are some designers that focus only/ primarily on on-axis measurements, and they listen generally on- or slightly off-axis. The mammouth "Beyond the Ariel" thread at diyAudio, Lynn Olson has said he cares most about on-axis measurements and doesn't get very hung up about power response. Consequently, he's using horns that don't have as a goal a great power response. He's well-respected and I take him at his word on whether or not power response is important.

Others, like Earl Geddes, give no more thought to the on-axis response than they do to any one off-axis measurement -- it's about the total power radiated into the room. Generally, people who listen to these speakers do so off-axis or, in my case, frequently from another room. I often have my stereo on while I'm cooking or doing other various duties and it's important to me for the sound to be right from anywhere on the first-floor. And an even power response helps greatly with that.

Horses for courses...

Regards,
John

Thanks John and Trader _ I get the concept now and John's explanation of the practical consequences helped immensely. My system is on all the time (one reason I use SS, not tubes) and I find that it is way different once I move outside the 40 degree dispersion of the horns.

[sts9fan]

Thats one thing that I LOVE about the Nathans.  You can move all around the room and they still sound great.  The soundstage shifts but is still sharp and in focus.  I also have my system on all the time and it provides music to the whole 1st floor.

[JoshK]

Most hornies align the drivers in an attempt to match the acoustic centers for time alignment, but that results in the time alignment for only the on-axis direction.  Move off axis and they are no longer time aligned.

Not to pick nits, Josh, but isn't that the case with most all loudspeakers (conceptually, I'll except coaxial speakers), that it can only be time-aligned on one specific axis? On any other axis, you could be close to time-aligned but the trig just doesn't allow it.

Your right.  However, if the horns are CD, and the mouths are aligned, then the forward directivity should be fairly close for reasonable off axis angles, don't you think?  At least closer than that of dislocated mouths.

Therefore the power response isn't even into the room.

My larger point, then, is that I don't think this is true. I don't think time-alignment is either necessary or sufficient to achieve a decent power response. You can achieve decent power reponse without aligning the acoustic centers, and you can get poor power response with closely aligned acoustic-centers -- think Altec 604s. I would think that it is more a matter of matching increasing directivity of one driver to the widening directivity of the other driver, and paying close attention to phase-coherence across a wide range of on- and off-axis responses.

I hope that's not an incohernet mess. Does that make sense?

Regards,
John