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ninjai18

Properly towing in speakers when you are sitting off axis?

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For off-axis listening, where circumstances place the listener somewhat to the left or right of center stage, an adjustment of the balance knob can prove most useful. That offsets the SPL at the listening position while maintaining stereo geometry everywhere else in the sound field. No other adjustments (ie. asymmetric toe) required.

Edited by Quiet_Hollow

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has the thread header changed recently or did I missed it originally???

Edited by Schu

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:blush:

 

Whoopsidoodle.

 

I dont remember anything about "off axis" when I originally responded. so bad.

Edited by Schu

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have to say, it really sounds good actually....and the sweet spot does extend! I can move my head now easily 1-2 feet without a dramatic collapse of the phantom center image.

 

Also the sound seems slightly less "direct" as I experience with certain recordings (eg. Eva Cassidy tracks - such a powerfull voice).

 

Now my only concern is for the back-seats. Some time ago I constructed a little stage with an additional couch (2-seat) begin the main 3-seat couch, but now with the even more "toe-in" from the fronts I wonder what the effect will be during movies. For 2-channel, I briefly sat on the back couch and it was not THAT dramatic or anything. I'll leave the fronts like this and try to re-calibrate to include my 2 SVS subwoofers so I can re-evaluate the whole overall system.

 

Yes, the trade off is having to rebalance your fronts due to the increased off-axis angle directed at your LPs.  Most home theater-type front loudspeakers (tall and narrow with a midrange horn mouth of approximately 15 cm square and a crossover somewhere between 1-2 kHz to a direct-radiating woofer) will tend to have a fall off in polar coverage starting at 20-30 degrees off-axis (as your figure that you posted shows above for the RF-7 II).  So you have a bit of a dilemma in terms of what to do with re-EQing for the new "on-axis" response from the side of the loudspeakers, and the fact that more HF energy is covering the space between the loudspeakers (non-uniform coverage center-to-outside). 

 

In the final analysis, you have to work with what you've got to balance the pros and cons of more than just one performance variable--like stereo imaging width in this case.  In my set up (see profile), I really don't have to trade off loss of coverage as I toe-in in my fronts, simply due to the midrange horn mouth sizes and coverage of the K-402 horns with their compression drivers.

Edited by Chris A

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I agree with what Chris has said and would like to make a couple of additional/expounding points--one more relavent to your RF-3s that the other--based only upon my personal experience.

 

The ir- less-relavent one first.  I think an underappreciated, or seen as a negative, aspect of an exponential horn is the decreased output off axis of the horn. In a set up as described above, with a LP slightly behind the intersecting ceterlines of the speakers, as you move off-center of the center LP sweet spot and closer to one speaker, the closer speaker's output is less at your LP since you are off it's center axis. At the same time you have have moved closer to the center axis of the farther speaker therefore increasing the volume level at your position. To me this can be an advantage of this traditional exponential horn Heritage set-up vs. a CD horn. The affect is significant in two channel.

 

My other, and related point, and the other more relavent for you, involves the addition of a center speaker. In my experience (Heritage only), an identical center added to the set up as described above, sitting +/- 20 degrees of the center sweet spot presents no loss in the stereo presentation. It yields sweet-spot performance to three seats on a sofa or three closely spaces chairs. Perhaps or likely with the RF3s this is slightly less effective but the additional of a third main channel imho is indispensible to serious listening, Without a center channel, any movement of the listener off centerline moves the apparent source any content equally present in both channels--vocals and often solo instruments--to the closer side thus destroying any live illusion.

 

Lastly, Chris mentioned Toole's book and I wholeheartedly recommend it to all serious seekers of recreating the live illusion. It is a well-written, easy read of technical issues the encompasses a lifetime of study.

 

All the best,

 

Mike

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So I listened a bit in "pure" mode to both degrees of "toe-in" : "on-axis" listening and "off-axis" where the center of the compression driver "cross" about 2 feet in front of me.

Both DO sound good actually, however I do feel that when listening "on-axis" the stereo-image is a bit more "upfront" (= closer to me) where otherwise it seems a bit "recessed" begin the speakers.

 

I used REW to measure a few thing and something odd became visible that I cannot really explain.

There seems some "ringing" around the 3kHz region when measuring a single speaker ... the combined response L+R is OK , no traces of this ringing...??! My measurement point really never moved or anything.

 

 

See following measurement (waterfalls zoomed to the 1kHz - 5kHz region)

 

L-channel , OFF-AXIS listening

offaxis_lchannel.jpg

 

 

R-channel , OFF-AXIS listening

offaxis_rchannel.jpg

L+R , OFF-AXIS listening

offaxis_bothchannels.jpg

 

 

 

 

L-channel , ON-AXIS listening

onaxis_lchannel.jpg

R-channel , ON-AXIS listening

onaxis_rchannel.jpg

 

L+R , ON-AXIS listening

onaxis_bothchannels.jpg

 

 

 

 

TO MY EARS , it seems I do prefer the "on axis" listening, but the sweetspot is narrow ;-)

Now I always listen 2-channel by myself so that's not really an issue.

 

Now I will perform my Audyssey PRO measurement sequence again on top of that.

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Describe your microphone, how it is held (the microphone stand), where it was in your room during the measurements (assuming it didn't move), the dimensions of your room, and whether or not you used a projector, refrigerator, printer, ceiling fan, desktop computer (fan), etc. at the same time.

 

Chris

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I'm using a good old Radioshack analog dB-meter with LINE-OUT for REW. (with the calibration/correction file applied)

The meter was "lying" on the back of the couche, horizontally facing the RF7's pointing to the center-channel  just about where my head would be.

This couch is located a certain distance from the backwall, about 26% of the lengte of the room (+- 170cm's)

Except for a laptop (indeed with fan) there is nothing in the room that makes any noise like PJ,airco or anything.

Room is a 640cm x 640cm with a sloped (pyramid) ceiling and quite some acoustic treatments. RT60 is low.

 

An impression :

PANEELRIJ.JPG

Various aborsorbing elements. 4 (in the corners) specific performated-panel absorbing elements that I've calculated & build to deal with a certain (lower) range of frequencies

8 small panels (4 on each row) , 50mm thick, 10cm "floating" from the wall to deal with flutter between the parallel walls. Sure there are these cabinet-doors but nothing much can be done there without impacting

visuals.

The "floating" ceiling is "open" and filled with absorption materials too.

 

 

Then the back of the room, begin the large thick curtain, behind the curtain there is a window-frame with a thick package or absorbers (rockwool based, about 10inch thick)

Again 2 perforated panel absorbers at the back.

 

TESTHOOGTE.JPG

 

 

 

...all in all this leads to RT60 times like here below, measured by an acoustics-guys that I've invited for a cross-check compared to my own measurements.

ss_rt60.jpg

 

 

What I find strange is that is becomes visible on separate L or R channels measurement ONLY , but on a combined L+R there is no trace of this...and the decay is nice as it should be.

Edited by jvanhambelgium

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I believe what you are seeing is noise floor of your room-and something that is at very low level that turns on (like air handling blower or self-induced vibrations/whistling from an air grating) or perhaps something that is actually ringing at 3 kHz, like a bell-like object, but in direct line of sight from the tweeters-microphone. 

 

The characteristic distance for 1/4 wavelength is about 2.6 cm at 3 kHz, so whatever it is could also be reflecting off the body of the SPL meter itself. 

 

I've included a waterfall of my room for a full range sweep of my left front loudspeaker and subwoofers (crossed at 40 Hz).  You can see the noise floor of the room.  The room's RT60 is 0.3-0.45, depending on frequency and analysis type used to calculate reverberation time.  There is a refrigerator about ten metres away and perhaps a ceiling fan running at the same time.  The dip in response at about 240 Hz is a non-minimum-phase cancellation that disappears when I move the position of the microphone.

 

Chris

 

Left Jub+subs 2 Dec 2014 waterfall.png

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By the way, you've done a nice job with that room--acoustically and visually.

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Thanks.

btw, that is a pretty loud measurement you are making there Chris... :D :D

But that is good thing, it often reveals more then taking low-SPL measurements.

 

I'm rather happy with the overall result looking at the various acoustic measures I've taken.

Even the acoustics guy - who visits many listening rooms - said I should be really happy with the *BIG WIDE* stage that can be experienced on this attick.

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btw, that is a pretty loud measurement you are making there Chris

 

The microphone was at one metre from the front face of the loudspeaker (Jubilee) and about 1.5 meters from the mouth of the closest subwoofer.  That's only about 1-1.25 watt input into the Jubilee (KPT-KHJ-LF) bass cabinet and less than a watt into the TAD driver. 

 

Many small loudspeakers simply cannot achieve good clean output at realistic peak ensemble levels (i.e., greater than 110 dB unweighted at one metre).  But it's not a problem for fully horn loaded loudspeakers.  In fact, in order to realistically measure distortion levels, you need to be well above 100 dB(unweighted at one metre).  Measuring distortion at 90 dB(unweighted at one metre) tells you nothing.

 

 

KHJUB.GIF

 

As J.S. Bach used to say: "...the instrument must have good lungs!", so he'd reportedly pull all the stops and lay his body and arms across the keyboard to test any new organ that he was about to play for the first time--to the horror and amazement of the local church fathers....

Edited by Chris A

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Going further on this, are there any RF7 owners that "tilt" their speaker slightly to the front ? From the ground up, the phase-plug of the driver is about 110cm from the ground.

At my MLP, being 324cm away, I'm about 90cm from the ground.

This means I'm not listening (vertically) on-axis.

 

Now it has been a looooong time since school, but with some trigonometry-formulas on a right triangle this would mean :

 

Opposite side = +- 20cm

Hypotenuse side = +- 324cm

1 angle of 90°

 

So sinus of this corner would be 20/324=0,061728395

To get the actual degrees we invert and this results in 3,539026459° degrees "off-axis"

 

Soooo, this does not seem much and only becomes even less if you sit further away from the speakers.

 

Anyway mounted the spikes on the back-feet of the RF7-II's so the "point" even more directly to your head ?

 

I've mounted the spikes and in pure mode (no Audyssey since it is not valid anymore with this "tilt" it sure sounds sweet, but I did not yet do A/B comparisons)

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