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ligs

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  1. Now I have three different BP(Bi Polar or ambience) speakers to play with my main imaging(Infinity R152) speakers including an extra pair of R152. I have found several Infinity TSS 750 satellites with 150 Hz to beyond 20 k Hz response. I estimate Bose double cubes are similar except the highs are not as extended. https://www.soundandvision.com/content/infinity-tss-750-speaker-system-ht-labs-measures Some observations: They all sound better turning away from the main speakers instead of directly forward. Bose double cubes can produce some wield sound fields because each cube can turn totally independently from its mate. It is hard to tell apart what is preferred from what is merely different. Isn't that the dilemma when we are facing multiple of choices:)
  2. The Bose cubes could probably be made to work and I am sure you can make this work with the cubes. So far the acceptable BP speaker will likely to be: 1. Delayed by at least 20 millisecond from the front speaker(as mentioned in Stereophile about AR MGC-1). It can be easily met by pointing BP speaker away from the main speaker or perhaps behind the main speaker by about 3 inches or more in the x-axis. 2. A frequency range of perhaps 300-5000hz or wider. Yes, Bose cubes could work. But, you could just move your rear facing Infinity closer to the wall, which may be what you were saying, and experiment until you like what you hear. Are you using music or test tones to evaluate your success? Here comes the empirical part. In general moving the BP speaker closer to the wall will decrease the delay, vice versa. I have not thought about should the wall be reflective or sound absorbing, etc. So far I have not seen any acoustic measurements of the BP speaker so one would have just to try and listen😊 “Regarding Classic ARs. I have been listening to AR5s and my stack most of this afternoon. I can verify that a properly working AR5 with rebuilt tweeters sitting away from the wall can image very well. I used to accept what others have said about the less than stellar imaging capabilities of the classic dome ARs but no more. Indeed. Unless placed properly, the stereo imaging can be destroyed by placing too close to the wall. I wonder when placed away from the wall the main speaker’s edge and side/back radiations could serve as its own BP twin. These radiations will already be delayed(simply because they will take longer time to reach your ears) with respective to the main speaker. Could this phantom or pseudo BP radiations serve to improve the image quality of the direct radiating main speaker? Many European stand mount (to differentiate from bookshelf) speakers have excellent imaging quality but you need to mount them on dedicated stands at your ear level and away from corners and back wall, very different from the bookshelf position recommended for many classic speakers. “The flaw in all this IMO is when imaging came into vogue with high dynamic range recordings most classic AR tweeters had deteriorated putting them at a disadvantage. Another problem is classic ARs are almost always near or against a wall to preserve the bass performance. “ You nailed it. Unless the frequency response of the left and right speakers is closely matched(at least in the mid and high), the image will suffer. Has anyone measured the performance of vintage drivers after 30 to 60 years of service or storage? “If you pull them away from the wall you get bass roll off but the image improves dramatically. This would be where your well set up sub woofer comes in handy.” I agree totally!
  3. More information worth considering. The relative spl level of the BP(bi-polar or rear facing) speaker. One can achieve 6 lower db than the front speaker in a number of ways. My listening distance to each speaker is about 9 ft. The wall behind the speaker is 2ft away . So the sound from the BP speaker bounced to the back wall would have to travel 13 ft to arrive at my ears at about 3db lower than the front speaker. This -3 db is estimated from the db vs distance table for 3m and 4.3m. The sound bounced to the 15 ft ceiling will travel at least 30 ft to my ears at about -10db level. 2. While it may sound unrelated to our discussion but Acoustic Research MGC-1 does use a set of direct radiating module and an indirect sound module to achieve a unique sound field. According to the write up in Stereophile about AR MGC-1, the indirect sound module is electronically delayed by 20 milliseconds and covers only 300 to 5000 hz. https://www.stereophile.com/content/acoustic-research-mgc-1-loudspeaker 3. The 20 millisecond-delay for the indirect module is to make certain it would not smear the stereo image of the front speaker, which is very precise unlike most classic AR speakers. So perhaps we can use BP speakers with less extended frequency range( 300 to 5000 hz as in AR MGC-1), such as Bose cubes or double cubes after all. How about 20 millisecond-delay? I think the rear facing BP speaker in my current setup will provide about at least 67 milliseconds delay. This delay is calculated by the extra distance(9 inches) the BP speaker has to travel to my ears divided by the speed of sound of 343 meters/sec.
  4. My initial impression was there was a bloating of the midrange response when I replaced the rear facing R152’s with two Bose double cubes. I did not try with single cubes. This begs these questions? 1. Does the rear facing speaker have to be identical the front speaker so not to alter the frequency balance. 2. Efficiency match between the front and back speaker? Instead of experimenting further I decided to do some reading. Definitive Technology is probably the largest established company making Bi-polar speakers. In an inside view of their BP9080x speaker, it has a front and a rear module. There is also a top facing Dolby Atmos module. All modules seem to use the same driver units. There is also a discussion that the rear module being 6 db less efficient than the front one. So it appears the suitable rear speakers would likely to be identical to the front ones and perhaps at lower efficiency as well. Bose double cube is mostly a midrange module without extended highend and appears to be too loud as a BP speaker for Infinity R152. According to the review at “Sound and Vision” “Of course, these wouldn’t be BP’s if they weren’t bipole designs that fire in two directions. In keeping with Definitive’s long practice, the towers each have two midrange/tweeter arrays: a front-facing mid-tweet-mid assembly and a rear-firing mid-tweet array. As you might expect, thanks to all those intentional reflections from room surfaces, bipoles tend to produce a bigger, more spacious, and somewhat more diffuse sonic fingerprint than conventional direct-radiating, front-firing-only, cone ’n’ dome speakers. This can come at a certain penalty in hard-imaged soundstaging, something Definitive addresses with a further refinement in this series of the “Forward-Focused” design it introduced in the 8000 series bipolar. This results in the rear-radiating pattern being attenuated 6 decibels down from the front-firing array.” https://www.soundandvision.com/content/definitive-technology-bp9080x-speaker-system-review-inside-bp9000-series
  5. Just want to ponder further what would make suitable ambience speakers for your main speakers? Probably they don’t have to be identical to the main speakers and may not require a very wide frequency response. Searching my parts bin in my basement, I came up with these gems, these are Bose double cubes used in Bose Acoustimass systems. The DCR is comfortably high at 7 ohms and the sensitivity is around 86db. Bose also has a single cube which has 3.5 ohms DCR but with the same sensitivity. I think the double cubes are better than the single cubes for our current purpose.
  6. Thanks for sharing your insights on the effects of musical instruments and venues on the recorded sound. Having experienced the benefits of ambience control, I found myself now listening into the music instead of listening to the speakers. I suspect I would not get where I am without some encouragements and helpful suggestions from fellow like you.
  7. Indeed, pointing the satellite speakers away from the listener is not an obvious approach to enhance the listening experience. I am glad we both find this arrangement enlightening. At the same time, we seldom see any musical instruments radiating sound only in one direction. Bose is partly correct in wanting to broadening the radiation pattern of the speaker. I believe we need sufficiently strong front arrival sound to get good stereo image, but Bose 901 only radiates 1/9 of the sound toward the front. Perhaps we need like 50% sound radiating from the front as in our setups. Just a thought.
  8. I will be very interested in hearing your opinion about your testing of the ambience control. AFAIK, the BP in Definitive Technology speakers suggests they are bipolar speakers. Several Snell speakers designed by Kevin Voecks (now at Revel) also have rear facing tweeters.
  9. Among the many configurations I tried with two Infinity R152 speaker in each channel, mounting one R152 on top of each other but pointing to the opposite directions sounded the best to my ears. In this bi polar configuration, the stereo image is stable, the added reverberations from the rear facing speakers give a fuller and more satisfying sound field . Since there is a 9-inch depth between the front and back drivers, there would be at least 6.6/10000 sec delay for the rear facing drivers. The speed of sound is 343 M/sec, 9 in=0.229 M. What is surprising is the highend musical notes such as cymbals and bells sound pristine and not strident at all. I guess the rear facing speakers don't even have to be identical to the front facing speakers to give this bipolar effect.
  10. ligs

    AR-2t

    The blue trace was from a pair of AR 4" poly and a Dynaudio D28 in MTM configuration. The yellow trace was from Infinity Primus 162 and red was from KEF Reference 102. Since they were measured at different times and so the conditions were not identical. Each division of the vertical scale is 5 db. The X-axis is the frequency. But the general smoothness and flatness made this little AR MTM sound very pleasing especially for vocals, IMO. I remember I bought 4 of AR 4" poly midwoofers(#210095, TNG) from an AR service center in Pennsylvania in 1988. George
  11. These JBL LSR speakers are indeed very attractively priced for their performance. At this price point I doubt any DIY speakers can come anywhere close to match them. One thing good about DIY is you can modify and replace the parts without voiding the warranty plus you can learn a little bit about acoustics and electronics.
  12. Pointing the top pair of Infinity satellite speakers outward as what Bose recommended for its dual cube smoothed out the harshness a lot. Since I can rotate the top satellite speakers independent of the bottom ones , the next thing I tried was pointing the top speaker backwards to form a pseudo-bi-polar pattern. It did give a more spacious sound field and was quite enjoyable.
  13. At this point, the upper range of the stacked pair sounds too analytical and a little harsh for my taste while they are nice and balanced when played in singles. In another word, the octave -to-octave balance of the original speaker is perturbed by stacking.
  14. ligs

    AR-2t

    "Over the years I have seen other AR-1MS, older and there are differences in the cone paper, I am also attaching the mid photo of my AR48s (square magnet, different basket) and cone made with a particular paper, with a treatment and cone cut (visibile nella foto ad h.6), welded and joined, in my opinion the most well-sounding cone mid ever heard" I seem to recall , a reviewer said something about AR used felt instead of regular paper cone for the 4" midrange. The same reviewer also said about the crossover was also quite unique. I had a few pairs of AR 1MS before, one pair had the the same kind of seamless cones as in your picture. But one pair had a straight seam through the cone from the dust cover to the foam edge.
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