High Quality 92 db 2-way Speakers Using JBL 127H-1 and Dayton RST 28 F-4

[ligs]

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. 

[ligs]

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.  

[Aadams]

The ability to economically experiment with speaker placement in such a modular way has only happened in the last few years.  Ironically, AR was on the path with the 3t below but, without practical, affordable, electronics to crossover and biamp there was no path to wide market acceptance.  What you are doing looks DIY and belies what I know to be true,  the sound can be superb.  I will try the rear facing ambience trick today and see what changes.

 

[ligs]

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. 

[Aadams]

This is the configuration I have used for over a year.    Over the last two days I have pointed the top speaker pair in 3 other directions.  The arrangement that works best is to turn the top speaker 60 degrees toward the wall behind it which, from the listening position, looks as seen below.   The sound is more expansive but the image is clearer and it was already good. I have to admit PeteB encouraged me to try this pointing at the wall several months ago but I was tired of fiddling and had already gotten a good result but this is better.   I probably would not have bothered if you had not stacked your satellites.

[ligs]

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. 

[Aadams]

12 hours ago, ligs said:

At the same time, we seldom see any musical instruments radiating sound only in one direction

Especially true with acoustic instruments recorded before live audiences or in large venues.  Forgot to mention I used orchestral music to work out the satellite placement.  I use pop/rock to set up the bass and mostly orchestral to gauge the image.  The studio recordings of pop/rock seem to always benefit as a result. 

[ligs]

4 hours ago, Aadams said:

Especially true with acoustic instruments recorded before live audiences or in large venues.  Forgot to mention I used orchestral music to work out the satellite placement.  I use pop/rock to set up the bass and mostly orchestral to gauge the image.  The studio recordings of pop/rock seem to always benefit as a result. 

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.

[Aadams]

On 4/2/2019 at 1:17 PM, ligs said:

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.

I didn’t care about imaging beyond channel balance and phase until about 3 years ago when my listening distance was severely constrained by my desire to stay married.  As a result, I started noticing nuance that can only heard in a sweet spot, which can be a several foot section of perpendicular center line between the stereo pair or just a small spot depending on how beamy the speakers are.   Anyway, I use orchestral recordings to gauge speaker image quality because of this diagram below, which you probably already know about.

All modern orchestras setup in the depicted pattern or a close variation.  If you use a quality orchestra recording of a full-scale piece you can follow the music across the orchestra from side to side and front to back.  When everything is dialed in well enough in your system the aural image fits the visual image you see above.  A good recording of “A Young Persons Guide to the Orchestra by Benjamin Britten” is excellent for this purpose.  EDIT: Another is Rite of Spring.  You'll need some dynamic range for both to hear the very soft passages on a modern recording.  

[ligs]

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. 

[Aadams]

And the result is?

On 4/3/2019 at 12:27 PM, ligs said:

I think the double cubes are better than the single cubes for our current purpose. 

 

[ligs]

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

[Aadams]

Are the rear speakers above really 6db less efficient or is it the placement in the rear with their sound completely diffuse and off axis that causes them to sound 6db down from the front drivers at the listening position?  You got a good result with your Infinity stack with which you could try greater distance from the wall or angle it to create greater diffusion before the first reflection.  My 3 unit stack has always had two forward facing and a third facing off axis in some fashion and it seems to work.  Not saying they must be identical but I would say they must cover the same sonic range and unless you are prepared and inclined to engineer a solution with disparate parts I would think the path to success would be shortened by using identical parts.

 

[ligs]

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.

 

 

 

[Aadams]

The Bose cubes could probably be made to work and I am sure you can make this work with the cubes.  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?

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.  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.  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.

[ligs]

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!

[Aadams]

2 hours ago, ligs said:

I wonder when placed away from the wall the main speaker’s edge and side/back radiations could serve as its own BP twin.

IIRC, According to Allison and Toole reflections are ok as long as they don't cancel or reinforce. In general most of the concern should be in the area below 400hz which is why it is important to get the big drivers in the domed ARs away from boundaries or at least not have them squarely placed against a wall or near the floor.  This for imaging mind you not bass.  The area of radiated sound from an AR domed mid is impressive and easily matches a multiple small satellite array positioned to achieve flat off axis response.   This brings up why the old suspended domed tweeters are so important near the crossover point.  They maintain the off axis power of the mid into the last audible octave. 20khz in music is BS .  20k only matters if you are trying to win a hearing contest or stay alive in the wild. 

As for speakers way out in the living space, away from reflective surfaces, it seems to be a small scale version of curved line arrays in massive arenas where reflections are ignored and the only thing that matters is directing beams of sound into an audience from the front to as far back as necessary.  The downside of using a single pair of small speakers for stereo sound is the tiny sweet spot.......if you move off axis both the sound field and the image collapses.  The upside is there are many small modern speakers that can image well.

[ligs]

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:)

[Aadams]

29 minutes ago, ligs said:

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:) 

It is bewitching but if you have a good reference recording for imaging you will know which is best.  What I like about this approach is the level to which the speakers can be tailored to the listening environment rather than the reverse.

[ligs]

After back and forth listening between the regular front facing MTTM vs bi-polar(front and back) MTTM using 4 stacked Infinity R152’s, here are the findings.

1.       Regular MTTM has higher sensitivity, narrower sweet spot, more extended treble.

2.      Bi-polar MTTM sounds more diffused and can tolerate less pristine music sources.

3.      Regular MTTM is more dynamic (perhaps due to higher sensitivity) and better separation of music instruments.

Thus, stacked speakers offer 2 very different sound fields and you may prefer one arrangement over the other depending on the music.

[Aadams]

Ligs

Did you find a sonic downside to stacking small speakers?    Did you hear any comb filtering?  Earlier you were using Bose cubes in combination with the 152s.  Does your stacking experience reveal some guidelines for stacking?  Are you currently listening to multiple pairs and if so what is your preferred configuration? 

Adams

[ligs]

Nowadays I am listening to 2 pairs of Infinity R152's in the normal  stacked MTTM fashion(both speaker facing forward with tweeters close together in a vertical line). Listening to the beginning of this youtube piece, the delicate music box-like  instrument sounds so pristine and so pure. 

The sensitivity of Infinity R152 is 87db. The stacked R152's connected in parallel will theoretically produce 93 db. I suspect the improved sensitivity is responsible for the cleaner perceived sound. 

 

[ligs]

Just a quick update of this thread. 

I sold my JBL 127H1 woofers.

I continue to like stacked Infinity R152 in MTTM as R/L speakers.  Recent test results showed the frequency response was   +- 1.7db from 300 to 10000 hz for Infinity R 152 .

https://pierreaubert.github.io/spinorama/index.html

I sealed the vents of R152 to limit the woofer excursion for a cleaner sound(to my ear). I also paralleled each channel with a sealed 8" Revel woofer which helped the overall balance and had better bass definition. 

I constructed a pair of 2x Infinity Perfect 6.1/Dayton RS28A4 in a MTM configuration. The design was a revision of 2x RS180-8/RS28A4 MTM Studio Monitor by the late speaker designer Jeff B. The vocals sounded very natural to me. 

[Aadams]

Are you talking about two different projects?  MTM VS MTTM.

Are the Revels blended with the infinity’s or running wide open?  

What happened to the big subwoofers?

[ligs]

2 hours ago, Aadams said:

Are you talking about two different projects?  MTM VS MTTM.

Yes, MTTM is stacked commercial Infinity R152 x2. MTM is a DIY with two Infinity Perfect 6.1 woofers and one single Dayton RS28 in a sealed enclosure.

 

2 hours ago, Aadams said:

Are the Revels blended with the infinity’s or running wide open? 

Revel IW80 is a 8" ceramic based woofer.

I use a simple 12mh/30 uf low pass crossover to roll off the mid and high frequency so it blends better with my main speaker. 

 

2 hours ago, Aadams said:

What happened to the big subwoofers?

They are still in service. The extra Revel woofer brings out enough clean bass that I often listen without turning on my sub. 

Thanks for your questions!

 

George