Modifications to Elac Uni-Fi Reference UBR62 Bookshelf Speakers

[terryforsythe]

That's really nice, a hobby on its own, aside from audio, etc.
A silent night, outside, on a wide area and put somewhere fairly high can work its way out pretty good.

I have a 19 ft. ladder (Little Giant), and nothing but trees behind my house for a few hundred meters. I'll still get some reflections off of the house and the ground, though. A portion of my house only is one story. If I put the ladder on that side of the yard, the speaker will be above the bottom of that portion of the roof line, thus reducing direct reflections.

To address ground reflections, I'm considering building an A-frame out of two 4ft. x 8 ft. plywood panels, covering that with insulation, and placing it on the ground between the speaker location and the microphone location. That may help reduce ground reflections a bit.

 

[terryforsythe]

With both horizontal and vertical measurements I'll end up with more measurements for each driver than VItuixCAD handles. I'll need to decide whether to use measurements evenly spread around the full 360 degrees, or use a tighter spread +/- 90 degrees and a wider spread for the back of the speaker. If anyone has insight on that, I would like to hear it.

 

[Sokel]

With both horizontal and vertical measurements I'll end up with more measurements for each driver than VItuixCAD handles. I'll need to decide whether to use measurements evenly spread around the full 360 degrees, or use a tighter spread +/- 90 degrees and a wider spread for the back of the speaker. If anyone has insight on that, I would like to hear it.

I would take as much as I can, tag them and store them like treasure and then decide which ones I would load to VituixCad.
Data is always valuable and you never know the possibilities down the road.

 

[terryforsythe]

I recieved the new 15mm timing pullies and belt. That solved the belt slipping issue.

I have been pondering over whether it is critical to keep the axis of rotation directly aligned with the drivers when taking measurements at 2-3m. With the original rotating platform the tweeter is around 85mm from the center. I think this probably is insignificant. Anyway, I played with the design to allow me to precisely line up the tweeter with the axis of rotation. Here it is:

It is a little bulky. I'm not sure yet whether I am going to use it. I also had to raise the bottom of the rotating platform up so that it clears the stepper motor since it extends further out. I may just order a longer timing belt, which would allow me to lower it back down to where it was.

 

[terryforsythe]

Here is a short video of a test of the prototype measurement swivel:

 

[Hubi74]

What was your initial reason for moving the crossover frequency? Were you just curious and experimenting, or did you have a concrete thought behind it?

 

[terryforsythe]

What was your initial reason for moving the crossover frequency? Were you just curious and experimenting, or did you have a concrete thought behind it?

In stock form, the THD is a bit high at the lower end of the midrange's range, peaking to about -34dB at 86dB SPL at about 220Hz, and about-25dB at 96 SPL at the same frequency. Also, the woofer is fairly flat to 1kHz.

I only can speculate as to why Andrew Jones chose to cross them over at 180Hz. It could be that he did it to optimize the vertical off-axis response, to avoid the core losses of the laminiated steel core inductors from interfering with the midrange frequencies, to optimize time alignment, etc., but I really don't know.

Nonetheless, the use of DSP opens up a lot of flexibility in the design. Just moving the woofer/midrange crossover frequency to 400Hz reduced the THD quite a bit. I also added additional internal bracing and glue fillets at the cabinet joints, which reduced the THD even further. Using steep crossover slopes mitigates the vertical off-axis response penalty of moving the crossover frequency from 180Hz to 400Hz.

As far as the midrange/tweeter crossover frequency, I have been experimenting with trying to optimize the directivity index. I have come to the conclusion that my initial measurement set is not adequate for modeling that in VituixCAD, which is why I built the spinorama turntable. I have that working. My next task is to work out a way to mount it to my Little Giant ladder. The next chance I get to borrow my son's truck I need to pick up wood, etc. to build a mounting frame.

After I have a more complete driver measurement set I will get back to optimizing the design model. Really, though, the speakers sound really good at this point. I'm not sure how audible future refinement will be, but it is a fun project that I enjoy.

See the full measurements of the stock UBR62 from Erin's Audio Corner here: https://www.erinsaudiocorner.com/loudspeakers/elac_ubr62/

 

[terryforsythe]

What was your initial reason for moving the crossover frequency? Were you just curious and experimenting, or did you have a concrete thought behind it?

Also, take a look at Erin's Response linearity graph. The midrange is being pushed a little hard below 400Hz.

Moreover, in stock form with the passive crossovers, the speakers were a bit lackluster with regard to dynamics. The bass was not as tight as I like, and lacked impact, even when using a subwoofer. The DCR of the two inductors in series with each woofer measured 1.6 ohms. The woofers themselves are 4.15 ohms. The damping factor is way too low for my preference. Running straight from the amplifier to the woofers significantly increased the damping factor. See this post where I compare the damping factor with the passive crossover vs the passive crossover removed: https://www.audiosciencereview.com/...e-ubr62-bookshelf-speakers.51780/post-2269616

 

[terryforsythe]

Here is a screenshot from my tuning session today. Specifically, I have been working on the THD. I set the SPL to 86dB @ 1m, then moved the microphone to 0.5m to minimize the impact of room reflections, though they still are there. By stuffing the midrange cavity full of damping material, moving the woofer/midrange crossover frequency to 300Hz resulted in the lowest THD. I am not sure whether I will leave it there, though. I'll know after I run some linearity measurements. Nonetheless, the THD is significantly improved over the stock speakers:

The worst offender now is the tweeter up around 6-7kHz, but there is not much I can do about that.

For reference, here is the THD of the stock speaker as measured by Erin's Audio Corner at the same SPL:

 

[Waveform Fidelity]

There is another aspect of moving all active worth discussing, and that is the impact of the passive filters (crossovers) on the sound.

1. Going all active increases the efficiency of the speakers:

All of the UBR62 drivers have a DC resistance slightly over 4 Ohm (the woofer is 4.15 Ohm if I remember correctly). The stock passive crossovers implement two inductors in series with the woofer, one having 1.2 Ohm DCR and the other having 0.4 Ohm, for a total series DCR of 1.6 Ohm. The inductor in series with the midrange has 1 Ohm DCR.

Thus, the inductors in series with the woofer are dissipating somewhere between 25-30% of the power driving the woofer, and this is ignoring inductor core losses. The inductor in series with the midrange is air core, so no core losses, but still is dissipating 15-20% of the power driving the midrange. (The impedance of the drivers varies with frequency, so these are just estimates.)

2. Going all active increases the damping factor (DF), significantly:

DF correlates with the amplifier's ability to control speaker motion. A high DF results in a more controlled (e.g., tighter) bass response. DF is defined as the ratio of the rated impedance of a loudspeaker (the actual driver) to the source impedance of the power amplifier (it's output impedance), and is calculated as DF = (ZL + ZS)/ZS, where ZL is the load impedance (of the driver) and ZS is the amplifier's output impedance. (https://en.wikipedia.org/wiki/Damping_factor). The more simple form of the equation, DF = ZL/ZS, commonly is used.

This definition is overly simplistic for passive speakers, though. It only considers, for the source impedance, which is the output impedance of the amplifier, without any consideration to the impact of passive filters (crossovers), speaker wire, etc., in the circuit between the driver and the amplifier. There is much confusion in the audio industry regarding these considerations. Even KEF confuses this issue, taking into consideration the speaker wire, but completely ignoring the significantly larger issue of passive filter components in the circuit (https://us.kef.com/blogs/news/damping-factor-explained).

Here is an article that explains DF pretty thoroughly: https://sound-au.com/biamp-vs-passive.htm. As explained in that article, passive filter components do need to be considered when determining DF. From the view of the driver for which DF is computed, the passive filter components add to the source impedance (ZS).

With my speakers, let's do a very simplistic computation of DF for the woofer, assuming the output impedance of the amplifier is very low so as to be negligible (mine is) and the DCR of the speaker wire is low enough, in comparison to the passive filter components, to be negligible. Thus, this computation just is using the DCR of the inductors, and ignoring all other contributors to the source impedance to make this calculation simple while still getting into the ballpark: DF = (4.15 + 1.6)/1.6 = 3.6. That is very low, and may be one of the issues causing me to perceive a lack of dynamics in the stock speakers - the amplifier does not have adequate control over the woofers, and thus they have sloppy bass.

Going all active, my source impedance is the sum of my amplifier's output impedance (< 50 uOhm) and the speaker cable (< 150 mOhm). Now, DF = (4.15 + 0.15)/0.15 = 28.7. That is nearly 8x higher than the DF computed based on using the passive filter.

One big caveat to the above calculations is that I only computed DF using DCR and did a lot of hand waiving to make the calculations simple, but in reality the DF is determined by the actual impedances, which vary with frequency. Still, these simple calculations show the benefit of going all active and the positive impact on speaker dynamics. The article to which I posted the link delves much further into this topic.

Just following your post here. Most really good passive loudspeakers are let down by their crossovers. Its not that the passive crossover design is bad, but because tradeoffs with sensitivity, power loss and impednace put heavy constrains of the filter design for the crossover. Most crossovers are 2 port networks and easy to analyze. If one looks “backwards “ to the amplifier from the crossover output, one can see the source impedance which is driving the speaker driver. The driver impedance alone is highly variable - so you have the interaction between highly variable source impedance and variable driver impedance too - not simple when the signal is music. Bring along a active design driving the voice coil directly by the amplifier and you get the intended transfer function of the crossover. Thats why, in my opinion, active designs sound more “dynamic” KEF have realized this for years. The LS60 is try and see approach in to big dsp loudspeaker. They (not the engineers) have been clinging to the old days of people buying Amps and passive speaker separately. The cost of DSP and class D amps is now very small and the benefits to sonic improvements huge, its a no brainer to transition to active. I hope they transition before its too late.

On your point about cables….its all about product marketing and fueling the imagination that the sound is affected by ultra low resistance cables. That power of suggestion makes people part with hundreds of dollars despite scientific reasoning that no practical difference is present. I find it funny that these esoteric cables have micro-ohms of impedance up to the loudspeaker terminals, and then just inside the cabinet is a series resistor in the crossover and thin wire to the driver, which of course offsets esoteric cable claims.

 

[Cbdb2]

Did you measure the passive crossover (before the drivers) or are you assuming its flat except for the resonance? Because thats not always the case, and what you might be hearing is an EQ change. Im speaking from experiance. I "activated" a pair of decent passives and used my crossover measurements ( not flat at all) ,to set up the active filters so the freq. response of the signal hitting the drivers was the same . I also time aligned the drivers. After I finished one I compared them (which I would recomend if you want to hear the differance) and could not tell the difference. Maybe the passives crossovers were well designed maybe the drivers werent the greatest, maybe they needed to be louder (making the passives hot) dont know.

I believe that the bigest advantage with actives is dsp, not an easy diy, and in high power monitors. But mainly more income for the manufacturers, active filters are free if your going to use dsp anyway where as high power low distortion caps and inductors are expensive. And the buyer now buys the amps from the speaker maker, win win for the manufacturer.

 

[terryforsythe]

Did you measure the passive crossover (before the drivers) or are you assuming its flat except for the resonance?

I don't know to which post you are replying, nor to which type of measurement to which you are referring. Impedance? If you are referring to the damping factor, the following post is where I presented the comparison of the damping factor with the passive crossover to the damping factor without it: https://www.audiosciencereview.com/...-bookshelf-speakers.51780/page-3#post-2269616

EDIT: I re-read your post. Perhaps you are referring to frequency response measurements. Yes, I had taken measurements. I had a miniDSP SHD I used with the speakers for about a year. I did a lot of tuning, both with EQ and Diract Live, and experimented a lot with different crossover slopes and frequencies for the subwoofer integration. The upper midrange and highs sounded good, but the bass from the Elacs lacked dyamics and was not tight, regardless of how much tuning I did. At first I thought I could live with it, but after a while it became annoying. I sold the SHD and purchased a HTx and amplification. The first time I fired up the system, even before tuning, I could hear the difference in the bass. Since then I have added additional bracing, damping material, etc., which have further improved the speakers both objectively (see the THD graph above and the damping factor data) and subjectively.

 

[terryforsythe]

The LS60 is try and see approach in to big dsp loudspeaker.

I have a pair of KEF LS60s (you can see the bottom of one of them in the cover photo for the video in post #65). They are dynamic and have very tight bass; they sound very good.

 

[Cbdb2]

I don't know to which post you are replying, nor to which type of measurement to which you are referring. Impedance? If you are referring to the damping factor, the following post is where I presented the comparison of the damping factor with the passive crossover to the damping factor without it: https://www.audiosciencereview.com/...-bookshelf-speakers.51780/page-3#post-2269616

EDIT: I re-read your post. Perhaps you are referring to frequency response measurements. Yes, I had taken measurements. I had a miniDSP SHD I used with the speakers for about a year. I did a lot of tuning, both with EQ and Diract Live, and experimented a lot with different crossover slopes and frequencies for the subwoofer integration. The upper midrange and highs sounded good, but the bass from the Elacs lacked dyamics and was not tight, regardless of how much tuning I did. At first I thought I could live with it, but after a while it became annoying. I sold the SHD and purchased a HTx and amplification. The first time I fired up the system, even before tuning, I could hear the difference in the bass. Since then I have added additional bracing, damping material, etc., which have further improved the speakers both objectively (see the THD graph above and the damping factor data) and subjectively.

What I was asking was if you did frequency response measurements at the driver inputs after the original passive crossover, with a DMM.

 

[terryforsythe]

What I was asking was if you did frequency response measurements at the driver inputs after the original passive crossover, with a DMM.

No. The only frequency response measurements I took were with REW and Dirac Live. Nonetheless, frequency response was not a significant issue for me; in stock form the frequency response was pretty good, and with my SHD I had the ability to optimize it further, including room correction. The significant issues I intended to address by going all active and changing the woofer/midrange crossover frequency were THD, damping factor and response linearity. You can check out Erin's measurements (https://www.erinsaudiocorner.com/loudspeakers/elac_ubr62/) to see the THD and response linearity issues. For the damping factor refer to my simulation to which I provided the link.

 

[Waveform Fidelity]

I have a 19 ft. ladder (Little Giant), and nothing but trees behind my house for a few hundred meters. I'll still get some reflections off of the house and the ground, though. A portion of my house only is one story. If I put the ladder on that side of the yard, the speaker will be above the bottom of that portion of the roof line, thus reducing direct reflections.

To address ground reflections, I'm considering building an A-frame out of two 4ft. x 8 ft. plywood panels, covering that with insulation, and placing it on the ground between the speaker location and the microphone location. That may help reduce ground reflections a bit.

I do the same, Just place out the acoustic foam on the floor.and it does attenuate the floor reflection at medium frequencies. The other thing you can do is to mount the loudspeaker with the drivers facing skyward. With the cabinet a few feet off the ground, the ground reflections are much smaller as the drivers are mostly radiating towards the sky with only a little energy backward towards the ground. If you put absorber there it helps also. At low frequencies you need LF absorber a foot or so thick.

 

[terryforsythe]

Someone requested information on the speaker swivel setup. Here are links to the code and notes in Google Docs.

c++ code for the Adafruit ItsyBitsy controller:
https://docs.google.com/document/d/10wD4b7UR8v50WHPFHFuK0yz3xInsSkIPP4k2B9Npf-0/edit?usp=sharing

Python code for the User Interface:
https://docs.google.com/document/d/1oOfAn9XkeB79seE6KC5B5qNTPhNGkp3o4Nadbv5lvgk/edit?usp=sharing

The user interface runs on Linux and Windows using Python. It also may work on a Mac, but I have not tested it.

Here is a link to notes for using it:
https://docs.google.com/document/d/1qE0cRJhmeEhFoTQvvIdHkSx0EpI7wzNtZMJEaeFMAA8/edit?usp=sharing

I am still playing around with the CAD design for the swivel setup. After that is done and I will put everything in Github. It will be some time before I get to that. I have been entrenched in other projects and, frankly, the speakers sound terrific. I'm not sure how audible will be any improvements to the DSP. Nonetheless, I should get around to doing the full set of measurements before summer.

 

[Domi222]

 

[Domi222]

My idea. Profile 45x45. Diameter 60cm. Nema 23. Lazysusan 16 inch. Load capacity up to 150 kg