Modifications to Elac Uni-Fi Reference UBR62 Bookshelf Speakers

[terryforsythe]

I just went back and studied all of the harmonic distortion data that I have in more detail. I hypothesize that the passive crossover used in the stock speaker had the effect of moving the midrange's HD peak from about the 150 Hz frequency in my measured data to the 220 Hz frequency shown in Erin's data. Since I am not using a passive crossover, that shift is not happening.

At about 320 Hz you can see the harmonic distortion getting above the noise floor in my woofer data, though. The DSP is affecting it somewhat, and it peaks at 372 Hz in my 86dB/1m distortion measurement.

The other aspect of these measurements worth noting is that the midrange's harmonic distortion primarily is 2nd harmonic. From about 260 Hz to 410 Hz the woofer's harmonic distortion primarily is 3rd harmonic, which tends to be harsher than 2nd harmonic distortion.

I gave consideration to shifting the woofer/midrange crossover frequency down to 350 Hz to see if I would tame down the woofer's 3rd harmonic distortion before the midrange's harmonic distortion begins to have a significant affect. However, after going back and looking at Erin's response linearity data (again, Erin's Audio Corner - check it out if you haven't, it is a great website - https://www.erinsaudiocorner.com/), I think that would be counter productive. In fact, after reviewing Erin's data, I may bump up the woofer/mid crossover point to 500 Hz. Here is Erin's graph:

 

[terryforsythe]

Regarding the issue at 700 Hz in the above graph, the stock midrange crossover has a tuned resonant circuit at that frequency. Perhaps the resonant circuit is contributing to the non-linearity issue at 700 Hz, perhaps it is just the midrange, or perhaps it is a combination of both. At this point I don't know. But, that anomaly looks very abnormal. I lean toward thinking the resonant circuit has something to do with it. At some point I am going to try to generate response linearity data using REW to check if my midrange, without a passive crossover, exhibits the same non-linearity there.

 

[droid2000]

Why are you doing this?

 

[dfuller]

I am thoroughly enjoying seeing your crossover design process.

 

[terryforsythe]

Why are you doing this?

Multiple reasons:

1. There are aspects of the UBR62 speakers that I like, such as imaging and soundstaging, but in certain music to which I listen they lack dynamics. Some music is not as fun to listen to on them as it was with my old speakers, which my wife referred to as "coffins". I really miss having dynamic speakers in my family room.

2. Replacing the UBR62s with something better is not an option unless I can find speakers just as small that match our decor just as well. (See the last paragraph of my first post). I looked, but did not find any. I did get a pair of KEF LS60s "for my office" hoping I could work my way to moving them into the family room. That was shot down, but I am really enjoying them in the office,

3. It is a fun project. I'm enjoying it. With the results I am hearing it makes it even more rewarding. Really, the performance improvement so far is significant, and I have not even finished tuning them.

 

[terryforsythe]

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.

 

[terryforsythe]

I have been working on the harmonic distortion issue. My initial assumptions regarding the midrange were incorrect, at least partially.

I originally thought the harmonic distortion peak between 180 Hz and 380 Hz in Erin's measurements (as well as my original verification) was completely due to the midrange. This was not correct. It is the cabinet. This surprised me because the cabinet is relatively sturdy and has a pretty beefy vertical brace extending top to bottom. Anyway, I added more "No Rez", trying to cover every surface I could inside the cabinet. This helped.

Comparing the THD of the two drivers in their respective portions of the cabinet, the woofer now has lower THD below 300 Hz and the midrange has lower THD above 300 Hz.
So, today I changed the woofer/midrange crossover frequency to 300 Hz, and tuned for that. The response linearity did not seem to suffer a whole lot,

I still have not ran Dirac Live. I'll do that when I am done fiddling around with the crossovers and EQ.

Below are the midrange and woofer FR and HD plots at high output, measured at 1m (in-room, NOT anechoic) - I had crossovers active since I was focusing on the upper bass/lower midrange, but equalization was turned off.

Midrange:

Woofer:

I hypothesize that the midrange has lower THD above 300 Hz due to its small sub-volume within the larger enclosure - it is a little more isolated from the cabinet vibrations.


In the following chart I SPL matched the midrange frequency response at approximately 76 dB to the frequency response at about 96 dB. I used 500 Hz as the matching frequency. Again, it was done in-room and not anechoic, but it gives an idea of the midrange's response linearity.

 

[terryforsythe]

I think I have settled on a 400 Hz crossover frequency. In comparison to the 300 Hz crossover frequency, I didn't hear a difference between the two with regard to harmonic distortion, but the dynamics are slightly better using 400 Hz.

 

[terryforsythe]

I have adjusted the time delay on the drivers to get them time aligned at the crossover frequencies. The sound stage is improved. Greater height, width and depth.

At this point the overall improvement of my Elacs in sound quality over their stock form is vast. More dynamic, cleaner, tighter bass, bigger sound stage, more transparent, etc.

 

[kemmler3D]

Very cool thread, and thanks for taking the time to share all the measurements and thought processes going into this. Frankly I have seen ground-up DIY projects that are not thought through this well.

Since you're already this far along and cabinet resonance has been identified as an issue, have you thought about adding bracing in addition to the damping material? If you do it right, you can kick the resonances up to frequencies high enough that they don't get excited much by music content and diminish their overall influence.

 

[rirelien]

The discussion on damping factor is interesting. Is there any discussion about this when thinking about active (whether analogue or DSP) vs passive crossovers you or anyone can point to?

Amplifier efficiency gains you postulate are significant too.

Next step: design from scratch!

 

[terryforsythe]

Very cool thread, and thanks for taking the time to share all the measurements and thought processes going into this. Frankly I have seen ground-up DIY projects that are not thought through this well.

Since you're already this far along and cabinet resonance has been identified as an issue, have you thought about adding bracing in addition to the damping material? If you do it right, you can kick the resonances up to frequencies high enough that they don't get excited much by music content and diminish their overall influence.

Thank you!

Not much more room for additional bracing. There is a vertical brace, parallel to the baffle and back of the speaker, that runs top to bottom and left to right. It is attached to all 4 sides of the enclosure. It has a large cutout in the center bottom and two small cutouts at the top sides.

I covered as much of the inside as I could, without interfering with the drivers, with "No Rez". In the midrange cavity there is not much room at all, but I put No Rez on the outside back of it and No Rez, with the foam pulled off, on the outside bottom (the top and sides are the enclosure top and sides). (No Rez is a 2mm thick rubber sheet with 25mm of moderately dense foam attached. The back side has an adhesive that is very sticky - very hard to pull off once it is on).

The No Rez helped quite a bit. But, even after covering as much of the inside as practical, and considering the brace in the enclosure, I am surprised how much the enclosure still vibrates around 460 Hz. The back of the enclosure was a little thinner than I expected, maybe 1/2" or so? That may be part of the issue. The next time I pull them apart I will measure the wall thicknesses.

I have built speakers before using 3/4" MDF, with internal braces, but don't recall having an enclosure vibrate that much. I'm wondering what type of adhesive Elac used to glue the enclosure together, and whether that also is part of the issue. I used to use Elmers wood glue, which worked well.

On a positive note, due to its small size, the midrange cavity does not resonate nearly as much as the rest of the enclosure - the midrange is significantly less affected by the vibrations at 460 Hz than the woofer. That is why I moved the crossover frequency lower - previously I was playing around with 450-500 Hz. I tried 300 Hz, and it was OK, but I think 400 Hz is a better balance - I am using 48 dB/octave L-R crossovers, so the woofer output drops very fast above 400 Hz, which significantly reduces the vibration.

 

[terryforsythe]

The discussion on damping factor is interesting. Is there any discussion about this when thinking about active (whether analogue or DSP) vs passive crossovers you or anyone can point to?

The link I posted is to the most in-depth discussion I found on the topic: https://sound-au.com/biamp-vs-passive.htm

 

[terryforsythe]

I have built speakers before using 3/4" MDF, with internal braces, but don't recall having an enclosure vibrate that much. I'm wondering what type of adhesive Elac used to glue the enclosure together, and whether that also is part of the issue. I used to use Elmers wood glue, which worked well.

Pondering over this, in hindsight I wish I would have put a a fillet of wood glue at all of the joints inside the enclosure. This may have helped a little, I don't know. It is too late to do it now, though. Detaching the No Rez from all of the walls to actually get to the corners would be a nightmare. That stuff is very sticky.

 

[terryforsythe]

I came across the following video. In it, John Heisz experiments with different damping materials for a sealed enclosure, measuring cabinet vibrations with an accelerator:

That gave me motivation to add fiberglass insulation inside the main (woofer) section of the enclosures. It helped. For the woofer, it brought the THD down about 2 dB or so, almost across the entire range I have the woofer operating.

After that, I played some more with the woofer/midrange crossover frequency. 325 Hz provides the lowest overall THD.

Previously I compared 300 Hz to 400 Hz, but I thought the dynamics were slightly better at 400 Hz. I am going try 325 Hz for a while, then go back to 400 Hz, and see if I notice a difference. If not, 325 Hz looks like a good choice, at least from the perspective of THD.

Side Note: In John's experiment rubber actually made the cabinet vibrations slightly worse. The No Rez I used has a rubber backing, so it may not have been the best choice. At this point it is staying put, though. It is so sticky that pulling it out will be a P.I.A.

 

[terryforsythe]

A Tale of Two Speaker Cabinets

Initially all of my harmonic distortion (HD) measurements were made on one speaker. I finally got around to measuring the other one. The second one had a bit better HD and, crucially, did not have two HD peaks the first speaker had in the mid 400 Hz and 800 Hz ranges. I had a mystery to be solved.

I disassembled the first speaker and measured the drivers outside of the cabinets. The HD peaks were not there. I inspected the inside of the cabinets and noticed there was not much adhesive visible around the seams. I got to work adding fillets of wood glue where I could reach, let that dry, and then re-assembled the speaker. The two peaks improved significantly. More glue might improve it further, but with all of the No Rez I added inside it is difficult to get into some places.

This morning I disassembled the second speaker. In that speaker I could see that enough adhesive was used so that it oozed out of the seams before drying. Clearly, the second enclosure was glued together much better than the first and, hence, the better HD measurements - the cabinet vibrates less.

Another thing I noticed is that the HD of the first speaker was a little worse in the most recent measurements (before adding the glue) compared to my initial HD measurements. That speaker has been moved around a lot and disassembled/re-assembled multiple times. I hypothesize that in doing so, with a deficit of adhesive, the joints had loosened up a little.

Crossover Frequencies

For the midrange/tweeter crossover point, 2500 Hz provides the best directivity index for these speakers, though still not perfect, while 2250 Hz provides the lowest HD. I mostly have been using 2500 Hz but decided to give 2250 Hz a try. That negatively affected sound staging - the width narrowed so as not to extend much beyond the right and left speaker locations and the depth narrowed a bit. I went back to 2500 Hz and the sound stage opened back up. I do not hear the difference in HD changing between the two crossover frequencies. My conclusion here is that the directivity index is critically important to sound staging and, for these speakers, it is worth compromising a little bit of HD to optimize the directivity index.

For the woofer/midrange crossover point, 325 Hz provides a bit lower HD than 400 Hz. I left the crossover point at 325 Hz for a few days, and then went back to 400 Hz. Again, I do not hear the difference in HD, but the speaker sounds more dynamic with the 400 Hz crossover point. Previously I measured the response linearity of the midrange (bottom chart of my Feb. 6 post above), and it leaves a little bit to be desired. I suspect that is the reason for the difference that I am hearing.

The midrange's HD is significantly lower than the woofer's above 300 Hz due to the cabinet, so moving the crossover point higher than 400 Hz will introduce more HD. Nonetheless, I am going to go back into the first enclosure to try to add glue to more seams to try to improve the HD a bit further. Then I will try 450 Hz and 500 Hz crossover frequencies to investigate whether dynamics can be improved even further without an audible increase in HD, though at 400 Hz the dynamics already are very good - vastly superior to the 200 Hz crossover frequency of the stock speakers. Eliminating the passive crossover components (especially the 3 steel core inductors in the woofer section and the one steel core inductor in the midrange section) and going all active probably also does contribute to the improved speaker dynamics.

 

[terryforsythe]

Here's an update on the project:

To address the cabinet resonances, I ended up pulling out most of the No Rez (pain in the butt), and added fillets of wood glue to the cabinet joints.

I also added an additional brace, placed perpendicularly between the existing brace and the back of the cabinet, extending from the top of the case down about 12 cm (that was the largest brace I could fit through the binding post plate cutout).

I then stuffed the cabinets with fiberglass insulation, leaving a bit of room around the drivers. The ports are plugged, so I didn't need to worry about interfering with them.

I don't have an accelerometer to measure the cabinet vibrations, but just putting my hand on top of the cabinets I can feel the vibrations have been reduced quite a bit. I also put some inexpensive isolation pads (from Amazon) between the speakers and the stands. This helped mitigate audible vibrations I could hear when running frequency sweeps.

Today I again played with speaker locations, equalized the speakers for my listening position, and then I ran Dirac Live. I tuned to the Harman curve, but with the bass boost lowered about 2.5 dB from the stock curve (still around about 4.4 dB of bass boost).

With the latest round of modifications and tuning, the sound staging and imaging have improved even more. The bass response is very good and the speakers are very dynamic. At this point the system sounds extremely good, even better than I anticipated when starting this project. The project was well worth the effort, and it was fun.

For the time being, I have three pairs of speaker cables running between each speaker and the wall plates. I received new 8 x 13 AWG cable. I will switch over to that after the connectors arrive (Weipu SA28) and I 3D print new connector plates for the speakers. For the wall plates I have blank plates I will drill out for the connectors.

Since the new cable has 8 conductors, I will double up on wires for the woofers. I am going to sleeve the cable to make it look nice. The primary cables will be short, for when the speakers are placed against the wall for the wife approval factor, but I am going to make extension cables to use when I pull the speakers into the room for my listening.

At some point I will do a side by side comparison to my LS60s. The LS60s are heavy and a little awkward to move. I don't want to risk damaging them, so I won't do it until I have someone to help me move the LS60s. It will be an interesting comparison and, at this point, I'm not sure about which I will like better. My family room, where I have my Elacs, is much larger and more open than my office, where I have the LS60s. Thus, my family room is a much better fit for my music listening tastes. So any comparisons now would be apples to oranges and not provide any insight as to how they truly compare.

 

[Ze Frog]

I have removed the passive crossovers from my Elac Uni-Fi Reference UBR62 Bookshelf Speakers and gone all active. In doing so, I moved the woofer/midrange crossover frequency from 200 Hz to 450 Hz.

Side Note: Elac specifies the woofer/midrange crossover point as being 260 Hz, but my pair measured 200 Hz, which coincidentally is the specified crossover frequency for the Uni-Fi Reference towers. I don't know whether the published specification for UBR62 is wrong or the factory put the wrong crossovers in my speakers. It is water under the bridge now.

I only have a short time listening to them, and I have not yet tuned with Dirac Live. I'll do that after I get the extra cables I need for the individual woofers, midranges and tweeters ran through the wall. Hopefully this week.

Nonetheless, yesterday I did a quick comparison of one all active speaker to the other speaker in stock form (level matched, but not performed as a scientific experiment - just a quick comparison only to give me a quick sense of whether I was proceeding in the right direction). The improvement in the upper bass/lower midrange dynamics is significant. The changes took the modified speaker to the next level. This morning I modified the other speaker and spent some time listening to them. Wow, what an improvement!

I think Elac crossing the midrange at 200 Hz was pushing it a little hard, which can be seen in the harmonic distortion and linear response data Erin posted in his review of these speakers at Erin's Audio Corner. Also, eliminating the passive filter components probably helped with the dynamics.

I'm sure the question will be asked as to why I modified the Elacs instead of just getting better speakers. Long story short is that after our home renovations the boss (a.k.a. my wife) insisted on NO speakers in the family room. I wanted my stereo system operational, so a compromise was needed. The Elac UBR62 speakers in oak/white with the gray grills were the best fit I could find to match the aesthetics of our family room, and the reviews generally were favorable. I purchased them, having never heard them, and a pair of nice looking stands. I set them up while the boss was away. She came home, saw them, and stated “those look OK, I could live with them.” Mission accomplished, at least so I thought. The sound staging and imaging of the UBR62s was impressive, and initially I was pleased. But after spending some time with them, and turning up the volume a bit when the boss was away, the dynamics of the speakers were underwhelming and left me wanting something better. Now I have it, and the boss still is happy.

Sometimes there's no need to buy new speakers, and as you have seen. A lot of crossovers in even vastly more expensive stuff can be a bit of a ' it's good enough ' kind of approach and then just be done with nearest component values for the cheapest price. Glad to hear you finally unlocked what the speaker really could actually be, always extremely rewarding.

 

[terryforsythe]

The top picture is my temporary binding post setup. The bottom picture is the new terminal plate with the 8 pin connector. This is just a sample connector I got off Ebay. Once I confirmed it will work I ordered all the connectors I need from Weipu, though in silver. Black looks fine on the back of the speaker, but not on the wall plate.

 

[dagfinn]

Nice, fully active is another level . I'm converting my 4-way JBL250Ti's, one speaker is ready while I'm waiting for parts for the second (currently bi-amped). I'm considering 2x speakon, but one 8-pin is even cleaner. What do you call that connector?

Dagfinn