XR6 Frequency Response

[whoaru99]

What is the sweep time typically? Do you have to wear ear protection when the system chirps?


-Gregory

There are a couple of factors that affect the sweep time, but looking at my setup it appears sweep is roughly 5 seconds, then a couple seconds for the system to compute and plot the graph.

 

[c_dk]

The two in parallel are replacing the one 5 ohm. I believe R5 in series knocks it down and with the change in c2 there is less overlap with mid dome. Note polarity change was only on the 16.

It takes a bit of time for the signal to load up the room so lower frquencies take longer to register.

Since the test signal is superimposed with white noise it is much easiler on the ears at a 70 to 80 dB and much more indicitive of actual music.

Like I've said many a time you need to eq the speakers while they are in the listening position with the microphone near your prime sitting area. This will allow you to use the 104 for it's intended use, to help control the rooms standing waves.

Again the XR series of speakers are 30 year old designs and if you want to try to update the sound I would first try to solve the physical problems before trying to eq out the percieved problem.

 

[Gregory]

The two in parallel are replacing the one 5 ohm. I believe R5 in series knocks it down and with the change in C2 there is less overlap with mid dome. Note polarity change was only on the 16.

It takes a bit of time for the signal to load up the room so lower frequencies take longer to register. Since the test signal is superimposed with white noise it is much easier on the ears at a 70 to 80 dB and much more indicative of actual music.

Like I've said many a time you need to EQ the speakers while they are in the listening position with the microphone near your prime sitting area. This will allow you to use the 104 for it's intended use, to help control the rooms standing waves.

Again the XR series of speakers are 30 year old designs and if you want to try to update the sound I would first try to solve the physical problems before trying to EQ out the perceived problem.

I'm starting to lose focus on the project. Isn't the purpose of the MQ104 Bass section to correct loudspeaker response? Since there are multiple complex nulls (standing waves) in a room, and since we have no "listening position" except for maybe DVD video viewing, the objective of these exercises is to acceptance test the rebuilt speakers and generally balance them in frequency response.

In looking at the XR6 and XR16 schematics, the series inductors L1 & L2 in the bass section define the low pass filter edge along with shut capacitors C1 & C3 to form 2nd order filters. The input capacitors C2 & C4 in the LM cone and UM dome driver circuits define the high pass filter edge along with shunt inductors L3 & L4.

Increasing the series capacitor lowers the high pass filter freq.
Decreasing the series capacitor raises the high pass filter freq.

Increasing the series inductor lowers the low pass filter freq.
Decreasing the series inductor raises the low pass filter freq.

and so forth with the shunt elements.
​

If you transpose L3 & R6 on the XR16 schematic (redraw it) it looks to me like R5 & R6 form a voltage divider and act like a fixed volume control or attenuator. If so, that means amplifier power in that band is dissipated as heat. What about cutting those frequencies with the EQ instead of dumping the power?

It's been a long time since the circuit analysis days. :yes: I'm seeing what looks like Zobel filters (the series R & C elements) in the bass and LM circuits parallel to the dynamic drivers. Also note how the tweeter circuits haven't changed. Before modding the crossovers, it would be a very good idea to model the circuits first before chopping.


-Greg

 

[c_dk]

My interest in this thread follows two paths:

Exploring ways people can use their MQs for room equalization without someone like me bringing over my equipment.

Finding solutions to XR speaker prolems whether bad drivers, replacement drivers, bad crossover parts, or known or suspected cabinet issues.

You have asked a number of times if I had ever close micked the XR speakers and quite frankly I never did because I had no interest in "checking" Roger's work.

I did have hundreds of occasions to measure them interacting in a customers room and can supply insight only in that type of senario. The MQ's were called enviromental equalizers not speaker equalizers. So maybe we should open a new thread.

In the case of the first 4 XR designs, as well as the MLs, we all knew there were issues with the grille/door because they sounded so different with them open or off. THERE WAS NOTHING WE COULD DO for it because music lovers were not going to remove grilles to listen like audiophiles might so we did the best we could and quite frankly most did not care. Now 30 years later we KNOW that there are cancelations caused by the interactions as shown in the comb filter plot we saw years ago and Gregory has shown with his plots.

So do you all hear a different sound with the grilles off also? Gregory did you run a plot of the speaker with the doors open vs door closed? This is where modern FFT analysis would allow us to see the interactions in time. I know where a pair of 3s are available to test, maybe I can find a pair of 6s.

One more note on the MQ104. Since room issues seem to come in 3s the 104 often did not have enough filters so the 107 gave much more flexibility.

Gregory if you don't like the timbre balance of Roger's work in the XR6 changing the level of an original driver by a resistor change of an ohm or two is not significant.

 

[Gregory]

My interest in this thread follows two paths. 1) Exploring ways people can use their MQs for room equalization without someone like me bringing over my equipment. 2) Finding solutions to XR speaker problems whether bad drivers, replacement drivers, bad crossover parts, or known or suspected cabinet issues.

You have asked a number of times if I had ever close Mic'd the XR speakers and quite frankly I never did because I had no interest in "checking" Roger's work. I did have hundreds of occasions to measure them interacting in a customers room and can supply insight only in that type of scenario. The MQs were called environmental equalizers not speaker equalizers. So maybe we should open a new thread.

In the case of the first 4 XR designs, as well as the MLs, we all knew there were issues with the grille/door because they sounded so different with them open or off. THERE WAS NOTHING WE COULD DO for it because music lovers were not going to remove grilles to listen like audiophiles might so we did the best we could and quite frankly most did not care. Now 30 years later we KNOW that there are cancellations caused by the interactions as shown in the comb filter plot we saw years ago and Gregory has shown with his plots.

So do you all hear a different sound with the grilles off also? Gregory did you run a plot of the speaker with the doors open vs door closed? This is where modern FFT analysis would allow us to see the interactions in time. I know where a pair of 3s are available to test, maybe I can find a pair of 6s.

One more note on the MQ104. Since room issues seem to come in 3s the 104 often did not have enough filters so the 107 gave much more flexibility. Gregory if you don't like the timbre balance of Roger's work in the XR6 changing the level of an original driver by a resistor change of an ohm or two is not significant.

First off, I appreciate all of your input both here and by PM/email. After thinking about it more today, the OBJECTIVE at this point is to verify the rebuilt XR6s are working and that ALL of the rebuilt drivers are functioning and balanced Left vs Right, for instance the buzzing woofer. Of major concern is whether the UM domes, sent back to Mc Parts Dept under RA are functioning properly. They either have LOWER output than the originals, or the XR6s had weak midrange response. Maybe it's because the lower midrange CONES are predominant? THOSE are the immediate goals.

I've not yet decided to replace the Thiels in the main system with the XR6s but it's possible, possibly switching them for months at a time. Maybe I should move the XR6s to the open side of the room and check for output energy there? So let's ask the TWO immediate questions.

1) Are the stock upper mid domes typically weak? or are the rebuilt domes somehow down 6 to 8 dB.

2) Are the lower mid cones typically predominant by 3 to 5 dB?​

Roger says he doesn't know what materials are used in the UM dome rebuild and what their sensitivity is.

There's a replacement UM dome (MDM-55 or something) but I'd not want to modify the system that much yet, and besides I've well over 4 figures into them already, but still less than last retail.


-Greg

 

[c_dk]

I am not going to go into the attic and dig thru boxes to find my old graphs. However to my memory and using Whoaru99's Paradigm 100s as an example:

Paradigm 100 +2 dB at 100 0 at 1000 and -1 at 10k
MLs +5 dB at 100 0 at 1000 and -4 at 10k
Early XRs +3 dB at 100 0 at 1000 and -3 at 10K
Later XRs +2 dB at 100 0 at 1000 and -2 at 10k

I know that Roger changed the timbre balance of the speakers (they became "brighter sounding") and many liked it and many hated it. Remember early on in the OP about where people choose to sit at live musical events. Row 3 sounds different than row 18.

I believe that your speakers are in 1977 spec. as Roger designed them.

 

[whoaru99]

For a point of reference to the above post, the Studio 100v2 spec is 39Hz-22kHz, ±2dB on-axis; 39Hz-20kHz, ±2dB, 30 degrees off-axis

 

[c_dk]

All the measurements I did back in the day were at 12 to 18 feet (normal listening distance) at 15 to 20 degrees off the centerline. I believe that toeing the early XRs helped some with the comb filtering.

I have been puzzling over updates for the XRs. Roger speaks of using a salad bowl as a back baffle for the 8 in driver and later using a plastic dome for this enclosure. I would think that replacing that with a 3/4 in MDF sub enclosure would be much better at isolating the 8 inch from the back waves of the woofer.

Still thinking of a way to tame the door frame cancelations.

 

[Gregory]

All the measurements I did back in the day were at 12 to 18 feet (normal listening distance) at 15 to 20 degrees off the centerline. I believe that toeing the early XRs helped some with the comb filtering.

I have been puzzling over updates for the XRs. Roger speaks of using a salad bowl as a back baffle for the 8 in driver and later using a plastic dome for this enclosure. I would think that replacing that with a 3/4 in MDF sub enclosure would be much better at isolating the 8 inch from the back waves of the woofer.

Still thinking of a way to tame the door frame cancellations.

One way is to open the doors for each listening session, but you wouldn't want to wear out the cloth or 'catches' by repeated opening/closing. There is still the top panel overhang that will reflect energy. IMHO speakers should not be left with their grills off and drivers exposed.

The previous owner of the Thiels left the grills off (later he got them re-clothed at the factory) and the drivers became contaminated with dust and micro-dirt. His son poked one of the tweeters. The whole front baffle board was a cruddy mess. Was able to restore them nicely with lots of help from Thiel.

Had some time yesterday to play around with characterizing the MQ104 NARROW response curve on page 6 of the Owner's Manual and was able to scale, translate and add the bandpass functions.


The 200Hz MQ104 NARROW filter response digitized, translated, scaled and added.


The 200 Hz log response (at 1/3 octave) was translated down to 160 and 80 Hz. The numbers work but there must be a more elegant and automatic way of doing it instead of having to finagle the arrays for each new center frequency.

It looks like using two closely spaced NARROW filters will produce too much ripple in the combined bandpass. I noticed the MQ104 does not hold all of the cap leads tightly in its little press-in receptacles. Suppose they could be soldered /desoldered if done carefully. Those connections could degrade or oxidize over time. An MQ107 would be nice.

It's great to get the old Mc systems back into operation!! :yes


-Greg

 

[Gregory]

XR6's back in the Main System

Wow.. two years have gone by already with this thread.. more like over 2-1/2 years since buying these classic speakers. Starting earlier in the week, the XR6's were hand trucked from the corner to the rack area.

Ain't they beauties!! It's like the 2205 has met its old classmates. :yes:


McIntosh XR6's uncovered and pulled out from the corner a few days ago. Rebuilt UM drivers are lacking damping pads.


What do you mean? Stuck in WHAT era??

Who was it that said: "the flexibility of the C33 is almost mind boggling?" These devices can actually go in the EXT PROC loops (plural) ... the RECORD loop even. Then just hit REC MONITOR.


Bass equalizers for both the XR6 and CS3.5 speakers on test stand.


Time to replace input connectors

Getting underneath.. I noticed that the connector strips are in great need of replacement with a new type banana jack/binding posts. One of the four tabs is broken and they are no longer bright and shiny. The putty isn't sealing the cabinet well and there's probably air leaks at those spots.


Speaker input with broken tab. This whole area needs attention.. and some new sealant around the wires.


Any specific binding posts that you'd recommend?

The two pass-through holes in the bracket are 0.62" dia. It may be a good idea to spray paint these brackets with a coat of satin black, as the existing paint or coating is thin and nonuniform. Then upgrade to and solder gold plated connectors in their place.


Two bracket pass-through holes are 0.62" diameter. QD connectors to be replaced with soldered wires.


In position - or in similar position as before

Here are the XR6's down range.. or make that down room. The furniture is arranged symmetrically LEFT vs RIGHT but will need a little more fine arrangement. The eleven sectional sofa cushions (and six cushion seats) can be used as absorber pads against the walls and hard furniture.

So what happens... get them running and BLOW a FUSE like a dunsky.


Blown fuse on the RIGHT side from too much CW power (25 - 30 watts) at 10 kHz.


Reading SLM externally

On this go-round, I'll be setting up a NEW method of reading the SLM. In 2010 and 2011, I'd walk up to the unit and read the meter, sometimes switching ranges, but merely being "close" to it will introduce errors from reflected energy.. and BIG errors! It wouldn't be difficult to create a CAL curve for the external OUTPUT voltage.


Will be rigging up the EXT OUTPUT circuit and reading a proportional voltage REMOTELY for the next tests.


Wrap-up

Earlier in the discussion the XR6's were tested at 1 meter, 3 meters and in the back corner of the room at 1 meter. Several worksheets were created with the capability to customize SLM cal files (columns of numbers), add an arbitrary UM correction function, apply a C33 EQ curve at any percentage from -100 to +100% knob rotation, and add or subtract a MQ104 function from the measured speaker response.

Many of the problems were solved.. like using the 2205 power meters to set excitation level, adding absorber pads to specular areas, etc. After doing all this the HARD way.. it will be time to switch to Room Eq Wiz later on.


-Greg

 

[Gregory]

SLM Cal for remote measurement

Today was SLM Cal day!! Let's run through this without a lot of explanation.


Step #1

Check out general operation of SLM and the voltage range at the OUTPUT jack. Yep, the DVM is a joke right. It works quite well but someday I must spring for a Fluke. The output at the RCA port ranged from 0.1 to ~0.8 volts with mV resolution. The instruction manual doesn't recommend going above +4 dB to take a measurement because the internal amplifier could go into clipping.


DVM connected to SLM OUTPUT port. A voltage from 0.1 to 0.8 volts is observed. Sig Gen cable (shorter) used above.


Step #2

Arrange a test setup where the Sig Gen can easily be reached and the SLM clearly observed. Cut one plug off a ~12 ft. RCA cable, then strip and tin the ends. The meter below is ~12 in. from speaker grill with the RCA cable connected to the meter.

Two tests were run: at 400Hz in the 70dB range, and 60Hz in he 80dB range. Best to be seated 90° off-axis when doing this.


Setup for characterizing SLM OUTPUT. Sig Gen must be within reach and the sound meter needle visible "straight on" to land it on each tic.


Step #3

Start radiating audio and tweak Sig Gen attenuator so that SLM meter lands precisely on each dB "tic" from -6 to +6 dB, recording the DVM reading in mV at each setting. It's more difficult to land readings at the low end of scale. The charted test data with curve-fit (which tends to smooth out measurement errors) will look like the following.


Plot of raw data measured from SLM OUTPUT jack at each meter "tic."


Do this several times until you're satisfied with the results. You may want to exclude data above +4 dB. Then crunch the numbers to convert voltage to dB and plot.


SLM OUTPUT data converted to dB and re-plotted.


If this is looking good, then apply a CURVE FIT to the charted data and generate a 2nd order Polynomial. Use the three polynomial coeffs to reconstruct the action of the SLM using its output voltage. As a final check.. generate a column of 51 "calculated" sound readings and overlay them on the measured points and model. All should correlate well.


2nd order curve and 51 calculated dB SPL values overlay measured points.


Wrap-up

There.. that only took 3 - 4 hours, but it will be WELL WORTH IT because SPL in the room can now be electronically measured at 1 mV resolution and there will be no "approaching" the SLM in order to read it, except to change range switch in analog versions. BOTH of these improvements (1mV Res and remote measurement) will greatly reduce errors and enhance repeatability.


-Greg

 

[CruzBay]

Hey Gregory, as you know; you're local to me. Want to borrow my AA2 for your research?


Mike

 

[Gregory]

Hey Gregory, as you know; you're local to me. Want to borrow my AA2 for your research?

[IMG http://www.hifirelics.com/mcintoshanalyzer-B.jpg[/IMG]

Mike

Wow Mike.. what a surprise!!

We should discuss that more, and I'm looking to hook up with local Mc enthusiasts.. collaborate that is. :thmbsp:


-Gregory

 

[CruzBay]

I'm local, and would love hook up, but family issues keep things from coming up.

In any case, my AA2 is available at any time, we can make the transfer process by PM's.

I'm in Springfield, I understand you're towards Leesburg, as per previous correspondence.

At this time, I'm caring for my father who recently had a knee replaced, so I'm not at home; rather I'm where the AA2 is. Don't have the graphs (used to have them...) but c-dk has provided them, I see.

PM me, I'll be in Arlington for another few days. Looked at the AA2 (complete with microphone) a few minutes ago.

I was a little late for the '104, but I used this meter to tune a handful of MQ-107's.

Mike

 

[Gregory]

my AA2 is available at any time, we can make the transfer process by PM's. At this time, I'm not at home; rather I'm where the AA2 is. PM me, I'll be in Arlington for another few days. Looked at the AA2 (complete with microphone) a few minutes ago. -Mike

Sounds great.. check for PM or email.

There's a very good change the AA2 "Meter Output 1 Volt FSD" can be rigged-up to a DVM in the same way described above. First I'd like to give it a run according to procedures in the manual. Speaking of manual, do you have one with the unit? are there any floating around to download?

-Gregory

 

[twiiii]

Take your speakers out doors and lay them down pointing straight up. Make sure there is nothing with in 20ft of each speaker and repeat the tests with the mic one meter above the mid range units. This will tell you if there are driver problems. but the resulting curve will be meaningless. Its impossible to make repeatable measurements in a room with furnishings where the slightest movement of the mic, temp. and humidity can make changes in the readings. Plus you are using an uncalibrated sound meter and source. The out door readings will be relative. They won't tell you which is right or wrong only if there is a difference.

Another issue is you cannot EQ the ambient sound of the room only the direct sound. If you EQ at the listening position the direct sound your ear hears first will be inaccurate, throwing off depth perception, and localization information of the images you are try to recreate. Find the position where the direct sound level matches the ambient, Dc. Then voice your system there. If the results at the listening position are unsatisfactory, move your speakers and your location until they become so. To find the Dc, critical distance, start with white noise and the sound level meter being 3 ft from the speaker with a level of 85 db. Then move the meter back slowly to where the level stops dropping with distance. That's Dc, this where is you voice the system using your MQ equalizer. If your listening position is more than 3.16 times from the speaker as Dc, then you are too far away to get the intelligibility necessary for listening. Now I know some will say this method only applies to large spaces, and that's mostly true, but if you want to hear what was the intent of the engineer and the producer and you can't make your room into a listening studio, then the closer to the point source speaker the better. Line source speakers are a totally different species. If a point source has a directionality number of 4, where 1 is a sphere, 2 a hemisphere and 4 half of that , then a full line array such as a XR290 may have a Q of 32, where an Altec speaker with a Large mantaray horn might have a Q of 50. That means a Xr290 has an effective Dc that is possibly 8 times further than XR6. So if you listen to your XR-6 at 6 ft, you could listen to the 290 at 48 ft in the same room. Now because you have two sources playing in the room at the same time, you have to reduce the Dc by half. 3 ft for the XR-6 and 24 ft for the 290. That means if you want to hear the sound with all the imaging originally captured on the recording you buy a Xr290, Xrt 20, 22, ,30, Ik, 2k etc. If you want a more ambient sound like you would hear at a live concert, you might want a shorter column or a hybrid, XRT, 18, 28, or Xr200. For a surrounding all enveloping sound the point source speaker. None is right or wrong, just depends on what your after.

I prefer a live un amplified concert sound, so I have shorter line arrays, with a roll off on the high end above 4 khz to give the live sound presentation. If I want to replicate a small Jazz venue I flatten the response curve and move closer to my speakers.

 

[Gregory]

Take your speakers out doors and lay them down pointing straight up. Make sure there is nothing with in 20ft of each speaker and repeat the tests with the mic one meter above the mid range units.

Another issue is you cannot EQ the ambient sound of the room only the direct sound. If you EQ at the listening position the direct sound your ear hears first will be inaccurate, throwing off depth perception, and localization information of the images you are try to recreate. Find the position where the direct sound level matches the ambient, Dc.

I prefer a live un amplified concert sound, so I have shorter line arrays, with a roll off on the high end above 4 khz to give the live sound presentation. If I want to replicate a small Jazz venue I flatten the response curve and move closer to my speakers.

Thanks but it won't be possible to take an XR6 outdoors. There's not enough open space, the grade is sloped and the area is usually wet after bad weather. If they were beater cabinets, I might consider burying one in the ground up to the baffle plate. Will have to digest what you typed in para #2. Have read it over 2 or 3 times and must boil it down some.

Looks like Mr. Mike will be loaning his AA2, and there are manuals on the web, one at Roger's site: roger-russell.com/ AA2_Manual. That will be a whole new ballgame for me!! The AA2 uses narrow band noise measurements but no test tones? That seems like a defocused way of doing it but I see the advantages. It will be nice to try out some professional gear for a change.


What are the merits of narrow band noise measurements in this case? keeping in mind that I never stated the objective of this project was to EQ the room or environment..except for bass response in the room vs corners. That's probably why the seller held back the cap kit and sold it separately. :nono:


-Gregory

 

[Gregory]

The AA2 is in-house after an exciting day and a trip to CruzBay's place. Unfortunately the meter slowly rises until it pegs at full scale regardless of what meter range, frequency band, mode or meter speed is selected. It remains pegged. There IS output voltage at OUTPUT jack roughly proportional to the sound at the Mic. The meter doesn't settle down even when the Mic is disconnected. This is a big disappointment and I'm afraid it's not working properly.

The NOISE generator and filters are ok it seems. The large BAND switch works smoothly except for the last three positions near 20 kHz where a loud SNAP is heard through the loudspeakers when switching. I called and emailed CruzBay and hope to get in touch with him soon.


-Gregory

 

[c_dk]

I had one fail right in the middle of voicing a pair of B&W 802 D's...on the sales floor a couple of years ago. Recap it, typically the W. German axial caps have failed.

 

[Gregory]

I had one fail right in the middle of voicing a pair of B&W 802 D's...on the sales floor a couple of years ago.
Recap it, typically the W. German axial caps have failed.

Looking at the schematic, and taking the symptoms into account, it appears like a time contact issue with a cap.

From the schematic, C117 is a big gold W. German cap.




Looking at the circuit.. does it seem more like C118 is the problem? The meter is getting pulled high.




Switch connections




I can't think it through too clearly... without making voltage measurements.



-Greg