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XR6 Frequency Response

Gregory

Gregory

Soundco Kid

Have you ever seen the frequency response of a McIntosh Isoplanar Loudspeaker?

Neither have I, so let's go ahead and set up the test and collect some data. There were TWO separate stepped CW measurements (three actually but the first one doesn't count.) Here is a photo of the XR6s positioned close-in with the Tiltall tripod at 1 meter distance, on top of which is the Realistic model 33-2050 Sound Level Meter.

XR6_test_09.jpg
SLM positioned at 1 meter from the speakers, spaced 2 - 3 cm apart.


About 1 week ago I became suspicious of a L-R imbalance in the midrange as mentioned to Ryan at AC by email. So.. there is a question if the rebuilt MIDS were matched. On Friday the L and R speakers were switched side-to-side and the imbalance seemed to move with the speaker, but the next day they seemed to be about the same.

The following are the two measured curves from this afternoon.


First response plot

At each frequency the GAIN of the 2205 was set to produce 2 watts of power with one channel operating and the other channel cut to zero. Then 3dB was subtracted from the numbers to correct from a 2 watt power level to 1 watt. This measurement went up to 12,000 Hz and showed the LEFT speaker having a deficiency as suspected.

Frequency_Resp_2.png


Second response plot

The second measurement went up to 16,000 Hz and the furniture was rearranged to make the surrounding area more the same for each speaker. The two plots generally agree but I'm not sure the test was conclusive. Much of the 'woops' are gone in the second test, which were probably reflected waves beating with the incident.

Frequency_Resp_3.png


It was a FUN afternoon!! Will have to switch RIGHT back to LEFT and run the test again, the main object being to find out if the midrange is weak on one speaker. Each crossover component was checked except for the inductors. If it's a driver deficiency, do you think it could be the lower mids? or the upper mids? Maybe the MC2205 power meters are balanced at 2 watts??


-Greg
 
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SPL meter accuracy

Gregory, please be aware that the Radio Shack SPL meters are down in accuracy be 8db at 20 hz, and are only correct at around 1000 hz.
Contact the Boston Audio Society for a complete graph of correction curves.
 
Yes I have, somewhere in my 30 years of sales files I have 2 notebooks with over 280 room/speaker curves. The first pair I did was a pr. of ML1s in 1978, the last, a pair of B&W 802Ds a couple of years ago.

I hoped you would have plotted your curves on the McIntosh graph paper I sent you because it allows greater detail in the critical 50 to 10k Hz range. Have you corrected for the Realistics known frequecy aberations?

When you swapped the the furniture around I see a substantial change in the 200Hz suckout and the +7 gain at 1000Hz. You need to spread out the plots between 100 and 10k to really get insight as to what is going on, and of coarse when you place the mic near the listening postion you will be able to see the room interaction where it really counts.
 
sumicron said:
Gregory, please be aware that the Radio Shack SPL meters are down in accuracy be 8db at 20 hz, and are only correct at around 1000 hz. Contact the Boston Audio Society for a complete graph of correction curves.
Click to expand...

Thanks, I've seen that data set around and even downloaded it to my last PC. The only correction applied was to adjust from 2 watts to 1 watt as the -20 dB tic mark (ref 200W) is easy to set.


-Gregory
 
c_dk said:
Yes I have, somewhere in my 30 years of sales files I have 2 notebooks with over 280 room/speaker curves. I hoped you would have plotted your curves on the McIntosh graph paper I sent you because it allows greater detail in the critical 50 to 10k Hz range. When you swapped the the furniture around I see a substantial change in the 200Hz suckout and the +7 gain at 1000Hz. You need to spread out the plots between 100 and 10k to really get insight as to what is going on, and of coarse when you place the mic near the listening position you will be able to see the room interaction where it really counts.
Click to expand...

I'd imagine you would have a few curves from past jobs. Care to forward or post some samples of typical near-field 'open room' XR6 plots?

Someday I'll do a "listening position" measurement but for now it's d = 1 meter tests. Thing is, we have no "listening position" (except for DVD video viewing) and the response can vary greatly depending on where in the room the observation point is. I've pulled up the Mc CHART that you sent on Sept. 17th.. thanks!! Let's use that next time as a guide, but I'll still need to enter numbers in a spreadsheet to apply correction factors.

The objective now is to confirm if the two speakers are matched L vs R in response, as they seem to have been manufactured in different years, yet they are consecutive S/Ns. Also there's still a BUZZ in one of the woofers. These measurements are of great use in setting a GRAPHIC equalizer. Really wish the AudioControl unit had an illuminated front panel. I'm missing the MQ104 cap kit but probably could order some caps that would work.


-Gregory
 
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From what I can see from your truncated curves the blue speaker's level is about 3 dB down from the purple, and if would superimpose them the plots would be within + or - 2 dB except where you have already documented nulls caused by room and furniture.

Standing wave nulls (and peaks) will not be affected by using near field measurements, the wave lengths are so large. Remember the old Audio magazine articles when they would bury the speakers in the ground outdoors to do tests. I was in Mac's anechoic chamber back in the day and until FFT and TEF testing equipment came out, outdoors or in a chamber were the only ways to make accurate test comparisons.

From the PM you sent me of your room I don't doubt the will be a large response difference from the wall loaded RH speaker and what I believe is the large glass low pass filter near the LH speaker.

I am quessing the crossovers where made in different years but the speakers were assembled and tested in the same batch. Fran would never have let invetory of finished goods get that far out of whack.

I still believe you have an air leak. What have you done to find it so far?
 
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As for posting room/speaker response curves....

I am an old school brick and mortar guy who grew up in this business when dealers and salesmen like myself had a personal relationship with our McIntosh customers. This is something that most manufactures/dealers/customers do not understand. Gordon Gow would give away my time to non McIntosh customers after his seminars for a free room voicing so I had the chance to see many brands interacting with many different rooms. Almost always the customer was looking for affirmation of their speaker choice and were not open to how badly their room screwed up what where good speakers.

The ability to adjust the room to correct what could be changed, the chance to LISTEN to the customers perspective (and the spouse) to affect the sound characteristics, and then in the end using the MQ104/107 to effect changes, made this such a powerfull tool.

The lack of good ol'fashin room adjustment, commonsense audiophile insight; the lack of concrete documentation let alone todays let the computer fix it mentality: dooms the room fix products now included in most theater processors.
 
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c_dk said:
From what I can see from your truncated curves the blue speaker's level is about 3 dB down from the purple, and if you would superimpose them, the plots would be within + or - 2 dB except where you have already documented nulls caused by room and furniture.

Standing wave nulls (and peaks) will not be affected by using near field measurements, the wave lengths are so large. From the PM you sent me of your room I don't doubt there will be a large response difference from the wall loaded RH speaker and what I believe is the large glass low pass filter near the LH speaker.

I am guessing the crossovers where made in different years but the speakers were assembled and tested in the same batch. Fran would never have let inventory of finished goods get that far out of whack. I still believe you have an air leak. What have you done to find it so far?
Click to expand...


Was able to locate and digitize the Rad Shack Sound Level Meter (SLM) Cal data and apply it to the measures #3 plot today. Since this is a McIntosh top level product discussion, the SLM Cal will be posted in the AK Speakers forum. First I think we can have a look at the SLM since this post is intended to set a good example for fellow AK'ers. :)

XR6_test_SLM.jpg
Late 80's or early 90's Realistic analog SLM on Tiltall tripod 1-meter in front of speaker pair moved in close together.


Now for the CORRECTED XR6 response curves

Two corrections were applies. First the digitized Cal data for the SLM was subtracted from the measured data. Second the AVERAGE DIFFERENCE between L and R was found and ADDED to the weak channel simulating an increase in GAIN to balance the two channels. The DIFF factor was 2.28 dB meaning the BLUE channel was ~2-1/4 dB low.


Here's the NEW response chart

Frequency_Resp_Corr_3.png
Corrected in-room frequency of the recently restored XR6 speakers with 2.28 dB added to the LOW channel.


That chart means there's an imbalance in the system somewhere. It could be the 2205 WATT scale tracking isn't so accurate. These curves seem to indicate the midrange is lacking. Does it look normal for the XR6? At least L and R are well matched.

Do you have any typical XR6 response charts that could be used for comparison?


-Greg
 
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A couple of thoughts....

I never saw a need to do a 1 meter measurement because it means nothing...

What we really need to see is how the speaker interacts with the room and the response as the wave disapates into the space.

From what I see, is the blue speaker the problem woofer? To make sense of this you really need more data points wich is why we would do this in 1/3 octave increments. Between 100 and 1000 there should be 11 data points,125,160,200,250,315,400,500,630,800, with so few your data is inacurate.

The peak at 13 or 14k will probally be gone as you listen off axis and as the High freq. disipate in space.

I will repeat... There are no typical response curves BECAUSE ALL ROOMS ARE DIFFERENT. We do not listen in test chambers.
 
You should hook up with Room Eq Wizard...you can even use that output jack on the side of the meter. It makes it all automatic, probably more accurate, definitely more things can be measured, and oh so quick & easy...and free.
 
c_dk said:
We do not listen in test chambers.
Click to expand...

No, but without the basis there are no points of comparison. And, actuallly, Harman has put some logic to the technical measurements that tend to indicate, given a choice under the same listening conditions, the speaker identified by most people as the best sounding just happens to be the top performer in several key technical aspects. So, the old satement that specs don't matter doesn't necessarily seem to be true, and Harman seems to have qualified several technical measurements that define a good-sounding speaker.
 
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whoaru99 said:
No, but without the basis there are no points of comparison. And, actuallly, Harman has put some logic to the technical measurements that tend to indicate, given a choice under the same listening conditions, the speaker identified by most people as the best sounding just happens to be the top performer in several key technical aspects. So, the old satement that specs don't matter doesn't necessarily seem to be true, and Harman seems to have qualified several technical measurements that define a good-sounding speaker.
Click to expand...

I have measured and ploted hundreds of speakers in customers music rooms, trying to get their system to work better in their room, not a test chamber. I do understand that a speaker that sounds good in the real world deserves to be studied in the test chamber, to allow future replication. All the measurements I have are at 10,15, 20 feet, therefore not relevant to Gregory's 1 meter test.
 
I pulled out a old Mac graph paper and plotted out the blue speaker and found 1/3 octave points once i quit trying to guess freq. points. I beleive I see room issues but with a 1 meter distance I can not be sure. I am sure the choppiness from 500 to 6k is from the cabinet door interacting causing peaks and valleys. Try one with the door open. FFt analysis could be interesting.
 
Hi
Take the speakers outdoor (free field) and see if there is a different compared to indoor. There is lots of factors in a reverberant room that can mess up the measurements, speacially with a SPL meter. It is best to use a RTA meter instead.
Thanks
 
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whoaru99 said:
You should hook up with Room Eq Wizard...you can even use that output jack on the side of the meter. It makes it all automatic, probably more accurate, definitely more things can be measured, and oh so quick & easy...and free.
Click to expand...

That looks very promising, I've downloaded it but haven't installed yet. Recently added Sonos to the system, so the PC and LAN are integrated with the Mc system now!! I'd imagine that CW tones could be piped out through Sonos for test purposes.


-Greg
 
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c_dk said:
I pulled out a old Mac graph paper and plotted out the blue speaker and found 1/3 octave points once i quit trying to guess freq. points. I beleive I see room issues but with a 1 meter distance I can not be sure. I am sure the choppiness from 500 to 6k is from the cabinet door interacting causing peaks and valleys. Try one with the door open. FFt analysis could be interesting.
Click to expand...

No need to guess frequencies, the worksheet is attached.

Roger that... door open! :idea:


-Greg
 

Attachments

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Having had a chance to turn my brain on this morning....

I see from your data 3 interesting triples in your data points. Can you post the corrected dB readings in a chart so I can better examine their interaction.
 
I opened your xls file and I see you did not test at 1/3 octaves. Without 1/3 octave data it makes it much harder to evaluate data with other standard tests. I believe you can see ceiling interaction, floor interaction, as well as the afore mentioned grille door interaction. Measure again at 1/3 octave and post.

What did you change to cause the 7 dB gain at 1000 Hz for the blue speaker?

Also, you can see in your plots the lack of rear wall and MQ--- reinforcement!! If you look in the old literture or Roger's papers the overdamped drivers will roll off dramatically and are designed to be placed against a wall with the appropiate EQ added. These speakers were designed, no expected, to work with the room.
 
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c_dk said:
I opened your xls file and I see you did not test at 1/3 octaves. Without 1/3 octave data it makes it much harder to evaluate with other standard tests. I believe you can see ceiling interaction, floor interaction, as well as the afore mentioned grille door interaction. Measure again at 1/3 octave and post. What did you change to cause the 7 dB gain at 1000 Hz for the blue speaker?

Also, you can see in your plots the lack of rear wall and MQ--- reinforcement!! If you look in the old literature or Roger's papers the over-damped drivers will roll off dramatically and are designed to be placed against a wall with the appropriate EQ added. These speakers were designed, no expected, to work with the room.
Click to expand...

The response test was done last weekend before you reminded me of the McIntosh 039-050 Charting Paper that you sent by email in mid September. Also the test started out as just a few frequencies in the midrange. In order to do this correctly and make it repeatable, the Sig Gen should be re-settable at each test tone. The AA2 apparently has a large rotary switch at discrete freqs.

The 7 dB change at 1,000 was probably caused by moving furniture (i.e recliner chair) near the BLUE speaker. Just walking up to the SLM will cause the meter needle to swing 3 to 6 dB p-p when you move to and fro, or even side to side. A remote mic should be used to do this correctly. If the p-p excursions are observed, a 'mean value' can be recorded on the data sheet.

As for placement against the wall, the XR6 Owner's Manual states in the first paragraph on pg-2 "By using the equalizer you may locate the XR6 anywhere in the room and adjust the acoustic output for proper low frequency response."

Roger uses room walls to make the point that radiating into a solid angle increases by 3dB each time to cut the solid angle in half. Going from a spherical free space condition to a 'floor' will increase the omni-directional energy by 3 dB. Further by placement against the wall on the floor, another 3dB is gained and so on with 9 dB in the corner of room. I agree that the speaker is designed to work "with the room." The speakers are positioned 60" from the back wall and 32" from the side walls.

As for buzzing woofer diagnosis, I've not had time to dig into the cabinet again and check for air leaks, lose wires or to operate the woofer uninstalled. There are a lot of distraction, one being the lady of the house!


-Greg
 
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