Quad 11L2: different frequency response between left right speakers

alpha1

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I have 15 year old Quad speakers which have been performing stellar, however right from initial days I always felt one speaker is slightly brighter than the other.
Recently I did REW measurement using my laptop and inbuilt microphone. Yeah, it might not be calibrated microphone - but then any coloration of microphone's frequency response will cancel out when I take difference between left and right speaker readings.

What came out confirms my ears - there is a slight difference in the frequency band from 2.8 kHz to 7 kHz. Peaking between 4.5 and 6 kHz.
What could be causing this? What could be possible solution?
Right now I am running an EQ (pulse effects) on my PC to correct for this.
 

aeroash

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I have 15 year old Quad speakers which have been performing stellar, however right from initial days I always felt one speaker is slightly brighter than the other.
Recently I did REW measurement using my laptop and inbuilt microphone. Yeah, it might not be calibrated microphone - but then any coloration of microphone's frequency response will cancel out when I take difference between left and right speaker readings.

What came out confirms my ears - there is a slight difference in the frequency band from 2.8 kHz to 7 kHz. Peaking between 4.5 and 6 kHz.
What could be causing this? What could be possible solution?
Right now I am running an EQ (pulse effects) on my PC to correct for this.
Is one of the speakers closer to the side wall?
 

amrutmhatre90

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After switching the left channel to right the same speaker sounds bright or the same side sounds bright?

This used to happen with me on the right channel as there was a large French window on that side. Addition of a absorption panel fixed it, sometimes I even close the curtains.
 

alpha1

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Checked all possibilities by reversing the speaker placement, amp channels etc.
Also as I mentioned it has been confirmed by room EQ wizard measurement also. Which I did one speaker at a time, by keeping the speaker, microphone and room placement as exactly same in both cases.
 

arj

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Since its 15 years perhaps the crossover of one has some component deteriorating ?
 

alpha1

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Since its 15 years perhaps the crossover of one has some component deteriorating ?
Thanks, what would be the effect of component deterioration on crossover frequency response? (I suspect only electrolytic capacitors may deteriorate)
 

arj

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Not sure but I would assume its frequency ranges might be impacted if it is a small deterioration. maybe the more tech savvy folks here can answer this better :) capacitor/inductor will impact the frequency ranges being sent to the drivers.
Thanks, what would be the effect of component deterioration on crossover frequency response? (I suspect only electrolytic capacitors may deteriorate)
 

k-pad

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Checked all possibilities by reversing the speaker placement, amp channels etc.
Also as I mentioned it has been confirmed by room EQ wizard measurement also. Which I did one speaker at a time, by keeping the speaker, microphone and room placement as exactly same in both cases.
If you have done all this, then I am assuming you would have given a thorough physical inspection of the speaker and the drivers...
Which will leave only something internal as the troublemaking component, like Arj said...
 

IndianEars

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You have not mentioned the extent of the difference (in dB) between the 2 speakers....

This could be due to differences in the driver efficiency, Tolerance between xOver components of the 2 channels or a repair before being sold to you. (FWIW: I Recently replaced a Metalised Polyester - Non Electrolytic - Capacitor (8.2 mfd) in a Speaker XOver. So its not just the electrolytic caps that fail.)

ASYMETRICAL PLACEMENT

If differences are relatively small (though distinctly audible) my I suggest exploring the following 2 :

1. Shift the louder speaker back about 3 inches compared to the other speaker

2. Toe-out the louder speaker.

ELECTRICAL EQUALISATION

If this does not yield the required results, you are still in luck...

The Quad 11 L2 is a 2 way speaker, with separate LF & Tweeter connections at the rear.

Assuming that you have not bi-wired the speakers, connect the wire from the amplifier to the LF terminals of the Quad.

Connect a Jumper from the LF -ve to the HF -ve terminals.

Remove the jumper from the LF +ve to the HF +ve terminals.

I suggest you buy 4 Nos of 1 Ohm, 5 watt resistors (each will cost less than Rs 10).

Start with 1 resistor in between the HF+ & LF+ terminals.

If that does not equalise enough, put 2 resistors in series.

If the 1 Ohm equalises too much, put 2 resistors in parallel.

If necessary, go upto 4 resistors in series or 4 resistors in parallel.... (I think this speaker uses a 4 Ohm LF driver and probably an 8 Ohm (Not sure) Tweeter.
 

alpha1

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If you have done all this, then I am assuming you would have given a thorough physical inspection of the speaker and the drivers...
Which will leave only something internal as the troublemaking component, like Arj said...
Well the foam surrounding the speaker cone has really deteriorated at some locations - which I have fixed using rubber based glue.
However, the Quad 11L2 comes with crossover of 2.2 kHz and therefore the differences (please scroll down for details) are more on tweeter side.


Folks thanks for the suggestions.
I have sat patiently and come up with the EQ difference between the two speakers. Pretty different - in my opinion far beyond the manufacturing differences.
Generate white noise and put a parametric EQ with Q value of ~8. This allowed me to focus on only a narrow band of frequencies around 24 dB difference between desired frequencies and rest of noise. Next I used 30 band graphics EQ on pulse effects (linux PC) which has separate EQ for left and right.
This signal was fed into the speakers, and I adjusted the 30 band graphic EQ for left speaker till I could get a stereo image straight ahead. Also verified the same by moving left and right in order to hear the center-point move symmetrically.

The following is the correction I need to make in the left speaker to make it symmetrical to right speaker:
567 Hz 0 dB
714 Hz +1.5 dB
899 Hz +3 dB
1.1 kHz +1.5 dB
1.4 kHz 0 dB
1.8 kHz +1.5 dB
2.3 kHz +1.5 dB
2.8 kHz +4.5 dB
3.6 kHz 0 dB
4.5 kHz +5 dB
5.7 kHz +1.5 dB
7.1 kHz 0 dB
9.0 kHz +3 dB
11.3 kHz +3 dB
14.3 kHz +1.5 dB

@IndianEars , do you think the resistance method would be able to bring down these differences?
 
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sunder

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In the stereo recordings, usually the Left side will be more in strength and the both channels will not be in equal strength (The both channels of the amplifier will be in equal strength. Can be checked by interchange the interconnect cables). Also, in the hearing efficiency of human will not be the same in the both sides and the slight differnce can be felt when hearing the high frequency. In the old age , the difference might be increased. Thanks.
 

aeroash

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In the stereo recordings, usually the Left side will be more in strength and the both channels will not be in equal strength.
When you give us a rationale for the aforementioned practise, it is good for all of us to grasp.
 

IndianEars

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Well the foam surrounding the speaker cone has really deteriorated at some locations - which I have fixed using rubber based glue.
However, the Quad 11L2 comes with crossover of 2.2 kHz and therefore the differences (please scroll down for details) are more on tweeter side.


Folks thanks for the suggestions.
I have sat patiently and come up with the EQ difference between the two speakers. Pretty different - in my opinion far beyond the manufacturing differences.
Generate white noise and put a parametric EQ with Q value of ~8. This allowed me to focus on only a narrow band of frequencies around 24 dB difference between desired frequencies and rest of noise. Next I used 30 band graphics EQ on pulse effects (linux PC) which has separate EQ for left and right.
This signal was fed into the speakers, and I adjusted the 30 band graphic EQ for left speaker till I could get a stereo image straight ahead. Also verified the same by moving left and right in order to hear the center-point move symmetrically.

The following is the correction I need to make in the left speaker to make it symmetrical to right speaker:
567 Hz 0 dB
714 Hz +1.5 dB
899 Hz +3 dB
1.1 kHz +1.5 dB
1.4 kHz 0 dB
1.8 kHz +1.5 dB
2.3 kHz +1.5 dB
2.8 kHz +4.5 dB
3.6 kHz 0 dB
4.5 kHz +5 dB
5.7 kHz +1.5 dB
7.1 kHz 0 dB
9.0 kHz +3 dB
11.3 kHz +3 dB
14.3 kHz +1.5 dB

@IndianEars , do you think the resistance method would be able to bring down these differences?
Thanks for the detailed revert, Alpha1.

My Gut feel on the readings that you have shared is that they have probably been heavily influenced by room reflections.

I would personally:

1. Try the Speaker Re-alignments that I have mentioned earlier. If they are insufficient...

2. Try starting with a 2 Ohm series resistor between the LF & HF terminals as I have also outlined.


P.S: Regarding the deterioration of the Foam Surrounds ... Takes me back 3 decades when I informally provided service support for BOSE products in India... (Before Bose was officially sold in India)

All Bose speakers of that era ( 1980s ... The 301, 501 & 901 used Foam surrounds which crumbled in Mumbai's high humidity. Bose faced the same problem with their speakers in Florida, and ultimately switched over to Bextrene rubber surrounds.

See if you can get original Foam Surrounds from Quad ... Its the only way you cab get the original performance from yr speakers.
 

alpha1

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Thanks for the detailed revert, Alpha1.

My Gut feel on the readings that you have shared is that they have probably been heavily influenced by room reflections.

I would personally:

1. Try the Speaker Re-alignments that I have mentioned earlier. If they are insufficient...

2. Try starting with a 2 Ohm series resistor between the LF & HF terminals as I have also outlined.
To some extent, but the REW graphs and the difference between left and right speaker also shows almost the same differences. REW measurements were done one speaker at a time, keeping the speaker, mic and room position exactly same. So I have reasons to believe that room coloration in REW measurements will cancel when taking a difference between Speaker A and Speaker B.

Thanks, I will try the 1-2 ohm thing, what I understand is that the more ohms, the more roll off of higher frequencies?
 
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