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Pair of 8030A frequency response difference

petzo, modified 12 Years ago.

Pair of 8030A frequency response difference

Youngling Posts: 5 Join Date: 9/19/09 Recent Posts
Hello!

I wanted to ask a question regarding a new pair of 8030As that I have received about a week ago. Now that I have placed and arranged the speakers along with a complimenting 7050B and listening to it for some days, I have found something. Given the fact that I'm not in audio production and just wanted quality speaker system just to listen to music, I didn't have time to fully inspect it's qualities until now.
What I notice is that there is some difference in the sound spectrum represented by the speakers. I don't have measurement equipment, but making some tests that should rule out any other factor I have reached to the conclusion, that the cause seems to be the speakers.
What I hear is that one of the speakers is representing the highs much more louder/clearer. I first noticed that when panning left->right->left->right while listening to a song. After I noticing that I began doubting if the cause may be my non studio setup, totally imperfect room and acoustics treatment or the lack of such... I also doubted my to-be-replaced sound card...
To rule these thing out, I have placed the speakers side by side in the center of my room away from any walls, I have sit in front of them and started panning some pink noise to see if there is a difference. After still noticing the difference I have started switching the places of the two speakers (one in the place of the other). Regardless of the position of the speakers one of them continued to sound "louder at the higher end". After that, to rule out any issue with the sound card, I have switched the audio inputs on both speakers (left one playing right channel and vice versa) - the obvious difference was still present and the speaker showing if was not influenced by that cable change... Just to be on the safe side I have tried switching the power cables too..
While performing the test I have switched all the switches on the back to off. I have tied leaving the number 2 switch to on (Bass roll off - as it is supposed to be with a 7050B sub). That didn't show any difference.
I have performed the test not only by pink and white noises, but with music and some exact frequencies, from which I could not tell much... but they have at least confirmed that the tweeter is working properly and the awful quality of my sound card...
I know it is stupid, but I have even tired to listen to the speakers only from one of my ears at a time just to be sure that I don't have any problem with them or that I'm not doing something wrong...

So ... Given the methodology above, I am quite convinced that the cause of difference is in the speakers (or one of them - I don't know).
They have following serial numbers: XXX6792 and XXX6793. Produced Nov 09.
The input signal is not balanced. It is coming out of the line out of my sound card.

I can describe the perceived difference as a highly noticeable one, but not huge. I suppose it depends of the person who describes it... In stereo/normal listening I would hardly notice it.

What I am willing to ask is if this is normal? Am I too picky? What can you recommend me. Should I find some equipment and measure the frequency response of each of the speakers? Should I ask the dealer or the manufacturer directly for some advice?

I just wanted to say that aside the described issue I am Extremely! happy with the system. The low distortion in higher levels, the very nicely complimenting sub and everything... except of the above.

Thanks very much for your attention.

-----

PS. Now that I have written all that I recall that I have done the testing only on a relatively low volume input levels (the volume knob on the speakers was all the way to the max). So now I have tried some music (but not the other tests) in higher volume and the problem seems to be bigger...
christophe-anet, modified 12 Years ago.

Re: Pair of 8030A frequency response difference

Jedi Knight Posts: 188 Join Date: 3/23/09 Recent Posts
Hello,

Thanks for your post. Your testing methodology has been very good and complete - well done. Few more comments here:

To exclude the room acoustic influence while listening to your loudspeakers, the only way is to setup your system outside, in the open air, or in a very large hall with short listening distance. You can arrange a mono signal also and do the listening one after the other, switching between the speakers in less than 5 sec (the help of a friend might be necessary to do that...)

Your idea of the speakers sertup side by side will not reveal much as you will have serious comb filtering between the two speakers in that configuration... So, if you can make the open air test you can then make absolutely sure that your speakers either sound the same or not. If not, then something might be damaged in one of your tweeter. Please, let us know your findings.

Now, as you have unbalanced connections, please consider to make the test again with balanced cables. That might be revealing. Also, try to do some test with something else than a soundcard, a good CD player for example.

Given your test procedure and the info you have provided so far, I still think that your room acoustic might be the parameter altering the sound quality. But as said above, something might be wrong on one tweeter also....

Your additional tests should give us a better idea of the situation. Speak to you soon.

Best regards,
gue-, modified 12 Years ago.

Re: Pair of 8030A frequency response difference

Youngling Posts: 7 Join Date: 12/20/09 Recent Posts
Hi pezo,

Perhaps your measurement device "lies". You can also check if the soundcard is the source
of the problem by making a "loopback" test of the soundcard with RMAA.
RMAA: http://audio.rightmark.org/index_new.shtml
example loopback measurements: http://www.amb.org/rmaa

Also, did you set the high-frequency dip switches on the back to the same on both monitors?
If yes try to toggle the switches anyway, perhaps one is not switched correctly.

You can also try to exchange the left and right monitor to see if the problem is elsewhere
in the monitoring chain (or in the Room response?).

Please carry out only one step after another to see what was the root of the problem.

HTH
gue.
petzo, modified 12 Years ago.

Re: Pair of 8030A frequency response difference

Youngling Posts: 5 Join Date: 9/19/09 Recent Posts
Thank you very much for your kind responses.
I'll take your advices into account and will perform some additional tests.

But now - the most important - I want to wish you all happy holidays and a very cheerful and successful new year!

I'll post here as soon as I have some updates.
petzo, modified 5 Years ago.

Re: Pair of 8030A frequency response difference

Youngling Posts: 5 Join Date: 9/19/09 Recent Posts
Hello again,

Sorry for the delay but it wasn't until yesterday that I have done some more tests.
I've met with a friend of mine who has a studio of his own. I went there, bringing my Genelecs to have some second opinion, and make some more precise measurements.

I have some mixed results after that, but I suppose it is better to post something on the subject already...
So my friend has his studio set up around a couple of 8040s, we have put mine 8030 in their places and both listened to some mono signals, including music and pink noise. We both agreed on the obvious difference. The input signal was coming form a professional m-audio sound card. And where my speakers clearly were showing difference, his - the 8040s - were not, of course. Wondering at what exact frequency was the problem we were perceiving, we decided to make some measurements.

Unfortunately we did not set up the system outside in open air as Christophe has suggested, because of the weather. That said mine friend's studio is pretty decently acoustically treated, so I decided to give the test a try. The room itself clearly has it's problems, and we have moved stuff around in it, but I think in the case where we are comparing speakers located in the same place, the room response is of much less importance. So we have set up one of the speakers and placed a measurements mic in front. In our case this was a Behringer ECM8000.

Here is a picture of our setup:


We have aimed the mic, at the acoustical axis of the speaker. The procedure was to measure one speaker - record, and place the other in it's exact place and plug the existing cables in it - record again, so the only difference to be the speaker itself.

We have tried recording some pink and white noises. The pink noise was taken from this site's sample signals, which was not a great idea since it was an mp3 and has clear cut at 16kHz, but we have realized that a little bit late and did not repeat the test with our own better noise signals, since we haven't got enough time.

Here I'm posting the measurement based on around 5 sec of recorded and analyzed pink noise. Each line represents a speaker. This picture is from the speakers position at about 30cm away from the mic.

Maybe it would have been better to analyze the white noise recordings but we didn't save them by mistake...

I don't feel qualified enough to make conclusions based on this... It seems to me as the treble tilt was switched on, but it was not, all switches were to off... We tried to switch the speakers treble tilt on and off, and it clearly showed difference, so I assume the switch was working properly, but the speaker overall response - not. Also the measured difference at 15K is around 5dB in our analysis, where the treble tilt should be -2dB at 15k...

I'm attaching some 2 sec sample of each of the recordings.


I've put up a file containing a representation of the pink noise test signal - after that one of the speakers recordings - and after that the other - and again the reference noise. I've normalized the signals so they are relatively the same power. Listening to this reveals exactly the difference that I'm trying to explain. Due to the attachment size limit of 500k I'm pasting a link, rather than attaching a file. So here it is: http://basta.bg/pix/genelec/noises.wav

Another thing we noticed is that it seemed that one speaker is around 1dB louder than the other. As we are no experts, we thought that maybe the perceived difference was caused by the level mismatch. So we tried and calibrated one speaker, using the knob to be outputting the same level as the other.

After that we have put them again in listening position and HEY! it seemed that they sound the same now. We have tried listening to music, we have tried listening to noise, and it seemd OK now. It was kind of strange... they were just working now. Given that, we've said - what would happen if we turn the level knobs on both of them to the max again? So we did. It seemed that the difference was not audible now either. They sounded the same now, even with the both levels set to max... I suppose that 1dB is not much of a difference...

It was very strange... did they just fixed themselves somehow? I don't know but we have listened them for a couple of more minutes and the perceived difference was gone... We were wondering if we should make the test again but we really didn't have much time left .... So we assumed that they somehow magically fixed themselves.

That would have been great, but now that I have returned home, I'm again hearing the difference ... I feel frustrated. They are not ok ... again. Was it us, that we have had too much listening and the difference began to blur on us ... Maybe they were OK for a moment and they are now back to the previous situation, or we were just wrong and they wasn't OK when we though they are...I really don't know what to think. It is just as clear to me now that I'm listening to them, as it was before our test, that there is difference. So I'm stuck in the beginning...

Sorry for the long post but just wanted to be as precise as possible.

What could be the cause? Is it possible that the switches in the back are not working properly? Can it be a faulty tweeter as Christophe suggested? Or is it possible that there is some miscalibration of the speaker?

I'm not sure if it is appropriate place to ask, but are those thing on the picture trimmers? I suppose that they are for some sort of service, but none the less I'm curious :P Is it possible that the speaker can be calibrated from here (not by me of course)? Here is a picture:


Thanks again for your time and interest. What would you suggest. I'm leaning to the decision to visit the dealer.

Kind regards,
Milen
christophe-anet, modified 12 Years ago.

Re: Pair of 8030A frequency response difference

Jedi Knight Posts: 188 Join Date: 3/23/09 Recent Posts
Hello,

Thanks for your comprehensive post and various documents. It is too bad to see that your test procedure did not really bring any valuable information about the missmatch. Even in a very well designed audio control room, the room acoustic has a major influence on the perceived listening quality. So, once again, a useful test would be to either setup the system in the open air (not possible in the current season, I understand well) or to set it up in a very large room at a normal listening distance - say, 1.3 m. To implement the test properly you would need to just have the two speakers on stands at 1.3 m and a chair, nothing else between the listening position and the speakers. All other equipment should be placed away from the test setup. That way you could really confirm the response missmatch, as you would take away all room boundary effects and interactions (beside the floor, of course).

Now, I trust your report that you do hear a difference between the two units, and the next step I would recommend is that you bring the two units to a local service center to check the calibration of the speakers and the possible damage to one of the tweeter.

The missmatch is unlikely coming from faulty DIP switches. It appears to be more likely a drive unit problem of some sort or a speaker calibration abnormal deviation. Only a service center could confirm these hypothesis.

The calibration trimmers shown on your picture are used in the final speaker calibration stage in our production. They are also used in service, when a driver is replaced for example, to make sure the repaired unit is perfectly calibrated. These trimmers should not be adjusted by anyone but one of our service center.

Here is a link to our worldwide distribution network and service centers. Please contact the distributor of your country: http://www.genelec.com/sales-network/

Hope that your 8030A's will be back in order very soon. Sorry for the inconvenience.

Best regards,
petzo, modified 12 Years ago.

Re: Pair of 8030A frequency response difference

Youngling Posts: 5 Join Date: 9/19/09 Recent Posts
Hi Christophe,

Thank you very much for your prompt response. I really appreciate it. I'll contact Genelec's support in my country in the near future and post the results of that here.

As a side note I wanted to say how pleased I am by the presence of Genelec's staff in this forum. I am amazed by your comprehensive and detailed responses. Great work and commitment! Thank you very much and keep it up!

All the best,
Milen
petzo, modified 12 Years ago.

Re: Pair of 8030A frequency response difference

Youngling Posts: 5 Join Date: 9/19/09 Recent Posts
Hello again,

After a trip to the service, the speakers are now working perfectly the same, frequency wise.
It turns out that there indeed was a problem, and the cause was improper calibration. The service measured exactly the same difference of 5-6dB at 15kHz. They have calibrated the speakers and everything is OK now. They have told me that they have used some internal adjust trimmers in conjunction of the ones I have posted earlier. Now, maybe there still is 1-2dB difference in the level, but that is easily adjustable by the level knobs.

So thanks again and all the best!
I'm happy now :D