Need to re-measure room response?

[RPG]

Hello,

So, please forgive my somewhat newbie question.

I've just put this spiffy new AHB2 amplifier in my system. Last year, I had painstakingly measured the room response with my former amp in the chain and had implemented appropriate (and very successful, IMO) EQ corrections via my ADI-2 DAC. Speakers, subs, etc. are all unchanged. I've left the EQ corrections unchanged, too, and just dropped in the AHB2 which sounds wonderful (and different--in a better way, albeit subjectively).

I've noodled around the web some and really haven't found any answer to my question which is: does the installation of the new amplifier necessitate a re-measuring of the room response and, with that, a likely change in the EQ parameters? Or, since the dac, speakers, and subs were not altered, is the room response actually independent of what the amp does or does not do?

Thanks for any help on this....

RPG

 

[suttondesign]

New measurements are not needed unless your former amp had serious frequency response anomalies, and that's pretty doggone rare. What are the speakers in your setup?

 

[RPG]

That was what I was hoping to hear, heheh. While I learned a lot from the measurement process, I wasn't totally relishing having to go through it again (and neither was the Mrs.!) The speakers are Revel F-208.

 

[Worth Davis]

re run it or not doing it will haunt you and keep you up at night...

 

[Soniclife]

If it was a valve amp, or something with high output impedance you replaced maybe slightly. When you have time and inclination re-run the measurement, always good to check theory's hold up in practice.

 

[Hipper]

I would agree that rerunning one test measurement (relearning all the connections, REW etc. - oh what fun!) would be a good idea. I would also agree that there shouldn't be any noticeable difference from replacing just an amp and perhaps its cables (that's what this site will tell you and I accept).

I would point out though that it is very difficult to get exact repeat measurements when comparing old and new measurements. That's mostly because it's really hard to get the microphone in exactly the same position. 1dB here or there then should not be considered a change.

There is one possible way the amp might affect the sound and that is it's influence on reflections, therefore the higher frequencies. In the past when I had the gear placed on the front wall I could hear the reflections off their front panels. That means that a bigger or smaller amp may change this effect. My solution was to angle the gear so the reflections didn't reach me direct. I now have the gear on the side wall but that can still lead to reflections.

 

[thewas]

That's mostly because it's really hard to get the microphone in exactly the same position. 1dB here or there then should not be considered a change.

True and another reason I prefer moving microphone measurements as they not only give a psychoacoustically more relevant representation but also much better repeatability.

 

[SIY]

Some work @jan.didden and I were doing last night really emphasized how critical mike position is when doing stereo measurements. Try this yourself- run a single mike measurement of impulse response (whether an actual impulse or derived from a Farina sweep) playing through both speakers. Move the mike a couple centimeters and do it again.

When you see that, you'll stop worrying about likely inaudible power amp differences.

 

[RayDunzl]

Try this yourself- run a single mike measurement of impulse response (whether an actual impulse or derived from a Farina sweep) playing through both speakers. Move the mike a couple centimeters and do it again.

https://www.audiosciencereview.com/forum/index.php?threads/sweet-spot-and-not.640/

Sorry, the little movie mentioned is no longer available.

Basically, as the mic moves off center, little waves show up in the highest freqeuncies, and the farther you move it, the lower the waves extend into the lower frequencies.

The waves aren't fixed, as they might appear in the graphic, they "wave" as you move the mic. So, at one mic position 10kHz might be at max, and move the mic a little more, and 10kHz becomes a min, with more extension of the waviness into the lower frequencies.

 

[SIY]

https://www.audiosciencereview.com/forum/index.php?threads/sweet-spot-and-not.640/

Sorry, the little movie mentioned is no longer available.

Basically, as the mic moves off center, little waves show up in the highest freqeuncies, and the farther you move it, the lower the waves extend into the lower frequencies.

The waves aren't fixed, as they might appear in the graphic, they "wave" as you move the mic. So, at one mic position 10kHz might be at max, and move the mic a little more, and 10kHz becomes a min, with more extension of the waviness into the lower frequencies.

Trust me, it looks even worse in the time domain.

 

[RayDunzl]

Trust me, it looks even worse in the time domain.

Yes, impulse response is "duplicated" as the sound arrives at different times...

 

[SIY]

That looks like a difference of about half a meter, which is extreme. For purposes of comparison, people try to estimate the mike position and if it's off even a minuscule amount... let's just say it swamps a lot of other variables.

 

[RayDunzl]

That looks like a difference of about half a meter, which is extreme. For purposes of comparison, people try to estimate the mike position and if it's off even a minuscule amount... let's just say it swamps a lot of other variables.

I use the impulse to find the center when concerned with high frequencies (that I can't hear).

For low frequencies, a few millimeters doesn't make any difference.

 

[RPG]

Interesting, thank you all! No, the former amp was a solid state integrated---nothing too esoteric.

I think I'm being convinced that remeasuring is quite likely to produce differences from my original data, but those differences are likely not going to be related to changing the amplifier. Plus, I have learned that precise mic positioning is critical to getting repeatable and consistent results if one performing multiple measurements from the same measuring position!

Part of this "remodel" was also a change from RCA to XLR interconnects between dac and amp.

Would be accurate to say that, if I were able to put the mic in the precise position of the original measurement (which I most certainly cannot), it also seems that the change of cables isn't likely to be a contributor towards a change in frequency/room response?

 

[RayDunzl]

Would be accurate to say that, if I were able to put the mic in the precise position of the original measurement (which I most certainly cannot), it also seems that the change of cables isn't likely to be a contributor towards a change in frequency/room response?

Not too likely.

Opinion from Experience:
Cables can make a tiny difference, depending on what the difference in the cables is.

Going from some "experimental" twisted AWG18 to "just-as-experimental" biwire AWG2 for the speaker cables made a tiny difference in the level of the highest frequencies by a dB or two where my speakers dip down to an ohm or so.

That's an extreme case.

 

[QMuse]

Trust me, it looks even worse in the time domain.

Very true. But it is also true that in time domain things are looking much worse than they sound.

One would get a better picture by taking RTA pinkn noise RTA while moving mic around LP so at least 50 measurements are taken. Such spatialy taken measurement is the best basis for any room EQ one plans to do.

Once FR is corrected FR based on spatially taken measurements a sweep measurement can be made to fix the phase. Here I have to admit I really don't understand why practically all room EQ solutions are trying to do correction based on a bunch of sweeps when a proper spatial mesaurment can easilly be taken and you can always fix time domain later with a single sweep.

 

[Soniclife]

Would be accurate to say that, if I were able to put the mic in the precise position of the original measurement (which I most certainly cannot), it also seems that the change of cables isn't likely to be a contributor towards a change in frequency/room response?

Not unless the old or new set were broken.

 

[QMuse]

Would be accurate to say that, if I were able to put the mic in the precise position of the original measurement (which I most certainly cannot), it also seems that the change of cables isn't likely to be a contributor towards a change in frequency/room response?

First of all, you don't need to re-run room EQ if the only thng you've changed is your amp.

Reagding your other question - assuming your room EQ SW took 9 sweeps when doing room EQ then you would need to put mic in those same 9 spots if you would to replicate that same measurement with that same SW. But that is not how you normally control how good job your room EQ SW did, it is much better that you do it with moving microphone method using RTA pink noise.