Revel C52 Speaker Review and Measurements

[napilopez]

While that is true my point was that all of that would not come to play if you put it vertically on a stand as a standard stereo speaker. This speaker was designed to be placed horizontally, the way Amir mesaured it.

Yep, not saying otherwise

 

[KSTR]

The impulse response is, for all practical purposes, the frequency response.

To be more specific, the DFT/FFT of the impulse response is the frequency response of magnitude and phase (phase also is important).... that's why I asked @amirm to publish the IR data directly so anyone can analyze it at will... like loading it into REW, ARTA, HolmImpulse etc

 

[sam]

The impulse response is, for all practical purposes, the frequency response.

Yes, you are right. I meant the time domain graph of the frequency response. One that looks like a fallen pine tree.
But the impulse response is not as meaningful in the system compared to the transducer itself.

 

[Krunok]

Yep, not saying otherwise

Sure. I said that as a comment to the folks who are thinking of putting this speaker vertically and using it as a stereo speaker. As current vertical response would in that case become horizontal and would have different ponders than vertical I doubt spinorama would in that scenario look this smoothly.

 

[Krunok]

To be more specific, the DFT/FFT of the impulse response is the frequency response of magnitude and phase (phase also is important).... that's why I asked @amirm to publish the IR data directly so anyone can analyze it at will... like loading it into REW, ARTA, HolmImpulse etc

In my opinion IR data would not be of interest to us amateurs but only to professional speaker designers, which is leading me to the idea that he would better be offering them for a fee to be able to help cover his costs of speaker testing.

 

[folzag]

@amirm did you place all 7 horizontally?

 

[amirm]

The "normal" Klippel used for measuring transducers can also measure the impulse response and diaphragm excursions, which I think it's only necessary for engineering purposes.
Not sure if this can also be done with NFS, but it will be great if we can also see the impulse response of woofers and midranges.
Transducers mounted on one enclosure and separating each linked speaker to one binding post will be an issue though.

The "normal Klippel," the KA3 analyzer is part of NFS and it can indeed measure many things. I can't show individual drivers since that would involve taking apart the speaker.

Here is the composite impulse:

I have zoomed in to show the active portion.

 

[amirm]

@amirm did you place all 7 horizontally?

I did.

 

[folzag]

I did.

I allow.

 

[KSTR]

In my opinion IR data would not be of interest to us amateurs but only to professional speaker designers, which is leading me to the idea that he would better be offering them for a fee to be able to help cover his costs of speaker testing.

Offering the full set of preprocessed IR data for a reasonable fee might well be a good compromise for those who want do dig in deeper, IHMO not neccesarily a thing only we seasoned professionals would like to do.

 

[amirm]

To be more specific, the DFT/FFT of the impulse response is the frequency response of magnitude and phase (phase also is important).... that's why I asked @amirm to publish the IR data directly so anyone can analyze it at will... like loading it into REW, ARTA, HolmImpulse etc

I have not yet figured out how to save an impulse file. I can save it numerically but not as a wave file.

 

[KSTR]

I have not yet figured out how to save an impulse file. I can save it numerically but not as a wave file.

Any format is fine with me. Converters (SoX) are available or easily written.

 

[mitchco]

Because in your room you would probably be chasing Harman preferred response which would look something like this so you would more be bothered to reduce a peak at 1.5kHz.

View attachment 46216

There may be some mixup here. The blue curve is the "old" Harman room curve from some of their DSP processors, whereas @amirm red curve is indeed the preferred in-room response based on Sean Olive's research. See History of Harman Target Curve.

Same results with headphones:

And with room correction products:

There are several other references to this that I did not include that folks can find in the AES papers.

And the measured in-room response of my constant directivity JBL system:

Also there seems to be a bit of confusion as to how room corrections products work as folks need to understand frequency dependant windowing (FDW). The top end room correction products not only allow you a partial correction let's say up to Schroeder for example, but also allows one to calculate the analysis and correction windows above Schroeder. This allows you to correct for "loudspeaker and room" below Schroeder and just a gentle tone control "direct sound" correction above Schroeder. The number one mistake people make when using room correction products is over correcting the high frequencies. Edit: Followed closely by the number two mistake of including room reflections above Shroeder in the eq correction.

 

[amirm]

Any format is fine with me. Converters (SoX) are available or easily written.

To be clear, I mean I can export the numbers from a graph, not any kind of sound file.

 

[Krunok]

Also there seems to be a bit of confusion as to how room corrections products work as folks need to understand frequency dependant windowing (FDW). The top end room correction products not only allow you a partial correction let's say up to Schroeder for example, but also allows one to calculate the analysis and correction windows above Schroeder. This allows you to correct for "loudspeaker and room" below Schroeder and just a gentle tone control "direct sound" correction above Schroeder. The number one mistake people make when using room correction products is over correcting the high frequencies.

Thanks for clearing the Harman target curve shape.

Btw, as I explained and showed in my previous posts, although my Harlechs have linear response I applied a few very gentle filters above transition region (+/- 1-2dB and Q of +/- 1-2) in a tone control manner only to suite my personal taste.

Below Schroeder frequency and in the transition region (300-600Hz) my corrections were based on spatial measurements done at LP. I used sweep at LP to do phase corrections and there I applied FDW. Getting time domain stuff right (excess phase close to 0 and matching phase of left speaker to the phase of right speaker to avoid LF cancellations with both speakers response) turned out to be much more complelx job than getting the FR right.

 

[mitchco]

If one looks at Figure 11 in the ANSI/CTA 2034-A, “Standard Method of Measurement for In-Home Loudspeakers" which one can download for free, we can see that the predicted in-room response is almost identical to the measured in room response:

This is of course is based on the research from Olive (and Toole) referenced earlier in another thread where the details of how this was developed, (several AES papers worth reading) and proving that it is repeatable and reliable predictor of in-room response.

Of course, below Schroeder the room dominates. But that is why we have room eq

 

[KSTR]

@amirm I understand, I think that'll be perfectly fine, let's give it try and see how it works out?

 

[Krunok]

There may be some mixup here. The blue curve is the "old" Harman room curve from some of their DSP processors, whereas @amirm red curve is indeed the preferred in-room response based on Sean Olive's research. See History of Harman Target Curve.

View attachment 46254

Same results with headphones:

View attachment 46255

And with room correction products:

View attachment 46257

There are several other references to this that I did not include that folks can find in the AES papers.

And the measured in-room response of my constant directivity JBL system:

View attachment 46260

Also there seems to be a bit of confusion as to how room corrections products work as folks need to understand frequency dependant windowing (FDW). The top end room correction products not only allow you a partial correction let's say up to Schroeder for example, but also allows one to calculate the analysis and correction windows above Schroeder. This allows you to correct for "loudspeaker and room" below Schroeder and just a gentle tone control "direct sound" correction above Schroeder. The number one mistake people make when using room correction products is over correcting the high frequencies.

Here is FR of my Harlechs, not as smooth as yours but still sounds pretty decent to me.

 

[Krunok]

Of course, below Schroeder the room dominates. But that is why we have room eq

For my room I have noticed that in the transiton region room effects are, although not as drastic as below Schroeder, still very noticeable and audible.

And yes, is really a good thing we have room eq.

 

[amirm]

Any chance, after yo get some sleep, you can do a simple RTA MMM measurement with REW so it can be compared with predicted in-room response?

Not in the garage where it is. I have to get a microphone in there to measure. And at any rate, the garage is not what was modelled in Devantier paper where the formula came from. Fortunately I have a snapshot of the speaker in my theater. It is heavily smoothed but here it is:

Compared to Predicted In Room Response from the review:

Seems similar.

The unfiltered one is in this article: https://www.audiosciencereview.com/...ds/perceptual-effects-of-room-reflections.13/

I have to see if I still have the REW file to refilter it....