Neumann KH 80 DSP Monitor Review

[thewas]

It looks like a ported design so i would expect a little more.

That depends on the port tuning frequency, at 100 Hz (and above) most current speakers don't have much gain from it as their ports are usually tuned significantly lower.

 

[Krunok]

That depends on the port tuning frequency, at 100 Hz (and above) most current speakers don't have much gain from it as their ports are usually tuned significantly lower.

This is true. Port is probably tuned to somewhere around 50Hz so it's contribution at 100Hz is -10dB or less.

90-91dB at 1m still looks a little low though.

 

[thewas]

In the end its a really optimised loudspeaker, but we shouldn't forget that its a tiny 4" midwoofer that has to go quite deep for its size and the size of the speaker and has to play very cleanly and linearly till the mids, unlike a pure 4" (sub-)woofer driver that can be optimised for more SPL (in German we call those "mud-movers" ), as you know, everything is a compromise.

 

[Pio2001]

Hello guys,

We are just on the beginning of something great, so we rather carefully adapt and further perfect the procedure now before we regret it later after having measured dozens of loudspeakers.

I agree that things should not be rushed.
About the measurement level, here are the results of old measurements that I made at home with REW, that uses Farina deconvolution to measure the frequency response (measurements with a sine sweep, I guess that the Klippel uses the same method), at various levels.
I made 4 identical measurements in a row, the playback volume being the only thing that changes between the curves. The vertical position of the curve was not modified, and shows the actual volume difference.
I didn't measure the real SPL level. I guess that the maximum level was above 80 dB at 2 meters, with both speakers playing. The background noise in the room is around 35 dB SPL(A).

Fort = Loud / Faible = Quiet

They look similar. The Farina method has a weak sensitivity to background noise. I've asked REW to show the difference between these curves (arithmetic division) :

Here, it is very interesting to see that the difference curves at -10 and -20 look the same. Which means that the odd man out would be the loudest measurement, here taken as a reference.
If we trace the difference between the two intermediate curves, here is what we get :

I Don't think the speaker were playing at more than 90 dB at 1 meter. I am too afraid to fry a tweeter by pushing the volume during measurements.
In spite of the moderate level, compared to the >100 dB at 1 meter, we can see that the playback level is a stronger source of inaccuracy than the background noise of the room… at least during this measurement.

Therefore I agree that some more experiments would be interesting in order to choose the right playback level for measurements.

However, my opinion about the reference axis is different. I think that all speakers should be measured with the tweeter as a reference axis, even if the manufacturer says otherwise.

The two reasons are :

The listening window, early reflections, and power curves can only be compared to the tweeter curve. Comparing them to another reference curve would introduce a lot of confusion about the directivity of the speaker. The listening window curve might even be louder than the custom reference on-axis curve is some cases, if that one is not taken in front of the speaker ! How could we interpret that ? Every speaker measurement would have to be interpreted differently, since the spinorama curves would be measured differently. I Wonder if we might not be breaking the CEA 2034 spec if we followed the manufacturer recommendations for the reference axis !

And secondly, when we are listening to speakers in a room, the room doesn't care if the reference axis is in front of the tweeter or not. The predicted in-room response, (as well as the actual in room response, by the way), will be the result of the speakers complete acoustic behaviour. We must expect a speaker calibrated for flat response at mid-height measurement to sound brighter than a speaker calibrated for flat response at tweeter's height… and we want to see this difference on Amir's measurements, since that will make the speakers sound actually different !

 

[Krunok]

However, my opinion about the reference axis is different. I think that all speakers should be measured with the tweeter as a reference axis, even if the manufacturer says otherwise.

I don't agree. Measuring the speaker should be done at speaker's reference axis (recommended by manufacturer), not at tweeter's reference axis.

Btw, according to your logic, how would you measure these speakers?

 

[thewas]

I am too afraid to fry a tweeter by pushing the volume during measurements.

Don't worry about frying a tweeter at a KH, that simply won't happen as their limiters (separate for each driver) are quite well designed and intelligent.
Also a single sweep does not necessarily tell the situation happend at the NFS, because the KH has intelligent limiters that considers the thermal power at the voice coil, so a short peak won't be as reduced as a long term signal.

 

[Pio2001]

I don't agree. Measuring the speaker should be done at speaker's reference axis (recommended by manufacturer), not at tweeter's reference axis.

In this case, we'll have to discuss what sounds best : speakers with the reference axis at tweeter's height, or speakers with reference axis offsetted from the tweeter ?
The measurement won't tell us, since measurements for the first category will have a bias towards that category, while measurements for the second category will be biased in favor of that category.
We would end up with two categories of "good speakers", with no objective way to tell which kind is best.

Measuring everything according to the same standard will, at least, tell us what's the difference between the two designs.

Btw, accordng to your logic, how would you measure these speakers?

If they were not tilted towards the ceiling, the reference axis would certainly be in the middle of the speaker. But as they are intended to be used in this special position, the whole spinorama should be interpreted differently.
The Sound Power curve would be very important, as it would be the only one (together with the horizonal early reflections) to be able to be directly compared to the measurements of classical designs.

 

[Krunok]

In this case, we'll have to discuss what sounds best : speakers with the reference axis at tweeter's height, or speakers with reference axis offsetted from the tweeter ?

It's not about what is sounding best - it's about measuring a speaker at the reference axis specified by manufacturer.

If they were not tilted towards the ceiling, the reference axis would certainly be in the middle of the speaker. But as they are intended to be used in this special position, the whole spinorama should be interpreted differently.
The Sound Power curve would be very important, as it would be the only one (together with the horizonal early reflections) to be able to be directly compared to the measurements of classical designs.

Instead of guessing, the only correct procedure to measure a speaker like this would also be to do it at a reference axis specified by manufacturer.
As they designed the speaker they certainly know where it's reference axis is.

 

[dukanvadet]

That depends on the port tuning frequency, at 100 Hz (and above) most current speakers don't have much gain from it as their ports are usually tuned significantly lower.

This is my simulation of a 5 liter box with sb12nrx25-08 a 4 inch woofer with +/- 5mm xmax. The contribution of the port is dashed in dark blue. Still pretty good at 100hz.

Max output level is in light green at the top of the graph but same as frequency response its affected by calculated room gain so not exactly comparable to nuemanns numbers.

 

[Deleted member 65]

It's not about what is sounding best - it's about measuring a speaker at the reference axis specified by manufacturer.

Instead of guessing, the only correct procedure to measure a speaker like this would also be to do it at a reference axis specified by manufacturer.
As they designed the speaker they certainly know where it's reference axis is.

Just a question, none of my speakers (Gauder Akustik, Evolution Acoustics & Swan) have a ref axis specified by the manufacturer. Will we then have two categories of measured speakers: ASR determined ref axis & Manufacturer specced?

 

[Krunok]

Just a question, none of my speakers (Gauder Akustik, Evolution Acoustics & Swan) have a ref axis specified by the manufacturer. Will we then have two categories of measured speakers: ASR determined ref axis & Manufacturer specced?

Are you saying that the fact that your speakers don't have reference axis specified by manufacturer is the reason not to use one when it is specified?

 

[Deleted member 65]

When no reference axis is specified, the usual default position is to treat the tweeter as the reference axis.

So I guessed, implicitly we’ll then end up with two categories.

 

[thewas]

This is my simulation of a 5 liter box with sb12nrx25-08 a 4 inch woofer with +/- 5mm xmax. The contribution of the port is dashed in dark blue. Still pretty good at 100hz.

Max output level is in light green at the top of the graph but same as frequency response its affected by calculated room gain so not exactly comparable to nuemanns numbers.

How did you get the exact dimensions of the KH80 port?

 

[Deleted member 65]

Are you saying that the fact that your speakers don't have reference axis specified by manufacturer is the reason not to use one when it is specified?

No, I’m asking a question.

 

[thewas]

So I guessed, implicitly we’ll then end up with two categories.

Why should there be necessarily 2 categories?
This way we could do have categories for each other different characteristics.
It's just something that has to be considered when measuring them, like for example also placing them correctly.

 

[Krunok]

This is my simulation of a 5 liter box with sb12nrx25-08 a 4 inch woofer with +/- 5mm xmax. The contribution of the port is dashed in dark blue. Still pretty good at 100hz.

Max output level is in light green at the top of the graph but same as frequency response its affected by calculated room gain so not exactly comparable to nuemanns numbers.

According you your simulation port response is 11-12dB lower than driver's response.

Just as an example, 90dB+79dB=90.331dB, so I wouldn't say port contributed "pretty good".

 

[Krunok]

No, I’m asking a question.

And I'm letting you answer your own question.

 

[pozz]

I don't agree. Measuring the speaker should be done at speaker's reference axis (recommended by manufacturer), not at tweeter's reference axis.

Btw, according to your logic, how would you measure these speakers?

View attachment 47183

"On-axis" for these speakers corresponds to 0 degrees at the floor. If they were elevated and set on the Klippel platform for measurement the response would be incorrect.

https://www.xlrtechs.com/dbkeele.com/CBT.php

• (2015) Don Keele - Constant Beamwidth Transducer Loudspeaker Arrays (9-Part Playlist)
• (2017) Don Keele - Broadband Constant Directivity

 

[edechamps]

(I decided to delete my earlier post to provide more detail, didn't realize you had already responded to it, sorry for the confusion.)

Just a question, none of my speakers (Gauder Akustik, Evolution Acoustics & Swan) have a ref axis specified by the manufacturer. Will we then have two categories of measured speakers: ASR determined ref axis & Manufacturer specced?

Actually this is specified quite clearly in CTA-2034-A:

The reference axis should be specified by the manufacturer. It approximates the direct-sound listening axis for a seated listener in the prime listening location, at a normal listening distance.

Defining the reference axis requires that assumptions be made, and perhaps for this reason manufacturers rarely specify it. Because the reference axis is needed to perform the tests described in this standard the following method shall be used to define it whenever the manufacturer has not specified it.

The starting point of the reference axis shall be either the center of the high-frequency driver (normally a tweeter) or a point midway between the high-frequency and midrange drivers. The specific point that is used shall be specified in the final report. The orientation of the reference axis depends on the design of the loudspeaker. For most conventional loudspeakers with a front baffle, the reference axis shall be perpendicular to the front baffle. If the loudspeaker design is such that there is not a conventional front baffle, the reference axis shall be in the direction of the intended forward radiation of sound from the loudspeaker.

Note this mention: "the following method shall be used to define it whenever the manufacturer has not specified it". In other words, if the manufacturer did specify a reference axis (as Neumann did for the KH-80) then that's what should be used. It follows that measuring the KH-80 with the tweeter as the reference axis is not compliant with CTA-2034.

 

[Krunok]

So I guessed, implicitly we’ll then end up with two categories.

?