Understanding measurements

[JeanKazamer]

hi all, sorry to bother but the neophyte here as some problems following all you experienced folks ( brain sweats all over my desk from reading this forum )

1- Do we have ( or could you please point ) to what " IDEAL " measurements of directivity should look like ?
( most of the other measurements i can understand with the " ideal " lines added thanks for that

2- I am looking at different types of drivers trying to understand and learn, and i am having difficulties understanding or rather comparing distortion measurements graphs. It's like every manufacturer use a very different scaling and or test methodology and makes it diff. for the noob in me to understand what is going on.

For example in this test of a compression driver :

Is that by any measure good performance ? I understand those drivers are usually used in " loud " pro setups,
but what about at normal listening levels ? Can we get useful info from those graphs with crazy high DB ??




3- If i understood correctly, when designing a loudspeaker system, it would be easier to have " too much DB " to start with than too little ?
As in X tweeter has a good 5-10db shelve from let's say 8k to 12k as opposed to having a dip down in the same range.
Is it because it is much easier to EQ down than up thus getting lower distortion simultaneously ?


4- Lastly ( sorry i know to many questions my bad ..i'd have 200 more but i'll try and find some of it by myself )
Is the goal with sound pressure and distortion getting the lowest amount of distortion at the highest listening sound power for the intended purpose ?\
THD plots with very low efficiency drivers in the low 80db don't mean much then ? I'd guess that drivers of any type should have lower distortion when output is lowered right ? ( unsure i formulated my thought right here sorry lol )

And as always, thanks to all of you for helping out and sharing info much appreciated !

 

[sweetchaos]

1- Do we have ( or could you please point ) to what " IDEAL " measurements of directivity should look like ?
( most of the other measurements i can understand with the " ideal " lines added thanks for that

Yes.

Here's Preference Score of 9.6:

Here's Preference Score of 8.8:

This was simulated by MZKM on this post.

 

[JeanKazamer]

This is an example of a similar driver .... not even sure what to make of this data lol

 

[JeanKazamer]

Ic thanks for those ....that clarifies that one ..quite logical

I guess it all ties to the " bandwidth " data and the hori/vert directivity graphics ?

like this one ...

The Ideal there would be smooth " elongated triangle " of red centered with very smooth transition into the exterior colors ?

 

[sweetchaos]

I personally don't like the normal directivity graphs (aka the non-normalized ones), as there's too much going on.
So the one that Amir posted is:

Spoiler

Now, here's the same graph, but normalized to on-axis, and the scale is now in +3db increments.

Spoiler

See how you can easily tell where the +-3db wall of sound is, and where the +-6db is as well. These are the most important ones anyway.
Im my opinion, the 2nd graph shows me more useful information than the 1st. But, to each his own, as some people prefer the first one.

To answer your question, about what the ideal directivity graph looks like...well it's something like this:

Spoiler

In this case, the +-3db point is somewhere around 30 deg off axis.


Here's an example of a very wide horizontal directivity that Amir measured, the In-wall Speaker Measurements (Monoprice THX-365IW):

Spoiler

UPDATE: Here's an example of a very wide horizontal directivity that Erin measured, the Philharmonic BMR (normalized to on-axis):

Spoiler

Now, note that people will like either narrow directivity (like the Kef and Genelecs) or wider directivity (like the Revels).
That's a personal preference.
Here's a few examples of each:

Spoiler

Source

I hope that helps.

 

[abdo123]

Here's an example of a very wide horizontal directivity that Amir measured, the In-wall Speaker Measurements (Monoprice THX-365IW):

this speaker does not radiate beyond 90 degrees at all since it's on an infinite baffle, it was a graph error and i pointed it out to Amir that this way people would think it's omni-directional when it's not but he couldn't really fix it. it's not a wide directivity speaker at all.

The philharmonic BMR is what i would consider wide directivity.

 

[hardisj]

I created a series of videos for my channel so I could simply reference that rather than explaining the data in detail every time. You might find it helpful:

https://youtube.com/playlist?list=PLnIxFR_ey0b37Ex4KV2mBz-kYB7QLffR1

 

[hardisj]

Also, in this video I do some compare/contrast between different results of speakers I have reviewed which might give you some insight into things to look at that matters to you.

 

[JeanKazamer]

Thanks both for great info.

This cleared a few things .

hardisj : i'd already seen some of your tubes ! nice stuff there! +1 sub and a few likes for you !​

You have a Klippel testing system ?


Now what's left is understanding Distortion measurements.

Anyone has good reading links on that subject ?

 

[BoredErica]

Now, note that people will like either narrow directivity (like the Kef and Genelecs) or wider directivity (like the Revels).
That's a personal preference.

It seems like in the interview with Sean Olive by Erin, Sean said people generally preferred wide directivity. Advantage narrows when walls are very far apart, and narrow are better for surround.

Spoiler

 

[fluid]

1- Do we have ( or could you please point ) to what " IDEAL " measurements of directivity should look like ?

There is no agreement among the best designers and researchers on what constitutes the "ideal" directivity. Earl Geddes targets 90 degree horizontal with high and flat DI. The best cone and dome speakers tend towards the sort of directivity as shown in the graph above, smoothly increasing from low to high. Companies like Dutch and Dutch, Genelec and Kii make speakers that can be placed closer to room surfaces without suffering as much boundary interference.

I find the difference between the scores shown above to demonstrate why you have to be very careful of the values. Those two speakers have virtually identical directivity and due to a small amount of noise in the response the score drops from 9.6 to 8.8.

Is that by any measure good performance ? I understand those drivers are usually used in " loud " pro setups,
but what about at normal listening levels ? Can we get useful info from those graphs with crazy high DB ??

Have a read of Earl Geddes papers on the perception of non linear distortion. You may spend less time poring over low order harmonic distortion graphs.

http://www.gedlee.com/Papers/papers.aspx

http://www.gedlee.com/Papers/The Perception of Distortion.pdf

3- If i understood correctly, when designing a loudspeaker system, it would be easier to have " too much DB " to start with than too little ?

In general yes

4- Is the goal with sound pressure and distortion getting the lowest amount of distortion at the highest listening sound power for the intended purpose ?\
THD plots with very low efficiency drivers in the low 80db don't mean much then ? I'd guess that drivers of any type should have lower distortion when output is lowered right ? ( unsure i formulated my thought right here sorry lol )

As an engineering exercise yes.

 

[JeanKazamer]

There is no agreement among the best designers and researchers on what constitutes the "ideal" directivity. Earl Geddes targets 90 degree horizontal with high and flat DI. The best cone and dome speakers tend towards the sort of directivity as shown in the graph above, smoothly increasing from low to high. Companies like Dutch and Dutch, Genelec and Kii make speakers that can be placed closer to room surfaces without suffering as much boundary interference.

I find the difference between the scores shown above to demonstrate why you have to be very careful of the values. Those two speakers have virtually identical directivity and due to a small amount of noise in the response the score drops from 9.6 to 8.8.

Have a read of Earl Geddes papers on the perception of non linear distortion. You may spend less time poring over low order harmonic distortion graphs.

http://www.gedlee.com/Papers/papers.aspx

http://www.gedlee.com/Papers/The Perception of Distortion.pdf

In general yes

As an engineering exercise yes.

Awesome stuff! Greatly appreciated mate! i'll take time to real Earl Geddes stuff completely later !

 

[JeanKazamer]

Blind reliance on measurements can be misleading ‐ one needs to tie those measurements back to subjective perception y It is the perceived sound quality that matters not the measured quality – unless that measurement has been scaled and correlated to subjective perception through valid psychoacoustic tests.

If i understood correctly, this is what Big Boss Amir discusses about, in some of his Tubes, mentioning the work of dr Floyd Toole for correlation
between measurements and psychoacoustics ?