Speaker directivity, waveguides and apparent lack of them

[fluid]

It's the dip at about 280hz and also the roll off starting at 10khz and 100hz. I'm not an expert and I know it's not that bad but once you've bought all the parts and had the woodwork made that's not a budget speaker so I would hope for a flatter response.

Speaker design is a matter of balancing priorities, the on axis dip at 280Hz comes from the on wall mounting, the wall mounting provides even wide directivity above 1K. The directivity narrowing quickly above 10K comes from the large diaphragm tweeter used, that tweeter allows for high output with low distortion. The rolloff below 100Hz is because it is a sealed design with a small woofer that is not boosted actively, this will work well with a subwoofer at an 80Hz crossover.

 

[DanielT]

Regarding the shape of baffles and its impact, this may be interesting information. When you look at the manufacturer's data sheet on different loudspeaker elements you can often see that the measurement is carried out on an IEC baffle. But then what is that?
Here an example with tweeter SB26ADC-C000-4. SB Acoustics' own measurement of that tweeter, performed on an IEC baffle:

SB26ADC-C000-4 / Aluminum - Sbacoustics

Phase optimized diaphragm design for coherent high frequency radiation, copper cap for reduced voice coil inductance and minimum phase shift.

sbacoustics.com

And this is the shape of that IEC baffle:

What is a Frequency Response Chart? | Jensen Loudspeakers

www.jensentone.com

Edit:
Incidentally, SB Acoustics also measures bass drivers on an IEC baffle, see for example here:

15″ SB42FHCL75-6 / Honeycomb - Sbacoustics

Light weight rigid honeycomb cone (hard paper honeycomb with fiber glass skin layers), 3" copper voice coil for improved power handling.

sbacoustics.com

 

[JakeK]

Speaker design is a matter of balancing priorities, the on axis dip at 280Hz comes from the on wall mounting, the wall mounting provides even wide directivity above 1K. The directivity narrowing quickly above 10K comes from the large diaphragm tweeter used, that tweeter allows for high output with low distortion. The rolloff below 100Hz is because it is a sealed design with a small woofer that is not boosted actively, this will work well with a subwoofer at an 80Hz crossover.

That all makes sense and I'm sure it's not a bad design. It does seem like more speakers are designed to be used with a sub lately which is all very well but not everyone wants to spend time finding the sweet spot for the sub or setting up the crossover to the sub or indeed giving up floor space for one.

 

[Digital_Thor]

Some people actually still cough up the argument, that directivity(controlled or not) is an unnecessary feature and over-hyped, since listening to speakers way off axis, never is their intent - and on-axis looks fine. Of course, totally ignoring the fact a lot of what they listen to, is reflections from the room.... mostly no matter how they damp the room.
But like any rigorous belief - you can only show them the water trough.....

 

[ctrl]

Some people actually still cough up the argument, that directivity(controlled or not) is an unnecessary feature and over-hyped, since listening to speakers way off axis, never is their intent - and on-axis looks fine. Of course, totally ignoring the fact a lot of what they listen to, is reflections from the room.... mostly no matter how they damp the room.
But like any rigorous belief - you can only show them the water trough.....

I have to totally agree with you.
It's often the same people who only pay attention to the most linear on-axis frequency response possible, consider off-axis measurements to be of little relevance and at the same time emphasize how important room treatment is.
Of course, the poorer the off-axis quality of a loudspeaker, the more room treatment with absorbers is necessary (to achieve a tolerable tonal quality).

The importance of the overall radiation of a loudspeaker can easily be shown by looking at direct sound versus reverberant sound (contains only the early reflections and higher order reflections at the listening position). This distinction can easily be made in the measured impulse response, where reflections are easily recognizable as small peaks:

Then you can look at the corresponding frequency responses of direct sound versus reverberant sound to show their SPL ratio - in our example measured for a loudspeaker at a distance of 1.5m (below 200Hz gated measurement is not valid):

Even at a distance of just 1.5m, the reverberant sound is dominant in many frequency ranges.
This means, for example, that the tonality and timbre of a loudspeaker is dominated by the off-axis behavior of a loudspeaker in a normal listening room and listening distance.

So if one does not have 10cm thick absorber panels in one's listening room and thus pushes the reverberant sound below the direct sound, one should pay a lot of attention to the radiation of a loudspeaker.

Update: To show what the "room sound" (direct sound + reverberant sound, with 1/3 smoothing) looks like at a distance of 1.5m from the speaker, here is a diagram showing everything together:

 

[OCA]

I have to totally agree with you.
It's often the same people who only pay attention to the most linear on-axis frequency response possible, consider off-axis measurements to be of little relevance and at the same time emphasize how important room treatment is.
Of course, the poorer the off-axis quality of a loudspeaker, the more room treatment with absorbers is necessary (to achieve a tolerable tonal quality).

The importance of the overall radiation of a loudspeaker can easily be shown by looking at direct sound versus reverberant sound (contains only the early reflections and higher order reflections at the listening position). This distinction can easily be made in the measured impulse response, where reflections are easily recognizable as small peaks:
View attachment 341409

Then you can look at the corresponding frequency responses of direct sound versus reverberant sound to show their SPL ratio - in our example measured for a loudspeaker at a distance of 1.5m (below 200Hz gated measurement is not valid):
View attachment 341412
Even at a distance of just 1.5m, the reverberant sound is dominant in many frequency ranges.
This means, for example, that the tonality and timbre of a loudspeaker is dominated by the off-axis behavior of a loudspeaker in a normal listening room and listening distance.

So if one does not have 10cm thick absorber panels in one's listening room and thus pushes the reverberant sound below the direct sound, one should pay a lot of attention to the radiation of a loudspeaker.

Update: To show what the "room sound" (direct sound + reverberant sound, with 1/3 smoothing) looks like at a distance of 1.5m from the speaker, here is a diagram showing everything together:

View attachment 341423

I would like to add that whichever speaker you place at the exact same location in that same room, the reverberant impulse peaks will be at exactly the same location bar very small (less than 1ms) differences in the first couple of peaks due to different driver heights. It's the frequency content in these impulse peaks that differs from speaker to speaker and this is determined by the very first reflections within the speaker:

This seems to be a two-way ported speaker but check all these reverberations (red arrow) between the twitter (T), woofer (W) and the port (P). See how similar the next impulse peak is to that original one and then the peak shapes deviate more and more from that in time. It's these very early reflections that change phases of the sound waves and cause frequency magnitude deviations which are carried over to the room. Sound waves otherwise always spread as a 3D sphere growing equally to all directions.