Stereophile just reviewed an interesting bit of kit, the Manger P1. The mid-tweeter is a bending wave transducer, while the woofer is conventional. Crossover point is around 400 Hz.
The DIY community has a similar type of design called Woofer Assisted Wide Band. It is 90% wide-band, plus a woofer.
https://www.stereophile.com/content/manger-p1-loudspeaker-measurements
Of course, you have to listen to make any sort of real assessment
as to the value of the speakers and their suitability to your own home, I
just wanted to share with the measurement readers how I might look at a
crossover and the paths not taken so others can gain some insight into just how much is happening in the crossover design of a speaker. Let's take a looksie ...
There are many who feel the best crossovers are 1st order (6 dB / octave) as high order rob dynamics or something. This is not an effect I have heard. Lots of 1st order, time aligned speakers I have not like at all, and one with active woofer system, was spectacular. So for me this is not a compelling sales pitch.
But still, lets say low-order or no-order filters is a very desirable characteristic, so lets talk about the negative consequences of having a very simple crossover, as apparent here.
Comb Filtering
Those armchair speaker designers who get frothy mad at driver arrays, claiming "comb filtering" when there's no evidence in the measurements are oddly silent when it's right in front of them. This is a good example. Look at figure 5. Plenty of comb filtering visible here. What's going on? The low-order filters used is letting the woofer interfere with the mid-tweeter. Lots of great speakers do much better off-axis than here.
Next, lets look at the impedance chart, Figure 1. See that 3 Ohm dip around 200 Hz? With a low rise above 8 Ohms around 1,500 Hz? This is evidence of a minimalist crossover. It's quite possible that the woofer is run full-range with no low pass filter at all, and the mid-tweeter may have only a cap.
I will say that I do not like speakers with a dip in this region,
as I find them quite demanding of amplifiers. My usual reaction is "WHY
WOULD YOU DO THIS?" and then I am reminded that audiophiles LIKE
demanding speakers. We are rather masochistic when it comes to the care
and feeding of speakers. Some manufacturers deliberately drop the impedance in this range for exactly this reason.
Lastly, lets look at the overall shape of the output, Figure 4, showing a subdued mid-range. Not exactly recording studio attributes here, but possibly a good speaker at lower volumes. The shape here is a function of the cabinet, drivers and crossover design. No one thing contributed to the speaker's tonal balance, which we can lay it the foot of the designer, but if you choose to use a minimalist crossover as evidenced here there's only so much you can do to change things.
So, to recap, the designer picked a minimalist crossover and accepted poor lateral response and a low minimum impedance, and a lumpy frequency response curve as trade-offs. Or we could say he/she wanted all three.
Best,
E
