So if the comb filtering is solely the result of the mid-tweeter driver, that implies at least 2 discrete surfaces with a significant distance between them, no?
How very peculiar.
How very peculiar.
Bending wave, low order crossovers and tradeoffs
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
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
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- 12 posts total
I dunno. Frankly, I don’t really understand how they work. At CAF the designer Paul Paddock was there with a guy doing the dog and pony, and PP was pretty cagey about the details. This is him: https://patents.justia.com/inventor/paul-w-paddock They were a real sleeper at the 2018 CAF, but now this year after the 2019 CAF everyone is oohing and aahing over them. Go figure. |
Here is the old thread we had on bending wave transducers: https://forum.audiogon.com/discussions/gobel-and-the-bending-wave?highlight=bending%2Bwave |
I'm probably going to offend people who actually know bending wave transducers, but I think the Ohm Walsh drivers are great examples. In a normal cone, you want the whole thing to move, like a solid piston, but without the mass. :) That is, ideally, the voice coil, dust cap and cone all move at exactly the same time. The Ohm Walsh driver looks like a piston, but here's what's different: The cone bends. The signal starts at the voice coil and then, over time, travels down the length of the cone to the ends. I'm not even sure if the end of the cone is allowed to move or not, it may be fixed. And to me this is the overall principle of a bending wave transducer. They are excited at one point, and then at some point in time the signal finally reaches the edges. With a cone, ribbon, ESL, AMT the ideal situation, the signal reaches the edges of the driver at the same time it reaches everywhere else. Of course, there are no absolutes, but that's the definition I work on. |
- 12 posts total