Yeah I was also wondering exactly what you are envisioning for the 3 way.
How did you discover all of the peaks and spikes and troughs?
What measuring gear are you using to take SPL curves?
Right now @Andre Bellwood I’m using a umik-1 that’s in the middle of a foam microphone audio booth, with acoustic panels on all the surfaces between the speaker I’m testing and the mic, behind the speaker for testing on the wall is my unused acoustic absorption ceiling panels with 1.5cm thick wool over them.
I spent a while today building 60x120x8cm sound absorbing panels so I can get a more accurate reading.
I spent a while today building 60x120x8cm sound absorbing panels so I can get a more accurate reading.
So for bass 80hz up I have a 10cm diameter acrylic disc, with two exciters on it. The disc sits on top of a 8cm diameter hole cut into 2mm thick non-foam neoprene rubber.
For mid I have a few options since the 1000-5000hz is the easiest to find for exciters.
A strong candidate is cardboard with honeycomb core, that has been firm rolled with two part epoxy to give it a hard but lightweight finish, and to stop the walls of the cut hexagon core from flapping, and that is glued to a 2mm foam neoprene that is held tight and flat in a frame.
The candidate for 5000-16000+ hz is garolite and something else in a composite.
Maybe glass. Maybe brass.
Although one of these would be very helpful in tracking exactly what changes when the composition changes.
@Andre Bellwood i can’t reply or quote your post, the button isn’t showing up.
But yes, I’ve got a three way crossover which has 12db/octave attenuation slope, with crossover at 1000 and 5000.
It could very well not be the crossover that gets used pending the tweeter range.
But I was curious what the panels would sound like when given only the frequencies that they were best at.
When I first got a good enough match on all three the music sounded different… it’s hard to describe but it made it feel like seeing higher resolution, or putting on the imax 3D glasses.
And so I’ve been on the continual process of chasing that down, making is reproducible, and also making it aesthetically appealing.
Because an acrylic circle on a piece of rubber strip, while sounding good looks like trash.
But yes, I’ve got a three way crossover which has 12db/octave attenuation slope, with crossover at 1000 and 5000.
It could very well not be the crossover that gets used pending the tweeter range.
But I was curious what the panels would sound like when given only the frequencies that they were best at.
When I first got a good enough match on all three the music sounded different… it’s hard to describe but it made it feel like seeing higher resolution, or putting on the imax 3D glasses.
And so I’ve been on the continual process of chasing that down, making is reproducible, and also making it aesthetically appealing.
Because an acrylic circle on a piece of rubber strip, while sounding good looks like trash.
I would like to use the concept of a folding room divider for each speaker, whether I make them full size or tabletop size will end up be down to my wife’s tolerance levels for them.
Examples from my design look book:
Examples from my design look book:
Keep in mind that one of the massive advantages of DMLs is virtually zero phase shift on the impedance curve.
This gets destroyed by crossover networks.
Another big DML advantage is that one does not need crossovers in the midrange where the ear is most sensitive to anomalies.
This gets destroyed by crossover networks.
Another big DML advantage is that one does not need crossovers in the midrange where the ear is most sensitive to anomalies.
@Andre Bellwood thanks, I wasn’t aware of that.
the sound I was getting was very enjoyable, better than what a single panel was producing.
I’ll have a look at the phase graph after I wire it back up and see what it’s doing there.
the sound I was getting was very enjoyable, better than what a single panel was producing.
I’ll have a look at the phase graph after I wire it back up and see what it’s doing there.
Jamie ..Also be mindful that there's a size effect in these panels and that test results on 300x300 panels will likely not be reliable when applied as a selection criteria for larger panels
Eucy
Eucy
@Eucyblues99 hm… do you know the difference it makes? I could cut a panel or two to a few sizes and measure it.
My assumption is the larger panel has a larger amplitude, and the ratio of the sides can affect some resonance peaks and dips, and the material affects the speed of sound.
But I can test this and see what changes
My assumption is the larger panel has a larger amplitude, and the ratio of the sides can affect some resonance peaks and dips, and the material affects the speed of sound.
But I can test this and see what changes
Hello André,
Not sure to understand that.
The phase shift on a FR occurs in relation with the level changes. For example, at each end of the bandwidth of a loudspeaker. With standard pistonic speaker it is something to manage in the crossover design. The DML being a full range or at list a wide range, the desired cutoff frequency might be further than in the case of a pistonic speaker but...
- The phase change very quickly also at each peak of the FR linked to modes or panel resonances and here by the nature of DML probably with more local changes than with a pistonic speaker.
- The impedance curve is not as smooth as the curve of a pistonic speaker (see my posts before). The crossover design suppose the loudspeaker being resistive. Additional networks are used to reach this requirement. For DML... everything has to be said. I just made a 12dB High Pass for a panel; without thinking more than that, I mitigate the effect of the multiple mode peaks by putting a 6.8Ohm resistor in parallel of the exciter which not good for the efficiency.
Christian
Hi Christian,
Here's the impedance and impedance phase curve of a panel with 4 drivers on it. No cross-over. Green curve is impedance, the dotted curve is impedance phase.
The important thing to note is that eventhough there are several peaks in the impedance response, they are minimal, a few ohms at most, and nothing like the massive swings presented by piston speakers and their cross-over networks.
If I had to add cross-overs to the drivers in the curves shown, then besides amplitude changes in magnitude to the individual drivers, there would be at least 90° opposing phase shifts at their associated cross-over points. Bessel or Linkwitz-Riley filters attempt to address this problem, but the over-all, relatively flat system impedance phase response would be negatively affected.
To me, it's anathema to introduce standard cross-overs into DML panels, but I do agree that there are ways of cheating a bit, and adding passive components (shorting caps! 😎 ) to modify driver responses a bit without stuffing up the impedance phasing too much.
IMO Mechanical "cross-overs" (ortho-springs) are a much better way of retaining DML action while separating the panels into their own bands where they work best.
Here's the impedance and impedance phase curve of a panel with 4 drivers on it. No cross-over. Green curve is impedance, the dotted curve is impedance phase.
The important thing to note is that eventhough there are several peaks in the impedance response, they are minimal, a few ohms at most, and nothing like the massive swings presented by piston speakers and their cross-over networks.
If I had to add cross-overs to the drivers in the curves shown, then besides amplitude changes in magnitude to the individual drivers, there would be at least 90° opposing phase shifts at their associated cross-over points. Bessel or Linkwitz-Riley filters attempt to address this problem, but the over-all, relatively flat system impedance phase response would be negatively affected.
To me, it's anathema to introduce standard cross-overs into DML panels, but I do agree that there are ways of cheating a bit, and adding passive components (shorting caps! 😎 ) to modify driver responses a bit without stuffing up the impedance phasing too much.
IMO Mechanical "cross-overs" (ortho-springs) are a much better way of retaining DML action while separating the panels into their own bands where they work best.
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A larger panel will extend the FR downwards. Experiment with edge damping to modify your bass response.
If you want to increase efficiency then use multiple drivers and/or lighter density materials and composites.
Lighter density materials will generally increase your midrange response.
There are standard length/width ratios that give you the best node coverage.
Large peaks and dips are generally caused by incorrect driver positioning and/or poor dimensional ratios.
Take lots of measurements and store them for later reference. Judging by ear alone is a perfect recipe for blinkered opinion and your panels will eventually sound "good" (whatever that means) only to you.
Eucy is in general correct here. But I do think the 300x300 "free" test is a reliable indicator of the relative efficiency(loudness) of different materials, as well as at what frequency and how fast their response starts falling off at the high frequency end.
But as Andre pointed out, the low frequency response is dependent on the panel size, aspect ratio, and boundary conditions, in combination with the properties of the panel (elastic moduli, density, thickness...). So testing a 300x300 mm panel gives you very little (if any) information about how to get low frequency response (except telling you which material will go the lowest at that particular size).
It's a little too complex to "measure it" with a few tests of different sizes.
Actually, the size and aspect ratio of the panel (and boundary conditions) arguably affects all (not some) of the resonance peaks and dips. But the biggest effect will be at low frequencies, where the density of modes is small. At higher frequencies there is more overlap so individual modes (resonances) have less impact.
FEM (Finite Element Modeling) is a good way to get an idea of how these things work if you have the interest.
Eric
Ah, so you mean a three way where each of the elements is a different DML. Not many (if any?) of us are doing that. I'm not saying it's a bad approach, just that the more common is to combine a DML with a pistonic sub, as I do. I typically get 100 Hz to say 12-15k with a single panel. At my age I can only hear up to about 11k, so adding a separate panel for highs would be superfluous. Hence, a two way with a sub crossing over at around 100 Hz is all I think I need.
Eric
Interesting!
And the parallel resistor I suggest will limit even more the impedance variation. let's suppose 6.8Ohm in parallel of this DMLwith a mini 5Ohm to max 17Ohm, it will result... oh, oh 2.9 to 4.8 Ohm. A bit too low probably (6.8Ohm was what I had close to me!).
Some simulation might say more!