Hi,
I hope this is the right circle for this topic, I couldn't find any which would suit better.
I posted this message few weeks ago to DIYaudio, but I didn't get any replies so I'm hoping better luck from this discussion board.
A while ago I made a discussion about similiar project, but back then I was thinking about OB design. After finding out more about ob speakers and realizing how hard it is to get it work, I decided to postpone that idea and go with sealed/reflex boxes for this project.
The drivers I bought for this project:
ScanSpeak D2010 Seas MCA12RC Peerless 830868And this is what I've been planning:
Layout Or at least this is the latest layout as I've been trying to tweak it for few weeks now. I've tried many different tilt angles and now it's 15 degrees.
At the moment the crossover has lowpass for the woofer, bandpass for the midrange and a lpad and highpass for the tweeter. All 2nd order electrically. The midrange polarity is inverted.
This is how the responses look like:
http://koti.mbnet.fi/twisted-/3way/frequency_responses_01.gifI made the measurements by myself in a "infinite" baffle (and added near field measurements), then added baffle diffraction to the midrange and woofer. After that I substracted -6d from the woofer and midrange so the levels matched with the tweeter. The woofer will be placed in a reflex box but as the box doesn't exist, the response is lacking the port output. The midrange will be placed in a closed box.
I didn't mount the woofer flange to the measurement baffle, as I thought it would be best for the relative acoustic offsets.
Now the thing I've been using most of my time is to get the phase responses to match at xo points.
This is how the responses looks like without the relative differences in the tilted layout (just for a comparison):
Phase responses Red is tweeter, green is midrange and pink is woofer.
And here is the system phase responses with relative offsets included:
System phase responses XO points are 450Hz and 3250Hz.
And here are my questions :
- The 15degree tilt sounds quite a lot to me, is this a reasonable amount of tilt? Has anyone of you made anything similiar and how did it turn out?
- I've been using 300cm for the mic distance in the system frequency simulations as I though this would be pretty close to the real listening distance. Is this the right way to do it? Changing the mic distance obviously has an effect to the relative phase responses.
- The bass output at ~150hz is about 2dB above the midrange level and I've been wondering if it's going to make the sound too boomy. If the sound turns out unsatisfactory, can I low down the woofer with series resistor just like a tweeter or is there any kind of problem with this (or alternatively using l-pad)?
- How does the phase responses look like to you? Whatever I've tried to do, the responses at 450Hz xo point hasn't been significantly improved. Is this good enough?
-Have I done the layout in Z direction correctly? The tweeter is 300cm away from the mic, but the midrange and woofer is more closer. Now I tried to put the woofer to value 0, the midrange to 10,30cm and tweeter to 13,7cm. The relationships are equal to
this , but now all of the drivers are more than 300cm away from the mic and the phases look like this:
System Phase responses 2 Again, red is tweeter, green is midrange and pink is woofer.
Which is the correct way? Can any of the drivers be closer to the mic than the defined mic distance?
And here's two questions that aren't exactly related to this particular project, but if someone wants to clarify these things to me it would be appreciated.
- There are lots of commercial 3-way designs where the bass driver is located to the side of the cabinet like
this. How the xo point phase can be matched in this kind of situation and how low the xo point has to be this to work properly? I'm guessing the flaw of this design is that the woofer is quite a lot more far away from the listening point than the mid/tweeter.
- Does the location of the reflex port have any real effect to the driver/port output combined response? I am guessing there is somekind of phase difference between these two outputs? Does it make a difference how far away from the driver the port output is? (for example in the front or the back of the baffle)
