Hello,
I can not seem to post an image. But, I modeled the following on The Edge and Xbaffle.xls:
406mm wide
914 mm tall
81mm driver centered on width, located at 711mm.
With The Edge, I get a peak in the mid range (100-1300Hz). It goes up ~2dB by going to open baffle. Is this due to the reflections off the back wall? Something else?
In an Audio Kinesis' blurb from another thread about why their bipole is shaped the way it is, it seems that the rear wave cancellation/dip is explained (seen at 1800Hz in The Edge's model).
In Xbaffle, no midrange peak is seen, but a dip around 175Hz is seen.
What is the difference in the two models that creates this "discrepancy" between them?
I can not seem to post an image. But, I modeled the following on The Edge and Xbaffle.xls:
406mm wide
914 mm tall
81mm driver centered on width, located at 711mm.
With The Edge, I get a peak in the mid range (100-1300Hz). It goes up ~2dB by going to open baffle. Is this due to the reflections off the back wall? Something else?
In an Audio Kinesis' blurb from another thread about why their bipole is shaped the way it is, it seems that the rear wave cancellation/dip is explained (seen at 1800Hz in The Edge's model).
In Xbaffle, no midrange peak is seen, but a dip around 175Hz is seen.
What is the difference in the two models that creates this "discrepancy" between them?
croat47 said:
The 2-3 dB emphasis in peaks and dips is due to the backside radiation of the speaker coming to the front. Since EDGE does not care about any walls or the floor, it can not simulate any reflections off any walls.
The baffle model of Xbaffle is not as sophisticated as that of EDGE. But Xbaffle accounts for the reflections off the floor and off the back wall and nearest side wall. As with any speaker, the room related effects by far outweight the baffle related ones and tend to mask them in your diagrams.
Thanks!
So, for a best guess on what a particular driver would do in a given baffle/room position, Xbaffle is a little better approximation?
I am trying to determine a rough point for using a monopole bass driver as compensation for baffle step loss. Based on Xbaffle, it looks like rolling in around 250 for that width.
So, for a best guess on what a particular driver would do in a given baffle/room position, Xbaffle is a little better approximation?
I am trying to determine a rough point for using a monopole bass driver as compensation for baffle step loss. Based on Xbaffle, it looks like rolling in around 250 for that width.
croat47 said:
IMHO the best strategy would be to first determine the optimal driver position on the baffle and the dipole loss frequency with EDGE (try off axis microphone positions too to see what happens there), and then the best baffle position in room with Xbaffle.
Look what happens if you move the upper right corner of the baffle 15 cm to the left. For a 3" driver the 40 cm baffle is too wide by far.
Thanks again!
Rudolf: I did as you suggested in The Edge. I did not re-center the driver. Significant reduction in the peak and null! Then I read the link that John K said was worth reading.
John K: thanks for the link. Certainly worth reading. To Rudolf's point: 40cm is too large based on the sim and on your discussion about the directionality. Does a driver become directional at a point where it's effective diameter is 1/4, 1/2, or 1 lamda?
Then, would one use a baffle that creates a situation in which the driver is operating as much as possible in the omni-directional range? Let's say I used a tweeter: would I target the crossover to a point below where the midrange becomes directional?
If I am in any way moving in the right train of thought: how would I determine an optimum offset within the baffle? This would change the actaul baffle width a bit as one shifted to either side.
Or: would one decide on the best circular baffle, and create an equivalent rectangular baffle per another discussion on John K's site?
Good stuff.
Rudolf: I did as you suggested in The Edge. I did not re-center the driver. Significant reduction in the peak and null! Then I read the link that John K said was worth reading.
John K: thanks for the link. Certainly worth reading. To Rudolf's point: 40cm is too large based on the sim and on your discussion about the directionality. Does a driver become directional at a point where it's effective diameter is 1/4, 1/2, or 1 lamda?
Then, would one use a baffle that creates a situation in which the driver is operating as much as possible in the omni-directional range? Let's say I used a tweeter: would I target the crossover to a point below where the midrange becomes directional?
If I am in any way moving in the right train of thought: how would I determine an optimum offset within the baffle? This would change the actaul baffle width a bit as one shifted to either side.
Or: would one decide on the best circular baffle, and create an equivalent rectangular baffle per another discussion on John K's site?
Good stuff.
croat47 said:
That is the place, where the distance from the driver to each edge is as different as possible and where the distances are no entire multiples of each other. The 'golden mean' (~1:1,618) is a good starting point for experiments.
Between 1/2 and 1 lambda. This depends on the actual radiating area of the cone, which may be smaller at higher frequencies.croat47 said:
Directionality does not depend on the baffle, but on the cone size. Baffle size commands the smoothness of the on and off axis radiation.
By and large: Yes.
Rudolf said:
So, where is that high frequency shift from 1/2 to 1 lambda?
I think I understand that the directionality is based on the driver. Maybe I did not pose the question well. You have shown me that the smaller baffle works better with respect to the peak/null behavior. John K shows that increasing the baffle size above a certain point magnifies the effect of directionality in a given model of a driver of arbitrary size ( I think that is what it shows
.)That driver becomes directional at say 1/2 lamda. I would want to keep the baffle small enough to prevent the magnification of that. Or, I would want to cross to a tweeter before that directional behavior kicks in, yes? Referencing John's site, when he shows the increased size of a circular baffle: the null after the dipole peak gets deeper and moves to 2K from 1K. So, going too big would drive a null as well as then require (in this case) a too-low crossover for typical dome tweeters.
In my case, the driver by calc and by published response becomes directional around 2200Hz. So, crossover to the right tweeter could help on any baffle.
But, what would be an "optimum" baffle size? You pointed me at 25cm. Was that arbitrary, or is there some rough math that pointed you there?
How far off track am I? 😕
[Edited to switch "1K to 2K" to "2K to 1K"]
All baffle effects are generated by a driver radiating at least 180° (half space). When the driver becomes increasingly directional (which is not a singular frequency but a range), those baffle effects are generated less and less.
So for baffle effects we concentrate on frequencies below the range where the driver is directional. It has been shown that for a most even horizontal polar response a baffle should be no wider than 2.2 times the effective cone diameter. 3 times does not hurt much, 4 or 5 times does.
What happens, if the baffle is too wide? For some frequencies the off axis response will be louder than the response on axis. This may look like reduced directionality to you, but it is a kind of frequency dependent off-axis-beaming. No good thing to have.
For practical reasons a wide baffle can not be avoided all the time. In this case it helps to move the driver sideways on the baffle. This will straighten the horizontal response in a certain direction, but worsen it in other directions. At least you can optimise it for your listening angle.
What would be a good strategy? My 7" midrange dipole driver with an effective radius of 13 cm is mounted on a 30 cm wide baffle, offset 5 cm from the middle. To one side radiation stays within 2 dB from 0° to 30°. Thats the side where I listen. The other side is worse.
The midrange driver becomes directional above 1 kHz. So at 2 kHz I cross to a 1" dome tweeter on the same baffle. A 2.5 cm driver on a 30 cm wide baffle?
Yes, because the tweeter has a small waveguide making it directional above 3 kHz. So it "does not know" much of the baffle width.
Hope this helps.
Rudolf
So for baffle effects we concentrate on frequencies below the range where the driver is directional. It has been shown that for a most even horizontal polar response a baffle should be no wider than 2.2 times the effective cone diameter. 3 times does not hurt much, 4 or 5 times does.
What happens, if the baffle is too wide? For some frequencies the off axis response will be louder than the response on axis. This may look like reduced directionality to you, but it is a kind of frequency dependent off-axis-beaming. No good thing to have.
For practical reasons a wide baffle can not be avoided all the time. In this case it helps to move the driver sideways on the baffle. This will straighten the horizontal response in a certain direction, but worsen it in other directions. At least you can optimise it for your listening angle.
What would be a good strategy? My 7" midrange dipole driver with an effective radius of 13 cm is mounted on a 30 cm wide baffle, offset 5 cm from the middle. To one side radiation stays within 2 dB from 0° to 30°. Thats the side where I listen. The other side is worse.
The midrange driver becomes directional above 1 kHz. So at 2 kHz I cross to a 1" dome tweeter on the same baffle. A 2.5 cm driver on a 30 cm wide baffle?
Yes, because the tweeter has a small waveguide making it directional above 3 kHz. So it "does not know" much of the baffle width.
Hope this helps.
Rudolf
So, my situation is this:
81mm midrange driver
2m separation between speakers
2 meter distance from speakers is the listening position
I am modeling a 178mm x 914mm baffle with the drivers 68mm off of the edge to the outside (away from the other speaker) and 711mm off the floor.
If I am using the Edge correctly, I have placed the mic 2m from the baffle, and at a horizontal location 1m to the "inside".
This gives me a situation where I could cross at ~500 and ~2300Hz...just right for the drivers I've got to support the bass and treble.
Does that look reasonable to you, Rudolf?
Again, thanks for all the input!
81mm midrange driver
2m separation between speakers
2 meter distance from speakers is the listening position
I am modeling a 178mm x 914mm baffle with the drivers 68mm off of the edge to the outside (away from the other speaker) and 711mm off the floor.
If I am using the Edge correctly, I have placed the mic 2m from the baffle, and at a horizontal location 1m to the "inside".
This gives me a situation where I could cross at ~500 and ~2300Hz...just right for the drivers I've got to support the bass and treble.
Does that look reasonable to you, Rudolf?
Again, thanks for all the input!
I played around some more and got a broader and flatter range by lowering the driver to 0.68m off the floor.
So, 450/2500 crossover points look possible. Please advise if those are okay for target points.
Do you have better results with 2nd order? 4th order electrical? The real question is: what filter types work well for OB?
So, 450/2500 crossover points look possible. Please advise if those are okay for target points.
Do you have better results with 2nd order? 4th order electrical? The real question is: what filter types work well for OB?
croat47 said:
Aaron,
did you look at the scale of the y-axis in EDGE? You are equalizing a 1 dB "hump"!
Anything between 400-500 Hz is perfect for the highpass. Xover to the tweeter can be anything from 2000-3000, depending on the tweeter capabilities.
I don´t believe in crossover sound. And definitely there is nothing special for OBs. It´s hard to design acoustically symmetrical crossovers without measurements. So I don´t think I can be of much help here.
For the integration of all drivers on a single baffle LineSource already gave some good advice.
Rudolf
Rudolf said:
Aaron,
did you look at the scale of the y-axis in EDGE? You are equalizing a 1 dB "hump"!
Anything between 400-500 Hz is perfect for the highpass. Xover to the tweeter can be anything from 2000-3000, depending on the tweeter capabilities.
I don´t believe in crossover sound. And definitely there is nothing special for OBs. It´s hard to design acoustically symmetrical crossovers without measurements. So I don´t think I can be of much help here.
For the integration of all drivers on a single baffle LineSource already gave some good advice.
Rudolf
I wasn't really "worried" about the 1dB bump. I was just moving things around to see what effects driver placement made. The 450-2300 range looked flatter when I put things as stated in my last post. So...wasn't "trying to eq"...just happened. 🙂
I am looking to do something like Tony Gee's Modulus
http://www.humblehomemadehifi.com/Modulus.html
So, the tapered baffle falls out. But, that gives me an idea on how to use some leftovers of drivers and lumber...
The mid and tweeter that I am using have been crossed over around 3200 in another design. Too high? I posed the question about crossover topology in the event that something about open baffle behavior required a certain type. On that subject: will using a 2nd Order L-R to the bass give a 18db/octave slope when combined with the 6dB slope from the baffle loss?
Again...thank you!
Following that Modulus design a 3 kHz crossover should be almost identical for a box and an OB. Taking the crossover from the original design would be a good strategy.croat47 said:
None that I would know about. Just the usual precautions: Since dipoles generally are excursion challenged, first order highpass is critical in many cases.
Yes.
Rudolf:
The wave guide that you mention...is it a pre-fab unit or did you chamfer the front side of the cut out for the tweeter?
Is this setup shown somewhere on your site? Headed there to look...
Also: in another thread about MJK's article on the Jordan/H-Baffle, the cross section is 16"x16" and the length 16" (8" either side of the centered driver mount). Which drives the 1/4 lamda response? That is: if one made a 10" driver version of the same, does an 11"x11" section with the same length have the same resonance.
Read about TL theory...just not polished yet.
Thanks!
The wave guide that you mention...is it a pre-fab unit or did you chamfer the front side of the cut out for the tweeter?
Is this setup shown somewhere on your site? Headed there to look...
Also: in another thread about MJK's article on the Jordan/H-Baffle, the cross section is 16"x16" and the length 16" (8" either side of the centered driver mount). Which drives the 1/4 lamda response? That is: if one made a 10" driver version of the same, does an 11"x11" section with the same length have the same resonance.
Read about TL theory...just not polished yet.
Thanks!
I am doing a partial open baffle design with a refex bass and am also concerned about midrange peak and optimum diffraction.
I thought it would be easier to ressurect this thread rather than start a new one.
Does anyone know what the effect of curved OB wings would be?
I am thinking of having a flat wedge shaped baffle not much larger than the drivers, and then large radius ( 6" - 8" ) wings that sweep back with a depth of perhaps 5" at both the sides and the top - kind of like a cross between a theil a Stadavari, but open baffle. The open baffle would also have a base ( similar to Tony Gee's Modulus ).
Background:
I will be using a Supravox 215 EXC full range on a smallish open baffle sitting on top of the reflex box ( similar to Tony Gee's Modulus). There will be a support tweeter and a 15" bass.
I want to keep the crossover as simple and unobtrusive as possible, and want to optimise the acoustic behaviour of the open baffle.
The Supravox will have no LP or HP filters, and will use the 6dbl roll off of the OB at around 250Hz to 300Hz to match into the Bass which will have a 1st order LP filter. The support tweeter will come in around 6KHz to just add to the Supravox's output.
From modelling flat OB's, I had anticipated that I would need a broad series notch filter to take out a 3db midrange peak from about 300Hz to 3K, but would like to avoid this if possible.
Thanks
David
I thought it would be easier to ressurect this thread rather than start a new one.
Does anyone know what the effect of curved OB wings would be?
I am thinking of having a flat wedge shaped baffle not much larger than the drivers, and then large radius ( 6" - 8" ) wings that sweep back with a depth of perhaps 5" at both the sides and the top - kind of like a cross between a theil a Stadavari, but open baffle. The open baffle would also have a base ( similar to Tony Gee's Modulus ).
Background:
I will be using a Supravox 215 EXC full range on a smallish open baffle sitting on top of the reflex box ( similar to Tony Gee's Modulus). There will be a support tweeter and a 15" bass.
I want to keep the crossover as simple and unobtrusive as possible, and want to optimise the acoustic behaviour of the open baffle.
The Supravox will have no LP or HP filters, and will use the 6dbl roll off of the OB at around 250Hz to 300Hz to match into the Bass which will have a 1st order LP filter. The support tweeter will come in around 6KHz to just add to the Supravox's output.
From modelling flat OB's, I had anticipated that I would need a broad series notch filter to take out a 3db midrange peak from about 300Hz to 3K, but would like to avoid this if possible.
Thanks
David
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