aubergine said:
I understand discussion is about interaction between a CD/waveguide and a woofer ?
The ringradiator I think came in from the side as maybe having near ideal loading of the waveguide...I dont think it was about BMS in any way...well, Earl did mention a tube in the throat of the BMS, but has also stated clearly that he really disslikes the coaxes, so I reckon they are out of question ?
Seems there is a bit of confusion...maybe I am wrong
Well of course its confused, these threads seldom stay on any course of topics.
To me the issue was about statements claiming that group delay was all that mattered for polar response, which was completely incorrect. It doesn't matter if we are talking about waveguides or direct radiators or whatever. The claim is wrong in all cases.
To me the issue was about statements claiming that group delay was all that mattered for polar response, which was completely incorrect. It doesn't matter if we are talking about waveguides or direct radiators or whatever. The claim is wrong in all cases.
gedlee said:
So Earl, please explain why that is so...maybe we will understand, maybe not
I may understand a bit why group delay may have influence on the mutual resulting polar response of 2 drivers, as everything seem to matter...if there is such thing as a mutual resulting polar response of 2 drivers
Not really, but one would probably look at data at different points off-axis to determine at what center frequency to implement this filter. Although I have not actually used this in XO design, but after proper time alignment, if one decides that the off axis response due to inter-driver interaction needs some modiication, changing group delay using that kind of phase shift filter could alter off-axis response with minimum impact on horn on axis amplitude response. This is possible because interaction between drivers are most significant around the XO frequency which is due to cancellation due to phase differences.gedlee said:
tinitus said:
So Earl, please explain why that is so...maybe we will understand, maybe not
I may understand a bit why group delay may have influence on the mutual resulting polar response of 2 drivers, as everything seem to matter...if there is such thing as a mutual resulting polar response of 2 drivers
The polar response at the crossover is a result of the complex summation (both magnitude and phase) of the responses from two sources. It depends on the magnitude and phase response of each driver at every point in the field. Group delay is only the phase aspect but the amplitude is equally as important. In fact its not even group delay that one cares about its the specific phase.
An electrical filter can alter the amplitude and phase of the source in an arbitrary way, but this change has to be independent of polar angle - the change is the same regardless of direction. Thus if the axial response is correct, but not the off axis response, it is impossible to change the off axis response without simultaneously changing the on axis response. There is no possible way that one can "correct" one without degrading the other unless they both started out wrong in the exact same way.
This is what makes a good crossover so difficult to do. 90% of all crossovers try to maintain a flat axial response with little of no regard to the off axis effect that this has. I don't do that. I optimize the frontal 30 degrees as a total response not just the response at some unique angle - such as the axis. In fact I tend to de-emphasize the axial direction in my speakers as this is not a direction that any listener will tend to be in.
I hope I am not hijacking this thread but does anyone have any recs regarding the lowest xover point for the B&C DE250 in a 10-inch DDS waveguide and using a 48 dB LR xover with the Behringer DCX2496? It is used with 2, 15-inch bass/mid drivers ala Emerald Physics CS2.
I thought I read that Earl uses this driver in the Summa and crosses it over around 900 Hz but doesn't disclose the slope or xover type.
I thought I read that Earl uses this driver in the Summa and crosses it over around 900 Hz but doesn't disclose the slope or xover type.
Horizons said:
I have before, I use a third order on the Summa and a psuedo second order on the Abbey and Nathan. You have to remember that the whole DE250 pass band is on a + 6 db/oct slope.
How to recognize a CD waveguide
Dr. Geddes,
Can you tell me how to recognize a CD waveguide from FR data taken at various angles. Can you also tell me how to define the angle of a waveguide from FR data taken at various angles.
Regards
Peter
Dr. Geddes,
Can you tell me how to recognize a CD waveguide from FR data taken at various angles. Can you also tell me how to define the angle of a waveguide from FR data taken at various angles.
Regards
Peter
I am not sure that there is a one-to-one relationship here.
My waveguides can be seen to have very smooth on and off axis responses with few ripples due to reflections and diffraction. If you are looking at and un-EQ'd response it will have a falling response with frequency (about -6 dB/oct) as any CD system must. The polar curves will all be parallel as they fall. The wall angle will be approximately at the -6 dB line.
My waveguides can be seen to have very smooth on and off axis responses with few ripples due to reflections and diffraction. If you are looking at and un-EQ'd response it will have a falling response with frequency (about -6 dB/oct) as any CD system must. The polar curves will all be parallel as they fall. The wall angle will be approximately at the -6 dB line.
If there is less rise in the impedance with frequency, then there will be less falling of the response with rise in frequency.
The fall in response is due to the radiation efficiency NOT the voice coil inductance. In the DE250 there is a shorting copper cap at the voice coil which basically nulls out the inductance, so there is very little inductance rise in this driver. Any loss due to the inductance is minimal.
gedlee said:
BMS says nothing about that , but they do inform about that on some of their other CDs 😕
I think that you mean B&C, not BMS, but you are right, they don't say that and in fact, I'm not positive now, I'll look. But the real point is that even in the DE250 the inductance rise is not such that it would cause any significant loss of output at the high end. The drop in HF SPL is a direct result of the waveguide being Constant Directivity not impedance rise.
gedlee said:
Right, B&C
Its true that inductance seem to be exactly the same whether shortring is mentioned or not
but, impedance doesnt seem completely without rise, as those with shortrings does
B&C seems to have changed some specs. When I bought the 8NDL51 a year or so ago it was listed as having an aluminum demodulating ring, while the 8NW51 did not. A couple months ago I noticed the 8NDL51 no longer said anything about a ring, while teh 8NW51 then mentioned having a copper cap. IIRC both had a straight pole piece.
Now looking today both list a copper cap-still no rings- and the 8NW51 has a T pole and the 8NDL51 has a straight pole piece.
I thought I remember teh DE250 have a copper cap listed in the design tab, but no in the pdf. Now there is no design tab.
Now looking today both list a copper cap-still no rings- and the 8NW51 has a T pole and the 8NDL51 has a straight pole piece.
I thought I remember teh DE250 have a copper cap listed in the design tab, but no in the pdf. Now there is no design tab.
I always look at a driver's voice coil inductance when designing the crossover. Ironically, I rarely find inductance to be a big issue in tweeters. It's usually direct radiating midranges and midwoofers that have inducance I have to consider. Direct radiators have radiation resistance and polar response that differs from horns, so the effect of voice coil inductance is a little different too.
In the case of horn loaded tweeters, I believe diaphragm mass is more an issue, in that is what causes the 6dB/octave droop starting around 3kHz - 5khz, depending on the driver. That's why we provide what I call "top octave compensation" - the equalization for constant directivity devices. Horns that beam at high frequency provide some acoustic EQ as a consequence of their collapsing directivity, but horns that provide uniform coverage do not. So when a constant directivity horn is used, power response equalization must be done another way, electrically, in the crossover.
Voice coil inductance causes another 6dB/octave rolloff, but it doesn't start until much higher, at the top of the passband. There are other things that act as low-pass filter too. The cavity between diaphragm and phase plug forms a low-pass filter. Path length differences and the size of the openings also start to cause interference issues up high. That's where phase plug design becomes important. These all set the limits of what the driver can do at the top end.
One other thing that I always consider when designing a passive crossover is the overall impedance curve of the device. Voice coil inductance is just a part of the equation, and as I said, I rarely find it to be a big part of the equation in horn loaded tweeters. Not that I would discount it, but the bigger issue is the impedance peaks near the low end of the horn's passband. Those peaks interact with a passive crossover, and can sometimes cause more signal to be present across the tweeter than expected.
Usually, a damping resistor is all that's needed and if the designer uses padding, the damping can be incorporated into the padding. This is also a convenient place to provide the top-octave compensation. To me, the padding should be done this way, as a triple-purpose network, to provide CD equalization that corrects the driver's power response, to provide reactance damping that swamps the driver's impedance peaks and to provide padding that matches the voltage sensitivites of the subsystems used in the loudspeaker.
In the case of horn loaded tweeters, I believe diaphragm mass is more an issue, in that is what causes the 6dB/octave droop starting around 3kHz - 5khz, depending on the driver. That's why we provide what I call "top octave compensation" - the equalization for constant directivity devices. Horns that beam at high frequency provide some acoustic EQ as a consequence of their collapsing directivity, but horns that provide uniform coverage do not. So when a constant directivity horn is used, power response equalization must be done another way, electrically, in the crossover.
Voice coil inductance causes another 6dB/octave rolloff, but it doesn't start until much higher, at the top of the passband. There are other things that act as low-pass filter too. The cavity between diaphragm and phase plug forms a low-pass filter. Path length differences and the size of the openings also start to cause interference issues up high. That's where phase plug design becomes important. These all set the limits of what the driver can do at the top end.
One other thing that I always consider when designing a passive crossover is the overall impedance curve of the device. Voice coil inductance is just a part of the equation, and as I said, I rarely find it to be a big part of the equation in horn loaded tweeters. Not that I would discount it, but the bigger issue is the impedance peaks near the low end of the horn's passband. Those peaks interact with a passive crossover, and can sometimes cause more signal to be present across the tweeter than expected.
Usually, a damping resistor is all that's needed and if the designer uses padding, the damping can be incorporated into the padding. This is also a convenient place to provide the top-octave compensation. To me, the padding should be done this way, as a triple-purpose network, to provide CD equalization that corrects the driver's power response, to provide reactance damping that swamps the driver's impedance peaks and to provide padding that matches the voltage sensitivites of the subsystems used in the loudspeaker.
i am listening a couple of month with my new horn system , using in the midrange channel a Lecleach horn with T = 0, 8, 19" at 180 degree expansion at the mouth. I made some tweaks at the crossover point, getting already a significant better integration with the midbass channel. I suspect however, improving the midrange horn, i should be able to get even better integration, and also more natural tone. Specially on voices i think i can get a better result. I would like to make and try out a horn, very similar to Oblate spheroid. My question : what might be the best size ? at the drawing i choose 25" size at 180 degree on the mouth, same length as the existing LeCleach horn, and 70 degree aperture. What cutoff Fc might i get ?
I don't know if someone made already direct listening comparsions between a LeCleach horn and WG similar to oblate spheroid. I guess it will be quit interesting ....
Angelo
I don't know if someone made already direct listening comparsions between a LeCleach horn and WG similar to oblate spheroid. I guess it will be quit interesting ....
Angelo
While the goals of each design are different, I wouldn't be surprised if they sound similar. This is because both designs invest a lot of attention into termination of the horn/waveguide, and I believe this has a tremendous audible effect.
I'm listening to an OS waveguide right now and I'm very happy with it. If I have any complaints at all, it's that the design reveals the weaknesses in the rest of my system. Specifically, I need more and/or better subs, and I never knew how bad the recordings from the 80s were until I bought these speakers.
It's amazing how much better modern recordings are. Just night and day.
To make a long story short, I don't spend any time obsessing about my speakers any longer, and spend most of my time looking for quality recordings of the music I love.
Some of the people who've followed my posts here on the forum may have noticed I'm not very active any longer, and that's why. The speaker problem has been solved.
I'm listening to an OS waveguide right now and I'm very happy with it. If I have any complaints at all, it's that the design reveals the weaknesses in the rest of my system. Specifically, I need more and/or better subs, and I never knew how bad the recordings from the 80s were until I bought these speakers.
It's amazing how much better modern recordings are. Just night and day.
To make a long story short, I don't spend any time obsessing about my speakers any longer, and spend most of my time looking for quality recordings of the music I love.
Some of the people who've followed my posts here on the forum may have noticed I'm not very active any longer, and that's why. The speaker problem has been solved.