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Eliptrac 400 as a three way and time alignment


coolhandjjl

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On the ALK site, if you have Dave's Eliptrac 400 and wish to try the three-way route, they recomment either the Bob Crites' tweeter or Dave's Fastrac Contrac hybrid horn with a B&C DE10 driver.

In either case, the drivers will not be aligned. Is there an electrical component designed to delay the tweeter, or does one simply give up on true time alignment. My active crossover does not have time delay features.

How important is it to keep the center spread of the mid and HF drivers as tight as possible on the motorboard? The larger Contrac horn means the HF driver is further away above the mid driver than if one uses the Crites' tweeter.

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In a typical passive network 3-way speaker, you are correct, there is no time alignment. Par for the course. I wouldn't worry too much about it.

If you delve into active systems with digital processors and multiple amps...........then you can get into the time alignment plus more.

However..........there is a thread floating around that a couple of guys found a software program that acts like a digital processor, separates out the various frequency ranges and allows delays and EQ to be added to each range............then sums them back up and outputs to your passive networks..........so you can get time alignment with a passive network speaker. This may be the future as it is simple and requires only 1 amp............not much info on it though yet.

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However..........there is a thread floating around that a couple of guys found a software program that acts like a digital processor, separates out the various frequency ranges and allows delays and EQ to be added to each range............then sums them back up and outputs to your passive networks..........so you can get time alignment with a passive network speaker. This may be the future as it is simple and requires only 1 amp............not much info on it though yet.

Hey Mark thats not possible.......the frequency area were time alignment is most critical is the frequencies that both drivers share and reproduce together so alignment correction isn't possible with the method mentioned here. To bring two sound sources covering the same frequency range(ie: crossover region) into time alignment the correction must be applied to only one of the sources without at the same time causing the other source to time shift which the above method mentioned can't do.

miketn

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How important is it to keep the center spread of the mid and HF drivers as tight as possible on the motorboard? The larger Contrac horn means the HF driver is further away above the mid driver than if one uses the Crites' tweeter.

Interdriver spacing is very important. Increasing the spacing between the horns effectively increases the acoustic delay between drivers. Delay between drivers affects the polars - the polar pattern shifts in the crossover overlap region, toward the delayed driver. In vertically stacked arrangement that means the pattern will shift downward, as most tweeters are shallower than the midrange they are on top of in a three way system. This can affect the summation of the acoustic output of those two drivers thus changing the frequency response in that frequency range.

There are inexpensive digital processors such as MiniDSP and Behringer that can correct this. Several people on this forum are using these or other more expensive processors in their systems.

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I agree with the previous post. A timedomain EQ can not fix everything in a passive loudspeaker. In the ranges were only one speaker contribute or at least much more than the other ones say 20 dB it is possible to time EQ. For example 10-20 kHz were only the tweeter is working.The problem is in the crossover region were two drivers are working perhaps around 5 kHz were both midrange and tweeter is contrributing. what every delay you will have at 5 kHz will only fit one of them.

I have built speakers with passive crossovers since the late 70s and recently bought some second hand active crossovers. It such a joy to be able to adjust xover and level by turning a knob. I might use som passive crossovers but my guess in going forward to miniDSP is more likely than back to passive.

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.....the polar pattern shifts downward in the crossover overlap region, toward the delayed driver. In vertically stacked arrangement that means the pattern will shift downward, as most tweeters are shallower than the midrange they are on top of. This can have the affect the summation of the acoustic output of those two drivers thus changing the frequency response in that frequency range.....

Isn't a 24 dB/octave Linkwitz-Riley slope supposed to minimize driver overlap?

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Yes it does minimize overlap, but that alone is not the whole story. There is still about an octave wide range that will be affected. Here is an interesting article with a lot of good info but be sure to pay special attention to the paragraph on time or phase correction. Design parameters and proper operation of that crossover type assume that the drivers are time-aligned:

http://www.rane.com/note160.html

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Although I have not investigated this yet, what I understood was that in software you could have a processor similar to a digital outboard speaker processor. You feed the full range signal into several digital channels, set up your crossover points and filter types for each driver (channel), apply the proper delays to any driver (channel), add any EQ to any channel................all just like a EV-dx 38 or other digital speaker processor........................then digitally SUM the channels back and D/A to simple L/R outputs for a single amp.

From there it goes to your passive networks in your speakers. If the digital crossover points, filter types, and delays were carefully chosen to match the passives and horn lengths.......why wouldn't this work for time aligning a passive speaker?

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Guest David H

On the ALK site, if you have Dave's Eliptrac 400 and wish to try the three-way route, they recomment either the Bob Crites' tweeter or Dave's Fastrac Contrac hybrid horn with a B&C DE10 driver.

In either case, the drivers will not be aligned. Is there an electrical component designed to delay the tweeter, or does one simply give up on true time alignment. My active crossover does not have time delay features.

The simple fix is to use an ALK ES network for hf section, the crossover skirts are sharp enough that the drivers have minimal interaction.

Another good fix is use a Mni DSP and properly time align. I have been very pleased with the Mini DSP, however I don't like having to cross back and fourth between digital and analog domains especially when using an analog source - Seems counter productive although I dont hear any degradation in sound quality.

Using time delay software and resistive crossovers in series would not be one of my choices.

Dave

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Although I have not investigated this yet, what I understood was that in software you could have a processor similar to a digital outboard speaker processor. You feed the full range signal into several digital channels, set up your crossover points and filter types for each driver (channel), apply the proper delays to any driver (channel), add any EQ to any channel................all just like a EV-dx 38 or other digital speaker processor........................then digitally SUM the channels back and D/A to simple L/R outputs for a single amp.

From there it goes to your passive networks in your speakers. If the digital crossover points, filter types, and delays were carefully chosen to match the passives and horn lengths.......why wouldn't this work for time aligning a passive speaker?

Mark using the 2-way Jubilee with active crossover EV DX38 as an example we maintain independent channel control (of SPL, Frequency and Delay compensations) until the LF and HF acoustical outputs are summed at the listening position. Thus all delays (electrical and physical) have taken effect before the acoustical summing and thus the system is optimized.

Now if instead you sum the LF and HF channels after the EV DX38 (as has been suggested to drive a single amplifier and the passive crosovers to the LF/HF Horns) then at this time the Physical Delay has not occurred and any electrical delay(EV DX38 settings) used in the HF to bring it into alignment with the LF will not sum together as we need and will actually cause constructive/destructive interference causing frequency and phase errors which will be amplified and heard by the listener. The polar lobing issues in the crossover region due to any physical delay between the LF and HF still exists because of the summing of the EV DX38 channels before the amplifier and thus the summed signal (with frequency/phase errors now created) will be received by both the LF horn and HF horn without the ability to bring the LF horn and HF horn into time alignment in the crossover region. So again the most critical and beneficial area (ie: crossover region) of bringing a loudspeaker system into time alignment can't be accomplished this way.

Even if you had a DSP unit with the resolution that could do perfect brickwall crossover with delay and you then summed the outputs to the amplifier you would still be limited by the passive filter's rolloff rates which wouldn't be sufficient(unless it could do effectively brickwall filtering) to prevent frequencies (with the intended delays) from reaching the unintended LF/HF drivers/horns causing errors in the acoustical summing in the crossover region.

Keep in mind my comments are based on typical real world technology available to us in Driver/Horn, DSP and Passive Crossover designs.

miketn

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