A Question About Time Alignment

 

Monopulse Loudspeakers here in the UK have made this time alignment issue their main selling point for decades.

The designer Allan Hendry has been stating that impulse precision is hard wired into our evolution for survival itself and thus it’s importance cannot be overstated.

Everytime I’ve listened to Monopulse speakers they did seem to be easy on the ear, very listenable for long durations. That led me to also wonder whether they are onto something.

If so, does that mean most others aren’t?

http://www.monopulse.co.uk/

Technically having a good impulse response means having higher fidelity.

There many speakers that do it, but it is easier to have speakers that may not be so good.

Time alignment: a simpler illustration. The acoustic centers of a cone midrange and a dome tweeter when both are mounted in the same plane (e.g., on a flat front of a speaker) will not be in the same plane. The tweeter would typically be ahead of the cone speaker. Thus even if the two speakers are in electrical phase the harmonics from the tweeter will arrive slightly ahead of the lower frequencies of a cone speaker whose acoustic center is near the apex of the cone which could be a couple inches behind the plane if both components are mounted on the same plane. 

@soundscapemd

The acoustic centers of a cone midrange and a dome tweeter when both are mounted in the same plane (e.g., on a flat front of a speaker) will not be in the same plane. The tweeter would typically be ahead of the cone speaker.

Monopulse employ this mechanical way of aligning the drive units.

Others claim to be able to do it electrically via the crossover.

Some prefer to horn load their tweeters so that the tweeter is behind the physical plane of the woofer(s).

Time alignment might not be the be all end all of speaker design but I think it does help to reduce the so called ’listener fatigue’.

I remember reading that the more unnatural the sound is, the more tiring it is to listen to. The reason usually given is that your brain will have to engage in considerably more processing with those recordings that don’t sound authentic or genuine.

I would bet that this is particularly true when listening to a recording of the human voice.

Hold on for one moment. Consider the piano. It's roughly 5 feet wide. So sound from a bass string is going to arrive at the mic way after sound from the treble side. Worse, that bass string is several feet long, so sound will arrive at different times from different parts of the string. Worse yet there are the reflections off the lid arriving all out of phase and time  alignment. So explain how moving a tweeter a fraction of an inch is going to make any audible difference.

Hi Paul,

    I have a time / phase aligned, and room corrected system at the listening position by way of digital crossovers processed through my Mini DSP using a mic that has a 30Hz-30KHz sensitivity range. Let me first speak to the basic principle of time alignment. You are correct, all frequencies being played travel at different speeds to your ears. Assume that the microphone is your ears. It has captured that moment in time of the recording when all those different frequencies met. You want to reproduce that at the listening position so that you hear what the microphone heard. If you time align the speakers, all the frequencies hit your ears at the same moment in time so you then hear the same “time distortion” that the microphone picked up. You are hearing what you would have experienced live. If the system isn’t time aligned you are compounding distortion by the variation in wavelength speeds. The highest sound we can hear is a sine wave about an inch long and the deepest sound we can hear is a wave 25ft long, they travel at very different speed so the higher sounds need to be delayed and the lowest played first. If one wants to truly create a “realistic” experience the system needs to be time aligned. This is not quackery as some have suggested but one of many important pieces of the puzzle in music reproduction. The speakers and their interaction with the room combined with their time / phase alignment are the factors with the most impact on creating a 3-D Holographic image “like being there.” I think physically aligning the system by ear would be next to impossible and the manufacturer can’t do it unless they tell you exactly the distance you would need to sit for them to be aligned as will as how far apart the speakers should be placed. I can turn off time alignment and room correction with a click of the button. Without time alignment the system is flat, with it I would put my listening experience against the most expensive system you can find. I hope this explanation helps. 

Thanks,

Steve