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Using REW to Determine Time Delays Between Drivers

Chris A

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On 1/29/2021 at 2:54 AM, Wirrunna said:

Now, a question - how flat should the phase be ? Certainly the first music I played back in early January when I got this flatish phase cross over working was a revelation. There were some tracks that you could swear it was a mono system and the speaker was disguised as a slow combustion wood fire sitting near the wall in the middle a long way from the two corner cupboards with Klipsch labels. While other tracks had instruments coming from further out than the corner cupboards. And Dark Side of the Moon when the alarm clocks went off frightened everyone.


Is there some acknowledged measurement for phase, e.g. + - 30 degrees from 200 to 10,000 ?

I think there is another portion to the answer to your question that I really haven't addressed, above.  It's the portion that lets the listener actually hear the effects of phase flattening.  This is perhaps the most important part, because I believe just about everyone is missing it (except perhaps one or two researchers):


I've found that the audibility of flat phase (not just linear phase, but rather flat phase) is controlled by how the direct arrivals compete with the early reflections coming to the listener's ears.  This is also at the root of some audio enthusiasts advocating extreme nearfield listening to their loudspeakers.  I was made aware of this again last night when I read the "advice" from Mapleshade audio:



Get Better Sound From Your Speakers With Better Room Set-Up


• Almost everybody sits way too far from their speakers, that is, 8' to 10' or more. Try a low chair (or floor pillow) 5' away. You’ll hear a phenomenal increase in clarity, bass impact, and soundstage—roughly like spending 100% more on your speakers. Sitting close (aka near-field listening) tremendously reduces all room acoustic problems and the need for expensive room treatments.

I had to laugh when the author got the "and the need for expensive room treatments" part.  The expensive part is actually the stuff that he sells (Pierre Sprey-- a now discredited defense fighter aircraft systems analyst [something I personally know something about--having spent about 20 years of my life doing it]).  Acoustic treatments are actually quite inexpensive, if you want them to be.  They get expensive (like everything else in this hobby) when you look to buy from someone else that will sell them at a 500+ percent markup.


But the point he made has been made elsewhere, many times in fact: suppression of the nearfield early reflections in-room in order to hear mostly the direct arrivals from the loudspeakers.  What kind of loudspeakers do this on their own without having to sit in the extreme nearfield?  Fully horn-loaded ones.  Who makes these kind of loudspeakers?  Klipsch.  Which loudspeaker models can do this?  I wrote this down in another thread recently:



I find that those using loudspeakers not having controlled directivity down to ~200-300 Hz (horn-loaded bass bins with directivity control using large mouth bass horns like Jubilees, Khorns, La Scalas, Belles, Peavey FH-1s, etc.) usually cannot hear the effects of phase flattening.  This is because in-room reflections from nearby room objects and boundaries interfere from direct-radiating woofers destructively cancel out directed acoustic energy from these types of bass bins.




Horn-loaded bass bins having directivity control to below the room's transition frequency (the Schroeder frequency):


PeaveyFH-1 next to JubeKhorn.jpg

Klipschorn and FH-1 bass bins



Belle Klipsch



Klipsch La Scala



Sound Physics Labs Unity/ Danley Sound Labs Synergy Horns


Klipsch - Jubilees w zebrawood and guard dog - DSC_2907-resize3.jpg

Klipsch Jubilees


These type of loudspeakers have an advantage that other loudspeakers don't have: the ability to control early in-room reflections down into the midrange and below, and when coupled with DSP crossovers having FIR filter capability, produce an almost unbelievable soundstage image fidelity that is seldom experienced by listeners.  I've talked about this effect before here. Here's a summary of the effects:


1. significantly increased perception of bass--so much so that I had to remaster my stereo recordings

2. overall subjective depth and seamless soundstage improvements,

3. an indescribable naturalness of sound that's easy hear with live acoustic instrumentation recordings, and

3. elimination of harshness, particularly of acoustic instrumentation like acoustic guitars, violins/violas/cellos/double basses, and wind instruments (brass & woodwinds).

So there are two extra requirements on phase flattening in-room:


1) Full range loudspeaker directivity below 1 kHz provided by fully horn-loaded bass to below the room's transition frequency (generally below 100-200 Hz), and

2) Suppression of nearfield reflections in the first 2-->4 feet (~1 m) from the loudspeaker front baffle to enhance the direct/reflected ratio of acoustic waves.


If you don't have both of these (full-range loudspeaker directivity--or an anechoic chamber to listen) most folks will never hear the difference.  It's not all reflections that are undesirable--rather it's the early reflections from just around the loudspeakers within the first 3-5 milliseconds (about a full wavelength of a two hundred [200] Hz wave and shorter wavelengths/higher frequencies) that are the problem.  If you control this early reflected energy, the effects of phase flattening become quite audible and produce the effects that I mentioned above.


I've found that floor bounce is the major contributor (something that almost everyone deals with), but the most critical reflections seem to be those from the room's walls and ceiling.  And the critical frequencies to control are ~200 Hz to 2000 Hz.  If you already have full-range directivity loudspeakers, in general, the acoustic treatments to suppress the early reflections within the first 5 ms from the direct loudspeaker arrivals is comparatively easy and inexpensive to achieve. (Note that this also includes the front baffle of the loudspeakers in the case of truncated mouth "W" section bass bins, like the Belle, Khorn, and Jubilee bass bins.)



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