Not really sure what you mean here.
In any case, I have been looking at other peoples results for some time now. In EVERY case, I see compromise. A particular room may excel at a couple things, but be merely average or below average in some others.
I think its neat to focus on one thing for a while and see how it turns out. I do this myself. FR, ETC and Decay have been victims of my pursuits in the past. Each was valuable, mostly because I learned so much.
Many in this thread are focused on the timing thing (step/phase/GD). What a wonderful pursuit! Wonderful because its one of those areas I know the least about. How better to get it than from those whose thoughts are convoluted by the subject while they are in the shower
In your case Greg, I am wondering and thinking about what a flat phase in the early (<7ms) portion, turning lawnmower later (love this expression of yours), would sound like.
Unless I find a tricky way to delay my mids and highs, I dont know how I would get there myself. But try to keep me informed on how its going. I am interested.
Thanks Greg, just what I wanted to know. I think I have a clue where it's coming from. Think impedance curve... Look at the well behaved speaker from Jim and know that one has a lot of passive hardware to balance the drivers, otherwise known as impedance correction.
(*) = Jim, that comment was directed at me, gmad has a single full range in a sealed enclosure. I have 25 full rangers in a somewhat bigger enclosure. Yet they act similar in time.
As my room is doubling as a living room where kids play it has to excel at things that contradict with my personal goals
. A second goal in that room seems to be to place all kinds of ringing accessories around the room for me to try and avoid.As a man, I don't always understand such accessories but I do know it's important to keep a certain someone happy
.So I make a compromise and place as much damping in the room as possible without other people noticing it's there. It did help though... but I do understand your point. For me the above world I described is very real and is the reason to make insanely large arrays. They will flood the listening position with sound, have less floor and ceiling problems than usual speakers and stand a chance of being time coherent. Far from ideal but more ideal than I would get with more traditional speakers, except for big horns maybe, but those were forbidden to me, banned by that certain someone I'm trying to keep happy. I'm not sad about it, I am lucky I get to play with these huge monsters. A lot of significant others wouldn't want to put up with that.
But like I said before. Actual live music would still sound "live" in my room. So with that in mind I can still focus on getting my speakers to mimic that. It's actually working pretty good! Up to a point, And I'll keep chasing that point for a while longer.
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I think that's maybe one way of describing good speakers in a minimally treated (but pleasant sounding) room with a few feet of breathing room around them. One thing I should point out is that the loudest reflection at my seat is -20db (according to my 4 cycle corrected IR). I think it's enough to let you know you're in a room, but without masking important details in the recording. You could check out the "virtual audition" of my room on the "Hypercube Loudspeakers" thread, but in real life the room sound is less noticeable than what you'll hear with that. If you wanted to hear a similar sound in your room, I think you'd have to be less aggressive with the treatments and perhaps sit a bit closer to the speakers.
No problem. I checked my nearfield measurement though, and there are no phase issues, so it seems like more of a room issue to me...
That's good to keep in mind! How does the nearfield phase plot look gated the same way at 6.8 ms? Is it similar to the listening position?
Gating the nearfield measurement doesn't really change the phase plot; it looks a touch smoother if no smoothing is applied.
Evidently, I havent learned a thing about GD.
Here is what is up.
My mains are about the same distance in front of the LP as my main sub is behind. But it seems I can only achieve a 15ms 40hz GD when the Sub is reversed. I thought a even response determined GD.
Ballpark the same response
GD at 40hz skyrocked to 35ms
Green = Reversed Sub
Purple = Normal Sub
Someone please tell me what basic lesson I have seemingly misplaced
Here is what is up.
My mains are about the same distance in front of the LP as my main sub is behind. But it seems I can only achieve a 15ms 40hz GD when the Sub is reversed. I thought a even response determined GD.
Ballpark the same response
GD at 40hz skyrocked to 35ms
Green = Reversed Sub
Purple = Normal Sub
Someone please tell me what basic lesson I have seemingly misplaced
Maybe you could tell from the IR which way is the correct polarity for the sub? Reversing polarity is like flipping the waveform upside down (compression vs. rarefaction) rather than shifting frequencies forwards or backwards in time, so I'm not really sure how to interpret what you are showing. I don't really understand group delay all that well myself...
Its obvious I dont either. But what I thought was true was when you put a sub the same distance away from the LP as the mains, you would want both in the same phase. Not one normal (mains) and the other (sub) reversed.
I can get a decently flat FR either way. But as one can see, the GD is very different.
I can get a decently flat FR either way. But as one can see, the GD is very different.
Its obvious I dont either. But what I thought was true was when you put a sub the same distance away from the LP as the mains, you would want both in the same phase. Not one normal (mains) and the other (sub) reversed.
I can get a decently flat FR either way. But as one can see, the GD is very different.
I can get a decently flat FR either way. But as one can see, the GD is very different.
The easiest definition to understand that ive seen is this:
I'll offer this layman's definition: Group delay (GD) can be thought of as
related to the time elapsed between a signal of a specific frequency applied to the driver and the cone's
attempt to recreate that stimulus, as compared to the next adjacent frequency. (And the next -ad infinum.)
This delay is a function of the phase of the system at those frequencies. For a constant group delay, and
freedom from waveform distortion, the system phase has to change linearly with the frequency response.
group_delay
What this seems to be saying is that if your FR matches your phase curve, you will keep GD to a minimum. Hmmmm.
I'll offer this layman's definition: Group delay (GD) can be thought of as
related to the time elapsed between a signal of a specific frequency applied to the driver and the cone's
attempt to recreate that stimulus, as compared to the next adjacent frequency. (And the next -ad infinum.)
This delay is a function of the phase of the system at those frequencies. For a constant group delay, and
freedom from waveform distortion, the system phase has to change linearly with the frequency response.
group_delay
What this seems to be saying is that if your FR matches your phase curve, you will keep GD to a minimum. Hmmmm.
Correct description, also look at what Mr. Waslo said earlier in this thread.
Zero group delay isn't necessarily flat FR plus flat phase. Confusing isn't it?
To be picky, that's not quite right, I think you meant "gives zero GD variation".
To further embellish the discussion and further confuse anyone puzzled by phase and delay: A constant time delay isn't the same as constant phase, it just means the the phase is everywhere proportional to frequency (phase is =SomeMagicConstant*frequency). On a linear frequency scale, the phase response will have a constant slope. On a log-frequency scale the phase curve slope will increase continuously (get more steep downwards) with frequency. With linear phase response data, you can remove some fixed amount of delay to arrive at a phase response that is a flat line at 0 degrees on a linear or log-frequency graph.
Fun fact: flat group delay, or even 0 seconds group delay, doesn't guarantee waveform fidelity, even if the magnitude (dB) response is also flat. For instance, if a phase response were to be 90 degrees at all frequencies, any waveform going through that would be extremely distorted but the group delay would be 0 at all frequencies! For faithful waveform replication, the constant group delay phase response has to be one in which, when the magic value of delay is remove to make the phase line flat, that phase value is 0degrees. (If 180 degrees, just reverse some wires)
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Your mains are ported. Earlier in this thread it was stated the port usually has a delay of 180 degree. The sound coming out of the port is from the back side of the driver, 180 degree out of phase. The conclusion was the sound coming from the port at the tuning frequency would be in phase but delayed. Somewhere between the direct sound of the mains and the port tuning you are integrating a sub. Think about that...
Maybe a doable experiment:
I'd move the sub around with reverse phase and measure at the listening position with an SPL meter to a sine wave corresponding to the the crossover frequency.
Start with the sub closer to the LP. Move the sub back till you get the lowest output reading on the SPL meter. Flip phase back to normal and measure with REW.
This could also be done with time alignment but the sub would have to be closer to the LP than the mains or you would be tuning the sub a cycle too late.
Aha, so I guess as long as the total phase response is very close to the minimum phase response there should be minimal group delay issues. I have noticed this happening with my DRC correction.
The sound from the port has its polarity reversed relative to the cone. However, there is no cancellation between the two because of the 180 deg phase shifting. This works well enough for reproducing sine waves, but for reproducing natural sound waves it will be extremely difficult if not impossible to get right.
With modern low distortion drivers and efficient amplifiers, I'm not sure why ports are still so widely used...
The sound from the port has its polarity reversed relative to the cone. However, there is no cancellation between the two because of the 180 deg phase shifting. This works well enough for reproducing sine waves, but for reproducing natural sound waves it will be extremely difficult if not impossible to get right.
With modern low distortion drivers and efficient amplifiers, I'm not sure why ports are still so widely used...
Here is a thought that maybe some clarity can be given to. An example.
Lets say your looking at a ported speaker at 50hz. You have the wave off the front of the woofer, and then another through the vent. If the vent energy is in phase, it must be 360 degrees out of phase. So that would mean the port wave would be 20ms behind the front cone wave.
So you essentially have 2 waves.
1) 0ms
2) 20ms
(at 50hz)
Now lets say your trying to integrate a sealed box sub to this. It seems you could either time it to the 0ms wave or the 20ms wave in order to be in phase with the first (ported speaker).
If you were trying to integrate a ported sub to a ported main, you could either time the front wave to the 0ms or the 20ms to stay in phase. If you choose the 20ms, you would then have three time responses.
1) 0ms (front wave of main)
2) 20ms (back wave of main, front wave of sub)
3) 40ms (back wave of sub)
This is all theoretical because driver/box responses are not all alike. Two different speakers aligned in distance may not (probably not) respond exactly the same in time.
Just grasping for understanding here.
Lets say your looking at a ported speaker at 50hz. You have the wave off the front of the woofer, and then another through the vent. If the vent energy is in phase, it must be 360 degrees out of phase. So that would mean the port wave would be 20ms behind the front cone wave.
So you essentially have 2 waves.
1) 0ms
2) 20ms
(at 50hz)
Now lets say your trying to integrate a sealed box sub to this. It seems you could either time it to the 0ms wave or the 20ms wave in order to be in phase with the first (ported speaker).
If you were trying to integrate a ported sub to a ported main, you could either time the front wave to the 0ms or the 20ms to stay in phase. If you choose the 20ms, you would then have three time responses.
1) 0ms (front wave of main)
2) 20ms (back wave of main, front wave of sub)
3) 40ms (back wave of sub)
This is all theoretical because driver/box responses are not all alike. Two different speakers aligned in distance may not (probably not) respond exactly the same in time.
Just grasping for understanding here.
You're getting there... that sounds about right. If the sub's port was also tuned to that 50 Hz number.
But also remember the port won't play at only 50 Hz. It will have output above that and it's timing isn't the same as the mains. So you are creating a phase shift going from mains to the port output frequency.
Sealed subs and sealed mains would be easier to integrate in correct timing. Ported subs and sealed mains is still easier than ported mains and ported subs.
The question is, how much of this is audible. Where does it end
.
You're getting there... that sounds about right. If the sub's port was also tuned to that 50 Hz number.
But also remember the port won't play at only 50 Hz. It will have output above that and it's timing isn't the same as the mains. So you are creating a phase shift going from mains to the port output frequency.
Sealed subs and sealed mains would be easier to integrate in correct timing. Ported subs and sealed mains is still easier than ported mains and ported subs.
The question is, how much of this is audible. Where does it end
Thats the million dollar question.
Ive read several, seemingly knowledgeable people say, 1 cycle or even 2 isnt audible at the bottom.
At 40hz, 1 cycle would be 25ms. My original tests were right at that mark for that frequency and several here thought that was too high.
Another school of thought says 400. That is, F*GD<400. So for 40hz, this school says the GD should be kept to 12.5ms (1/2 cycle).
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