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Discussion Starter #1
This questionnaire is for a school research paper, and I would appreciate as many responses as I can get. I understand that building loudspeakers involves a lot to take into consideration when designing one. But, for the sake of this paper please answer the following questions Yes or No, knowing that I understand there is no one size fits all approach. Designing, building, or buying our own loudspeakers adds a certain element to what we perceive or hear in a loudspeaker, making the audiophile topic highly subjective. I would like to get an idea of the averages concerning the questions involved.
Questionnaire:
Considering a room size of ~400sq. ft., with typical obstructions. A subwoofer is used, and crossed at 80Hz. The build is for front LR mains and consists of drivers no larger than 6.5 in. Cost and build complexity is not considered. And, multiple listening positions is the goal.
1. Is the phase audible at frequencies other than 180 degrees out of phase?

YES, or NO?

2. Considering phase shift is non-linear throughout the room at different frequencies, does it matter if it’s introduced by the speaker, if it can’t be controlled anyway?

YES, or NO?

3. Is the time alignment problem that can be introduced when using a 3-way 4th order crossover, important in considering whether or not to use a single driver or simpler (less components) two-way design?

YES, or NO?

4. Is a time aligned crossover important considering that the other components in a stereo introduce their own misalignment, i.e. Microphones/distance in recording, filters and enhancements added to the recording before release, amplifier used and any equalizers, DAC and ADC, and speaker voice coils not aligned?

YES, or NO?

5. Does the number of components and complexity of a 3-way 4th order crossover add more distortion and phase/time shift than any intermodulation introduced by using only two drivers covering the frequency range of 80Hz-20KHz? Room size considered.

YES, or NO?

6. Do you believe intermodulation distortion is audible in a two-way speaker given the parameters listed above?
YES, or NO?

7. Considering the cost, complexity, and time involved, would you build a two-way or three-way loudspeaker for the conditions stated above?

TWO-WAY, or THREE-WAY?
 

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TWO-WAY, or THREE-WAY?
I won't bother with the questions other than this one, although most of the answers are no. As to two-way versus three-way, the primary reason for a three-way is dispersion versus displacement. A large woofer or midbass driver gives lots of displacement, but at the cost of midrange dispersion, which can necessitate the use of a midrange driver. One way around that is to use two or more smaller woofers or midbass drivers, so that both high displacement and wide midrange dispersion are realized without having to go 3-way. That in a nutshell is why 2-way MTMs are far more popular than 3-ways, or for that matter why line arrays tend to use very small midbasses.
 

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1. Is the phase audible at frequencies other than 180 degrees out of phase?

YES, or NO?


to the extent that it creates cancellation, yes.

2. Considering phase shift is non-linear throughout the room at different frequencies, does it matter if it’s introduced by the speaker, if it can’t be controlled anyway?

YES, or NO?


yes. direct vs reflected sound is perceived differently by our brains. this is why the "sound" of a person you know is instantly recognizable in any room with any amount of treatment or not while the measured frequency response can look completely different.


3. Is the time alignment problem that can be introduced when using a 3-way 4th order crossover, important in considering whether or not to use a single driver or simpler (less components) two-way design?

YES, or NO?


see aes research on topic. under very controlled circumstances, with some test tones and headphones, phase distortion is audible. for most all practical purposes, it is not audible.


4. Is a time aligned crossover important considering that the other components in a stereo introduce their own misalignment, i.e. Microphones/distance in recording, filters and enhancements added to the recording before release, amplifier used and any equalizers, DAC and ADC, and speaker voice coils not aligned?

YES, or NO?


same as above.

5. Does the number of components and complexity of a 3-way 4th order crossover add more distortion and phase/time shift than any intermodulation introduced by using only two drivers covering the frequency range of 80Hz-20KHz? Room size considered.

YES, or NO?


depends how loud you want to play it and what size drivers you use. 6.5" ain't much to work with.

6. Do you believe intermodulation distortion is audible in a two-way speaker given the parameters listed above?
YES, or NO?


same as above.

7. Considering the cost, complexity, and time involved, would you build a two-way or three-way loudspeaker for the conditions stated above?

TWO-WAY, or THREE-WAY?


a 6.5" driver is too small for an 80hz crossover for realistic reproduction, but the listening level of folks varies by more than 20db, so there isn't a one-size-fits-all answer.
 

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^^ Given the use of a subwoofer, I would almost always choose 2-way over 3-way designs for the reasons you gave.
When you have a sub plus 2-way it is a 3-way, contained in two different boxes. But yes, having a sub for the lows removes most of the reason for the traditional 3-way configuration.
 
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Discussion Starter #7
Thanks guys! This is for a paper I'm doing. I'm trying to get an idea of what different people perceive as important in these circumstances. You are absolutely right that technically a sub crossed at 80Hz makes a two-way speaker into a three-way system. Currently I have MTM's for my mains using 2 Dayton 6.5 woofers and a silkie. I need to rebuild them because I made some mistakes. Part of the reason I chose this topic was to see if it would be worth adding an upper-mid when I do. The driver spacing on the woofers is currently about 12" apart and crossed at 2K. I think I need to bring them closer together. MMT. Also, I never considered the sensitivity issue. Tweeter is 89db and 2 Daytons is around 93db I think. The weird thing is that when I run a measurement sweep I have nearly flat response from 20KHz all the way down to 42Hz (where there is about 8db peek due to room and port tuning). I do have a down 3db at 1Khz but that is fixed with EQ. Now for the part I can't figure out. I have a center channel MTM using 2 3" daytons and a 1" vifa textile dome that reproduces the vocals sooo much better. This speaker also has flat response down to the 80Hz crossover point (haven't tested it below 80Hz). Why does the center channel sound so much better? Both are tested at the listening position.
 

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Thanks guys! This is for a paper I'm doing. I'm trying to get an idea of what different people perceive as important in these circumstances. You are absolutely right that technically a sub crossed at 80Hz makes a two-way speaker into a three-way system. Currently I have MTM's for my mains using 2 Dayton 6.5 woofers and a silkie. I need to rebuild them because I made some mistakes. Part of the reason I chose this topic was to see if it would be worth adding an upper-mid when I do. The driver spacing on the woofers is currently about 12" apart and crossed at 2K. I think I need to bring them closer together. MMT. Also, I never considered the sensitivity issue. Tweeter is 89db and 2 Daytons is around 93db I think. The weird thing is that when I run a measurement sweep I have nearly flat response from 20KHz all the way down to 42Hz (where there is about 8db peek due to room and port tuning). I do have a down 3db at 1Khz but that is fixed with EQ. Now for the part I can't figure out. I have a center channel MTM using 2 3" daytons and a 1" vifa textile dome that reproduces the vocals sooo much better. This speaker also has flat response down to the 80Hz crossover point (haven't tested it below 80Hz). Why does the center channel sound so much better? Both are tested at the listening position.
I would guess it has something to do with the phase tracking in the xover region. Can you post your measurements showing the phase?

Also, you might head over to the PE techtalk forum and start a thread with your questions over there. Lots of other knowledgeable guys there that will provide more opinions on your questions. There are more speaker designers over there than over here. Most over here are building kits and subs, not that it's a bad thing, just the way it seems to be.
 

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The driver spacing on the woofers is currently about 12" apart and crossed at 2K. I think I need to bring them closer together.
You don't. Even Joe D'Appolito doesn't concern himself with CTC spacing in a vertical MTM anymore, as whatever lobing might occur at the baffle will have dissipated into a uniform wave front at normal listening distances, while any combing won't be heard on the horizontal plane. The only reason for adding a separate smaller midrange is if the midbasses are down more than 6dB at 30 degrees at the crossover frequency.
The weird thing is that when I run a measurement sweep I have nearly flat response from 20KHz all the way down to 42Hz (where there is about 8db peek due to room and port tuning). I do have a down 3db at 1Khz but that is fixed with EQ. Now for the part I can't figure out. I have a center channel MTM using 2 3" daytons and a 1" vifa textile dome that reproduces the vocals sooo much better. This speaker also has flat response down to the 80Hz crossover point (haven't tested it below 80Hz). Why does the center channel sound so much better? Both are tested at the listening position.
What do off-axis sweeps reveal?
 

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Discussion Starter #10
I would guess it has something to do with the phase tracking in the xover region. Can you post your measurements showing the phase?

Also, you might head over to the PE techtalk forum and start a thread with your questions over there. Lots of other knowledgeable guys there that will provide more opinions on your questions. There are more speaker designers over there than over here. Most over here are building kits and subs, not that it's a bad thing, just the way it seems to be.
I'm using REW for my measurements. Is there a way to test phase with that? Seems like I would need to take that measurement with leads hooked up to the output, using an oscilloscope or something. Either that or spent the money on the right software/hardware from parts express.
 

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I'm using REW for my measurements. Is there a way to test phase with that? Seems like I would need to take that measurement with leads hooked up to the output, using an oscilloscope or something. Either that or spent the money on the right software/hardware from parts express.
REW will measure phase, it's displayed in the SPL/Phase tab which is usually the first one that opens. You'll need to collect data from both the tweeter and woofer individually though to see if they match up.

The other option is to simulate the response in WinPCD, but again you'll need FRD and ZMA files to do so, but depending on the drivers you'll be using the published data might be good enough to use for simulations. This can get pretty complex and you have to do a lot of manipulating of the FRD files to get them to do what you want. You can find a lot more info on this over at the PE techtalk forum.
 
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