First order vs. First order time-aligned and a dilemma

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Andy, your speaker is NOT 1st order. Look closely at the roll-off slopes of both the woofer and tweeter. The woofer rolloff is 12 dB/octave, which makes it a second order. The tweeter rolloff is 1st order making it an asymmetrical crossover network. Not sure how your delay network work to make them "time aligned". In crossover design, you must consider the equivalent circuits of the drivers. They are part of your crossover and it is an unavoidable fact. Using a single crossover component in the woofer path usually results in a 2nd order rolloff.

With a 2-way system, you will need a RLC tanking network to tame the woofer break-up around 4.5 KHz. I can see that the woofer breakup bump caused a broadband drop in the upper midrange in the reverse polarity version. It can give a completely different impression of the system and has nothing to do with "time alignment".

Looking at the phase response curves of the 2 systems, the first one with the reversed driver connection actually has less less phase variation, but a much more rugged frequency response due to the woofer breakup. It may be partially due to its much higher crossover point (compared to the 2nd system).

I was in the same situation as you are 2 years ago. I came to this forum and received a lot of help from many members, particularly, wintermute, Zuhl, jReave, AllenB and System7 who were all very gentle to the new comer, me, and extremely helpful. See my thread about that experience.
The crossover for a modest DIY bookshelf speaker project
I prefer higher order crossover to compensate for driver imperfection. I got a system with excellent sound staging including depth.

Good luck with your adventure. It is NOT mysterious. It is solid science and physics.

I think the roll-off is 6db/octave. I am using 3db per division. Maybe at the tail end of the woofer it's a little higher than 6db but by then it's probably not critical. As for "time aligned", yeah, that's pretty mysterious.
 
Anyway, just got my Illuminator 5.5in and got to try it out with the SBA dimple tweeter. Sounds really nice. The revelator is nice but it a bit lush and lacks a little bit of micro detail. The Seas Nextel has lots of micro details but maybe a little a bit too much of it so one has to be careful with xover. The Illuminator is like the best of two world - still does not have the micro details of the Nextel but it just has enough but at the same time very natural sounding and really good bass for its size.
The SBA dimple tweeter is a little bit subdue sounding vs. its Satori version. On the other hand, the Satori dimple tweeter could be a handful. It has a slight peak around 2K to 4K then after around 8K it perks up to around 2db. With mass strings playing, there is a brittleness on the treble that sometimes can be very distracting. I wished I had bought the AirCir.

So I switched back between the Illuminator and the Seas Nextel and I am not sure the Nextel is less superior. I am not sure why but the SS revelator and illuminator seem to get a lot of attention while I do not hear much of people using the Nextel driver. But between the revelator, illuminator, and Nextel, I actually think the Nextel has a better midrange and maybe a little more transparent. What the revelator and illuminator have over the Nextel is the bass output, but they are all 5.5in so it's not like night and day difference on the bass. The Nextel does have a slightly rougher higher freq. roll off so once just has to be careful in xover design.
In term of sound, the illuminator is definitely a warmer sounding unit vs. the Nextel and maybe better overall, but even then I thought I was enjoying the Nextel more than the illuminator.
 
I think the roll-off is 6db/octave. I am using 3db per division. Maybe at the tail end of the woofer it's a little higher than 6db but by then it's probably not critical. As for "time aligned", yeah, that's pretty mysterious.
It is easier to determine the roll-off slope if you plot the target low pass filter response along side the woofer+LP filter actual response curve. Your crossover frequency appears to be about 2.5 KHz. The segment of roll-off around 2.5 KHz is 12 dB/octave. Slower before and steeper after. Below is my final 3rd order crossover result using Peerless HDS 830875 and Dayton Audio RS28A-4 in a 15 litres closed box.
woofer_wintermute3.gif
I had many failed attempt along the way. When the drivers were not properly compensated, the response curves of individual drivers could look like a 2 or 3-slopes curve after attempt to get a smooth summed response. Below is one of my failed attempt which did not sound the optimal. The bass roll-off toward lower frequency was due to the lack of Baffle Step Compensation.
response_peerless-dayton2.gif
Most speaker cabinet and crossover design work were based on well established electrical filter theory. It is nothing mysterious about them until the idea of passively time aligned speaker comes along. Using DSP for electronic crossover with time alignment is well understood too, but not the passive one.

Two years ago, X-Sim did not yet include geometric features (such as varying mic position, baffle or boundary-bounce effects) as in Jeff Bagby's very successful "PCD" Passive Crossover Design program. I wonder if the X-Sim had add those geometric features now? They are essential to design a minimum phase system for good staging performance.
 
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So I switched back between the Illuminator and the Seas Nextel and I am not sure the Nextel is less superior. I am not sure why but the SS revelator and illuminator seem to get a lot of attention while I do not hear much of people using the Nextel driver. But between the revelator, illuminator, and Nextel, I actually think the Nextel has a better midrange and maybe a little more transparent. What the revelator and illuminator have over the Nextel is the bass output, but they are all 5.5in so it's not like night and day difference on the bass. The Nextel does have a slightly rougher higher freq. roll off so once just has to be careful in xover design.
In term of sound, the illuminator is definitely a warmer sounding unit vs. the Nextel and maybe better overall, but even then I thought I was enjoying the Nextel more than the illuminator.
Are you talking about the Seas Excel M15CH-002 Nextel paper midrange driver? It is a dedicated midrange and not recommended for use in bass reflex according to Seas' spec sheet. Recommended Enclosure: 0.15 cu. ft. (4.2 liters) sealed, F3 = 150 Hz.

The Seas cone breakup is at a much higher frequency than the SpeakScan drivers which were designed as woofers. The Nextel paper cone is also more forgiving. But I have not seen a Seas 5" Nextel paper cone woofer.
 
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It is easier to determine the roll-off slope if you plot the target low pass filter response along side the woofer+LP filter actual response curve. Your crossover frequency appears to be about 2.5 KHz. The segment of roll-off around 2.5 KHz is 12 dB/octave. Slower before and steeper after. Below is my final 3rd order crossover result using Peerless HDS 830875 and Dayton Audio RS28A-4 in a 15 litres closed box.
View attachment 653376
I had many failed attempt along the way. When the drivers were not properly compensated, the response curves of individual drivers could look like a 2 or 3-slopes curve after attempt to get a smooth summed response. Below is one of my failed attempt which did not sound the optimal. The bass roll-off toward lower frequency was due to the lack of Baffle Step Compensation.
View attachment 653378
Most speaker cabinet and crossover design work were based on well established electrical filter theory. It is nothing mysterious about them until the idea of passively time aligned speaker comes along. Using DSP for electronic crossover with time alignment is well understood too, but not the passive one.

Two years ago, X-Sim did not yet include geometric features (such as varying mic position, baffle or boundary-bounce effects) as in Jeff Bagby's very successful "PCD" Passive Crossover Design program. I wonder if the X-Sim had add those geometric features now? They are essential to design a minimum phase system for good staging performance.

Can you show on the graph how it is 12db/octave?
 
View attachment 653420
The thick black line from 2 KHz to 4 KHz (1 Octave across crossover point) is the slope of the woofer response through the crossover region. It is far from 6 dB and much closer to 12 dB.

That is the dip due to baffle diffraction - not part of the filter. You have to consider the entire roll off. If you know how to design a baffle to get rid of the diffraction, maybe you could share your ideas.
 
That is the dip due to baffle diffraction - not part of the filter. You have to consider the entire roll off. If you know how to design a baffle to get rid of the diffraction, maybe you could share your ideas.
No, it is NOT a "dip due to baffle diffraction".

The concept of baffle diffraction is one of the new idea I learned during my building of the 2-way bookshelf. The baffle diffraction is compensated in the crossover design in a step usually called BSC. It is a well established concept like the minimum phase in speaker design and is not mysterious. It is described in detail on how to handle using Jeff Bagby's PCD by Paul Carmody.

Paul_Carmody said:
Step 7: Simulate for baffle diffraction and loss.
This is where the real learning comes in. Response Modeler has the amazing ability to model for diffraction and baffle step loss of our drivers when mounted in an enclosure. This is very important! In this section, I entered the baffle dimensions and driver location on the baffle. I also told the program that the driver’s diameter is about 6”. You will notice that the graph will change significantly as you adjust values. For example, if I change the width of the baffle to make it wider, the baffle step “hump” and “roll off” will go lower in frequency. Also notice that the size of a driver has a large impact on how much diffraction (ripples above baffle step) it exhibits, as well as where the driver is placed on the baffle. This is very important stuff to consider when doing your next design!
An externally hosted image should be here but it was not working when we last tested it.

Teachable moment over. Now, I will click the button to “Save Diffraction Curve to BDS Register Above.” This will apply this curve to our Frequency Response graph at the top. So let’s scroll up and take a look.
An externally hosted image should be here but it was not working when we last tested it.

Whoah! Suddenly, the bass response has just dropped off by 6 dB! This, folks, is called “Baffle Step Loss,” and it will happen on any speaker that isn’t mounted into a wall. You can compensate for Baffle Step Loss when doing your crossover design (this is aptly known as “Baffle Step Compensation” or BSC).
Two years ago, X-Sim did not yet include geometric features (such as varying mic position, baffle or boundary-bounce effects) as in Jeff Bagby's very successful "PCD" Passive Crossover Design program. I wonder if the X-Sim had add those geometric features now? They are essential to design a minimum phase system for good staging performance. The PCD is Excel based. Dave Ralph's Windows Passive Crossover Designer (WinPCD) is a Windows application intended to emulate the Excel spreadsheet created by Jeff Bagby.
 
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No, it is NOT a "dip due to baffle diffraction".

The concept of baffle diffraction is one of the new idea I learned during my building of the 2-way bookshelf. The baffle diffraction is compensated in the crossover design in a step usually called BSC. It is a well established concept like the minimum phase in speaker design and is not mysterious. It is described in detail on how to handle using Jeff Bagby's PCD by Paul Carmody.


Two years ago, X-Sim did not yet include geometric features (such as varying mic position, baffle or boundary-bounce effects) as in Jeff Bagby's very successful "PCD" Passive Crossover Design program. I wonder if the X-Sim had add those geometric features now? They are essential to design a minimum phase system for good staging performance. The PCD is Excel based. Dave Ralph's Windows Passive Crossover Designer (WinPCD) is a Windows application intended to emulate the Excel spreadsheet created by Jeff Bagby.

No, diffraction in its strict definition is not "BSC". They are related but not exactly the same. BSC is when the radiation pattern goes from 2pi to 4pi at low frequency. Diffraction can happen at any frequencies although mostly, but not exclusively, at high frequencies
 
No, diffraction in its strict definition is not "BSC". They are related but not exactly the same. BSC is when the radiation pattern goes from 2pi to 4pi at low frequency. Diffraction can happen at any frequencies although mostly, but not exclusively, at high frequencies
I hope that you find Fitz LINKWITZ a respected authority in speaker design and will not call him BS. He does not agree that "Diffraction happens mostly at high frequencies". He said, at those (high) frequencies almost all tweeters are highly directional and little sound reaches the cabinet edge to be diffracted! For a small woofer, the pattern becomes directional around 1 KHz for most design.

Diffraction from baffle edges by Fitz LINKWITZ
LINKWITZ said:
Loudspeaker cabinet edge diffraction is a subject of never ending debate. I am not aware of any scientific study as to the audible effects of diffraction, but since it adds ripples to the steady-state frequency response of a loudspeaker, especially for symmetrical driver layouts, there are many claims to its detrimental effects. Especially popular are time domain explanation using a sound impulse or pressure step of infinitely short rise time. In reality the fastest rise time is given by the tweeter's high frequency cutoff. At those frequencies almost all tweeters are highly directional and little sound reaches the cabinet edge to be diffracted. Thus, the portion of a sound pressure step that travels along the baffle surface has a much slower rise time than the portion that propagates on-axis. Consequently the magnitude of any diffraction effect is greater at the low frequency end of a driver's range. All this must be taken into account when modeling radiation from a loudspeaker on the computer, otherwise the effects of diffraction are overestimated.
I am almost certain Fitz LINKWITZ did not come to that conclusion by LOVE. I am sorry that he did use the term "scientific study".
 
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Nextel 5.5 vs. Revelator 5.5 vs. Illuminator 5.5

After having spent sometimes with these drivers I got to be more familiar with their own sound. This time the Rev5.5 and Illum 5.5 are properly fitted with the AirCirc tweeter while the Nextel 5.5 still hobbled with the Toyota ... err I mean the Satori dimple dome. Hopefully I'll get it fitted with the AirCirc soon. Before that, just a few words comparing the Satori dome vs. the AirCirc. Although they are both categorized as softdome, the AirC dome is made of much harder dome material. While the Satori is reasonably smooth, the AirC is more robust sounding and more 3 dimensional. The AirC gives the sound an extra presence that definitely is worth the price.

Nextel 5.5: I still think it has the most interesting midrange not found in the other drivers, although it does give up on the bass. It has really nice micro detail and mid range clarity. Maybe I have to get the Ceramic to get something better. Using supercar analogy, it's probably the Ferrari 458 Speciale.

Revelator 5.5: A very good driver. Maybe a bit lush in the mid range but still has very good detail. This driver has an interesting split personally though. At the low freq. it's a bit lush, but as you go up the upper mid range, it's a bit elevated, so you get the impression that the sound is both warm and bright at the same time. The Nextel on the other hand, is a lot more consistent the entire frequency range. So you have to be careful with xover. It's probably the Ferrari 488.

Illuminator 5.5: Is it the most perfect driver ... maybe too perfect? It comebines the best of the Nextel 5.5 and the revelator 5.5. It has micro detail of the Nextel and the bass (even more powerful bass) and warmness of the Revelator. It also has a very well behaved high frequency response. The sound is very smooth. And due to its well behavior, you can fine tune the sound to anything you want. If you want slightly bright, or warm, or more bass, you can do it all with this driver. Whereas on the Nextel or Revelator,
you don't really have a lot of options. But then is it too smooth too perfect? Listening to the Illum 5.5 I have a feeling I respect it more than loving it. Maybe it's just me. Is it the price of being too perfect and on its way there it may have lost some of its soul? It's probably the Porsche 918.
It's known as a hypercar that you can take it for grocery shopping. Hm... If I could afford one, I'd probably get the LaFerrari. Can you take the LaFerrari to get groceries? I suppose if I could afford one, I'd probably have my own chef. If I were Porsche, I probably would make something like a 9DD.
 

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So I've been listening to the Illum 5.5 to understand why I felt like it's a perfect driver but I can't find any love for it.
So, I asked myself, why why why?

I think I may have found one or maybe two reasons. First it has an incredible bass for its size and a super smooth treble especially when mating with the AirCirc. But it may have compromise on the midrange. I feel like the mid range sort of take a back seat and may be just a touch too lean. The other two drivers for all their flaws the first thing you notice is the beautiful midrange.
Leonard Bernstein once said the difference between a good performer and a world class performer is the animal within. I feel like the Illum may be a bit too much of a control freak. Maybe it should let its hair down a bit. It tries a little too hard to be balance. Scan Speak engineers in their quest to make a perfectly engineered driver, they might have forgotten to give it a soul.

So in summary:
Nextel 5.5 : the sexiest.
Revellator 5.5: the charmest.
Illuminator 5.5: the soulless (get it?)
 
Hallo Andy,

Unless you make very detailed off axis measurements of the systems, your are attributing qualities to individual drivers that actually may not there. It is all in the system, not in the magic of one or another driver.

One cannot engineer "soul" into a driver: it basically pumps air and higher up breaks up in one way or another.
 
If you are willing to try a new woofer, I will recommend the SB Satori woofers 5-6.5" they are the over all best mid-woofers I have tried. If you could go one size up, the old Scan Speak 18W/8535 is still my favorit Scan Speak midwoofer, especially for its midrange qualities.
 
Hallo Andy,

Unless you make very detailed off axis measurements of the systems, your are attributing qualities to individual drivers that actually may not there. It is all in the system, not in the magic of one or another driver.
Well I don't know of any measurement that can tell me whether a driver has a soul or a beautiful midrange or a smooth treble. I think our hearing is just too complicated for some of basic measurements I see out there.

One cannot engineer "soul" into a driver: it basically pumps air and higher up breaks up in one way or another.
I suppose you don't think we humans have any soul either? After all we are just a bunch of molecules pumping air ... some actually pump air out of their behind.
 
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