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2 way V 3 way designs

  • Thread starter QuestForThe13thNote
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Q

QuestForThe13thNote

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Can some more knowledgable people about techie matters please help me out with this.

Why are some speakers designed as 3 way against others as 2 way. As far as I can tell it’s to do with more faithfully reproducing bass in a 3 way design. This video is quite good https://m.youtube.com/watch?v=F98MB3m8jCs

So therefore as this guy explains it, if you have a bass driver that just deals with low frequencies you achieve that with a bigger driver just by the properties of the driver and how much it can vibrate. You then need a mid driver to fill in the gap and the hf unit for the top frequencies. He also explains that if you then have a two way speaker, it tends to be one with a 5-8 inch bass/mid driver to be able to cope with low bass (but not quite as low as a bigger driver) and mid range, and so you can achieve cross over adequately with the high frequency unit.

so what this means then is that if you really like lots of low bass you go for a 3 way design of a decent sized speaker maybe an atc scm40, but if you like modest bass you’d tend to find a 2 way as acceptable. It tends to be 3 ways are in bigger designs. I’ve never found you can make distinctions between 3 way being better than 2 on overall quality of sound. Also depends on quality of drivers, how it crosses over. Also I’ve heard ‘phase problems’ being mentioned with 3 way which is presumably because in a 3 way design you need two crossovers, one between low and mid, and another between mid and hf.

Have I got the above right and does the above adequately explain the design considerations about these two types of designs ie 2and 3way. The thing that got me stumped is why would something like a neat iota alpha be a really small speaker and have a 3 way design but utilise small drive units as a 3 way design.
 

insider9

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Neat Iota Alpha is a three driver two and a half way design. This means that two drive units overlap partially.

The purpose of 3-way design doesn't have to be bass depth at all. There are advantages and disadvantages to each of these approaches.
 

abacus

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Forget whether it is 2, 2 ½, 3 or 4 way as it is only relevant to the manufacture, and so long as the speakers match the rest of your system and are acceptable to your ears, then how they are made up is irrelevant.

Bill
 

Vladimir

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insider9 said:
Neat Iota Alpha is a three driver two and a half way design. This means that two drive units overlap partially.

The purpose of 3-way design doesn't have to be bass depth at all. There are advantages and disadvantages to each of these approaches.
My oddball Sony's have partially overlaping dual 8" drivers in separate sealed chambers to mimic a larger bass driver (deep palpable bass with low distortion) yet maintain 8" driver features (rich timbral character) in the lower midrange. Then 4" driver follows for upper midrange, and tweeter for highs. Its essentially a 3 way with an integrated sub.

 

insider9

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Have a look at my Jamos. Love these and what they do but at the minute don't have a system for them.

Incorporating two isobaric loaded 8 inch woofers that go down cleanly to 30Hz in room.

 

insider9

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For me the biggest advantage of 3-way is not in its bass at all but midrange.

Most two way designs rely on speaker cabinet contributing to bass. See PMC with transmission line as an example. However the drive unit still needs to produce long strokes to produce low frequencies. This is the same unit that also needs to produce much shorter strokes to produce mids. Now imagine how much clearer the same driver could play through midrange should it not have to do long strokes that are needed for bass.

As you say most 2-way design will rely on 5-8 inch drivers. Problem is 5" is to small to reproduce bass but 8" is to large for higher midrange.
 

Vladimir

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insider9 said:
Have a look at my Jamos. Love these and what they do but at the minute don't have a system for them.

Incorporating two isobaric loaded 8 inch woofers that go down cleanly to 30Hz in room.
I love that. I see they use the same Seas tweeter as mine.

Impressive build, someone was thinking and not just screwing huge expensive drivers in a 1000L plywood cottage. Acoustic Research AR9s would be also on top of my list.

 

insider9

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Vladimir said:
insider9 said:
Have a look at my Jamos. Love these and what they do but at the minute don't have a system for them.

Incorporating two isobaric loaded 8 inch woofers that go down cleanly to 30Hz in room.

 
I love that. Impressive build, someone was thinking and not just screwing huge expensive drivers in a 1000L plywood cottage. Acoustic Research AR9s would be also on top of my list.

BTW, I see they use the same Seas tweeter as mine. 
Absolutely, they're well engineered and even they're close to 30 years old still measure according to specs with all genuine parts. THD is insanely low all the way down.

Yes, I believe the drive units are Seas indeed, well spotted :) I absolutely love the sound of them which is nothing like speakers that are made nowadays.
 

insider9

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Look great, I'd love to hear a pair of these. Would also love to hear your Sony speakers. I like a 4" midrange they're usually better suited than 5"
 

Vladimir

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insider9 said:
Look great, I'd love to hear a pair of these. Would also love to hear your Sony speakers. I like a 4" midrange they're usually better suited than 5"
The Concert VIIs have 150Hz/4kHz frequency crossovers. The 6.5" driver covers all the midrange, which is good because there is one less gap compared to my Sony's (300/1200/4500). However, you get a diaphragm trying to do 150 and 4000 cycles at the same time. Unless it is a pretty good driver (stiff, light, self dampening), it will act like a bottleneck.

Back the moto of engineering: You can't have your cake and eat it too.
 

insider9

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Vladimir said:
insider9 said:
Look great, I'd love to hear a pair of these. Would also love to hear your Sony speakers. I like a 4" midrange they're usually better suited than 5"
The Concert VIIs have 150Hz/4kHz frequency crossovers. The 6.5" driver covers all the midrange, which is good because there is one less gap compared to my Sony's (300/1200/4500). However, you get a diaphragm trying to do 150 and 4000 cycles at the same time. Unless it is a pretty good driver (stiff, light, self dampening), it will act like a bottleneck.

Back the moto of engineering: You can't have your cake and eat it too.
Very true!

When I converted them to actives I've looked to move crossover points. It so happens that drivers naturally roll of around these frequencies. Crossovers mostly work to even out the load to amp as opposed to do a lot of filtering. It's mostly done via good design and well chosen drive units. Mid effective range is 250-3,500Hz. It rolls of naturally on both sides. Woofers start rolling of around 100Hz.

No doubt that upgrading the main driver would do wonders. I might be tempted to do it one day.
 

Vladimir

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If you try to shoehorn inadequate drivers via crossover tricks, you may end up with cone breakups, nasty phase shifts etc. in certain transient extremes.
The drivers for the Sonys were custom made one-offs, even the Seas tweeter. It had to be done so to get this oddball design working.
 
Q

QuestForThe13thNote

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insider9 said:
For me the biggest advantage of 3-way is not in its bass at all but midrange.

Most two way designs rely on speaker cabinet contributing to bass. See PMC with transmission line as an example. However the drive unit still needs to produce long strokes to produce low frequencies. This is the same unit that also needs to produce much shorter strokes to produce mids. Now imagine how much clearer the same driver could play through midrange should it not have to do long strokes that are needed for bass.

As you say most 2-way design will rely on 5-8 inch drivers. Problem is 5" is to small to reproduce bass but 8" is to large for higher midrange.
Yes that seems to make a lot of sense and I’m sure you are right there, but I guess what’s interesting in a transmission line is how much the bass from the driver augments the power of the driver so what’s coming out of the transmission line port is deeper bass than the driver, so maybe this frees up the driver to do the mids better?. In other words it doesn’t need to have a long throw for the bass as much. But then this must be just as true for a conventional ported speaker but maybe not so much given the tl absorbs all but lowest frequency as they pass along and the length is critical to the tuning of that I understand. I notice my bass driver on my pmcs seems to move hardly at all even when quite loud. I think this is one of the advantages of the tl, but that’s an aside to the issue of 2 versus 3 way designs, not to concentrate on tl’s which the thread isn’t about. But I agree with you that speakers with a third mid range driver do seem to have better control of midrange, which it seems obvious to say.

Im not sure what you meant by the neat iota alpha having 2 and a half?. I can see it looks like it has one downward firing bass driver and then one midrange on the front with the ribbon tweeter of course. But as I say they are all quite small which has me confused.
 

Andrewjvt

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I've compared ATC 2 way and 3 way actives

The immediate difference you notice is the unstrained delivery.
As the drivers have a job to do with no overlap

Normally it will mean greater clarity and less strained delivery but will depend on the manufacturer as lots of good 2 ways may still sound better than some 3 ways
 

insider9

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Vladimir said:
If you try to shoehorn inadequate drivers via crossover tricks, you may end up with cone breakups, nasty phase shifts etc. in certain transient extremes.
The drivers for the Sonys were custom made one-offs, even the Seas tweeter. It had to be done so to get this oddball design working.
Yep and no tricks were intended. With digital crossover phase is a non issue. The only thing to be vary is cone breakup which was exactly my concern. 6.5" driver crossing over at 4kHz just seems high to me. I was consider lowering this if tweeter behaved. Unfortunately wasn't possible with that tweeter.
 

insider9

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QuestForThe13thNote said:
Yes that seems to make a lot of sense and I’m sure you are right there, but I guess what’s interesting in a transmission line is how much the bass from the driver augments the power of the driver so what’s coming out of the transmission line port is deeper bass than the driver, so maybe this frees up the driver to do the mids better?
Not quite. The drive unit still resonates at these frequencies. So not that much benefit to midrange. However the lowest notes are out of phase at the driver so you can't hear them. As the sound travels through transmission line it comes out in phase.

QuestForThe13thNote said:
Im not sure what you meant by the neat iota alpha having 2 and a half?. I can see it looks like it has one downward firing bass driver and then one midrange on the front with the ribbon tweeter of course. But as I say they are all quite small which has me confused. 
Number of drivers isn't relevant when considering if it's a 2 or a 3-way. You could build a 2 way speaker using many drivers. It's all about how many ways is the frequency spectrum split.

With a 2 driver 2-way the frequency spectrum is split into two. Tweeter handles high frequencies and driver mids and lows. But you could use more than one tweeter or one driver.

This JBL is a 2-way speaker. Both drivers are doing the same thing, covering the same frequencies.

As I already mentioned Neat Iota Alpha is a 2.5-way. One of the drive units covers only a part of frequency spectrum of the other.

Have a look below for a pic of earlier mentioned Jamo speakers. They appear to be a 2-way design. They're in fact a 3-way but 4 driver design :)
 

andyjm

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Crossovers are generally a bad thing. It is very difficult to get two speakers to crossover in a decent way without one amp per driver and DSP trickery. Three drivers are worse, there are now twice the problems. This is a good argument for limiting the number of drivers in a speaker.

One of the reasons for full range electrostatics having such a natural delivery is the lack of crossover issues.
 
Q

QuestForThe13thNote

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Thanks for your reply. What do you mean when you say the lowest bass notes are ‘out of phase’. Doesn’t that still mean that the audible parts of the useful mid range frequencies are in phase and can be heard.

I suppose with neat it creates bass by firing it down and all the reflections that creates and then use the top driver to give the mids and tweeter for hf obviously.
 

insider9

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andyjm said:
Crossovers are generally a bad thing.  It is very difficult to get two speakers to crossover in a decent way without one amp per driver and DSP trickery.  Three drivers are worse, there are now twice the problems. This is a good argument for limiting the number of drivers in a speaker.

One of the reasons for full range electrostatics having such a natural delivery is the lack of crossover issues.
Can't disagree with that. In principle a full range driver would be best. There are many design problems trying to deliver this well at reasonable volume and with dynamic expression. Far too many to bother in fact.

As you say DSP crossovers make what previously was nigh on impossible with steeper slopes and especially with very accurate phase correction now possible. Not just that but passive speaker crossovers can nowadays be quite easily linearised using DSP.
 

insider9

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QuestForThe13thNote said:
Thanks for your reply. What do you mean when you say the lowest bass notes are ‘out of phase’. Doesn’t that still mean that the audible parts of the useful mid range frequencies are in phase and can be heard. 

I suppose with neat it creates bass by firing it down and all the reflections that creates and then use the top driver to give the mids and tweeter for hf obviously. 
Love the avatar by the way. No, midrange will be fine.

In your twenty5.23 sound travelling through transmission line is coming out of the port will be delayed as it travels additional 2.4 meters. Should it be sent via transmission line in phase to the driver there would be phase issues invariably causing cancellations. Hence transmission line is tuned so that it reinforces low frequencies but also that what comes out is in phase with the driver.

Here's info from PMC website that will explain it better.

PMC’s innovative approach places the bass driver near one end of a long tunnel (the Advanced Transmission Line). This tunnel is heavily damped with acoustic material specified carefully to absorb the upper bass and higher frequencies radiating from the rear of the bass driver. The lowest frequencies are allowed to pass down the line and emerge from the large vent in the same polarity as the driver’s frontal radiation, the vent acting essentially as a second bass driver.

An important benefit of the approach is that the air pressure inside the cabinet, loading the bass driver, is maintained. This helps to control the driver over a wide frequency range and significantly reduces LF distortion. Consequently, the upper bass and midrange detail is not masked by harmonic distortion and the result is PMC’s characteristically transparent midrange, fast, attacking bass and outstanding clarity.

A further advantage is greater bass extension and loudness than a ported or sealed design of a similar size, even if similar drivers were used. Moreover, the very consistent bass driver loading brings the welcome benefit that the frequency response remains consistent regardless of listening level, and analytical auditioning can be conducted without the need for high replay volumes to achieve optimal bass response – a unique and very valuable characteristic.
 

Vladimir

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insider9 said:
I was consider lowering this if tweeter behaved. Unfortunately wasn't possible with that tweeter.
It's possible you have the same custom order driver without ferro-fluid like in my speakers (I contacted Seas 2y. ago). It can't go down to 2.5kHz like the standard off the shelf Seas which had FF, and the power rating is reduced, but oh boy does it sound alive and airy. Good string recordings can give you goose bumps. Cymbals shimer for days.
 

insider9

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Vladimir said:
insider9 said:
I was consider lowering this if tweeter behaved. Unfortunately wasn't possible with that tweeter.
It's possible you have the same custom order driver without ferro-fluid like in my speakers (I contacted Seas 2y. ago). It can't go down to 2.5kHz like the standard off the shelf Seas which had FF, and the power rating is reduced, but oh boy does it sound alive and airy. Good string recordings can give you goose bumps. Cymbals shimer for days.
Quite possible indeed. If you're interested have a look here I've overlaid mid and tweeter. Midrange driver was in fact rolling off earlier and it was a natural roll off. Like I mentioned 6.5" to go to 4kHz is usually wishful thinking. (I believe the measurements are at 1m on axis in free space if I believe my notes.)
 

Vladimir

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insider9 said:
Vladimir said:
insider9 said:
I was consider lowering this if tweeter behaved. Unfortunately wasn't possible with that tweeter.
It's possible you have the same custom order driver without ferro-fluid like in my speakers (I contacted Seas 2y. ago). It can't go down to 2.5kHz like the standard off the shelf Seas which had FF, and the power rating is reduced, but oh boy does it sound alive and airy. Good string recordings can give you goose bumps. Cymbals shimer for days.
Quite possible indeed. If you're interested have a look here I've overlaid mid and tweeter. Midrange driver was in fact rolling off earlier and it was a natural roll off. Like I mentioned 6.5" to go to 4kHz is usually wishful thinking. (I believe the measurements are at 1m on axis in free space if I believe my notes.)
I bet your tweeters are dry as a bone with no ferro-fluid as well. Its easy to check, just take out few screws, no desoldering required, just take off the front plate. The equivalent early 90s Seas drivers all had FF and went down to 2.5kHz flat. (check the pdfs in their vintage driver web section)

People intentionally scoop out the FF out of Seas, Scanspeak and Vifa drivers to make them more lively and present. The downside is being carefull not to have any amplifier clipping or they'll fry. Also you'll be aware of the thermal/electromechanical limitations of the driver. The lower you try to play it, less of a power handling capability it will have.

Ferro-fluid cooling was invented by AR in the 70s to increas the power handling of their dome tweeters (which they invented in the 60s). People played AR speakers loud with undersized amps and the manufacturer was faced with a dead tweeter plague and thousands of drivers replaced under warranty each year. FF was born out of necessity, not as an improvement of sound quality.
 

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