Crossover Designs: 2 1/2 Way

[Yesfan70]

But I have seen speakers listed as being "2.5 ways" before. If there is such a thing, how is that possible? How is a 2.5 way different from a conventional 2 way or 3 way speaker?




*****EDIT BY ZING*****
This is shaping up to be a great discussion and I thought it would be better to have its own thread. Carry on, Gentlemen! :handgestures-thumbup:

 

[jamhead]

Re: The Ghetto Stands

Yeah, that happens a lot with me. Gets me in trouble with the wife constantly.

 

[Zing]

Re: The Ghetto Stands

But I have seen speakers listed as being "2.5 ways" before. If there is such a thing, how is that possible? How is a 2.5 way different from a conventional 2 way or 3 way speaker?

The SVS MTS speakers are a good example of a 2.5 way. Let's say the tweeter is crossed over to one of the bass drivers at 2kHz. That bass driver plays from 2kHz all the way down until it runs out. The other bass driver won't even kick in until, say, 400Hz and then play down from there.

The new Klipsch RF-7 II is an example of 2-way. It also has two bass drivers but both of them operate from when the tweeters hands it over at 1800Hz.

Let's use Bats' 5.4's as a 3-way example. The tweeter (1) hands it over to a mid range (2) which in turn hands it over to the bass drivers (3) which both operate in the same range. If only one of those bass drivers took over fromt he midrange and the other kicked in at a much lower frequency, then that would be a 3.5 way. Capice?

 

[Huey]

Re: The Ghetto Stands

But I have seen speakers listed as being "2.5 ways" before. If there is such a thing, how is that possible? How is a 2.5 way different from a conventional 2 way or 3 way speaker?

I'm not positive, but I think 2 1/2 way speakers, are the ones where the mid woofer is positioned in the same area as the woofer, and the crossover positioned between the two.

 

[Yesfan70]

Re: The Ghetto Stands

^^ But what would be the crossover frequencies? As Zing alluded to, 2ways have one crossover point and 3ways have two crossover points. How is a 2.5way's crossover point configured?

 

[jamhead]

Re: The Ghetto Stands

But I have seen speakers listed as being "2.5 ways" before. If there is such a thing, how is that possible? How is a 2.5 way different from a conventional 2 way or 3 way speaker?

A 3 way speaker sends bass to a dedicated driver(s); mids to another dedicated driver; highs to a third.

A 2 way speaker sends bass/mid to a dedicated driver(s); highs to another.

A 2.5 way speaker sends bass to one driver; bass/mids to another driver; and highs to the tweet.

What I'm not sure about is the crossover involved for a 2.5 way. I may have to look that one up.

 

[Yesfan70]

Re: The Ghetto Stands

But I have seen speakers listed as being "2.5 ways" before. If there is such a thing, how is that possible? How is a 2.5 way different from a conventional 2 way or 3 way speaker?

A 3 way speaker sends bass to a dedicated driver(s); mids to another dedicated driver; highs to a third.

A 2 way speaker sends bass/mid to a dedicated driver(s); highs to another.

A 2.5 way speaker sends bass to one driver; bass/mids to another driver; and highs to the tweet.

What I'm not sure about is the crossover involved for a 2.5 way. I may have to look that one up.

Ok, that's answers part of my question (and makes sense). I'm interested in what the crossover points would be as it seems like it would be no different than a 3 way's crossover.

 

[Zing]

Re: The Ghetto Stands

^^ But what would be the crossover frequencies? As Zing alluded to, 2ways have one crossover point and 3ways have two crossover points. How is a 2.5way's crossover point configured?

It's simply a third crossover point except it applies only to one driver.

Garden variety example:
3 driver speaker (1 tweet and 2 woofers) 2.5-way design
XO points 2.6kHz and 200Hz
From 20kHz down, the tweeter plays.
At 2.6kHz just one of the woofers starts to play
At 200Hz, the other woofer starts to play

To be clear, at 1000Hz, only one woofer is playing. But at 100Hz, they're both playing.

 

[Yesfan70]

Re: The Ghetto Stands

So both woofers still play down to the same lowest frequency, but it's only one that tops out at 2.6kHz, right?


OK, makes sense now.

 

[jamhead]

Re: The Ghetto Stands

^^ But what would be the crossover frequencies? As Zing alluded to, 2ways have one crossover point and 3ways have two crossover points. How is a 2.5way's crossover point configured?

It's simply a third crossover point except it applies only to one driver.

Garden variety example:
3 driver speaker (1 tweet and 2 woofers) 2.5-way design
XO points 2.6kHz and 200Hz
From 20kHz down, the tweeter plays.
At 2.6kHz just one of the woofers starts to play
At 200Hz, the other woofer starts to play

To be clear, at 1000Hz, only one woofer is playing. But at 100Hz, they're both playing.

So, this would indicate two crossover points then?
That doesn't make sense to me that it would be a typical crossover because the mid/bass woofer continues to play. Let me think about it.

 

[Zing]

Re: The Ghetto Stands

F L I N T ! ! ! ! Help me out here man!

:text-feedback:

 

[Yesfan70]

Re: The Ghetto Stands

....So, this would indicate two crossover points then?
That doesn't make sense to me that it would be a typical crossover because the mid/bass woofer continues to play. Let me think about it.

To me does (kinda).

I look at the frequency response as a line, from lowest to highest Hz. There's (in a 3 way) 2 points on that line that divide that bandwidth into three sections.

In a 2.5 way, I see that line splitting at one of those points. One line goes up higher than the other, but from that split down, it's the same.

 

[Maximo]

Re: The Ghetto Stands

I think Zing is right. The xo only filters out the HF.

Edit: Wait, no that's not right because then the tweeter would also be fed the full range signal.

Unless the second xo is different. Which it may be.

 

[jamhead]

Re: Crossover Design: 2 1/2 Way

Here's the thing. A 2.5 way speaker supposedly gains the benefit of a 3 way in the bass area while also having the benefit of a 2 way with a simpler crossover design. That's the selling point. If two crossover points were being used, then it would negate the "benefit" of a simpler crossover.

 

[Zing]

What gives? We were having a great discussion, I move it to its own thread and now no one has anything to say?

 

[jamhead]

I got busy at work. Will be back later.............

 

[Maximo]

I took a nap.

 

[PaulyT]

I've been getting some real work done while all you slackards are wasting time on this forum. Sheesh.

 

[Flint]

When discussing crossovers, keep in mind the term "crossover" isn't exactly accurate. In fact, each driver has a filter, or two, or three, between it and the amp.

A tweeter has a set of filters on it which typically do three things - three filters:
1) one to flatten out the hump in the impedance at the resonant frequency, a form of a notch filter centered onn the impedance resonance.
2) Another to reduce the voltage reaching the tweeter because most tweeters have a higher sensitivity than the rest of the drivers.
3) A high pass filter to limit the voltage reaching the tweeter below a certain frequency.

A midrange usually has two filters, but sometimes three or four:
1) One to limit the voltage above a certain frequency which is being handled by a tweeter.
2) Another to limit the voltage below a certain frequency which is being handled by a woofer.
3) Sometimes a third and forth to flatten the impedance curve to make those high pass and low pass filters work better.

A woofer will often have just one, but sometimes two or three filters:
1) One to limit the voltage above a certain frequency where the midrange (or tweeter) operate.
2) Sometimes an impedance leveler, and sometimes a shelf filter to compensate for the baffle step phenomenon.

A crossover is not one circuit, but a set of filters, each connected to one driver (or identical drivers in parallel) only to affect the voltage reaching each driver.

The description above is for a 3-way or 2-way "crossover".

In a 2.5-way crossover, as was already mentioned, one woofer will act as a mid/woofer and another will be a straight up woofer and not operate in the midrange. Both woofers operate below a certain frequency but only one of them operates up the frequency where the tweeter takes over.

This is accomplished by having three sets of filters:

Tweeter (same as above)
Mid/Woofer (same as above but for a two way speaker)
Woofer (same as above but for a three way speaker system).

In all cases, all of the filters are tuned to work together so the output of each driver compliments the output of the other drivers to get a combined performance as desired by the designer.


Now to the heart of the question that keeps coming up...

What frequency does the woofer driver have it's low pass filter tuned to?

It will vary depending on the needs of the design and goals of the designer.

For maximum output the woofer's crossover might be tuned to coincide with the frequency where the baffle step effect takes place. In other words, above a certain frequency the forward output of the mid/woofer is 6dB SPL louder because the full acoustic wave output is reflected forward versus below that frequency where the output is 6dB SPL quieter due to the acoustic wave wrapping around the cabinet. For a 12" wide speaker baffle, that frequency is around 300Hz. For a 8" wide baffle that frequency is about 425Hz. So, if the baffle is about 12" wide, the low pass filter for the woofer would be well suited to be around 300Hz, or so. For an 8" wide baffle the woofer's low pass filter would be suited to about 425Hz. The net result is a speaker where the output in the midrange sets the overall sensitivity of the entire speakers. Whereas, with a 2 way speaker the output SPL below the baffle step frequency will define the overall sensitivity of the speaker and shelving filter will have to be added to the mid/woofer to lower the output above the baffle step frequency to match the output in the bass.

Pros of this approach?
1) Higher sensitivity
2) Higher max SPL in the midrange and bass
3) Simpler mid/woofer crossover with fewer passive components to muck up the sound

Cons of this approach?
1) Cost
2) Size
3) Not using a driver specific engineered for the range it operates in (the best speaker for 100Hz performance is not the best speaker for 1,000Hz performance).
4) Phase issues on the woofer's crossover impacting the clarity in the lower midrange or upper bass (depending on the frequency).


Another option is to use the woofer only to drive the deep bass output and extend the bass performance. With sealed speaker, specifically, placing a second woofer in a matching enclosure space below the mid/woofer and putting a low pass filter on it to operate below the -3dB point of the mid/woofer, the output could be extended by as much as 1 octave. So, if the -6dB bass extension with only a mid/woofer is 60Hz, the bass extension from adding a woofer below that point could be as low as 30Hz, though in reality a full octave of extension is almost never achieved.

Pros of this approach?
1) A surround sound system can be designed with larger mains with deeper output for lower bass management crossover settings.
2) Deeper output in pure stereo operation.

Cons?
1) Cost
2) No real improvement in max SPL or sensitivity other than it can absorb twice the power in the deep, deep bass.
3) Size


So, there you go.

 

[Vinyl]

Classic !