2.5 vs 3 way

[bbcmp1979]

Can someone explain the difference between the two and the benefits of each?

For me, I'm planning a build for the Quad RS180 from Pete which is 2.5way since I have most of the drivers on hand from the Natalie P. I'm hoping it'll be a significant upgrade in sq (both midranges and lower end extension).

[Wolf]

3-way divides drivers into 3 separate ranges. You have less overlap, and still need to comp for BSC. Normal ranges are not outside of wavelengths/distances to become a lobing issue.

A 2.5-way involves many times an MTM, TMM, MTMWW, etc where all the midbasses are typically the same. One midbass covers the mids and bass, and the second covers the bass only. This second driver adds amplitude/output below the baffle-step frequency of baffle-width to bring up the bass level to nominal. This way you don't have to compensate for it separately. It also makes up the difference for the differing wavelengths/distances from the mid to tweeter to prevent comb-filtering or same frequencies arriving different times at your ear. It kind of 'smears' the arrival time if this is not set. That is why TMM's should normally be 2.5-ways.

Later,
Wolf

[David Gatti]

3-way gives you 3 specialist drivers - typically a 10" woofer, 4" midrange and 1" tweeter. In theory it should be capable of greater performance.

A 2.5 way is essentially a 2-way speaker with an extra bass driver to improve the system sensitivity (provide baffle-step compensation). It involves more compromises but is a more simple design.

[Deward Hastings]

A 2.5 way . . . involves more compromises but is a more simple design.Mostly unnecessary compromises at that. It leaves low bass on the midrange (which probably has rising distortion on the low end which will also translate to midrange distortion when the driver is operating at high excursion) and fails to take advantage of available-at-no-greater-cost drivers with better LF performance. For a (typically small when compared to overall system cost) saving in crossover parts there is a significant sacrifice in overall performance.

[fbov]

To build on Wolf's note, in the case of 4 identical speakers, you also need it because the driver centers are getting too far apart. Cynosure from the project showcase is the best example, as it's got 6 pairs.
http://www.parts-express.com/projectshowcase/indexn.cfm?project=Cynosure

The farther apart a pair of drivers is mounted, the lower they must cross to avoid the wave interference known as lobing. The rule of thumb is less than 1 wavelength at the XO nominal frequency. the Cynosure has bigger inductor on each pair of drivers, moving out from the tweeter. I'm not familiar with all Pete's designs, but I suspect this one's similar in this regard; the 0.5 drivers are those farther from the tweeter.

They should be louder, but I don't know if the 3dB you'd expect will be worth it. My NatPs are awfully sweet-sounding speakers... Being DIY, you get to build them and find out which you prefer. At worst, you're half way to another pair of Nats...

Have fun,
Frank

PS Deward, you miss the advantage of narrower baffle width, and fail to consider the excellent distortion performance of the RS180. Your objections are generic 3-way arguments(consider the Statement design), and 3-ways add a lot of complexity to a design.

[Pete Schumacher ®]

Mostly unnecessary compromises at that. It leaves low bass on the midrange (which probably has rising distortion on the low end which will also translate to midrange distortion when the driver is operating at high excursion) and fails to take advantage of available-at-no-greater-cost drivers with better LF performance. For a (typically small when compared to overall system cost) saving in crossover parts there is a significant sacrifice in overall performance.

Any two way is going to have the compromises you talk about compared to a three-way. A 2.5-way mitigates the most obvious compromise, providing less distortion at any SPL compared to the 2-way. Double the surface area for bass reproduction is nothing to dismiss so glibly.

By adding the second driver to augment the midbass in a 2 - way, you decrease the excursion required for the midbass, so there is a definite benefit over not doing so. And if you were to simply turn a 2.5-way into a 3-way, you may reduce midrange distortion, but you do nothing for performance below baffle step.

Is a three-way better than a 2.5-way? Depends on the drivers involved.

A 2.5-way using the Usher 894X series of drivers would be one awesome system.

But getting back to the OP question:
"For me, I'm planning a build for the Quad RS180 from Pete which is 2.5way since I have most of the drivers on hand from the Natalie P. I'm hoping it'll be a significant upgrade in sq (both midranges and lower end extension)."

SQ at low volumes will be minimal over a simpler 2-way. Low bass is also no more extended than the 2-way. However, the differences show up as you begin to demand more SPL, with the larger driver compliment providing the radiating area of a 12" woofer at low frequencies. Having the additional headroom allows greater dynamics at lower distortion than not having the ".5" set of woofers.

[Deward Hastings]

you miss the advantage of narrower baffle width, and fail to consider the excellent distortion performance of the RS180There is no "narrower baffle width" advantage (a woofer crossed at 150 Hz or below does not have to be forward firing), and as much as I like the RS180 there are better performers below 80-100 Hz. A RSS315, for example, will provide a better foundation under a RS180/RS28 MT than three more RS180 will.

An argument can be made for adding a second, rear firing, RS180 to eliminate (well, raise to the MT crossover) baffle step, but that configuration does not require a 2.5 crossover . . . a simpler two-way will do.

[curt_c]

There is no "narrower baffle width" advantage (a woofer crossed at 150 Hz or below does not have to be forward firing), and as much as I like the RS180 there are better performers below 80-100 Hz. A RSS315, for example, will provide a better foundation under a RS180/RS28 MT than three more RS180 will.
On the flipside, the RSS315HF-4 will need 6 times the amplifier power to provide the same SPL as a quartet of RS180-4's. (89 dB vs. 97 dB) -both 4 ohm loads.



An argument can be made for adding a second, rear firing, RS180 to eliminate (well, raise to the MT crossover) baffle step, but that configuration does not require a 2.5 crossover . . . a simpler two-way will do. Can't say I agree with the 2 way statement here. A 2 way bipole configuration (which is what it would be with the rear woofer going up to the tweeter fc.) would provide a much different power response than an front firing monopole MTM or TMM layout, as so much of the woofer passband would be above the 150 Hz limitation you specify.

C

[spasticteapot]

There is no "narrower baffle width" advantage

Side-firing woofers have some dispersion oddities, and crossing below 150hz is generally a bit difficult for many midrange drivers. Furthermore, a 2.5-way arrangement is often very cost effective, and makes for a simple crossover. It's a compromise, but an effective one.

[6thplanet]

Dosen't adding the second woofer in a 2.5 arrangment double the enclosure size? Verses a 3 way you'd just have the one woofer's requirment on air space?

[Pete Schumacher ®]

Dosen't adding the second woofer in a 2.5 arrangment double the enclosure size? Verses a 3 way you'd just have the one woofer's requirment on air space?

You need the mid's airspace too, unless you use a dome mid with an integral rear chamber. If you use a midbass for your mid, anything larger than 5" will require a pretty decent sized enclosure, unless you run open baffle.

[Wolf]

If they are the same woofer in both designs, and 1 in the 3-way/2 in the 2.5-way; yes.

Later,
Wolf

[Wolf]

Simultaneous post!! :p
Wolf

[Deward Hastings]

Side-firing woofers have some dispersion oddities, and crossing below 150hz is generally a bit difficult for many midrange drivers.Not below 150 Hz, and not for the RS180 (the midrange in question).

[Deward Hastings]

A 2 way bipole configuration (which is what it would be with the rear woofer going up to the tweeter fc.) would provide a much different power response than an front firing monopole MTM or TMM layoutYes, and that's a *good* thing. The "bipole" has more nearly uniform polar, and thus power, response. "Baffle step" is bad for accurate reproduction, "corrected" or not.

[David Gatti]

Another point is that the 2.5way, with it's 2 bass drivers operating in parallel at low frequencies, may have an unacceptably low impedance.

[Pete Schumacher ®]

Another point is that the 2.5way, with it's 2 bass drivers operating in parallel at low frequencies, may have an unacceptably low impedance.

That's why you build a 2.5 way with 4 drivers . . . :D

[spasticteapot]

Not below 150 Hz, and not for the RS180 (the midrange in question).

In this case, the issue is cost-effectiveness. Three-ways often have twice the components of their 2-way counterparts, and inductors aren't cheap. A second RS180 is an economical and practical way to add a bit more bass.

[Deward Hastings]

In this case, the issue is cost-effectiveness. Three-ways often have twice the components of their 2-way counterparts, and inductors aren't cheap. A second RS180 is an economical and practical way to add a bit more bass.A little more, yes, (for the cost of an additional driver). So make it a two-way MTM . . . nothing is gained by the 2.5 configuration. If you add still more drivers then it becomes necessary to keep the mids off the more (physically) separated drivers, and it becomes more reasonable to add a real woofer instead.

[Pete Schumacher ®]

A little more, yes, (for the cost of an additional driver). So make it a two-way MTM . . . nothing is gained by the 2.5 configuration. If you add still more drivers then it becomes necessary to keep the mids off the more (physically) separated drivers, and it becomes more reasonable to add a real woofer instead.

What if the builder doesn't want MTM, but TMM?

Then 2.5-way makes a lot of sense to control the forward lobe.

[Paul W]

Can someone explain the difference between the two and the benefits of each?

For me, I'm planning a build for the Quad RS180 from Pete which is 2.5way since I have most of the drivers on hand from the Natalie P. I'm hoping it'll be a significant upgrade in sq (both midranges and lower end extension).

To me, the largest difference is more natural upper midrange with a 3-way. Better to have good clean midrange with complementary polar patterns than to push a tweeter low and a mid-bass too high. Of course you need a good crossover design, but spending just a little money on a decent mid can bring a smile to your face.:)

If you want to reuse your RS180's, the RS52 with the 22TAF at 900/3.2k can be very satisfying...or the 2" Morel should also work quite well.

[Deward Hastings]

Then 2.5-way makes a lot of sense to control the forward lobe.But then TMW makes *more* sense. A lot more sense. As does staying two-way and making the second M driver rear-firing (which has additional advantages to just "control [of] the forward lobe"). About the only justification for all-forward firing TMM 2.5 way is cosmetics. While "making it look good" is certainly reasonable late in the design making it a defining criterion of the design is . . . not productive of best acoustic performance.

[Pete Schumacher ®]

But then TMW makes *more* sense. A lot more sense. As does staying two-way and making the second M driver rear-firing (which has additional advantages to just "control [of] the forward lobe"). About the only justification for all-forward firing TMM 2.5 way is cosmetics. While "making it look good" is certainly reasonable late in the design making it a defining criterion of the design is . . . not productive of best acoustic performance.

TMW makes more sense? But then you only have half the surface area available for producing the bass frequencies.

Loudspeaker design is nothing more than weighing the compromises. Is a rear firing driver better than a front firing driver? Depends.

Are cosmetics important? Of course!

There's nothing inherently wrong with 2.5-way approach.

Is a 3-way better? Possibly, depending on drivers chosen. But if you're using the same woofer for the mid AND the low end, then 2.5-way does offer more low end SPL vs. the three-way implementation, and the same low end capacity of MTM with the benefit of a TM forward lobe.

I've got 6 of the venerable Peerless 850439 laying around. I'm considering a TMWW 3-way build using two of them for the low end, one for the mid, crossing at 400Hz and 1500Hz to a 27TBFC/G.

[jmc]

TMW makes more sense? But then you only have half the surface area available for producing the bass frequencies.



The basic assumption here is if you're going 3-way: you're going to use an actual woofer instead of a midbass since you only need to reach 375-800 hz in the 3 way. This driver would likely be '2 sizes' bigger than 2.5 way woofers making bass output about the same and doing it cleaner.

I would only go 2.5 way if space absolutely dictated it.

[Pete Schumacher ®]

The basic assumption here is if you're going 3-way: you're going to use an actual woofer instead of a midbass since you only need to reach 375-800 hz in the 3 way. This driver would likely be '2 sizes' bigger than 2.5 way woofers making bass output about the same and doing it cleaner.

I would only go 2.5 way if space absolutely dictated it.

I'm a fan of 3-ways. In the process of building a 12" 3-way right now, using the RSS315HF-8 in a PR loaded enclosure, with a ScanSpeak 15W for a midrange and RS28A up top. Better than the 2.5-way Schumakubins? Absolutely!!!!

But when you have eight 7" woofers laying around and want to get the most bang out of them, MTMWW 2.5-way is a darn good approach.

[jmc]

I'm a fan of 3-ways. In the process of building a 12" 3-way right now, using the RSS315HF-8 in a PR loaded enclosure, with a ScanSpeak 15W for a midrange and RS28A up top. Better than the 2.5-way Schumakubins? Absolutely!!!!

But when you have eight 7" woofers laying around and want to get the most bang out of them, MTMWW 2.5-way is a darn good approach.

Well yeah, if i had 8 matched woofers then yes. Going from scratch, fewest compromises system, it's 3-way all day for me.

[bbcmp1979]

I've already decided with the 2.5ways as I do have 8 drivers around. It'll be a minimal cost for me as I only have to pick up xover parts + mdf and improve the low end a bit. Eventually, I like to build a 3 way when I have more room. Right now all my mains + center are sitting in the corner of the room and smaller baffle width (9") is preferred.

With that said, clearly a 3way is the way to go.

[Pete Schumacher ®]

I've already decided with the 2.5ways as I do have 8 drivers around. It'll be a minimal cost for me as I only have to pick up xover parts + mdf and improve the low end a bit. Eventually, I like to build a 3 way when I have more room. Right now all my mains + center are sitting in the corner of the room and smaller baffle width (9") is preferred.

With that said, clearly a 3way is the way to go.

Then again . . . add a high sensitivity mid to each tower and do WTMWWW. :eek:

[Deward Hastings]

if you're using the same woofer for the mid AND the low endWhy would you do that ? ? ?

[jmc]

Why would you do that ? ? ?

Because his assumption was you have 8 matched midbasses.

[Pete Schumacher ®]

Because his assumption was you have 8 matched midbasses.

Some people just don't pay attention . . . sheesh!!! :D;)

[Deward Hastings]

Because his assumption was you have 8 matched midbasses.Why even post something that would apply to maybe .0001% of readers? The implication becomes that one is proposing it as a desirable alternative to a 3-way (or a 2-way), and the danger is that it might encourage someone to go out and *buy* 8 "matched" drivers when they'd be better served spending the same money on drivers for a 3-way.

But even if you already have 8 mids it makes more sense to use them as a 2-way rather than a 2.5, and more still to save 4 of them to use for surrounds.

[jmc]

Why even post something that would apply to maybe .0001% of readers? The implication becomes that one is proposing it as a desirable alternative to a 3-way (or a 2-way), and the danger is that it might encourage someone to go out and *buy* 8 "matched" drivers when they'd be better served spending the same money on drivers for a 3-way.

But even if you already have 8 mids it makes more sense to use them as a 2-way rather than a 2.5, and more still to save 4 of them to use for surrounds.

No, read the thread again please.

[bbcmp1979]

Pete, hahaha that would be an upgrade to a 3 way wouldn't it? It would definitely out do the Natalie P...Why didn't I think of that. Anyhow, I have limited experience with PCD and RSmodeler to play around too much. Therefore finding a design already built is the route that i'm taking.

Then again . . . add a high sensitivity mid to each tower and do WTMWWW. :eek:

[Pete Schumacher ®]

Pete, hahaha that would be an upgrade to a 3 way wouldn't it? It would definitely out do the Natalie P...Why didn't I think of that. Anyhow, I have limited experience with PCD and RSmodeler to play around too much. Therefore finding a design already built is the route that i'm taking.

Yours and Turn2's are both modeled-only designs, though it has had extensive listening on Turn2's part.

I'd be willing to see what adding a mid to yours would do. The RS150-4 would probably be just about perfect, crossed around 400Hz. Reference sensitivity would probably be running right around 90dB after baffle step.

[bbcmp1979]

Deward, I do have 8 rs180 drivers on hand as I said in the first post. I wouldn't go out and buy 8 Rs180 for this drivers as there are many 3way design that'll fit the budget of 8 rs180. So yes this thread is only applicable to .0000001% of readers out there.


Why even post something that would apply to maybe .0001% of readers? The implication becomes that one is proposing it as a desirable alternative to a 3-way (or a 2-way), and the danger is that it might encourage someone to go out and *buy* 8 "matched" drivers when they'd be better served spending the same money on drivers for a 3-way.

But even if you already have 8 mids it makes more sense to use them as a 2-way rather than a 2.5, and more still to save 4 of them to use for surrounds.

[bbcmp1979]

fbov, I fully agree with you that the Nat P are sweet sounding speakers. I cranked up my system today and they were awesome.. Some kanye west for the lowend, and shakira for voicing....



To build on Wolf's note, in the case of 4 identical speakers, you also need it because the driver centers are getting too far apart. Cynosure from the project showcase is the best example, as it's got 6 pairs.
http://www.parts-express.com/projectshowcase/indexn.cfm?project=Cynosure

The farther apart a pair of drivers is mounted, the lower they must cross to avoid the wave interference known as lobing. The rule of thumb is less than 1 wavelength at the XO nominal frequency. the Cynosure has bigger inductor on each pair of drivers, moving out from the tweeter. I'm not familiar with all Pete's designs, but I suspect this one's similar in this regard; the 0.5 drivers are those farther from the tweeter.

They should be louder, but I don't know if the 3dB you'd expect will be worth it. My NatPs are awfully sweet-sounding speakers... Being DIY, you get to build them and find out which you prefer. At worst, you're half way to another pair of Nats...

Have fun,
Frank

PS Deward, you miss the advantage of narrower baffle width, and fail to consider the excellent distortion performance of the RS180. Your objections are generic 3-way arguments(consider the Statement design), and 3-ways add a lot of complexity to a design.

[fbov]

Pete, hahaha that would be an upgrade to a 3 way wouldn't it? It would definitely out do the Natalie P... ...

... assuming the 3-way were as well executed as the 2- or 2.5-way used in the comparison. It certainly has the potential, but there's a lot of work required to realize that potential if you're really going to sound better than a NatP.

Only one thing is certain; it'll play louder given comparable BSC.

Frank

[MikeSkiba]

GO FOR IT!
I built half of what you're looking for, and I'm happy with the results.

I threw a pair of series RS180-4's in each tower with a Morel CAT378 up top, using an off-the-shelf XO at 2K and an L-pad. Certainly not exotic, but I'm still pleasantly surprised at the bang-for-buck outcome. These play very well down to about 50 Hz and stay clean up to the very top at respectable SPL's.
The midrange is actually startling with some program material!

You'll do even better with 4 RS180 drivers and a properly designed XO, and still stay within a narrow enclosure. You'll also have the benefit of splitting low and mid duties among drivers.

Someday I'll finish these cabinets...

http://i273.photobucket.com/albums/jj226/handmadebronze/026.jpg

Mike Skiba

[bbcmp1979]

Mike,

they look good, are they birch plywood?

[MikeSkiba]

They're actually an experiment in laminating 1/4" Oak plywood over 3/4" MDF in an attempt to simplify flush mounting the drivers.

A bit trickier than real veneer because the extra (1/4") thickness is more difficult to work with, but the additional enclosure wall thickness seems to provide benefits.

I managed to get all the oak grain to be book-matched for each panel by ripping up a full 4'x8' sheet, but I don't think I'll pursue this method again.
All things considered it didn't really save any labor, which probably explains why I haven't found the energy to put a finish on them yet.

Mike Skiba

[jakeparsons]

For those coming to the Iowa event, I am taking a 2.5 way with all Scan-Speak drivers. I am very happy with it, but we'll see what others think.