PA speaker cabs - 2way vs 3way

[thudfromafar]

With the growing trend of 3-way bass cabs, I'm just curious why PA cabs usually seem to be 2-way? I assume one reason is cost. But is the sound different when comparing a good 2-way to a good 3-way cab? I know the whole deal about the 3-way bass cabs is to get a better, "flatter, smoother" frequency response, so I was curious about if it makes a big difference for vocals.

 

[modulusman]

With the growing trend of 3-way bass cabs, I'm just curious why PA cabs usually seem to be 2-way? I assume one reason is cost. But is the sound different when comparing a good 2-way to a good 3-way cab? I know the whole deal about the 3-way bass cabs is to get a better, "flatter, smoother" frequency response, so I was curious about if it makes a big difference for vocals.

For vocals you don't need alot of low-end. Most serious PA rigs have subs so they are 3 way.

 

[CapnSev]

For vocals you don't need alot of low-end. Most serious PA rigs have subs so they are 3 way.

+1

I think it's because a good PA will have a subwoofer or two taking care of the real lows.

 

[rpsands]

The difference is between cheap top cabs and expensive top cabs; there are two types of two way top cabs, to paint with broad strokes: those that have horns crossed around 2khz and therefore a hole in off-axis response, and those with horns down around 1.2khz and no hole (and also less upper mid speaker rattiness, usually).

Medium-cost 3-way cabs can be a way to get around the use of a cheaper horn and waveguide which can't go down to 1.2khz or lower like the high end stuff. They just use a midrange driver in between the woofer cutoff and the horn.

IMHO, higher end 2-ways with good horns and quality DSP to correct frequency issues from horns is the way to go, since very often you want more volume up top which the horns provide, but midrange drivers don't necessarily.

Just my 2pence

 

[synaesthesia]

With the growing trend of 3-way bass cabs, I'm just curious why PA cabs usually seem to be 2-way? .

A. there is no 3 way trend, maybe on TB but not with manufacturers.
B. PA manufacturers don't read TB's trends

 

[MNAirHead]

There are better quality speakers now..

 

[thudfromafar]

A. there is no 3 way trend, maybe on TB but not with manufacturers.
B. PA manufacturers don't read TB's trends

You missed my point. I was essentially asking if including a midrange driver is better or worse than a typical woofer/horn top for vocals.

 

[Zooberwerx]

You missed my point. I was essentially asking if including a midrange driver is better or worse than a typical woofer/horn top for vocals.

This is a good question for Bill Fitzmaurice although I've seen his response(s) in similar threads...just can't recall what was said! I do know a lot depends on enclosure design and component selection. He has plans for some perfectly killer PA tops which utilize 12" or 15" woofers and either compression horns, piezo arrays, tweeters, etc. OTOH, I've heard some 3-way cabs which sounded like ass when handling vocal duty.

Still a subject for discussion as you did specify "typical" (which I read as affordable and easily accessible) enclosures.

Riis

 

[modulusman]

You missed my point. I was essentially asking if including a midrange driver is better or worse than a typical woofer/horn top for vocals.

Depends on the cab. I have some JBL PRX535s that are a powered 3-way cab and they sound very good. I also own some EAW NT59s that are a powered 15 and a horn that sound even better but they also cost 4 times as much.

 

[synaesthesia]

You missed my point. I was essentially asking if including a midrange driver is better or worse than a typical woofer/horn top for vocals.

You misunderstand the typical 2 way PA tops if you think they are spec'ed with 'woofers'. Not all 12" drivers are LF drivers, as a matter of fact the bulk of them aren't.

 

[thudfromafar]

Well, whatever they are called...

 

[Steve]

I don't think it's all that significant if it's just vocals you're talking about.

The instant you try to run any bass or left hand heavy keys through the cab you're gonna know the value of a dedicated low frequency driver.

IMHO

 

[synaesthesia]

Well, whatever they are called...

It's not a matter of the nomenclature. Take your average 12", say an Eminence 12" Alpha. It is a mid-bass driver because its useable performance is roughly from 100hz upto 4- 5 Khz before it tails off.
Most PA cabs use compression drivers, and some go as low as 1.5Khz. The majority of 2 way PA cabs are fairly strong in the mids.

The same is not true for bass cabs, as when say a 12" driver is chosen and loaded in a box for some desired sub 100hz performance, typically it will reach about 2khz and tail off, and often they tail off or beam much lower,...the tweeters that are employed typically have useful performance from 3.5Khz onwards and therefore you have that mid gap that is common; in say a typical 2 way bass cab like those of SWR, for example. Notwithstanding, the mid ravine or valley is popular with some people as it does take some honk out of the bass guitar tone and you get that typical funk or slap tone.

 

[TimmyP]

Three way can be better, or it can be worse - it depends on the skills of the engineer (and whether the bean counters leave the poor guy alone). Cost is certainly a factor. With PA speakers, efficiency is commonly of high importance. I expect that this complicates matters when going three way.

 

[uhdinator]

2 way or 3 way are designed to split the workload between the drivers
which improves audio quality. Many 2 way cabs cannot reproduce the low end well as in this spec from JBL MRX515 cabs (Frequency Response 65 Hz - 20 kHz). Hence comes the 3 way cab which extends the low end and lets the mid take some of the load. Better Quality than 2 way but makes for bigger cabs and less friendly moving them.

Using active crossovers instead the the built in ones in the cab is better also as the internal network wastes some of your power and disipates as heat. If you get a 3 way cab the better quality ones have inputs for high mid and low so you can use active outboard crossovers.

My preference is a good portable 2 way cab combined with Sub cabs and you basically have a 3 way system. Most 3 way cabs are not ported optimally for the sub freqs as then it effects the mids as well, and they are too big to be draggin them in and out doing Gigs.

Sub cabs usually have a range of 30-40hz up to 250hz and their ohms rating is based on the lowest ohm rating with in that range so an 8 ohm sub may be 8 ohms at 200-250 (where you are not using it) and as high as 20-30 ohms at 40hz! Generally I set my low to mid x over point at about 90-100hz. This is why you need power for subs!

An amp that says it is 500w RMS average power at 8 ohms might give your sub 500w at 250hz but you are only letting the sub have 35-90hz and so you are not getting as much power as you think. A lot of sound guys say they may have a sub that can take 1000w peak and they run an amp that may be 800-1000 RMS into it. But you better have a limiter and know how to use it and not clip the amp!

Limiting/compressing the freq bands separately is and advantage of active 2 and 3 ways systems as well. That way when the kick is slamming its not compressing the vocals in the mids and highs also.

 

[Petebass]

OK lets assume we measured the frequency response of a 2 way speaker and a 3 way speaker and found they measured EXACTLY the same. Which would perform better live?

IMO the 3 way will work better live because the dispersion of those frequencies will be better, so the the off-axis response will be better. And lets face it, you are very rarely lucky enough to have EVERYONE in the audience standing directly in front of the speakers.

 

[Rockman]

OK lets assume we measured the frequency response of a 2 way speaker and a 3 way speaker and found they measured EXACTLY the same. Which would perform better live?

IMO the 3 way will work better live because the dispersion of those frequencies will be better, so the the off-axis response will be better. And lets face it, you are very rarely lucky enough to have EVERYONE in the audience standing directly in front of the speakers.

You can't answer a question like this without making a lot of assumptions.

 

[Petebass]

You can't answer a question like this without making a lot of assumptions.

What assumptions? The bit about the 2 speakers measuring the same was hypothetical aimed at zeroing in on the OP's intention within the original question. The part about dispersion is physics. The larger diameter speakers start beaming at lower frequencies than smaller diameter speakers, typically in the high mids. If you instead give those frequencies to a dedicated mid driver, beaming is greatly reduced.

 

[rpsands]

With appropriate speaker, compression driver and waveguide choices, a 2-way top will have equal to superior dispersion of the 3-way cabinet. From the graphs I've looked at, good quality waveguides provide admirable dispersion. They require more corrective eq than midrange drivers, but with autoeq on affordable dsp units that's hardly a concern.

For my tastes, 3-way system with 2-way tops and subs, using DSP and electronic crossovers. Lighter and cheaper.

Electronic crossovers are superior to passive crossovers in pretty much every way including weight these days, so it makes no sense to bother with them in my opinion, for live sound.

 

[realbadgroove]

The number one reason is that most pro acts require you to bi amp everything no passive crossovers in anything. Three way is fine but trying to power three way bi amp with a horn and mid range driver is a pain in the ass and you really don't need a mid range driver if you have a good two inch horn. Now that being said if you run a big custom system like I do we do a 4 way cross but we use 2" compression drivers 12"s 15"s 18"s and it sounds great but I would not fool around with trying to power little mid range drivers.