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Author Topic: P.A speakers -12" or 15"??  (Read 55815 times)

scott klenner

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P.A speakers -12" or 15"??
« on: April 15, 2010, 07:31:12 pm »

Hi all, newbie to the forum here looking at upgrading our band's tired p.a (old powered mixer plus two cheap JBL 15" FOH speakers). I am leaning toward powered gear (standard reasons - less parts to carry and set up) and did a lot of research on forums but am losing my mind slightly so thought i'd just try asking.  typically we are playing pubs 50-150- people, seldom mic anything up so typically only vocals going through the p.a but are starting to think of micing up a little now we are attracting bigger crowds. We certainly need more wattage than what we currently have (170ish a side) From what I have read people tend to recommend 12" for vocals/ 15" or added sub to run a little bass/kick etc. BUT the local shop tells me I ought to go for 15" (they are recommending JBL eon g3) because for the kind of gigs we are doing (as described) we will get a "bigger" sound, and that 12" speakers just don't push/punch enough. I am wondering is this sale talk or are they right? Can't compare cause nobody in this small town stocks anything you have to buy it then they get it in. I have the chance to buy online 2 x RCF 312a (12") plus 1 18" sub for reasonable money or do I take the shops advice get 15" and rent a sub when we need for bigger gigs. Thanks so much for any advice/experience you can share.
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Derek Shawver

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Re: P.A speakers -12" or 15"??
« Reply #1 on: April 15, 2010, 07:47:07 pm »

It's personal preference. I prefer a 12" speaker over a 15". IMHO, I think vocals sound better through them. You would get a 'bigger' sound if you added a couple single 18" subs. I'm not too familiar with the EON's and am not sure if they make a 12" version, so I'm curious if they comfortably go down to 100hz. If you want to go powered, I would suggest getting the JBL PRX stuff over the (p)eon stuff.
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Rob Spence

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Re: P.A speakers -12" or 15"??
« Reply #2 on: April 15, 2010, 10:08:50 pm »

Go with 12" cabs for better vocals.
The local shop wants to sell 15" cause they make money on them. Keep in mind that most of the local shops such as banjo center are not in the business of helping you but are in the business of selling! They also deal lots with folks who hear with their eyes so big cabinets must sound better,right?

If you need more after the new 12s, get some subs.
I have a pair of QSC K12s and they do a a rock band in a bar with a couple of subs under them.

Of course, dual 15s would look louder Smile
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Scott Smith

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Re: P.A speakers -12" or 15"??
« Reply #3 on: April 16, 2010, 09:14:41 am »

scott klenner wrote on Thu, 15 April 2010 19:31

..the local shop tells me I ought to go for 15" (they are recommending JBL eon g3)..

DJ speakers.. Shocked
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Weogo Reed

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Re: P.A speakers -12" or 15"??
« Reply #4 on: April 16, 2010, 10:11:04 am »

Hi Scott,

I remember years ago telling folks that 12" was better for vocals.  
And that is true whem comparing some 12" woofer & 1" throat horn boxes
vs.
15" woofer & 1" throat horn boxes.

But with many of the 1.4" and 1.5", or 2" throat horns, you can cross lower to a 15" and have it work well.
And high quality 1" drivers like the BMS 4552ND can be crossed quite low and have plenty of output.

Another factor is crossing over where the woofer dispersion and horn pattern are similar.
So if you are going with a 60 degree conical box, this is different from a 90 degree box for 12" and 15" woofers.
With a smaller cone you can go a bit higher in frequency and still have wider dispersion than a larger cone, which will start beaming at a lower frequency.

All things being equal, a 15" box is going to go a bit lower, and if you aren't going to use subs could be a better choice.
If you are going to use subs, a 12" box could do just fine.

More important than 12" or 15" is what dispersion is going to work best in the venues you regularly play, and
buying a better quality box.
There are way too many mediocre boxes out there - please support better quality!

Thanks and good health,  Weogo
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Tom Reid

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Re: P.A speakers -12" or 15"??
« Reply #5 on: April 16, 2010, 10:13:26 am »

Is it that time of year already?

We haven't had a recent 12" vs. 15" conversation.

A rule of thumb that helps most people out.  If you don't have subs, 15"s are going to be better to help with the low end.  If you have subs, 12"s will get more midrange out of the system.

The larger the cone area of a loudspeaker, the more issues it will have producing high frequencies.  A good way to figure this out is to raise the crossover point of a sub.  When you go above 120hz the sub starts to get obnoxious in most cases.  A larger area of speaker cone narrows high frequency reproduction and the subs starts to get "beamy" when highs are introduced.

The same is true of a 15".  At some point in the upper frequency range the full range sound starts to get narrow and distroted.  Hopefully the user has hit the crossover point by then and the horn is playing those high bits.  If not, the PA might be considered "honkey" by those who's ears aren't soaked in beer.

A 12" won't have as much problem faithfully reproducing this upper range, but because the upper range is good, now some lows have to suffer.

Which is the right driver to use?  It depends.  
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Jay Barracato

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Re: P.A speakers -12" or 15"??
« Reply #6 on: April 16, 2010, 10:16:47 am »

Weogo Reed wrote on Fri, 16 April 2010 09:11


More important than 12" or 15" is what dispersion is going to work best in the venues you regularly play, and
buying a better quality box.
There are way too many mediocre boxes out there - please support better quality!

Thanks and good health,  Weogo



I was thinking the same basic thing. I really can't say there is a difference in vocal quality between my 10 inch K10's and my 15 inch HPR's (in both cases I have the same instruments mixed in with the vocals) as long as I have selected the right box to cover the space.

Jay
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scott klenner

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Re: P.A speakers -12" or 15"??
« Reply #7 on: April 16, 2010, 06:59:38 pm »

thanks all so far - so, to put in laymans terms to make sure I am getting what has been said correctly (which occasionally goes beyond my ability to handle the jargon) 12" speakers keep up a lot better than in the past; they produce vocals better typically but at the cost of losing some lows if no sub is present; 15" speakers the opposite though with larger horn size are pretty good at comprise between lows and highs because they have an earlier crossover to the highs (would the qsc kseries with 1.75" horn be a good e.g. of this?); more important than speaker size is picking the right speaker to suit the shape etc of the room and making sure you are using quality over mediocre or worse speakers. This much I think I have got - please someone confirm if I am interpreting this right Smile
Couple of things I am still unsure of - the talk about dispersion; and the problem for many of us who are musos buying gear  - i easily justify having several guitars and amps for different situations but can't spend the $$ to get a variety of speakers - so guess I'm looking for a quality all rounder, given that every room we play is a bit different for sure. - perhaps from what's been said 2 x 312a rcf's plus 1 x 18" rcf sub might not be a bad option - will cover the lows and midrange/highs , are pretty good quality (from what I can gather), and gives me some variety - won't need subs when we are playing cafe gigs e.g. Or a nice 15" with larger horn might do, especially given it's one less (heavy) speaker to lug around - but not eons by the sound of it. What do people think of this reasoning?? Thanks again - i'm learning heaps.
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Art Welter

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Re: P.A speakers -12" or 15"??
« Reply #8 on: April 16, 2010, 07:30:00 pm »

You are on the right track.
But think in terms of one sub cone to one high cone.  
Each octave reduction in frequency requires four times the air displacement to equal the same SPL (sound pressure level) , while at the same time our ears are far less sensitive to low frequencies.

If you don’t have large cones, or small cones capable of a long stroke (displacement) your subs will run out of gas way before the tops, regardless of how much power put in.

A “bigger paddle” does not have to move as far to move the same amount of air as a small one.
But a “bigger paddle” requires more energy to move.

Horn loading can reduce  excursion by coupling a bigger slug of air to a smaller throat.
Most PA HF is horn loaded, but as you go down in frequency, horn size must increase, requiring rather large horns (or multiple long, smaller horns) for LF.  
Tom Danley’s tapped LF horns cheat this requirement a bit, but there is no way around it, low and loud takes up space.

Displacement applies to high frequency diaphragms as well as LF or MF.

One problem in comparing HF compression drivers is there are two dimensions to consider,  exit diameter, usually 1, 1.4, 1.5, and 2 inch, then diaphragm size, ranging from 1 inch  up to 4 inches.
Then of course, the horn the driver is coupled to makes a big difference.

As for dispersion, 90 degree is a good compromise for most rooms with one speaker per side.

Art Welter
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Rory Buszka

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Re: P.A speakers -12" or 15"??
« Reply #9 on: April 17, 2010, 08:54:36 pm »

See my post in the "Gunness Focusing" thread on the main LAB on the distortion mechanisms in loudspeakers.

The 15" two-way PA speaker is probably the most compromised design in pro audio, or at least most of them are. There are a few exceptions, like the Meyer CQ-2 and Acheron stuff, which uses a very low crossover frequency to a 4"-diaphragm compression driver, but both of those are way out of your price range and neither will go on a pole.

The problem with 15" woofers (and to a lesser extent with 12" woofers but it's still a factor) in a two-way design is that the midbass driver inevitably gets asked to reproduce midrange information. At midrange frequencies, the wavelengths are short enough that multiple wavelengths can fit on the surface of the large cone, so standing waves form in the cone material itself. These waves travel outward to the cone edge and are reflected by the frame back to the center of the cone, where they combine constructively at some frequencies and destructively at others, which is why a woofer's response curve becomes more rippled at the upper end of its range. It's also at the upper end of the driver's passband that the temporal effects of this chaotic wave propagation through the cone material are most pronounced. You hear this as a smeared or 'woofy'/'wooly' character to the midrange, which makes it tough to achieve intelligibility. A smaller-diameter cone is slightly more rigid, and the distance from the apex of the cone to the cone edge is smaller, so a 12" woofer will sound slightly more defined than a 15", but they are both operating as distributed mode devices instead of pistonic devices - neither driver is acting like a perfect piston in the midrange.

The obvious way to solve this is to bring a smaller, dedicated cone driver into the picture to handle the midrange. The trouble is that not many of the speakers that have these dedicated midrange devices are pole-mountable. Mackie (HD series) and Community (S series) both have pole-mountable models with separate midrange drivers that provide added clarity through the midband, and these will be invaluable if you want to reinforce vocal or complex acoustic music with high quality instead of just blasting rock or heavy metal all the time (and the separate midrange delivers benefits in rock music reinforcement as well). The Mackie HD series HD1531 (15" 3-way) is powered and uses the EAW Focusing DSP, while the Community S-series S3294 (12" 3-way) and S3594 (15" 3-way) are passive, so you can use your existing amplification.

So if you're even concerned about whether a 12" or a 15" sounds better, consider going with a three-way speaker like the ones mentioned above.

http://www.mackie.com/products/hd1531/

http://www.communitypro.com/index.php/product-list/109-s-ser ies
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