A new set of line array PA speakers for our bluegrass band


#1

This summer’s project was to build a set of line array speakers for our bluegrass band that would encompass a wider frequency range than my previously built set. If you are unfamiliar with line array speakers, think Bose L2 or the huge arrays that you find centered above the crowd in large concert venues. The idea with a portable lie array is that they sound good nearly anywhere in the room, they do not need to be loud to be heard clearly nearly anywhere in the room and when judiciously placed, they can act as the band’s monitor as well as the main speakers for the audience (less stuff to carry). In addition, line arrays have a relatively narrow vertical sound spread yet a very wide horizontal sound spread (less reflective noise distortion bouncing off the floor and ceiling and more folks reached on the horizontal axis).

The older set I built included two stackable cabinets of four 5" coaxial drivers. I would use these with a 15" subwoofer. The design parameters were to have lightweight cabinets that could throw high quality sound a large distance with relatively low wattage. The line array cabinets fit these parameters with these specs:

19.5lbs each
100db @ 1W/1m @ 1000hz
95db @ 10W/32m (approx 100 feet) @ 1000hz

http://drguitar.opendrive.com/files/MF8yMzE1OTQyXzBPUU42/Rebuilt%20line%20array.jpg

These worked extremely well in most situations, especially when inside a small to moderately large room. In fact, they worked too well when we recently played at a festival and our band could be heard inside a facing concert location about a half block away (both locations had their fronts wide open). Oops… The upside is that it brought more folks to hear us… Anyway, the downside of these cabinets is that they do not produce much below 150hz and so the subwoofer is needed to allow the bass to be heard. The subwoofer is a point source speaker and does not throw like the array speakers do.

So this summer, I decided to build new cabinets that could be used in conjunction with these smaller cabinets. The new cabinets have these parameters: they need to be able to fit in my Scion XB (small car), they need to produce full frequency sound including notes down to 44hz, and they need to be stackable. The new cabinets incorporate four 8" full range drivers in each cabinet (2 cabinets total). They have speaker mounts on both the bottom (for mounting on a speaker tripod) and on top (for mounting either the other 4 x 8 speaker or the 4 x 5 speaker). The 8" drivers used have a frequency response of 39hz to 14000hz (relatively flat). Since our acoustic band does not produce much sound above 14khz, I figured that these should work fine. They have a power handling of 60watts rms and produce individually 91 dB @ 1W/1m. In an 8 speaker array, this should produce approximately 100 dB @ 1W/1m. These will be very similar to the output of the smaller cabinets.

At this point, the cabinets are ready for paint, yet still need to have the hardware mounted (speaker mounts, jack plate, speakers…etc). The plan is to use one of these cabinets along with 1 smaller cabinet on smaller gigs and all 4 cabinets on large gigs. Also, I will bi-amp the cabinets so that I can control the sound traveling to cabinet. I will do this with a Carvin 12 channel/4 amp powered mixer. Each amp provides 400w rms @ 4 ohms (300w @ 8ohms).

These cabinets are quite a bit heavier and that worries me a little. I’m closer to 60 than I am to 50 and I am not a big fan of carrying heavy speaker cabinets just before playing a gig. However, my 16 year old son plays with our band and this duty may be passed on to him.

I will post pics and sound clips when they are finished.


#2

Don’t worry about the weight… just let your son handle it :smiley:

Actually, if you don’t already have a few, grab some small furniture dollies. They make moving speakers so much easier. I am interested to hear how your new speakers work out. Not to sound like a pessimist, but if the 8" drivers can truly stay pretty flat down to 39 hz, that would really surprise me. I’ve always needed to get big drivers to get the low frequencies out there. I look forward to hearing how they sound.

On the previous versions, where was the crossover point? I am guess it was up there a bit since the 5" drivers got weak below 150 hz. If you could get the low pass frequency down to around 80hz, your sub sound shouldn’t act as a point source. In a huge room, it still won’t keep up with the directional cabinets, but for a moderate sized room, I suspect it should be plenty. I am wondering if it might work well to use the 15" cabinets for about 80 hz and below, and then the 5" and 8" boxes for everything above (maybe putting a high pass filter on the 5" boxes to keep them from dealing with the low mids).

Great looking speakers!!! Again, I look forward to hearing a recap when you fire them up.


#3

About the 8" drivers… you are definitely right about them reaching 44hz flat. In the cabinets I designed to house them, the best I could do was get them flat to about 95hz with a 7db/octave roll-off from there down. Still, that gives me a usable low E on the bass if I EQ it slightly (one of the reasons for the separate amp for the different cabinets).

When I first built the smaller 5" driver cabinets, I had a 200hz crossover with a 12db/octave roll-off below 200hz. I didn’t like the way it sounded so I removed the crossover and used the EQ on the amp to control the frequencies going to the small cabinets and the 15" sub. With the “active” crossovers, I rolled off the frequencies below 150 and allowed those frequencies to be handled by the sub. The result was a very clear sound and a full sounding bass. I tried to allow the small cabs the full spectrum of sound down to 100hz, 80hz and 42hz and they tended to break up (distort) with any frequencies below 150hz. Above 150hz, they sound amazing (the coaxial tweeter does and very nice job). The only crossover in these cabs is the one that the speaker company (Aura) installs on their 5" speaker driver.

The idea with the new cabs is that I might be able to take just one of these to a gig and get a decent full, clean sound. In any case, I have designed them to be able to stack either with the other 8" cab or one (or two) of the 5" cabs on top.

Finally, I love building speakers (been doing this since my teens), however crossovers and the physics behind their design alludes me. If I use a crossover, I research what my needs are and then tend to purchase them off the shelf. With line arrays, I definitely prefer full range speakers that do not need crossovers as this avoids all sorts of phasing, time distortion problems and audio/tonal coloration. So using either an active crossover that I can program or a bi-amp with EQ system works nicely for my feeble brain capacity. :confused:


#4

Your feeble brain capacity… you are a funny guy :smiley:
I haven’t built speakers for many years (maybe my early twenties), but I agree with you, it is a blast. It’s amazing what a difference a box makes. The first one I made, was a 2X15" cabinet for a bass guitar cabinet. I made it out of plywood (probably 1/2 inch). It was a random size and leaky. It sounded like crap. I did some reading (this was before the days of google) and learned about all sorts of things. Made a new cabinet out of MDF and matching the volume to the driver specs. I lined it with damping and sealed it up. With the same drivers, it was a whole different world. They sounded really decent and got used for quite some time after that.

You’ve got my brain ticking… wife wanted a small PA for karaoke. Are those 5" drivers still manufactured and available?


#5

— Begin quote from “mreisz”

You’ve got my brain ticking… wife wanted a small PA for karaoke. Are those 5" drivers still manufactured and available?

— End quote

Unfortunately no. I originally used a simple 5.25" full range driver, but they sounded awful after I installed them (dull and bassless). In the process of looking for replacements, I found some Aura 5.25" coaxial car speakers on closeout (at Parts Express). They were cheap enough to give them a try and they worked very well. Not only did they sound much, much better, but they were polypropylene (weather resistant) and had better power handling than the original speakers.

— Begin quote from “mreisz”

Your feeble brain capacity… you are a funny guy :smiley:
I haven’t built speakers for many years (maybe my early twenties), but I agree with you, it is a blast. It’s amazing what a difference a box makes. The first one I made, was a 2X15" cabinet for a bass guitar cabinet. I made it out of plywood (probably 1/2 inch). It was a random size and leaky. It sounded like crap. I did some reading (this was before the days of google) and learned about all sorts of things. Made a new cabinet out of MDF and matching the volume to the driver specs. I lined it with damping and sealed it up. With the same drivers, it was a whole different world. They sounded really decent and got used for quite some time after that.

— End quote

I try my best to straddle the fence between weight and solid build. I generally use Baltic birch plywood (high quality with many layers of laminates and very few voids in the wood) that is relatively lightweight. I find that this is better for PA cabs because they are much more resistant to wetness (MDF can fall apart when it gets wet). However, you must do as you say and dampen the interior walls of the cabinet to kill cabinet resonance and standing waves. I also use silicone caulk to seal all the interior joints in the cabinet (as air tight as possible). Finally, in the design phase, I use WinISD to determine the type, size and shape of the box. It is a relatively simple program once you get all of your drivers thiele-small parameters typed in.

My very first cabs I built were black painted MDF three way speaker cabs. They sounded amazing (beginners luck). I have built probably another dozen ofr so pairs over the years, but have been getting into more interesting designs lately. Line arrays are the way to go (IMHO) for PA use. They fix a lot of the problems that are part of the 15" mid-woofer & horn tweeter box design that we have all been lugging around for many years. The problem is that most of the portable line arrays you can buy are very expensive, require you to use proprietary hardware or both. I wanted to build a portable line array that I could use with varying mixers, power amps and such. I’m hoping that these new ones will fill that bill even better than the first ones.


#6

Baltic birch plywood is a great choice. I can’t remember who made them, but I have seen it used on some high dollar cabinets. It also cuts and works well. I used some on some drawers. MDF is excellent except it weighs a ton and like you said, you can’t get it wet. It works great for car enclosures, but I wouldn’t want to have to lug it around all the time.


#7

Am I getting this right or not . you are EQing the speakers individually is that right . ?


#8

Yes and no.

I am sending an EQed amplified signal to each speaker cabinet. For the small cabinets, I send a signal that is mostly 150hz to 20khz (20,000hz). The frequencies below 150hz are rolled off so that those cabinets do not have to try to handle the drive (long excursion) of the lowest frequencies which cause distortion at higher power levels. Then I send most of the signal below 150hz to the 15" subwoofer.

The new cabinets I am building, I hope will not need any roll-off of the low frequencies. The plan is that they will be clean from about 40hz to 15,000hz. There is definitely a taper off of the lowest frequencies (because of the sealed cabinet size). That taper is from about 95hz down to 40hz (about 8db all together if I designed these cabinets right). I may need to boost those frequencies slightly to compensate, or I may not. Can’t really tell till the build is complete and I run the power amp though them.


#9

It’s done.

The first speaker is finished and I could not wait to put the second one together to try it out. The early results are that they do exactly what they should do, produce full, crisp audio that throws a long distance without distortion at a pretty low wattage.

I tried playing various audio tracks to test the full range capability. I love using Tower of Power’s Walking up Hip Street because it has it all, fat bass with a heavy bass drum, punchy midrange organ and guitar, with bright horns and cymbals on top. Sounded great with a smooth, punchy bass. The upper mids were slightly harsh at first but mellowed very quickly with just a few minutes of break in. I then tried Suite Judy Blue Eyes by CSNY and it sounded very nice. The vocals were natural and forward slightly. I played a Bryan Sutton track and the guitar sounded really nice, clear, crisp and full.

These speakers are not high quality home system speakers. Although they sound very smooth, they need slight EQing to get a flatter tone. To get the results above, I needed to raise the 80hz slider about +4db, 6khz slider +2db and the 12khz slider +4db. Not a lot of EQing, but with these adjustments, the speaker sounds quite nice. I want to try the new cabinet out in various configurations, including with one of my old 4 x 5" cabinets mounted on top (like in the picture below).

The new cabinets are the lower ones and the old cabinets are the upper ones. With just the lower cabinets (4 x 8"), they stand 6’ tall on this speaker stand (which is set to it’s lowest setting). With the old cabinets on top, they are about 8’ tall!

Honestly, I am excited to get the second cabinet assembled and try these out with the band. I will definitely need to find much shorter speaker stands (or make some sort of portable mount for them). I’ve got a lot of testing in front of me to see how to best use these cabinets. They may be best just for the larger gigs. While playing music into it this morning, I walked about a block away to hear how they sounded. They were as clear as a bell without any distortion. I have not cranked them up yet but have tried them out at what I would consider concert volume for our band.

More to come…


#10

Nice job! And just think… it will sound much better with the second array. They look great and I am glad they sound great too. I hope they serve you well for many years to come.

I can just see it at 6:00 AM in your neighborhood this morning… “I’ve got an answer… I’m going to fly away… what have I got to lose”


#11

You were right Mike. With the small cabs added, these sound nothing short of amazing. I was going to say “for the money”, but they just sound amazing with the second array. I finished the second cabinet and listened to the two new (large) cabs in stereo. They sounded good, really good. I played a cut of Cherryholmes and the studio recording sounding like a fine studio recording should, clear, full and smooth. However, when I added the small cabs to the top of each of the new cabs, it sounded like Cherryholmes was in my back yard playing a solo concert for me… really. The smaller cabs brought forward the sound. They definitely added some brightness, but they also made the music sound more ***alive ***(best way I know to describe it). So I set the amp to put out about 15 watts rms and walked away a few hundred feet. Clear as a bell. Another hundred feet. Still clear and full but starting to notice frequencies below about 100hz fading. What was most startling was at about 300 feet distance, I heard the sound echoing off buildings about another 1/4 mile away behind me. That is when I decided that I needed to turn down.

If these cabs were to be used for a rock band in a large auditorium (or outside), you would probably want to add a stack of sub-bass bins to keep up. However for a bluegrass band, these are just right.


#12

Wow, those are some efficient speakers. Do you know what impedance you ended up with?

Congratulations on the speakers! It sounds like they came out as good as you hoped and maybe even better than you expected. I wish it was closer and I’d come give them a listen. As I think I mentioned before, my wife was wanting a small PA for karaoke (I have just used my bass amp for the several times we had karaoke going for the local kids). If you don’t mind, I might get some guidance from you if a PA moves to the top of the to-do list.


#13

— Begin quote from “mreisz”

Wow, those are some efficient speakers. Do you know what impedance you ended up with?
…If you don’t mind, I might get some guidance from you if a PA moves to the top of the to-do list.

— End quote

Yep. The large cabs are 8 ohms each. I have them wired so that they can be connected in parallel to equal a 4 ohm load with both together.

The small cabs are wired for 16 ohms. Two of those together equals an 8 ohm load.

Now for the interesting part. Today, for the sake of ease, I wired both the 8 ohm cabinet plus the 16 ohm small cabinet together in parallel (for a 5.333 ohm load at the amp). Honestly, the 16 ohm (small) cabinet does not get as much wattage as the 8 ohm (large) cabinet in this scenario. However, the sound was amazing.

What will really be interesting is when I actually bi-amp the two cabinets (the original plan), each with their own 400 watt amp and EQ. :open_mouth:

Any little bit of info I can pass along, you are welcome to anytime. You are right that I did not expect this level of quality in sound from drivers this cheap. http://www.parts-express.com/grs-8fr-8-full-range-8-speaker-pioneer-type-b20fu20-51fw--292-430 They are plenty cheap at $11.50 each, however I bought them when they were on sale for about $8 each. I originally wanted the Goldwood 8" coaxial speakers for this project ( http://www.parts-express.com/goldwood-gw-8004-8-coaxial-speaker--290-378 ), but they were on back order for over a year and I finally bought the GRS 8" drivers. In hindsight, the Goldwood drivers would probably not need the smaller cabs running at the same time to sound just as amazing as the combination that I came up with (which is why I wanted them in the first place). But I’ve got what I got and I am very happy with the result.


#14

Had a chance to use them with the band yet?


#15

Nope. We played a gig this weekend but it was an acoustic gig (no need for a PA). I am excited to try them out, but not so excited that I am willing to set it up in 90+ degree weather. :slight_smile:

Soon enough I suspect.