How can I improve this "line array"?

[duronboy]

We've been kicking a similar idea around a while.

$200 8x Eminence Alpha 4-8

$88 4x PRV Audio DT175Ph-S

$50-ish 4x "line array" wave guides from a chinese site. They don't show the signal path, but they might be path length corrected?

$746 small patch of moldy baltic birch

.17 cu ft x 8(1.36 total) tuned to 94hz, 81hz F3 but limited to 88hz at RMS due to xmax(I'm not sure I did the best possible, here)

Should have no trouble at 121dB, at RMS I've exceeded xmax, but I'm still 1mm away from xmech

At half RMS my 1.25" wide port air velocity is just over 12 m/s

[Chris Roemer]

Put all the 4"ers in ONE vertical line. (Your layout will have comb-filtering in the horizontal axis.)

To me, it looks like you're Xmax-limited @ around 140Hz, to about 120 RMS? (near 120dB down to about 100Hz @ 4ohms)

[billfitzmaurice]

Depending on the midbass line CTC and crossover to the tweeters they may not have comb filtering, but they will have less than half the midrange dispersion that they would if all were on a single vertical line. I wouldn't use 4 inch midbasses for pro-sound, unless it's for a low volume situation. At the very least I'd use 5 inch, preferably 6.5 inch. The PRV driver is pretty weak above 7kHz.

[duronboy]

After a breaker blew and I had to recreate everything I saw what you were talking about. I added a simulated filter at 140hz so I could power at RMS without exceeding the rated xmax, and it resulted in a dip of about 3.2dB. I think it's going to be acceptable. I loaded some tracks with audacity and did an even more heavy-handed EQ and it sounds acceptable. At lower power levels the limiter wouldn't even kick in, I think. Is there a more appropriate solution? I should say, is this acceptably professional? I know I don't like it(feels like cheating), but I don't know what else to try to get the most output out of these little woofers and have an F3 this low.

With a 3dB filter and half RMS, I don't have xmax issues.

With no filter and 80% RMS I don't exceed xmech.

Again in Audacity I selected a part of a song, copied it to another track. On one track I killed everything between 100hz and 200hz, and did the opposite on its counterpart. On the 100-200hz track I added harmonic distortion, like a lot, but I don't know how much is fair to add?

[duronboy]

Mmmkay, I guess that's why most line arrays have a dispersion-narrowing waveguide in front of the line array waveguide to more closely match the woofers. I see some line arrays where the woofers are angled in to an extreme angle, and I guess that's to bring them closer together so the dispersion is less restricted? I do see some where they're angled out, too, though.





So a theory I'm hearing is a single, larger woofers require a splay, or curve toward the bottom. whereas the smaller drivers can be mounted flat and straight which I guess is easier. I feel like multiples of the design in the OP is getting as difficult for one person to setup as many line arrays. The desire for flat/square cabs is just less time consuming, even if you need help because you can just stack them on top of each other and lock them to each other. The splayed setups require a lot of alignment steps.

[billfitzmaurice]

I don't know what you mean by single woofers requiring a splay. If you mean a J Array that's only necessary with large multiple cab systems, This SLA Pro uses four Alpha 6 woofers, which have more output capability than eight Alpha 4:

[duronboy]

I guess with one row of woofers it's starting to look like SLAs and some high-end linesource speakers I've seen.

Yeah, the J-array splay. My dad read Bob McCarthy's Sound System book and was under the impression that with 4" drivers it would be easier to create an actual linesource and keep it straight. I need to read that book, although I'm not certain how much I could absorb. But yeah, he wants the ability to add multiple cabs to stack as many as 4 or more per side. Although we don't have enough subwoofers to keep up with that... an issue for another day.

The SLA reminded me I needed to add some front lip for protection/grill holding. I was thinking I could raise just the top and bottom so the tweeters would have better dispersion.

[billfitzmaurice]

If you need to go four high for sufficient output you don't want to be using this sort of box. Something like OTop 8 or OTop 12 will be much better. I don't recommend more than two 4x6 SLA Pro per side. If you need more than that it's not the right cab for the job. As for J Arrays, you use those with tall arrays that are either flown or stacked on staging where the lowermost cab is well above the head height of the nearfield audience. When the array is six feet high or more the narrow vertical dispersion of the array can necessitate aiming the lower box or two downward for nearfield coverage. The size of the driver has no bearing on this, but again, if you're flying an array that large it shouldn't be loaded with smaller than 8 inch woofers.

[duronboy]

I might to have to make my boxes a couple inches wider than the two pictured unless I can mount the horn driver at an angle so the motor isn't occupying the same space as the outside of the box :-)

If you need to go four high for sufficient output you don't want to be using this sort of box.

What's the technical reason someone wouldn't want to use multiples of this sort of box? And what sort of box is this? I was thinking it was a modular, utilitarian version of something like this:

[billfitzmaurice]

If you need that much output 6.5 inch drivers aren't cost effective. For that matter even 8s are marginal in high output situations unless they're horn loaded.

[Paul O]

I might to have to make my boxes a couple inches wider than the two pictured unless I can mount the horn driver at an angle so the motor isn't occupying the same space as the outside of the box :-)

Don't make the boxes any larger than they absolutely have to be, even consider making them sealed as response below 80hz is irrelevent. Design in a way to lock boxes together and/or pole mount them.

What's the technical reason someone wouldn't want to use multiples of this sort of box?

There isn't one if it has performance to complete with a standard PA speaker and offers something they don't. A column about 4-6ft high should have enough output to replace 4 conventional speakers, the thing to remember is that those line array horns have a very narrow vertical coverage angle so the box has to be positioned and angled just right for a job or the column has to be long enough to cover all listening positions.
There have been a few commercial products like this, SLS Audio made a box called the LS8695 which was 4ft tall and contained eight 6.5" drivers and nine ribbons. All reports I have read indicated it was a great performer but the market for this type of speaker was nil, people either want a conventional speaker or a modular line array product.

[duronboy]

My attempts at a sealed box looked pretty dismal. Input power limited to like 10W and an F3 half way to 200hz? Somewhere in the mid 100s.

As far as output, a lot isn't really needed, much of the time.

The limited vertical dispersion is a boon, sound bouncing off ceilings and floors is not good.

More gradual falloff of overall volume from front to back is also good.

Looks like that SLS is on ebay right now. A pallet of them for a few grand.

[duronboy]

Kinda interesting, the seller on ebay must have bought those SLS from England about a month ago for what would be about $2200 USD and has doubled the price. edit: although shipping 880lb from England to Cali can't be cheap.

https://www.gumtree.com/p/speakers-m...ers/1430683306