Line array with varying length TL (pipes)?

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Get stuffed -- or not?

Badman...thanks, bookmarked!

I realize the following is out of character for me :scared:

but I have a question that may actually be relevant to audio theory in general and my current project in specific :idea:

Unlike most TL tubes, should mine remain unstuffed? My reasoning is this: since one goal of the design is to deliberately spread out the peaks and nulls of a single tube by having multiple tube lengths, also the whole point of using a TL is to increase sensitivity and finally

To have more sound bouce off rear walls, though said wall beith not of concrete, nor beith not the ratio of reflected sound 89% as decreed St. Amar of The Mountain :worship:

...perhaps the Marimba should have no stuffing, for it is an abomination unto the backwave.
😕
 
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I should have said "Use a quarter-wave-resontator for each driver, to try and extend the low end response of each driver." (which would increase the sensitivity of the composite array.). I know my ideas are goofy and many of my experiments fail, but unless I've gone horribly wrong, isn't this the main reason that people build all variations of the quarter-wave-tuned pipe?

Some times the theoretical principle is sound but my execution of it isn't :blush:
 
Review rev 2

[Even though it's not yet April Fool's, I love to write silly stuff, as well as experiment with speaker building. Here is a slightly revised version of my March 9 posting. Some of this is true, the rest is made-up. Use your judgment; clearly I have none [grin].

Review of Soldermizer Technology Marimba Mark I

This is the first time that your reviewer has had the opportunity to review a product from this new manufacturer. ST produce, or as they like to say, "perpetrate" hand-built sound producing apparatus for the gullible public.

The Marimba I is the first in an envisioned line of speakers that ST plans to name after musical instruments. They chose "Marimba" due to the unconventional use of tubes behind each driver, much like the Mexican malleted instrument of the same name. But there the resemblance ends. Rather than wood, plastic or metal that higher manufacturers would use, ST scouts out old cardboard tubes that are leftovers at carpet dealers. These tubes, ST claims, have the "sonic smoothness" of the textile they previously were wrapped in. Particularly sought-after are those that were the core of Berber carpet, as wool is known to have exceptional audio properties.

In the same tradition of careless component selection, ST's employees (primarily day laborers sober enough to show up for work, sometimes even former ST employees that were laid off for being too drunk (is that possible???) are sent to scour local thrift shops and yard sales for authentic Bose 901 speakers. Not just any, but the originals having the coveted CTS 4C1077 drivers, long out of production. Rarely, NOS versions will surface from a collector but at $20-30 each, these are beyond the reach of the typical ST hire. In a pinch, ST will use comparable modern drivers. The usually superior technical quality of today's drivers, ST claim, is a drawback; they lack the tweet and blast that authentic CTS were known for. [Actually, some people say the CTS was a fairly good driver spec-wise in its day.]

The cabinet: as much respect as ST had for the late Dr. Bose and his hugely successful company, the Marimba I has little in common with the Bose 901 save using nine identical or similar drivers and active EQ (not the Bose 901 curve, of course).

Theory of Operation

ST hit upon the apparently unique idea, or unwarranted, depending upon whom is condemning their latest product, idea of having a Direct/Directing [tm] vertical array of nine drivers closely spaced. Not just a line array, each driver also has a tube (quarter wave resonator, also called, somewhat incorrectly, a transmission line) behind it, tuned to a different frequency. While critics can validly claim that all but the "center" tube is mis-tuned (to maximize bass from the driver having an FS of approximately 106 Hz), ST decided to try and "fill the hole", which is the Achilles' Heel of QWT designs: the nulls at higher multiples of the resonant frequency of each tube. ST believes that by having 4 tubes spanning the half octave below and above, respectively, that the peaks and nulls will be spread about and minimized.

There are many techniques to reduce unwanted harmonics in a tuned pipe. Perhaps the most common with TL variants is to use a stub.

While none of the above concepts taken alone is a new idea, ST believes that this is the first attempt of multiple transmission lines intended for a full range driver. Of course they could be wrong. The Patent Office has issued millions of patents including some that appear to violate established laws of physics or other aspects of the real world. Unlike some of the more spectacular offenders, ST claims no otherworldly magic here, just a "new to him" idea that may not have been attempted before.

Many minutes of design went into the planning for this reproducer. It was carefully assembled using the above materials, plus 16 feet of 2x4 for supports and 4' of 2x10 for a base. Gorilla Glue is applied liberally to keep stuff from moving about (although ST claims to have found the speaker works better if this adhesive stays out of the voice coil.) Early production was plagued by adhesive foaming onto the backs of cones as well but this has been eliminated by closing the open bar at the cafeteria during lunch hour.

Amazingly, ST's half-baked design appears to work. Initial testing shows reasonably flat response down to 71 Hz, substantially lower than a stock Bose 901. While not a true line source, ST's Inept/Defective [tm] rear sound wave is actually an unruly mix of out of phase frequencies. Like the Bose 901, this sound is intended to spread to the rear walls and rebound towards the listener.

Listening Tests.

Equipment break in. To test such an odd speaker, equipment of comparable quality is needed. Your reviewer had to pack up his Levinson and Madrigal electronics and inquire discreetly for more conventional equipment, lest his snooty audiophile friends catch wind of what he was up to. Good fortune answered. His son, a heroin addict in a punk band, had recently obtained some equipment "that needed to stay out of sight for a few months." Rather than press for details, your author gladly offered to borrow the "friend's" Behringer electronics for the auditioning. In a pinch Pyle may also work.

Reviewer break-in. Prior to listening, your reviewer drank a "40" of malt liquor. A twelve pack of Natural Ice was in the fridge if additional protection was required.

Impressions:

Other than the major problem, "its existence," your reviewer could only find minor issues with the Marimba I.

With no EQ applied, the Marimba I clearly has more bass the un-EQ-ed stock 901. Of course, both of these will lack the high end since a sharp roll-off begins above 2K Hz.

With proper EQ however, is where the Marimba really begins to show its ordinariness. Many speakers are sensitive to placement, and the Marimba is no exception. Just being a line array demands a small sweet spot. However, the rear ports, which are in effect nine TL outputs, will combine unpredictably depending upon the room acoustics. Even small movements of a few inches dramatically change the timbre of the music. Perhaps this is to be expected, since in the case of one speaker set, there are nine in-phase signals vying to peak or null with nine more or less random signals and the results are very unpredictable.

Stereo imaging: not tested, as only a single Marimba exists currently. The R&D guy thinks with two ST may be able to claim "stereo nowhere" (tm). The phasy sound reminded the auditioner of the more egregrious examples of "stereo synthesis" from the 1970s and earlier.

Disposal: the Marimba is made mostly of environmentally friendly material. It is best destroyed by burning. However, the Bose drivers contain lead (and Bose) and should be removed and handled as hazardous waste.

Future Plans? The Marimba project shows much promise for inexpensive, yet visually appalling DIY speakers. ST believe that such a speaker answers the demand of the tiny, but still potentially profitable market of the male DIY-er who has no WAF to worry about (typically because most females avoid him).

There is no reason that the Marimba idea couldn't be adapted to conventional (looking) speaker enclosures; however it would require very intricate carpentry or other assembly skills to achieve such a product. Judging from the DIY forums on the internet, nevertheless, there exists a market for hopelessly complex speaker plans. An even more profitable market, judging from photos posted, is selling expensive carpentry tools and materials to such men. Nothing wrong with spending $25,000 in equipment to make something you could have bought for $1,500, right guys? Just make the wife an inlaid jewelry box and we'll call it even.

Design Variations:

Using readily available (but some what more costly) materials such as rubber tubing or perhaps PVC pipe would permit (literally) a "flexible" array of options: each "speaker" would be a composite unit of several (nine in current design) tuned pipes: the "Line array" would still be present (small vertical array) but the rear pipes could be twisted and shaped any way desired. This would produce even more random reflecting sound than the Marimba I.

Unlike Gorilla Glue, the cements and solvents needed to work with these materials typically have volatile organic hydrocarbons, and for the DIY-er or listener desperate to either seek inspiration, or to escape the hellish reality of half-assed prototypes, provide an option to inhale and become intoxicated from said fumes. While this certainly possible, it should only be considered a last resort. It must be noted that due to the much higher risk of brain damage and other health issues it is recommended that more convention substances such as alcohol or various prohibited drugs be considered first.

Further information: Patent attorneys, probation officers and mental health professionals, please contact ST at the address above.

One of ST's engineers showing his time-tested formula (fermented at least one week!) which provides him inspiration for his designs.
 

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Now a breeding pair [emoji41] A new feature I'd add to the blurb would be something like:

The haphazard design and construction process virtually guarantees that there will be deviations from intended specifications (Fs, height of each drive); this helps create a random distribution of temporal-spatial loci to excite indeterminate room mdes.

How does it sound? Well, er...it makes noise...more to come...
An externally hosted image should be here but it was not working when we last tested it.
 
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Initial listening impressions

I listen to music several hours a day. Fortunately I had a sweep of the first Marimba available (only one to date) so loaded it as the EQ into the MiniDSP. Right and left balance is off for some reason. Adjusted to taste (ok to "hearing" I suppose). Yes, with some material I can now hear actual separation and panning of instruments. As much as I like the 3x pair of Bose 901, imaging I getteth not with them 🙂

I think they are a "keeper" at least for the medium term. This is my first listen to anything resembling a line array (not counting public performances of course). Especially considering that I seem to be violating every rule of good LA design. I mean, I am using Bose and not even real, but some counterfeit (clone) Bose-like drivers. The quality of this thing should be not only lower than whale s--t, but lower than the s--t of the strange creatures at the bottom of the sea that eat the whale s--t. :clown:

Wiki entry tastefully calls this dubious Manna from heaven "organic material that falls from above."
Deep sea creature - Wikipedia, the free encyclopedia

Onward to fine tuning and positioning of this electro-mechanical apparatus. Future revisions might tackle the problem of a speaker that looks like something you'd find in the torpedo room of a submarine 🙂
 

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I've actually disconnected the Bose...

...for the first time in a few years. I am listening to the pair of Marimbas and have re-acquainted myself with the "novelty" of a stereo image, at least between the arrays. I definitely get some depth to the image, the vocalist is in the center. I've switched the MiniDSP to a GEQ and am adjusting to taste.

Virtually all the music I have is lossy mp3 or streaming. Still pretty good sound overall considering what they're made of 🙂

A real line array may be in my future. If I build one, I would very likely use the Typhany TC9FD or similar as a driver espoused elsewhere. For enclosure I would consider the vinyl fence posts. I priced these at Lowe's last night. 5" square by 8 foot ~ $25 each; a pair with caps might be $60 total. I know there are a few old posts here and on Google. I'm surprised more people haven't used these to build arrays, it would seem like the perfect solution.

Here's some clever guy who stole my idea five years before I thought of it 🙂

My Line Array Project
 
Now they are sealed (plugged ports)...

After about six months of listening to the Marimbas, I got bored and made them "sealed boxes" (er, tube) just plugging the ports with closed cell foam and Gorilla Glue (of course). My hands look like I am recovering from a bad sunburn 🙂

After re-EQ-ing, they sound...not so very different. Gone is the phasiness one would expect from having nine pairs of out of phase ports adding to the sound field. The imaging is still very good .. compared to stock 901 anyway.

I ran some REW scans again. Surprisingly, the FR is pretty much the same (chart). The group delay is a lot less scarier (not shown) 🙂
 

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Graphs speak for themselves and it's all foul language 🙂

Here are the before (ports) and after (plugged) of just Left unit. I can't read an impulse response well, but the frequency and phase 0-100 Hz tells me to scrap the TL idea.
 

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Project Obiturary

I was tinkering some more with my Marimbas a few nights ago when one of them collapsed. Rather than glue back together a failed design I scrapped them. The garbage truck hauled them away this morning 🙂

To all the nay-sayers: "You were right!" After months of listening to them, and a week or two of "sealed box" sound, I do like the sound of them, good imaging relative to my reference stacks of Bose 901s, which whether you love or hate them, I am quite sure no one ever claimed holographic imaging from a pair 🙂

I will attempt a more conventional pair of line arrays using even worse drivers than those found in the Bose 901 🙄
 
WELL DONE!

You my friend, have succeeded in producing something audibly sublime from a Bose 901 speaker! Something no one has *ever* done before, (except maybe in spastic fits of sarcastic disdain). You sir created at least 87 db of something sonically useful from a Bose 901. You did it! Measured scientifically by a free app on my Galaxy S3, you have achieved 87 db of Pete's constantly directed unmitigated laughter! You really should write for those fools at you know what magazine, surely room temperature is due for one of them?

Hmm thinking... as this place is so good at making us do... (hello EG) if you took a 901 and did place all the drivers in a closed box lightly tfuffed line array (of the correct volume and using appropriate active EQ, you might actually have a halfway decent speaker if hung from the ceiling in the corners. I'd be willing to bet it would not be bad at all. Everything about the 901 box as designed just sucks, a bad concept, poor understanding of the physics in involved, truly mediocre components, Drivers working their rear ends off into thin air, yada yada. Put it in the corners in a line array and a lot of that will be fixed automatically. Be interesting to see what the components would sound like with some actual sense behind them.

I was tinkering some more with my Marimbas a few nights ago when one of them collapsed. Rather than glue back together a failed design I scrapped them. The garbage truck hauled them away this morning 🙂

To all the nay-sayers: "You were right!" After months of listening to them, and a week or two of "sealed box" sound, I do like the sound of them, good imaging relative to my reference stacks of Bose 901s, which whether you love or hate them, I am quite sure no one ever claimed holographic imaging from a pair 🙂

I will attempt a more conventional pair of line arrays using even worse drivers than those found in the Bose 901 🙄
 
You write literately and with some intelligent comments. Obviously you are a very small minority 😂even here on the board. I like your comment about this board. I used to be a regular on Audio Asylum and it lives up to its name very we[emoji603], sort of like one of the lunatic fringe audio mag$ mutated into an online forum 🙂

I continue to be an avid fan of the "original" (series I, II) Bose 901. I have often sung the praises of this ancient speaker here and elsewhere. To recap (Something absolutely impossible to do to a 901, in a different sense!) they are a venerable, if dubious design; they can be had reasonably cheaply (I've paid around $100 to $300 for each pair); they are easy to work on. I enjoy pursing a hobby that in my childhood (when the Bose 901 was "new") would have been unaffordable. The Bose's standardized parts makes it easy to repair and to make DIY variants thereof. My Marimba was ultimately a failure but it was fun. And they are an ok speaker, depending on one's tastes (obviously I lack any) and equipment, etc. Currently I have running three each, left and right channels, and a horrible DIY subwoofer for lows and also footrest 🙂

Sent from my NV570P using Tapatalk
 
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