DIY Near Field Line Array

[hitmanray]

Evening All

I am in the process of building a pair of speakers based on a DIY near field line array concept. Each speaker will consist of 25 "full range" drivers and the plan is to run them from my MonAmour Amps.

The driver is the Tymphany TC9FD18-08 from parts express. I will try and insert a link to the product page below.

https://www.parts-express.com/peerless-by-tymphany-tc9fd18-08-3-1-2-full-range-paper-cone-woofer--264-1062

My intent is to wire the array as 5 paralleled groups of 5 drivers connected in series. I am not intending to apply any power tapering which some folks employ to reduce the output of driver groups as they move out from the center. My fairly basic understanding of the electronic impact is that by having the same number of driver groups as drivers in a group, the amplifier would effectively see the same load as a single driver. But because of the increase in effective surface area achieved through having multiple drivers I should expect to see some increases in the overall efficiency vs a single driver.

My amps are currently wired on the 8 ohm taps and I was planning on leaving them in that configuration.

So I guess the question is, does anybody see any major concern with my plans from an amplifier loading perspective or should I consider utilizing a different set of output taps to provide better protection and/or performance?

Any thoughts or opinions greatly appreciated.

Phil

[Paul Joppa]

There should be no problem with the array impedance.

You will however need some equalization for this array. I don't know what it needs in the treble, but the deep bass will need a LOT unless you plan to use subwoofers. That might be beyond the capability of a 6-watt amp.

[hitmanray]

Thanks for the quick reply Paul.

I am planning on supplementing with subwoofers for bass production. I have been doing a lot of reading about subwoofer "swarm" type arrangements, but am trying to limit myself to one ridiculous project at a time.

I have also read a lot about needing some equalization and think to get started I will probably get hold of a Behringer DEQ just to try and get things smoothed out, but this is another area where I have very little knowledge and am going to have to learn some more when the time comes. In my head I like the idea of doing equalization in the digital domain until I figure out what sort of filter works and then trying to create something passive. But again, way outside of my comfort zone here.

I have seen some folks reporting being able to get these speakers to work well down to about 60Hz, but as you mentioned I am guessing they are throwing a lot more power than 6W at them. I figure if I am committed to a sub solution then I can roll them off higher than that at gets the subs to manage the really power hungry stuff.

The speakers themselves are constructed of a bunch of 3d printed elements, and given the size I still have about 40 days until I get all the modules printed. But I am hopeful that it won't be long until I can start doing some measurements (another area I know very little about) and start to work some of these things out.

[Paul Joppa]

Sounds like a well-thought-out plan. The MonAmour will drive the array very well if it does not need to cover much below the LF resonance.

[Deke609]

@hitmanray: if you're up to it, it would be great if you started a build thread about these speakers and post periodic pics. I'd really like to see this project come together, as I am sure many other forum members would too. A pretty cool project all-round: the use of series and parallel wiring to get 25 speaker drivers to appear as the equivalent of a single driver to the amp is ingenious; and the 3D-printing of the enclosure bits is equally cool and interesting.

cheers, Derek

[pboser]

Sounds like a cool project.  I can't picture how near-field you intend it to be, though, in light of the fact that it will be over 7 feet tall at a minimum!  I guess you're not thinking of a desktop speaker? 
Also, did PE give you a good price for the quantity?
And I too would love to see a build thread!

[Doc B.]

Will the array be curved? All speaker designs have warts. Arrays have a special set of warts. A nearfield array that is straight will suffer in terms of time alignment and thus imaging will be somewhat vague. A curvilinear array will fix that and can sound amazingly coherent at the focus point, but it tends to overemphasize the mid and treble at the expense of the bass. Understanding the issues can help to overcome them.

[hitmanray]

Evening All

Thanks for all the replies and comments. Lots of good thoughts to chew on.

I do have a build thread that I started over on another forum. Hopefully no one will be offended if I link that thread here, rather than regurgitating as it's been going on several weeks now.

https://www.diyaudio.com/forums/full-range/361696-tc9-line-array-project.html

pboser: Near-field is a relative term. I did some reading of some technical stuff on line arrays, and (based on the little bits I absorbed) line arrays have an effect where depending on the overall length of the array there is a step change in the drop-off rate based on distance from the speaker. Essentially these designs (because I am by no means the first) are designed to operate with the listener located in an area before that drop-off point occurs for a given array length. The opposite woudl be what you se at concerts where there are lots of line arrays set up to operate in the far-field region.

On the opposite side of the problem is the comb-filtering issue where identical drivers next to each other will exhibit comb filtering for frequencies of a wavelength less than the linear distance between the driver centers. This is why most at home line array speakers are at least 2 way, and often with ribbon tweeters and low-passed mids to get around this effect. However lots of folks have reported that the comb filtering effect with these full range speakers quickly resolves as you move back away from the drivers. So essentially I am hoping they will work well in the envelope I sit where I am not too close for comb filtering issues, and not too far for the steep drop-off from the far-field transition.

Theory all sounds lovely but guess I won't know until I get them built and fired up.

Doc B.: Time alignment is one of those nagging issues that I am a little unsure about at this point. I don't think I have the skill to produce a curved array, but a lot of folks talk about power tapering to achieve the same effect by reducing the output of the drivers as you move away from the center. Most favored method of power tapering is to alter the wiring setup to change the impedance of the relevant driver groups and therefore adjust their output. For my wiring plan I was thinking of running my cables a bit long to allow me to potentially change the driver groupings without having to redo all the wiring. Of course, once the impedance of the driver groups start varying then I will need to pay much more attention to the overall speaker impedance and whether I need to make any changes to my amps to match the resultant impedance.

Again some of the practical feedback seems to be it's not such a big issue, especially with longer lines, but as with all things audio, beauty is in the ear of the listener and who knows about the folks commenting on these forums and what their personal preferences may be.

I have also seen a lot of advice that every line array will require some sort of correction via equalization, particularly in regards the overemphasis points you mentioned. Again, I don't really know what to expect here, but do plan on getting a relatively cheap DSP so I can do some playing in the digital domain, with the ultimate hope that I can perhaps figure out how to build something to allow me to create the right type of filter in the analogue domain, once I understand the speaker performance and interaction with my room. As you might have figured out, I am the type of guy with a ton of big ideas, not all of which tend to see the light of day.

Thanks again for all the interest. Please take anything I have said with a grain of salt as there is at least a 50% chance I have misunderstood some of these incredibly complex technical papers, and I am always open to learn more.

Will be sure to keep this thread updated, especially once I move into the electrical side of the build process.

[Paul Birkeland]

That's a pretty sweet project!

[Doc B.]

Very interesting stuff. I can't say that I have heard power tapering that was as effective as a curved array for coherence. Kinda depends where you're coming from. Someone who has listened to the giant image of Magnepans might marvel at the coherence of a tapered array, while someone who is used to single driver designs might think the coherence is pretty bad. I listened back to Straight 8s after we came up with a few other non array designs and thought the midrange coherence of the 8s was pretty bad. It certainly sucks compared to the Jagers. We never came up with power tapering or frequency shading for the 8s that I liked much, but shading works well in the Jagers. In the end it's all about choosing your own priorities, as no speaker is remotely perfect and everyone hears differently. You should have a lot of fun making this setup suit your taste. Lots of interesting ideas to try.

[pboser]

hitmanray,
Thanks for the additional info.  The "near-field" definition makes sense.  I'm following your build on diyaudio now - wow, cool project! 
Pete