DIY Speakers for the Room of size: - Page 3

Don't forget to look at the mini statement center channel and "Frodaddy's custom Statement center- WMM/TW"

http://www.htguide.com/forum/showthread.php4?t=31523

and you also have the "Monitor Statements"

http://www.htguide.com/forum/showthread.php4?t=29605

If I didn't already have speakers I'd build a system based on the Statement Line...

Good Luck, you should have a lot of fun.

Jose

One thing to keep in mind with the Statements is that they are designed to be placed away from the wall at least 18 inches. If you need to put them closer to the wall, the Statement Monitors have a 'near wall' crossover so you can put them ~12 inches from the wall (this is what I am building).

If you still want to go the Statement route and want to keep you LCR & sub budget under $1500, you will probably want to do this:

Phase 1: 2 Statement Monitors, Statement Center, & DIY sub
Phase 2 (when you have more $) 2 Statements or MiniStatements for your mains, moving your monitors to surround duty.

Depending on your choice for a sub, and prices when you pull the trigger, the Center may have to become phase 2 and the new mains phase 3.

And yes, building these is a lot of fun...

Tightbond 2 for MDF.

I use a standard Dow "adhesive caulk" for ports that don't require any kind of plumbing fitting for corners, etc. PVC cement for those. But if your port length is that long, you might want to consider another design...

For acoustic damping material, I use polyfill made for quilting, you want "extra high loft poly quilt batting". It's mildly sintered, so it doesn't spread all over the place, you can tack it in place a few places and it behaves, and it's not at all expensive.

And it's so much less annoying than fibreglass.

Does the polyfill work as well as the denser fibreglass choices though?

I know its good for increasing volume in a box but I didnt really think it was good enough to be placed against the walls vs the denser wall products.

I use "ultra-touch" cotton on some of my walls (easier to work with then fibreglass). I had a HUGE box left over from when I built my HT room so I figured what the heck. I have also used the "under carpet mat" stuff. I have a big roll of that in my garage too.

This is kind of a mis-information thing.

If the walls are well treated behind the speakers you can place the close to the wall since there is really no reflections from the speakers. The BSC settings is all that needs tweaking and that can be done with proper EQing anyways.

I think carpet padding works great in damping the walls. Fiberglass is just the worst stuff on the planet to work with

Carpet padding may be too solid, and not do what you want. Fibreglass is just as awful as penngray says.

So I go with quilt batting. It's light, it gives you good damping, and it's (*(* cheap by mail order.

Pillow forms also work just as well.

This for inside the cabinets, that is.

I go with SoundSoak (tm) or Acousticore for walls.

Zero,

Loudspeaker system design poses several "assumption traps" that causes us to waste time and expense on parameters that have little or no impact in the real world while limiting our choices on the ones that actually do.

Zero said:

"You're right - could be a magic driver where the laws of physics don't apply. Or it could be the huge peaks in the upper frequency range that you're not taming helping the off axis. In any case, you can look at off axis measurements of people who use this driver in a full range system and see that its about 12db down at 6000 from its level at 1000"

rob r. sez:

Angle of relative incident (up/down, left side/right side) plays an important role in determining what the useful range of a driver is.

To assume that all drivers must be omnidirectional and that audition occurs 180 deg hor. and 180 deg vert. limits the designer's ability to optimize first arrival flatness (the perceptual leader of your hearing), unity transfer (all the terms in the numerator of the s plane transform of the crossover equalling the terms in the denominator) and sufficiently low IM (6% is considered quite an accomplishment at 90dB@1M).

In fact, a more appropriate assumption would be that the useful angle of audition would be more like +/-20 deg horizontal and +/- 40 deg vertical.

With these parameters established you could then intelligently make decisions on appropriate crossover points to realize the best possible fit between on- axis flatness, minimum IM and unity.

This tends to fly in the face of many first timers as the assumption is made that the higher the xover slopes, the better (wrong), asymetry is better (wrong) or controlling out of band driver behavior is more important than minimizing IM (yes, wrong).

If lobing error is a worry, then one should welcome the MTM or WMTMW array as symmetry about the array center cancels lobing error along the lengthwise axis over a reasonable audition angle.

You may use first order crossovers (unity transfer) with MTM (lobing error cancelling). You may even make the xover points higher thus limiting IM.

Zero said:

"Intellectual games? Ah, here's the scientist trying to intimidate the layman... sorry, I'm just stating basic speaker building ideas. If we go by what the creator of the mtm configurations suggests, the CENTER to CENTER spacing of adjacent drivers should be kept close to one wavelength of the crossover frequency."

rob r. sez:

This incorrectly assumes omnipolar behavior.

Zero said:

"I don't really care that you think your driver is 2.75" in diameter, every other w4-1337 out there is 4 15/16". So you're going to tell me your mtm with a crossover of 5600 does not have any vertical lobing? Guess you're powering that with FM (not frequency modulation)"

rob r. sez:

The directivity limitations of spaced 4" drivers (mechanical mount limited with even a large tweeter in between) would have to demonstrate an amazingly omnidirectional polar pattern to end up with an end-fire lobe of any consequence (even at the crossover).

I believe that jj has made some excellent reality based decisions on his design

rob r. (who has designed more bad speakers than anyone )

Well, more to the interesting point, he's presuming that the diamater of the radiating part of the speaker is the same as the outside edge of the mounting diameter. If someone actually accomplished that, aside from wanting to know how they actually mounted the speaker on the cabinet, I'd wonder just how they did the edge terminations, and when the glue was going to cut loose.

Indeed.

There are still those that assume that the effective radiating surface of an imperfect piston is constant in planometry, shape and phase with frequency (BTW, it ain't).

While laser interferometers are expensive, I believe Strobotacs are cheap (if you can find them). If anyone can find one, buy it and use it (very simple).

I remember my shock when I saw EFS/Freq for the first time. Diaphragmatic breakup is ugly to look at, but the gained insights resulted in adoption of measurement circumstances based on statistics and probabilities.

It's a miracle that a loudspeaker sounds like anything.

rob r. (who watched science theater 3000 one too many times)

Sigh - I kinda wish these posts would have gone away, but they're not. I said a few things in haste that I regret, and I don't want to get into an advanced technical discussion about audio theory since it's (obviously) above my level of knowledge.

My comments were based on the simple fact that mtm systems laid on their side for center channel use is universally considered a bad idea because anyone off-center will be subjected to deep nulls in the response; lobing. Therefore, a horizontal mtm will have those nulls placed in the vertical response. The Loudspeaker Design Cookbook has some lovely graphs showing this effect in the Loudspeaker Baffle chapter, B. Woofer Spacing for 2-way WTW Center Channel Speakers

The comment about keeping the driver spacing to one wavelength from the center of the drivers is also not of my origin; it is from Joseph D'Appolito's 1983 paper "A Geometric Approach to Eliminating Lobing Errors in Multiway Loudspeakers".

As far as your last quote, you are welcome to believe it. I'll believe it when I see it.

Guys, out of respect for the OP and this build could we keep the very, very techy discussion to a minimum for him. I doubt back and forth over the very technical stuff helps him.

He just wants to build some nice DIY speakers not learn everything about speakers, that is for the next project!

Yes, inside the cabinets. It helps deaden the sound of the speaker boxes but I believe that proper bracing does 99% of the job anyways so its not a HUGE concern.

Keeping in mind the open back midranges of the statements?

If the walls are heavy MDF, for most home speaker systems, I don't think you have a wall problem, but you do want to damp resonances from side to side, top to bottom, etc, which is best done with absorbtion in the center of the box.

This is what I use quilt batting or pillow forms. They don't move around, they don't shed fibres that get into voice coils, and they absorb quite nicely.

Hm, is that for which purpose? Creating a diffuse field, or keeping power equal to direct, or what?

It can be an iffy thing to do in my experience, unless you want a lot of diffuse energy in the room. That's a question of taste.

My current project, about 6L 5" 2 ways, I measured drastic differences with and without old fiber type carpet pad on the walls. 3/4 MDF, and lightly filled with cheap pillow polyfill. I am guessing what I was fixing was through-cone reflections. Whatever, it worked so says my nearfield plots. I found denser center fill not to be as effective, but did help the box Q a tad. Actually, I removed some to tune the boxes to 95Hz. ( sealed) . The particular fill I used is different from what I had before. It feels slippery.
"Soft & Crafty 100% polyester fiberfill" I tested fiberglass of various stuffing as I had some on hand. It was no where near as effective as the old pad so it was placed in the very best position for fiberglass batts. My Attic.

My apologies. The professionals (at least the ones I know) on this forum are only here to educate and assist.

I personally appreciate conversing with people that know more than I do (which is just about everyone) on any subject.

There is no need to "look good" while researching or learning. Ask any "dumb question", experimentally fail with remarkable vigor and learn from your results.

This is part of the scientific process. (philosophical rant off).

Now then...

The idea that an MTM array on it's side is considered a universally bad idea needs to be qualified. Where is the audience vs. the axial behavior of the outer drivers? What is the driver spacing? what is the crossover point?

If you qualify the application, you may find that an MTM array is an excellent application. Remember, symetric arrays freeze the length wise interferometry of the array. That means that the main polar lobe won't tilt toward the lagging driver through the crossover point. Without symmetry, or "coincedence", the main lobe will very actively rotate from the woofer to the tweeter through the xover point (unless you use a more complicated and non-unity Linkwitz-Riley xover). I suspect this is the advantage that Joe D' envisioned.

What you shouldn't do is build the loudspeaker first and then decide on the audience placement.

This is the downside of buying "prebuilt" loudspeaker systems and the advantage of DIY.

If you define the audition area beforehand, this will make your design time much more useful and assist you in picking the drivers as you now know what the polar boundaries need to be. This is far easier (I promise) than trying to build a universal loudspeaker system.

I'm sticking to my guns...I believe jj's speaker will sound great.

rob r. (I've just bored myself to sleep)

Penn,

Stop making sense!

Sometimes it's difficult to know how deep to go down the rabbit hole

rob r. (ask me what time it is and I'll tell you how to make a watch)

So get your butt down here into lowrentville and listen.

Yes, drivers and assembled crossovers with good quality parts.

How about Wenesday evening?

rob r. (don't let jj fool you...his house and family are cool)

Good luck, and let us know how they sound.

I'm sorry I don't have a lot of the cutting plans, etc, that one would expect, but like I said, I don't get to do most of my own building any more.

Good choice, sometimes the hardest part is just picking the speakers and get moving on the build

Definitely take lots of pics and post them for us to enjoy your build success!

I just received a whole bunch of kits/drivers/amps from Jack (NHT) ..I think I have too many projects myself now