New to DIY? FAQ's in here - Page 2

The Pi Speakers FAQ mentioned above has a section on multiple subs too. I think it's most worthwhile, because it not only describes Geddes method, but also the Welti procedure that preceded it. The "room modes" thread in that FAQ includes comments from Geddes back when he was refining his approach, so it gives historical perspective. It also shows my helper woofer or "flanking sub" approach, which can be used with either Welti or Geddes methods (or others). The flanking sub approach addresses the upper end of the modal range as well as the self-interference from nearest boundaries. So it smooths the upper midbass to lower midrange, where more distant distributed subs cannot because of localization problems.

On a related note, the FAQ also includes things like box construction, internal standing waves, crossover design and baffle step, and whether to use it or not. The baffle step discussion sort of segues from the multisub discussion, because multisubs and flanking subs are intended to smooth the modal range, below the schroeder frequency, where directivity becomes meaningless. Since baffle step is truly a directivity issue (that is sometimes treated with equalization or "response shaping"), one might wonder whether or not that even makes sense if the baffle step happens near the Schroeder frequency. This and many other things are covered in the Pi Speakers FAQ. So while it is primarily about horns and waveguide speakers, it's not just about horn and waveguide speakers.

Topics include:

General Information

• High-Fidelity Uniform-Directivity Loudspeakers
• Horn speaker design philosophies
• Various design philosophies
• Pi Cornerhorns - a brief history
• Fully Horn Loaded?
• Corner pi speakers
• Klipschorn vs seven Pi cornerhorn
• Notes for the DIYer

Models, Upgrades and Driver Characteristics

• Info to compare Pi models
• Options in a nutshell
• Upgrades
• Electro-mechanical properties and diaphragm motion
• Magnet structures
• Push-pull verses shorting rings
• Push/pull benefits
• Heat exchanger effectiveness
• Speaker Voice Coil Cooling System Valve
• Radiant Cooling System (Cooling Plug) Patent

Cabinet Design

• Hoffman's Iron Law
• Vented Speaker Systems
• Response curves of closed vs. vented systems
• Speaker damping - Overdamped, Underdamped or Critically Damped
• Acoustic filter Q and PiAlign's "Qe"
• Pi Alignments compared with B4, C4 and QB3
• Helmholtz formula
• Helmholtz frequency of each model
• Displacement calculations (or measurements)
• Cabinet design, port placement and internal standing waves
• Golden ratio for loudspeaker cabinets
• Trapezoid enclosures
• Damping material placement
• Altering dimensions

Horn / Waveguide information

• 12Pi Basshorn Subwoofer
• Basshorn or Transmission Line
• Midrange Horn
• H290C Horn/Waveguide
• Horn phase
• Pattern control and mouth size
• Matching directivity in the vertical and the horizontal planes

Crossovers

• Speaker motors and passive crossover filters
• Crossover Electronics 101 Seminar Handout
• Phase angles, crossovers and baffle spacing
• Baffle spacing, phase angles and time alignment, revisited
• Tweeter circuits for constant directivity horns and waveguides
• Woofer size for uniform directivity loudspeakers
• Crossover configuration
• Baffle Step

Room Effects and Loudspeaker Interactions

• Constant directivity verses on-axis EQ for non-uniform directivity (aka baffle step filters)
• In-wall Baffle
• Floor Bounce
• Imaging, placement and orientation
• Speaker placement and wavefront launch
• Room modes, multisubs and flanking subs
• Helper Woofer Location

Simulations and Measurements

• Pi Speakers Measured Datasets
• Spice crossover models
• Determining mechanical reactance values for Spice models
• Clarification of attenuation values
• DI-matched two-way loudspeakers
• Crossover optimization for DI-matched two-way speakers
• Crossover optimization for DI-matched two-way speakers, revisited
• The Acoustic Center: How it applies to Loudspeaker Measurements

Miscellaneous

• Mounting Screws and T-Nuts
• Gaskets
• Midhorn Bracing
• Finishing details for Pi cornerhorns

Glad to help. Been active with DIY loudspeakers for over three decades now, and it would be ashame to underutilize the lessons learned along the way. I see some of the information in those threads mentoned in various forums here and there, most notably the Econowave and SEOS and related threads. But sometimes the lessons learned are forgotten for a season or two and then "rediscovered". So here's hoping it helps.

Thanks Wayne, I'm about to check it out right now.

Wow, this HAS to be a sticky. I almost feel like even I could pull it off after reading through this thread. Great work Andrew.

Agreed! Very comprehensive for sure!

Rilla, I know this thread is going to evolve just get better and better. With that said, I was thinking of something that you may want to add.

I see no references to addiction or wife/hobby balance. Maybe it would be a good idea to throw up a disclaimer of how addicting DIY can be. Not sure about everyone else, but designing and building something from scratch is super gratifying to me... Guess it's a pride thing.
Edited by popalock - 12/15/12 at 11:09am

Fantastic work here, Andrew. Enough to get anyone started with DIY, where the sky's the limit.

this looks like a nifty tool. curious if anybody used it for driver cutouts

http://www.amazon.com/Hole-Pro-X-425-Kit-Hardie-board/dp/B000G1OISI

For the price you can buy a 1/3 HP router and Jasper jig, and do a lot more than just cut holes.

I've used hole cutters like that, and I think they're great. Especially for building smaller speakers with 8" and 10" woofers. But once you get past that, hole cutters are expensive and it probably makes more sense to use a router and a circle jig instead. Besides, with a router, you can cut a groove to flush mount the drivers.

One thing I find interesting from a historical perspective is the thread on AudioRoundTable.com where Geddes begins to talk about his "random" subwoofer placement. This is virtually the same conversation in a discussionboard thread that Earl Geddes, Duke LeJeune and I had at the Great Plains Audiofest in 2005. In fact, it's the same three of us and a few other ART regulars having this discussion online. So you can really see where Earl was coming from, and how his approach evolved.

Since then, Earl has refined his approach from just saying "place them randomly" to saying "one in the corner, one at a wall midpoint and one in a random spot" to having people do a measurement sweep before installing each sub. But in the end, his approach is still basically the same, but with measurements to help dial it in. That's always a good practice.

Back when we first started talking, I expressed interest in the Welti multisub method. I was starting to form my "flanking sub" approach as an adjunct to the Welti method, because I felt that the upper midbass and lower midrange needed to be addressed too. This is something the flanking sub approach deals with that really isn't addressed in any other multisub configuration, so I felt it should be included alongside the Welti approach.

Earl said he thought Welti mis-assessed the situation entirely by not studying random arrangements. He though that since all of Welti's configurations were symmetrical, an important piece of the puzzle was overlooked. I reminded him that this wasn't really the case - that Welti had used a random structure of subs as a baseline, that it was sort of the target, but it was also a huge number of subs. Welti was seeking the performance of a massive number of randomly placed subs using a small number of subs placed in an organized and repeatable fashion.

The conversations always ended up sort of spiraling around with no real conclusions except that we all agreed once you get past four subs, it doesn't really matter where you put them. This was an important take-away for me.

Another important take-away for me was that everyone was looking at response below 100Hz, and nobody even considered the (more important, IMO) 100-200Hz transition region, where not only room modes live but also self-interference from nearest boundaries. That's why I always recommend flanking subs as first priority, and more distant distrubted subs to smooth lower frequency modes, if they are troublesome. Flanking subs will smooth the range down to about 60Hz to 80Hz, and that gets the most objectionable modes as well as the lower midrange notch(es) from nearest-boundary self-interference. More distant subs can be setup per Welti or Geddes, I don't care, nor should anyone else because as we all agree, once you get to four subs, it doesn't matter where you put them.

But anyway, for historical perspective, see the "Sub Placement" thread on AudioRoundTable.com. To reach it, go to the Pi Speakers FAQ, and click on the "Room modes, multisubs and flanking subs" thread. Go to the end and click on the "Geddes configuration" link. There you'll find the original Geddes setup instructions. You'll also find "Welti configuration" and flanking sub setup instructions.

It would be nice to have a link to how to build a relay to auto power on your pro amp...

Thanks for the effort Gorilla. Getting into this stuff can be very intimidating, and it's really nice to have a place to start.

I don't see any mention of Infinite Baffle setups. Sure many would argue that IB is really just sealed, but the newbie to which this is targeted isn't going to understand that. It might at least be worth a mention. That's especially because it seems like it's been getting more popular around here lately. The cult site has a nice FAQ that ThomasW might not mind you linking.

The IB FAQ is here:
http://home.comcast.net/~infinitelybaffled/index.html

I'm not the marketing type, so maybe somebody else can provide a clever blurb to put with it. But if you want a simple description, here's mine.

If you own your space and have the flexibility to make some modifications, you don't have to limit yourself to building a subwoofer that sits in your room. With an infinite baffle subwoofer you make the subwoofer part of your room by installing it into the floor, wall, or ceiling. These type of subwoofers have the best WAF of all, because they can be completely hidden from view. And because the drivers don't have to work against the air spring of a box, you get ultra low distortion and ultra deep bass output for very low cost. Check out the FAQ at the "Cult of the Infinitely Baffled" for more details.

First.... This thread is fantastic! Big Kudos to all those that put this together. It's great to have everything easily accessible for a newbie like me. It makes taking the plunge a lot less scary... : )

One thing I've been looking for though is a good source for in wall designs, or adaptations of designs.... I'm considering doing in wall and an AT screen for my upcoming remodel, but the only good info I've seen is the Zaph 5.2 adaptation for in wall use... Sounds like there are a lot of other good designs out there (I'd like to try the SEOS), but I've had a lot of difficulty finding a good cribb sheet or cliff notes on how to adapt a design for in wall use, or if it's even possible, etc... I'm definitely NOT good at talking speaker (Vas, Qt, etc), but have plenty of skills to build a proven design that someone has shown here...

Are there any good links out there/here for in wall designs? I think that might help a lot of folks to centralize a link to that type of use in the guide, but could be wrong... : )

Thanks everyone!
-j

Jcr159, pm me about my design and a few others I've done off the record.

http://www.diysoundgroup.com/forum/index.php?PHPSESSID=3582d73e0e6df5278d47e8f65d925e83&topic=127.msg1650#new

Thanks for the ping gorilla.

Haven't seen this mentioned yet and it looks like it would fit nicely under the "wiring section" of your consolidated post.

Need an idea of the size of wire you need for your application?

Speaker Wire Size Selector Assistant

*Credit - This post by Bill Fitzmaurice.

Possibly take it with a grain of salt? It's my understanding that 300 circular mills is the industry standard. The higher the "circular mills" the less of a problem one will have with heat. I just did some calculations and it's saying that I need 8 gauge to obtain a minimum of 300 circular mills per amp of current.

Guess my speakerwire might get a little warm, because I'm not running multiple 20ft runs of 8 gauge...lol.

Today I went searching for threads about router bit selection. Is there any way, maybe under the router section, you could add recommendations for manufacturers of quality bits? I found several threads on the subject and thought it may another idea to add to an already very comprehensive FAQ page.