BillFitzmaurice.info

Hey all,

I've spent a few hours combing through the message boards looking for answers, but I still have a few questions. If my questions have already been answered, please forgive me and point me in the right direction.

Drivers -
Is there a list of acceptable drivers/suppliers somewhere?
I know that the plans center on the Goldwood specs, but aside from the odd, stumbled upon, closeout, finding acceptable drivers is like looking for Big foot; everyone say they are out there, but actually finding any is a completely different story.
I also understand that building a BF design using parts other than what is specified renders the finished product something other than a BF design. But, isn't that why we DIY? Take a known design and make it fit our needs, budget, and tastes? No disrespect intended to Mr. Bill as I am impressed and grateful for his placing his work within our grasp.
With the Goldwood drivers either out-of-stock, or priced out of range, I'm on the hunt for something suitable but am turning up with nothing.

Cabinet design -
I've worked as a master carpenter, master model maker, wood worker, technical director... No, I'm not bragging. I enjoy making things and love a good challenge - especially if it makes sawdust. The cabinet plans are a quite simple (I'm not complaining!) but wonder how much the cabinets could be changed without altering their performance.
Here is what I mean: The curved SLA has a faceted panel on which all of the drivers are mounted. Would it be okay to mount the drivers to a curved piece of wood?
Does it matter if the drivers are surface mounted, recessed, or back mounted?

In musical instrument building, the type of wood, it's thickness, grain pattern, etc all affect the sound you hear. Does this ring true with the SLA design?

Do the SLAs prefer to be mounted on a wall or can they be built into a freestanding cabinet? Assuming that the speakers would work best properly aimed at the listener, I'm thinking about incorporating the SLAs into some sort of monolithic speaker stand, or build them into a cabinet?

Lets say that I build my SLAs out of MDF. Will what I cover the MDF with affect the sound? I'm thinking of materials like carbon fiber, copper sheet, stainless steel, engine turned aluminum, colored acrylic, ceramic tile, leather etc. I have not finalized my aesthetic plan yet so I'm just spit-balling ideas.


In the SLA plans it states, "The four midbass version has wider vertical dispersion, making it the better choice for listening distances of six feet or less. The six midbass version is the better choice for listening distances of nine feet or more; either may be used in the six to nine foot range."
I find that a bit confusing.
I'm building a home theater that is 18' x 12'. With the "sweet spot" being at least 4' off of the back-wall, this puts my listening distance at 10 - 14'. Would I notice the difference between the 4 or 6 driver configuration?

7.1 -
Assuming that my main SLAs contain either 4 or 6 drivers, would my 4 surround speakers need to be configured the same way? For many reasons (none if which really consider sonic quality), it seems logical to build surround speakers containing a lesser number of drivers.
I'm planning on building the Table Tuba so, along with that, what would be the best surround/main speaker combination?

Lastly, the center channel design.
It is my understanding that the best center/main set-up is for all three speakers to be identical. In order for best placement, the center speaker should rest behind an acoustically transparent video screen. If I'm going to hide one speaker, I might as well hide all three (center+mains), or even 5 (center+mains+upper 1.1 surrounds). Would doing so negatively affect the "sweet spot"?

I've built a lot of things in my life but speakers has only been a want. I know a little bit about a lot of things but this is a new frontier.

Thanks in advance for you time in reading all of this, as well as your opinions, ideas, and answers.

I will take a stab at a few of these:

There is always a set of acceptable drivers in Bill's plans. HE also lists the critical specs in case you want to use a different driver. If the specs match you are pretty good to go, but the eminence drivers Bill recommends are usually the best route if you can get them.

You could create a "curved piece of wood" but the speaker fronts are not curved and I would be concerned about the mating surface of the speaker not having continuous contact with the wood. You cannot afford air leaks around the speaker gasket, this will result in low-end loss, so a series of flat fronts is better.

As for MDF, it just plain sucks. Yes it is cheap, yes you can glue a surface to it but you are putting vibrating motors into the cabinet and MDF is not as strong in the presence of external forces over time. Things shake loose. God forbid your cabinet gets wet, too. At that point its a pile of dust. I would stay away. Then there is the laminate you put on it. it will also be shaken by vibrations over time and if it starts to peel away you could end up with extra slapping and vibrations you may hear. You don't have to use BB if you cannot find it, but it is the best quality for Bill's designs.

I would go with the 6 driver version, but you could consider the 4 driver version for your center channel since that mostly carries dialogue. The surround channels are even less important to me. I don't agree that the center channel must be placed behind a screen, I find that above or below works pretty well, depending on your room and what is important to you. putting the center channel behind a projection screen does give the illusion that the sound source IS the screen and that is how most movie theaters work, but it is also the most expensive approach.

atdnr wrote:Hey all,

Lastly, the center channel design.
It is my understanding that the best center/main set-up is for all three speakers to be identical. In order for best placement, the center speaker should rest behind an acoustically transparent video screen.

If you're going to use an acoustically transparent screen there's no reason to build the curved center, it exists just to be snuggled up next to a non-transparent screen. It's curved because putting an SLA on its side negatively affects dispersion. You can use a standard SLA in the center with an AT screen.

SLA's with more drivers have tighter dispersion patterns, so if you have a seating position a long way away they'd be preferable. (tighter dispersion = less reflections off ceiling and floor)

[quote="dswpro"]HE also lists the critical specs in case you want to use a different driver."

And that seems to be the problem (for me, at least). I've looked at a lot of different drivers but they all fall short of Bill's min. specs. Either that or they are no longer in stock, a no longer available closeout, etc.

"You could create a "curved piece of wood" but the speaker fronts are not curved"
I would, indeed, seal the driver the curved stock. How? I could recess the driver from the front, or back. Is this the easy route? Hardly, but it's within my realm of skills. What I Don't know is if it will negatively affect the sound.
On that same thought, the plans call for the concave driver board to be recessed thereby creating a rectangular cabinet. I can easily see how this drastically simplifies the construction, but again, would not having this top/bottom around the drivers negatively impact their performance?

MDF - I've used more of this stuff than I care to think about, the same goes for Baltic Birch. Having built many projects for museums, movies, trade shows, etc. out of the stuff, I am fairly familiar with the pros and cons of both.
But, does the cabinet material, it's weight, it's density, it's thickness, (assuming the internal cabinet dimensions remain unaltered) affect the sound? I'm not saying that I'm stuck on MDF, but I'd like to know a bit more about how these materials might affect the sound.

You said, "I would go with the 6 driver version, but you could consider the 4 driver version for your center channel since that mostly carries dialogue. The surround channels are even less important to me."
The "surround sound craze" isn't going away anytime soon and with that, more and more movies/TV shows are adding more and more content to the "extra" channels. I'd hate to cut myself short by skimping on these speakers. Granted, the vast majority is always going to come from in front of you as that's just the way we hear things, abd if money and space wasn't an issue I'd build 7 identical SLAs. So without building 7 "main" speakers, what should be acceptable companions to the the mains, 3? 2? 1? drivers in each?


Center channel design/placement.
If I mount my center channel behind a screen then aesthetics are pretty much unimportant. With it being the workhorse of the system I'll build three main speakers all alike and hide them all.
I still need to make up my mind on this point.

Thank you for your input; I do appreciate it.

[quote="whines"]...It's curved because putting an SLA on its side negatively affects dispersion. You can use a standard SLA in the center with an AT screen.

SLA's with more drivers have tighter dispersion patterns, so if you have a seating position a long way away they'd be preferable. (tighter dispersion = less reflections off ceiling and floor)"


I find the above both interesting and confusing

Logic tells me that a convex horizontal array would be the best design for room coverage but the opposite is true.
I would also assume that fewer drivers would be more effective at lessening room reflections but you say that's not so.

If that's the case (and I'm not arguing with you) then having fewer drivers in the surround speakers seems to make sense as these speakers are most usually used to provide ambient, non-directional, sounds, no?

atdnr wrote: Logic tells me that a convex horizontal array would be the best design for room coverage but the opposite is true.
I would also assume that fewer drivers would be more effective at lessening room reflections but you say that's not so.

Correct. When it comes to acoustics ignore logic, as it's usually wrong. The assumption is made that speakers radiate sound the way lamps radiate light, and they don't.

If that's the case then having fewer drivers in the surround speakers seems to make sense as these speakers are most usually used to provide ambient, non-directional, sounds, no?

Also correct.

In musical instrument building, the type of wood, it's thickness, grain pattern, etc all affect the sound you hear. Does this ring true with the SLA design?

Welcome to the forum

What you say is true for musical instruments.
I have a luthier mate who hand selects timbers from all over the world for his guitars, because he believes that.

Lots of drummers I know argue the benefits of shell construction and grain direction (proposal being that horizontal on the inner and outer plys being better than vertical) in ply constructed shells, but don't for a moment consider a stave shell drum to defy their rationalle (in a stave shell drum the grain is, by default, vertical).
In a random double blind situation, said drummers invariably can't tell what a drum shell is made from purely based on sound/tone. They can qualitively say things like brighter, warmer, deeper etc, but not usually, quantative statments like "that shell is made of maple, or birch or kapur, or mahogany" etc. It's only afterwards, upon discovery of shell material, that people will modify their initial response and say for eg "The maple was best", based on their own personal preference.

All in all, you want musical instruments to resonate to varying degrees, usually for increased sustain.

And some of this thinking has made it's way to speaker cabs, the end result being a statement like "The best sounding speaker cabs are made of BB and are made from 3/4" ply".
All of us here who have built pro sound/auto sound/HT cabs of Bill's designs know this to be nonsense, because they are all built with 1/2" ply (of many varieties), but that can be achieved because of adequate bracing!

What is actually more important in speaker cabs is that they are structurally sound, don't resonate, and are leakproof to air, other than where you might want them to "leak", eg a port.

We often say here, it's the design that dictates response and sound, not so much the driver(s).
However, to guarantee results to a certain standard, the drivers specs are also utilised in the design process (by Bill in this case).
So sure, it's DIY and you could use "anything", but if you use drivers that fall within the specs suppplied in the plans, the results will be better.
In the current case of not being able to source goldwoods, you need to source something as close as possible to those specs, if you want best results.

As much as I personaly dislike MDF for anything, it has been called suitable by Bill for HT use.

The influence of construction material in speaker cabs, in relation to how they sound, is a myth...