PRO Woofer Mounting Technique ?

[Scott L]

I'm in a design process quandry here. I'm using the Eminence 12" HO4012, or some such model number unit, and the neat thing about it, is, it has the option of either front or rear mounting, as there are gaskets on either side.
In the past I had always done rear (of the baffle) mounting, mostly because there was always this thick gasket I wanted pressed tight against the baffle board, AND along with that, the rear of the driver sees full space potential. In other words, there are no physical obstructions to the rear wave.
Here's where the quandry mix comes in: I'd like to use the new(er?) black threaded bolts that PE offers, but, only the ones with the plastic clamps come with any length long enough to extend through both the thickness of the cast woofer frame, and a measly 3/4" baffle board. The intended enclosure volume is 1.85 ft^3 gross, so, for the most part, I am thinking 3/4" MDF is sufficient enclosure material (?)
I guess what I am really asking here, is how do some of you guys tackle this situation? I'd especially like to hear from BFM, as he does this sort of thing for a living, thus, he gets my nod for a "true source" of knowledge. Thanks to anyone, though, for their willingness to share your techniques.

[billfitzmaurice]

The mounting technique is usually defined by the cabinet design.
I am thinking 3/4" MDF is sufficient enclosure material (?)Why? Pro-sound cabs don't use MDF. Well designed pro-sound cabs don't use 3/4" material, 1/2" is all one needs.

AND along with that, the rear of the driver sees full space potential. In other words, there are no physical obstructions to the rear wave.You completely lost me with that one. 'Physical obstructions' must be at least a full wavelength in dimension, otherwise they are acoustically invisible.

[Paul O]

What are these "Black Threaded Bolts" you refer to? By definition any bolt has threads on it so your description leaves the door wide open.

I use t-nuts and whatever length bolt is required to mount heavy pro drivers, and I typically mount the driver on the front of the baffle or recess it flush with the front of the baffle.



http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-779

[Scott L]

Greetings to both Paul and Bill:

The black threaded bolts are from PE part #260-340. The bolts are 2" although it does not tell you that in the decription. I don't need the clamps.
I'll recycle them.

On the Eminence Definimax4012HO: It's cast frame unit whereby the little aperatures for the rear of the cone to vent thru are approx 2.5"x2.5"
That equals 6.25in^2 each times eight of them=50 inches squared for an SD of 85 to exit thru. So.... it already exists that it's restricted. Maybe it was engineered that way on purpose(?). If I were to front mount these things, that would further introduce obstructions. No matter... I have since slept on this predicament and have arrived at this solution. The baffle board is going to be 3/4" MDF + 3/4" birch ply. The drivers are to be rear mounted against the front board which is the birch ply. The MDF will be cut to fit around the O.D. of the woofer frame; flush with the rear if you will. Most of the final enclsure will be dbl wall thickness MDF+ Birch ply. At 1.85 cu ft, that should be sufficient for me to NOT HEAR THE BOX. This is part of a massive music playback system, 2 channel audio only, and is the only box part of it all. Today, I need to build a 1 ft^3 test box volume to check the Vas, as this enclosure's dimensions are so small, I am having trouble fitting all this together (ports, etc.) to fit. That's both good and bad, but proper enclosure size is tantamount to this design. Once again, thank God I don't have to worry about group delay, and my acceptance into the lollipop audiophile club.
I'll post pictures in due time. You know the old saying about 1000 words.

[billfitzmaurice]

On the Eminence Definimax4012HO: It's cast frame unit whereby the little aperatures for the rear of the cone to vent thru are approx 2.5"x2.5"
That equals 6.25in^2 each times eight of them=50 inches squared for an SD of 85 to exit thru. So.... it already exists that it's restricted. Maybe it was engineered that way on purpose(?). If I were to front mount these things, that would further introduce obstructions. No matter... No matter is the correct answer. If your theory was correct then ports would have to be the same area as the cone. But that was once accepted practice, like 50 years ago, so your error is understandable.
The baffle board is going to be 3/4" MDF + 3/4" birch ply.Silly, unless your intent is to use the cab for sound reproduction and as practice for Power Lifting competition. :rolleyes:
Not to be condescending, but these are not errors that would be made by someone with the necessary knowledge to design their own enclosures. IMHO you need to do quite a bit more research before you reach that point.

[Scott L]

No matter is the correct answer. If your theory was correct then ports would have to be the same area as the cone. But that was once accepted practice, like 50 years ago, so your error is understandable. Silly, unless your intent is to use the cab for sound reproduction and as practice for Power Lifting competition. :rolleyes:
Not to be condescending, but these are not errors that would be made by someone with the necessary knowledge to design their own enclosures. IMHO you need to do quite a bit more research before you reach that point.

These aren't for sale. These are for me, and YES I do intend to use these for sound reproduction. I have made no errors, in fact I have thought this through. Port area has also been calculated to avoid power compression. Not only that, but, the port frequency is below the operating passband.
The research I intend to do today is to measure the T/S parameters myself.
I have only been doing this for 38 years. The FACT I noticed the aperatures from the rear cone exit is proof of paying attention to details. There's nothing erroneous about mounting this model woofer from the rear of the baffle. Anyone can do their own as they please. The last time I checked I still lived in the USA. I think I have had just about enough of this forum.

[Paul O]

Scott why so defensive? Pro sound reproduction was a well travelled road long before Bill or I came along, everything has been tried and those things that work are well established. MDF is generally not used by the major manufacturers because it makes the enclosure unnecessarally heavy, an 18" reflex sub for example typically only weighs about 75lbs and 12" fullrange speakers are often in the 30lb range with composite cabinets or maybe a bit closer to 45lbs when wood is used. Lighter is better when it's something that going to be lifted a lot.

[billfitzmaurice]

Anyone can do their own as they please.Quite so. And obviously you intend to do so come whatever. But if you have no interest in taking advise from those who actually know what they're doing you should save everyone's time and not ask for any in the first place.

[meep]

I built 4.5' tall scoops (rear horn loaded 12's) for PA use. They had a warmth and impact that couldn't be easily matched. They used particle board, were heavy as all get-out, but remarkably efficient. As nice as they sounded, I hated gigging with them. Too dam* heavy.

5 years later, I built a pair of cabs based on 1/4" and 3/8" ply, with substantial ribbing and fiberglass inside and out. Extremely light. I think the baffle was reinforced at the woofer-- 1/4" + 3/8" laminated together to support a selenium 12". One-hand carry. sounded good, cab didn't resonate, and nobody complained about unloading them and sticking them on a pole. I gigged 3-4x per month.

my $0.02.

Meep

[badman]

'Physical obstructions' must be at least a full wavelength in dimension, otherwise they are acoustically invisible.

Not at all accurate.

[billfitzmaurice]

Not at all accurate.

Read section 1-5:
http://www.jblpro.com/pub/manuals/pssdm_1.pdf

However, only after the OP clarified what his reasons were for wanting to rear mount the driver rather than front mount it did it become clear that his question wasn't related to diffraction but rather to Bernoulli's Principle.

[badman]

Read section 1-5:
http://www.jblpro.com/pub/manuals/pssdm_1.pdf

However, only after the OP clarified what his reasons were for wanting to rear mount the driver rather than front mount it did it become clear that his question wasn't related to diffraction but rather to Bernoulli's Principle.

Large and small WRT wavelength I can agree with, however, a full wavelength is much larger than is needed to be a significant obstacle. A TL is usually only a quarter wavelength and boy does that give us some significant results. Indeed, you only need to do a quarter wave to make a significant difference (3dB+) in wavefront summation, and much less if you lower the threshold from 3dB of interference to 1.

It's not complicated to test either. Hold your hand in front of an 8" driver playing 500Hz. That's a 2 1/4 ft wavelenth, much larger than your hand. Funny how it's very easily obstructed.

[billfitzmaurice]

It's not complicated to test either. Hold your hand in front of an 8" driver playing 500Hz. That's a 2 1/4 ft wavelenth, much larger than your hand. Funny how it's very easily obstructed.That assumes you're hearing a pure 500 Hz tone with no harmonics. That assumption is incorrect. Even laboratory grade gear is incapable of delivering that, as all drivers create harmonics of the fundamental signal. What your hand is obstructing is those harmonics. Bringing up quarter-wavelength resonance is totally off the wall, so you might want to do a bit more book learnin' before taking on trollish behavior with someone who is an acoustical engineer by profession.

[badman]

That assumes you're hearing a pure 500 Hz tone with no harmonics. That assumption is incorrect. Even laboratory grade gear is incapable of delivering that, as all drivers create harmonics of the fundamental signal. What your hand is obstructing is those harmonics. Bringing up quarter-wavelength resonance is totally off the wall, so you might want to do a bit more book learnin' before taking on trollish behavior with someone who is an acoustical engineer by profession.

You're simply wrong. TLs were just an example of less than a full wavelength being necessary for an effect, naturally it's not 100% applicable here. If sound merely went around an obstacle less than a wavelength, your horns wouldn't work. And your statement about distortion is ludicrous. There's no reason this test would need to be performed at such a level as to have audible distortion components. Additionally, if there weren't significant diffraction taking place at less than full wavelengths, you wouldn't see impedance ripple low in frequency when you place a small object near the driver.

Here's the effect of a 1/8" proud tweeter flange relative to flush mounted from Zaph http://zaphaudio.com/mtg-surface.html. http://zaphaudio.com/mtg-surface-tw-.12.gif.

Quick: What is 1 wavelength at 1/8"?

Don't tout your "profession" to me, when you make such foolish mistakes. Here's another example of you being plain wrong since you're being insulting:

http://techtalk.parts-express.com/showpost.php?p=1598544&postcount=11

[billfitzmaurice]

You're simply wrong.
And you are a troll, to be ignored.

[badman]

And you are a troll, to be ignored.

Indeed. You can't debate the matter at hand so you insult. Easier than attempting to defend a provably false position.