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[quote="William from NOLA"]What audiobass10 was referring originally to is the fact the actual driver impedance rises as cross bracing is added (or turbulence rather).

That is how you find an amp, after total driver impedance is reached at the burp frequency. Look for an amp that is capable of supplying the maximum power recommended for the sub, at the given impedance. The amp may have to be wired for a .5 ohm load, even though it is only stable at 2 ohms (say you may have measured 2.3 ohms, then you would only use that amp at that frequency).[/quote]

yeppers..

or wait, are you saying more impedence rise is a result of the turbulence caused by bracing?

What audiobass10 was referring originally to is the fact the actual driver impedance rises as cross bracing is added (or turbulence rather).

That is how you find an amp, after total driver impedance is reached at the burp frequency. Look for an amp that is capable of supplying the maximum power recommended for the sub, at the given impedance. The amp may have to be wired for a .5 ohm load, even though it is only stable at 2 ohms (say you may have measured 2.3 ohms, then you would only use that amp at that frequency).

[quote="audiobass10"]And I stand corrected. I guess this is where the fact that nominal impedance means nothing when choosing an amp comes in, as far as SPL goes?[/quote]

on da nose :)

[quote="spkrman"]that is FAR from true.

impedence may go up, but so does effeciancy... you just need to choose amps accordingly.[/quote]

And I stand corrected. I guess this is where the fact that nominal impedance means nothing when choosing an amp comes in, as far as SPL goes?

"impedence may go up, but so does effeciancy"

very very true.
sorta funny the way that works.

the enclosure flexes, and you're losing energy that would otherwise translate into sound. it's decreasing output.

as for turbulance, if you're talking about a ported enclosure, turbulance increases volumetric flow. laminar flow will or at least can, hinder volumetric flow through the ports, which in turn can reduce or restrict air flow.

yes I've built a lot of SPL enclosures. Anybody is bound to after over a decade of doing this for a living. if all you're concerned with is SPL and SPL only, then impedance isn't going to vary since you're going to tune the box for one specific frequency, at a quarter wave-length to the dash.

[quote="audiobass10"]"Bracing a box for a sub that's high output is always beneficial. It improves efficiency which translates to higher SPL and better sound quality from the enclosure with less cabinet flex."

Kiki, i'm gunna disagree on this one. A "stiff" enclosure will actually cause impedance rise, which is never good in an SPL install. Any type of interior bracing is BAD in an SPL install.[/quote]

that is FAR from true.

impedence may go up, but so does effeciancy... you just need to choose amps accordingly.

"Bracing a box for a sub that's high output is always beneficial. It improves efficiency which translates to higher SPL and better sound quality from the enclosure with less cabinet flex."

Kiki, i'm gunna disagree on this one. A "stiff" enclosure will actually cause impedance rise, which is never good in an SPL install. Any type of interior bracing is BAD in an SPL install.

[quote="KikiTheCat"][url]http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=18797&item=5771339413&rd=1&ssPageName=WDVW[/url]

saw a couple others earlier but price went over 200 already.

The SX isn't designed to be a SQ sub. It's general purpose to SPL oriented.
[/quote]

So, the 2500d is not "200 bux" on ebay.

The SX sounds fine to most people.

[quote]
Bracing a box for a sub that's high output is always beneficial. It improves efficiency which translates to higher SPL and better sound quality from the enclosure with less cabinet flex.
[/quote]

You have not competed in SPL I see.

Bracing causes turbulence... which is bad. If you need a stronger box double up the wood on the outside. Any gain you get from bracing is thwarted by turbulence in all but the weakest of boxes.

[quote]
If you want to stick a 120 pounts of subs into a single piece of 3/4" MDF you be my guest, but for a pair of XXX 12" subs, 12W7, 13W7, etc subs, I always reinforce the front panel of teh enclosure to support the weight. I've seen boxes where people didn't, and paid for their foolishness the hard way.
I've been doing this for a little while. I know what I'm doing.
[/quote]

I have also been doing this for a little while, and I also know what I'm doing.

If your baffle isn't large you dont need to double it up with ANY amount of weight on it. An example of this would be a 12" wide baffle with a 12" woofer mounted to it.

I've been there done that... and double baffle has its uses, but its not ALWAYS needed.

[quote]
However, speaker size is a good general method for guessing efficiency.
[/quote]

In what way?

[quote]
Keep in mind that when considering subwoofers, or any speaker that will get more than ~100 watts RMS of power, these measurements are affected by other factors that make this specification less than useful when choosing between speakers.
[/quote]

Not "any" speaker with greater than 100 watts of power.

The "SPL" rating of a speaker is generally useless period.

[quote]
The Efficiency of the XXX isn't going to mean the speaker won't put a tremendous amount of force on the enclosure it's in. Especially considering anybody with a XXX should be giving it at least 1Kw of power to begin with. I've seen weaker subs in poorly built enclosures destroy the box during high excursion due to exerted pressures.
why take the chance with a cheap box by cutting corners?[/quote]

I've got an idea.

I'll drop a 12" XXX into my current SPL box (single baffle) and throw 2500 watts at it. If it blows up the box, I'll let you know, when it doesnt, i'll let you know. I will be doing this anyway this weekend.

Right now, with the single type R... it has had 100's of burps at 149+db... perhaps one that was just 150+db, but it knocked the power cord for the computer out of the wall before it got a full reading... also knocked over a few boxes in the garage.

And no, the box hasnt fallen apart...

Its not cutting corners, its called building the box properly.

[url]http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=18797&item=5771339413&rd=1&ssPageName=WDVW[/url]

saw a couple others earlier but price went over 200 already.

The SX isn't designed to be a SQ sub. It's general purpose to SPL oriented.

Bracing a box for a sub that's high output is always beneficial. It improves efficiency which translates to higher SPL and better sound quality from the enclosure with less cabinet flex.

If you want to stick a 120 pounts of subs into a single piece of 3/4" MDF you be my guest, but for a pair of XXX 12" subs, 12W7, 13W7, etc subs, I always reinforce the front panel of teh enclosure to support the weight. I've seen boxes where people didn't, and paid for their foolishness the hard way.
I've been doing this for a little while. I know what I'm doing.

"Sensitivity," which is expressed in dB, should not be confused with "efficiency" that is expressed as a percentage of power out relative to power in. Efficiency data for loudspeakers suffers from many problems such as failure to consider variations in frequency response.

Speaker efficiency is the ability of the speaker to do work or use power. The more efficient the speaker; the less power is required for the speaker to produce sound. Voice coil design, type and size of the magnets, speaker cone design and material, speaker size, etc. all play a critical role in determining speaker efficiency. However, speaker size is a good general method for guessing efficiency.

Typical speaker efficiency (for physicists) is about 5%. Meaning that for 100% power input, you get about 5% acoustical work back.

Keep in mind that when considering subwoofers, or any speaker that will get more than ~100 watts RMS of power, these measurements are affected by other factors that make this specification less than useful when choosing between speakers.

The Efficiency of the XXX isn't going to mean the speaker won't put a tremendous amount of force on the enclosure it's in. Especially considering anybody with a XXX should be giving it at least 1Kw of power to begin with. I've seen weaker subs in poorly built enclosures destroy the box during high excursion due to exerted pressures.
why take the chance with a cheap box by cutting corners?