Convince me I need bracing for a Mid Q Tempest box........ (1 Viewer)

[Mike Allen]

I'm about to start putting together a sealed Mid Q Tempest box tomorrow. The box is a perfect 21-1/2" cube made of 3/4" MDF.

I've built a number of boxes for car audio subs about this same size, for subs that are running up to 1200 watts with a LOT(20mm+) of xmax. I have NEVER had an issue with boxes flexing. I would almost guarantee that I could put 200-300 pounds on top of these size boxes without any flex.

So can anyone convince me that I really need to go to the trouble to brace this box like is blueprinted in Adires plans? It's the second box on this page http://www.adireaudio.com/Files/Seal...plications.PDF

I would MAYBE agree that it needs bracing if I was running 600-1000 watts. But I'm only going to be using a PE 250 watt amp.

And let's just say there would be a little flex. What effect is this actually going to have on the performance or sound of the sub? I'd think the cone/surround would blow off the sub before I had any significant flexing.

Any thoughts on this? Thanks

 

[TimForman]

Me thinks there are other issues than flexing. Bracing will lower the resonance of the cabinet by increasing the mass. Added mass also means added weight which is desirable when dealing with subs. Also, don't think that "only" 250 watts will not get a lot of movement out of the Tempest. 120 watts can get it to full excursion.

 

[Mike Allen]

Bracing will lower the resonance of the cabinet by increasing the mass. Added mass also means added weight which is desirable when dealing with subs.

Okay, I can go for that. But in a box this small how much added mass is really needed? It's pretty small and will weigh quite a lot already. I'm going to shorten the 21.5" cube to a 20" cube to account for the extra room that won't be occupied by the bracing. So internal dimensions will be a 18.5" cube.

I guess a better question would be......

In a box this small(widest span of MDF is 18.5"), will any resonance be noticeable to a non-audiophile like myself? Would a side-by-side comparison of this size box with bracing and a box without bracing provide any noticeable difference?

 

[Vince Bray]

Generally bracing will raise the frequency of the panel resonance. A smaller panel resonates at a higher pitch, which is good, since you get the panel resonant frequencies above the useful limit of the sub. You should always brace every enclosure where you have room internall to do so. It never hurts unless you encroach the area needed for drivers, crossovers, etc.

 

[ThomasW]

So can anyone convince me that I really need to go to the trouble to brace this box.....

Convince you? Sure no problem.

Build the box and leave out the bracing. Then play a 20Hz test tone. Place your hand on the cab and feel vibrations. All those vibrations are decreasing the quality and quantity of the bass

 

[Mike Allen]

Convince you? Sure no problem.

Build the box and leave out the bracing. Then play a 20Hz test tone. Place your hand on the cab and feel vibrations. All those vibrations are decreasing the quality and quantity of the bass

Already beat you to it The whole reason I'm asking is because I get no vibration in a box this small. I have a box in my car that has a 18" span of unbraced MDF. It has a 12" sub in it that has an xmax of 25mm with 500 watts on it. The only thing that DOESN'T vibrate in my car is the box. I just went out and played a 10-40Hz sweep for the fun of it and I could feel almost zero vibration on the box, but the rest of the car was shaking very bad. You aren't going to convince me like this, because this is exactly why I'm NOT convinced

So, if I braced the box in my car I would hear a night and day difference? Also, are you saying that it's only an issue in the 20Hz range?



Maybe I'm just ignorant and unconvincible?

 

[Dan Hine]

Maybe I'm just ignorant and unconvincible?

Probably.

So how about this for convincing you...and I honestly don't mean this as a slight against you...

"Because ThomasW as well as the folks from Adire know A LOT more about this sort of thing than you do."

 

[Mike Allen]

So how about this for convincing you...and I honestly don't mean this as a slight against you...

"Because ThomasW as well as the folks from Adire know A LOT more about this sort of thing than you do."

You aren't telling me something I don't know I'm sure 99% of the people on this forum, including you, know more about it than me. And I don't deny that you are all right. All I'm asking for, is for one of you brilliantly minded people to simply describe the difference I'm going to hear from a box this sized(braced vs unbraced), and how subtle or extreme that diffence is. Sorry if I don't accept "because that's how it's supposed to be" as a fact carved in stone. Maybe I should just build my box out of stone and brace it with titanium, and then brace it some more. Would I hear a difference though?

 

[Craig Woodhall]

you're the guy that has to live with the box. what do i care if you brace it or not and why would i waste my time trying to convince you of it?

i personally would go the stone/titanium route myself!

 

[Vince Bray]

Will I ever be playing a movie/music....and say, "I really wish I would have braced this box because the resonant frequency is really effecting the prestine sound of my new sub?" Is this a NIGHT AND DAY difference??....Or the kind of difference people claim to hear with their new $1000 cable? What exactly is the diffence that I will hear?

No you won't. No it isn't. Don't know. You won't. The problem is that the 500 watts in your car has left you deaf and devoid of reason Welcome to manhood.

 

[AjayM]

What's the difference between a cheap store bought sub and an expensive store bought sub? One of them is the enclosure.

Why do you think manufactures go out of the way to use materials even more dense than wood, despite them being a HUGE pain in the butt to work with?

Why does everybody who knows something about subs and the construction of them recommend lots of bracing?

So will it be a night and day difference? Only you can answer that depending on what you are looking for. There are people here who can no doubt hear the difference between a well built sub enclosure and one that isn't. Are you that critical, or do you just want it to make a lot of noise regardless of how good or bad that noise is?

Andrew

 

[ThomasW]

Sorry if I don't accept "because that's how it's supposed to be" as a fact carved in stone. ... Would I hear a difference though?

Gee I guess you won't know until you build a 'flexible flyer' and compare it to one that has adequate bracing.

BTW It's not the job or responsibility of anyone here to 'convince' you of anything. Freedom of choice gives you the opportunity to build anything, anyway you want, and then live with the consequences of that decision.

Good luck
Thomas

 

[Ronnie Ferrell]

Mike,

Email Dan at Adire and ask him the question about the difference in sound. He is going to be the one most likely to have actually heard the midQ cabinet braced or not when he was designing it. Personally I braced mine from the start and it did not even enter my mind to not do it. Frankly I don't see why it should have. I already had the MDF. All it took was a few passes on the table saw, a few min. with the jigsaw, slapped on some glue and it was done.

But if you want to save the 4 buck and 30 min. of time then by all means, don't brace it.


Ronnie

 

[DanWiggins]

Brace it. It will sound better. When a panel vibrates, it generates audio. You use bracing to stiffen the panel, making it more resistant to flexing at lower freqencies.

An 18.5" square panel has around 3X the surface area of a Tempest. You'll have 3 of those panels (top and sides) free to vibrate (assuming the rear panel has an amp placed in it), so your box has 9X the surface area of your Tempest to generate audio. So if your box moves just 0.5mm (about half the thickness of your fingernail), it's equivalent to your Tempest moving 4.5mm. Of course, it's also out of phase with the output of the Tempest, meaning it's REDUCING the output... And it can be a measurable amount too, in the 5-10% range of things.

Pure and simple - use bracing. And if you don't want to use bracing, you don't get to save 1.5" like you're expecting; those panels are more than 60% open from the perforations. You save around 0.5" of width instead.

So ask yourself: is it worth saving 0.5" in width, and $5 in MDF, to have my box unbraced? Personally, if I was buying a Corvette, I wouldn't argue that the tires Chevy includes are too sticky/high speed rated for the 'vette, just because in the past I've never driven that fast...

Dan Wiggins
Adire Audio

 

[Frank Carter]

I'm convinced.

 

[Craig Woodhall]

hehe! me too.

 

[Mike SJ]

ditto

 

[Mike Allen]

Dan,
Thanks for the actual technical explanation. That's all I was asking for You HAVE convinced me and I'll brace it according to your design. Thanks again for the professional reply. And thanks to the one or two other people who tried to help.

To the others who just wanted to give me some smart-*ss remark without taking the time or having the knowledge to actually explain things to me....whatever. I see no reason why I don't have the right to know something if I want to know it. If you don't want to waste your time convincing me, then please don't waste your time trying to insult me or posting something that doesn't help me. Some people just do things because that's the way it's supposed to be, and some people want to know why they have to do something before they do it. I now realize that's a crime and won't ask such questions here anymore.

Have a groovy day everyone

 

[Brian Tatnall]

Maybe people wouldn't give you flippant remarks if the title of your thread didn't have such an egotistical twist to it. I don't think it is the fact you wanted to know why, but how you wanted to know why. My .02

Lot's of people ask questions about how things work everyday on this forum. It isn't a crime. As a matter of fact that is much of why this forum exists. To help people and make them informed buyers or DIY people.

Glad to see you got your answer.

Yet again another case where one of our five sensations 'touch' leads us astray. My ears are two easily decieved by my brain and I can hardly feel my box causing me to losing 4.5mm of excursion. People aren't designed to be very accurate.

 

[TimForman]

Maybe people wouldn't give you flippant remarks if the title of your thread didn't have such an egotistical twist to it.

On other forums Mike's question would have been considered nicely phrased. Here on HTF the members are accustomed to a certain decorum. I would suggest treating newer members in a kinder fashion, drawing them in, rather than thumping them. I recall a young man visiting this forum for the first time who needed considerable direction on use of expletives. Mike hasn't come close to that.