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Old 3rd March 2014, 09:55 AM   #1
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Question why ported and why sealed for a given driver?

my question is not about any of the characteristics about box and how it sounds but the driver.

why is it that some sub woofer drivers are suited mainly for ported enclosures while others are mainly for sealed enclosures. i understand that some parameters are the reason but thats not enough for me.

1, why is it that some speakers are suited for ported or sealed? what construction/material mean sealed or ported? why do these things equal one box or the other?

2, how would it effect the sound if a speaker designed for sealed box was placed in a ported box and vice versa? how would it behave? how would it sound differently to what its designed for?

just been thinking about it and every time i try and google the answer all i find is the sealed vs ported debate; which i dont care about.

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Old 3rd March 2014, 10:07 AM   #2
S4m is offline S4m  Germany
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In my opinion the TSP are only to be seen as a tool to simulate a possible good working cabinet. You also can try different types of cabinets and decide by your hearing or measurements. Don' take these parameters and resulting cabinets too strict/serious!
They are only meant as an iteration...
And it is much easier to calculate with them than building several enclosures
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Old 3rd March 2014, 09:21 PM   #3
rigtec is offline rigtec  United States
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Quote:
Originally Posted by ubza1234 View Post
my question is not about any of the characteristics about box and how it sounds but the driver.

why is it that some sub woofer drivers are suited mainly for ported enclosures while others are mainly for sealed enclosures. i understand that some parameters are the reason but thats not enough for me.

1, why is it that some speakers are suited for ported or sealed? what construction/material mean sealed or ported? why do these things equal one box or the other?

2, how would it effect the sound if a speaker designed for sealed box was placed in a ported box and vice versa? how would it behave? how would it sound differently to what its designed for?

just been thinking about it and every time i try and google the answer all i find is the sealed vs ported debate; which i dont care about.

go!
Hi ubza'

I think the greatest tool used to help me to understand some of these things was the reading. I was a young (now old), "up and coming" fender bass player back in the seventies/eighties... and needed to better understand the problems associated with "Live bass reproduction" e.g., my guitar player uses a 50 watt "Fender Twin Reverb" amp w/two 12 inch speakers, and I'm using a 120 watt "Ampeg BT-25L" w/TWO, 2x15 inch (Altec Lansing) cabinets, and I'm being drowned out!!

So I started to read everything available (no internet) on the subject of bass reproduction. Imho, it's not enough to understand why one driver will work and not the other but rather, what are the rules that all drivers must follow, giving you a more through understanding. PS: you seemed really determined to understand these things (much like myself), hence the little personal background; no offense I hope...

Here's a really good "Pro-sound audio" book that I studied from a while back from Hal Leonard publishing; only $25 bucks: Live Sound Reinforcement (Mix Pro Audio Series): Scott Hunter Stark: 9780918371072: Amazon.com: Books An "EXCELLENT" read, and must have in any audio aficionado's library, enjoy!

rigtec, best regards
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Old 3rd March 2014, 09:37 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

There are speakers that can only be sensibly used sealed.
There are speaker that can be used for either option.
There are speakers that are sensibly only used vented.

All can be used sealed, if fact all can be stuck in whatever
you like, but you may not like the result in a poor choice.

Any driver with a Qts of 0.6 or more = sealed.

Speakers of around Qts = 0.4 can be used for either.

A speaker of Qts = 0.5 is more suited to sealed.

A speaker of Qts = 0.3 is more suited to vented.

A speaker of Qts = 0.2 for bass really needs vented.

A speaker that should be used sealed vented ? A one note peaking boom box.
(For some that are marginal you end up needing huge boxes for good sound.)

A speaker that should be used vented sealed ? Very tight but very drooping bass.
(You can make the bass flat in a very small box, but you lose all the low bass.)

rgds, sreten.
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Last edited by sreten; 3rd March 2014 at 09:48 PM.
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Old 4th March 2014, 12:33 AM   #5
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awesome, thanks guys so far, really helping me out and I really appreciate it. definitely going to check out that book rigtec. sounds interesting.

sreten,

you are so close to answering my question, but I feel I really need to understand TSP before understand WHY the qts dictates what type of box it would perform best in. I sorta get the various qt x parameters but not enough to see the relation to box design and general performance.

any where I can go to get some easy to understand explanations on thielle small parameters? allot I've read just give 1 sentence answers just aren't quite enough for me..

Last edited by ubza1234; 4th March 2014 at 12:52 AM.
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Old 4th March 2014, 01:09 AM   #6
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by ubza1234 View Post
WHY the qts dictates what type of box it would perform best in. I sorta get the various qt x parameters but not enough to see the relation to box design and general performance..
You have to think of (1) what a Qts is (2) what performance expected (3) how things correlate.

A musical signal will push the cone and this cone should not just jump out but there should be spring mechanism to hold it in place. Mechanics such as spider contribute to Qms, magnet flux holding the coil I think to Qes (I might be wrong, not essential). Total Qms and Qes is Qts. Now the spring mechanism is not built from Qts only but also the air behind the cone or inside the box. Push the cone in a sealed box, there will be air pressure holding the cone and after you release your hand the cone will go back with certain "energy". Compare this to a sealed box of different volume, and compare also to vented box.

The quality of bass box is not only lowest frequency to be produced, but it must be flat etc. We want sufficiently "damped" system, not under not over. If the driver originally under damped (due to small magnet for example), we can use air behind the cone (hence sealed) to increase or make it sufficiently damped.

Last edited by Jay; 4th March 2014 at 01:12 AM.
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Old 4th March 2014, 01:16 AM   #7
rigtec is offline rigtec  United States
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Quote:
Originally Posted by ubza1234 View Post
"...any where I can go to get some easy to understand explanations on thielle small parameters? allot I've read just give 1 sentence answers just aren't quite enough for me..
ubza'

Takes years to begin to understand acoustic theory/engineering/physics. This is why no "one answered question" will satisfy your quest for this knowledge. Would anyone go to school for, four, five, six, or ten years, just to learn about some speakers if they could figure it out themselves... hahahaha! And then there's the tuition $$$$$! Think about it...

This is not to say that "I have arrived" (nor has anyone else that I know??!) But this is part of the fun, there is always more to learn; even Einstein was still learning when he died. ubza... take your time(!) what's the rush(?), we are all here still learning, so relax, read, think, enjoy!!!!!

riggy
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Old 4th March 2014, 01:36 AM   #8
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I hope this helps. To add to what the others have said, the Q of the driver is the inability to return to rest. The higher the number, the more it will flop back and forth before stopping. Therefore a high Q driver likes to be in a sealed box as the air inside acts as a spring and being sealed it helps to damp the woofer and bring it to rest.
A low Q woofer comes to rest sooner and therefore, the venting of the box allows for the sound inside to be used outside of the box. If it wasn't vented it would seem like the bass it too 'tight', or simply not enough.
This is very simplistic and doesn't tell the whole story but hopefully it helps a little.
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Old 4th March 2014, 01:36 AM   #9
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Maybe another way to look at it is that some drivers are optimized for a box that will aid in the damping of the cone (sealed box) and other drivers don't need much if any damping to work well (ported box). It's about cone compliance, if I'm not mistaken.

Personally, I prefer closed box woofers because the box can be smaller, and it works much better when you use active EQ (ahead of the poweramps) to force the woofer to be acoustically flat down to 20 or 30 HZ (which I do). Closed box is slightly less efficient, so pretty rare in large scale PA systems where efficiency is a higher priority than low bass extension. With active EQ and a sealed box, I suspect that you could use a driver with any Qts and get very good results. Using a high Qts driver in a ported box on the other hand might be pretty bad (ringy).

Last edited by Bob Richards; 4th March 2014 at 01:42 AM.
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Old 4th March 2014, 02:26 AM   #10
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heck yeah! I get it! basically, some speakers rely on the box to center the speaker, and only a sealed box will do as the internal pressures are high then a vented box.

some speakers are stiff enough to to more or less center them selves and you can get away with a ported box.

does that sound about right?

thanks everyone, especially rigtec who I thinks a bit like me, and Cal Weldon for using words like "flop" that really helped me out. XD

does that mean that in general a high qms (I know we where talking about was before but.. ) would mean a more sensitive driver?
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