About the woofer:Passive Radiator or Double Woofer for Vetend - diyAudio
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Old 28th December 2010, 05:59 PM   #1
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Default About the woofer:Passive Radiator or Double Woofer for Vetend

In a 3-way design. If I would like to use 7" woofer.
The following two choices:

I. 7" woofer + 7" Passive Radiator

II. The two same 7" woofers are shunted in Vented box

I have known that using a passive radiator is another kind of vented.

So, what are the pros an cons of the two choices? (If the cost just a little different)

Thanks for your help !
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Old 28th December 2010, 06:08 PM   #2
sreten is offline sreten  United Kingdom
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Hi, II needs a twice as big box as I, its also 1/2 impedance, rgds, sreten.

You cannot use a woofer + PR in a vented box, the PR is the vent.
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Old 28th December 2010, 06:18 PM   #3
TerryO is offline TerryO  United States
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Quote:
Originally Posted by kevinlin1013 View Post
In a 3-way design. If I would like to use 7" woofer.
The following two choices:

I. 7" woofer + 7" Passive Radiator

II. The two same 7" woofers are shunted in Vented box

I have known that using a passive radiator is another kind of vented.

So, what are the pros an cons of the two choices? (If the cost just a little different)

Thanks for your help !
Kevinlin,

First off one 7 inch passive radiator probably isn't going to be enough. The general rule of thumb is to use 1.5 to 2 times the area of the woofer for your passive. So two 7 inch PRs would be good, but you can calculate to find what size you'd need for a single PR. My inclination would be to use two PRs on opposing sides of the cabinet to have a better balance of force when the PRs are at work.

Using two woofers will allow you to use a .5 setup for bafflestep correction without loss of overall efficiency which, with a single driver would be around 3-4 dB overall. It also needs an additional inductor for the second woofer and depending on the frequency of the baffle step these can get fairly pricey.

It's all about compromises and calculations.
Good luck on your project!


Best Regards,
TerryO
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Old 28th December 2010, 07:06 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

The general rule is the PR needs 2 x Vd of the driver, its not size related always.
A good PR can be designed for a similar sized driver, its all in the finer details.

rgds, sreten.
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Old 29th December 2010, 02:04 AM   #5
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Quote:
Originally Posted by sreten View Post
Hi, II needs a twice as big box as I, its also 1/2 impedance, rgds, sreten.

You cannot use a woofer + PR in a vented box, the PR is the vent.

Sorry for my poor expression.

I knew the PR is the vent.
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Old 29th December 2010, 02:10 AM   #6
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Thanks for your imformation.
Very useful!

If using the doubble woofers , will there be a new issue
3 way(The two shunted woofers) or 3.5way design?




Quote:
Originally Posted by TerryO View Post
Kevinlin,

First off one 7 inch passive radiator probably isn't going to be enough. The general rule of thumb is to use 1.5 to 2 times the area of the woofer for your passive. So two 7 inch PRs would be good, but you can calculate to find what size you'd need for a single PR. My inclination would be to use two PRs on opposing sides of the cabinet to have a better balance of force when the PRs are at work.

Using two woofers will allow you to use a .5 setup for bafflestep correction without loss of overall efficiency which, with a single driver would be around 3-4 dB overall. It also needs an additional inductor for the second woofer and depending on the frequency of the baffle step these can get fairly pricey.

It's all about compromises and calculations.
Good luck on your project!


Best Regards,
TerryO
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Old 29th December 2010, 02:12 AM   #7
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Quote:
Originally Posted by sreten View Post
Hi,

The general rule is the PR needs 2 x Vd of the driver, its not size related always.
A good PR can be designed for a similar sized driver, its all in the finer details.

rgds, sreten.
Thank you! Take it into my notebook.

Always learning lots of things on Diyaudio.
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Old 29th December 2010, 05:56 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

With double woofers and PR's (though its likely a vent will do the job),
a 3 way or 3.5 way depends on the bass mid c/o point, for a high
point 3.5 way is possible, for a low point it will be a 3 way with
some other arrangement to deal with the midrange baffle step.

e.g. a high point 3.5 way : Zaph|Audio - ZDT3.5

rgds, sreten.
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Old 12th January 2011, 07:13 PM   #9
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Quote:
Originally Posted by kevinlin1013 View Post
In a 3-way design. If I would like to use 7" woofer.
The following two choices:
I. 7" woofer + 7" Passive Radiator
II. The two same 7" woofers are shunted in Vented box
I have known that using a passive radiator is another kind of vented.
So, what are the pros an cons of the two choices? (If the cost just a little different) Thanks for your help !
The different is, that you need approx. the twice of cabinet volume, if you will realize also a vented box in case of two same 7" woofers.

If you compare this two chassis variantes with the same volume, you must realize a closed box in case of two same 7" woofers. The different is now the acoustical slope of the resulting high pass function. Vented box create a curvature with 24db/oct and closed box only 12 db/oct.

If you sure, that you don't carry out an enhancement through a subwoofer system (e. g. because there is no enough room space), then the closed version is clearly to prefer.

In other case (as a transitional solution) vented box is to prefer, because in case of an exist/retrofitted subwoofer below 70 Hz you can enhance the reflex tuning frequency to an so called "boom box" (large enhanced level arround the tuning frequency of approx 70-90 Hz) include an electronical attenuation with help of passive components (additional passive high pass in series - 1x coil, 1x cap, 1-2 resistors for modelling curvature).

This I have carried out several times - have a look to the photos of my website www_tiefbassuebertragung_de.

By tuning frequencies of 70-90 Hz the surface of vented port is much more larger and more distortionless (and more efficiency) than by 25-40 Hz - very very important to know.
Therefore is by the use of low cabinet volume and low tuning frequencies at the same time a passive radiator the best compromise - unfortunately the efficiency is very low, i. e. low audible power.

Concerning the number of rails the best choice is the connecting in series or parallel both transducers, if the crossover frequency to the midrange is below 400-500 Hz (3-way).

Last edited by tiefbassuebertr; 12th January 2011 at 07:25 PM.
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