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First Speaker Build - Need help
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damianmitchell View Drop Down
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Joined: 15 October 2018
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    Posted: 15 October 2018 at 5:50am
Hi Guys,

I'm new to speaker building and have been educating myself via youtube and other resources.  I want to build a small Bluetooth speaker for my wife and I am trying to design the enclosure using winisd.  I have picked the speakers and want to go with a passive radiator but I am confused with the results I am getting in winisd.

I understand that a passive radiator needs to be about double the size of the speakers and I am sure I have picked the right one but I am still confused with the results coming from winsid.

So....The following is my speaker I am wanting to build:

Speakers: 

PS95-8 3-1/2" Point Source Full-Range Driver x 2


Passive Raditor:

DS175-PR 6-1/2" Designer Series Passive Radiator x 1


Enclosure Volume:
Around 7 Litres or .247 Ft^3

The tuning frequency calculates at 54.09Hz but my F3 comes in at 101.9.  What is going here?????

I have saved the project in winsid so if anyone needs the file I can send it to them.  Please help me out here as I am getting frustrated and just want to build a simple and nice sounding speaker.

Thanks
Damian
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Shortrope View Drop Down
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Joined: 08 July 2013
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Points: 1232 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Shortrope Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2018 at 8:47am
I'd say it's because the useable frequency range of that driver starts at 110hz.
My Tinnitus is coming along nicely!!
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damianmitchell View Drop Down
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Joined: 15 October 2018
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Points: 4 		Post Options Post Options   Thanks (0) Thanks(0)   Quote damianmitchell Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2018 at 8:59am
I suspected that might be the case.  So does that mean I cant use the passive radiators or I should choose speakers with a lower frequency response?
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Aman Gebru View Drop Down
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The PR's tuning freq is too far from the useful output of the driver and winisd calculates the f3 at the first -3dB point below the drivers output.

I bet the true f3 will be around 51Hz and that there is a dip in the response around 76Hz. Its this dip that is confusing winisd as the dip will be more than -3dB in amplitude. You have 3 options. Live with the dip in response, tune the PR higher or find a driver with specs that will give you more output below 100Hz. A driver with a lower Vas would achieve this.

If it were me and I already had the driver and PR I would live with the response and its dip as it will probably not be very noticeable. You can always calculate the real f3 point by looking at the amplitude plot. If its fairly flat down to say 54Hz look at which frequency below this that is 3dB lower in amplitude. That will be the f3.

Basically you tuned the PR too low. But this isn't always a bad thing to do, it does mean you won't have a flat response, but does mean you will be able to play lower frequency from the system. One thing to watch out with tuning too low is that the maximum electrical input and hence maximum acoustic output will be lower. Cone displacement and GD will also be effected.
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damianmitchell View Drop Down
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Points: 4 		Post Options Post Options   Thanks (0) Thanks(0)   Quote damianmitchell Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2018 at 9:36am
Originally posted by Aman Gebru Aman Gebru wrote:

The PR's tuning freq is too far from the useful output of the driver and winisd calculates the f3 at the first -3dB point below the drivers output.

I bet the true f3 will be around 51Hz and that there is a dip in the response around 76Hz. Its this dip that is confusing winisd as the dip will be more than -3dB in amplitude. You have 3 options. Live with the dip in response, tune the PR higher or find a driver with specs that will give you more output below 100Hz. A driver with a lower Vas would achieve this.

If it were me and I already had the driver and PR I would live with the response and its dip as it will probably not be very noticeable. You can always calculate the real f3 point by looking at the amplitude plot. If its fairly flat down to say 54Hz look at which frequency below this that is 3dB lower in amplitude. That will be the f3.

Basically you tuned the PR too low. But this isn't always a bad thing to do, it does mean you won't have a flat response, but does mean you will be able to play lower frequency from the system. One thing to watch out with tuning too low is that the maximum electrical input and hence maximum acoustic output will be lower. Cone displacement and GD will also be effected.



Thanks for that detailed response.  I understood most of what you said and it's kind of what I had suspected was happening.  I haven't bought anything yet so my I think my best option is to find a better speaker with a lower range.  I wanted to use a full range speaker  as I didnt want to mess around with crossovers but I'm thinking I might have to switch to a woofer tweeter setup and just learn how to make a crossover :)
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