Compound or Composite Isobaric - diyAudio
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Old 16th January 2008, 10:42 AM   #1
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Question Compound or Composite Isobaric

Morning all, I have the following drivers which I want to build an isobaric enclosure for -


Click the image to open in full size.

Check out the Fs!


Now they question I want to ask is this -

Should it be built Compound (push pull)

OR Composite (push push)

I have been reading that there may be differences but does anyone have the knowledge to explain this further. This is going into a car and is a pure SQ system, not interested in boom boom.

The Subs will be driven by a Soundstream Class A 10.2 amp.

Thanks, Rod.
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Old 16th January 2008, 05:44 PM   #2
simon5 is offline simon5  Canada
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Best isobaric is clamshell.

http://mobile.jlaudio.com/support_pages.php?page_id=157
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Old 16th January 2008, 06:11 PM   #3
simon5 is offline simon5  Canada
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BTW, there's a parameter that is wrong on this spec sheet.

I guess it's Fs.

Fs calculated by WinISD using Vas, Qms, DCR, BL, Mms and Sd give me a Fs of 40.27 Hz.

I hope that doesn't break your design, but I hope you expected this also.

A Fs of 11 Hz with an Mms of 60g is suspicious

If I use the Fs of 11 Hz instead of using Vas to calculate parameters, then either you get a Vas of 600 liters and a Qts and Qes of 0.1.

Good luck !
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Old 16th January 2008, 06:25 PM   #4
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Thanks Simon. I did think the fs seemed a little low!!!

So what would be the ideal volume to load the subs against in a clamshell design in your opinion?
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Old 16th January 2008, 06:38 PM   #5
simon5 is offline simon5  Canada
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It depends on what you want, the bigger the better usually, but most normal people have size constraints !

The volume is critical for a vented enclosure, but I guess you are going sealed. Those drivers seem to be better for vented OTOH, but since Fs is so high, they are hard to tune lower than 40 Hz.

In a sealed enclosure, you can achieve 0.707 alignment with 9 liters, 0.6 with 15 liters, 0.577 with 18 liters and 0.5 with 32 liters.

So it will be ok in a sealed box between 9 to 32 liters ( 1/3 cu.ft to 1.15 cu.ft internal net volume )

Good luck !
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Old 16th January 2008, 07:04 PM   #6
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Yes I really have the option of going sealed as its going in/under the dash of a Porsche 914.

So is there not one volume of air that is ideal? I didn't realise that the range was so broad, which affects the alignment as you call it-what is this exactly??

Sorry noob. !
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Old 16th January 2008, 07:16 PM   #7
simon5 is offline simon5  Canada
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Hi again,

0.5 will achieve deeper bass but some people prefer 0.707 because it has more punch (louder midbass), some take the compromise with 0.577 or 0.6.

I'd go with 0.5 but that's me !

I also suggest you to connect those drivers in parallel (2 ohms load) and bridge your amplifier (2 ohms bridged) so that you will be able to use 500W. OTOH, this will get quite hot hehe !

Isobaric is not very efficient so better use as most power as possible.
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Old 16th January 2008, 07:38 PM   #8
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Thumbs up Why Thank-you

Thanks again Simon, The Q, ok I now understand I'll get the build as big as I can under the dash and reduce it's size if midbass is lacking (doubt it in a car though)

The Amp really does get hot but thats no problem, i'll cool them.

Thanks for your input, appreciate it
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Old 16th January 2008, 07:49 PM   #9
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Rug Doctor... could you crop that pic to the width of the info please?

I was going to say that something didn't jive with the T/S.

dave
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Old 16th January 2008, 08:04 PM   #10
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No problem, I will as soon as I'm back on the same IP address, it wont let me because I'm not at the same computer (work/home) at the moment....
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