OpenBaffle vented sub cont.

[kipman725]

I figure all the off topic discusion in the OB gallery thread was too much so new thread!

For reference read FRS8 posts from:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=123512&perpage=25&pagenumber=7

Anyway according to bassbox by using two of the FRS 8 (4ohm) in push pull isobaric in a vented enclosure bass exstension is down to 66Hz (-3dB) with a SPL @ 60W of aproximatly 100dB. The awsome thing about this is the enclosure volume is reduced to just 4.23L

This bass unit as per the design by Chris would be paired with a single 8ohm FRS8 running in open baffle. It should be relativly easy to cross them over with a passive 1st order crossover @ 150Hz. Due to the units intended usage as speakers to be along side a computer monitor I don't think the poor off axis hf response will matter too much as they will be positioned at ear height.

Due to the dimensions of the intended box and needed port legnth the port will have to fire upwards. The vent air velocity peaks at 7m/s.

The 10 - 15Khz dip from the FRS8 should be able to be equalised out in the crossover:
http://www.visaton.com/bilder/frequenz/gross/frs8_8_fs.gif

If the simulations are acurate don't think that this speaker looks bad for something only using a total of £40 of drivers per pair.

 

[PeteMcK]

kipman, consider the FRS8M - has a bigger magnet and is more efficient, for the same $...

personally, for something this small, I'd use an FRS8M as a full range & the WS130 for the low end (although that might be a bit big for you, would need ~20L to get down to 40 Hz, ~12 L isobaric)

 

[kipman725]

what governes the upper frequancy limit at which a driver can be used? I ask because the WS130 goes upto 12K. If I used this in a vented enclosure what prevents me crossing it @ 4Khz with a tweeter?

 

[PeteMcK]

Re:'what governes the upper frequancy limit at which a driver can be used?' - for me, it's the breakup mode of the driver, the w130s looks to be at 1.5Khz, although you could probably use it a bit higher , but it starts to get peaky above 3KHz;

Actually, I think your original proposal is better, use a driver BR i.e. the W130s up to 150-200Hz, (or w170 if you want more grunt)and the FRS8M above that, this will reduce the low end distortion and probably give a clearer overall sound, as well as a simpler crossover

 

[454Casull]

Directivity should also be considered. Some people prefer to cross before directionality, some people prefer to cross to match dispersion, etc.

 

[kipman725]

I can't find a directivity plot for the W 130 S 8ohm but I can for the same speaker with aluminium cone:
http://www.visaton.com/bilder/richtdiagramme/gross/al130_rd.gif

The 4Khz plot looks pretty good to me. If I could get it upto that frequancy with no issues it could be crossed with:
http://www.ribbonspeaker.com.tw/ (RT001A)
which I have already two of and are cheap (for ribbons), enclosed (so just need a hole cutting in the enclosure as no backwave to worry about). Strange how the design has changed so much