Bass reflex woofer selection and modeling - diyAudio
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Old 11th October 2013, 03:08 AM   #1
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Default Bass reflex woofer selection and modeling

Hi folks, first time posting. I have long studied the serious bass research that goes on here. I got started wanting to build some BFM T60s, of course, years ago and have also become enamored with the eloquent TH designs that have evolved over here - and yet, I still have not done...anything.

Recently at an outdoor event on a beach I was dismayed by the sound. Long story short, I'd like to build some decent subs that have BIG wheels on them to be lugged on a sandy downhill path 1 mile to the beach. I know that I want BR boxes because I have hand tool only woodworking skills (and patience!)

8 cubic ft (240l) boxes are fine and I'd like to hit 40Hz.

My question is in regards to modeling BR boxes. I have been using WinISD .50a7 and have found that my designs always reach xmax well before approaching the thermal limits. In the graphs below you will see a graph of each box SPL @ 1 meter given the maximum amount of power to hit xmax (each noted in the key). Are BR boxes known to experience over excursion above the port tuning frequency - as you will see from the 2nd graph, showing cone excursion, it is the 50-60Hz range that is causing problems. Then again, maybe all of my modeling is wrong! The cheapo MCM drivers did not list BL - I entered it as "10" but have thought about calculating it and/or moving on to HornResp.

Thanks,
J.P.

PS: 110dB/1m sounds fine to me...it's only for about 20-50 people.

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Old 11th October 2013, 03:38 AM   #2
Lusk is offline Lusk  Australia
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Is there any reason you have the port tuning for example with MCM at 41 Hz? Is this for more output?

why not lower at around 32Hz like WinISD should suggest.
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Old 11th October 2013, 04:01 AM   #3
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Yes, it is for higher output around 50Hz. A lower port tuning does not significantly raise the response at 40Hz so I figured I'd rather just take the extra SPLs.
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Old 11th October 2013, 07:36 AM   #4
GM is offline GM  United States
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A pair of these in 8 ft^3 puts out far more SPL: Dayton Audio PA460-8 18" Pro Woofer 295-036

GM
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Old 11th October 2013, 08:15 AM   #5
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I just modeled a single PA460-8 in the 8cuft box tuned to 40Hz and it does not reach xmax until 300W (it's 500W RMS) which is much better. This means that it can reach a solid 120dB 1m at 40Hz and peaks at 122dB at 50Hz. Thanks, that's just the sorta lead I needed.

Modeling the suggested sizes, 4cuft and 53Hz, shows that it does not reach xmax until 500W but lacks extension.
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Old 11th October 2013, 08:49 AM   #6
GM is offline GM  United States
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Considering their relatively low cost, then why not [2] in 8 ft^3/~40 Hz?

GM
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