Suggestions please on OB with 15" H frame - diyAudio
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Old 26th July 2011, 05:42 PM   #1
syyma is offline syyma  United States
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Default Suggestions please on OB with 15" H frame

A full range driver mount on an ob and sit on top of a 15" or 18" h frame always intrigue me for long time. MJK's Jorddan/Goldwood looks awesome but just out of my budget.
Can anyone point me to the direction that won't cost me too much to build? My room size about 14'x16' with 20' ceiling. Most of my music are classic rocks play from cd player and ipod. My Simple SE can drives the ob and a 120w ss amp hopefully can make the h frame sing. I do have some basic woodworking power tools like table saw, radial arm saw and routers.
Any recommendations are more then welcome.

Sid
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Old 26th July 2011, 08:42 PM   #2
ra7 is offline ra7  United States
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Get an Eminence Alpha15 into the H-frame. That should be a great starting point. It will go plenty loud and deep with minimal crossover work.

For full range, there are plenty of options. Remember that cone area is everything on an OB. Bigger the better. If you plan to cross low (100 Hz - 150 Hz), I'd suggest at least an 8" driver.

My personal favorite is the Audio Nirvana 8". It is very cheap compared to most full range offerings and it will give stellar performance in this setup. Compared to some of the more advertised drivers on this website, the cost to performance ratio is very high.
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Old 26th July 2011, 10:50 PM   #3
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>>> If you plan to cross low (100 Hz - 150 Hz), I'd suggest at least an 8" driver.

I agree with going for larger diameter drivers in your room. I think you can start around 6.5" but 8" or larger might be best. There are larger AN choices to consider and Fostex has a few 6.5 and 8" choices. Betsy, GRS (really cheap option), etc.
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Old 26th July 2011, 11:16 PM   #4
MJK is offline MJK  United States
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You don't need a big full range driver if it is not covering the bass frequency range. I have been using the smaller Fostex drivers on my H frame's OB and in my experimental OB speaker systems. Try the FE83En, FF85WK, FE103En, FF105WK, FE126En, or FF125WK. Look at the small Fountek FR88Ex or FR89EX. They will all work really well if you can dial in the crossover, adjust the woofer's boost level up or down depending on the driver, and are all very affordable. I personally like the Fostex drivers the best for the money.

Martin
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Old 27th July 2011, 12:11 AM   #5
syyma is offline syyma  United States
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Thank you for the advises.

Alpha 15 is one of my option. Somehow Zilla's project link broken, I can not take a look of those great things. Definitely I will go back to MJK's site to learn more about those basics.

I do have a pair of B20 and Dayton neo press fit tweeter from my half chang. I might consider to re-cycle them to the ob/h-frame project.
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Old 27th July 2011, 01:21 AM   #6
MJK is offline MJK  United States
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I forgot a couple of other Fostex drivers I like a lot, the FX120 and the FE-108E Sigma. Another one is the F120A but I have not liked that driver's sound as much as the others and it is the most expensive of the bunch. All of these are more money then the other FE and FF series drivers. The nice thing is if you cut the hole and drill the screw mounting holes for the FE-126En then the FF125WK, older FF125K, FX120, and F120A are all drop in replacements.

Martin
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Old 27th July 2011, 02:03 AM   #7
syyma is offline syyma  United States
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Thank you again Martin. I will keep that in mind and look for the drivers with the cutout in same size and easy to swap between drivers.
You mentioned earlier about to dial in the crossover point and adjust the woofer's boost level up or down. Are these fine tune done by the pro sound digital crossover? I personally prefer passive crossover because I don't have the budget for this gadget yet.
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Old 27th July 2011, 01:31 PM   #8
MJK is offline MJK  United States
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Yes, the pro sound crossover does all of the adjustments. It is a very powerful tool.

If you are going passive then you need to be much more careful in your driver selections to make sure the final SPL/W/m of the H frame and OB match. Also, you will find that crossover parts for a frequency this low are very expensive. Do the design work forst so you don't waste money on parts that do not perform as expected.

One final thought, tube amps and these type of H frame and OB systems with low crossover frequencies don't seem to work well together. I tried a tube amp and the bass disappeared, the same result has been reported back to me by others with tube amps. I don't know much about amps, but I have to wonder if the tube amp struggles with the impedance of one of these types of speaker designs at low frequencies.

Martin
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Old 27th July 2011, 01:58 PM   #9
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>>> I do have a pair of B20 and Dayton neo press fit tweeter from my half chang. I might consider to re-cycle them to the ob/h-frame project.

I think that's a great idea! I simply use a solid state subwoofer amp on the H-frames and leave the tubes to power the full range driver... but you can use what you want. A little T-amp would work well too on the fullranger.
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Old 27th July 2011, 07:10 PM   #10
syyma is offline syyma  United States
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Godzilla,

That's what I am going to use my Simple SE to power the OB and the sand amp to taking care of the H frame.

Martin,

Thank you again for your advise.
I went back to your site and read your "Open Baffle Theory", getting the idea of the size of the H frame. I'm most likely will go with the Alpha 15". The internal size of the H frame will be 16"x16", 7.5" each between woofer's baffle. 3/4" thick board will get the out side dimension to 17.5"x 17.5"x15.75". The open baffle will be 17.5"x 28", the pioneer B20 will sit 16" above of the bottom edge of the baffle and 2" offset from the center line of the baffle. The Dayton press fit tweeter will be locate 21" above of the bottom edge of the open baffle and 1" offset of the center line.
If the above dimensions not make any sense feel free to point it out for me.
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