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Old 23rd September 2013, 09:35 AM   #1
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Default OB thinking - comments please

Hi,

I've been reading a heap on OB speakers lately and am giving serious thought to attempting an OB build. I would like to use passive crossovers and cobbled together the following thoughts from various places. I'd really appreciate feedback as the cost to freight these parts makes the total cost very high and I don't want to put it all together and be disappointed!

Tangband w8-1772 full range
Tang Band W8-1772 8" Neodymium Full Range Driver 264-893

Two GRS 15PF woofers in parallel
GRS 15PF-8 15" Paper Cone Foam Surround Woofer 292-415

I've modeled the system in Basta (yes I know, models vs real world) and the total system appears to be quite good with 1st order crossovers and the full range speaker offset from centre.

3.3mH for the woofers and 12u for the full ranger (with 4R in series to pad down the relative response to 90dB).

Any comments or suggested improvements?
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Old 23rd September 2013, 11:17 AM   #2
Juhazi is offline Juhazi  Finland
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Does Basta have open baffle/dipole simulation option? Unless, when measured in yor baffle, you will get very different on-axis response. The width of the baffle is also very important. Runnig bass drivers in that wide range as dipole is difficult and you will lose roughly 12-18dB of their sensitivity.

These OB/dipole constructions are difficult to simulate, measurements are necessary! At least don't make a passive xo before measuring. Or try to find another program that has dipole simulation also off-axis to get some idea of power response.

You can use single 2x4 minidsp to handle xo and equalizations. When you have found the parameters toyy like, you can try to make same kind of transfer functions passively.
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Old 23rd September 2013, 11:24 AM   #3
jlaakso is offline jlaakso  Finland
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Isn't W8-1808 more suitable for OB arrangements? with little higher Qts.

And I would also recommend the small MiniDSP for prototyping and testing various crossovers and filtering. It saves itself after couple of different crossover point tests as no passive components are required for testing.
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Old 23rd September 2013, 01:02 PM   #4
Pano is offline Pano  United States
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I have a pair of OBees here with the same woofer, 2 per side. Works well with a big inductor for the low pass. 3.3mH is not nearly enough. Think more like 15-20 mH.

Don't know if I'd use that midrange. An 8" mid is a good idea, but there is better value for money, IMO. I've tried a few mids from 4" to 8" on the rig. They all sound different.
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Old 23rd September 2013, 02:24 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Your x/o point is way too high. Don't believe that TB frequency
response for a second,they are notoriously oversmoothed.

http://www.quarter-wave.com/OBs/OB_Design.pdf

Also see :

Beer budget "Version" of $10,000+ Jamo Open Baffles
rgds, sreten.
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Old 24th September 2013, 09:24 AM   #6
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Thanks to everyone for the feedback!

My preferred commercial speakers are quad 57's, quad 67's and quad 22L's. I think the reason I like them all is due to what some all the BBC response which typically has a drop from about 10 or 15 KHZ.

I've previously tried a fostex full range setup (boxed not OB) but the fostex sound is not good for me at all.

Is it a credible option to use the passive xo on the mid range driver with a tube amp and, the minidsp on the woofers with a solid state amp?

I appreciate the comments, as this is all new to me.

Kind Regards
Andrew

Juhazi: Basta does let me simulate an OB baffle but not the off axis response. The minidsp sounds like a good idea but I am put off my the thought of sand in my tube system...

Jlaakso: Yes the w8-1880 was a consideration but it has a higher peak in the 2khz to 5khz range

Pano: Great to hear of someone using the same woofers. What are the other good speaker drivers you've used?

Sreten: woofer xo is 250Hz. Thanks for the links, i've just surfaced about reading them over the last few weeks
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Old 24th September 2013, 09:53 AM   #7
jlaakso is offline jlaakso  Finland
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Quote:
Originally Posted by Drewaudio View Post
Is it a credible option to use the passive xo on the mid range driver with a tube amp and, the minidsp on the woofers with a solid state amp?
I don't see why not. But I don't see why yes either MiniDSP can take care the low pass for woofer and high pass for midrange/full range + response shaping for both. And You can use which ever (well, almost) amps you want after minidsp. Tubes for upper range and SS for woofers. Actually with DSP the requirements for amp are "lowered" as the amp won't have to fight against the driver _and_ crossover, just the driver.

Quote:
Juhazi: Basta does let me simulate an OB baffle but not the off axis response. The minidsp sounds like a good idea but I am put off my the thought of sand in my tube system...
I don't see why minidsp would inhibit you from using tube amps.

Quote:
Jlaakso: Yes the w8-1880 was a consideration but it has a higher peak in the 2khz to 5khz range.
I haven't looked closer to either driver, so take my comments with grain of salt If it's just peak in response, it can be fixed with minidsp. If it is caused by bad motor design or such, then it's a bugger Not sure if the driver parameters meen that much in this case as you use dedicated woofers for low end. More experienced users are welcome to correct me
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Old 24th September 2013, 10:04 AM   #8
Juhazi is offline Juhazi  Finland
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Drew, I know many people don't like any AD/DA conversions. I understand your urge to to go purely analog, but believe us, minidsp is such a wonderful tool! If you don't need it with the final system, use it as roomEQ for some other system or sell it! You couldn't spend 200 monetary units more wisely!
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