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Old 4th March 2009, 02:08 AM   #1
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Default Help!

Hi everyone:
I have these 6 inch (frames are the same as 6.5 inch Fostex) mid range (or single drivers) with bloody huge neodium (??? however you spell it) magnets. I need help to determine the style and size of the cabinet. The driver specs are:-
Fs = 63.5004, Vas = 15.6353, Qts = 0.2087. Freq range is around 53 to 21000....bizarrre but true! (We ran a test with the speaker unmounted sitting on a bench...I was shocked..even at 53 years of age I can still hear 20,000hz!!!)
I was going to build another "Bigger is better" cabinet....I've recently completed a pair with Fostex FE167e and they sound superb.......but the shape for these drivers would look like a 4inch by 6inch wooden downpipe and nearly 90 inches tall to get the bass down to around 40hz! I can do this and would love another pair...but maybe I could try another shape!!!????
I have Bob Brines FT1600 plans and many, many others but nothing suits these specs. Do I 'bite the bullet', and go two way or worse 3 way and use these as mid range as the specs would suggest...maybe a 3 way TL?????
I thought of a 1200mm high Transmissionline cabinet with straight baffle, (similar to Humblehomemade Hifi: Optimo) opening on the back top and a super tweeter...(if the highs aren't crisp enough..) ....anyway...................some suggestions would be great!
All the best.
Rgds: dave
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Old 4th March 2009, 12:18 PM   #2
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There isn't much you can do with that very small Vas. The drivers were probably designed for small BR's. You might try an EBS alignment, but getting low is going to be a problem. Do you have the rest of the T/S specs?

Bob
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Old 4th March 2009, 01:07 PM   #3
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Nearly 90in tall for 40Hz? 180in of total flare length? What BIB have you been listening to? They're set to 1/2 wave tuning frequency, so F10 is an octave below that. A 70in tall box (140in flare) is ~flat to 30Hz.

Other than that, as Bob said, I imagine they were intended for a small BR. A conventional kind of BLH would probably be a popular choice, but for me mass corner is way too high to be ideal for that sort of load, up around 510Hz.
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Old 4th March 2009, 02:25 PM   #4
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Well, with these specs I couldn't resist........

A two way system consisting of a corner loaded max gain BW TH to cover ~13 - 605 Hz and a FLH to cover the rest with of course the wow! factor being the ~4400 L TH's imposing 20,792 cm^2 mouth and the visibly tiny driver mounted on its lip pumping out live SPLs with 'flea' power in a well constructed room.

GM
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Old 4th March 2009, 03:16 PM   #5
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Er... crikey.
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Old 4th March 2009, 09:09 PM   #6
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Hello guys: thanks so much for the responses........well, er, yeah???? I've attempted to up-load the specs sheet for you to check-out. Bob the "Ts" specs...well I have no idea mate? Scott I've been listening to my BiB with Fostex Fe167e...these are fantastic...they stand about 170cm high and are chunky...I have not worked out how to reduce the size of the picture file so that I can post it on here, I'll send you an email with a picture.....they're not finished..that is, they are in natural ply...I used this 16mm 11ply..have great edges....anyway, I was calculating on Zilla's site using the BiB calculator and at that time I didn't have a clue about the Fr of these weird FR (???) speakers that are casuing me some concern, so I set the Fr on the calculator to 40 and enterd the other figures and got the mesaurments of an 84 inch high BiB...(alright it isn't 90 inches!)...and the internal size was 6& 3/4inches deep X 4&3/4 inches wide! It would be a funny looking BiB.........but I dont have to build another BiB...there's some other great cabinets out there...if only I knew what I was doing????!!
Now GM, I can appreciate your candor, but can you translate for me ..obviously being a lesser mortal, it is a difficult field to make headway. Especially when you start in your 50's, suffering the impact of years of personal abuse, work and family crisies and different hobies! Now I know that you aere talking about Back loaded horns and Front loaded horns....but this could be a breakthrough and I'd hate to miss it due to my now apparent 'internationally recognised' ignorance and slowly failing enthusiasm............can you give it to me a little less abreviated so that I might have a chance at gaining some understanding?
Regards to you all and thanks for your time...
Dave
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Old 5th March 2009, 03:44 PM   #7
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Greets!

You're welcome!

Hmm, a 53 yr old that can hear 20 kHz is hardly a lesser mortal. Indeed, my understanding of age related hearing loss indicates you might qualify for the Guinness Book..........

Yeah, my hands have me down to two finger typing, so I tend to use a lot of abbreviations and need to use more, so one of these days I guess I'll have to write an audio version of Net Lingo to decipher me.

BW = (frequency) band-width, i.e. from 10 - 100 Hz/whatever

TP = tapped pipe, basically a 6th order band-pass (BP6) alignment taken to its logical extreme, i.e. morph its filter chambers and vents into one continuous 1/4 WL pipe (AKA TL = transmission line), ergo in its simplest form folds back on itself with one side of the driver located near/at the terminus (mouth, AKA Sm or Am) and the other side near/at the closed end (throat, AKA St or At).

TH = tapped horn, in its simplest form, same as TP except positive expansion (closed cone or pipe horn).

If you're curious enough about TP, TH design and/or just want to try one to see what all the fuss is about, wade through these threads and any referenced links as well as do a forum search since there's some isolated threads:

Collaborative Tapped horn project

LIVE SOUND Specific Tapped Horn thread...

Critical Tapped Horn Parameters Collaborative

Hornresp

GM
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Old 5th March 2009, 09:16 PM   #8
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Thanks GM for the leads and thoughts. I have much to learn and consider. It seems that heading further down the 'Horn path' is a bit too complex for me at this point. There is so much 'new' knowledge being developed quite rapidly, with its' abreviations and "house terms", that it is impossible for me to process it. I'm trying to simply work-out what to do with these unusual drivers for a new project following the success of a previous excursion into the 'horn' world! Ah, the simple world of BiB...where obviously much smarter people than me have done the math!
Thanks though, but, it is all simply beyond me. My brain is bleeding! I'll slide back into ignorant bliss for a while longer!
Kind Regards: Dave
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Old 5th March 2009, 09:56 PM   #9
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You're welcome!

Understood, I did the design just to do it because I can, i.e. a bit of audio humor not to be taken seriously.

On a more realistic note, it's not all that efficient a driver from a box design POV at ~94.5 dB/W/m, but with a mass corner (the point where its response flattens out) up around 577 Hz, a long, large WG (waveguide) is required to go down to anywhere near its Fs. In a simple box tuned to Fs, it needs a lot of EQ to play ~flat in-room unless driven with either a matching impedance SET tube amp or p-p amp with variable DF (bass boost) of at least 20 ohms, so all things considered, a BIB with a BSC filter seems the best inexpensive, simple choice.

That, or put it in a tiny sealed cab or preferably OB and mate it to some type of large HE woofer/mid-bass vented cab with an XO in the ~175-500 Hz BW depending on the 6" driver's Xmax, peak Pe and box size/no box chosen.

Regardless, this is the type of driver made for high output impedance SET tubes, so long term this is the goal IMO and you design a new box based on this combo when the time comes.

GM
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Old 6th March 2009, 01:49 AM   #10
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Thanks GM. I think I'll pack them away...noting your remarks and figures and in time turn some attention to them. I like the idea of another pair of BiB, even these would be interesting. They could make some good 'mids' in a sensitive 3way system...just need to locate some sensitive woofers and tweeters...and then wait for a good plan that could work well with a SET...or even a nice P/P (like Gabes MAG 1515?). However, over here the economic downturn has shot prices high due to currency conversion and Aussie dollar tumbling. Added to the other more complex issues; with making a few mistakes and miss-judgments along the way the 'beloved' is getting a bit sensitive when I mention more purchases! I reckon she hits about 115dB herself when I mention Hifi!!!!!!!!!!! So all in all, costly errors and missjudgemtns means having to wait longer and do any work or purchases by stealth!!!!
Kind Regards: Dave
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