coral 4A-70 - t/s parameters....
hi,
sometimes forget own head ....
did a little reading around - will ask for vas, re, qms, qes, qts.... and impedance vs freq... those are the key values?
some good news though, a technician friend at the local university has made friends with the tech in the acoustics dept - may well be able to make use of his skills in iterative testing and refinement of speakers as they develop. get some nice rich data for the thread to chew on (the dept has a full anechoic chamber....)
one step at a time,
will report, cheers, a
hi,
sometimes forget own head ....
did a little reading around - will ask for vas, re, qms, qes, qts.... and impedance vs freq... those are the key values?
some good news though, a technician friend at the local university has made friends with the tech in the acoustics dept - may well be able to make use of his skills in iterative testing and refinement of speakers as they develop. get some nice rich data for the thread to chew on (the dept has a full anechoic chamber....)
one step at a time,
will report, cheers, a
Re: Help with 208Esigma/T90 BIB
Hi Chris, I had not checked the thread for awhile. You have helped me. Now I have something I might be able to help you with. A 0.25mH coil!
My amp is a Cary Rocket 88 which also uses KT88s. I have loved my 208/T90A BIBs more and more as time goes on, but when I had my princess and the pea fits, I think I was hearing the 3.7kHz cone break up mode that Dick Olsher mentions in his plans for The BassZilla which uses the Fostex 208 sigma. I think I had my speaker/ listening positions just so, to eq down that part of the spectum.
I tried the triangle suspended in the 2nd chamber of the horn. I made a long one, and put a lot of padding on it at first. It just reduced the wonderful dynamics, and I removed it. Later, I removed most of the padding, and suspended it so that it was not touching the cab itself. I think that helped. The excessive mid-range did not bother me on really good recordings, but did bother more on lesser recordings.
At last, I went to an "audiophile party' several weeks ago, and mentioned my "complaint" to Kara of dehavland amps, who was there. She played with a calculator for awhile, and told me to try a 16 gauge 0.25mH coil in series with the plus lead of the 208. I ordered a pair from Madisound for $5.30 each. It had been "the cats meow" for me! Maybe later I can replace them with a more heavy gauge, more botique coil. Now I can concentrate on bass, image, depth, etc. in speaker/listening placement.
I still only have my ears to measure with, but I really recomend the 0.25mH inductor, and its cheap.
Sincerely,
Benjamin
ChrisMmm said:
Hi Chris, I had not checked the thread for awhile. You have helped me. Now I have something I might be able to help you with. A 0.25mH coil!
My amp is a Cary Rocket 88 which also uses KT88s. I have loved my 208/T90A BIBs more and more as time goes on, but when I had my princess and the pea fits, I think I was hearing the 3.7kHz cone break up mode that Dick Olsher mentions in his plans for The BassZilla which uses the Fostex 208 sigma. I think I had my speaker/ listening positions just so, to eq down that part of the spectum.
I tried the triangle suspended in the 2nd chamber of the horn. I made a long one, and put a lot of padding on it at first. It just reduced the wonderful dynamics, and I removed it. Later, I removed most of the padding, and suspended it so that it was not touching the cab itself. I think that helped. The excessive mid-range did not bother me on really good recordings, but did bother more on lesser recordings.
At last, I went to an "audiophile party' several weeks ago, and mentioned my "complaint" to Kara of dehavland amps, who was there. She played with a calculator for awhile, and told me to try a 16 gauge 0.25mH coil in series with the plus lead of the 208. I ordered a pair from Madisound for $5.30 each. It had been "the cats meow" for me! Maybe later I can replace them with a more heavy gauge, more botique coil. Now I can concentrate on bass, image, depth, etc. in speaker/listening placement.
I still only have my ears to measure with, but I really recomend the 0.25mH inductor, and its cheap.
Sincerely,
Benjamin
Build a BIB in a Day! (SE Qld, Australia)
Speaker builders in northern NSW or SE Queensland may be interested in a proposal for a working GTG at Greenie512's place.
He has a well-equipped workshop with a table saw, etc.
The object? To bring along a pair of FR drivers and the necessary ply/MDF, and to rough build a pair of BIB's (screws, not glue) and then spend the afternoon / evening sitting back at a comparative listening session.
The object is to provide a BIB experience to those who may not have built a speaker before. (Let's face it. They're pretty simple!)
www.stereo.net.au/forums/showthread.php?p=213668#post213668
Perhaps others might be interested to take up this concept in their local area? We could have an "International Build-a-BIB Day"! Any takers ...
cheers
Doug
Speaker builders in northern NSW or SE Queensland may be interested in a proposal for a working GTG at Greenie512's place.
He has a well-equipped workshop with a table saw, etc.
The object? To bring along a pair of FR drivers and the necessary ply/MDF, and to rough build a pair of BIB's (screws, not glue) and then spend the afternoon / evening sitting back at a comparative listening session.
The object is to provide a BIB experience to those who may not have built a speaker before. (Let's face it. They're pretty simple!)
www.stereo.net.au/forums/showthread.php?p=213668#post213668
Perhaps others might be interested to take up this concept in their local area? We could have an "International Build-a-BIB Day"! Any takers ...
cheers
Doug
Re: Re: Help with 208Esigma/T90 BIB
Benjamin,
When you mention replacing the "16 gauge 0.25mH coil in series with the plus lead of the 208," with "a more heavy gauge, more botique coil" did you, or have you, asked about why she was so specific about the 16 AWG coil? Many times a crossover is designed with a certain gauge coil in order to have a higher DCR which can save on parts count and yet kills two birds with one stone. I'd ask for her opinion before going to a larger gauge coil.
Best Regards,
TerryO
BenjaminWebber said:
Benjamin,
When you mention replacing the "16 gauge 0.25mH coil in series with the plus lead of the 208," with "a more heavy gauge, more botique coil" did you, or have you, asked about why she was so specific about the 16 AWG coil? Many times a crossover is designed with a certain gauge coil in order to have a higher DCR which can save on parts count and yet kills two birds with one stone. I'd ask for her opinion before going to a larger gauge coil.
Best Regards,
TerryO
Botique Coil
Thanks Terry. I did ask her about a more botique coil. Her advice was to worry about getting the right amount of inductance first. I think 0.25mH is the right amount. I knew the peak was somewhere between 3200Hz and 4000Hz, but could not remember exactly was I talked to Kara. I discused the matter with someone at Madisound before ordering, thinking maybe I would try about 3 sets of coils, one bigger, and one smaller, etc. The guy who helped me gave me a formula, did the calculation himself, looking at the Fostex FR for the 208. He said, "Wow, she is right on the money!" He also said his opinion was that getting the right inductance was most important. So, I just ordered the 0.25mH coils for $5.30 each. They sound right to me. I guess that is what matters most.
Do you think the Goertz air foil inductors of 12 awg at $27.00 each would offer any significant improvment?
Sincerely,
Benjamin
Thanks Terry. I did ask her about a more botique coil. Her advice was to worry about getting the right amount of inductance first. I think 0.25mH is the right amount. I knew the peak was somewhere between 3200Hz and 4000Hz, but could not remember exactly was I talked to Kara. I discused the matter with someone at Madisound before ordering, thinking maybe I would try about 3 sets of coils, one bigger, and one smaller, etc. The guy who helped me gave me a formula, did the calculation himself, looking at the Fostex FR for the 208. He said, "Wow, she is right on the money!" He also said his opinion was that getting the right inductance was most important. So, I just ordered the 0.25mH coils for $5.30 each. They sound right to me. I guess that is what matters most.
Do you think the Goertz air foil inductors of 12 awg at $27.00 each would offer any significant improvment?
Sincerely,
Benjamin
Calculations for vintage FR drivers in a BIB?
Hi,
I'm wondering if it's possible to back-calculate the BIB dimensions for a vintage driver.
What I have is:
Diameter of driver:8"
Res Freq: "between 30Hz and 45Hz"
The dimensions of a ported cabinet, including port dimensions: See attached.
20 W, 94dB.
Hi,
I'm wondering if it's possible to back-calculate the BIB dimensions for a vintage driver.
What I have is:
Diameter of driver:8"
Res Freq: "between 30Hz and 45Hz"
The dimensions of a ported cabinet, including port dimensions: See attached.
20 W, 94dB.
Attachments
Greets!
Not really without an accurate measured frequency response, but doing a forum search yielded some measured specs to work with: http://www.diyaudio.com/forums/showthread.php?threadid=84036
GM
Not really without an accurate measured frequency response, but doing a forum search yielded some measured specs to work with: http://www.diyaudio.com/forums/showthread.php?threadid=84036
GM
8cx - i think its a coral
hi brisso 57,
just read the post about your 8 inch driver... next on my shopping list from axent audio... assuming this is an eight inch driver with a small hornloaded tweeter attached, link to more coral info in one of my earlier posts in this thread. will be interested to see how your project develops.
my coral 4a-70 still lingering at axent waiting to have its t/s values determined....
thanks gm for your patience with new folk on the forum
bon voyage, a
hi brisso 57,
just read the post about your 8 inch driver... next on my shopping list from axent audio... assuming this is an eight inch driver with a small hornloaded tweeter attached, link to more coral info in one of my earlier posts in this thread. will be interested to see how your project develops.
my coral 4a-70 still lingering at axent waiting to have its t/s values determined....
thanks gm for your patience with new folk on the forum
bon voyage, a
You're welcome!
Hmm, I used the specs from the link and came up with a bit shorter pipe. Regardless, a higher tuning with less gain can be calc'd, though as in any alignment where the cab is too small for the BW, it may require some BSC which of course limits dynamics a bit.
Anyway, using a Fs to get TC's 'standard' 69" i.d. folded height and shrinking it by cutting Vas in half, it's still fairly large due to its relatively high Qts with a 10.2" i.d. width, 14.43" i.d. depth, but still has solid output into the 30s with some room gain as long as you don't play them at 'Headbanger Ball' SPLs.
GM
Hmm, I used the specs from the link and came up with a bit shorter pipe. Regardless, a higher tuning with less gain can be calc'd, though as in any alignment where the cab is too small for the BW, it may require some BSC which of course limits dynamics a bit.
Anyway, using a Fs to get TC's 'standard' 69" i.d. folded height and shrinking it by cutting Vas in half, it's still fairly large due to its relatively high Qts with a 10.2" i.d. width, 14.43" i.d. depth, but still has solid output into the 30s with some room gain as long as you don't play them at 'Headbanger Ball' SPLs.
GM
