|Multi-Way Conventional loudspeakers with crossovers|
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|21st December 2005, 02:03 AM||#1|
Join Date: Feb 2004
Vintage Goodmans updating advice?
I have inherited (for free) some old 3 way speakers. They are home made, using Goodman drivers. It looks like a kit with a diy box.
After auditioning I thought there may be some potential, though they are not earth shatterring, they are kinda 'warm' and quite efficient (suits my other 'vintage gear).
The mid range is very 'honky', (almost JBL and probably needs padding.
Also the cross over is ancient and the 'lytics are probably stale.
Can any-one help with driver specification. If I am to attempt a 'rejuvination', it might as well be scientific.
The drivers are (and the sum total of info available printed on them):
1" dome, DT3, 8ohms
150 ish mid, 8 ohms, blue dot label.
Audiom 200 bass, 8 ohm, 40 to 4k, 60 watts
The xo is 5000, 8000 to 1200 mid and 1800 bass. From what I can work out (but this is not my forte - and the thing's a rats nest anyway). the high is 2nd order and the rest single.
The box is about 73 litres and there is a port, 75 dia, 218mm long. The 'squauker' is in a separate enclosure of about 7 litres.
Before I get to the box is any of this salvageable?
I thought a 'modern' xo, say 1.5 and 6.5K, 12db?
I thought the box could be reused, placing the drivers in line on the 'narrow' face - 400 wide, rather than where they are now, 500 wide baffle and in a loose 'triangular' formation - as was the fashion in the 70's.
A long post I know, but I thought I'd get the facts out first, and collect opinions.
Or should I just give it new caps and leave it at that?
|21st December 2005, 12:36 PM||#2|
Join Date: Nov 2003
Location: Brighton UK
from your numbers port tuning is a relatively low 26Hz.
You should replace the old electrolytics.
An off the shelf c/o will highly probably be worse than the current c/o.
Padding of the midrange driver would presumably make them even warmer,
if this is OK then try a L-pad arrangement to reduce the midrange output.
Changing baffle width from 500 to 400 will have only minor impact,
it will slightly reduce the amount of lower midrange warmth.
Closely vertically aligning 3 ways is nearly always a good idea,
but offset the mid and tweeter to a centerline 0.6 of the width.
Once closely spaced experiment with relative driver phasing
to make sure they are wired into the most suitable phases.
|27th December 2005, 10:19 AM||#3|
Join Date: Feb 2004
Hello Streten, Thank you for your comments, which proved most accurate, as I was to find out.
with Christmas and other things I could not get back to this project until recently.
The original XO is :
tweeter: series cap 2.8 mic, parallel choke - wire over ferite annulus - unmarked value.
mid: series cap 16 mic, series choke 0.18 and series 6.8 resistor (yes all in a row)
Bass: series choke 0.64
Some mods and repairs I have done so far:
I have resealed all the drivers onto the baffle as the original sealant had dried up.
Stuffed the mid sealed box and put a 2db pad on the driver.
Put larger cables. (more than the bell wire...)
I have plans to recap the existing network, but as an experiment substituted a 'modern' 12db cross over, 800 and 5K, just to see (until the shops reopen tomorrow ;-)).
All these mods have only been done to one speaker, leaving the other 'original' to gauge progress (or not).
So far its like a curates egg..
the mid is still too bright, (so the original 6.8 ohm resistor was there for a reason - and 2db ain't nuff). The tweeter is also brighter but this maybe just the new caps actually working cleaner.
This gives the sound more air, and gives the impression of more detail. However its still sibillant and fatiguing after extended listening.
The biggest disappointment is the bass, as I expected better sealing to improve the ported response. Unfortunatly its very much like the song...one note ..
On the other hand the 'original' is better integrated, with the mid quite mellow, but not much highs either. The tweeter is very discreete.The original XO maybe 'optimised' after all...
Further disapointment came with both setups (modded and original) when the volume was cranked up. The bass became better (but not really tight) but -quelle horreur- the mid started to really shout, almost painful (certainly to my aesthetic sense..); so it gets out of its comfort zone pretty quick.
Before I race out and get some expensive caps tomorrow, should I be resigned to the fact that these drivers are really not much chop after all?.. Shallow bass, shouting mid and shy tweeter, (sounds like..)
I could really use some pointers about these old Goodman drivers, some ffacts and figures, and some idea whether they are capable of better. (I don't know...more complex XO, zobel ect..)
|4th January 2006, 10:41 AM||#4|
Join Date: Nov 2003
Location: Brighton UK
the electrolytics should be replaced with dirt cheap modern equivalents,
there is no point buying "expensive capacitors", its a waste of time / money.
The "modern" c/o is probably designed for 8R loads, and consequently
not likely at all to be providing its advertised c/o points and slopes. As
you hinted, zobelling the drivers is probably neccessary for this c/o to
work as intended. You'll also need L-pads on the mid and tweeter.
IMO if with the caps replaced the sound isn't good enough, quit.
You could build a more modern design with modern drivers in the cabinets.
73 litres is loads of volume for an 8" driver. Its about right for a
reflexed 10" (or 2x6.5") or a sealed 12" (or 2x8") bass driver(s).
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