| Acoustic 301 cabinets "with new driver upgrade"
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I have decided to post this subject because it seems That there are so many "Acoustic 301/360" enthusiasts around these days (including myself), who require an 18" driver replacement, but with limited information to make an intellegent driver selection. I'm hoping that some of my research will make things a lil' easier for someone else who would like to perform their own, professional speaker upgrade.
The way it all started for me was...back in '73, as a kid, and a giging bass player, I thought the "Acoustic 371" bass amp was the coolest amp on the planet. It seemed that every "successful bassist" had one. You saw them on concert stages, tv shows, local clubs and disco's, but I couldn't afford one.
I had mostly Ampeg equipment, usually w/2-15's, driven by a head that was grossly under powered, at least by todays standards. But I was determined that one day I would have my own 370/301 bass amp combo, just never thought that it would be thirty years later (lol).
In Aug of '04 I purchased my 1'st "301" cabinet on ebay for $399.oo. The tolex was in bad condition but everything else was ok. The speaker, a Cerwin Vega "L-187" was in good shape, and according to the hand written documentation on the backside of the cone, it was reconed in '89.
But I already had plans to replace the original driver no matter what condition it was in, due to the relatively high power capability of my Crown power amps.
I knew the replacement driver would need to be capable of handling 2kw "program", just in case I would ever decide to run the amp in "bridge mono" mode. The 301 cabinet is a "w-bin" with a 3 1/2 ft horn path, so the lowest fundamentals that the horn is capable of is about 80hz.
I wanted to explore the possibility of adding a port to the speakers rear chamber to draw a little more low frequency extension from the drivers resonant rear wave. So now I would need to chose a speaker that would be comfortable in a short horn, and peform properly in a "bass reflex" enclosure.
I also wanted high sensitivity, low Vas, and a Qts around .30 from the low freq 18. After auditioning quite a few very high end 18" drivers using data sheets and industry reviews (JBL, RCF, Electro-voice Etc...), I finally decided on an excellent candidate from a relativly new Italian manufacturer; Eighteen Sound.
And the unit that matched every theoretical demand that was put forth was the "18LW1400". Based on the drivers specs, t/s parameters, and cost, this device is at the top of it's class. Now since our Acoustic 301 is to become a "hybrid", utilizing a rear chamber port, an internal volume measurement is needed so box tuning parameters can be set.
The loudspeker enclosure design program that I've selected for this project is by "Ishtek"; a free, online speaker design program for guys like me, who find it difficult to use "winISD".
They have an applet for 'horns', and for 'bass reflex', but nothing for hybrid (horn/reflex) cabs so I chose to use their bass reflex app. I also looked into just how much the horn would affect box tuning and was reminded that a "horn variant" will not accommodate true horn loading at box frequency, therefore will not impact box tuning consequencially.
So for this particular alignment, I've chosen the "B-4", maximully flat tuning which places F3 at 64Hz, and Fb (box freq) at 51.8 Hz. Now the horn "unloads" just below 80Hz, while the box is starting to load within that same half an octave range, keeping driver excursion under control.
The highly acclaimed 18sound,"18LW1400" was purchased from "Canal hifi", Nyc. The price seemed very resonable @ $299.oo; about 1/3 the cost of Jbl's 2242H. A couple of sq yrd's of blk cabinet carpet were ordered from "Pts expr", as well as spray adhesive, steel corner protectors, (2)3x5 duct ports, new wheels, screws, etc...
Once the parts arrived the cab was stripped and re-covered w/cabinet carpet according to plan. This project turned out better than expected, and ahead of schedule.
I was so pleased with the results that a second Acoustic 301 was purchased; this time on Craigslist for $250.oo,"without speaker". All of the parts for the 1'st cab were re-ordered. A 2nd 18sound driver was also purchased. After the port work was complete, some "egg creat" foam was added to the rear chambers for better low mid clarity. Both new drivers were installed, sound tested, and are amazing!
I think by porting the rear chambers, not only did we extend the low freq response of the cabinets, but it seems we may have picked up a few extra db's of low mid sensitivity in the process.
Btw, I do plan on posting some restoration process, and finished work photos at some point; need to x-fer old polaroids to disc 1'st. ( : \
There is so much more info in my files as a result of this project wrt "w-bins", both ported and sealed. Unfortunately, there's not enough time here to share all of it.
But feel free to post on this thread if you have comments or questions regarding this subject; I'll be checking in periodically to respond.
Greg, best regards
Last edited by rigtec : 03-27-2012 at 09:16 PM.
Reason: spelling errors, words left out
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