Big Bertha

Hi guys!

it has been a while since i have been on this forum, have been building a lot of enclosures.
i have been sitting on the plans for the EAW BH 882 and finally got the courage to actually build it. have been testing it out and i am very impressed with the response. does not go that low though but boy! chest slamming stuff!
yesterday i did a modification in the back chamber where the two 18" subs are mounted. i ported the back chamber halfway into the horn throat. i do not know all the physics related to what i have done here and some of you might say " now you ruined it all" the result was a percieved increase in the lower frequency range. lots of bass at low level input and i can tell you that at about six meters from the box, my eyes were starting to vibrate in their sockets.
i used to play outdoor events utilising 6 off 18" bass reflex subwoofer enclosures. this one box surpasses that! the next step now is to build four off the JBL 4818 enclosures and add it to the EAW! that is just for the bass frequency range. still have another 12 off 15" drivers which i am still figuring out what type of enclosures to build for. :cool:
 
Hi guys!
yesterday i did a modification in the back chamber where the two 18" subs are mounted. i ported the back chamber halfway into the horn throat. i do not know all the physics related to what i have done here and some of you might say " now you ruined it all" the result was a percieved increase in the lower frequency range.
Porting the compression chamber in to the horn certainly may have increased the LF output.
It will be now be more important to use a high pass (low cut) filter just below the tuning frequency, as the compression chamber will no longer "put the brakes" on the speaker's suspension below Fb (tuning frequency).
 

ticknpop

Member
Paid Member
2005-05-28 9:43 pm
toronto
That's right a Bertha is fairly close to the BH 882 , just add the 8 foot wide mouth extension (called a Levan) and double or triple stack them for real fun...... And real bass..... And remember Richard Long and Leroy Levan. I had a club where we had an RLA system with 4 Berthas with the ultra rare 10 foot wide triple bend mouth extensions double stacked in each of 2 back corners .... Boom shakalaka........
 
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Porting the compression chamber in to the horn certainly may have increased the LF output.
It will be now be more important to use a high pass (low cut) filter just below the tuning frequency, as the compression chamber will no longer "put the brakes" on the speaker's suspension below Fb (tuning frequency).

Point taken! the low cut-off frequency is switchable on the amplifier between 50 and 30 Hz. i tried it first on the 50 Hz and when switched to the 30 Hz, i could definitely hear a decrease in the lows. i guess it should be ok then?

Another interesting experiment i did was to build one of Selenium HB1805C1 enclosures and also port that with the ports firing to the front. Also loaded with 2 x 18" subs. when put next to the EAW and fired up one could hear a definite decrease in the lows. at first i could not understand what is happening. when played on its own each of the two enclosures sounds excellent, together there is a definite bass cancellation. i reversed the polarity on the Selenium design and actually got a fright when i fired both up again, heavenly base!
can someone perhaps explain to me the reason for the phase cancellation. is it the difference in horn lengths between the two enclosures or is it maybe the placement of the ports within the throat?
 
Another interesting experiment i did was to build one of Selenium HB1805C1 enclosures and also port that with the ports firing to the front. Also loaded with 2 x 18" subs. when put next to the EAW and fired up one could hear a definite decrease in the lows. at first i could not understand what is happening. when played on its own each of the two enclosures sounds excellent, together there is a definite bass cancellation. i reversed the polarity on the Selenium design and actually got a fright when i fired both up again, heavenly base!
can someone perhaps explain to me the reason for the phase cancellation. is it the difference in horn lengths between the two enclosures or is it maybe the placement of the ports within the throat?
Probably a combination of path length difference and different port tuning frequencies.
The upper bass response can be "fixed" by inverting the polarity, the horn path length of around 3 meters is equivalent to one wave length at 116 Hz.
The lower "phase inverted" response of the ports evidently also happens to combine, likely because they are at two different tunings.
You might get even better response moving the BR cabinet forward or back in a bit in relation to the horn.

You could also get a cardioid response (less bass behind) by placing the BR about the same length as the horn path behind the FLH, then running them both in polarity.

That said, the placement of the ports within the horn, and not knowing either tuning makes predicting what will happen difficult.
 

rpa

Member
2006-02-20 9:25 pm
berlin
@ ticknpop

I think you mean Larry Levan ;)

I wish i'd had to opportunity to visit those late 70's & early 80's clubs, to experience the sound systems. It must have been something back then :)

I partied in and worked with some of that kind of gear at the end of the 90s and beginning of the naughts, and to be quite fair I think that time has come and passed.

It must have been something, because the overall experience was somehow both fresh and matured at the same time. However, if you notice, almost nobody involved at the time who is still alive is doing things that way, and its not for lack of budget.
 

Zero D

Member
2009-08-06 11:11 am
@ rpa

It was the music too, great disco/dance tracks :) Most people won't have heard many of them, as most didn't chart in the mainstream charts :(

However, if you notice, almost nobody involved at the time who is still alive is doing things that way, and its not for lack of budget.

Yeah, funny how a lot of them are dead now ! I know why, but still.

Times change, & so does equipment/drivers/knowledge etc etc. But to able to achieve back then with what they had is fantastic :)
 

rpa

Member
2006-02-20 9:25 pm
berlin
@ rpa

It was the music too, great disco/dance tracks :) Most people won't have heard many of them, as most didn't chart in the mainstream charts :(



Yeah, funny how a lot of them are dead now ! I know why, but still.

Times change, & so does equipment/drivers/knowledge etc etc. But to able to achieve back then with what they had is fantastic :)

Yes, total experience. im just 33, but i had a chance to learn a lot when i lived in nyc. AIDS took a few way too early, but in recent years, some of the industry survivors also succumbed to the reaper.

What would Richard Long use today? He'd probably be digital. Would he have continued with eaw, would he and danley have hooked up? The power available to modern drivers and amps would blow him away.
 
thanks for the valuable insight.
some questions though, in a "W" bin there are two paths and two mouths for the same driver, does the total length of the two paths combine to form the total length and for the mouth area, does the two mouth areas combine to form one total mouth area. if this is not the case, what is the purpose of splitting the paths then for the same driver?
Also, what effect does splitting the path have on total SPL. my understanding regarding horn response is that horn length are related to SPL and mouth area are related to low cut-off frequency. am i on the right path here?
 

more10

Member
2011-02-08 10:00 am
Solna
The reason for the W shape is ease of construction. The driver compartment and back chamber is simpler to build than a horn with one horn path.

The total length is only one leg of the W, but the mouth area is the two mouths together.

If you get a miniDSP 4x10 Hd you can delay your other speakers so that they dont canel each other out at crossover frequencies. You will get a harder bass.
 

ticknpop

Member
Paid Member
2005-05-28 9:43 pm
toronto
Yes Larry not Leroy, what was I thinking? I met Richard Long in 1985 when we did a club with him. Richard believed most speakers were compromised with not a long or large enough horn or mouth area to be cheaper to build, sell, and transport. Gary Stewart Audio and Sound by Shorty are 2 still using a lot of Richarid's basic designs, updated where possible and original components are unavaiable, the basic concepts - RLA 3000 crossover and cabinets of the Paradise Garage system is pretty much what Gary Stewart still uses. Yes all of them gone too soon, the clubbing lifestyle and AIDS.
 

ticknpop

Member
Paid Member
2005-05-28 9:43 pm
toronto
The crossover on a horn mouth extension Bertha should be 100hz on the top end. The ear isn't too sensitive to low frequency phase. Stacking the mid and high cabinets at the rear of the Bertha/Levan cabinet will minimize the phase difference and was the reason the systems were stacked this way, rather than the horn mouths aligned with front stacking the upper end cabinets
 
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Been exposed to those bass notes in the early 80's with Studio 54 and Palladium night clubs. Those Bertha's with the Levan horn threw some massive in your chest bass like a freight train.:)

I am still contemplating on building 4 Emeralds (half Bertha) with a tear down Levan Horn I still do not know how to start the extension horn maybe with massive bolts and plates.

Also the drawings of the Bertha on the net EAW is 15 mm BB. But the original is 18 mm BB would doing the Emerald's in 15 mm would change the tuning of the cabinet since thinner walls more air movement??? Thanks!:crazy:
 

ticknpop

Member
Paid Member
2005-05-28 9:43 pm
toronto
The Levan mouth bolted/screwed on to 3 or 4 inches of the left and right side of the Bertha. The Levan mouth was built as left and right sides which the front top to bottom braces bolted together and the nose left and right sides glued together. same for the Emerald. The mouth only attached on the sides, the front nose of the horn didn't attached to the Bertha, it was just part off the mouth extension.( I built the 10 foot and 8 foot mouths on sites) The Bertha was 42 x 36 x 60 - size limited by what would fit through a fire exit door to get it into a club and why the mouths were always assembled on site. The Emerald got it's name from the Emerald City Disco in New Jersey where it was first used, the RLA Waldorf got it's name from the Waldorf Astoria.

18Mm would be better, but heavier, 15mm works too - depends on how good a cabinet maker you are more than the thickness. Tuning wouldn't be affected. Not sure why porting is of interest, the mouth extension would add LF extension and porting can be hard on cones in ported horn boxes.

Phase isn't so audible at 100 Hz.
 
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