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Old 22nd March 2013, 05:41 AM   #1
arrie is offline arrie  South Africa
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Default 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.
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Old 22nd March 2013, 05:22 PM   #2
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Originally Posted by arrie View Post
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).
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Old 23rd March 2013, 12:29 AM   #3
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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........

Last edited by ticknpop; 23rd March 2013 at 12:35 AM.
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Old 25th March 2013, 05:36 AM   #4
arrie is offline arrie  South Africa
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Originally Posted by weltersys View Post
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?
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Old 25th March 2013, 07:35 AM   #5
Zero D is offline Zero D  United Kingdom
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@ 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
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Old 25th March 2013, 05:03 PM   #6
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Originally Posted by arrie View Post
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.
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Old 25th March 2013, 07:27 PM   #7
rpa is offline rpa  Germany
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Originally Posted by Zero D View Post
@ 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.
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Old 25th March 2013, 10:19 PM   #8
Zero D is offline Zero D  United Kingdom
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@ 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

Quote:
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
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Old 25th March 2013, 11:27 PM   #9
rpa is offline rpa  Germany
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Originally Posted by Zero D View Post
@ 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.
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Old 26th March 2013, 04:52 AM   #10
arrie is offline arrie  South Africa
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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?
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