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Old 27th December 2016, 03:11 PM   #1
gadut is offline gadut  Indonesia
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Default Need advice on my open baffle build

my open baffle panel dimension is 50cm x 110cm with 18mm plywood. I have used Alpair 10p with additional $7 cheap car tweeter but they dont integrate well. Today I receive my package for tweeter JBL gto 19T, using 2nd order XO @10.5kHz (1.5uF & 0.15mH) plus 1ohm series resistor, now they blend nicely. I think that i have settled on HF driver.

Now I'm still not sure which driver for bass, my previous plan was to use Eminence Beta 15A 2pcs per side which seems commonly used. But when I read on SBAcoustic article that they also produced PA driver (ACR brand but only for Indonesia market), I find 15" driver with T/S parameter which seems 'better' than Beta 15A.

15″ 38H156SCF ACR SPECIAL NEW | ACR Speaker

I have compared both T/S value and most significant differences are Qts, Xmax, and for sure their price. from the graph also shows that ACR reach 95dB on 30Hz, while Beta 15A reach it on 110Hz.

I get a feeling that this is too good to be true, but i have limited knowledge and experience on speaker driver. can anyone give me advice whether should I use this ACR driver for my OB bass instead of Beta 15A?

Regards
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Old 27th December 2016, 03:26 PM   #2
adason is offline adason  United States
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Nice work so far...
I spent quite a lot of time optimizing crossovers between fullrage and tweeter, and its not always easy and straightforward. In my humble opinion you have to use low pass on fullrange, once you decide on tweeter. See, fullrange will try its best to reproduce some heights, which will interfere with tweeters output an results in rugged response and poor integration. If you use well behaved midrange with no breakups, you could get away without low pass, but with fullrage I always end up 4th order LR, and 2nd LR on tweeter. I measure and listen, and swap parts...till all is good and sound is seamless, sweet and coherent. Bass is another story.
Good luck.
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Old 1st January 2017, 12:52 PM   #3
gadut is offline gadut  Indonesia
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@adason
I find that playing with FR & tweeter seems easier, only need to combine capacitor value ( I use multiple 0.5uF to get the treble that sounds good to my ears)

finally bought 2 pairs of ACR driver @ $28 each and started to make 15" holes. "it's stupid but it works" is all I can say about making 4 holes of 15" by using hand drill, hole saw, and hand saw.

to stabilize the panel, i order metal triangle from nearest workshop. it's strong and look nice too. I should put my 3way to living room since no more space with this huge OB (my wife and twin boys are happy now to have this 3way to watch TV and movie )

the drivers are connected in parallel, use 2nd order PLLXO @80Hz after dcb1 and powered by FirstWatt M2 clone. I have set the volume in maximum position to get strong bass but the vocal is still dominant, maybe 24dB is required for this 15" which is listed as FullRange.

another try is playing with my old laptop + mauropenasa gainclone with Eq, set on V-shape Eq and surprisingly this 15" has good treble, even no need to connect A10p or jbl tweeter. with only left speaker connected (another one is still on progress), I'm blown away with what I hear now, compared to the 3way, this OB create HUGE sound and fills my 3x4m living room.

Size does matter, the bass which come from 2x15" seems like effortless compared to 7" in BR. Increasing the volume does not show any compressed sound, I dont dare to test on maximum volume yet in order not to get my neighbor complaint. Vocal and treble is more enjoyable than 3way, my memory says that Alpair 10P is good on low volume but not stable on high volume. seems that this PA driver is so much fun for DIY.

This 15" OB is the best $150 that I have spent on DIYaudio, never regret to choose this route
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File Type: jpg IMG_20170101_172210_HDR.jpg (927.4 KB, 118 views)
File Type: png Eq.png (23.4 KB, 110 views)
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Old 1st January 2017, 05:00 PM   #4
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Wow! Nicely done,enjoy. I Love big open baffle bass!
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Old 3rd January 2017, 10:54 AM   #5
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Hi Gadut,

I am building a open baffle, 02 x 15" bass drivers with 01 full range driver. But it when bass driver play, the baffle vibration is quite a lot, it make the full range vibration also.

Have you experience that issue?
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Old 3rd January 2017, 02:33 PM   #6
gadut is offline gadut  Indonesia
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finished another set with rounded top corners. it's time to build LP/HP filter + bass boost
Quote:
Originally Posted by bitinhvi View Post
Hi Gadut,

I am building a open baffle, 02 x 15" bass drivers with 01 full range driver. But it when bass driver play, the baffle vibration is quite a lot, it make the full range vibration also.

Have you experience that issue?
No, my OB does not vibrate at all eventhough with massive low freq Eq.

my consideration during this build:
- use strongest plywood that you can find, mdf is a big no
- what kind of supporting side panel that you use? my panel is supported by 30x30x3mm reinforced steel and additional decoration from solid rectangular steel
- additional carpet at the bottom will give better grip to the floor

I have tried to push the panel as strong as I can but it barely moved, maybe only 1-2mm and for sure my hands are not weak. hopefully it can give some insight
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Old 3rd January 2017, 05:06 PM   #7
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Quote:
Originally Posted by bitinhvi View Post
Hi Gadut,

I am building a open baffle, 02 x 15" bass drivers with 01 full range driver. But it when bass driver play, the baffle vibration is quite a lot, it make the full range vibration also.

Have you experience that issue?
Yes the baffle vibrates a lot. You need to have a very stiff baffle. The old style double layer baffle with sand filled in between the two sheets would be a good method to reduce this. I have a plan on my mind but haven't yet got to trying it out. The single layer ply used for an initial test visibly vibrates on bass notes. I have used sand filled baffles earlier . They are quite stable and 'dead' ! My speaker stands for my bookshelf speakers are all sand filled ! Makes them very heavy too.
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Old 3rd January 2017, 09:13 PM   #8
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Hi,

15″ 38H156SCF ACR SPECIAL for 29$ looks very very interesting driver. Could you provide some links where we can buy this driver?

Regards
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Old 3rd January 2017, 11:18 PM   #9
gadut is offline gadut  Indonesia
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@ashok
if my memory is good, you have used Eminence Beta 15A rite? did you try to give massive Eq low bass? is it good? I choose this ACR since i get advice from my neighbour who has PA business that Eminence is weak, while ACR cone that i boosted is moving like subwoofer because it has 7mm xmax

@matejsirk
this ACR driver is produced by Sinar Baja for PA market and I think it's only available in Indonesia. you can look at below distributor list that they are all located locally

DISTRIBUTORS | ACR Speaker

I dont think those distributor will ship overseas and the cost will be high

SBAcoustics (SB ~ Sinar Baja) product line is for international market but they are for high end audiophile
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Old 4th January 2017, 02:14 PM   #10
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Quote:
Originally Posted by gadut View Post
finished another set with rounded top corners. it's time to build LP/HP filter + bass boost

No, my OB does not vibrate at all eventhough with massive low freq Eq.

my consideration during this build:
- use strongest plywood that you can find, mdf is a big no
- what kind of supporting side panel that you use? my panel is supported by 30x30x3mm reinforced steel and additional decoration from solid rectangular steel
- additional carpet at the bottom will give better grip to the floor

I have tried to push the panel as strong as I can but it barely moved, maybe only 1-2mm and for sure my hands are not weak. hopefully it can give some insight
Unfortunately, I using MDF .

Thanks for your advice. I will change to plywood.

Thinking to try as attached cabinet, shared by a forum member (sorry I do not remember), I think it may help to reduce vibration and the size of baffle.
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