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Which cab formy beyma 12mi100's?

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JBK View Drop Down
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    Posted: 02 September 2016 at 6:40pm
Greetings fellow audio nerds,

As some may have seen in the scoop pr0n section (http://forum.speakerplans.com/scoop-porn-part-2_topic46967_page219.html) , our soundsystem have a mid section of 4 x 12" drivers running the 250-1400Hz frequency band in a closed enclosure (2x12" per box, no angle at all)
They're Beyma 12mi100 drivers powered by a crest cc4000(2 a side , rated 1350W/channel @ 4ohm)

Until this summer everything where fine, but we have increased the system subs (scoops) and tops (horn & tweets) bud not the mediums, and we found that when playing at full volume drowned in the crowd the sound was fine except the mediums, they clearly lacked volume (i'd say definition but maybe the issue was only volume)
I think the amp is not the issue.

I plan to lower the frequency cutoff to lower the 12" to cut them at 180ish (we got g subsunder)
I would like to add an angle between drivers so the 12" wouldn't overlap, to cause less phasing issues, the problem is i can't find any info on dispertion vs frequency on these drivers.
Also, I'm thinking of adding a horn to gain some db, to save the cost of adding cabs.

On the web I found people saying those drivers are OK in a mt122 mt121 or mt130, or even altec m17, but not frequency plots etc, neither simulated or recorded.
I was thinking of building just the 12" part of those cabs, so I have a horn and angle.
However, I'm a bit suspicious because the plans are not intended for those drivers
I tried to sim one of those cab on hornresp  to see what design would sound best, (even if it's not a guarantee of in real life success). but i think i need some more experience because after some time I felt like hitting my computer.

So my questions to your ladies and sirs are :
- Do you have experience with this driver and can recommand an angle, or even better a plan for the frequency band I intend to use them?
-Do you think I need not only to add an angle and a horn but also more cabs? (or just put an angle and see if i need more cabs)
- Am I doing this completly wrong?
- Am I over thinking this?

I really want to the take time to find the best option I'm not in a hurry, to my ears our sound sounds sweet and stillloud when it's not pushed too hard  but at the festival we played at, they're was a serious crowd screaming etc (check the video in the link before to see what i mean) but on normal duties I think we come close to what we wanted (well I'm not 100% satisfied on the low medium also but each thing in its time)
https://www.facebook.com/rootikalvibeshifi

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JBK Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 8:53am
Come on guys, don't let me slip to 2nd page :'(
Nobody has experience with 12mi100?
Advised enclosures
At least hints on how i can estimate best angle?
Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 12:46pm
Originally posted by JBK JBK wrote:

mid section of 4 x 12" drivers running the 250-1400Hz frequency band in a closed enclosure (2x12" per box, no angle at all)
 Beyma 12mi100 drivers powered by a crest cc4000(2 a side , rated 1350W/channel @ 4ohm)

Originally posted by JBK JBK wrote:


I would like to add an angle between drivers so the 12" wouldn't overlap, to cause less phasing issues,

"phasing issues" doesn't seem like a proper term for me (I might be wrong). What do you mean with this?

Also, what is the reason you want to do this? Is there a real problem in the mids that you can hear? If you have the time, listen to only your mid box, and move in front of it to see if the sound is bad or changes a lot while you move. If it doesn't, there is probably no problem. 

For most of the frequency band you are using the 12"s in (up to maybe ~1 kHz)  that shouldn't be a problem. They should sum just fine. Comb filtering starts when the drivers play back frequencies with wavelengths shorter than the distance between each other. In your case there might be a little bit of comb filtering in the upper end of your mids since you are running frequencies which have smaller wavelength than driver diameter (30 cm). If your HF driver/horn combination is strong enough, you could try lowering your crossover point towards 1 kHz. 


Originally posted by JBK JBK wrote:

Also, I'm thinking of adding a horn to gain some db, to save the cost of adding cabs.

On the web I found people saying those drivers are OK in a mt122 mt121 or mt130, or even altec m17, but not frequency plots etc, neither simulated or recorded.

If you look at the picture that I posted in the scoop porn thread around the same time as you, you can see the mid section of Ivah sound. It consists of four single 12" horn sections of mt122 (IIRC!) loaded with Fane 12" (IIRC!). It is operated 200 Hz - 1kHz with a little boost between 500 and 1000 Hz.

I can't comment on the suitability of your driver (I'm sure there are other members who can), but I think 200 Hz to 1 kHz is doable with a decent 12". Not too much low frequencies, but also not too high to have problems or need a phase plug.

Originally posted by JBK JBK wrote:

I plan to lower the frequency cutoff to lower the 12" to cut them at 180ish (we got g subsunder)

why? Gsub doesn't go high enough? 15" design might be better (also less heavy Wink) for this purpose

 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 1:30pm
I simulated two 12MI100 in closed box in Winisd.

on paper 12MI100 seems quite a good choice. It has good sensitivity and high BL. But xmax is not very high, so for direct radiating you can't expect too much bass.

According to my simulation for closed box, above 200 Hz enclosure size doesn't matter too much. Excursion stays mostly below xmax regardless of enclosure size. So without knowing your exact enclosure I can say that if you cross over at 250 Hz, you can give your drivers full power without a problem, and reach 130 dB with a pair of 12MI100. 

But dropping crossover frequency below 200 Hz will very likely get you into trouble. You will exceed xmax and get distortion! Maybe even damage your driver. 

The datasheet also has a power compression chart, according which you might get up to 4 dB of power compression at full power. So there is a limit to what you can get out of these guys in closed box.    

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JBK Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 1:40pm
Well thanks for taking the time !

Originally posted by bob4 bob4 wrote:

"phasing issues" doesn't seem like a proper term for me (I might be wrong). What do you mean with this?
Also, what is the reason you want to do this? Is there a real problem in the mids that you can hear? If you have the time, listen to only your mid box, and move in front of it to see if the sound is bad or changes a lot while you move. If it doesn't, there is probably no problem.


Well I noticed, when turning on the amps whil signal was in, that I heard a different "tone" when playing the 2 box together vs just one box playing.
I mean, instead of beeing a bit louder when powering the 2nd box, it also change a bit the "tone" the "sound" of the music playing through, that's what I thought about phase issue.
Sorry I'm no pro in audio and I'm a french guy so maybe I do not chose the right words. But to my (quite inexperienced) ears it sounded like comb filtering, which (I've read, been told, and a bit understood) is due to the driver aiming a bit at each other, resulting in some frequency adding and another frequency substracting in one point. Might be wrong
I did not made the test you mention, will do that next time we stack the sound.
When I say 1400Hz, in fact each time we stack the system I set the crossover frequency by ears, most of the time it's between 1.2k and 1.6k. I'll try to lower that


Originally posted by bob4 bob4 wrote:


If you look at the picture that I posted in the scoop porn thread around the same time as you, you can see the mid section of Ivah sound. It consists of four single 12" horn sections of mt122 (IIRC!) loaded with Fane 12" (IIRC!). It is operated 200 Hz - 1kHz with a little boost between 500 and 1000 Hz

Exactly the kind of box I was thinking about

Originally posted by bob4 bob4 wrote:


why? Gsub doesn't go high enough?


Well it is an asumption, real world will confirm, but letting just the g subs play I hear some lower frequencies of the voice or instrument and i does not sound ultra sweet ...


Originally posted by bob4 bob4 wrote:

5" design might be better (also less heavy Wink) for this purpose

Yes I know now, but I wasn't in the crew and hasn't that knowledge when the sound was first built ;) so for now we stick to the g subs that still do the work.

Maybe just the core of problem is that we don't have enough speakers ....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 2:24pm
A quick search threw up this:

http://www.dancetech.com/index.cfm?loading=pa&pa_loader=175

Note what it says there:  "These again are short-throw cabs", so I´d say that you´d definitely be better off making some horn-loaded cabs, like the MT122.




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Post Options Post Options   Thanks (1) Thanks(1)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 2:33pm
most of the dancetech designs don't strike me as being very refined. Seems more the kind of "build dis kinda box, throw in whatever driverz yu have, it will make some noizz (proceed to drink beer)" 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JBK Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 2:52pm
Thanks earplug but as bob4 stated I'm not fond of throwing any driver in a random enclosure ... Hence why I come searching for someone with real world experience with them drivers.

Also, if i made two or three of them boxes stacked side by side, some drivers would aim directly at each other? this doesn't feel right...

Again I mentionned mt122 130 121TDA etc but they're not made for this driver. We can't afford building boxes and then see if it's good, I'd hope someone would've made the test and give their experience.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 3:03pm
@JBK: 

1. do you use speaker management/DSP?
2. do you know how to use winisd?

looking again at the pictures of your stack (looks nice btw Thumbs Up) I see the mid boxes have a big distance between the individual 12" drivers. This is the reason why you hear this "phasing", and it is the first thing you may want to change. The drivers will couple much better if they are right next to each other (like the bullet tweeters in your array). Maybe you could build one smaller box with tighter spacing to try it. That should decrease the "phasing" sound you described significantly. 

I estimate that your current mid box has an internal volume between 80 - 100 litres.  

According to winisd, closed box will have very similar frequency response for a wide range of box sizes. Basically it doesn't matter if the box is 20 or 100 litres. The only difference will be that cone excursion is limited more by small enclosures. 

here is a link to an old but very useful book written by bob mccarthy. There is a lot of useful information in it. Although it refers a lot to Meyer Sound products, it contains a lot of useful acoustics, electroacoustics and system design knowledge:
 


Edited by bob4 - 06 September 2016 at 3:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JBK Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 3:30pm
1. do you use speaker management/DSP?
No we use the 4way crossover from the preamp (dubsonic) and filter the mid section for the 12"/compression drivers
(hence why I can change this cutoff frequency but not the others)
I'm actively trying to convince the rest of my mates that a lms would actually be a good idea, I think I will end buying a berry ultradrive on my own and not let them the choice (I'm the youngest and last arrived in the crew but the most curious technically I always try to improve things and I'm never 100% satisfied, but it's hard to convince others to start building again and spending €€€ on gear because "it already works fine" if you know what i mean )

2. do you know how to use winisd?
No but I'm curious about it so I can try ( For what it's worth I'm a software engineer so I'm not afraid of softwares ;) ) However I tried to sim one of the horn cab in hornresp and it was a pain in the a.s.s however I think I need more than a few hours to fully understand the soft.

Thanks for taking the time :)

Originally posted by bob4 bob4 wrote:

looks nice btw

Embarrassed thanks, it sounds pretty sweet also



Edited by JBK - 06 September 2016 at 3:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 3:48pm
don't worry, winisd is quite easy. The only bad thing about it is that you have to constantly switch the graph between different parameters.  

Happy to help :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2016 at 4:14pm
Originally posted by bob4 bob4 wrote:

most of the dancetech designs don't strike me as being very refined. 


That’s because a lot of them are copied straight from the old fane constructors handbook, however dancetech are missing the driver details and frequency plots that are in the book,  the angled box in the dancetech link was on page 44 of the book, the frequency plot in the book for the cab is dated 23rd March 83, so the design is at least 33years old!!


Edited by APW - 06 September 2016 at 4:15pm
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