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General setting for biamp 2x15”+2”

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serioussound View Drop Down
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    Posted: 20 February 2019 at 10:47am
I have came across a system with:

2x Dual 18” cabs RCF L18S800
2x Dual 15”+2” cabs Eminence Dela 15LFA and RCF N850.

Is there any general rule when biamping cabs with big hf driver + 2x15” drivers?

Maybe crossover around 1200Hz but what else settings are pretty general that I need. - 10dB on the high frequency?

Delay on high frequency?

This is not going to be the nicest sounding rig of all times but I want it to be an alternative when I need little bit more muscles then my small active pub systems.

All general tips are welcome!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Finjby Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2019 at 1:17pm
What's the spacing between the 15" drivers?  This will determine the range at which they work together, and thus the wavelength/distance that they work as independent sources...causing comb filtering.  
With such a big horn you should be looking at lowering the xover point to say 800hz to reduce the lobing between the 15"s.
Sensitivity wise you can expect to reduce the dB level by at least 10dB for the hf...probably more.
Delay wise you should be delaying the 15"s back to the horn origin...but all depends on the slopes you use and the physical layout of the box.
Stick with linkwitz 24db per octave to begin with.
Do you, or anyone you know, have access to SiaSmaart?

Twin 15" and horn boxes suffer from lack of vocal, due to the size/spacing between drivers.  Vdosc is twin 15", but gets around the issues by adding 4x7" midrange and lowering the operating range of the 15's to 400hz.

Good luck!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2019 at 7:12pm
I've worked with a variety of twin 15" + 2" boxes and although you're always going to get a better midrange from other driver configuration, it is possible to get an entirely usable system, even for live music with a lot of vocal.  One of the advantages is you get a lot of authority in the low mid so you can get really good drum mixes etc.

There are a few key ingredients to making it work.  One is a 15" driver with as smooth a midrange as possible.  Although the crossover point might be quite low, if there's a big peak at 2kHz for example, it's hard to escape it though any kind of EQ.  Unfortunately the Delta15LFA is not a good option here.  The best driver I've found for the job so far is the RCF MB15H401 so you might need to consider an upgrade at some point here.

The RCF N850 should be fine but it will very much depend on the horn flare which needs to be large to support a low crossover point.  The boxes I've worked with have all had 2" horns around 500x300 (18"x12") in size.

I've generally found somewhere in the 1-1.2kHz range is the optimum.  Not many compression driver and horn combinations can really go much below that.  Any higher and the midrange starts suffering from the 15".

Some form of measurement system would be useful for doing the setup but not essential.  Personally I fine tune the alignment of the cone drivers to the horn using the phase response but if you start with just the physical depth of the horn that'll be better than nothing.  Again, if you have measurement equipment available you can use that to balance the level of the 15's and the horn through the crossover region but if not you'll have to do it by ear.  As above, -10dB is not unreasonable as a starting point.

At this point the system will most likely be lacking any real high frequencies, assuming you have a constant directivity horn flare.  Use a 6dB/oct high shelf to compensate.  Start at about 8kHz and about +6dB of gain.  Play with the frequency and gain to get the best balance.

Crossover between the subs and the 15"'s could be anywhere between 80-120Hz depending on the exact cabinet designs and a certain amount of personal preference.

Hope that helps!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2019 at 11:21pm
Yeah the Delta 15LFA drivers are a poor choice for this system but they might do OK with some processing. 
How big are the double 15 boxes and what size ports does it have?
How big is the Horn?
Does the system come with amplification and processing?

The whole idea with using a 2" exit horn and CD is to bring the crossover frequency way down so that the 15's never get up into cone resonance and breakup frequencies, but the horn they are loaded on has to support lower crossover frequencies. The system will still require some processing though.. more than just crossovers, it will need some specific EQ to address resonance peaks from the dual drivers, some out of band EQ to tame the midrange response of the 15's perhaps and to tame the CD output in this region so it's not rip your face off bright, and to boost the HF response of the CD back up.. even if the horn isn't constant directivity. This is a common thing with large CDs. Then you need crossovers, time alignment and limiting. That all means you need to get these things in front of a test mic to see what you're up against. With that you should be able to dial these in to sound very good overall.

My double 15+2 boxes are loaded with KappaPro 15s and a DE750 crossed at 1khz, unprocessed they are ugly loud.. all mids, but it didn't take much EQ to make them sound sweet. These drivers don't generate any low bass when played alone but they are super efficient and over double 18 subs electric bass sounds fat so IMO LF drivers aren't required.


Edited by Conanski - 20 February 2019 at 11:42pm
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serioussound View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote serioussound Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2019 at 8:53pm
My cabs looks like pictures.

Volume is 145 litres not counting minus for magnets, braces and so on.

Horn size is:

420x260mm

Any suggestions with this new info?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote serioussound Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2019 at 8:54pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2019 at 10:00pm
15"s beam a lot on their own. with two of them they are going to beam like crazy. you can solve the on-axis problem with eq but then you will find the vocal's lacking off-axis. you can put up with a bit of beaming as long as you cross them before the pattern becomes a lot narrower than the HF horn (which will widen a bit at the bottom of its range). what you want to avoid is 'waistbanding' where the dispersion becomes very narrow and then widens up again as you hand over to the horn.

those horns look like they will go pretty low but test them and see. If they can manage it try crossover around 700Hz. start with 4th order on the LPF and 3rd order on the HPF. because the compression driver rolls off below 700 Hz you will end up with an approx 4th order response. if it doesn't quite sum try increasing HPF or reducing LPF. or try different crossover frequencies for the two sections. even order filter and using the drivers where they have well behaved directivity is your best chance of keeping pattern control through the crossover region.

forgot to say you may want to sort out the delay before doing the above. if you don't have equipment to measure you can use the auto-align on an ultradrive. or take a guess based on length of horn.


Edited by snowflake - 21 February 2019 at 10:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2019 at 11:55pm
It will of course depend on what you're using them for and where, what dispersion you actually need them to cover.  It may be that in practice the beaming of the 15's isn't that noticeable.  It's obvious when you set up one cab in the middle of a stage and walk across in front of it, maybe less so when you have two on stacks with some toe-in to keep it off the walls and fill in the front.  In which case there would be less stress on the compression driver by nudging the crossover point back up a little.  Plenty of experimentation and testing to be done in any case.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2019 at 2:55am
Serious... is that a "brand name" cab with different drivers or are they a complete DIY effort? Just wondering if there is a spec we can look up to see what horn that is. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote serioussound Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2019 at 9:17am
No its a DIY build.

I dont know maybe this box is not worth the energy?

Maybe its better of selling the drivers?

But the box is really well built with lots of handles and i like the way of putting them on a dual 18 cab without need of stands or special rigging..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2019 at 11:38am
no reason they shouldn't work well. cut some of that wadding away from behind the vents - it's obstructing the airflow.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cravings Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2019 at 12:23pm
people sometimes do what could be called a 2.5 way crossover on a box like this. rather than have both 15s doing mid and getting muddy.. if there's a way to cross the lower one over at something like 250hz, but still have the upper one play the full range of mid bass.. so putting a passive filter in there is a possibility. maybe expensive for a big coil like that, and may introduce other issues with the phase between the 2 15s.. but something to look into or consider anyway.

i've never thought a double 15" mid top made any sense unless specifically to stack over a double 18.. there's not really any other sensible way to deploy them.
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