Mid-tops, what to do....

chaudio wrote:
I've been tempted just to build single 12" versions.

Crlllue crlluuue (Ref: simpsons, the pidgin scene on "who shot mr. Burns.)

I know you like the 1.4" drivers cause of the top end I could probably be tempted to replace it with a angry 2" to keep up with the 12"'s, build another pair and run them of two amps in bridge mono..
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Building new tops with 1x12 would be easy to redesign and even better on your back.
Would there be a problem getting the HF high anough for the crowd? suddenly need to bring extra beer cases
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I have still not gotten to rip of you design here (yes. i know i first told you like over a year ago!, but I'm busy building my preprod studio freespeakerplans.com/forum/forum_posts.asp?TID=452 )
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Edited by: hansa

Ey... Chris...
What are the measure of you ports?
Are they like 12x12x20cm?? I'm moddeling a single 18" now and the front will look good with 15x15x35cm ports. But that is twice the area needed.. What do you think? Estetics or cut it down in size??

I think mine are 14x14x35 from memory.....

I generally choose the length as say 2/3 depth of the box then calculate the area. That way you get the largest port area possible without excessively long ports.

You obviously have to do it as an iterative process because as you change the port size, the volume in the cab changes etc etc...


Back on the subject of mid-tops. Having had a bit of time to consider it all on a job today/now yesterday I've decided for the time being to build a pair of single 12" + 1.4" boxes which can be run in parallel with the existing ones and act as infills etc. Something I've considered doing for a while. It's the cheapest solution for now, got some spare 12" drivers and horns, just need compression drivers.

That'll keep me going until I can design what I really want. Still can't decide between line array and point source.....

chaudio wrote: I think mine are 14x14x35 from memory.....

You gave your 18LW1400 about 160 liters?

quote=chaudio]
I've decided for the time being to build a pair of single 12" + 1.4" boxes which can be run in parallel with the existing ones and act as infills etc.
[/quote]

Can you get two more PD C14? They are pretty hard to get hold of now are they not?
I like the idea of "infills". The picture in my head looks sweet. I've been missing a setup like that when I'm rocking infront on a concert aswell.

BTW.. you don't work night shifts... You are up really early/late!?!Edited by: hansa

By the time you subtract the ports and driver, they're sitting in more like 140L

I've got one more PD C14, finding the last one might be tricky. More likely to just go for something else.

Gig finished at 11pm. Hour to load out, 12am, two hours to drive to unit, 2am, half an hour to unload wet soggy speakers, half an hour to drive from unit to home, 3am. Just waiting for all the caffeine I drank while driving back to wear off so I can go to bed!

Hohoho. Well. sleep tight
I'm really high on sugar and coffy self right now. Final day of 5, working night.. 0800 and I'm off!!

I'm going to give my 18LW1400 150-160liters after subtracting ports and driver.
Hoping to achieve a little more relaxed response.

Sounds good. Tune it to 40Hz or just below according to taste!

I'm off to bed!

This situation is one that may face and from a design situation poses a number of problems. If cost, transport, storage and weight/size are not too critical the easiest thing is to keep what you have for the smaller venues and build more speakers and buy more amplifiers for the bigger system.

Consider a very small line array system similar to the geo 805, with a single 8” cone and 1” drive unit. Unless you are using 4 or more cabinets per side it would be cheaper, easier and sonically just as good to use a more conventional cabinet. Most drive units available for home construction are 8 ohms so with four speakers already the impedance is down to 2 ohms. To keep within the 4 ohm loading limit, and assuming an active crossover, two amps per stack are already needed unless a method of series and paralleling cabinets is used to link the cabinets. Add to that the less than significant price difference between 8” and 12” drive units plus the instability of stacking a tall pile of small speaker and it doesn't look promising.

For a practical, scalable system suitable for pubs/clubs I think JBL and Peavey got it about right by compromising some of the theoretical considerations and using a 12” bass driver plus three comp drivers for JBL and two ribbon drivers for Peavey. As a side note, Don Boomer of Peavey took an active interest in the Harmony Central line array thread. Anyway this solution seems to work reasonably well and should perform well as a single cabinet. If I were considering a system using a single cabinet design, that needed to be scalable from 50+ venues upwards I would consider something similar maybe with a 10” and one or two compression drive units that would operate down to 1200Hz. Designing a wave guide is not too difficult but may be more tricky to implement for a home constructor. Some of the commercial ones seem just to be a tall thin parabolic horn which would be easy to do. If the mouth of the complete flare was made square, it could be rotated to allow the cabinet to be used vertically or horizontally. As the cabinet count goes up the problem with amplifiers still remains, but there is not much that can be done.

If you never operate without subs, and don't mind a larger cabinet, a co-ax horn system would give a more controlled dispersion. Take your pick of the VTC, my slot loaded horn or any other of the line array variants of the unity/co-entrant style design. The main problem is even with a relatively large mouth my horn was only flat down to 150Hz. The coupling of multiple enclosures would improve this but with a single cabinet the bass driver would need to operate up to 200Hz. VTC do claim a lower frequency limit but this is with their dedicated processor which may boost the bass.

With any multi-cabinet system it is sometimes, from a design view, helpful to consider the coverage as a crossover. With a single cabinet the acoustic output is the combined sum of high and low drive units at the crossover frequency. Just how much interaction there is depends on the filter roll off rate and whether or not there is any overlap of the crossover frequencies. A system that has two 40 degree horns splayed at 40 degrees will have the – 6dB point on the main axis and there will be minimum overlap. The only people able to hear both horns will be equal distance from either horn and all should be well. Move off axis and the coverage of one or the other horn will dominate. At lower frequencies where the low frequency drive unit has a wider coverage it is like using an overlapping crossover with a lower roll off rate. Even when off axis it is possible to hear both drive units. Depending on the relative distance from each drive unit, and the hence phase difference, will determine if the outputs sum or cancel. The response will be different at each position.

The Unity, Synergy or what ever you want to call them will have the advantage of controlling the dispersion pattern to lower frequencies (depending on the horn size) but by limiting the crossover region between cabinets the coupling and any increase in level derived from it will go, meaning that the maximum attainable level at any one position is that which can be obtained from one cabinet.

I've only scratched the surface here, but need to get back to the real world now. Good luck with your decision.

Thanks for your thoughts Steve.

As much as I'd like to go down the line array/vertically arrayable route, I'm coming to the conclusion that it's just not going to be practical at the moment. If I need to, I can lay my hands easily on D&B or L'Acoustics systems so for now I think I should leave that type of cab to the experts. If there were some off-the shelf line array drivers available in the configuration I want, I might have considered giving it a go. I might still have a play with the line array drivers for some installation boxes at some point. What I really want is a line array wave former that takes a 1.4" CD and converts it into a 6"x1" slot to mate onto a waveguide containing two 8" drivers. Exactly like dV-Dosc. I would also happily do it like D&B Q1 if a suitable waveguide was available. Beyma do the TDWL4 but it's quite pricey without the two 1" drivers to go on the back of it, and the coverage graphs aren't even that impressive.

So, point source is the way to go for now.....

I think for most of the jobs I'm likely to encounter with my own system, the most I'm going to need is two 60deg wide cabs per side with similar SPL capability as my current twin 12" boxes.

There's so many design considerations! Every time I think of a suitable box, I start thinking; will two fit on top of the stack of subs, will they pack into the van easily! In those respects, my current system is fantastic. Packs neatly in the van and I can lift the tops onto a stack on my own (very important as I do a lot of gigs on my own).

Building the extra mid-top will keep fullfil the rest of this years gigs (that I know about). Will have to work on new designs over the winter.

What I'd really like to do is use Mykeys XT8 flare and the big 18Sound flare pictured above to do the mid-highs. Then all I need is something to cover 100-400Hz. Now it does seem that a folded, port assisted 12" horn would be possible using the same type of configuration as my 15" ported horn design.......

Like a baby version of this:

Thats a 15+10+1.

So your baby would be 12 +8 +1?