Community speaker rebuild

dokkodo

Member
2017-03-15 7:26 pm
TLDR;
I would like to build some cabinets for my Community Audio CS70 drivers, which are 4 x 12 and horn/tweeter. I would consider breaking them up, as my previous attempt resulted in very large, heavy boxes. Perhaps into 4 2x12s and tweeter boxes (might look like a reggae system but thats ok in my books) or if there is such a thing as a 4x12 mid/kicker arrangement, that would work.

Any start point for designs much appreciated. Proffesional woodworker, total amateur electro-acoustic phsyician.

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Long version -

I posted on here a few years ago about a project and got some great advice, so im hoping for more.

I rebuilt some community audio csx70's, which have 4 12" drivers each, a compression horn and tweeters.

I am a joiner so I have a workshop and building boxes is very easy, however i know next to nothing about speaker design, so last time Bob4 amongst others kindly took me under their wise wings, and i came up with a PPSL design to house the 12"s with the horn on top. See attached.

So, initially i was quite happy with them. Especially once I found a pair of brand new 15"s in a charity shop for £20, for which i immediately made a dual 15 PPSL cabinet. Using a DSP to Xover everything, sounding much better as a 2.1 system. Especially as the speakers and cabinets cost me very little.

However, the top boxes are very large, and heavy, and i think on reflection dont do such a great job. They have a very narrow field, seem to be missing fullness and struggle to give decent warmth/punch. I have a reference mic and software but have yet to set the system up for proper testing. Must do that sometime, but parties tend to be waiting for music.

So especially now that I have invested in the expensive parts of the amps, dsp, graphic eq and various other stuff, i feel like id like to rebuild the top boxes in a better fashion. I might also sell the original sub to finance 2 pairs of matching drivers, so I can have subs both sides.

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Anyway i appreciate this might be an annoying newb question but any thoughts most welcome!
 

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Hi there!


I will start by saying that now is probably a good time to assess the merits and disadvantages of your components before you commit more expensive material and precious labour to your project.

You have basically two choices:
1) incorporate some or all of the CSX components in your new build(s)
2) go for something completely different


a couple of general thoughts on the original CSX product, the components etc.

Spectral balance of the box
I had a look at the datasheet again. It is fairly obvious that the M200 midrange compression driver is the strongest, loudest and most valuable part of the system. One obvious clue is that four 12" woofers are required to keep up with it, and this begs the question, do they keep up at all? The grainy frequency plot in the datasheet shows that the M200 is substantially (about 6dB, maybe more) louder than the low end of the box. The box also has a "midrange boost" switch on the crossover, that can be engaged for extra midrange output and "vocal clarity".

personal guess/interpretation dislaimer
My hunch is that this is the natural sensitivity offset between the woofers and the midrange/HF section. Normally such kind of discrepancies are dealt with in the passive crossover by "padding" the HF output (using a voltage divider to lower the voltage sent to the midrange and HF section). I assume that the graph shows the basic frequency response of the box with "boost engaged", which basically means the pad of the mid/HF circuit switched off.
What is the conclusion from this? The original woofers are lacking in sensitivity.
end of personal interpretation

the conclusion from this is that when you operate your DIY box, you have to expect to have to set an according gain structure to significantly reign in your midrange, with anything between 6-12 dB or even more level reduction compared to your woofers.

Mid Horn size, crossover points, integration
Precise dimensions of the mid/HF horn are not available, but judging from the drawing in the datasheet, and compared to commercially available 2" throat horns the CSX mid horn seems slightly undersized for the 700Hz crossover point.
As you have already found out, physical layout is a problem as well with four woofers. As I pointed out in the thread on your previous build, the result of the 700Hz crossover frequency, the size and spacing of the woofers, there are two massive dips in the frequency response of the box around the crossover.

personal opinion
If you decide to persist recycling the M200 mid section, your main challenge in your build is to avoid these cancellations between your lowmid and the M200.
end of personal opinion

Piezo HF section
The second potential weakness of the CSX components is the piezo HF array. Does it sound good enough? Do they still work reliably? If you have any doubts that you might want to not use it later on, now is a good time to consider the repercussions.

personal opinion
You could simply cut off the top part of the horn assembly, and purchase suitable 1" drivers with small horns (they don't need to be big, as they will be crossed fairly high between 3-4 kHz). But then you have to also consider if you don't want to upgrade the mid horn for the M200 to something larger, to enable slightly lower crossover to your woofers. So you will have increased cost, which you will have to weigh against simply going for a set of brand new 1,4" compression drivers with matching horns, which would cut down on complexity as well.
end of personal opinion


CONCLUSION and build options

Getting back to the initially proposed two scenarios, I will try to make a couple of build suggestions for you for inspiration:

1a) Hornloaded box incorporating CSX mid/hi horn section mounted in the horn mouth, like for example in a Nexo TS2400 (see attached picture)
http://hornplans.free.fr/mkb230.html

pros: - If the community 12" woofers work well in the horn, you will have a much better level match between lowmid and mid/hf section.
  • you can recycle all your components, and even experiment/upgrade with other horns or hf drivers later on.
  • with the leftover woofers you can build two more matching bins for added "kick" and stacking height
  • will probably be even louder than the original configuration
  • smaller than current tops

cons: -big
  • heavy
  • not polemountable

1b) directly radiating box with one sensitive 10" or 12" woofer per box together with the CSX mid/HF section
pros: - small and light
  • simpler build
  • polemountable
  • avoids multiple woofer geometry and cancellation problems


cons: - less output
- cost of new woofers

2) DIY, for example a basic single or double 10"/1,4", or hornloaded PM90 if you are ambitious
pros: - start from a clean slate
  • clear instructions/plan/goal
  • diy fulfillment

cons: - not being able to reuse your community parts
- higher cost


3) pair of second hand tops, maybe some slightly higher grade Community boxes that also utilize M200 drivers , such as RS220 (double 8" hornloaded, very compact and loud!!)
pros: - "plug and play"
  • maybe you can find a lucky bargain (covid misery fire sales)
  • you would have 2 M200 as spares

cons: -old stuff can potentially break / be faulty / on the edge


4) something brand new, for example Soundgear Orbit4 tops which are quite affordable
pros: - new
  • longlife
  • more music listening, less fiddling

cons: - no diy fun
-expense

whew, that was a long post o_O
 

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dokkodo

Member
2017-03-15 7:26 pm
Wow.

Cant thank you enough for the detail and thought put into this Bob!

Really super helpful.

My general thoughts in response are this: this sound system is purely a hobby activity, I take it to a few events a year, but it doesn't pay for itself. It is the process of learning, making and tweaking that I enjoy, on top of getting as much decent sound as possible without spending loads of money. In that vein of thought, I have looked up roughly what it would cost to build a PM90, for instance, and although the build itself would be no technical problem, the expense of the recommended drivers and everything else that would need to go along with them probably is outside my remit, for now.

So, priorities - making the best of what i have, the best sound for the least cash, or selling community parts and putting value towards components of equivalent value for a better build. I have time to tinker, but would rather not be splashing lots of cash on these. I also, however, do not want to be endlessly rebuilding or regretting design decisions! I am not opposed to ditching all the Community components and starting again, however i'm doubtful whether they are worth too much, without the original cabs as well.

For these reasons, id prefer to use the drivers I have -

1a) Hornloaded box incorporating CSX mid/hi horn section mounted in the horn mouth, like for example in a Nexo TS2400 (see attached picture)
http://hornplans.free.fr/mkb230.html

pros: - If the community 12" woofers work well in the horn, you will have a much better level match between lowmid and mid/hf section.
  • you can recycle all your components, and even experiment/upgrade with other horns or hf drivers later on.
  • with the leftover woofers you can build two more matching bins for added "kick" and stacking height
  • will probably be even louder than the original configuration
  • smaller than current tops

cons: -big
  • heavy
  • not polemountable

I am not pole mounting as they stack on the subs (and any other kickers I add) and im not bothered too much by weight, they only get wheeled out a few times a year as I say.

Options 1-b and 2 also appeal, but option 2 excludes the use of current drivers, and 1-b is a compromise of output, i wouldnt want to lose too much of that.

However a point you raise is the HF section. The comp driver is indeed way overpowered compared to the rest, however I can fix that with the processing. The tweeter array is ok, but only ok. I could do well to replace the lot with 1.4" horns. I have also been offered a deal on some 4" compression drivers with huge horns. I will look into the options as you are right to say this is the moment to consider replacing them.

The other factors to consider - I have just found a matched set of 4 15" drivers, so I can now have two matched dual PPSL subs. This liberates the current pair of 15"s in use, which i think could have been better suited to low mid all along. I also picked up a couple of yamaha power amps and another DSP over the christmas period on facebook marketplace so i have plenty of processing and powering options.

Drivers I have to play with -

2 x Community HF horn/tweeter array
8 x Community 12" drivers
2 x 15" woofers (will dig out spec)

So my current thinking is to build

2 x Dual 12" hornloaded box with integral HF section (which HF remains TBC)
2 x 15" kickbin
OR
3 way mid/tops? 1 x 15", 1 x 12", HF

2 (second) x dual 15" ppsl sub


For now, I am going to research the dual hornloaded 12 designs you mentioned and maybe some others, and investigate my HF options.

Thanks so much again bob for taking the time.
 

dokkodo

Member
2017-03-15 7:26 pm
I am being offered a reasonable deal on some 4" darQ CDs with large flare horns and spare diaphragms, recommended 2.5k and above... seems high compared to M200s.

annoyingly i just made this post and lost it just at the last minute so here goes again-

I have found a bunch of cab designs that are probably varying degrees of inappropriate, but interesting for one reason or another. I suppose the fact that I will not be using the recommended drivers means they will give varying and unpredictable results. However, if i use a certain design, I can always upgrade the drivers to those recommended, should I ever be inclined.

Ill put them all out there for comparison.

There is the design you proposed, with front mounted HF section somehow... would fit nicely on my subs (which are 600 x 600)

or i wonder whether the HF could just get their own box/housing to sit on top?
MKB-230 dual 12.jpg


Or I am wondering if i could adapt this design for 12"s, and whether that type of horn design will give the 12"s any extra oomph to keep up with M200.
mt102.jpeg


With spare 12"s left over could make a pair of these as kick bins, which could fill the low mid Xover gap between the subs and mid tops.
2x12 front horn loaded.jpeg


other mad designs that may or may not be adaptable -

doing this sort of thing but with a 15 and a 12 instead is appealing but have no idea how that would work
Simon_s_3_way_C.jpg


these sorts of 212 dont really appeal, too tall and thin
other 212.jpeg


another mid top option
2e022fb8bcfc68518e91f5bda6090194.jpeg

Lastly - perhaps a design like this, but adapted and/or without the 8" section at the top. However, probably inappropriate and not visually my bag.
4Pro.jpeg


Anyway all opinions welcome, just chucking things out there really, as usual, without much expert understanding.

Currently I feel most good about the MT102 on top of some fane design kickbins i think.
 

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dokkodo

Member
2017-03-15 7:26 pm
Since you are considering a lot of various different designs, it might be beneficial to actually measure the thiele-small parameters of the 12" woofers. There is a risk that the woofers might not be suitable to horn loading after all.

It would be a shame to build elaborate horn enclosures just to find out your woofers are completely unsuitable in the end.

Room EQ wizard is suitable for impedance and Thiele/Small parameter measurements. I believe you already own a proper audio interface for measurements?

Once you have the T/S parameters for your woofers, you can get opinions, and hopefully also simulations on how your woofers might or might not work in the horn enclosures that you are considering.
 

dokkodo

Member
2017-03-15 7:26 pm
Sorry yes I got excited and dumped a bunch of designs there, after further research I have eliminated a few.

I have just watched a great video on measuring TS parameters and have ordered what i need. i will be getting measurements in the new year, and looking forward to making some slightly more educated decisions.

thanks!
 
There is a risk that the woofers might not be suitable to horn loading after all.

While I agree/understand your point; as stated this is totally incorrect as over time I've posted various 'no can do' driver HR sims (up to 2.85 Qts + added series resistance) with excellent horn loading based on its specs, but like most things it's a matter of 'why bother' for various good reasons (typically way too big) and/or doesn't meet the needs of the intended app.

That said, short horns to just load over a narrow BW is often the goal such as BLHs to just boost the (mid) bass/lower mids for acoustic baffle step compensation (BSC), which has historically used high Qt (systems) to keep them as short as practical.
 
Happy New Year!

All of the front loaded straight horn tops (smt, mt102,mt212, selenium designs) dont load below 200Hz.

The Fane 2x12" kick bin is unneccesarily large, awkwardly shaped with lots of unused dead space and wasted wood (marked red in the plan).

Overall, just comparing the designs, I would vote strongly for the mkb230.


Because it is folded, it has a longer horn path and goes down to 100Hz. So there you have your kick. It also goes up to 700 Hz, and could be crossed over straight into your m200 or another compression driver.

See my crude illustration (n.b: scaling approximated, not verified!!!) of coaxial mounting of your mid/hf section in the mouth of the mkb230.

You would still have the option to relegate the mkb to kick duty and pursue other mid/high options later on if you desire.
 

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dokkodo

Member
2017-03-15 7:26 pm
Happy new year indeed!

Sorry yes i should have dumped all those designs elsewhere and had a proper look at each first. I drew the fane on sketchup and put it on top of my subwoofer, it was very obviously not the thing!

Done a bit of sketching of the MKBs, think i have them modelled correctly. Sub thrown in for thinking about stacking...

stack.jpg



There would be room for something between them in the stack (to get the horns up to about head height...) if that was appropriate - another one?! or something with one of the spare pair of 15"s)

MKB230  LAYOUTS.jpg

Otherwise id devise a stand. I also like that it will be possible to change both horn and 12" drivers in future, quite futureproof.

Only current minor issue is that they are deeper than my subs! I suppose shortening the horn messes with the output, i roughly modelled the modified version (on right), shortens the horn by 160mm - obviously i would adust the angles to keep them gentler, but id be curios what effect this has.

toodeep.jpg



MKB230 TOP DOWN.jpg


The overhang isnt the end of the world but would cool if they lined up

Or I have to build another sub anyway so i could modify them instead and build both.

one more from the inside... to make sure im not getting it wrong...

inside.jpg



phew bed time
 

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Hi,
Sorry forgot about your project, was busy with covid 😬

Unfortunately changing the box design will significantly alter the performance, making it a very different box altogether.
Consider the horn fold, any shortening of the box will result in twice as much shortening of the horn path. The lower cutoff will be shifted significantly higher.
 

dokkodo

Member
2017-03-15 7:26 pm
No worries. Ive changed all the plans anyway now!

Did a lot of research. Decided to stop trying to polish proverbial turds, and spend lots of money instead o_O

Current plan for stack is

dual 15 PPSL sub s
15" reflex kicks (b&c sub15 mod - single or double not sure yet, found a bunch of JBL 2226Hs going cheap to go in, which people seem to like)
MT121 with SN12B and b&c DE750 comps (horns tbc) - although now im wondering whether they are too narrow for indoor/smaller crowds?)