cab options for coral beta 10

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hi,
ive just bought some lovely coral beta 10s in the orignal coral cabinets with abr units.
they sound rather good but id like to explore other cabinet options,at the moment they sound great except for the bass,whats there is tight but they dont really have a lot of it.
any help is appreciated.


heres what they are in now.
An externally hosted image should be here but it was not working when we last tested it.




An externally hosted image should be here but it was not working when we last tested it.







An externally hosted image should be here but it was not working when we last tested it.



An externally hosted image should be here but it was not working when we last tested it.
 
Hi Jamie,


this is a very good find of what is, even after several decades, a veeery good fullrange unit. I had the Beta 8 30 years ago, and still bite myself in the a..., as I sold them some day...

To optimize it´s sound, I would work with:
- careful filtering of the FR unit, no FR is linear by itself.
- having a bass driver below, let´s say 200 Hz. That makes it easier for the FR.
- changing the enclosure to OB (together with a bass driver of course) will give you better results than any box, IF you´re able to maintain proper positioning of OB in your room.
- note that the Beta 10 seems to have a quite severe resonance at 2,1 kHz (look here, even if it´s in German: Hifi-Selbstbau - Coral Beta 10B) which should be filtered. This article also says that a proper BR enclosure will have several hundreds of liters...


Looking forward to hear from your project, I remain
with best regards


Mattes
 
hello Mattes.
thanks for your reply,i was begining to think no one would comment!
ive not seen that website before,it makes interesting reading.
coral themselves made a few cabinet designs for the beta 10.


for the sealed cab they state 2 sizes.
width= 660 depth=470 height=900=279 lires
and smaller one,
width=550 depth=380 height=750=143 litres

the bass reflex design is,
width=500 depth=400 height=670 = 134 litres
all in mm


the sealed cabs they are in now are,
width=375 depth=285 height=660
the bass in the original cabinets is very poor as you would expect when comparing the other size cabinets above.
im not looking for earth shattering bass just reasonble good accurate bass.
different cabinets and what they do is all new to me but iam an ex cabinet maker so the woodwork is not a problem,its the theory behind the designs and measurments etc that i find confusing.

regards.
jamie
 
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Hi,


yes, Jamie is a lucky man... some years ago, Betalust caught my mind again and I was searching for a good pair of Beta 8. Those are already rare and expensive, a Beta 10 in the state shown by Jamie will be worth serious money...
I have a Fertin 21M8EX now and I´m not looking back anymore.
The ABRs are also very rare, just saw them once in an ad, but never in reality.


In my humble opinion, Jamie has a few choices to make. All will mean to spend a little money on measurement equipment and such, a bit more financial effort will be needed to get all out of his find. He claims to be good at woodworking, that´s fine, because these drivers deserve the best of cabinets (and they derserve as well all efforts with measurements, filtering, adjustment, or better balancing of the FR unit).


The community could possibly help with ideas and input, but measurements and woodworking have to be done personally.
In the moment, I could imagine two main directions:


1. Keep the original set of drivers, but design and build a proper and acoustically correct enclosure. Therefore, TSP measurements of the actual drivers are needed (I have a DATS vers. 2, a most valuable tool for maybe 120 pounds). I need to search my archives if I find any info on the ABR... for a start of ideas, one could work with the set of TSPs given by Hifi-Selbstbau.

I would suggest mild filtering of the unit, for which REW with a decent mike (maybe another 100 pounds) would be my suggestion.



2. Have the Beta 10 in OB, together with a good 18-inch bass driver (like an AD 1830, cheap and good. Filter parts will be a lot more expensive, if done passive and with good quality. A miniDSP will be cheaper, but I feel that the Beta 10 deserves a better quality... YMMV)


Jamie, could you please provide, in order to of any help, some further infos:
- room size and placement possibilities?
- what electronics?
- what are you willing to invest in a rare, historic masterpiece?
- and last but not least, what music is preferred and how loud?


best regards


Mattes
 
hi Mattes,
i must admit to struggling with those improvements you mention,ive heard of rew but the other technical stuff ive not heard of at all,please bear in mind im a novice and have never done any measurements of drivers etc.


i normally use yamaha ns1000's in the nearfield postion. my room is 4580 x 3400 and i have the speakers against the long wall. i sit 1800 from them. as you can imagine i dont need to have the volume turned up very loud.


my musical tastes are norah jones,kate bush,pink floyd,paul weller,john william so a broad mix but mainly female vocal,acoustic guitar type of music.
i use a kt88 valve amp (approx 110 watts) with a paradise phono stage and sony tts-8000 tt,cdp is sony x555es.


i dont mind investing in the beta 10's as i very much like their sound but as i mentioned before id like the bass to go lower,if it can match the ns1000's id be happy.


may i ask why you mention an ob instead od the coral speaker cabinet designs already on the web? my only concern is i dont have much space to bring them away from the wall,do the ob's need a lot of room behind them?
iam tempted to just make the bass reflex cabinets from coral's measurements and take it from there,do you think thats a good idea?



looking forward to your reply.
j.
 
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GM

Member
Joined 2003
Definitely will need measured TS specs of each B10 driver; but FWIW​ in the meantime​, using these B10B specs, a classic reflex alignment [Vb = ~136 L net/Fb = actual Fs] damped to 'taste' is the best trade-off between size, LF extension, max power handling with a > 105 dB/40 Hz-up/2pi [half space], so near THX screen channel reference from a single driver, though how much more will depend on the driver's low distortion excursion capability and room acoustics.

Not all that many folks do HIFI this loud, so pretty impressive even by today's generally higher standards, though for modern levels of deep bass [< ~80 Hz​, i.e. Pink Floyd, etc.​] a separate sub system is mandatory​ for max bass satisfaction​.

GM
 

Attachments

  • Coral10BclassBR.txt
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Jamie, they really are minters. I'd not zoomed the images before.


cheers si,
do you think its worth taking them to paul at rfc to get some measurments done,the post and the file posted above yours might as well be in japamese to me.
please fella's remember im a novice,when replying,trust me it frustrates the hell out of me that i dont know what all thise figures mean or relate too :)
 
........and it 'frustrates the hell out of' at least some of us that bother to respond that without measured specs, especially older drivers, that any design we do is likely to be far from optimum, though with EQ, internal damping can usually be made to work well enough in room if the OP doesn't have too strict a size limitation.

As for my post, 'we' regulars are well aware that what we post often means little, if anything to the casual poster, so was just something for me, others to 'talk' from as time permitted.

GM
 
Hi Jamie,

assume your room is measured in mm, or were that feet???
OK, there seems not to be enough space for OB in the first case. An optimum BR enclosure will be relatively large, but doable. Still have a big question mark with your ABRs (which will lead to a BR as well), but time will tell. Still have to do my search...

Finding the right enclosure size (your original enclosures are for sure too small) will help with bass, it should be quite possible to obtain 40 Hz -3dB from a Beta 10 and the matching ABR. The other issue is that every FR unit will have a more or less rising response, therefore the balance of the whole speaker will benefit from some light filtering. Reducing the upper frequencies a bit will reward you with more bass, subjectively.

About the measurements: There´s no problem beeing a novice, everybody here has started some day... and is, as you see, willing to help.
But, as GM pointed out correctly, it is absolutely necessary to get your homework done. Both REW and DATS are easy to manage, the are tutorials and tons of information to be found online. Read and learn...
Both items are most valuable tools WHATEVER you do with loudspeakers, even if I must admit that I personally regard my subjective hearing impessions as at least of the same importance. Many may disagree, but I´m happy my loudspeakers have to please exactly one person...

Back to the subject: Without measurements (and knowing what to conclude, change and adjust - here the community will help for sure) your "case" is open for the wildest guesses...

So: First step: Buy a DATS (for example here: Dayton Audio DATS V2 Computer Based Audio Component Test System - Your favorite one-stop-shop for DIY audio components - SoundImports) and measure your speakers. It´s really very easy, connect the device to your computer and the drivers, run an impedance sweep, store the screen and report back... then we know a little bit more, even without adding a mass... by the way, measure both drivers independently.

Good luck and best regards

Mattes
 
Hi Janie,

in the meantime, I´ve searched my stuff and found the original Coral Beta 10 leaflet, attached, but maybe well known. Sadly, I couldn´t find any information regarding the ABRs.

I´ve also made some simulations with the Hifi-Selbstbau TSP, including your cabs (doesn´t look very good), the original Coral BR cabs (not so bad as assumed) and slightly bigger cabs (180 litres with the reflex frequency at 31 Hz. Looks good, no hill in the upper bass and a slight downslope below 50 Hz - good in smaller rooms. This should give a solid 30 Hz with a little bit of room gain and I can only second GM that 105 dB should be possible).
These simulations, however, are just "normal" BR simulations. Sadly, I don´t know the resonance frequency of the ABRs...

Question to all: How could Jamie measure the Fs of his passive units??? I have no idea myself, sorry.

Anyhow, it´s easy to measure the behaviour of the complete system once you have a DATS, and it´s easy to lower the ABRs Fs, just add a little bit of mass.

And, to answer your question: I would stay with the ABRs. They´re more beautiful than a hole in the box... and have some advantages as well, no port noise, no port resonances.

So, if you´re thinking about an enclosure, I would start with 180 litres.

For the Beta 10 it is absolutely necessary to avoid any inner reflections coming back delayed through the very thin membrane. Careful design of the box´ innards is required. Think about avoiding any parallel surfaces, think about avoiding any reflections back to the driver. Think about inner reflectors maybe...

As a suggestion, I would have a look at Troel´s Poor Man´s Strad built, but a lot deeper and with boattail back, to get the volume and to let the drivers breathe (Poor Man').

And yes, filtering means adding caps, coils and resistors. In the Fast 5 thread (FAST_5" speaker) I demonstrated how I personally do it with fullrange drivers, but of course YMMV, as usual.

Best regards

Mattes
 

Attachments

  • Coral Beta 10 BR simulations.doc
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  • Coral Beta 10.pdf
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hi,
ive ordered the dayton audio dats v2 software,its coming from the netherlands so a few weeks i reckon.
im actually getting excited about this project,i picked up a router table at the weekend so i can properly machine the cabinets.
do you think i should make up a frame to hold the coral driver in whislt i measure ?



 
Greets!

Cool! Due to T/S normally being measured at tiny power, many [most?] folks just set it face up on a rigid/massive work area, but I was measuring at its average working power, so made a rigid/massive pyramid shaped [2x3" angle iron] frame to 'slide' it down to a wedge fit, then used vice grips [locking pliers] to properly secure it.

So if practical, recommend at least clamping it to a workbench or similarly rigid/massive surface.

GM
 
hi,
so the dats software turned up today and i set about measuring the drives,i measured them with the cones facing upwards,i hope thats right? maybe i should make some stands so they sit in them?


anyway here's what i got,


1st driver.
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2nd driver,
An externally hosted image should be here but it was not working when we last tested it.



now even with my limited knowledge i can see one measures different to the other,how far apart or how bad that is i will leave to you to tell me.
 
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