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Posted by panwitz on
03-08-2018
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Hello guys!
I got an old Coral X-VIII from Japan. Its an Onken enclosure with a 400 Hz horn. And I want to give it a second life. The enclosure looks already like new. And the question is about the crossover. What would be the theoretical best points to cross? The midrange horn driver is the same as Coral M100 but with ferrite. Bass driver is Coral 12L 60 12 inch paper cone. Both drivers have very low distortion. M 104 goes down to 400 Hz and 12L60 goes up to 2000.
So I thought , that I ask here, perhaps you could give me some inspiration and I am missing something. I attached a photo, its not my system, but gives a basic impression how it looks.
http://audio-heritage.jp/CORAL/unit/ah-502.html here is the horn. Flare cut is 400. The horn is damped with sand and some kind of glue.
I would really appreciate some advise!
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Posted by martinshorn on
03-09-2018
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Hi panwitz
Resist the idiot-fashion of crossing too low. I recommend at least 1k for such Coral, 2nd order or higher. Also it gives nice lobing transition with the 12 inch (could even improve crossing 1.2 or 1.4). These biradial horns (i love the depth of soundstage very much!) got too much of coloration of mouth reflection below 1k. They work best from >1 till >6. Also driver will be lot more relaxed. cheers, Josh
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Posted by panwitz on
03-09-2018
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Hi Josh! That was basically my idea too. Although I read that the 12 inch driver loses directivity after 750. But I played around with Behringer dcx 2496, and I had the impression, that 1200 second order was the best sounding. The main reason for crossover change is the cheap and complex solution used in the original filter, I attached the photo. I also have a bullet super tweeter Coral H-105. What do you think if I cross second order 1200, 6k or 7k? But the midrange play will be very limited. just from 1200 to 6k. For midrange attenuation I have the transformer attenuator coral at-70. But only one pair and an usual lpad for the tweeter. I also have a microphone for measurements, but my conclusion is, that measurements give very basic impression for the actual sound.
have a nice day!
Alex
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Posted by panwitz on
03-09-2018
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El Cheapo from Japan. But very complex. With a switch for choosing different crossover points
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Posted by panwitz on
03-09-2018
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could not attach the picture
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Posted by martinshorn on
03-09-2018
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Hi alex. Sure the 12 incher starts narrowing around 700. But the horn does too. And in that area you cross both at -6dB. which contributes to narrowing vertically. The magic is, to merge in a way that off axis its not getting too odd in a complex sum. What i mean, if you measure linear gated nearfield on axis crossing at 1k its all looking nice. But then you measure 0 and -10 and -20 -30 -60 degrees on some meter distance. Then you add those or make a magnitude averaging, everything without any gating but a simple smoothing (like 12th oct)... then your linear speaker will not be so linear after all. Thats coz all off-axis oddness changes the complex energy sum on the listening position - and thats why measures and listening can be very different. Depends on your personal approach if you want to find by ear whats better - or measure more complex. Then you see that listening can actually find the good setup faster. Good measuring can take weeks. But ok, not the topic  With the tweeter crossover can be more difficult. You could cross at 5 or 6. Or go even to 10, or disregard it. The bullet is a very narrow dispersion, so it wont give more "air" to the top than the M104 would do himself. It rather gets stressed coz the diaphragm can absolutely handle no excursion at all, some say dont cross at 6 but rather 8-10 lowest. Well the M104 plays actually already nice in the highs, very colorfull dynamic and emotional but dull. The bullets are more clean fresh precise but colder. It could be a very nice combination to set a 10k first order lowpass to the M104 to roll off the very top gently, and then blend a little bullet-tweeter with a 10k 1st order hipass in to mix both. I think that might work best. But - important - to add an additional 5k 1st order for the bullet, so that he goes 2nd order below 5k, for excursion protection! (basically requires designated amps)cheers, Josh
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Posted by panwitz on
03-09-2018
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Ahm, I thought, that the midrange horn loses its directivity after 7000 and thats there I need the h-105. By the way its the only ring radiator from Coral. How can I add at the same time a first order 10k and 5k to the same driver? I always thought that 10k first order would be more than enough for protection. M-104 has at least a first order roll off after 10k by its nature already.
Tried again to attach the crossover
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Posted by martinshorn on
03-09-2018
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Hi, true thats why i wrote designated amp (Active). As a passive xover thats rather difficult, so try a low Q filter type that increases steepness slowly. Like a Bessel (Q 0.585) or if youre skilled calculate your own Q smaller than 0.5 (LR) as a 8-10k 2nd order. Definately, i wouldnt run a ringradiator thats suspension is the actual metal diaphragm that got screwed onto the bullet with a 1st order XO. It will increase xcursion a lot in the 2-6k range. Basically you stretch the knee by selecting a slightly smaller serial cap and bigger parallel coil.
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Posted by panwitz on
03-09-2018
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Hi! I wanted actually to get rid of the behringer. Because I have only 1 super high quality tube amplifier and it was difficult to marry different amps with the speakers. And you cant use a high quality dac with the active crossover. I ll right now look for my measurement of the m-104 in horn and post them.
The Coral itself suggests second order crossover for H-105, I have the original brochure.
Right now the Corals are running 1st order 750. I took the original filter apart and had only components for 1st order 750 or second order 1000. But I suppose that because of the quality of the components 1st order sounds much better.
What do you think of this filter 1200 (see attachment) it was the top of the line Coral filter of that time and I can get it for about 200 Euro. Or is it better to use brand new Mundorf parts like supreme evo for caps?
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Posted by martinshorn on
03-09-2018
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Hi. Well the behringer belongs probably to the most famous and also to the worst quality wise. Sure the passive sound better...Id go with the learnings from the behringer and apply it in a clean xover, either active or passive or even digital - but no behringer!Try, measure, calculate. Here is a nice website (german but with a silent video demonstration) how nice a passive XO can be done... http://tempuri.org/tempuri.htmlApp is from those guys: http://tempuri.org/tempuri.htmlMe personally, I left this not meat not fish things behind and switch to serious high end xovers with real perfection via finite-impulses : http://tempuri.org/tempuri.htmlThat app is done by Dr. Brueggemann, an Idol about doing such things right, read about his approach here : http://tempuri.org/tempuri.html
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Posted by panwitz on
03-09-2018
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Hi! Here is the measured response in 2,5 meter distance living room. 1st order 750. And you can see the roll off after 5k.
I know german, so its no problem So you have no opinion on the coral crossover from my last post? Only 26 minutes left for buying or letting it be.
I ll read about the xovers you use, but you will need 3 amplifiers for that in any case?
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Posted by martinshorn on
03-09-2018
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No i dont have oppinion about this specific one. The room response looks ok. Take the XO, try it, sell it but yes, the acourate XO requires 3 Amps then. Still, worth it!
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