| sunnycue |
Hi, Does anybody know these speakers?
I'm looking at a peak 8CX- 50 but i suspect it is a Coral. (same model# and specs).
Does anyone know anything about them? Thanks
Colin |
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| fred76 |
Coral OEM'd for a lot of other speaker brands, so it most probably is Coral if it looks exactly the same...
94db/1m/1W (100dB at shorter distance ~1/2m)
2uF cap for tweeter. Replace it with new polyprop if you can.
Highish Q.
http://www.h3.dion.ne.jp/~roktal/unit/8cx50.html |
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| sunnycue |
| Thanks Fred, appreciate the info. |
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| Brisso57 |
| quote: | Originally posted by sunnycue
Hi, Does anybody know these speakers?
I'm looking at a peak 8CX- 50 but i suspect it is a Coral. (same model# and specs).
Does anyone know anything about them? Thanks
Colin |
Hi Colin,
I too have a pair of the Peak 8CX50's and I'm building them a pair of Coral 8CX501 BR cabinets. Do you mind if I ask what you've done with yours?
Doug
PS I quickly knocked together a pair of OB's for them. Fantastic! |
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| Brett |
| Cool. I have a half dozen 10CX501 and have been wondering what to do with them. |
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| Brisso57 |
| quote: | Originally posted by Brett
Cool. I have a half dozen 10CX501 and have been wondering what to do with them. |
Sell me a pair?
Doug |
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| jamikl |
I had 4 of the 501s, two per back loaded horn enclosure - about 17 -18 inches footprint and 31 inches tall, Mouth was 10 X 17 inches.
Since these added to about 16 ohms imp. and I had two goodmans horn 15 ohm trebax horns I used the goodmans crossovers. I had some old dome tweeters which I put in series , one vertical and one facing forward. They sounded so immediate and impressive - effortless. The tweeters on top sounded better than the horn tweeters on the 501s, possibly due to lobing issues with speakers being side by side. The opening tracks of Dark side of the moon at any volume was scary. As were the alarm clocks!!! Not very scientific a setup but I want them back!!!!!!
These were the speakers I mentioned in an old thread to do with listening experiences. They were run off a Lynsley Hood 75 watt SS amp.
jamikl |
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| rjb |
Does anyone have the T-S parameters for these?.
GM posted a set (with a qualification) but I have not been able to reconcile my measurements with his.
Thanks |
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| Brisso57 |
| Here's a pic of my 8CX50's: |
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| Brisso57 |
| quote: | Originally posted by rjb
Does anyone have the T-S parameters for these?.
GM posted a set (with a qualification) but I have not been able to reconcile my measurements with his.
Thanks |
Yes, it's a problem. Good T/S data for old Corals is rarer than rockinghorse poo. I think the only stuff I've seen is from GM, but it may be worth your while to e-mail Howard at eastmarinedrive.com
cheers,
Doug |
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| GM |
| quote: | Originally posted by rjb
GM posted a set (with a qualification) but I have not been able to reconcile my measurements with his. |
OK, please elaborate. |
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| rjb |
Hi GM.
I'm not saying you are wrong, in facct just the reverse.
I'm measuring an 8CX unit using the system outlined in Rod Elliotts web page, which I have used successfully before, but am getting answers I don't trust.
Specifically
Qms 3.17
Qes 1.67
Qts 1.09
Vas 55.2 L
I have two possible problem areas.
The original cloth surround had gone hard, stiff and brittle so has been replaced with rubber. This has lowered the res.freq to 38 Hz. from your 40. The spider seems OK.
The sig gen is an old philips which I have just resurrected and may be off.
You commented your results were from reverse engineering, which I took to mean not from measuring an actual unit, so I was just looking to see if anyone had . Regards
Ross |
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| Brisso57 |
| quote: | Originally posted by jamikl
These were the speakers I mentioned in an old thread to do with listening experiences.
jamikl |
Can you point me to that thread, pls?
Thanks
Doug |
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| GM |
Greets!
Bummer, I was hoping you had more accurate ones that indicated a lower Qts since I fudged them on the high side to calc a too large a cab since it's easier to shrink one than stretch it.
Anyway, you're right, mine are a complete SWAG based on similar Corals and the two BRs designed for the 501, so could be pretty far off, though they would have to be in complementary ways to perform well in it. Note too that a Qts this high wouldn't have been put in a BR and the calc'd eff. is way low compared to the published specs, so something's amiss.
GM |
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| rjb |
I'm posting this for anyone that may be interested in the future.
I have four Coral 8CX, only one of which still has the tweeter. The surrounds have all gone hard and brittle, sufficently so to cause two of the cones to fatigue at the outer edge, with tangental cracks. Tested Fs in this state was of the order of 180Hz.
The spiders seem ok still.
On the principle I could not make matters worse, I replaced the surrounds of the two with cracked cones with new rubber, (not foam) surrounds and repaired the cracks as best I could. Then coated the whole cone with a light coat of PVA.
Using arta software and the added weight method, the following are the results of testing the best of the two units.
Fs 42.82
Re 6.9
Qes 0.53
Qms 2.63
Qts 0.44
mms 17.9 gm
Rms 1.746 kg/s
Cms 0.0000808 m/N
Vas 45.89 L
Sd 201.06 Cm2
Bl 7.76Tm
The second gave similar results, but because of the more extensive repair work the cone was slightly heavier and consequently Fs slightly lower, and other slight changes.
I have reasonable confidence in the above results being not dis-similar to a good condition unmodified unit. The manufacturer's specs claim a "moving mass" of 12gm, and an Fs of 40 Hz with a Qo (whatever that is) of 0.45, and recommend a BR cabinet of 68 litres. |
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| rjb |
Win ISD pro gives the following slightly different figures, (original test results in brackets)
fs 42.83 (42.82)
Qes 0.527 (0.53)
Qms 2.634 (0.63)
Qts 0.439 (0.44)
Vas 46.33 (45.89)
and calculate a BR cabinet size of 63.9 litres which is in line with manufacturers reccommendation of 68 litres less damping. |
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| GM |
Greets!
Thanks for sharing! Interesting, I have WinISD Pro loaded, but didn't think to check it.
Finding Qo (Qts) is a more basic way to get T/S type specs, though not as accurate for low or high Qts values:
GM |
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| planet10 |
| quote: | Originally posted by Brisso57
Good T/S data for old Corals is rarer than rockinghorse poo. I |
And due to aging, will have wandered from the original, Each pair is more likely to be different than the same.
dave |
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| rjb |
Yes Dave, as you say all units even of the same type age differently, particularly paper cones. I have four 8CX, three without tweeters, bought cheap so have been experimenting with them.
All four had widely different results.
The tweetered one had been over-driven at some stage, the "crossover"resistor badly burnt up. It also showed oddities in the impedance curve, so I dismantled it. Conventional design, except for what seems to be a slug magnet and associated W steel pole , rather than the normal tube type magnet with central steel pole. Normal paper former, and as far as I can tell, a two layer copper coil about 2 mm longer than the depth of pole-peice. So Xmax is quite short. The end of the coil former had hit something solid, and slightly squashed, lightly rubbing on the pole-piece, so this was sanded off and a very light coat of epoxy added. This now matches the others.
Overall, not particularly a well made unit under its impressive casting.
All the surrounds had gone hard, ( cloth plus some form of coating)so Fs were all above 150 Hz.
Due to this, two showed tangental cracks at the cone edge, one badly. These I repaired, and replaced all surrounds with off-the shelf rubber roll-edges. This dropped all back to near the T-S values I listed above, However the spead between the four was still wider than I expected, one in particular had a 10 Hz higher Fs.
I had treated two of the cones with PVA, and one of these was the problem. Some PVA had in my haste got on the surround, and once this was cleaned off, the Fs dropped to the common value.
I was surprised by the shift, as the PVA is quite flexible. Obviously the surround still has a significant effect, something I haven't seen on larger drivers.
These cones are very light, and quite soft and flexible. The possibly have absorbed moisture over the years. The impedance curve drops above about 4500 Hz on all four so obviously the cone fails mechanically there. When I get round to a frequency test I will post more.
I'm now going to clean all four surrounds, and sand lightly to see what happens to the T-S. I suspect Fs will drop slightly on all.
Coating the most damaged unit with several PVA coats on the front, has added mass, and the Fs is lower. So too is the impedance peak, but the other values have not shifted proportionally. Win ISD suggests cabinets close in size to three, the heavy cone one being the odd one out.
For the four units,at present Fs ranges from 36 to 42, (the two best units both close to 39.5), Qt 0.47 to .52, and Vas 47 to 51 L. ( with the heavy cone one being 57)
I will now do an open baffle frequence run on each.
With that done, I will treat two cones with an artists varnish and compare. |
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| rjb |
| Interesting. Lightly sanding the rubber surround with fine wet and dry, on one side only, just sufficient to take the shine off the rubber dropped Fs by 3 Hz |
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| fred76 |
The 8cx-50 widerange+tweeter driver has relatively heavier paper cone compared to most fullrange drivers that I played around with. It sounds 'dark' - the best way I could describe it, although it has good balanced tone. The horn tweeters comes in at ~6kHz, it would be nicer if crossed over several octaves higher because of it's size, and it's where the most design compromise went. OTOH, a ‘hole’ in the response would most prob occur if the cutoff is higher. Tweeters are okay but sounds quite colored when things get busy (Geddes’ HOMS?).
There's a latter model, 8cx-501 which is 8 ohms nominal and has a different and cone color/texture that has no annular rings. I'm not sure though if they are lighter. It looks like they retained the thick cloth surrounds.
http://www5b.biglobe.ne.jp/~tritium/8cx501.htm |
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| Brett |
| quote: | Originally posted by fred76
The horn tweeters comes in at ~6kHz, it would be nicer if crossed over several octaves higher because of it's size, and it's where the most design compromise went. |
Several octaves? Like 48k? |
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| fred76 |
| quote: | Originally posted by Brett
Several octaves? Like 48k? |
ok, wrong word. A few, at least maybe ~12k. |
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| Brett |
| An 8" driver is going to be extremely directional up at 12k, not to mention lots of breakup modes, so why not bring in a waveguided tweeter at a crossover point where the directionality of the 8 matched the WG? |
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| Brisso57 |
I have enjoyed my first rough attempt at an OB for my Peak 8CX-50's that I'm going to go a step further.
I like the look of the Visaton NOBOX design, so I'm going to try my 8CX-50's paired with a 12" woofer. (The Visaton design uses an 8" FR and a 15").
The woofers I've acquired are HokuTone W |
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| Brisso57 |
I have enjoyed my first rough attempt at an OB for my Peak 8CX-50's that I'm going to go a step further.
I like the look of the Visaton NOBOX design, so I'm going to try my 8CX-50's paired with a 12" woofer. (The Visaton design uses an 8" FR and a 15").
The woofers I've acquired are vintage HokuTone HW301's. The cast baskets are fabulously rigid. The design is suspiciously like the Peaks. I suspect Coral's design hand once again???
Anyway, I'm not after DEEP bass, just a bit lower than the Peak's can go, and also to take some of the load from their lower octave.
I'll post progress.
cheers
Doug |
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| fred76 |
| quote: | Originally posted by Brett
An 8" driver is going to be extremely directional up at 12k, not to mention lots of breakup modes, so why not bring in a waveguided tweeter at a crossover point where the directionality of the 8 matched the WG? |
Yes, I guess that was Coral's design goal due to the limits of the 8" cone. The tweeter is centrally mounted in front of the deep curvilinear cone. Relatively speaking, the Corals have done the cost cutting on the tweeters (as it should for a frugalphile and smaller 8"r IMO), I mean compared to some of the larger top tier coaxs from Tannoy and duplex drivers from Altec that have err more attention paid to their tweeters/hf comp drivers and xo etc. And as I mentioned earlier there would likely be a 'hole/dip' in the response apart from the directionality if xo'd higher. I just arbritralily picked 12k based on modern widerangers like the FE208ESigma, but of course there is no centrally mounted horn tweeter with that driver.
FWIW, the OB's I have with these Corals have very good bass response. They sound pretty darn good with acoustic guitar, male vox, and most jazz material (even Sabbath's early lp's capturing Iommi's SG tone). Maybe I shoud have placed the drivers higher at ear level. They were mounted a bit low. |
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| fred76 |
Brisso57,
Those are serious looking cast frames on the vintage woofers. Good score. |
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| Brett |
| quote: | Originally posted by fred76
Yes, I guess that was Coral's design goal due to the limits of the 8" cone. The tweeter is centrally mounted in front of the deep curvilinear cone. Relatively speaking, the Corals have done the cost cutting on the tweeters (as it should for a frugalphile and smaller 8"r IMO), I mean compared to some of the larger top tier coaxs from Tannoy and duplex drivers from Altec that have err more attention paid to their tweeters/hf comp drivers and xo etc. And as I mentioned earlier there would likely be a 'hole/dip' in the response apart from the directionality if xo'd higher. I just arbritralily picked 12k based on modern widerangers like the FE208ESigma, but of course there is no centrally mounted horn tweeter with that driver. |
There's also no whizzer on the 8CX either, so not comparing like with like. There is only so much you can expect from an 8" single cone driver. |
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| fred76 |
| quote: | Originally posted by Brett
There's also no whizzer on the 8CX either, so not comparing like with like. There is only so much you can expect from an 8" single cone driver. |
Of course. I was a bit lucky in getting a good condition pair for not so much $ outlay on the old Corals, for the price they're good drivers. With modern drivers... The FE208ESigma has no whizzer too but a pointy dustcap/phaseplug and goes up to ~14k on axis. Nice sounding drivers when I heard them augmented with Fostex supertweets.. The 8" Phy-Hp H21 LB15 has no whizzer either but cuts off sharply at 10k (haven't seen any off-axis response). But it is very expensive, and have yet to read any good feedback on them. |
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| Brett |
| They are good driver. I have some 10CX, but I find on-axis response to be a small part of the overall signature. The 'single driver' thing has become almost a religion amongst some folks. I feel there are better ways, but enjoy what you like. |
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| fred76 |
| quote: | Originally posted by Brett
They are good driver. I have some 10CX, but I find on-axis response to be a small part of the overall signature. The 'single driver' thing has become almost a religion amongst some folks. I feel there are better ways, but enjoy what you like. |
True, in my case. It's hard to go back to single fr's when you hear a 'properly' designed / set up compression horn driver system. JMHO. |
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| rjb |
| My tests of the 501 version indicate problems above about 4500 Hz. I'm investigating these. |
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