no effen kidding, Stew: putting all of those together in one system, including the transformers in a custom EL34SE amp by "Mr Carina" aka Obi Vaughn Kentubi, is as good a demonstration of synergism in "budget" audio system as I can immediately think of.
When I say "budget", that's compared to the rather steep price of admission to say, the Peter Q or Ivor T fan clubs.
Maybe this is a good time and place to ask...one thing I have often wondered about, but I have not come across an answer yet.
That is, if a speaker is say 83dB rated, does that rating remain unchanged when the speaker is fitted in an enclosure (or open baffle even)? Or to put it another way, do different enclosures for the same speaker give different volume of sound for the exact same power input?
The reason I ask is this - it is often stated on forums that one needs speakers of at least 90dB sensitivity if using using a small tube amp, say a 10 to 15W tube amp. Well here I was with CHR70's rated at 83dB in Lotus enclosure's driven by a 6W/channel tube amp and there was plenty of volume, then when I got an EL84 PP running recently there is more than plenty, in a listening room about 12' x 18'. So I'm also wondering why it is often said to use 90dB speakers with a small tube amp. I can understand that the higher the efficiency the better (more headroom), but that advice also discourages people from using CHR70 with small amps. I've never posted about this before but I just don't get it.
One more question, how do you know when you are pushing a CHR70 too hard, will it make bad noises when it reaches max cone excursion or will it simply pop the cone out of the frame, or will you hear distortion way before anything else happens? I've never heard anything bad come from mine but I have seen amazing cone excursion accompanied with beautiful bass, just wondering how one knows when the limit is reached? (i.e. besides hearing distortion).
Ian.
That is, if a speaker is say 83dB rated, does that rating remain unchanged when the speaker is fitted in an enclosure (or open baffle even)? Or to put it another way, do different enclosures for the same speaker give different volume of sound for the exact same power input?
The reason I ask is this - it is often stated on forums that one needs speakers of at least 90dB sensitivity if using using a small tube amp, say a 10 to 15W tube amp. Well here I was with CHR70's rated at 83dB in Lotus enclosure's driven by a 6W/channel tube amp and there was plenty of volume, then when I got an EL84 PP running recently there is more than plenty, in a listening room about 12' x 18'. So I'm also wondering why it is often said to use 90dB speakers with a small tube amp. I can understand that the higher the efficiency the better (more headroom), but that advice also discourages people from using CHR70 with small amps. I've never posted about this before but I just don't get it.
One more question, how do you know when you are pushing a CHR70 too hard, will it make bad noises when it reaches max cone excursion or will it simply pop the cone out of the frame, or will you hear distortion way before anything else happens? I've never heard anything bad come from mine but I have seen amazing cone excursion accompanied with beautiful bass, just wondering how one knows when the limit is reached? (i.e. besides hearing distortion).
Ian.
Hi Ian,
I've just come back to Hong Kong having spent my holiday time in Noosa and 1770- Agnes Water. Maybe I wasn't so far away from you although Queenland's a big place.
Regarding driver efficiency, many audio guys concentrate on this characteristic without taking into account power-handling and coil size. Solely relying on the driver's efficiency rating won't give a complete picture as to the suitability of amplification. As a general rule, drivers the size of the CHR-70 using 3/4" coils, rated @ 20 watts (Nom) usually can be successfully operated on tube amps from 4 watts per channel @ 4-Ohms. Much depends upon the box-driver optimisation, room size/gain, listening levels/tastes, amplification characteristics etc; I've had no dramas when using CHR-70's and Alpair 7's on 4 watt tubes.
The CHR-70 is reasonably robust. All the same it is small driver and shouldn't be driven constantly beyond an excursion of 4-mm (1 way). Ideally, you're looking for a odd peak bass (LF) signal to move the cone around 3-mm. This amount of excursion should be more than enough to get plenty of bass at higher volumes in most box designs.
Cheers
Mark.
aaahhahaa I can handle this question!
I have a pair of (1st gen) Chr-70s in sealed cabs as computer monitors, using some EQing to flatten out the bass. More on the speaks and EQing here
Anyway, I had an odd issue where, in a particular game, both channels were playing, but the high frequency was missing out of one of the speakers! This is obviously VERY ODD considering they're full-range drivers. When troubleshooting, I started swapping some cables around in my mixer.
*ahem* anyway... I got a little lesson in "TURN OFF THE AMP BEFORE SWAPPING CABLES 101". As upon plugging one back in there was a tremendous thump out of the right speaker, driving the speaker extremely hard into the extents of its suspension. It was rather impressive to watch, actually!
Anyway, the suspension held up great! All that happened was that the cone actually "crimped" slightly upon hitting the surround's limitation. There are now a ring of small creases evenly spaced around the rim of the cone.
On the plus side, I actually detect no obviously audible difference in the sound the speaker generates. It still sounds great. Under extreme scrutiny one might notice something, but I haven't, yet. Just cosmetic damage.
I think this is really a testament to the high standards of build quality in Mark's speakers. The even spacing of the crimps I think indicates the level of precision that goes into the assembly of these things. If the driver or surround were just the slightest bit off-center, I would imagine the cone would have perhaps torqued harder and perhaps caused damage to the driver, or perhaps much more significant damage to the cone itself, but as it was, the forces were distributed with startling consistency across the cone.
Picture included!
As an aside, Since I'm playing with crazy amounts of low frequency boost while EQing, I have also driven the drivers to the extents of their suspension under more normal conditions (you know, with audio signals instead of dead shorts), and though it sounds awful when they get there, they handle it like a champ and go right back on doing their business when you bring the levels back down.
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I checked. I have a large sample of CHR-70 Mk 1 average is ~83.5 (86,5 sensitivity), Jordan (just a pair meaured) is 86. So CHR is a bit more sensitive at 4 ohm vrs the JX92 at 8).
dave
Ian,
As far as I understand the acoustic output also depends on the enclosure (and not only on the dB rating of the speaker in "free space"). A closed box will only have output from the front and since there is a gradual roll off (due to the compression of the air in the box) often some compensation filter will be used to reduce the output at higher frequencies.
Bass reflex boxes use part of low frequencies that are radiated from the back of the speaker unit to compensate for the low end roll off.
Horn speakers can have a high acoustic efficiency of converting the output of the speaker. Unfortunately the horn often adds their own sonic signature to the sound.
Said differently: Same speaker mounted in a closed box will require (a lot?) more power than when mounted in a horn to achieve the same acoustic output.
Hope this helps, AM.
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Yep that helps AM. Thanks for all the replies, I really appreciate it.
Hi Mark, you were only a couple of hours drive up the road, a very nice place to take a holiday, I hope you enjoyed it. If you ever fly into Brisbane airport, let me know and we'll pick you up and have a couple of beers if you like (I live nearby). Just a quick thanks for designing and producing this wonderful driver. They seem to sound better and better as time goes by, I built my speakers about 9 months ago, they would have done at least 1000 hrs of playing by now.
Ian.
Hi Mark, you were only a couple of hours drive up the road, a very nice place to take a holiday, I hope you enjoyed it. If you ever fly into Brisbane airport, let me know and we'll pick you up and have a couple of beers if you like (I live nearby). Just a quick thanks for designing and producing this wonderful driver. They seem to sound better and better as time goes by, I built my speakers about 9 months ago, they would have done at least 1000 hrs of playing by now.
Ian.
I would also like to see something like this. Most designs I have managed to find are rear ported. I would like to see something with the port at the front, so the cabinets can be pushed back against the wall.
It is part of the microtower family.
http://www.diyaudio.com/forums/full-range/148901-microtower-bipolar-ml-tl-chr-70-el70.html
dave
http://www.diyaudio.com/forums/full-range/148901-microtower-bipolar-ml-tl-chr-70-el70.html
dave
Hi Tresch and Guys,
Many thanks for this feedback. I've been receiving a fair number of questions in recent times re bass delivery for CHR-70 and Alpairs. First off, can CHR-70's go low (<40Hz)? Yes they can go low, but like all smaller drivers there are performance and technical limitations. I've talked about potential distortion issues and recommended working excursion limits earlier in the thread.
On the practical side, Tresch's pic is a good demonstration of what happens when a CHR-70 (or Alpair) is over-driven. Indeed, most any full range driver that's subjected to persistent high levels of mechanical stress will suffer cone and power-train damage. It's important to remember that full rangers can't handle as much power compared to most multi-way bass drivers.
If you happen to "over-cook" a CHR or Alpair driver, they often can be rescued by some gentle rubbing with your small finger from under the cone. If a crease is more profound, use your finger nail. Gradually working your way around the cone, gentle rubbing usually produces good results. In more severe cases, the creases may remain visible but the driver will most likely remain functional, good for future experimentation and music making.
Cheers
Mark.
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Thank you for the idea, but I think that will be too wide. My desktop is rather cramped. I definitely have more spare depth than width.
Skinny folded halfTower with front exiting terminus.
folded halfTower 0v8 map
Someone build it and report back. Based on the microTowers built already should work fine
Would need to be reworked for the EL70
dave
when do you sleep?
Dave, I am always dumb-founded at the sheer quantity of stuff you and Chris and Daniel put out. I know we have similar sleep patterns, so I do know when you sleep (roughly), but the sheer output is impressive.
Still haven't tried the mini-OBs/Demetri combo yet. I think all I need is a single cap of say, 2.65μF, assuming 15k @4Ω across the CHRs to protect them a bit. Laura's off to work tomorrow, so perhaps a good time to try.
Dave, I am always dumb-founded at the sheer quantity of stuff you and Chris and Daniel put out. I know we have similar sleep patterns, so I do know when you sleep (roughly), but the sheer output is impressive.
Still haven't tried the mini-OBs/Demetri combo yet. I think all I need is a single cap of say, 2.65μF, assuming 15k @4Ω across the CHRs to protect them a bit. Laura's off to work tomorrow, so perhaps a good time to try.
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