Originally Posted by GM
the only other option that comes to mind is what I do, critically damp [~transient perfect] the vent’s peaking [‘ringing’] same as the pioneers of audio championed and accept its obvious deep LF roll off
He wrote:
“If the sound is a distinct “click” with no low frequency boom or “bong” in both positions, the damping is adequate. Chances are, however, that the “click” will be accompanied by some boom and additional damping in the form of acoustic resistance will have to be added...
Generally a 1-to 2-inch thickness of lightweight Fiberglass (1/2-lbs. density) stapled around the speaker so that the entire speaker is covered will provide a boom-free click”.
Not sure if this is the method GM uses to “critically damp” his speakers, but the method works. Of course, some alignments will need a lot more than just a 1-to 2-inch thickness of lightweight Fiberglass (1/2-lbs. density) stapled around the speaker to adequately damp the response. And the more damping, the less LF output...
As you put it, "somewhat subdued when fully stuffed".
Art
the only other option that comes to mind is what I do, critically damp [~transient perfect] the vent’s peaking [‘ringing’] same as the pioneers of audio championed and accept its obvious deep LF roll off
James F. Novak wrote in the January 1966 issue of Electronics World that one can place a resistor of around 1/2 ohm across the speaker terminals to simulate amplifier damping, then use a battery to excite the speaker. He used a switch arrangement, but one can also simply use wires and touch them to opposite sides of the battery, a 1.5v battery is adequate for small light cones.
He wrote:
“If the sound is a distinct “click” with no low frequency boom or “bong” in both positions, the damping is adequate. Chances are, however, that the “click” will be accompanied by some boom and additional damping in the form of acoustic resistance will have to be added...
Generally a 1-to 2-inch thickness of lightweight Fiberglass (1/2-lbs. density) stapled around the speaker so that the entire speaker is covered will provide a boom-free click”.
Not sure if this is the method GM uses to “critically damp” his speakers, but the method works. Of course, some alignments will need a lot more than just a 1-to 2-inch thickness of lightweight Fiberglass (1/2-lbs. density) stapled around the speaker to adequately damp the response. And the more damping, the less LF output...
As you put it, "somewhat subdued when fully stuffed".
Art
So it was Novak, good to know after all these decades, thanks! I actually learned about it during my visit to the Altec plant in ’68, though they used an impulse response to find the desired amount of damping to add at the vent. I was also made aware of Altec’s Don Davis’s and Alex Badmeiff’s book that had excerpts from some author’s paper/article you posted.
Having already seen how Altec did it, I tried it both ways and preferred the vent damping better overall, especially once I started experimenting with tower alignments [aka MLTL] later that year which usually either needs none or just a layer or two of double knit cloth tightly stretched over the vent the way I design them.
GM
Note too that a MLTL's 1/4 WL action will either shorten the vent for a given tuning or lower tuning for a given vent length which in turn lowers the peak, so if SWAGGed in a reflex program you need to lengthen the vent to account for this. Unfortunately, I never saw a simple pattern, so just used a sufficiently large area vent located near/at the bottom and found the vent length using impedance measurements. With MJK's MathCad software though, folks can sim it all fairly accurately if polyfil is used.
GM
I quoted James F. Novak (Jensen Mfg. Div.senior engineer) from Alex Badmaeiff and Don Davis' book "How to build Speaker Enclosures", copyright 1966 By Howard W. Sams & Co.
My copy is a first edition, seventh printing from 1970, I think I bought it that year at ACME Electronics in Minneapolis.
It is the most worn out, dog eared book I own. I still go back to it, lots of information packed in 144 pages, and funny too.
Although transducer design has advanced (primarily in power handling, other than certain exceptions such as what this thread is about ;^) since then, very few true enclosure advances have been made.
Enclosures are called by different names now though, tower alignments [aka MLTL] were called "Resonant Columns", TQWP was an "Acoustic Labrinth", page 115...
Art
Just a note to give some insight into what is happening here. So far I've had three sets of Mark Audio CHR-70 self destruct, two of which were speakers made for older family members. So I did an experiment with a single good unit I had from the initial dMar-ken build I did. So in the dMar-Ken box the single driver started to flex with lower bass tones(used classical as per request from one of the family members) at about 83-85dB measured at 1m. When volume was increased to 90dB the cone was flexing quite substantially with anything below 100hz. Failure began to happen at 90dB with complex dynamics, and seems to be affected more with the flexing and the presence of secondary frequency in the 2-400hz range as you don't notice destruction until you hear the 2-400hz buzz created by the stress fractures. I now have three pairs, yes three pairs all damaged due to what I believe to be an artifact of too much linear cone movement and not quite strong enough edge on the cone surface itself. I will say that I'm disappointed by the performance of these Gen1 drivers, and if Mark wasn't such a nice gent I'd love to rip him a new one via a friendly e-mail, but I will refrain and just say I am very disappointed in the longevity of these units.
So my conclusion is, unless you listen to strictly chamber music at levels much below 90dB the CHR-70 is not a great option. Both sets of speakers returned to me for repair are from older folks who listen to primarily Jazz and Classical, and probably never above 85-90dB. So now I have to replace 4 drivers, with something in Marks line due to frame size that will not stress at the edge of the cone due to excursion... Maybe the CHP-70... I just feel odd spending money for drivers from a company in which I put my faith into and failed me not once, not twice but three times...
So this cowboy has three sets of CHR-70's all with stress cracks around the edge of the cone at the surround that buzz like a kazoo on any female voice, acoustic guitar, hell anything.... Not happy, but what can you do?
So my conclusion is, unless you listen to strictly chamber music at levels much below 90dB the CHR-70 is not a great option. Both sets of speakers returned to me for repair are from older folks who listen to primarily Jazz and Classical, and probably never above 85-90dB. So now I have to replace 4 drivers, with something in Marks line due to frame size that will not stress at the edge of the cone due to excursion... Maybe the CHP-70... I just feel odd spending money for drivers from a company in which I put my faith into and failed me not once, not twice but three times...
So this cowboy has three sets of CHR-70's all with stress cracks around the edge of the cone at the surround that buzz like a kazoo on any female voice, acoustic guitar, hell anything.... Not happy, but what can you do?
What happened to the fabled 1mm of cone movement limit, that is meant to be max you can go before distortion starts kicking in through Doppler I think it was? Is this a load of rubbish or does it hold merit? If it does then surely any argument about large xmax ratings are null and void as it defeats the purpose of buying an audiophile driver for music fidelity, as you're just ruining the sound bouncing the cone around?
Hello Mark
.I first off would like to say after being a diyer between 10 to 13 years I can't remeber how long now? Also being in home hi-fi for 27 years now. Mark your drivers are one of the best I have come across. I had a pair of the Alpsir 6 p's and I broke them in from 0 hours to 130 hours. They were one of the easiest most enjoyable drivers I have ever worked with following the break in guide lines. I sold them to a friend who wanted to try a pair of your drivers. The alpair 6-p's don't have the peakness that the fostex Fe line of drivers have. I will say I am a paper man. I have yet to listen to a pair of any kinda metal type drivers to win me over. (Sorry Mark trying not to punch below the belt on your metal drivers?) Now about the xmax I agree with what 5th element is saying and I also agree with Mark about you can only do so much with a fullrange driver and its not a woofer. If the x-max is a problem then cross them over at 500 hz and use a 8 inch woofer from 600 hz on down to solve the problem. Like a Visaton Stella light kida deal. I wish there was a fullranger to do it all but, there is not. It would be called the holy grail speaker. I just buy and enjoy and if it doesn't work out I sell it and move on. Again I am on both partys sides. Also I let mark do what he does best design and building speakers. As for 5th element your a very smart man as I see and read in your post. Again sorry about your drivers. Its a bummer when these things happen. JD
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And I had never heard of a driver with an Xmech only half of Xmax, or a manufacturer that would refuse to even mention that in the specifications before this thread
.
I'm not so sure that Mark "refused" to state that Xmax is smaller than Xmech. I think it is probably more likely that it didn't occur to him that customers would try to get so much SPL out of so small a driver.
The problem stems for the fact that the MA driver do not have progressive suspensions. They can be driven to destruction without complaining. Most drivers have progressive suspensions and are difficult in varying degrees to drive to Xmech without burning out the voice coils.
I guess my question is what do you expect out of a 3" driver?
Bob
The problem stems for the fact that the MA driver do not have progressive suspensions. They can be driven to destruction without complaining. Most drivers have progressive suspensions and are difficult in varying degrees to drive to Xmech without burning out the voice coils.
I guess my question is what do you expect out of a 3" driver?
Bob
At least some of the the XBL drivers are similar.... they are quite linear right up till you smack the voice coil against the backplate -- with a very disturbing sound.
You will start to see MA drivers with the suffix A. These drivers have an arrestor built in. Instead of compromising the suspension, Mark has added a function specific design element.
dave
Bob,
I would expect a 3" driver to operate reasonably well up to Xmax, with commensurate SPL.
Mark has stated in this thread, but refused to mention in his specifications, that operation of this driver at just half of Xmax can lead to stress cracks.
Knowing this, I'd have to expect 6 dB less from the driver than drivers with similar Xmax ratings.
If I didn't know this, I would not expect stress cracks at what I would have thought was within normal operation range, and would be quite distressed when they occurred, just as those participating in this thread were.
Art
Ye gods, I wouldn't.
You would need to have the mechanical sympathy of Captain Caveman to continually hammer a 4in wideband driver (any) at ~1/2in deflections. A little common sense is in order. Whatever the stated Xmax might be, a widebander is not going to sound particularly good at such deflections for a myriad of both mechanical & acoustical reasons. The argument is akin to stating that your car should be able to run at its stated maximum speed all the time / for extended periods.
On the subject of Xmax, I've made this point elsewhere, but it's worth making a reminder here: it's a nebulous figure since there are multiple different ways of giving a figure for it. Most of these give different values for the same drive unit, manufacturers almost never state which method they used so there's no consistency there either, and while it might appear heresy, the fact is that none of them are particularly informative, or account for everything that is going on. At best, Xmax is a very general 1st order guideline, no more. It is not some hard & fast quantity, or a statement that a driver can be run continually to large excursions (assuming the Xmax figure is high). That is not what it's for, and it's certainly not what it does.
Here are three of the more common methods for producing an Xmax figure:
-Magnetic gap height minus height of VC winding
-As above, take absolute value & /2
-Set it at whatever point the driver reaches 10% THD.
The first and second do not provide give any distortion values whatsoever, while the latter simply states a point at which the driver reaches 10% THD, telling you nothing about distortion types, nor any information about the behaviour to either side of that point. The driver could be at 9.99999% THD for most of the supposedly linear region for all we know on that basis, nor do we know how rapidly distortion rises beyond it, or as previously mentioned, the character of said distortion. The plain fact is, you need to measure the drivers for yourself if a full set of distortion figures are not provided (as is usually the case) if you want to actually know what the driver is doing. And then you need to think for yourself about how much mechanical stress you are placing on the unit, which even these, let alone Xmax, do not tell you.
You would need to have the mechanical sympathy of Captain Caveman to continually hammer a 4in wideband driver (any) at ~1/2in deflections. A little common sense is in order. Whatever the stated Xmax might be, a widebander is not going to sound particularly good at such deflections for a myriad of both mechanical & acoustical reasons. The argument is akin to stating that your car should be able to run at its stated maximum speed all the time / for extended periods.
On the subject of Xmax, I've made this point elsewhere, but it's worth making a reminder here: it's a nebulous figure since there are multiple different ways of giving a figure for it. Most of these give different values for the same drive unit, manufacturers almost never state which method they used so there's no consistency there either, and while it might appear heresy, the fact is that none of them are particularly informative, or account for everything that is going on. At best, Xmax is a very general 1st order guideline, no more. It is not some hard & fast quantity, or a statement that a driver can be run continually to large excursions (assuming the Xmax figure is high). That is not what it's for, and it's certainly not what it does.
Here are three of the more common methods for producing an Xmax figure:
-Magnetic gap height minus height of VC winding
-As above, take absolute value & /2
-Set it at whatever point the driver reaches 10% THD.
The first and second do not provide give any distortion values whatsoever, while the latter simply states a point at which the driver reaches 10% THD, telling you nothing about distortion types, nor any information about the behaviour to either side of that point. The driver could be at 9.99999% THD for most of the supposedly linear region for all we know on that basis, nor do we know how rapidly distortion rises beyond it, or as previously mentioned, the character of said distortion. The plain fact is, you need to measure the drivers for yourself if a full set of distortion figures are not provided (as is usually the case) if you want to actually know what the driver is doing. And then you need to think for yourself about how much mechanical stress you are placing on the unit, which even these, let alone Xmax, do not tell you.
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Ok, I dig an old topic, but i'm interested in the developments the CHR-70 family has got over the years. For example, the latest CHR-70A has got a number of improvements, to quote:
D) and make disturbing sound to warn the listener they are reaching breaking point?
Also, what frq highpass is good for a FAST setup? I am going to try a FAST on my soundbar, with one CHR and one OAudio SW 6.01 (TB W6-1139 clone from omnes audio) per side, each with it's own amp. I will not need deafning levels, but watching an ocasional concert might need some bass and higher dBs. So, not to overload the CHR, would an highpass at what frq be good? 200Hz be ok?
The arrestor prevents the cone to go flying across the room
D) and make disturbing sound to warn the listener they are reaching breaking point?Also, what frq highpass is good for a FAST setup? I am going to try a FAST on my soundbar, with one CHR and one OAudio SW 6.01 (TB W6-1139 clone from omnes audio) per side, each with it's own amp. I will not need deafning levels, but watching an ocasional concert might need some bass and higher dBs. So, not to overload the CHR, would an highpass at what frq be good? 200Hz be ok?
I like 250Hz to 400Hz depending on what woofer you are using. Anywhere in that range will keep xmax on mains quite low. I now have several MA drivers: CHN70, A7.3, and A7P. They all have very soft long stroke suspensions that flap in the wind if you drive them with LF content. I don't think I takes much voltage, not anywhere near that required to reach max power rating.
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