Boris' Cheap & Quick semi-OB CHR70 Project - diyAudio
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Old 22nd October 2011, 01:58 PM   #1
borispm is offline borispm  Hong Kong
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Default Boris' Cheap & Quick semi-OB CHR70 Project

First of all, I must thank Mark for engineering these magnificent drivers! There is some minor build quality issues but for such a price, I can't complain on that! Yes, the surround is not exactly dead at center for one of my drivers, but that doesn't affect the sound much and you need pretty good eyes to spot that fault.
Right, I also want to thank Tony for his quick delivery. He's a really passionate gentleman too.

Okay, back to my project. I've bought a pair of CHR70 and had intended to built a pair of open baffle desktop speakers with them, but I still haven't got enough time to get myself a pair of decent woofers (I am eyeing for a pair of 6 1/2" SEAS and also iron core 13mH inductor, which is almost impossible to get at a reasonable cost as the shipping is going to kill me!). Anyway, I want to give them a try and bought a piece of foamboard. As you can expect, there's really little, if not no, bass with these guys, so I've teamed them up with my previous project speaker, i.e. the not-so-good-sounding Aurasound NS3-193-8A bipole. Those speakers are great in bass for their size, and mids are okay too, but they sound stressed quickly as the volume increases or as the track gets complicated. Treble's not extended and I can almost say "muted", so those guys aren't so pleasing.

Now, I've mounted the CHR70 in a foamboard with a 4 ohm resistor in parallel to shunt it a bit, and in series with the Aurasound, which has capacitors in parallel to perform a low pass. I haven't got the right value so I've used two 470uF in series to get somewhere around 230uF, so the xo point is slightly lower than 200Hz.

So far so good, I would say. Treble is pretty great even off axis, and is very extended too. Mids are quite transparent, almost unbelievable. The baffles are oversized and I know I'm not getting the best sound with foamboards, but at least I've got some idea of how huge open baffle mids sound.

I'll keep you guys updated. =]
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Old 22nd October 2011, 03:18 PM   #2
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Quote:
Originally Posted by borispm View Post
First of all, I must thank Mark for engineering these magnificent drivers! There is some minor build quality issues but for such a price, I can't complain on that! Yes, the surround is not exactly dead at center for one of my drivers, but that doesn't affect the sound much and you need pretty good eyes to spot that fault.
Right, I also want to thank Tony for his quick delivery. He's a really passionate gentleman too.
I'll keep you guys updated. =]
Hi Boris,
Glad you're project has started. The pics look very interesting. Hope you can tell us more as the project progresses.

The "build issue" to which you refer is correct, not a "fault" as you've described. You've made an error of judgment, due to a lack of driver design and build knowledge.

The front of the power-train must align with the coil and motor structure. The alignment will move off concentric typically a value of 0C/+2-mm depending on the design of the power-train. Thats why on most drivers the dimeter of the surround is some 3+mm smaller than the inner front lip of the mounting frame. Its to allow for this alignment tolerance. Every cone driver made on the planet follows this alignment regime, the majority of driver power-trains being non-concentric to some degree.

Cheers
Mark.

Last edited by markaudio; 22nd October 2011 at 03:28 PM.
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Old 22nd October 2011, 04:08 PM   #3
borispm is offline borispm  Hong Kong
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Quote:
Originally Posted by markaudio View Post
Hi Boris,
Glad you're project has started. The pics look very interesting. Hope you can tell us more as the project progresses.

The "build issue" to which you refer is correct, not a "fault" as you've described. You've made an error of judgment, due to a lack of driver design and build knowledge.

The front of the power-train must align with the coil and motor structure. The alignment will move off concentric typically a value of 0C/+2-mm depending on the design of the power-train. Thats why on most drivers the dimeter of the surround is some 3+mm smaller than the inner front lip of the mounting frame. Its to allow for this alignment tolerance. Every cone driver made on the planet follows this alignment regime, the majority of driver power-trains being non-concentric to some degree.

Cheers
Mark.
Thanks for your explanation, Mark. Every time I'm on this forum, I learn a thing or two. So that off-axis is for allowing the VC to align with the motor assembly?
I just thought it's some build issue that's well within tolerance or something done deliberately to compensate for the moment of the VC created due to asymmetrical mass, which should be interesting because you'll have to tell the Aussies to mount the driver upside down as their world's upside down.
The drivers sound really nice. I've listened to some Norah Jone, Diana Krall and Rod Stewart. They sound pretty transparent and clear, doesn't sound muffled or confused like some cheaper full range drivers do. Some more complicated and heavily equalized work like Mariah Carey's E=MC2 sound terrible though, but that's the fault of over processing in the mixing, and I guess it's supposed to sound terrible on any proper speaker! Never imagined I can run these guys filterless and without sounding strained.
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Old 22nd October 2011, 11:06 PM   #4
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Originally Posted by borispm View Post
Thanks for your explanation, Mark. Every time I'm on this forum, I learn a thing or two. So that off-axis is for allowing the VC to align with the motor assembly?
I just thought it's some build issue that's well within tolerance or something done deliberately to compensate for the moment of the VC created due to asymmetrical mass, which should be interesting because you'll have to tell the Aussies to mount the driver upside down as their world's upside down.
The drivers sound really nice. I've listened to some Norah Jone, Diana Krall and Rod Stewart. They sound pretty transparent and clear, doesn't sound muffled or confused like some cheaper full range drivers do. Some more complicated and heavily equalized work like Mariah Carey's E=MC2 sound terrible though, but that's the fault of over processing in the mixing, and I guess it's supposed to sound terrible on any proper speaker! Never imagined I can run these guys filterless and without sounding strained.
Hi Boris,
Yes, power-train alignment is critical. There's alway a little variance between the back and front of the power-train that has to be corrected during the assembly process. Take a look at the pics, you'll see a bright coloured object at the centre of the assembly. This component is called a "coil spacer" or "central spacer". Its function is to align the coil into the magnet structure, fix the coil height and control the positioning of the cone onto the coil head.

The first pic shows the spacer fixing the positions of the coil and spider into the frame prior to fitting the cone. The second pic shows the spacer with the cone aligning it to the lower section of the power-train. Once all the primary power-train fixing processes are complete, the spacer is removed to allow for the fitting of the cap. In all, Markaudio drivers use between 8 and 14 spacers/alignment tools (depending on model) of various kinds. Some are sacrificial (one time use only).

Re Mariah Carey's E=MC2, yes sadly its a reflection on some of todays sound recording-engineering skills. I sometimes wonder if "over-compression" is done deliberately for effect, more a "fashion" thing; An attempt to put extra "Zing" into the music. Ummmmmmph......... thick cones with reduced resonance performance might overcome such recordings. I'd rather avoid going down the road of adding mass to a cone to cope with these types of recording. The new CHP-70 Gen. 2 does a reasonable job of smoothing some of theses types of recording. Its design retains a low mass cone, the work being done by a re-tuned coil to smooth off the highs. It a technically better alternative than sticking on a "cheap" cone.

Personally, I much enjoyed doing the up-grade design work on the Gen. 3 CHR. For me, its the best CHR I've made to date.

Cheers

Mark.
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Last edited by markaudio; 22nd October 2011 at 11:11 PM.
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Old 23rd October 2011, 02:13 PM   #5
borispm is offline borispm  Hong Kong
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Hi Mark,

I definitely like what I'm hearing on the CHR70 Gen 3. Great piece of engineering!
The sound's absolutely right, and particularly the mid-treble.
Makes me wanna get a pair of CHP too, if it can sound soft without getting a heavy cone.
Now I'm listening to some "audiophile collection" CD, a.k.a. The infamous among stereophile editors "girl songs", and that's scarily realistic!
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Old 31st October 2011, 09:14 AM   #6
borispm is offline borispm  Hong Kong
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Here is the crossover network I've used.
I suspect it doesn't work so well as the impedance fluctuates a lot here, and the load should be pretty difficult as it drops below 4 ohm in its operation.
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