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Old 21st April 2013, 01:22 AM   #11
eladmi is offline eladmi  Germany
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Old 22nd April 2013, 06:50 PM   #12
mp9 is offline mp9  United States
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Bob B, is your MLTL's driver height a set measurement to the box design for any reason such as BSC, MLTL or other? Is there wiggle room to set it higher up on the baffle without a negative effect on the design?

Re: break in - I'm at 242hours on mine, listening to Tori Amos from the choirgirl hotel now, it's 100X better then when i tried @ 125hour point when it was unlistenable. If you're not familiar with the LP, it's from the point in her career when she went plugged! Her "MTV Unplugged" performance of it was a bit of a oxymoron since everything she did before it was essentially unplugged. Imo the last of her good stuff, i completly lost interest in everything she did after choirgirl hotel.

Anyway i had saw her perform the album live and plugged in when she originally toured it. Was front row center, technically our seats were more off to the left but everyone was standing and the two wedding gown clad little five footer club girls in the center seats didn't mind us standing next to them, lol. So i've found memories of how it should sound. At 242hours break in and not even in a proper box, driven by a 45 tube SET in the small office room ~80db/85db peaks sounds ridiculously loud, very clean, actually it's sounding pretty freak'n awesome. And no clipping either. I imagine they'll only get better.

Really it has me wondering what the seemingly forgotten 12P MarKen or even the Moosebox would do in this 13'x9'x8'h small room, although i suspect one of the two smaller MLTL's, Bob's or Scotts Std Pencil would probably be fine here too with more versatility for the larger rooms? Please feel free to comment on this idea of mine, so i don't have to feel so much like one of the three blind mice
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Old 22nd April 2013, 07:16 PM   #13
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Quote:
Originally Posted by mp9 View Post
Bob B, is your MLTL's driver height a set measurement to the box design for any reason such as BSC, MLTL or other? Is there wiggle room to set it higher up on the baffle without a negative effect on the design?
The position of the driver on the baffle is VERY critical to reducing unwanted harmonics. If you must raise the driver, add height to the plinth.

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Re: break in - I'm at 242hours on mine, listening to Tori Amos from the choirgirl hotel now, it's 100X better then when i tried @ 125hour point when it was unlistenable
I hope so! I have at least 100hrs on mine and there is a nasty peak a 1100Hz than makes the speaker very forward, almost shouty. I hope that this goes away with time. Otherwise, a notch filter will be required.

Quote:
At 242hours break in and not even in a proper box, driven by a 45 tube SET in the small office room ~80db/85db peaks sounds ridiculously loud, very clean, actually it's sounding pretty freak'n awesome. And no clipping either. I imagine they'll only get better.
Right! I am listening to mine at the moment (Vivaldi: Concerto for Violin RV270) in a 13'x15' room. 90dB peaks hardly move the drivers. These drivers are capable of damaging loud.

Quote:
Really it has me wondering what the seemingly forgotten 12P MarKen or even the Moosebox would do in this 13'x9'x8'h small room, although i suspect one of the two smaller MLTL's, Bob's or Scotts Std Pencil would probably be fine here too with more versatility for the larger rooms? Please feel free to comment on this idea of mine, so i don't have to feel so much like one of the three blind mice
Well, you might guess what my opinion would be. Let's just hope the peak goes away.

Bob
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Old 22nd April 2013, 07:55 PM   #14
chrisb is online now chrisb  Canada
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Bob: yes, I think you can expect the peak to diminish further after another couple of hundred hours - whether sufficiently for you is another story.

and yes, those composite resin flanges do make for some aesthetic and fabrication challenges compared to the stamped metal baskets of other driver makes

mp9;

The A12P is certainly capable of "pretty darn" loud, and in an uncompromised design, plenty good bass as well.

The Fonken/MarKen series have always been targeted for different performance goals than would generally be the case for a BLH, or full sized MLTL, and certainly the Pensils and Bob's M10-A10 .
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Old 24th April 2013, 02:40 PM   #15
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Here are a few measurements: Black is combined driver/port and 4ms gated. Gray is ungated 0.5m. Red is the published FR digitized from Mark's web page. Finally, the impedance at the bottom.

My measurements are anything but anechoic, but you can see the mid-range problem (the peak is actually 1259Hz). Here's hoping that the trace smooths out over time.

Given how ragged the FR trace is, I am surprised at how good these speakers sound. Speaks volumes to the fact that we hear a 1/3 octave smoothed version of the actual FR.

Bob
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Old 24th April 2013, 11:45 PM   #16
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Quote:
Originally Posted by Bob Brines View Post
Here are a few measurements: Black is combined driver/port and 4ms gated. Gray is ungated 0.5m. Red is the published FR digitized from Mark's web page. Finally, the impedance at the bottom.

My measurements are anything but anechoic, but you can see the mid-range problem (the peak is actually 1259Hz). Here's hoping that the trace smooths out over time.

Given how ragged the FR trace is, I am surprised at how good these speakers sound. Speaks volumes to the fact that we hear a 1/3 octave smoothed version of the actual FR.

Bob
Hi Bob, (Guys),
The 12P has no peak vices at the the point you mention (1.259kHz) under anechoic test conditions. You might need to revisit the box design. Possibly either driver position, the location of the nearest bracing to the driver or the effectiveness of the internal damping. Any internal reflections impacting on the rear of the cone will effect performance. I'm commenting with additional caution as without an anechoic test condition, its difficult to know the extent of external effects from the environment on your measurements.

The overall sound should be pleasing as the driver's wide dispersion profile will mitigate emittance variations. The driver's power-train will optimise at around the 500 hour (dependant on run-in loading).

I should let folks know that as I develop ever lighter cones, especially paper versions, increasing variance in the anechoic measured frequency range will occur. The design of new cones are lower profile delivering wider dispersion and central stereo imaging as these features add to optimisation of the overall listening experience.

Thx
Mark.

Last edited by markaudio; 25th April 2013 at 12:01 AM.
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Old 25th April 2013, 12:56 AM   #17
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Hi Bob, (Guys),
Further thoughts. Appreciating the requirement for a shallow MLTL depth to accommodate the characteristics of the driver, I'm wondering how close is damping located to the rear of the driver; And the type of damping?

Your box looks fab so give this system more run-in time. If you find that the peak is still audible at the 400 to 500 hour mark, if it were me, I'd opt for a filter rather than ditch the design. It not aways possible to get a perfect marriage between box and driver straight off the drawing board.

In many ways, Bob, in part raises the issue of overall driver operational sensitivity. I've been (and remain) happy to do my best to produce drivers that reflect member feedback. Much of the feedback over recent years encouraged improvements in efficiency. As often said in audio, there's no "free lunch". I'm happy to continue pushing driver design and performance efficiency boundaries, but it comes at a price. Driver frequency variance will increase but any negativity in this department I currently off-set with better dispersion and imaging characteristics by use of shallower cone profiling. Using more operationally efficient drivers might for system designers/builders, require extra effort. End users will have to pay attention to clean amplification and source signalling in order to get the best from the newer driver designs.

My recent experiences with listening tests on the new 10P caused me to take one of my favoured tube amps off line. The new driver revealed too many of its shortcomings. On Tony's 300B, I spent time swopping valves (tubes) particularly the 5u4 rectifier, before I got to the sound I like and the marriage with the E-308 improved dramatically at around 150 hours.

The doctors have got me on increased rest periods, frustrating, but its given me time to revisit several designs including the original Alp12 and the 12P (in Pensils). It is very interest to re-visit the relative "docile" emittance of the original 12, no surprise given its heavier mass cone. I personally wouldn't swop them for the 12P's, the new model is far more revealing.

........Food for thought....................

Thanks
Mark.

Last edited by markaudio; 25th April 2013 at 01:05 AM.
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Old 25th April 2013, 01:50 AM   #18
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Mark, I am sure you are right that all of the trash is box related. It may never be possible at my level to get a decent FR trace. In the display above, I did make one mistake. I adjusted levels to match at 1kHz.If I had brought my trace up 3-4dB, it can be seen that the envelope follows the published trace at least to 10kHz. I discussed my choices of cosmetics earlier. There are some consequences in the diffraction signature, which indeed may be what I am looking at.

The 1259Hz peak is really bothering me. That a 1/2-wave of ~5.5". Looking at the cabinet, the only dimension that jumps out is the front to back distance. I'm going to increase the thickness of the fiberglass padding behind the driver. Can't hurt.

Bob
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Old 25th April 2013, 04:07 AM   #19
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Quote:
Originally Posted by Bob Brines View Post
Mark, I am sure you are right that all of the trash is box related. It may never be possible at my level to get a decent FR trace. In the display above, I did make one mistake. I adjusted levels to match at 1kHz.If I had brought my trace up 3-4dB, it can be seen that the envelope follows the published trace at least to 10kHz. I discussed my choices of cosmetics earlier. There are some consequences in the diffraction signature, which indeed may be what I am looking at.

The 1259Hz peak is really bothering me. That a 1/2-wave of ~5.5". Looking at the cabinet, the only dimension that jumps out is the front to back distance. I'm going to increase the thickness of the fiberglass padding behind the driver. Can't hurt.

Bob
Hi Bob,
It might be worth giving the drivers another 50 hours or so of run time, then experiment with the internal damping. I suspect that the shallow depth of box might need to the damping to be adjusted to suit. The notch filter should be a decent fix if this particular peak persists.

Overall I reckon the box looks great, very stylish and should mellow acoustically around the 1000 hours. Us mech engineers like to build some operational reserve strength, so the 12P's will continue to "warm" well into the +1000 hour operational timeframe. In my living room, Im using Alp7's Gen. 2's with lots of hours on them (15000+), they are now verrrrrrry sweet.

Cheers
Mark.
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Old 25th April 2013, 01:00 PM   #20
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Bob, have you tried any acoustic insulation besides fiberglass? I've noticed different results from the denim material and the poly-based loose fill.
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