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Old 3rd April 2005, 04:13 PM   #1
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Default Dayton DVC & Rythmik 250SE results

Greeting all,

Okay, I decided to rebuild an againg M&K Volkswoofer with new parts as the old ones were getting pretty tired. The new driver is a Dayton 12" DVC. The new amplifer is the Rythmik Audio 250SE (special edition).

The Dayton 12" DVC is a dual voice coil woofer being used in resistively damped operation (the second voice coil is being used as a brake to precisely adjust the Qts to my box). After some careful calculations and with the help of a Dumax report, 7.5ohms was calculated as the correct resistor to give me a Q=.707 Butterworth alignment in this sealed 50L (net) box. Heavy stuffing is used.

The subwoofer design on paper:

Driver: Dayton 12" DVC, resistively damped operation
Box: sealed, 50L (1.77cuft)
F3: 33Hz
Fc: 33Hz
F6: 26Hz
(Note: figures without room gain)
Amplifier: Rythmik Audio 250SE


The Rythmik Audio 250SE is basically a tweaked Parts Express amp. This amp has some upgraded wiring & caps, and a 24dB/octave lowpass filter in lieu of PE's 12dB/octave. The phase control has been redesigned to perform better. Hum has also been reduced.

How does it sound? Well, I've heard a bunch of subs and this is a good design, especially for music. I also tried it with home theater and it works impressively (getting the music right is the tough part, HT will follow naturally). The sub is deep and tight with an excellent balance between the boominess of a high Q and the tight (but thin sounding) bass of a low Q design. I tried Q=.6 and it was just to thin and dry sounding for my taste - it was tight , though. I also tried Q=.9 and it had a little too much boom and overhang for my taste. I have new respect for a Q=.707 Butterworth alignment. The bass has punch and hits hard like a live performance - impressive.

With a meter, I'm pretty flat down to about 30Hz, good output at 25Hz, falling fast at 20Hz (but still useful). At 1 meter, I got 100dB at 20Hz (pure tone) before hearing the Dayton DVC just starting to distort - it was quite impressive (and a little scary) to see the Dayton woofer working that hard under heavy excursion. BTW, even with one voice coil hooked up, this sub plays quite loud with serious room pounding bass.

The Rythmik Audio 250SE barely was warm to the touch after a serious workout. Hum is minimal, power is entirely adequate for this sub design, and the 24dB/octave is a very nice feature (the high frequencies are so attenuated that is difficult to tell what familiar song your listening to by just listening to the sub - it was quite easy with the old 12dB/octave M&K). The 24db filter also keeps power from the amp being wasted (robbed) on unwanted upper bass frequencies.

The phase control is a VERY USEFUL feature on this amp. I am running my mains full range and the room has a natural peak at 40Hz (which, incidentally, is also my crossover frequency). Using my meter, I actually used the phase control to create a little destructive interference to tame the 40Hz resonance of the room and smooth the crossover frequency.

With the phase control set in 100% in phase, it would have reinforced some nasty overhang which is intrinsic to my particular listening room, set 100% out of phase, it would create a void in the bass reponse. The best setting is somewhere in between. Its funny that my mains alone have more overhang without the sub due to room resonances. The sub is actually is functioning as a room bass trap to reinforce some frequencies and reduce others. The discovery of the usefulness of the phase control in taming room resonances was serendipity for me. With the overhang removed from my room the bass really hits with the cleaness and authority of a live performance. Impressive.

Note: Interestingly, the phase control seems to be backwards: 100% in phase when set on 180 degrees, not 0 degrees. Yes, I have everything wired up right in the cabinet and everywhere - its the amp. (My sub is facing the same direction as my mains and is located beside my right speaker). This is NO disadvantage or problem, just important to know.

In summary, this is a good design that has exceeded my expectations and easily bests the original M&K components in everyway (no offense M&K, that was a very good sub). I am impressed with the versatile Dayton 12" DVC and especially with the Rythmik Audio 250SE plate amp. Also, during this project it was driven home that mating the driver and the box are critical - slight changes in the tuning of the box make PROFOUND differences in the overall sound. A driver is only as good as its design. The "resistively damped operation" design is simple, but effective.

BTW, Rythmik Audio was informative and helpful with my choice of amplifiers. Thank you.

Regards,

Loudnclear
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Old 4th April 2005, 01:07 AM   #2
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Additional note: I was looking at an error correction chart for my Radio Shack digital SPL meter (el cheapo $50). The chart said to add 7.5dB @ 20Hz (add 5dB @ 25Hz). If the error correction is right, my sub hit 107.5 dB @ 20Hz at 1 meter (in room) before any audible distortion. These meters aren't too accurate I guess?

Loudnclear
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Old 4th April 2005, 02:09 AM   #3
DcibeL is offline DcibeL  Canada
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Quote:
These meters aren't too accurate I guess?
No, they aren't. You can fix them though .
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Old 8th April 2005, 12:10 AM   #4
mike.e is offline mike.e  New Zealand
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No,they are consistently inaccurate according to online sites,meaning that the adjustment curve should be fine.

With a small room without leaks room gain can nicely complete a sealed sub,in some situations
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Old 8th April 2005, 10:50 AM   #5
RogerG is offline RogerG  United States
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Are you using the high power or low power Dayton?
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Old 8th April 2005, 11:40 PM   #6
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I'm using the high power 12" Dayton DVC - similar to the Shiva.

This sub is really sounding good. The bass is tight and full and is perfoming with my music in a most excellent way. Again, besting the M&K, easily.

Using 1 voice coil is giving me about a 10Hz lower F3 verses both coils in series (according to my BassBox software). With room gain and meter error accounted for, I'm pretty flat well into the 20's. I'm going to generate some more numbers this weekend - I'll post them.

Andy
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Old 9th April 2005, 12:31 AM   #7
drboyd is offline drboyd  United States
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Default You're kidding! I just did....

....a very similar change-out-the-guts project with an old Acoustic Research sub box I got off eBay. I used the Dayton DVC with both coils in parallel, and the Rythmik 250A amp with the crossover point set for 24hz.

Mine is in a vented 41 liter box, with the 3" by 18.5 vent.

Tell us some more about using that resistor as a brake, and how that improves the whatever. And whether it would work in a vented box...?
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Old 9th April 2005, 02:41 PM   #8
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I meant coils in parallel in my last thread not series (I did not model a series wiring of the voice coils).

Resistively damped operation is cool because you can use the second voice coil to act as a brake to ajust your Qts anywhere between the Qts of both coils in parallel (Qts=.37) and 1 wired voice coil (Qts=.71). I chose Qts=.51 for my design to give me an enclosure/driver realtionship of exactly Q=.707 (considered ideal balance of boom and tightness in a sealed enclosure - my ears do agree with this value). With Qts=.51 as my target, I calculated my damping resistor to have a value of 7.5 ohms.

You could use resistively damped operation for ported enclosures, but a Qts of .37 is pretty good for the ported design. Also, you could only go higher than .37, not lower.


Andy
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Old 9th April 2005, 05:52 PM   #9
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Okay, I just got finished generating some test tones and measuring them with a meter.

In my listening room (medium size), relative to 80Hz, this sub is:

-1dB @ 50Hz

+1.5dB @ 31.5Hz

+.5dB @ 25Hz

-6dB @ 20Hz.

Max ouput at 20Hz (before audible distortion) is 107.5dB @ 1m.

Note: NO bass boost is being used.

Reasonable for a sealed 12"?
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Old 9th April 2005, 08:00 PM   #10
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The last numbers were from my listening spot. These are from an up close microphone.

Relative to 80Hz:

63Hz = +1.5dB

50Hz = +1.5dB

40Hz = -1dB

31.5Hz = -1.5dB

25Hz = -6.5dB

20Hz = -8dB

With room gain these numbers obviously look better. My sub is located between the front speakers - it is not corner loaded. I'll have to try that too.
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