Aijan Posted May 8, 2014 Report Share Posted May 8, 2014 Hi, I have a JL Audio 13W7 in a small sealed cabinet (about 50 liters), but I find it hard to feed it enough power mainly because of the unusual 3 ohm resistance of the driver. I have an EP4000, but I can't use it in bridge mode when the driver is rated 3 ohms. So, the best I can supply the driver is a mere 750W RMS. I feel like I am leaving at least 3-4 db of output on the table. There is of course the option of building a much larger cabinet to get more low bass for less power, but that's something I don't want to do. So, I am thinking of building multiple dual opposed cabinets, and the idea of using Infinity 1260W for the job appeals to me for a number of reasons. 1. They have respectable Xmax (13mm) for such a low price ($50-$60). 2. They don't require a large cabinet - perfect for sealed dual opposed. 3. They don't require tons of power (need only 300W RMS per driver). Here comes the problem. When I model the box in WinISD, I have to keep the box really small (about 50 liters per box for 2 drivers). Otherwise I run out of excursion really quickly at peak 600W power per driver (I don't want to use an HPF). Either I am doing something wrong or the Xmax figure in the offical manual at http://fr.infinitysystems.com/tl_files/catalog//Infinity/Infinity-Car/Specsheets/Reference/Reference/1260w/REF1260W_PI_EN.pdf is not accurate. According to the manual, Xmax is only ~5.5mm at 20hz for 300W of power in a 35 liter sealed enclosure. WinISD, on the other hand, shows me about ~12.5mm of Xmax for the same amount of power. Which figure should I trust? The official figure looks too good to be true. Is it program power or something? Below, you can see WinISD's cone excursion figure for one 1260W in 35-liter sealed @ 300W. Link to comment Share on other sites More sharing options...
Ricci Posted May 8, 2014 Report Share Posted May 8, 2014 A couple of things... First don't worry about the nominal impedance of a driver. It varies constantly with frequency. A "4ohm" driver might have a minimum impedance much lower like 2.4 ohms. Go ahead and try bridging the EP4000 to the 13W7. It should be fine for the amp. If anything you may have to worry about the driver. Just monitor the situation for a while if you do this to see how the driver behaves. Believe the simulations over whatever information is saying the drivers only reach 5mm excursion with 300w. The infinity drivers have a lot of xmech past xmax for safety as well so its not like you will blow them if you go past the xmax rating. I heard the xmech was more than 25mm. Link to comment Share on other sites More sharing options...
Aijan Posted May 8, 2014 Author Report Share Posted May 8, 2014 Thanks for the tips Ricci! Since the DC resistance of the 13W7 is 2.4 ohms, the worst impedance the EP4000 would see bridged is 1.2 ohms per channel. Since you said the amp would handle it fine, I would probably give it a try (it helps that I have the stock fan). The 13W7 is rated for 1500W RMS, and in such a small cabinet, I doubt it would exceed xmax much. However, if I clip the amp hard (I normally only allow brief clipping), the driver would receive ~3000W continuous, right? I guess this is what you warned me about. As for the sealed dual opposed Infinity, In WinISD, I have set the box volume to 60 liters, and got ~16mm xmax at 20hz when powered with 1200W. Since you said xmech is >25mm, just 3mm past xmax should be ok. This would give me 99 db peaks at 20hz. Not bad. Link to comment Share on other sites More sharing options...
Ricci Posted May 9, 2014 Report Share Posted May 9, 2014 Correct. I think that will be OK for the Infinity's. They may make bad noises if you push the too far past xmax but they should give plenty of warning before any damage. The dcr being 2.4ohms on the JL means that in box with some cable resistance you are likely at 2.6 ohms and that is down near 3Hz. The min impedance above 10Hz is probably well above 3 ohms. You could try it. Just see how things react. I doubt you would bottom the driver. Just be careful of blasting prolonged bass tones near full power for too long as that could heat the coil up Link to comment Share on other sites More sharing options...
Aijan Posted May 12, 2014 Author Report Share Posted May 12, 2014 Thanks Ricci. I went ahead and bridged the EP4000. I had a relatively wide bw ~4.5db boost @20hz. I cut it back 1db just to be on the safe side. The bass did get more powerful alright, but it also became sloppier. An online search revealed the culprit. Apparently, bridging an amp cuts its damping factor in half, and I had a rather long cable run. Fortunately, I had used more cable than necessary, and shortening the cable tightened the bass again. BTW, the best cable loss calculator I have found is http://www.electrovoice.com/cableloss.php as it takes damping factor into account. There is one surprise though: I have gained about 2hz of extension (-6db point is 11hz now vs 13hz before). I am not sure how this happened (the gain is there regardless of volume or my 1db change in eq). Link to comment Share on other sites More sharing options...
Kyle Posted May 15, 2014 Report Share Posted May 15, 2014 The cable won't make a difference so don't worry about that. I would also be surprised if you can hear the difference in the damping of the amp. A measurement would reveal a lot but if you cut the power by 3dB does it sound about the same again? If you're really concerned still just run the amp in 2 channel mode rather than bridged mode. One channel to one coil and the other to the second. I'm assuming you have a dual 1.5 ohm 13W7 correct? Link to comment Share on other sites More sharing options...
Aijan Posted May 16, 2014 Author Report Share Posted May 16, 2014 I used to think that the cable resistance wouldn't make much of a difference, but apparently it does for subwoofers probably because of the heavy cones used and the relatively loose suspensions required for high xmax. When I first hooked up my 13W7, the only cable I had on hand was 1.5mm2 (~16 AWG) for a 10 meter run. The bass was heavy with that cable. Using 2.5mm2 (~13 AWG) immediately tightened the sound. Then I took Ricci's advice and bridged the amp, and despite the thicker cable, the bass became heavy again due to the damping factor being cut in half. Shortening the cable down to 8.5m has helped tighten the bass again. Various sources on the web recommends a minimum damping factor of 15 to 20 after cable losses. To my ears anything less than 15 does start to have a negative effect on the sound. Yes, I have a dual 1.5 ohm 13W7. I am happy with the sound with the amp bridged. Link to comment Share on other sites More sharing options...
MemX Posted May 16, 2014 Report Share Posted May 16, 2014 So you cut a 10m cable down to 8.5m, and that made a difference? I'm no expert in physics but I am struggling to see how that would have any quantifiable effect... Link to comment Share on other sites More sharing options...
Aijan Posted May 16, 2014 Author Report Share Posted May 16, 2014 MemX, I wasn't expecting much of a difference, but the slightly shorter cable did tighten the bass. According to http://www.electrovoice.com/cableloss.php given a damping factor of 150 at 8 ohms (half of EP4000's 300 DF due to bridging), the final DF at 3 ohms using 2.5mm2 cable will be ~17.7 (8.5m) vs ~15.7 (10m). The amount of attenuation that electrical damping provides is: DF10 = -20dB, DF20 = -26dB, DF50 = -33dB (ref: http://eaw.com/docs/6_Technical_Information/StudyHall_and_TechNotes/Damping_factor.pdf ) Link to comment Share on other sites More sharing options...
Archaea Posted July 8, 2014 Report Share Posted July 8, 2014 blllllllllllllind test this Link to comment Share on other sites More sharing options...
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