box size for 13" w7??.. The one I built is no good

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Stupify

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Joined 2005
mitulparmar787 said:
I apologise for bringing this thread back up, but I've got a 13W7 in a 5.7cu.ft enclosure tuned at 18hz with a 100sq inch slot port.

I definitely do NOT lack lowend whatsoever...and this is with only 300wrms @ 4ohms from a plate amp, I can only imagine what this would sound like with 1.2kw on it. As for musicality, the subwoofer is really good...would say 30:70 Music/HT.

If anything I'd say instead of selling your sub off, I'd make a new enclosure.
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I'm glad your happy with yours. I really wanted to stay with a sealed smaller box. So I sold the w7 and bought a custom built 15 made for HT and low low bass. Thanks for all the help though guys.
 
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AndrewT

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Joined 2004
Hi Simon,
did you think through that reply?

He wired the two VCs out of phase due to a manufacturing fault.

As a result there would be almost no movement in the VC as current was forced through it. Virtually a total loss of cooling due to no turbulent air around the wire.

To compound the problem he heard almost no output and so I suspect he turned up the volume control to try to force some sound out.

To me that suggests a risk of more heat being generated in the VC than normal and higher temperatures inside the VC and at it's surface.

That is why a warranty claim should be considered at this early stage, while the speaker is still newish.
 
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simon5

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Joined 2004
From this paper :
http://www.adireaudio.com/Files/TechPapers/DualVoiceCoilDrivers.pdf

Look at a typical dual voice coil sub, such as Shiva. It's N0 is ~0.4%. This number is VERY comparable to other 12" DIY high-end subs out there, and represents a driver with an 88 dB SPL rating.

Now, apply 300W electrical power. Wire the voice coils in parallel, in the same electrical phase. We'll get our acoustical output, or (300 * 0.004) 1.2 acoustical Watts of power out. The other 298.8W of electrical power is dissipated as heat.

Now wire the two voice coils out of phase. What will happen? Well, we know from the above that the two magnetic fields from the voice coils cancel each other out, so there's no net cone motion. Thus our acoustic power output is zero (can't have any, if the cone doesn't move).

That means ALL the power is dissipated as heat within the driver. How much? 300W. Compare this to the situation where the two voice coils are connected in the same polarity: 298.8W. Net difference? 1.2W of dissipation. In essence, you will cause exactly 1.2W of extra power dissipation in the system by cross-wiring the voice coils.

Now, is that 1.2W extra heat going to be a problem? Most likely, no. If a driver is rated to handle 300W, chances are it's not going to have a problem with 301.2W. 400W, sure, but a 0.4% increase in power dissipated? Well, the temperature of the voice coils may raise another 0.1 degree C, but that's about it.

Anyway, the net result is that the increase in heat from dissipation is essentially zero. The one area of consideration is that self-cooling of a driver is reduced when motion is reduced. So the driver can handle the out-of-phase situation for a little while, but because of the reduced cooling, heat will build up faster.
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I've just said that I doubt he damaged something. Yes, for extended periods of time, you are right, he could damage something.
 
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AndrewT

R.I.P.
Joined 2004
The one area of consideration is that self-cooling of a driver is reduced when motion is reduced.
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Reduced! It must have been almost zero, particularly if the DVC was accurately wound.

I fully accept that the increased dissipation due to zero sound output is of little ( <1%) consequence, but my point is that he has a two bar electric fire inside his magnet gap - with no ventilation cooling and finger on the volume control turning it up to try to produce a sound output.

Can any one with open ears give advice on whether a warranty claim should be made now or does he just hope that the insulation, glued joints, former accuracy etc are all completely as expected for a new drive unit?
 
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cyclecamper

Member
Joined 2010
simon5 said:
Maybe check the coils to be sure they are in series and in-phase.
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They are dual-coil, so you could have them wired wrong...

How does the output compare subjectively to the JL Audio powered home units?

I may be following in your path as soon as finances allow, and was planning on a sealed box (actually two sealed boxes with one 13W7 in each.

Oops, I guess I'm conversing with an obsolete portion of an old thread, please excuse me.
 
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