Recently my KLH 8" powered sub had a heart attack and the amplifier board is now dead. It seems one of the springs from the spring terminals popped loose on the inside, landed somewhere it shouldn't have, and now there is a large brown, burned spot on the amplification board. RIP.
I have a Dayton Audio SD215A-88 that I got from someone else's failed attempt to repair or upgrade a different powered subwoofer. I also have a two channel receiver collecting dust. What I would like to do is put the Dayton speaker in the KLH enclosure and power the Dayton with the two channel receiver. Since the Dayton sub is dual voice coil, I can power it with both channels of the receiver. I would have to split the subwoofer output from my 7.1 receiver and connect it to the two channel receivers CD or Aux input, and then use the two channel receivers volume as a gain for the (now passive) subwoofer.
In theory this should work fine, I've read about others doing the exact same thing on many forums. The problem that I'm concerned about is that the Dayton speaker is only rated at 80w RMS total, so 40w RMS per coil (dual 8ohm coils), while the two channel receiver is rated at 100w per channel. I've also read that overpowering speakers is much better (or less bad) than under powering them, but I'm concerned when it's 150% over the rated power handling. I'd like to hear some opinions or feedback on this idea.
PS: I'm not really interested in spending any money on this since I'd prefer to put money towards a larger sub instead of a Frankensub. If I can make this work for a while then I can save up to buy or build something better, eventually.
I have a Dayton Audio SD215A-88 that I got from someone else's failed attempt to repair or upgrade a different powered subwoofer. I also have a two channel receiver collecting dust. What I would like to do is put the Dayton speaker in the KLH enclosure and power the Dayton with the two channel receiver. Since the Dayton sub is dual voice coil, I can power it with both channels of the receiver. I would have to split the subwoofer output from my 7.1 receiver and connect it to the two channel receivers CD or Aux input, and then use the two channel receivers volume as a gain for the (now passive) subwoofer.
In theory this should work fine, I've read about others doing the exact same thing on many forums. The problem that I'm concerned about is that the Dayton speaker is only rated at 80w RMS total, so 40w RMS per coil (dual 8ohm coils), while the two channel receiver is rated at 100w per channel. I've also read that overpowering speakers is much better (or less bad) than under powering them, but I'm concerned when it's 150% over the rated power handling. I'd like to hear some opinions or feedback on this idea.
PS: I'm not really interested in spending any money on this since I'd prefer to put money towards a larger sub instead of a Frankensub. If I can make this work for a while then I can save up to buy or build something better, eventually.
Too much average (RMS) power will burn voice coils.
A clipped "under powered" amp can burn the voice coils because the average power delivered may exceed the thermal limits of the driver.
A clipped "over powered" amp can burn the voice coils faster than a clipped "under powered" amp.
Most music sources still have over 10dB dynamic range, so a clean signal peaking at 100 watts delivers at most only 10 watts average (RMS) power.
That said, some genres of music, like EDM may have as little as 3dB low frequency crest factor, same as a sine wave, and could let the magic smoke out of your drivers with only 40 "watts" after a relatively short time.
Thanks for the info, that's really good to know. I only recently learned what an amplifier clipping actually means as far as what happens to its output.
I should have mentioned that I'll only be using the subwoofer for movies and tv shows. 70% of my music listening happens in the car, 29% with headphones, and for the rare 1% (or less) when I want to make the house boogie I have a different set of speakers and amp for that.
You mentioned that the coils can burn... I don't suppose it would help to put a fan on them? My guess is probably not, since I imagine it's more like the heating of an element in a toaster rather than the heating of a chip which can be dissipated.
I had toyed with the idea of using two TPA3118 amp boards. I can get them for two or three bucks each and in mono config they put out about 30ish watts at 8 ohms, but then I learned that their lower frequency limit is only 35hz so I scrapped that idea. Maybe I should entertain that idea instead?
The Dayton Audio SD215A-88 has a vented voice coil, mounting it with the magnet out would allow better heat transfer.
If you need a fan to keep it from burning, you need more subwoofer ;^)
Two or three bucks each gets you started on an amp project, then you need the 26volt power supply, and the case and the heat sinks and connectors, and you already have a receiver that probably would sound better...
With a large amp on a lower powered sub woofer, the amp will cleanly drive the speaker passed its max mechanical movement. I think this is called Xmax of the driver. The subs voice coil will hit the back plate of the magnet, you will hear that. A clear sign to turn it down a bit. Other than that, nothing I would worry about.
You'll be fine.
An example of how silly you can be: a little while ago, I built a small pair of speakers with a 4" mini-subwoofer and a 2" full-range unit. Passive crossover in the 800Hz range. Total RMS power handling of the speaker was probably in the 100w area.
The amplifier I was using with them was a Crown MA5002VZ. 1300w/ch into 8ohm. That was mostly to get over the horrendously low efficiency - somewhere south of 80dB@1w - there's no getting around Hoffman's Iron Law.
The trick is this: pay attention, and listen. If the drivers are starting to sound ugly, you're sending too much power and you need to back off before they burn out.
Chris
Xmax is linear travel, Xlim or Xmech is the mechanical limit, which could be the voice coil former hitting the back plate, or more commonly in modern drivers, the surround or spider(s) reaching their limit. Most modern subwoofers have an Xlim double the excursion of Xmax.
The soft parts (surround spider, cone) don't "clack", and their "distress call" may be harder to detect at Xlim over the sound of the main speakers.
Driving past Xlim does cause permanent damage in the form of ripped or kinked soft parts or a crushed coil former.
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You guys have some very good points and information. Thank you all for the advice. I wish there was an easier way to keep tabs on whether the woofer is being pushed too far, but also I don't plan on trying to watch Jurassic Park or Jumanji at theater levels. I will definitely keep an ear out for the sub being tortured though. I'd be really sad if the little guy went up in smoke.
Just don't try and hit anywhere near THX reference peak SPLs [85 dB avg/115 dB peak @ the listening position] as you'll need way more power and/or more subs and/or much more efficient speakers even with decent room gain.
Well, all my concerns about overpowering the sub were for naut. Turns out this receiver has a very audible hiss with the volume up while no sound is playing. I never noticed it before since whatever it was playing was far louder than the hiss. But now with this setup, when there is no LFE activity during a quiet scene, I can absolutely hear the hiss. I guess I will look for a new amp for this project, or give it up and buy a new subwoofer.
Thanks again to everybody for all of the feedback and advice. If nothing else, I gained some valuable information here.
Thanks again to everybody for all of the feedback and advice. If nothing else, I gained some valuable information here.