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Luvs3rds, I'm tending towards buying or constructing a cabinet. Only prob is that Polk recommend a nearly 9L enclosure. That would be about 2 US gallons, more or less, and means more weight and less space in the boot (trunk). However, if that's what it takes...
Moreover, my auto enthusiast nephew tells me that if I were to cut or drill into the parcel shelf to mount the sub it might affect the cars roadworthy status ( and thus insurability).



Pay heed to yer nephew's advice. In today's autos there is no wasted sheet metal, quite often the case that it is part of unibody construction and therefore hacking away metal is the equivalent of removing frame parts, not good.

There are subwoofers designed for automotive use, with abs or other composite loaded cabinetry already tuned to match. You would do good to look into those.

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Silvertones, the bridging would be done using the external switch on the amp which provides for this (and suggests the amp designers are allowing for a mono use, such as a sub). I can't get hold of the manual for this amp, too old, but am assuming that if it is bridged using the external control, that ohmage applying doesn't drop below the 4-8ohms range printed on the side of the amp.



BUT -- the sub you describe has TWO VOICECOILS in it. Designed to receive the stereo signal. One voicecoil could be connected to the bridged amp safely, but the speaker was designed to have both voicecoils active. Leaving one voice coil unconnected adds MASS to the cone that was unintended by the designers and will change the specs of the woofer considerably. Connecting both voice coils in parallel will result in a 2 ohm load which is outside the safe range of that amp and will blow output devices to kingdom come in a short amount of time. One could connect the two voice coils in series to yield an 8 ohm load, but the polarity is important here so that one is not pushing while the other is pulling but the real problem I foresee in this scenario would be both a phase/time issue and also the fact that you would lose all of your apparent power advantage from bridging the amp by applying an 8 ohm load.

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Mac, your guidance is appreciated. I take on board your idea of running the amp in unbridged mode. However, the available subwoofer signal from the head unit is a one lead mono affair. If I run the amp unbridged, won't that mean that only one side of the amp, either the L or R, will deliver wattage to the sub, (at a maxium 35W RMS) even if both pairs of amp outputs are connected to both pairs of inputs on the sub?



Take the mono input signal and split it with a simple Y connection or adaptor such that it is applied to the input of both sides of the amp. You will then realize 70W rms from the two amps and the twin voicecoil speaker. This should be ample enough. Remember the "log10" decibel situation here, which in layman's terms states that you must have TEN TIMES the power to be twice as loud. Therefore a small amount of apparent wattage gain is neither seen nor heard.

Splitting the mono sig between the two amp inputs will not load down the line level signal enough to shake a stick at because the output if low impedence and the input of the amplifier(s) will still be higher than the output and cannot "load it down" then. Ohm's law.

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I would have thought that utilising the amps internal bridging mode (with the switch Aiwa provide on the case) would enable a mono signal, into either L or R, to exit the amp as a dual mono signal of up to 35 W RMS through each of the amps L + R outputs...unless for some reason it actually means you get an up to 70W RMS output out of ONE only of the amps outputs. And which one? Presumably the same side as the side you put a signal into...but that strikes me as too "suck it and see". The Japanese are better engineers than that.



NO.

Bridging a stereo amplifier results in using the L side for PUSH and the R side for PULL of a single voicecoil. (or vice verse, does not matter)

Most Bridged amplifier situations only have ONE speaker output left, typically connecting the one voicecoil from + of L channel to + of R channel and ignoring the - speaker connections altogether.

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I don't have an active crossover but provision is made for that on a "software basis" by dialling that into the head units menu of settings, once it detects the sub is connected. You can select (from memory) 50/80/120/160 hz as your desired points.



That is indeed an active crossover. It is just not separate from the head, it is build inside of it as a modular unit, if you will. That is a Good Thing.

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Finally, I note your comments about capacitors and will keep that in mind. Haven't seen them myself at auto stores but will keep my eyes open for them.



Read up on the how and why of the storage capacitor on the 12V powerline here.

Of particular interest here should be the fact that having that electron "tank" placed right next to the power input of the amplifier INCREASES available bass response and also provides an ample amount of joules readily available for reproduction of bass transient excursions, which translates simply to the ability to help your amplifier reproduce what it must reproduce. Without the big cap, DC voltage drop and "brownout" can occur, causing clipping that does not need to be there. This is an old and well known situation.

All amplifiers of any kind are simply Modulated Power Supplies. Hence the power conditioning caps are a Good Thing.

You can google "auto amplifier capacitors" to find suppliers and brands.

Be advised that some are simply way overpriced, some are way too cheap. Answer to that dilemma is simple enough -- don't buy the cheap and don't buy the super-expensive, find one that is prices somewhere between the two extremes and you will very likely get the best bang per buck along with good performance.

The amp running into that subwoofer's dual voicecoil as a stereo amp, with its input Y spliced together from your mono signal output, plus a good ample power capacitor, will indeed outperform any other possible hookup configuration given the equipments cited here. Period. (This is provable empirically "on the bench" BTW)


--Mac

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