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pixleboy 18th November 2006 07:28 PM

Subwoofer : Plate Amps or Monoblocks ?

I'm building a pair of subs that use big, high displacement drivers, which can
handle lots of watts (800 continuous, 1600 peak), and sit in really large sealed concrete boxes (Qtc = .56).

I recently bought a 1000 watt Keiga plate amp to test with them... Since I don't live in a stadium, I didn't think I would need to drive them with anywhere near 1000 watts; I was in fact originally planning to drive the subs with a nice pair of class A hybrid monoblocks that put out a conservative 100 watts each, and are supposed to be capable of driving extremely difficult loads (they are left over from another system). I bought the Keiga amp after reading what happens when using a bit of EQ to extend the LF capabilities, I see that in fact I do need quit a lot of juice. I was further swayed by the convenience factor that this type of amp typically offers, with the adjustable crossovers and a little EQ built right in.

If I had an active low pass filter with some EQ available (suggestions ???), I could also try driving the subs with the monoblocks and compare the two solutions, but I don't yet have that opition, and so am asking if it would be worth acquiring such a device, or if it I would be best off just sticking with the powerful plate amps and integrated filters.

Also, any thoughts on the not so pretty signal to noise numbers of the plate amps when
used with a cutoff (12db/octave) at 50-60 Hz ?

Thanks in advance to all for any thoughts on the subject,


DcibeL 18th November 2006 08:41 PM

Personally I would stick with the high power plate amp with parametric EQ options. A big subwoofer seems to me like a waste of a nice Class A amplifier. For higher output that may remove the need for the EQ, and lower power requirements, have you considered a ported design for the subs?

I don't believe that noise will be a problem at low frequencies.

pixleboy 23rd November 2006 12:09 AM


Just a quick note to thank you for your thoughts... the plate amp is working great with the first of the two subs... currently feeding it both left and right signals (second sub should be done in about 3 weekends from now, at which time I should have the second plate amp).

Yes I did consider the ported option, and almost went that rout... the boxes are in fact the correct size for a ported design (16 cubic feet), which also happens to be the right on for a sealed enclosure having a Qtc between .5 and .6. Since my priority is on accuracy, I decided to start with a sealed design and a lowish Qtc (better transient response and a more gradual roll off... this does however require a lot more power, hence the 1k watts). I knew that if I wasn't getting enough output I could always install big ports. These subs use high excursion 18" drivers, and it turns out that in a domestic environment (well anyway, it is where I sleep), even just running the one, there is plenty of bass. The amps have a switch for built in EQ at 25 Hz; my db meter needs a new battery, but to my ear the built in EQ seems to compensate about right for the earlier roll off of this sealed design. I also tested the sub with my synthesizer... and well it did what a big sub is supposed to do... the very low notes and a kick drumbs were reproduced without effort (I know its not supposed to be the goal, but it IS fascinating to feel the pressure in the room with low notes, and to watch the cone move when playing the drumb).

Though it was a pain, I am happy I made the enclosure from concrete. Before permanently sealing the top, I palyed some electornic music, closing off the box with a board held down by two 36lb weights... not a very good seal... even at very normal listening levels, the escaping pressure was enough to cause the board to lift and knock loudly (sounded like a diesel motor). Useless test. I would never have guessed the relatively fragile cone could do this.

Once properly sealed, when listenting to recorded music I noticed that I don't turn the main system volume knob up as much as without the sub.

If I can find a good active filter somewhere (suggestions ???) I will compare the plate amp with the monoblocks and post my findings here for those who may be able to use the info.

Well, not such a quick note after all...

Additional thoughts welcome.

Thanks again,


DcibeL 23rd November 2006 08:12 AM

Wow...concrete...hope you never have to move them ;). It looks like you a nice pair of subs there in which every minor detail is considered. Have some pictures to show?

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