[Texbychoice]

Have a single subwoofer cabinet with 2 -10" Infinity subwoofer drivers, each in separate chambers.  Each chamber is sealed, approx. 2 cu ft each.  Drive with an AR plate amp.  Listening room is small, 12 x 14.  Plenty of bass down to ~45 Hz.  Below that drops off.  30 Hz test frequency moves the drivers, but barely audible. 

The AR plate amp was garage sale find, think it is less than 100W.  It barely gets warm after a couple hours.  Understanding low frequencies require power, how much does it require to get decent 30 Hz output? 

[Speedskater]

a] the amp may intentionally roll-off sub-woofer frequencies.
b] old coupling capacitors may be going bad.

[Texbychoice]

a] the amp may intentionally roll-off sub-woofer frequencies.
b] old coupling capacitors may be going bad.

All caps replaced with new of same value.

What are sub woofer frequencies?  Why would a sub woofer amp roll off sub woofer frequencies?

[WGH]

...how much does it require to get decent 30 Hz output?

Probably 350 watts but...

Is this a homemade sub using Infinity car speakers? Are the drivers a 10" woofer or 10" subwoofers, it makes a difference. My old JBL L100 speakers have a 12" woofer but they roll off at 40 Hz, no amount of power will make them go lower.

The model number of the box and/or the drivers will help a lot.

[charmerci]

I'm not an expert but it seems like that subwoofer with two small drivers and a small box is designed to do what it's supposed to do and nothing more.

[Texbychoice]

Probably 350 watts but...

Is this a homemade sub using Infinity car speakers? Are the drivers a 10" woofer or 10" subwoofers, it makes a difference. My old JBL L100 speakers have a 12" woofer but they roll off at 40 Hz, no amount of power will make them go lower.

The model number of the box and/or the drivers will help a lot.

This is a home brew of various parts.  Enjoy and prefer that type of tinkering versus just grabbing the "best" reviewed product.

The sub was built by a speaker designer to go with his compact 3-way bookshelf speakers.  The enclosure is extremely robust, alone weighing about 75 lbs.  Finished like a piece of furniture.  Removed the original drivers.  Replaced with Infinity CMMD sub drivers, ILG250WS.  Definitely for home audio application.

The AR amp is from an S8HO subwoofer unit, therefore suspect under-powered.  Although, does quite well with everything but the lowest notes.  Not looking to crack plaster, just want to hear/feel the lowest notes as recorded. 

[WGH]

Your subs might be like a double CSW-10 so you will need 2 big plate amps, one for each woofer. The internal volume of the CSW-10 is 2 sq.ft., same as your box, so it looks like all you need is power.

I don't know anything about plate amps, just get the biggest one you can afford. As a point of reference my REL G2 (-6dB at 18Hz) has a 10", front firing long throw, carbon fiber woofer, with a 450 W (RMS) Ultra High-Current AB Power Supply.
 
Here is a review to get you started:
Subwoofer Plate Amps? Dayton SPA250 vs Yung SD300 Tested
https://www.youtube.com/watch?v=LsaXQJ_53R0

Infinity's CSW-10 powered subwoofer features a 650-watt amplifier and a 10" driver made with Infinity's exclusive Ceramic Metal Matrix Diaphragm (C.M.M.D.™) driver material
https://www.crutchfield.com/S-1Ohcy6GlwM6/p_108CSW10B/Infinity-CSW-10.html

acoustic suspension design
650-watt RMS amplifier
10" front-firing driver
frequency response 22-150 Hz (-3dB)
continuously variable 50-150 Hz low-pass crossover
line-level input with LFE/normal switch
R.A.B.O.S.™ low-frequency calibration system

Call Infinity and ask how much to buy two CSW-10 plate amps, that would be the simplest and best solution.

Klipsch KA-1000-THX Subwoofer Amplifier - This high-performance amplifier has a massive toroidal power supply that is capable of delivering 1000-watts into a 4 ohm load. It can also support two high performance subwoofers
https://www.bhphotovideo.com/c/product/643501-REG/Klipsch_KA_1000_THX_KA_1000_THX_Subwoofer_Amplifier.html

Bash 500S Digital Subwoofer Plate Amplifier 500W RMS - The Bash 500 watt Subwoofer Amplifier offers the combination of clean output and high power which makes the BASH amplifiers some of the best sounding subwoofer amplifiers on the market. Get 2 @ $250 each 
https://www.parts-express.com/bash-500s-digital-subwoofer-plate-amplifier-500w-rms--300-752?gclid=Cj0KCQiAhZT9BRDmARIsAN2E-J3KmqEwsKnCqtsv_BMx3GsWDEv6QJ8mGkehkv_c2VYCgdFEr4Bynl8aAubJEALw_wcB

[opnly bafld]

This is a home brew of various parts.  Enjoy and prefer that type of tinkering versus just grabbing the "best" reviewed product.

A 10" woofer or subwoofer in a sealed box without bass boost will only get down to @ 40-45 hz at best.
I have checked a lot of them over the years in a box builder program.

Driving them with an amp meant for use with what looks like an 8" ported subwoofer is not going to give the best results.
Sealed subs that go low need power because they have built in eq that eats up power.
Adding more power without proper eq will only get you louder, not lower.

[Texbychoice]

Thanks for the great information everyone.

[JLM]

While shopping for cheap A/V subwoofer a couple of years back found that most aren't what I'd call a subwoofer (something that can reach 20 Hz).  It seems that they are meant to supplement tiny desk top loudspeakers in small rooms. 

SVS SB-1000 or Rythmik L12 are two exceptions.  Both are sealed and small, equipped with 12 inch drivers, not expensive, but musical, and go deep (25 Hz or better).  So small and deep from a sealed cabinet is possible.  And points to the hazards of swimming in the unknown waters of DIY.

With the driver specifications a true DIYer should be able to predict performance for a given cabinet.  How are the drivers wired to the amp?  Suspect the drivers may be nominal 4 ohm loads.  Depending on how they're connected you could be presenting the amp with a 2 ohm load, which could be very hard on the amp or up to 16 ohms if the drivers are nominal 8 ohm loads which would result in loss of output. 

[Texbychoice]

Before the first use, load presented to the Amp was verified at just over 4 ohms.  25% volume on the plate amp produces a good volume level balance with the main speakers.  50% is overload for the room. 

Tried an Android phone app spectrum analyzer just for grins.  Around 60 Hz was predominant.  More 40 Hz than expected, even a little near 20 Hz.  Suspect the 20 Hz is a harmonic.  Did some EQ to bring down the 60 Hz resulting in smoother bass.  The spectrum analyzer app now shows pretty equal energy from 40 to 100 Hz.  Will live with this for a while before making more changes.  Room treatment might be next.

[Tyson]

While shopping for cheap A/V subwoofer a couple of years back found that most aren't what I'd call a subwoofer (something that can reach 20 Hz).  It seems that they are meant to supplement tiny desk top loudspeakers in small rooms. 

SVS SB-1000 or Rythmik L12 are two exceptions.  Both are sealed and small, equipped with 12 inch drivers, not expensive, but musical, and go deep (25 Hz or better).  So small and deep from a sealed cabinet is possible.  And points to the hazards of swimming in the unknown waters of DIY.

With the driver specifications a true DIYer should be able to predict performance for a given cabinet.  How are the drivers wired to the amp?  Suspect the drivers may be nominal 4 ohm loads.  Depending on how they're connected you could be presenting the amp with a 2 ohm load, which could be very hard on the amp or up to 16 ohms if the drivers are nominal 8 ohm loads which would result in loss of output. 

Agreed.  The Rythmik subs in particular are really good quality.  I had SVS subs for a while and they are beasts, but less refined than the Rythmik subs.  Not that they Rythmik subs are wimpy, they are actually very potent.  If you're doing a music system or a music/HT combo setup, I'd go with Rythmik.  If you're doing straight HT then the SVS is really hard to beat.

[JLM]

Trying to test your sub with an in-room analyzer is just going to show the combination of subwoofer and room behaviors.  Residentially sized rooms are notorious for having bass peaks/dips up to 30 dB. 

[Texbychoice]

Trying to test your sub with an in-room analyzer is just going to show the combination of subwoofer and room behaviors.  Residentially sized rooms are notorious for having bass peaks/dips up to 30 dB.

Isn't the point of in room measurements to identify problem areas?  What other method is there?

[JLM]

Measure them separately so the problem(s) can be identified.  Most try measuring speakers from very close and many DIYers do it outdoors way from any reflecting surfaces.