trying to add a subwoofer to a Mac system from before subs were a thing….

Ok, I have a vintage system. All McIntosh.

If you want specs on these pieces, please check out the awesome Mcintosh Compendium here:

Pre-amp: C-30

Amplifiers: MC7300 (two of them) 

main Speakers: McIntosh XR-7

Subwoofer: McIntosh HT-12 passive 4 ohm sub and without built-in crossovers. 

My goal: add a sub in a system without an LF sub output. 

Attempts so far: Using the "speaker B" output on the pre-amp, I've done the following:

1, I took the 2nd MC7300 and parallel mono'd it, sending 600wpc to the sub using home-built "Y" cables. The entire un-modified signal, full frequency was amplified. Having a single 12" woofer meant there was a lil gain in lower end volume, but not much bump. 

2, I created a low-pass filter coil. This has removed highs, high-mid and most of the mids. Now when I switch from "speakers A" (the mains) to "speakers B" (the sub), the mains have soooo much more volume than the sub. The lows are so quiet.

When the mains are on, I can switch on/off the sub and frankly, hear zero difference. Maybe my coil is too big. I can try removing some but the more I remove, the more low-mid to mid I'm revealing and my goal is to feel the bass, not just hear more. 

An idea floated to me was a MiniDSP between the pre-amp and the amp. Maybe this way only the low frequencies I want will be amplified. However, that seems like a complex solution and might stretch my audio intellect on the set up. Example;The word "latency" was tossed around. Had to look it up.

What would you do? 


A Rolls SX95 will work well. I used an RCA Y cable to get the left channel input into the SX95. You will need a separate amp for your passive subwoofer. Inexpensive class D amps work great for subs. 


Solid advice!! American made, simple and like you say, place between the pre and the amp, so I'm only amplifying the freqs I want. Thank you.

I Do have a separate amp. The mighty McIntosh MC7300. I have two of these, one on the main, and one bridged parallel for the sub.


Anybody else beat this guy? If not, the Rolls it is.

DBX made a downward firing 15", subwoofer using a niobium, rare earth magnet.

"I think it was a, DBX model, (DB-15)".

 It came with a separate amplifier and uses the "Speaker Level, Line-output" from your amp to the Rt./Lt., as the inputs are marked on the DBX amplifier.

The amp states (150 watts). But I swear it hits like my "Martin Logan Descent" subs do with their huge plate amps!

So, with the DBX, you use speaker cable from the speaker outputs on an "integrated", (Usually called the "B Speaker" outputs). Or the same, "speaker cabling" from your component, amplifiers binding posts to the amp.

The (Rt. and Lt.) speaker cables are both used from your amp and then into the "DBX" amp. Which has an analog "Output Level" adjustment pot/dial, on the front of the amp as well.

I do still have it, in case you or someone else happens to be interested...

And as a for the price? "But for a song and a dance"! The MSRP was about ($800). I believe "From Crutchfield", purchased new back in the mid 1990's.