# Connecting Martin Logan sub to c 1970s receiver



## spreston (May 21, 2008)

Ladies & Gentlemen:

I have really enjoyed learning about sound and EQ through the forum over the past few months. Now I am trying to integrate a Martin Logan Descent Sub to an old c1970s receiver for a 2.1 set up and am confused about connection strategy; could you guys help? 

Let’s start with brief background followed by four questions:

BACKGROUND
* Integrated receiver from 1970s
- No separate sub output 
- RCA outlet tape monitors
- RCA preamp outs and RCA poweramp ins, all in the same receiver box (FYI external left and right RCA cables connect the pre and power amps)

* Behringer DEQ2496 connected to Tape Monitor 2 (I would like to keep the DEQ connected to the “vintage” monitors)

* Powered sub
- Instructions “instruct” me to connect sub to the left + right preamp outlets via 2 Y RCA cables
http://www.us.martinlogan.com/pdf/manuals/manual_descent.pdf
- Generally useless to connect sub to the tape monitor (volume does not change!)
- Sub has a low pass filter, but low frequencies are still being sent directly to my monitors by the receiver

QUESTIONS 
1. Strategic thoughts?

2. Guess I need to buy a new EQ box dedicated to sub to EQ sub 70hz frequencies, true? Any inexpensive recommendations? Can do the measurements with sleek REQ software and manually input. 

3. Should connection from preamp to sub go in the following order: [left and right] RCA Y plugs from preamp RCA outlet to new EQ box to sub (and dangling part of RCA Y plugs [left and right] go right back into receiver’s power amp RCA outlets)?

4. What is best way to prevent low frequencies (below 70hz) from going to my monitors? Will the DEQ function (or PEQ) on the DEQ2496 do that for me or do I need some type of external crossover/filter/black box for best results? 

By the way, sub sounds great, despite lack of equalization or placement thus far

I think that is it for now…off to bed.

Thanks!


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

Welcome to the Forum, spreston!

Yup, it's always a challenge to integrate a subwoofer into a vintage system. You've already pretty much got a handle on things, so I'll cut directly to the questions.


> 2. Guess I need to buy a new EQ box dedicated to sub to EQ sub 70hz frequencies, true? Any inexpensive recommendations? Can do the measurements with sleek REQ software and manually input.


Around here we typically use the Behringer DSP1124 Feedback Destroyer (aka BFD) dedicated to the sub. It can usually be had for well under $150, or eBay'd for less than half that. It has twelve parametric filters per channel that will smooth bass response quite nicely.



> 3. Should connection from preamp to sub go in the following order: [left and right] RCA Y plugs from preamp RCA outlet to new EQ box to sub (and dangling part of RCA Y plugs [left and right] go right back into receiver’s power amp RCA outlets)?


Right. 



> 4. What is best way to prevent low frequencies (below 70hz) from going to my monitors? Will the DEQ function (or PEQ) on the DEQ2496 do that for me or do I need some type of external crossover/filter/black box for best results?


You won't be able to prevent low frequencies from going to your monitors, at least not without some additional equipment. That would require an electronic crossover connected after the receiver's pre-outs to divide the audio signal into lows and highs. The "highs" signal from the crossover would be fed back into your receiver's amp inputs. The "lows" signal from the crossover would be sent on to the subwoofer (or, to the "new EQ box" and then the sub).

Another method you could try that's not as sophisticated, but doesn't require any additional purchases (except the new BFD sub EQ, but you were going to get that anyway  ), would be to use the receiver's bass tone control, possibly in conjunction with your current DEQ2496, to"calm down" or reduce the level of the lows to the main speakers. The problem is that the range where the mains and subs overlap in output will be exaggerated once the sub is added, so the objective would be to reduce the level of the lows in the mains as much as possible. Naturally, any reduction in the bass control will show up at the subwoofer as well, but it could be counteracted with the dedicated sub EQ. Often a receiver's bass tone control will encroach into the lower midrange and make the mains sound a bit "thin" in the vocal range; if that happens, you could counteract that with the DEQ2496.

As you can see, this won't be nearly as effective as using an electronic crossover, but with some time and effort it might work. With REW (or REQ as you called it) you could see any peaks in response that might overlap - for instance, a peak at say, 80 Hz would probably be evident in both the main speakers and the sub. You could EQ that with the DEQ (which, being connected through a tape monitor loop, is global) and problems below the range of the mains, EQ with the BFD.

Regards,
Wayne


----------



## spreston (May 21, 2008)

Hi Wayne:

Thank you for your warm welcome and detailed response. I have enjoyed reading your posts all around the forum, especially those relating to new REW users (note my REQ typo) and house curves.

First, the Behringer DSP1124 looks like the correct choice for sub equalization regardless of my setup.

Second, your response to question 4 is especially helpful. If I choose to keep the great sounding vintage receiver it looks like I have two options to cut low frequencies from reaching monitors:

1. Rig some manual adjustments to bass tone dial and DEQ 
+ Inexpensive
+ Requires no extra gizmos
- Inelegant 
- Not too practical as room has lots of EQ issues to begin with

2. Add an active crossover 
On first read of your post, I though, “Oh no, more electronics between source and speakers.” Upon some reflection, it is logical that a crossover (inside the sub box, inside a modern receiver or via the external electronic crossover you mentioned) will be required in any system with a sub to reduce low frequencies to mains.

So option 1 is not especially appetizing and option 2 is a bit concerning relating to complexity (how to choose a quiet active crossover then adjust it along with all the EQ work awaiting the mains and sub) and cost. Perhaps it makes sense to sell my old receiver and just buy a good modern receiver with a dedicated sub output? Thoughts?

Thanks again!


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

I don't see a reason to ditch your vintage HK unless you want to upgrade to surround sound, or perhaps you find the prospect of a 130 page owner's manual appealing. :huh: As you noted, an HT receiver will also have a built-in crossover, so there's no avoiding the additional processing. I'd just go with a good-quality pro-audio crossover, used if you're budget concious, or perhaps a high-quality car audio crossover (you could power it with a wall wart). 

For the former, a unit from Rane or Ashly should do the trick without degrading sound quality. From Rane, perhaps an AC 22 or even better an SAC 22 unit. The SAC 22 has ganged one-knob controls that operate for both channels. The AC 22 has separate controls for left and right, but the critical frequency selector knobs are stepped to better assure precise settings. The vintage Ashly XR1000 doesn't have that feature, so you just have to trust the front-panel markings for precision. However it was available in an unbalanced version with 1/4" input jacks, which would eliminate internal balancing transformers that the Rane would have - i.e., less in the signal chain.

For car audio gear, a 2-way 24 dB/octave crossover from AudioControl would be sonically pure, and not take up any rack real-estate (it could be tucked out of the way somewhere). RCA connections would certainly be a plus. You could also seek out other quality units from companies like Phoenix Gold, Soundstream, etc. Any of these products can be found used for reasonable prices, now that the market for high performance car audio equipment is in decline.

Regards,
Wayne


----------



## spreston (May 21, 2008)

Thanks again for the insight; very helpful! The vintage receiver really does sound great so I think I will follow your advice and grab a Rane or Ashley active crossover.

For the time being I think I can use just one DEQ for both mains and the sub in this system with the following scheme:

preamp out =>DEQ ===>Crossover=> powered sub
....................................>Crossover=> power amp =>monitors

Just won't have a ton of PEQ memories to use...really looking forward to trying this out!


----------

