eq in a box

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skite30

eq in a box
« on: 27 Sep 2007, 10:48 pm »
I had a very pleasant discussion with Roger today about the em7 series. I have the em7 amp and was curious abbut the eq in a box. Roger was very patient with my non technical nature and explained everything so I could grasp his points. The upside is I ordered a eq in a box and am really looking forward to receiving it. I will report more after I get it.

EProvenzano

Re: eq in a box
« Reply #1 on: 27 Sep 2007, 11:05 pm »
Roger,
Where could we read more about this?

Thanks

Roger A. Modjeski

Re: eq in a box
« Reply #2 on: 1 Oct 2007, 05:18 am »
Here is a bit more about it.  Any questions/additions/suggestions will be appreciated. It is a little difficult to explain since nothing quite like this has been offered before. After hearing how bass shy many high efficiency speakers are I though something could be done to improve the situation. Below is the first draft of instructions.

There are 2 knobs, the left one selects the frequency where the level starts to rise. The first position (straight up) is flat so you have a reference to go back to. The next position is +3 dB at 320 Hz and reaches +6dB an octave lower at 160 Hz. From there on down the lift is constant all the way down to DC.

There are two more positions (clockwise) that start the lift at lower frequencies. Those being +3 at 160 and 80 Hz.

The right knob can be thought of as a lift volume control. When it is fully down, no matter what position the left switch is at there is no lift. This control allows adjustment from 0 to +6 dB in a linear fashion, i.e. each 1/3 rotation is 2 dB.

We can make the EQ with a variety of parameters. It is all passive and all the parts are very good quality. Because it is passive, the insertion loss will be equal to the maximum boost desired. Listeners using preamps often have too much overall gain and this insertion loss reduces speaker noise if that noise is due to too much gain preceeding the power amp.

I know a lot of you worry over phase shift. You may find it interesting to know that a speaker falling off in the bass at a gentle rate will have it's phase shift corrected by this box.

Roger

jrebman

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Re: eq in a box
« Reply #3 on: 5 Oct 2007, 10:23 pm »
Roger,

I'm really interested in this -- but mostly as a passive, line-level substitute to the typical parallel LR/LRC baffle step compensation network found in many single driver speaker systems (which rob efficiency, etc.).

I have a pair of small modified TQWT speakers for my office that are designed for the FE-127 and part of the design involves a parallel LR network in series with the speaker to correct the inherrent rising response.

It looks like your Eq in a box is working the same problem, but at the bottom end of the spectrum instead of from the mids up.

I'm trying to keep the amplifier speaker interface as clean as possible and thus had my speakers made without binding posts, and my speaker wire will simply go through a small hole in the back of the speaker and be directly soldered to the lugs on the driver.  For the time being, the LR networks will remain outboard and will sit between the binding posts on the amp and the new speaker wire (which, BTW, will be terminated with a small, very low mass, vintage-style spade, but designed for a 1/4" post, and gold plated.)  My goal is to eventually get this out of the circuit and do the compensation passively at line level, and coming full circle, I think this Eq in a box you are describing looks like it will do that very nicely.

-- Jim

Roger A. Modjeski

Re: eq in a box
« Reply #4 on: 12 Oct 2007, 05:09 am »
Jim,

You are on the right track removing all obstacles in the signal path especially at the speaker level. I congratulate you for your efforts. Often too much time and money is spent on cables that terminate into the thin internal wire, the coils and capacitors that reside in a speaker crossover. Make no mistake here, the capacitors, inductors and resistors in a speaker crossover, no matter how expensive, are better eliminated. One should realize that anything going on at the speaker level involves many volts and many amps. At 100 watts, an 8 ohm speaker passes 5 amps at 40 volts. On the other hand, if the same filtering is done at the line level, currents are less than a milliamp (1/1000 amp) and barely a volt.

You are also right about soldering the wires to the driver terminals directly. Push-on connectors should be banned from all serious speaker designs. Too many enthusiasts are all to concerned about what they can see on the outside and tend to be uninterested about what is going on inside where they cannot see it.

Quite frankly I think any consciences speaker designer selling a product at several thousand dollars is selling his customer short by not doing things the right way. Gold binding posts, fancy wire, caps with fancy pedigrees are no match for multi-amping and crossing over or filtering before the amps. The amps are happier, the drivers are happier, the wires have less demanding work to do, everything is better. In many cases the saving in these speaker level crossovers could go a long way toward buying the second amplifier. Think of the advantages of each driver having the right kind of amplifier. Tubes for midrange, solid state for bass, what's your pleasure. Why have 100 watts that the woofer needs supplied to a tweeter that only needs a few watts. How many tweeters are padded down to match the woofer's lower sensitivity. Those drivers are so different, they should be treated separately? In addition the level controls on the crossover allow the listener to tailor the response to his taste and room conditions. Having done this for years in my own system, I wouldn't want to be without this flexibility.

To your specific needs both the top and bottom ends can be handled at line level before the power amp. It can all be done with a few resistors and capacitors that will carry no significant current. This is an important point. All those glorious claims of oil, Teflon, poly this and poly that have little meaning when the voltage and current are removed from the application.

I welcome questions from those who would care to apply these ideas to their speaker/amplifier systems.



Bill Epstein

Re: eq in a box
« Reply #5 on: 24 Oct 2007, 07:52 am »
Hi Roger,
You and I had some interesting conversations about the direction you were going with RAM and audio in general about 7 years ago. (I had just acquired a used RM-10) You convinced me to use a passive with my CD-based system and sold me a Noble volume pot, some wire and RCAs. I built that as my first "kit" in a little Radio Shack box and still have it. That got me started in DIY audio and now I'm the DIY reviewer for an on-line audio mag.

When I'm not reviewing commercial speakers I run a 2-way bass reflex/horn system crossed-over and padded just as you describe. It would be a treat to review your EQ'd and filtered amps in this system.

Happy to see you break out with this Circle and touch a lot more music lovers. Much success to you.