Audio as a learning experience.

[Clipped and Shorn]

A year ago or so when I first mentioned that I was interested in assembling a speaker system utilizing some classic Altec components and that I would be either bi-amping or even perhaps tri-amping this system, I did not hear or see posted on this forum any warnings about impending disaster. I used this forum and others as a source of information from others who may have gone this route.

This project was to be in addition to my already functioning system which utilized some beautiful vintage Cornwalls and tube gear, a system which was improving every time I upgraded it.

Still, I was interested in pursuing the possibility of a larger sound. I had visited mdeneen who had an Altec speaker system he built and had biamped with an active crossover. His system sounded amazing to me in that he was able to achieve some dramatic volume without the harshness I was still hearing in the Cornwalls at higher levels. It wasn't that I was giving up on the Cornwalls, I just wanted to pursue this other project with all of its potential for learning about active crossovers and multi-amplification and with the potential for a bigger sound. I like to practice music to performance level+ sound reproduction.

I figured I could always have the Cornwall system as a single amped passively crossed example and later down the line I could possibly even have it amplified with SET because I knew there were those here who really recommended that configuration, and I was curious about that as well.

In the planning stages of the Altec boxes I was to build, mdeneen and Tom Brennen gave nothing but positive encouragement, and as mentioned, mdeneen's system sounded pretty darn good to my ears, fini's ears, and of course to mdeneen's. No one here was offering up anything to the contrary. Mark had been in the audio business in years past, had wide experience, and had a gift for explaining things simply to us beginners. In addition, he was able to exemplify audio electronic concepts graphically on his humble bench test equipment. The whole concept seemed exciting and of course his speakers where an inspiration. This was to be an ambitious undertaking involving the acquisition of vintage Altec components, running the parameters on software designed to help in the planning of the box construction, and then the actual carpentry.

At one point, when I posted mention of this project, a huge argument ensued between some engineering minds who hang out here. This was concerning "group delay" or some such stuff that was way over my head. It ultimately did not convince me to drop or alter the project which was essentially equivalent to mdeneen's working system that I had already heard and which sounded just fine to me. I wasn't expecting to revolutionize the audio world, just create a dramatic speaker system with a lot of bang for the buck, a system which utilized the Altec 515b/c which Tom and others had claimed to be arguably the best woofer ever manufactured especially in the mid-bass. Tom actually qualified this statement to include "horn loaded", but I figured it was still a strong recommendation even if perhaps used in a different configuration. One advantage to the bass reflex design was that the volume was the only critical factor, which meant I could design the box shape to fit exactly the limited and specific space availiable in the house. The volume was calculated for the Altec 416B as "sub" woofer, with the 515C used only for the "mid bass". Later the variability of the active crossover would be put to vital use in searching for the optimum points. The 511B horn with 802-8G drivers and the JBL 2404H tweeter would handle the top end with the addition of a JBL 3505 passive crossover. Even though other designs might be good or even better, I am not sure that they would fit in the house, nor would I be able to build them myself. The bass reflex is a relatively easy project to build.

So with the positive recommendations and without any other cogent arguments to the contrary except perhaps the one about my not knowing other systems besides mdeneen's bass reflex system, I bought the plywood and glue and set up the wood shop for the big project. Many a winter evening with the shop woodstove cranking I was out there with the legal size yellow ruled tablet that had page after page of calculations based on the software that mdeneen and I had run using the published specs on the Altecs.

I was not going to fret over the fact that strictly speaking it would have been better to run some tests of the actual drivers in order to determine the precise parameters. It is said that there may be as much as a 10% variance in the published parameters. Again I was trying to make the project a practical one that I could actually accomplish rather than one that would get so cumbersome in the planning that I would eventually abort the project like the 98% of other humans who pave the road with intentions and dreams but do not wear the little round button on their label that says "to it". Nothing was going to stop me from getting around to it. If mdeneen taught one thing, it was practicality in the face of ultimately inconsequential BS, or even inconsequential valid physics that was just too small a percentage to matter to my old ears. It was going to be close enough for jazz, as they say. And all prospects pointed to the possibility of the project being "awesome". It surely was going to be big enough, coming in at nearly 8 feet tall! They look like a giant version of those modern towers with the little 8" speakers, except this has two 15" Altecs and a 2' wide Altec horn sticking out.

In addition to the whole learning process at the DIY woodworking stage, there would be the welcomed interesting physics I would later encounter at the tweaking stage when the speakers where up and running. Like Luther Van Dam, I could hardly wait to to sink my teeth into those 4th order Linkwitz-Rileys and Butterworths all plugged into those electrical Pancake boxes that fini gave to me.

Since the system will be triamped there will be all kinds of opportunities to experiment with various vintage tube amp upgrades used in different roles in the frequency range. The keyword here is experiment and experience. Meanwhile, the mint vintage Cornwalls are right here in the house, it is not like I won't have that covered, even with the future possibility of SET, it is that I desire to have other experiences for the purposes of dreaming and learning. Being non-monogAMPomous in the audio hobby does not necessarily reflect this value in the domestic realm. It is a hobby and that, as far as I am concerned, predicts happiness! It is going to be great fun with enthusiasm and excitement. There simply is not only ONE holy grail in this case.

Next time I post about this system the topic might very well be

Triamp Triumph with 3 times the Umph! If you don't hear about it, it will mean I am still tweaking and having fun with it, eventually when I get "there" I will let you know how it sounds.

Here are some notes I found on the web about this approach:

Summary of arguments in favor of active crossovers -

1. An active filter is easier to tune to a given crossover point since it does not interact with the speaker element's impedance.

2. High impedance, lower voltage elements are smaller and have reduced sonic effects compared to higher impedance higher voltage elements.

3. The amplifier's damping factor is preserved.

4. An active crossover maintains the system's phase accuracy.

5. The amp sees a primarily resistive load for superior power delivery.

Active crossovers provide better control of the speaker element. Drivers sound more dynamic when driven directly by an amplifier.

Summary of arguments in favor of passive crossovers -

1. Quality speakers are designed with a crossover network matched to the particular characteristics of the drivers. Substituting an active crossover defeats the speaker designer's efforts to truly match the drivers, cabinet, and crossover together.

2. Anything that is added to the signal path alters it in some way. Passive components do too (a cable is a passive component, for example), but they may be less likely to add coloration than active components.

3. An active crossover performs a sophisticated function, roughly similar in complexity to a phono stage. An active crossover has the potential to degrade the sound of a system if its quality does not match the rest of the components.

Ultimately arguments for or against either configuration are academic - the proof is in the listening.

For further information check out these sites:

A Wealth Of Information

Taking Multi-Amplification $eriously

[NOSValves]

Holy post ! You have been doing your home work !!

[Deang]

Craig -- you have PM and/or email. See the link.

Clipped -- this kind of thing can work out pretty good if you're starting from scratch (building your own). If one is working with a set of speakers already voiced using passive components, going to external x-overs can make the same set of speakers sound very bad. It takes a heck of a lot of work and tweaking to get them "right" again. At least, this is what I have heard.

[Clipped and Shorn]

Craig,

The homework was done mostly online where there is a fair bit of information, although not as much as I would like. Those notes about biamping were just quotes from some website, not my words.

Dean,

This system is strictly from scratch. I was mostly curious to find out what was behind some of the Altec mystique. I would never attempt to design a complex passive crossover system nor would I modify an existing system like my vintage Cornwalls, although I did run across someone who put Altec 515b woofers in his Klipschorns.

c&s