AR 2ax Woofer replacement - Peerless 1727

[Pete B]

As I said, I don't really want to get into a back and forth. I do my best not to dismiss your opinions, from my perspective rather you seem to dismiss mine.

I'm not clear on what your point is in this below and I'm not sure if we're on the same "page" as they say. I've brought up air non-linearity over the years because many who favor acoustic suspension assert that it *is* linear. I fully understand the linear approximation and I certainly understand that air is also non-linear in vented systems. I also understand that vented systems rely on the box air spring as a compliance element and that it is also non-linear, this is obvious to me.

I'd say that one is controlled mainly by the air spring and the other by the suspension compliance below resonance. Indeed, there are benefits to using a stiffer suspension than would be suggested by T&S and small signal analysis in vented systems to improve the large signal performance.

Your statement about air linearity being "rarely a limitation in a sealed speaker box. " is certainly true for typical systems but in my opinion it can be an issue in ultimate designs where the lowest possible distortion is sought.

I agree that it is a fine point.

>1- I have designed many different types of bass enclosure,

>including sealed, vented, IB, TL, PR, horn, etc. I don't feel

>any one type holds >all< the advantages, and so I hope you

>don't dismiss my opinions as overly biased.

>

>2- I am confused about your comments on the differences

>between AS and Vented at LF. Yes, below resonance, one is a

>2nd-order and the other is a 4th-order. One is controlled

>below resonance, one is decontrolled. Clearly, they are

>different. However, through out much of the bass, some types

>of vented systems exhibit an alpha well over 1, indicating an

>upward shift in primary resonance that arises from "back

>pressure" or acoustic compliance. This acoustic compliance is

>in parallel with the suspension compliance. In a sealed

>system, it is always so. In a vented system, it is so above

>the port resonance. That's all I was asserting.

>

>3- Back pressures in modern, compact vented systems are not at

>all negligible over much of the operating range of the

>woofer.

>

>4- Most woofers designed for modern vented systems have much

>lower Fs than their earlier counterparts, to allow for the

>effect of acoustic compliance.

>

>5- Air linearity? It's not perfect. It is a limitation in

>high power horns. It is rarely a limitation in a sealed

>speaker box.

>

>I don't really thing these points are particularly

>controversial.

[Pete B]

Soundminded writes:

>If delta V/V is very small as I expect it would be, wouldn't

>the response be nearly linear?

I would not have brought it up if it was *completely* insignificant or "nearly linear", delta V is not small if the system produces 159 dB in box as Linkwitz showed for a typical 12" driver. 159 dB is LOUD, you should know that, damn loud. I believe that most underestimate the air non-linearity contribution to distortion and it's something I'll probably look into in detail someday. Villchur's invention was "low distortion" in it's day, by those standards, it is not by today's standards in my opinion. Villchur's 1957 AES paper shows 4% distortion at 30 Hz with a 10 Watt drive level. I simulated the system and it should have minimal (theoretically zero since it is below Xmax) distortion up to about 40 Watts at 30 Hz. Motor non-linearity probably contributes but I believe that the air does also, much more than people realize.

>I'm curious about why you chose the 1727 woofer instead of the

>0452 XLS woofer. It costs of course 2 1/2 times as much and

>has much less high end so I guess it might require adding a

>low midrange driver but this one seems superb. OTOH, its

>lower Vas would probably be a better match for the small box,

>wouldn't it??

I already stated that the XLSs (10 or 12") would not be my first choice for any design, look at the low Qts. I had the 1727s left over from another project. I did not intend to do a complete redesign or any major work on these 2axs.

>How did your project work out? Were you able to get the 1727

>to match fairly well? I'd think the sensitivity is about the

>same as the AR and could easily be compensated for with the

>tweeter and midrange level controls and the damping could also

>be adjusted for optimal performance relatively easily by

>simply adjusting the amount of stuffing. High end response

>extends out to 2800 hz so that shouldn't be a problem either.

I didn't intend this to be any sort of complex project, I dropped in the 1727s and they sounded good to my ear just wanted to let people know. I was being generous when I said they sounded good, they're good for what they are. I might take a few measurements just out of curiousity and because there seems to be so much interest. I have several other projects and these are not a strong interest of mine. Modern designs far outperform these and the Advents, they're not even close in stock form.