Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Vintage Asylum ]

---

[ Alert Moderator ]

---

Advent Evolution

Posted by Bold Eagle (A) on June 25, 2015 at 11:10:31

It has been a while since I posted here; so I thought to bring you all up to date on what I have been doing.

I have gotten very tired of replacing foam surrounds on my Advents and those of my relatives. So I have searched for an alternative woofer that's as good or better. Also, over time, I have replaced the original Advent tweeters. First, with the New Advent tweeter; and later with the SEAS 27TBFC/G.

The woofer that did the trick was the newer SEAS A26RE4. It's T-S parameters make it suitable for an Acoustic Suspension cabinet; and like the Advent woofer, it rolls off smoothly and naturally without needing a low pass filter. The earlier SEAS 25F-EW woofer is not suitable for Acoustic Suspension. All well and good; but the Advent woofer cut out is too large for the SEAS, the Advent woofer being built on a 12" pincushion frame. Since I wanted to be able to return to using Advent components, I needed to adapt the SEAS woofer to the mounting holes for a 12" pincushion frame. My solution was to cut the magnet structure off of a pair of derelict Advent woofers I had. The Masonite ring bonded to the frame is almost the right diameter to act as the mounting flange for the SEAS - all I had to do was notch the ring to clear the legs on the SEAS frame and transfer the six mounting holes. The result is an assembly that bolts in like an Advent woofer.

The crossover for the speaker is a simple first order high pass filter for the tweeter. For that I used a 10 uF Clarity PX capacitor and an 8 ohm adjustable L-pad. Although there is no low pass filter for the woofer, I did add a 0.47 ohm resistor in series with the woofer to get the desired Qts in the low bass, and to extend the bass a little. The cabinets were each filled with 2 lbs of Acousta-stuf. That much filler gives too low a bass Q; but prevents internal reflections and standing waves in the midrange, so the series R was needed.

OK, so how does it sound? Very smooth and natural. Vocals are very life-like, and all instruments are accurately presented. Transients and percussives are noticeably better than the Advent drivers. That's often accompanied by edgy highs in many speakers; but that's not the case here. The sound stage is wide with excellent imaging - partly due to the cabinets having mirror image tweeter locations. Bass is very similar to the Advent woofers, although mid-bass is a little fuller and that shows up as a better "groan" on bowed bass and cello. Baritone voices do not get chesty.

The idea behind this project was to build a speaker using the same sort of minimalist construction as many speakers of the '60's and early 70's (Advent, Dynaco A-25, EPI, KLH, Bozak, JBL's L-100, etc.); but using modern drivers.

I now have 3 pair of speakers like this. The Advents described above, a pair of 38 liter ported cabinets using the SEAS 25F-EW woofers and SEAS 27TBFC/G tweeters, and a pair of KLH 17's with the original woofers and Morel MDT-20 tweeters. In all three there is no low pass filter on the woofer and only a series cap for the tweeter. Later this year, the KLH 17's will receive SEAS 27TDFC tweeters, the soft dome version of the 27TBFC/G metal dome model.

Anyone wishing to try this needs to realize that there are almost no modern woofers that are suitable. Madisound claims the SEAS A26RE4 is the only current one they know of that can be used without a low pass filter. A number of older 8" and 10" woofers work well (Advent, EPI, KLH, etc.).

There are several suitable tweeters - the requirements being a low resonant frequency (650 Hz on the SEAS I used), high power handling, enough stroke to prevent overload, and very smooth response. There are several choices here.

Is it worth the effort? I think so. There's something about the sound from speakers like this that I don't get from newer speakers with complex crossovers and especially with several smaller woofers with severe breakup modes.

Jerry

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---