Jump to content
The Classic Speaker Pages Discussion Forums
Carlspeak

EPI 100 woofer relocation suggestion

Recommended Posts

Carlspeak    0

During a recent refoaming job I noticed the 003 woofers are set way down in a recessed cavity that measaures 3/4 inch deep. If these were my speakers, I'd try installing a 5/8 inch thick shim to bring the woofer out flush with the baffle board's face. In my view, this would accomplish two improvements.

1) Mitigate diffraction effects from the woofer edge wavefront interacting with the sharp edge of the baffle board recess hole.

2) Better time align the woofer's acoustic center with the tweeter's. It won't be ideally aligned but improved never-the-less.

Since these were not my speakers to experiment with, I'll await another opportunity when the owner allows me to 'tinker' a bit with them.

I can only wonder what Winslow Burhoe's thinking was when he purpousfully recessed that woofer down so low in the first place.

I also replaced the NPE caps with 10 uF PET film caps. Both originals measured about 9.9 uF at 10 hz and 8.7 uF at 20,000 hz. The replacement cap measured a consistant 9.8 uF throughout the 10-20,000 hz range.

Share this post


Link to post
Share on other sites
ra.ra    0

Carl raises a very good point and there appears to be no obvious answer to this positioning of the woofer with regards to the depth of the baffle board. Not only is the woofer recessed, but the tweeter is actually proud (in front) of the baffle board with its 1/4" masonite. I have included a pic that I believe represents the situation Carl has described. A similar head-scratching could be attributed to the AR-2ax's shown here, even tho' the tweeter cutout has been beveled.

[proud [praʊd] adj (of a surface, edge, etc.) projecting or protruding from the surrounding area]

Aside from the issue of driver placement in the depth dimension, and using this simple EPI speaker as an example, I've never really understood what benefit is gained by placing the tweeter cutout off the vertical centerline of the speaker cabinet. I've raised this question before in the AR forum with respect to the AR-6 woofer's placement, and there has never been a satisfactory rationale offered.

BTW, I really like the early walnut EPI 100's - - - great tweeter, great woofer, simple x-o, robust construction.

post-112624-0-83866900-1386034897_thumb. post-112624-0-75666700-1386035824_thumb.

Share this post


Link to post
Share on other sites
ra.ra    0

Thanks, Carl, for the interesting weblink. Even though some of the information might be a bit over my head (when I started reading about 2pi and 4pi space, my first thought was "uh-oh"), after reading it a couple of times, looking at the graphs and the baffle layout diagrams, I think I get the basic concept.

Curiously though, when I looked at the writer's own built speaker projects, most (but not all) of his designs more closely followed his own second option - Tweeter shifted up (or in some cases, down) with the tweeter centered equidistant from the long edges, rather than his third option - Best case scenario - Golden Ratio, where the tweeter is offset from the centerline of the baffle.

This guy makes some beautiful speakers and I have no doubt they sound as good as they look - - the build quality appears robust, the craftsmanship is high quality and creative, and the engineering seems well considered. Not unlike your original question about the EPI-100, one of this designer's primary objectives appears to be minimizing these unwanted diffraction effects, which is further evidenced by his (typical) lack of speaker grilles and frames, the flush mounting of driver faces, and frequent radiusing of baffle perimeters.

Looking at this issue with regard to an AR-3a, I'll have to assume that the tweeter placement, which is almost crawling out of the cabinet way up in the corner of the baffle board, has been thoroughly engineered with regards to these diffraction issues. Still though, when trying to understand high frequency dispersion from this driver, I remain perplexed by the severe frame edge (note deep shadow) immediately adjacent to the tweeter.

post-112624-0-89637300-1386182159_thumb.

Share this post


Link to post
Share on other sites
Carlspeak    0

The AR3a 'Improved' model did away with the large frame and deep inset of the driver for, I believe, the exact reason: reducing diffraction. Something the AR engineers learned about during the course of the speaker's life. That was only one of many tweaks and improvements made to the 3a during it's life. I'm sure the historians who post here could fill in much more detail on those improvements.

Share this post


Link to post
Share on other sites
ra.ra    0

I will admit that I am trying to buy into this minimal diffraction theory, but when I see:

* the deep lip on the AR-3a improved speaker, or

* the sequential progression of the AR-18 (tweet originally offset, later centered) series speakers,

I begin to think that the theory and the practice of speaker design had some degree of disconnect.

post-112624-0-55021000-1386648653_thumb. post-112624-0-03696700-1386648679_thumb.

Share this post


Link to post
Share on other sites

If the baffle is 3/4" mdf, how can the woofers be recessed 3/4 inch? Flush mounting the woofer (and tweeter for that matter) couldn't hurt, but I would be very surprised if the change would be audible. A coil on the woofer would probably be the most cost effective upgrade, and would definitely be audible.

Share this post


Link to post
Share on other sites
Carlspeak    0

If the baffle is 3/4" mdf, how can the woofers be recessed 3/4 inch? Flush mounting the woofer (and tweeter for that matter) couldn't hurt, but I would be very surprised if the change would be audible. A coil on the woofer would probably be the most cost effective upgrade, and would definitely be audible.

There's a second board glued to the back of the 3/4 inch BB that the woofer is screwed to. The woofer is designed to run full range. Putting a coil on it will cut it off too soon and probably create a dip in the response somewhere in the 1-3 kHz range.. One of the advantages of these Winslow Burhoe designs is the woofer. It's very difficult these days to find a woofer that has a relatively smooth roll off whilst running full range; thus negating the need for a 1st or 2nd order LP filter to suppress any woofer peaking above 1 kHz.

Share this post


Link to post
Share on other sites
ra.ra    0
I had my EPI-100's opened up today, and I began thinking about this perplexing issue that Carl raised in this post about the deeply set woofers. There will be no explanation for this coming from me, but clearly this decision was intentional on the part of the speaker designers. It is well-known that this terrific little speaker was engineered and marketed as a maximum bang-for-the-buck product to go head-to-head with the other leading small two-ways of the day (AR-4x, Dynaco A25, etc.), but from a purely cost standpoint, this decision seems to contradict the economy mantra behind fabricating this model. As Carl noted, this specific woofer placement required a second layer of baffle board: material + labor = added cost.
 

I really like these speakers, particularly my own pair that have the earliest tweeter (masonite) and woofer (rubber surround) and crossover (with tweeter pot or L-pad). The cabinets are robust with excellent veneer, and the grilles are quite decent, but the innards are where the penny-pinching shows up. Bargain-basement capacitors, cheap and inadequate spring-loaded terminals, and the thinnest internal wiring with an assortment of wirenuts and random electrical tape splices on exhibit hither and yon. How and why do these speakers sound so good? Hmmm.....must be the drivers.

 
So, back to Carl's (and mine, now) curiosity - - if this flagship budget speaker model was aimed at undercutting the prevailing competition in terms of pricing, what was the thinking behind this extra cost to assemble the woofer in this fashion? Obviously, the original design team determined that the added performance outweighed the added cost, but can anyone explain the performance benefits?

 

Share this post


Link to post
Share on other sites

I don't know anything about the actual engineering goal, but there was apparently some thought at that time that if woofers and tweeters were on the same plane, something bad happened. I'm familiar with the Genesis 3, that used the Burhoe woofer and tweeter (but added things), and they have a piece of plywood on the front of the baffle, to bring the tweeter (and midrange) forward.

Share this post


Link to post
Share on other sites
Robby1970    0

Hi Carlspeak, about the relocation of the woofers, i tought i ask this to the master himself. After all, the Epi 100 are his babys. Mr Burhoe says: 

The cabinet walls need to be thick so that they don't bend or vibrate.
 
The woofer needs room behind the grille cloth so that it doesn’t hit.
 
Greetings Robby
 
 

Share this post


Link to post
Share on other sites
Robby1970    0

I don't know, mr Burhoe says that the woofers need room behind the grill. But i dont think that the woofers come out that far do they? :huh: 

I agree that the cabinet walls must be thick so that they don't viberate. Maybe mr Burhoe means that the baffles must be thick so they don't viberate

 

Share this post


Link to post
Share on other sites
Pete B    0

The EPI woofers have about 1/4" linear throw in each direction but when driven very hard

will hit at least 3/8" in each direction so that probably explains the set back.  This is based

on a .75" long coil in a .25" gap providing .25" on either side outside of the gap.  Overdrive it

to 3/8" and there are half as many windings in the gap but the motor still has power.

I seem to remember reading in the AES that the air mass in the opening acts as a low pass

filter on the woofer.  I think it was with regard to the AR-2 series.

If it were a simple mass it would just slightly increase the effective moving mass of the

woofer cone, but there may be more to it than just a simple mass.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×