Frankenspeaker Crossover Calculation Question

jdjohn

I have a pair of Epicure Model 5 speakers from my dad's collection that I'm calling Frankenspeakers, since the tweeters are not original, but are Realistic dome tweeters, model #40-1276B. These are 8-ohm tweeters, with a range of 6,000-18,000Hz. In this pic, you can see that they came with an in-line cap, which has a value of 3.3uF.

The crossover for the speakers includes a 6.8uF cap, plus a 1.0mH inductor, as shown here:

The woofer is 6", and 6 ohms.

If I leave the caps in-series, I think I effectively have ~2.2uF, which (I also think) sends the crossover up to around 9,000Hz, which seems too high.

Should I remove one of those caps from the circuit? Maybe disconnect the 6.8uF, and just leave the 3.3uF?

Thanks for any advice!

P.S. I'm not expecting miracles from these speakers. They will likely be used for a workshop, or some other non-critical space, but might as well address any easy tweaks that the previous owner (before my dad) overlooked.

SeleniumFalcon

If you removed the 3.3uF capacitor and just used the 6.8uF the 6dB high pass filter would be around 3.0kHz.

mhardy6647

SeleniumFalcon wrote: »

If you removed the 3.3uF capacitor and just used the 6.8uF the 6dB high pass filter would be around 3.0kHz.

... which is probably right around the Fs of the tweeter (the rule of thumb for high frequency drivers is to set Fc at "at least" 2 x Fs). If the tweeter's really rated with a low frequency limit of 6 kHz, it might not last very long in service if challenged with high-ish power.
One thing in your favor: The EPIs are reasonably sensitive, so you may be perfectly happy to listen to them without applying gobs of power.
You know Burhoe's "trick", right? He used custom woofers with very well-behaved HF rolloff so that he could use a simple XO on the tweeter. In those days, this paid multiple dividends in terms of "phase linearity" and, of course, cost. It is interesting that this better EPI speaker (the "Epicure" name was reserved for the "better" EPIs, AFAIK) has an inductor in the XO, too.
The inverse dome "airspring" tweeters were likewise designed to fit the "Burhoe module" philosophy.

I have some EPI/Epicure inverted dome tweeters, and I'd be happy to send you one. Not sure I have two identical ones "in stock", though.
(I can check -- they may differ cosmetically).

PS Yes, the series capacitance of 3.3 uF and 6.8 uF should be 2.2 uF (assuming the capacitors are anywhere near their nominal values).

jdjohn

Thank you, gentlemen, for your insights. I will remove the 3.3uF cap...that's much easier to remove, so a bit of a relief. Of course, I might need/want to then put a higher quality 6.8uF cap in place. Even Dayton or Solen would be better than stock, and still relatively cheap.

@mhardy6647 Thank you for your generous offer regarding the inverted dome EPI tweeters, but I actually found a pair of those in my dad's schtuff (or did I harvest them from some cabinets?). The coils have continuity, so should be usable, although I'm not sure about fitment.

mhardy6647

Yeah, there were several different flavors of the EPI concave dome tweeter, and the Epicure bezels may have been different still. I've only ever had EPI branded Burhoe speakers of that era.

jdjohn

Indeed, it looks like Masonite was used for the bezels in early versions of the concave/inverted EPI tweeters. The pair I harvested have the round, metal bezel, and are (unfortunately) too large for these bookies I'm messing with.

So...with the Realistic tweeters, I'm detecting a slight channel imbalance. The woofers sound balanced to me. I switched speaker cables between right and left, and the imbalance stays with the same speaker, so I'm guessing either differing resistance in the voice coils, or the electrolytic cap is way out of tolerance at this point.

mhardy6647

jdjohn wrote: »

Indeed, it looks like Masonite was used for the bezels in early versions of the concave/inverted EPI tweeters. The pair I harvested have the round, metal bezel, and are (unfortunately) too large for these bookies I'm messing with.

So...with the Realistic tweeters, I'm detecting a slight channel imbalance. The woofers sound balanced to me. I switched speaker cables between right and left, and the imbalance stays with the same speaker, so I'm guessing either differing resistance in the voice coils, or the electrolytic cap is way out of tolerance at this point.

The frequency response (i.e., the LF 'cutoff') of the R/S tweeter won't be as good as the EPI, and it's also probably not as sensitive, either.

EPI (and Genesis) tweeters, from the collection

jdjohn

Nice! The original tweeters on the Model 5 were rectangular in shape with a 'regular' dome.



And with the replacement Rat Shack round tweeters I have, they had to be 'modified' a bit in order to fit.



The woofer cones are made of a flexible, foam-like material, with a pressed waffle-pattern to add some rigidity. They almost look like woven carbon fiber, but they ain't. The cabinets have horizontal vented ports at the bottom. I do have the grills for this pair, with only a couple of holes in the fabric The fabric could use a decent cleaning, though.

The guys at Human Speakers specialize in EPI and Genesis parts and service: https://www.humanspeakers.com/index.htm Heck, they're just right down the road from you @mhardy6647 They make and sell drop-in replacement tweeters (Aluminum concave dome), and crossovers, but I'm not looking to invest that much in these speakers I have. But, it's good to have options!

pitdogg2

Nice little guys there.

mhardy6647

ahhh! OK, not the airspring tweeters.
I guess I never encountered an Epicure Five.
So, I basically gave you no useful advice on these. sorry!

xschop

Those original tweeters look like sticky domes (ADS type).

jdjohn

mhardy6647 wrote: »

ahhh! OK, not the airspring tweeters.
I guess I never encountered an Epicure Five.

Well, now you have encountered them...at least, virtually This model is from the late 80's, so perhaps past their heyday...and beyond your focus/interest.

"mhardy6647 wrote:

So, I basically gave you no useful advice on these. sorry!

Maybe not for this specific model, but you did provide very useful info about legacy EPI tweeters, plus confirmation/reiteration of crossover component calculations. Ok...I will look like a fool if I try to mend @mhardy6647 's self-worth here, so I will simply say that his contributions are highly valued

I will add that IMO these speakers have very good bones, and are worth restoring/recovering. The cabinets are quite thick (I'll call it 5/8", without an actual measurement), and the rear-to-front taper provides both added cubic volume, and added strength, so again, good bones to build upon.

A few strips of Dynamat (or equivalent material) to the woofers might be worth the trouble. We shall see.

mhardy6647

Thanks @jdjohn!