Building Setup for FM Stereo; General Crossover Work Question

msg

I have a pair of old Fisher DS-177 speakers. Nothing fancy, just something that I picked up years ago when I was a kid in the Air Force. It was part of my first stereo system of my own that I bought from one of the older guys in the shop.


I've been using them for FM Stereo listening with an old Marantz receiver and Fisher Tuner. I'd like to give them a bit of attention, trying my hand at a few cheapie upgrades. Replace the internal electricals (is electrolytics the right word for capacitors, resistors, and the like, or is that only one of those components?), add some 5-way speaker terminals, maybe some spikes, or build some small stands for them.

They're about the same size as Monitor 10s, and have a 12" woofer, paper mid and tweeter. The woofer surrounds seem like some kind of fabric reinforced something or other, and the mids and tweeters seem to be rubber coated.

The cabinets are completely empty - no fill material to speak of - and there are two holes at the bottom of the front of the baffle, one on each side of the woofer, with mesh screens. No port tubes.

My questions are
With all the components just hanging free wired inline inside the cabinets, would it be a good idea for me to make a little bracket/shelf of some sort on which to mount the crossover components, and attach that to the bottom or back of the inside of the cabinet?

Second, should I add some sort of fill to the cabinets?
Should I keep the woofer area clear and mount the fill up above, or should I line the entire inside with 1-2" dacron sheeting or something like that?

Like I said, they're nothing fancy, use cheap drivers, but I'd like to use this as an experiment to see if I can pull some more detail out of them, and tighten things up. They're pretty fat and muddy right now, but it kinda adds to the experience of ole timey radio programming. Oddly, this combination works better for FM Stereo listening than does a B&K AVR 507 and 703s. The old stuff just sounds fatter, fuller, and smoother at lower listening levels, and I like that for this specific use.

msg

I'm also looking at grabbing an exterior FM antenna to try to pull in a stronger signal. Whenever I'm listening to our local public radio stations on these systems, the stereo signal is really staticky. Cleans up beautifully in mono, but loses a lot of body, not to mention... stereo. One of the Tuners, a B&K TS-108, has options for DX and Wide, which seem to increase the signal strength, but I think these are probably just amplifiers of some sort, and that having a cleaner signal from the get go would be better. These options don't do anything for the reduction of the static. Just seems to amplify everything.

I was planning to try something like this to replace the little FM dipole antennas I'm not having much success with so far.

mhardy6647

No gain on a 'turnstile' antenna but gettin' it up and in the breeze will help, perhaps a lot.

Won't hurt to secure the XOs in those Fishers. I tend to use perfboard and zipties (but I am kind of a Philistine when it comes to handicrafts).

Is there anything to the XOs besides two capacitors (for MR and HF)? Either way, a pair of PartsExpress ("Dayton" brand) capacitors will make more difference than one might expect.

I'd caution you not to over-invest in those loudspeakers, and to manage your expectations

Stuffing? You know what I'd do? I'd grab a bag of polyester pillow stuffing (there're a few in our basement, courtesy of the ol' Harvard, MA town dump), lightly (loosely) stuff 'em, button 'em up, and see what you think. Maybe do one and compare & contrast to the other. Stuffing a sealed box (EDIT: heck, any speaker enclosure, including these which, derp, aren't sealed) will make it "feel" bigger to the drivers (primarily, of course, the woofer), which will probably (i.e., should) lower "system Q" (Qtc), which is probably too high, anyway, for those as designed In other words, you might like them a tad better stuffed. I'll stop just short of telling you to "stuff it!" Ooops -- I guess I didn't stop short...

Just a bunch of semi-informed opinions; others may have more practical and appropriate suggestions than mine!

What else did you want to know?

mhardy6647

Oh, one more thing (as Lt. Colombo would have said)...



If they're not ported (EDIT: oops they are ported -- basically you could calculate the area of the two cutouts, add them together, calculate the volume of the box, and calculate the resonant frequency of the Helmholtz resonator that they represent!), make sure you button 'em up tight. Maybe get some "speaker gasket material" from PartsExpress.

https://www.parts-express.com/parts-express-speaker-gasketing-tape-1-8-x-1-2-x-50-ft-roll--260-542



Oh.

And.

Your DX setting on the tuner will sharpen the bandwidth of the IF section(s) to improve selectivity and might (???) alter the gain of the RF amplifier section (if so equipped). Wide IF bandwidth will give better sound quality (at least on paper), at the expense of selectivity and perhaps sensitivity as well.

msg

Hehe, good info there, Doc - AND - great point on setting a plan and sticking to it and not over-investing. Indeed, they've essentially been

Yeah, I was just going to see what an exterior antenna can offer for starters. Are amplified indoor antennas good? Do they work? I know a guy who got a Technics antenna for sebben ducks, and they go for $200, damaged, on eBay. I dohn kno nuthin' 'bout no antennee. I'll have to read up a bit more.

What's bass Q? Is it the tightness? I see that control on my better sub.

I need to get a proper survey of the Fisher internals and get a diagram together. Yes, it appears on quick inspection that there are in line components for at least the mid and woofer. Not at all familiar, but I think at least a cap and resistor on each. I'll have a closer look.

mhardy6647

System Q (damping) works like this. The ol' trick was put too large a woofer in too small a box; pushes a "bump" into the midbass that sounds like bass to the single-digit IQ class out there



Optimal Qtc (speaker system "Q") is 0.707; gives the flattest bass response. Qtc >1 starts to form a "bump" in the response, at the expense of LF extension. Look at the Qtc = 1.5 response graph above -- whumpa-whumpa-whump

FestYboy

I modded a pair of truck sub boxes back in the day to flatten the awful bump that was originally built into them... Took advantage of the cabin gain and had response down below 30hz with a pair of 10s shoved in a horrible spot behind the seats of my fiero.

I essentially more than tripled the length of the original port an added some poly fill. It will be much easier to figure the proper port length if you make one of the holes a dummy port and flair both ends to keep the port noise down.

Edit: looking at the boxes again, block both factory ports and drill another one @ 2.5-3" at the 11 o'clock or 1 o'clock position. And tune from there... The original ports are pathetic and inappropriately sized for the woofer.

westmassguy

Agree with @mhardy6647
Dayton 5% Metalized Polypropylenes, or if you want to splurge, Clarity PXs.
Doubt there's any large value Shunt Caps in the Low Pass, so you should be OK.
I'd go with 1" Bonded Dacron tacked on the rear wall, maybe the sides, and be done with it. It won't hurt, and may help.
Don't expect miracles.

P.S. On the binding posts, measure the opening for what's there. Parts Express should have something that's a drop-in, with better posts.

mhardy6647

^^^ Listen to him. He's a pro!

K_M

I would use lower priced caps, and like westmassguy said, apply some sound absorbtion on the back and sides.
But saying that, pretty sure this was meant to be a relatively loud, and more towards boomy bass at the expense of deep bass.
With ports that short (5/8" of particle board guessing) the bass will naturally be of the boomy upper bass sound, unless you want to get fancy and install longer ports to tune it lower.

mhardy6647

Here's a fun and (relatively) inexpensive way to play with port tuning.
Buy a box or two of plastic drinking straws. Stuff the port full of drinking straws to create a new port volume (assuming, of course, that the straws are longer than the port). Listen.

The straws can be trimmed to a different length, too, to re-tune the port This is, unfortunately, a one-way modification -- but straws are probably cheap by the carton from Costco?!

One may be completely empirical, or one may cheat and use the equation to calculate the resonant frequency of a Helmholtz resonator to "redesign" the port. If the T/S parameters of the woofer are known, the port can even be designed to give desired loudspeaker system tuning (Qtc)

Probably easier to just buy a new pair of speakers, though

jstar

mhardy6647 wrote: »

System Q (damping) works like this. The ol' trick was put too large a woofer in too small a box; pushes a "bump" into the midbass that sounds like bass to the single-digit IQ class out there



Optimal Qtc (speaker system "Q") is 0.707; gives the flattest bass response. Qtc >1 starts to form a "bump" in the response, at the expense of LF extension. Look at the Qtc = 1.5 response graph above -- whumpa-whumpa-whump

Hey mhardy6647, (and everyone reading this)

Did you notice, I would imagine you did, that the "0.707" is a very magic number. In this case it's the factor to convert peak power to RMS(Root Mean Squared) power. For those reading this who might not know, power(peak) x 0.707 = power(RMS)

jstar

If any of you out there come across any Fisher "studio standard" equip, get it!