XSchop's modded 5jr

xschop

Well, I got an email that the sonic barrier was on back order. I got on the line to the local foam supplier and asked if they had a piece of "Open-cell Poly-ether" and they had some in 1.5" so I installed some 4x4 pieces above and below crossover as WMG suggested..... Seams like the mids have opened up and I cannot hear any diminished bass.....Happy camper here. No Crown involved in this mod, sorry guys...

xschop

Round 2......

This time I have a later set of 5Jr X-overs with the boards and 1.0 ohm resistor that I will install to see what difference I will hear when I'm done with this second set... I took precise dimensions of these because I was going to machine adapters to recess them out of the cabinets and make a solid strip of sound barrier, but it would be overkill on the foam. Thanks Westmassguy for your advice.




Although I didn't use the internal billet braces to remove the cabinet flex because the faceplates solved that issue, I am sharing dimensions here....

Rear interface is 1.50" diameter tapped 1/2-20. A button-head 1/2-20 x1.75" length is perfect, just drill the box with 1/2" drill bit by hand.

Total length is 6.8125
Baffle end is 1/2" dia. Tapped 1/4-20.
A 1/4-20 countersunk head would also work great if the area was carefully drilled. But I would take it a step further and make some internal mounts for the top 2 midwoofer fasteners to mount....

xschop

I found a thread where the Poly switch was replaced with a 0.5 ohm resistor in SDA's. Does this make much difference in sound? I'm only going to be running 80 wpc to these....

westmassguy

There's more than one thread addressing Polyswitches. Replace it with a .5 ohm, 10 or 12 watt Mills/Mundorf Resistor

xschop

Thank you again WMG. I placed the order for them with the 1.0 ohm Mills and same 12uF Dayton caps. These will be much easier to mod/solder with the boards....

xschop

Sonically.....night and day....

heiney9

Dayton caps aren't all that great. For a little bit more, Clarity caps are preferred. Certainly better than 30+ year old electrolytics, but Dayton, Bennic and Solen aren't the best choice they aren't as smooth and artifact free as a Clarity or Sonicap.

H9

xschop

Thank you H9.... Where do you get them from?
Ill try them in my next setup.

deucekazoo

https://www.madisoundspeakerstore.com/claritycap-caps/

xschop

Question for Polksda....
What would a "Time Aligned Jr" do/sound?

westmassguy

The original Polk stands had a 6 degree backward incline. This "Time Aligns" the tweeter and woofer.

xschop

So technically that puts the center of the woofer cone in plane with the tweeter dome?

Polkaguy58

Theoreticaly low frequencies travell slower than their treble counterparts.
If the woofer is slightly closer to the listener than the tweeter is, the sound waves are supposed to arrive at your ears at the same time.
I'm no scientist, but I just finished "time aligning" my newest NHT (Victorian) sub to my KEF C-15 mini speakers and it seems to make a difference....at least to my ears.

xschop

Ah Ok. So Polk just cheated by placing -6° on the vertical plane instead of making a baffle where the woofer sets out further.

Polkaguy58

Tilted back stands have been around for years, so my guess is that the "Time Alignment Theory" has legs.....................as does my latest audio abomination, The Victorian Subwoofer:

pkquat

The crossovers also come into play. Wiki has some good info on time aligning, and there is a good diyaudio post July 25, 2003. Another reason for the tilt is keep the speakers low, but aim the tweeters and sound upwards so the highs are less muffled by carpet or reflected by hardwood. This helps keep the speakers smaller and on more stable stands vs. tall stands and towers.

xschop

Nice Polksda. I understand subs are electronically timed. Now I see what PKQ is saying.
So if the monitors are at ear level like my workbench without tilted stands, it would benefit from the woofer being stepped out an inch or so like Polksda commented originally?

pkquat

Possibly. It still depends on the crossover. I don't remember the specifics of hand, but I think the polks use a 12db, 6db combo that is supposed to flatten the response out.. It also depends where the "acoustic center is". Some times if the speaker is raised higher only a small tilt helps with the sound, or other times none is needed. Try some things and see how it sounds. On and off axis response of the tweeter also comes into play. My M4A's have a much narrower axis range than my 5A's regardless of the angle. The 4A's are also a little better off axis above the speaker than below. This has a greater effect than the time alignment.

A side question have you compared the SL5000's to the RDO-198's?

Polkaguy58

This sub is devoid of any electronics/crossover, just a nice heavy, laquered box, with a very springy 10" woofer and a pair of banana jacks in the rear.
It pairs up well with the Velodyne plate amp that I removed from an old blown sub and mounted into it's own heat vented box.
I borrowed the legs from a foot stool I spotted in the dumpster.
Being a double amputee, I hate seeing a good set of legs being tossed aside.

Polkaguy58

Don't know why this double posted..........please ignore

xschop

I have not heard 198's I don't believe. Just these old twangy sl-1000 and 2000's. These SL5000's are so much smoother, not as overbearing.

I love the sound of my new 5jr's, I'm only asking about the stepped design for future mod.

And to Polksda, I have seen 180° subwoofer dials, is what I was referring to.
Your sub is trick.

Polkaguy58

Google Technics Linear Phase speakers and you'll see some time aligned designs.
When you think of it, any speaker with horn tweeters have the tweeter's driver deep inside the cabinet (about three inches or so) , so thus could be considered time aligned.

xschop

Yes, but a horn inserted won't fix the baffle flex or the midwoofer air leaks.

I'm thinking of a 4 birds with 1 stone mod.

xschop

So at -6° tilt, the 5Jr's midwoofer is moved forward 14mm in relation to tweeter.
Those pics of the Technics speakers have them much further back obviously.

xschop

Got some time to play. Opened up the cabinets to start work and original X-overs are both also different, and still no board. I'll take a peek and see what value that SINGLE ceramic resistor is.....
Looks like Polk subcontracted with Groovfold on the cabinets. The bridge is also a flexy affair on these....

xschop

These 6502's state 33 & 35 Res.
Power Grab and sound deadener done....

msg

which brand sound damping material is that?

xschop

Tite Seal....60 mil
I've done complete custom vehicle interiors..... my own that is.
Better sound deadening at WAY less cost than Dynamat.
Here's my Porvette wheel well sub and exhaust sound isolation. Adding 4 more cyl. to the mix made the interior rumble.

xschop

I didn't mention it on last set because they were not off by much, but these baffles are off kilter the way they're installed from factory. .030 inset on one end and .070 on the other. I removed vinyl and will belt-sand face edges on these and square them up before gluing. Sound deadening foam is MUCH easier to install when cabs are empty hehe....
The bottom edge where the cabs are folded had separation, so I sealed it last night with glue and this morning went to work on spot-glazing. Auto body works great and dries quick and hard....

Polkaguy58

If you're going to attach a metal faceplate like the last job, maybe put a self stick foam gasket tape around the old speaker shelf to seal it off between the plate ?