Simple crossover cap replacement

[larrylarry]

This crossover came from my JVC SP-95’s. I ordered new caps from Parts Express, 1.5 cap for the tweets & 6.8 for the mids, woffers didn’t have any. These caps are direct replacements for what was on the crossover. The tweet cap I’m going to use but I’m having second thoughts about the mid caps. I have a couple of 8uf caps that test good. What kind of difference will I get by using an 9uf instead of a 6.8uf on a mid range, a little more bass or a lot more bass? Also what if I solder in a loop where this cap goes and temporarily splice the positive wire for the mid, alligator clip the 2 caps one at a time to that wire to see how it sounds. Otherwise I have to take everything off the speaker to have room to solder.

 

[Denten]

What kind of difference will I get by using an 9uf instead of a 6.8uf on a mid range, a little more bass or a lot more bass?

A 6.8uf @8ohms will cross at roughly 2900 hertz.
A 9uf @8ohms will cross at roughly 2200 hertz.
Replacement caps must be bipolar.

 

[toxcrusadr]

The usual rule of thumb is to stay within 10% of original since many of the original caps had a 10 or even 20% tolerance anyway, and may have drifted beyond even that. I would not normally use a 9 in place of 6.8, that's pretty far off. Your idea to use alligators to try different values is fine though. Just make sure you don't short anything and that there is always some kind of a reasonable capacitor in each spot. And make a note on the back of the speaker if you mod something from the original.

Changing the crossover frequency may result in a new peak in response around that area, or a dip, depending on how the speaker is wired up. It will widen the range where both woofer and mid are playing the same frequencies, which can affect imaging as well as response. But, a change that small will not hurt the speaker, only your ears, maybe.

 

[larrylarry]

So something like a 7.5 or 8uf at the most. Problem I was having was I replaced both tweets & mids with new speakers so now the new tweets & mids sound the same. Pulled out the caps an the 1.5 cap tested 1.69uf, the 6.8 tested 6.91uf. I’m guessing both are good. I was thinking that a slightly higher mid cap would help.

 

[toxcrusadr]

Oh, you replaced drivers. With identical drivers or different ones?

Is the problem that you wanted them to sound different but they don't? What was wrong with the sound originally and what are you hoping to achieve?

What are you driving these speakers with (amp and source)?

Give us a little more info and we'll probably be able to give you better answers.

 

[StimpyWan]

Oh, you replaced drivers. With identical drivers or different ones?

Is the problem that you wanted them to sound different but they don't? What was wrong with the sound originally and what are you hoping to achieve?

What are you driving these speakers with (amp and source)?

Give us a little more info and we'll probably be able to give you better answers.

More details here.

 

[larrylarry]

I replaced the original speakers because one tweeter & one mid failed or just stopped working, one in each speaker & about a month apart. Could not find any JVC replacements. I e-mailed Parts Express & they recommend a Peerless XT25TG30 4 ohm tweeter. The JVC tweeter was a 4 ohm. Also a Goldwood GM-85/8, 8 ohm mid range, bought 2 of each. I’m driving them with a JVC RX-318 or a Technics SA-AX530.
The Technics is 80 watts x 2, the JVC is the same I think.

 

[larrylarry]

The capacitors I ordered just arrived, there a lot larger than the originals. I can make them fit on the board but I’ll have to add some wire to the leads of the cap.

 

[larrylarry]

Since all the original JVC speakers were mounted to the face of the baffle I used my Rotor Zip an recessed the tweeter & mid holes. Added some additional bracing inside also.

 

[toxcrusadr]

Ok. It's good that the caps were close to the correct capacitance. They may have elevated ESR (resistance) from age but that should make the drivers quieter, not louder. It can also affect the sound balance though - ESR varies with frequency so it can throw off the response curve. This could be part of the problem and new caps should sound better if that's the case.

You've got film capacitors for replacements, which are fine, but have lower ESR naturally than electrolytics (which is what the originals were) so the drivers may be brighter. If either mid or tweeter is too loud, you can compensate by changing the resistors in series with each, or adding L-pads. OTOH the new drivers probably don't have the exact sensitivity of the originals so the relative volume is a crapshoot anyway.

Do the speakers have any info on the back like the sensitivity (db output at 1W input)? One way to gauge whether a driver will match another one as a good replacement is not only the ohm rating but also the sensitivity.

Bottom line, everything you've done so far sounds OK, and there may also be some room to tweak them. Just keep in mind these were not super duper speakers the day they were made, so don't expect miracles. The bracing and caps certainly can't hurt. Good project to get into speaker tweaking!

 

[toxcrusadr]

Would be nice to estimate the crossover frequencies for this thing, but all the charts I know of are for 1st order crossovers (inductor AND capacitor) and up, so I'm not sure they're correct if all you have is a cap. What I would do with that info, is check that the drivers you bought operate linearly in the range where they will be asked to operate with this crossover. They probably do, because 1) this is a fairly simple design, nothing weird and 2) it's a 3-way so each driver has a narrower range to cover. It would be more of a concern for the tweeter of a 2-way speaker, because it has to go low enough to work down to and a little beyond the crossover to the woofer, and not all drivers are suitable. But with a 3-way you should be fine - doubtful that PE would steer you wrong anyway.

 

[larrylarry]

Thanks a lot! I was waiting for reply’s before I solder anything on. I know that these speakers aren’t the best but they’ll be my main speakers because my garage is my listening room, turn down that F-ing stereo room, etc, etc. I’ve been searching for quality speakers on Craig’s list, I’ve seen a few but not much.

 

[toxcrusadr]

This is a fine start, and if you come across a pair of great speakers for cheap because they need a little TLC, you will be ready.

Let us know how everything goes.

 

[larrylarry]

I have one speaker done. I bought some Poly Fill sheets and stapled some inside the speaker, there was some at the bottom of the speaker already so I added some more to the top. I noticed earlier that the port wasn’t moving air so I made some gaskets from some gasket material, cork & rubber used for water pump sealing on a engine. I trimmed it to size and put it around all the speakers, now the port moves air. Soldered in the new caps,( pics) onto the board, they barely fit but got it done. Connected the speaker a gave it some power. At first I wasn’t sure if I improved on the sound so I let it warm it a bit then threw in a Cars CD, Candy O. Adjusted bass & treble to falt, crank up the volume & it sounds DAM GOOD,and that’s at 0 bass & treble. I’m happy I took the time to work on these Not So Great speakers. Being these are kind of large speakers, 12 woofers & there mounted next to the ceiling pointed down at about 12 degrees, they project a large wall of sound.

 

[larrylarry]

I pic of my DIY solder sucker. It worked but was a PITA to use. Duck tape & a couple of different sizes of tubing.
I guess I should say that changing the original caps to new ones did take care of the tweeters & mids sounding the same, there somewhat subdued now, not overpowering like they were before.