Cornwall Troubleshooting (Bass) NEWBQs

[classic5]

I'm going to try to troubleshoot a bass problem with my '77 Cornwalls this weekend. I've had them about a month. I recently noticed that they sounded good together but not individually. One has too much bass and one has too little bass.

I know I'm influenced by switching back and forth, but they seem to be over and under the correct sound I remember from other cornwalls (showroom and brother-in-laws). This unbalance destroyes the imaging because I have to adjust the balance and the total sound just begins to sound strained before it's gets "live sounding" loud.

I don't think they are out of phase,because that would effect both, but each would sound ok by themselves, right?

Proposed Methodology - Thoughts & comments welcomed:

1. Check Phase anyway.

2. switch positions left and right to rule out the amp.

3. switch woofers to check crossovers.

4. check x-overs for leaks (learned from other posts)

5. check terminals for corrosion.

With regard to crossovers, does the full signal from the amp reach the woofers or does some filtering take place?

What could make one be fat and one be thin?

Do drivers usually fail all together or in stages?

The fabric surrounds look undamaged - but can the spiders become unglued?

Notes: There is some sound coming out of all 3 holes in each speaker (all 5 holes if you count the ports - haha).

These are all stock.

They have probably seen some loud playing of and on since '77.

The "fat" sounding one has 2x or 3x the cone excursion of the other one.

There are no rubs or crackles and the cones have the same "feel" when pressed on lightly.

That's all the skattershot for now -

Thanks in advance for any help!

[JohnA]

Remove the backs and be sure the woofers are the same and both are K-33-Es. You can check their phase with a 1.5V battery. When the + of the battery is connected the the + of the driver, the cone moves forward.

[Good2BHome]

I would do your list as:

1

2

+Take the backs off and examine the back for ANY air leaks particularly in the corners.

+At this point, verify Johns' suggestion as to identical woofers?

5 This would be ALL terminals both exterior and interior. If you have or can get CAIG's Pro Gold use it.

4

3

The full "signal" does not reach any of the speakers. The Xover splits the sound into its component parts for each speaker.

Do drivers usually fail all together or in stages? Yes (read as: either can occur)

The fabric surrounds look undamaged - but can the spiders become unglued? You will know if you get to test #3.

Good Luck and Best Wishes!!! Let us know the results.

Mike

[WMcD]

I think you've got a good methodology going.

One thought is that since these are new to you, the seller might have had a problem with them and decided to sell them. We can't infer too much from that. In fact, the seller may not have had a problem. I'd just like to point out that we're here not dealing with, at least for you, a speaker pair which has been known to have worked properly for a long time, and then had a failure or compromise.

One thing which sets off a bit of a bell with me is that one bass unit has more excursion than the other.

If the weak one has excursion, I'd think it is an air leak. When the box is sealed, the effect of the sealed box and the mass in the port should cause less excusion and greater output. That is a bit counter intuitive, but true.

Let me suggest you first try to eliminate all issues of phase in the external wiring and the effect of the room. Put them side by side in a corner or against a wall. Check the wiring to them once again. I've messed up myself. You seem to have a balance control there. Shift from one to the other to make sure that with an identical input, there is a problem.

Gil

[ZAKO]

OR it could be a weak magnet on one woofer.& needs to be re gaussed.

[ricktate]

i noticed on my Cornwalls woofer bareley moves ,even at loud settings....so you say woofer has three times the movement of muddy one, makes me think something might be wrong with the loud one, maybe,,,,just a thought,,,,cant be sure since we are not there.....let us know what you find out...rick

[WMcD]

Whoops, you did write that the 'fat' ('phat?) sounding one has excursion.

Rick makes a good point. Perhaps the fat one has a malfunction. We're pretty much so happy with big bass that any error leading to a peak in bass response might be perceived as "better".

To answer one of your questions: If you trace out the wiring throught the cross over, you should find an inductor in series with the bass driver. It will look like a transformer. That is a first order crossover filter for the bass.

Naturally it is good to make sure all the connections, everywhere are clean and snug. But you knew that.

Let us know what you find. This is interesting.

Best,

Gil

I recall that Belushi in The Blues Brothers talked about "that fat sound" as something good. I wonder if it was "fat" or "phat" in the argot of the times. Does anyone know?

[Woodog]

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On 8/22/2003 3:30:51 PM classic5 wrote:

I recently noticed that they sounded good together but not individually. One has too much bass and one has too little bass.Proposed Methodology - Thoughts & comments welcomed:

1. Check Phase anyway.

2. switch positions left and right to rule out the amp.

----------------

This interested me because I was having the same problem with my '76 corns. I also have had them for about a month, and EBAY score, and I ended at #2. The problem was the pre-amp and not the speaker (whew)

This methodology helped. thanks all.

Forrest

[djk]

"OR it could be a weak magnet on one woofer.& needs to be re gaussed."

A '77 cornwall probably has a K33E with a square ceramic magnet, these generally have no magnet problems.

You probably have either a bad connection on the ring terminal on the back panel of the speaker, of a bad tinsel lead on the woofer.

Put an ohmeter on the directly on the woofer, it should measure 3R5, if it measures much higher, say 7R~10R, replace both tinsel leads and the dustcap. A speaker re-coner can replace your tinsel leads for very little money.

If the woofer measures 3R5 directly at the woofer, measure the DCR at the input terminals on the back of the speaker. This should measure about 4R. If it measures much higher than this cut off the ring terminals that attach the crossover wire to the input terminal block, replace them and the screws(these are both hardware store items).

[classic5]

Thanks for all the help - I've learned a lot!

Short version: Bach in Business - Thanx Forum

Long Version:

I put the perpetrator face down on the carpet and removed the back. All connections looked clean and no leakage at the "big silver cans" (hope that's not too technical) on the cross over 2mf - no PCBs.

It's all stock and clean. I'm the third owner, I knew the second owners and they knew the first - so there is a good chain of custody all the way back to Hope. K-33-E's, just as John predicted, /K-55-v /k-77. I've got to remember to write down the serial no.s of the components left and write - but I was just trying to keep from dropping a screw or screwdriver through the woofer.

I undid the leads and removed the woofer. The spider was intact (same resistance to light pressure forwards and back) and is much more substantial than I thought. The dust cap has a small "porthole" in it covered with cloth (voice coil vent?). The dust cap has what I can only describe as stess lines in it - barely visible creases where it looks like it wants to bend if it has too - and it is a lot more flexible than I would expect. I wonder if this has weakened due to the mass of that porthole's cloth and glue and the need to overcome it's inertia so rapidly. I noticed that more recent woofers don't have this.

I thought I had found the problem when I saw that the magnet was cracked! Anybody else seen this before? The magnet is the ceramic/"mud" square style and there is a through crack top to bottom at the middle of one side. There was no debris in the cabinet or stuck to the magnet. I think this left the Factory (supplier) this way because the epoxy used on the endcap/pole piece flows in the crack and the dish out around it. I didn't think that playing would generate this much force - heat maybe - and there is no dings on the case to show that much force either. My best guess is that it cracked when the plates were torqued down on the wet epoxy during manufacture. I wondered if maybe this didn't matter if it passed inspection - I guess magnetic force can bridge the crack.

I stitched everything back up as the wife and kids would be back shortly and figured I should place a bid on some K33s offered by a fellow forum member.

I hooked the leads back up to the receiver and it seemed visually to be still happening. Lo and behold, when I sat down to listen - Boy Howdy! - everything was like my Heresies except moreso (Klipsch aficionados will understand). I HAD thought that these Cornwalls sounded good but were big and lazy. Now it's the same transient response all over the scale.

What fixed what!?! I had fiddled with so many things that I can't isolate the cause for sure. I work on cars and PCs and this situation is frustrating because I like to get to the exact point where I can duplicate the error and make it be fixed/broke/fixed/broke... so you know you've got the culprit, but the great sound eases the pain. I really think the problem was in the receiver because I had moved the balance knob and backed the bass to zero and back (it normally stays flat) - I think this scrubbed the potentiometer clean. Klipsch vendicated.

I think the amp was somehow boosting the base (one knob only so I can't figure why one channel and not the other). (Source was CD so no turntable feedback)

The large excursion was probably clipping - but I didn't hear any problem in the high end. If you can imagine the low bass being overdriven while the mid and high aren't yet loud - that is what it sounded like. This matches with the situation user Woodog had. Now the woofer travel is within the 1/8th" I seem to remember was a spec.

Thank Again Forum