Wandering Soundstage

[wer]

G'Day everybody, this is my first post in here and (to nobodies surprise) it is a request for help.

I already asked a similar question on another forum, but did not get a plausible answer.

I recently got a pair of IMF Compact II, which i put on top of my JBL's for a first listen.

Playing a trumpet and organ LP, the sound is quite satisfactory, but the trumpet keeps wandering around between the speakers, whereas with the JBL's it stays in one place.

My first idea was compromised caps in the crossovers (already ordered), but waiting for the caps i am no longer so sure, because i can not figure out why they might have an effect like that. Meanwhile i have taken the speakers apart and found:

One crossover capacitor measures 7.8 uF, the one from the other side 8.4 uF. There is one small capacitor on each side, but they are almost identical at 94 and 97 nF. Wonder if that difference in capacitance might account for the instability of the soundstage, or whether there may be more problems hidden in old capacitors?

Suggestions and explanations would be much appreciated.

 

[themadlatvian]

I have a few trumpet and organ records, which sound very well.

The trumpet is a very 'directional' instrument, and it does have the ability to sound clearly from a particular position within the stereo soundstage.

If the trumpet is moving around within the stereo image on one set of speakers, but not on the other, then it would suggest that you have either a crossover problem, or a design/driver fault. Much of the trumpet's energy occurs in the upper midrange where the mid driver crosses into tweeter. There could also be a slightly defective driver causing the problem, or either the midrange or tweeter drivers are not matched with each other, so the frequency response of each loudspeaker overall will vary and cause exactly the problem you describe.

First thing to do - swap the IMFs over between themselves - take note of whether the trumpet wanders at the same moments in the music, and between the same positions within the image. If it is the same then it makes it less likely to be a particular driver, more likely a crossover malfunction.

AND - check your speakers are correctly phased.

:^

 

[barry2tone]

Hello Wer, welcome to the Wigwam,

'fraid I don't have the technical knowledge re caps etc, hopefully someone will be along soon.

But it does strike me that maybe the JBL's are acting as passive absorbers of certain frequencies, and to hear the IMF's au naturel, you'd be better off with the JBL's out of the room.

A friend worked for a while at Linn, and had the chance to spend time in the audition suite.

He was listening and enjoying one day, when people came into the room, put something down and left.

The music was badly disrupted.

Having spent some minutes wondering what-on-earth? could spoil things so much,

when he turned round, it was a large pair of speakers had been set down behind him.

Of course, this advice would be easier with almost any other speaker than JBL's.

 

[wer]

????????????????? sorry don't have a clue but what does trumpet & organ music soundlike strange combo imo

Hi Steve, there are quite few great recordings of organ with solo instruments

Voice: Emilia Petrescu and Valentin Gheorghiu 1960 (Recital de voce și orgă )

Nai: Gheorghe Zamfir and Marcel Cellier - Flûte De Pan Et Orgue

Trumpet: Jan Kritel Jiri Neruda Concerto in E-flat

and many more.

 

[wer]

Thank you John and Michael.

Tried all variations of phasing, no difference.

Wish i had had the idea of switching the speakers to find whether the problem is caused by a driver or the cross-over. Can not do it now since they are in pieces, but hope to be able to put it all together with new caps next week, when i get home again.

After i took the IMF's to pieces, i got a pair of B&W DM4's, which - also on the JBL's - have a rock solid soundstage.

At least they are not the heaviest JBL's, only 4311B's.

 

[wer]

Crossover recap done. Pleased to say that instrument location has improved a lot, albeit still not perfect (compared to JBL 4311B's and B&W DM4's). Still, easy to live with considering size and price

 

[themadlatvian]

Crossover recap done. Pleased to say that instrument location has improved a lot, albeit still not perfect (compared to JBL 4311B's and B&W DM4's). Still, easy to live with considering size and price

Sounds like an improvement Werner. The imaging of DM4s is a particular strength of those vintage speakers. You can obtain very good results with the right source equipment - they sound very nice on the end of valve amps of moderate power for example. Your IMFs will probably have a stronger bass.

 

[wer]

Yes John, and i am happy to have them in listenable condition now. Meanwhile i fell in love with the DM4's, so the IMF's will be a present for a friend to replace his horrid plastic cased squeekers.

Mine are the IMF Compact II, with only have a 6.5" bass unit in a very small enclosure, so the bass is not exactly earthshaking. The DM4's have a slightly larger driver in a larger box, so i think they are doing a bit better in the bass department.