Capacitors, ceramic or poly?

[stevie]

[quote name='escholl' post='909780' date='Jul 29 2010, 11:48 PM']Can you give us more information on exactly what you did, and how you measured and obtained these results? What was your break-in procedure?[/quote]

I used Liberty Audiosuite, an industry-standard measurement system, to measure the Thiele Small parameters of the driver straight out of the box. I used the added weight method to find VAS. I ran the driver in with a 20Hz signal from a signal generator into the unmounted driver for about 4 hours, I think. I normally leave them running overnight but fs had dropped to below the manufacturer's spec - so I thought that was enough.

If I’d known the data was going to be nitpicked, I would have measured several times to eliminate some of the inconsistencies. The only thing that running-in does is to reduce the stiffness of the suspension. So, VAS is raised and fs and Qts drop.

If you compare the green and blue curves of the simulation, you will see that these changes are self-cancelling because the curves for both drivers are virtually identical. (There seems to be a few bugs in my modelling software, because the f3 point is obviously the same, and not different as it states, and there is also a contradiction in the nominal efficiency figures and the 1W SPL figures.) Still, it’s the big picture that counts :-).

My conclusion would be that running a speaker in makes no difference to its frequency response when mounted in a reflex or sealed enclosure. I would expect the lower fs after running-in to be audible in a dipole, or an open-backed guitar cabinet, however, because VAS is more or less irrelevant to the performance of these boxes. Horns, as mentioned by Lawrence, may be similar, but that’s not my field.

Al, the measured frequency response differences of the 'before and after' driver mounted in a cabinet are negligible. I would not expect any audible difference. If there is an audible difference between a driver before and after running in, I have no idea what might be causing it, but I think escholl put his finger on the most likely cause earlier on. Did anyone mention cable burn-in?

[escholl]

[quote name='stevie' post='910462' date='Jul 30 2010, 05:29 PM']I used Liberty Audiosuite, an industry-standard measurement system, to measure the Thiele Small parameters of the driver straight out of the box. I used the added weight method to find VAS. I ran the driver in with a 20Hz signal from a signal generator into the unmounted driver for about 4 hours, I think. I normally leave them running overnight but fs had dropped to below the manufacturer's spec - so I thought that was enough.

If I’d known the data was going to be nitpicked, I would have measured several times to eliminate some of the inconsistencies. The only thing that running-in does is to reduce the stiffness of the suspension. So, VAS is raised and fs and Qts drop.

If you compare the green and blue curves of the simulation, you will see that these changes are self-cancelling because the curves for both drivers are virtually identical. (There seems to be a few bugs in my modelling software, because the f3 point is obviously the same, and not different as it states, and there is also a contradiction in the nominal efficiency figures and the 1W SPL figures.) Still, it’s the big picture that counts :-).

My conclusion would be that running a speaker in makes no difference to its frequency response when mounted in a reflex or sealed enclosure. I would expect the lower fs after running-in to be audible in a dipole, or an open-backed guitar cabinet, however, because VAS is more or less irrelevant to the performance of these boxes. Horns, as mentioned by Lawrence, may be similar, but that’s not my field.

Al, the measured frequency response differences of the 'before and after' driver mounted in a cabinet are negligible. I would not expect any audible difference. If there is an audible difference between a driver before and after running in, I have no idea what might be causing it, but I think escholl put his finger on the most likely cause earlier on. Did anyone mention cable burn-in?[/quote]

Thank you for posting all that. So, as I understand it, 4 hours (or possibly less?) of use may make a slight difference to the low end response of a dipole enclosure, otherwise the difference is negligible?

[stevie]

[quote name='escholl' post='910485' date='Jul 30 2010, 05:56 PM']So, as I understand it, 4 hours (or possibly less?) of use may make a slight difference to the low end response of a dipole enclosure, otherwise the difference is negligible?[/quote]
Despite thousands of unsubstantiated claims to the contrary all over the internet, yes. The driver itself changes quite a lot, but its real-life performance in a box doesn't.

[Phil Starr]

[quote name='Dom in Somerset' post='898088' date='Jul 18 2010, 02:50 PM']I'm about to order the electrics for my latest project, I know nothing about the subject, happy to follow a wiring diagram.
CH guitars do wiring kits for certain basses and guitars, they do two for Jazz bass, one with a ceramic capacitor one with poly- what difference does it make (if any?)[/quote]

going back to the original question I really don't think it will make an audible difference. In high end hi fi you wouldn't use a ceramic but you really aren't going to hear a difference through a bass amp/speaker. I recommended poly because I've found them more reliable.


[quote name='stevie' post='910572' date='Jul 30 2010, 07:36 PM']Despite thousands of unsubstantiated claims to the contrary all over the internet, yes. The driver itself changes quite a lot, but its real-life performance in a box doesn't.[/quote]

Actually this isn't true. The sound does change and you can hear the changes, they can be subtle or quite dramatic depending upon the speaker in question. Its not all down to Thiele/Small small signal changes either. Stevie is right about changes to Vas and Q being to an extent self cancelling and this is discussed in Bullock on Boxes (ISBN 0-9624191-5-X). These changes affect the bass response a little.

More important i suspect is the changes in the cone itself which will soften with time becoming less rigid. It will flex more and resonances will change which will change the upper frequencies.

Having said that we are all discussing angels dancing on the heads of pins. In reality we all use speakers for more than a few hours so they all get 'broken in' eventually and one person's dramatic change is another's subtle difference. Our hearing also makes fools of us all at times. I think where Stevie got us all so excited was by giving us actual data, a rare commodity on the internet. When I get time I'm going to have another look but for now I really ought to get some practice done.

Great debate guys, I dread to think what it says about bass players.

[stevie]

[quote name='Phil Starr' post='909800' date='Jul 30 2010, 12:14 AM']The figures show the sort of increase in compliance you would expect after a breaking in period though why Qes would change beats me.[/quote]

Because Fs is part of the equation for Qes: Qes = 2pi x Fs x Mms x Re/ (Bl)2. If Fs drops, so does Qes.