|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
220.244.218.142
It seems pretty common for drivers to have Qts and Fs higher than advertised, or for the units to change up between production runs. I imagine it is from construction shortcuts / using cheaper magnet materials.So far the drivers that are on spec:
Peerless midwoofers
Some P.Audio (and some not)
Fostex 105WK (kinda)Not:
Vifa (now made in China)
SB
P.AudioFrom this, and what I read, it seems like only the better Euro and US brands actually make stuff that routinely meets spec. Unfortunately, shipping then to Australia + customs blows the already high prices out for me (e.g. I bought a $500 pair of Focal mids years ago which cost $300 more to get to my door).
Are there any exceptions? It seems like for any Asian built woofer, you need to multiply the advertised Qts by about 1.3
On a related note, I just tested a HT sub. The raw driver has a Fs of 48Hz and Qts of 1.1, so in the ported box the response has a "M" shape under 80Hz.
Edits: 03/09/15Follow Ups:
There is a set of Altec 414-8Z on ebay which have new non-Altec cones.
Fs = 53Hz Qts = .6
The seller said the new stiffer cones might have something to do with the higher testing drivers.
I've been told that it depends on how you test sometimes, for example what the input wattage is. That is per Madisound. Sorry I don't recall the brand I questioned them about.
I have a friend who used to design speakers and tested all his drivers. He never found SEAS drivers that didn't meet specs for his form of testing. But other brands often didn't.
Usually, it's the suspension stiffness that is too high in a new driver - that drives both fs and QT up. However, the suspension will loosen up as the driver breaks in, so the drivers may meet their specs after a few (hundred?) hours.
The ratio fs/QT does not vary with stiffness, so if it matches the spec, that's a good indication that the driver will eventually meet specs. Also, the box design is usually very close to the same for the new and broken-in driver.
If fs/QT is lower than spec, that suggests the magnet is not fully charged. That's more of a deal-breaker. The magnet can be re-charged in theory, but it means removing and replacing at least the dust cap, not to mention finding someone with a magnet-charger!
Thanks. Fs is also slightly high, so I tried more breaking in, with positive results initially.-new 12" which had about 20 hours of mild break in
-an older 15" which has a couple of years of gentle play (living room use in a system with 6*15" PA drivers)After heavy LF noise (more excursion than I'd previously driven them to) for a few hours, both drivers changed. The 12" was still off spec, but the gap closed slightly: Qts 0.52 --> 0.50 when 0.4 is specified. The Fs shifted by a sliver, about half a Hz.
The 15" response curve changed - it gained a couple of dB in the low mids (> 100Hz). I didn't expect that. I obviously need to beat my drivers harder.
Will give a more extensive test / listen tonight (the break in is ongoing).
With the 12" driver, I can drop the Qts about 10% by applying an additional woofer's magnet (back to back orientation), so that's something else to experiment with.
I have plenty of drivers to repeat this with, so next time I'll be a bit more rigorous about setup and recording the changes.
EDIT: looks like all the benefit was in the first hour(s). Another ~20 hours of heavy LF seem to have made no further difference. Worth doing, but not as beneficial as I hoped.
Edits: 03/11/15
High Qts? Open baffles.
Just a suggestion.
all the best,
mrh
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: