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mashaffer 3rd September 2008 05:02 PM

Testing TS with driver vertical
In measuring TS parameters does it matter whether the driver is vertical or horizontal? The reason I ask is that it is not convenient for me to test vertically unless I just suspend it from the ceiling via some string and I presume that letting it hang free like that would be worse.

djarchow 3rd September 2008 05:34 PM

No matter how you measure, the driver should be rigidly mounted.

If I am doing free air measurements, I use a large wooden clamp and clamp the driver magnet to the table edge with the drver oriented vertically. Also if the driver has a vented pole peice, you need to be sure and keep the vent well away from any obstructions.



richie00boy 3rd September 2008 06:03 PM

I usually test horizontally and it's not really a problem unless the driver has very weak suspension.

Good tip on clamping the magnet to the edge of a table. I might add that to my measuring guide :)

planet10 3rd September 2008 06:40 PM

If the driver is facing up or down, the weight of the cone will throw off your measurements. The bigger the driver (n general) the less accurate your results will be.

Ideally the driver is clamped rigidly and in a "facing forward" position, free from any close objects and in a perfectly quiet room (if the background tunes are turned up too high you can see that in your measures). In parctise -- with the small drivers i am most often measuring -- holding the driver with my elbow resting on something solid (my chairs arm rest) is sufficient for me to get repeatable results.

John Janowitz (Stryke) somewhere here posted in some detail on this subject.


Dr. Ram 4th September 2008 04:18 AM

Keep in mind that if you are worried about errors in measuring the T/S parameters, what really matters is not the error in the parameter per se but what is the resulting error in your enclosure design that uses these parameters. For example, you may encounter Vas errors of 10% or more but 10% is not as terrifying if the resulting SPL errors for the enclosure are 0.5 dB (as is often the case).

forr 4th September 2008 09:52 AM

For some drivers, I found about 3% differences (fs and Qts) between vertical and horizontal moutings.

mashaffer 5th September 2008 12:49 AM

Thank you all for your comments. Ramkumarr, that point is something about which I was wondering. In simulations that I have run it seems that one can often vary parameters a fair amount without much change in performance.

When you think about it even individual samples of the same driver vary somewhat yet most people don't realign each cabinet for the individual driver. In my case most of these drivers will be used either as Open Baffle, Sealed or Tapped Horn.

Suppose that what I should do is model which the measured parameters and then run a simulation with each parameter varied by 10% each way and see what the tolerance for variation amounts to.

I suspect that sealed and OB will both be very forgiving. The TH however may be more sensitive.

planet10 5th September 2008 01:14 AM


Originally posted by mashaffer
When you think about it even individual samples of the same driver vary somewhat
20% variation is considered normal.


LineArray 5th September 2008 03:51 AM

i experienced that the driver should be
broken in for a while, to stabilize the drivers

Vas lowers dependent on the suspension materials
used in the driver.

I had a driver with a plastic surround, which contributed to
stiffness of suspension. The driver lowered its Fs
about 15% as far as i remembered in the first half hour ...

It is a difference with many drivers at which excursion
you measure.

I tend to measure somewhat below the limit of linear

mashaffer 5th September 2008 09:56 PM

All of the drivers I have been working with are used (most of them very used).

One thing that I should mention is that I am testing at very low volume levels under the theory that these are small signal parameters. Maybe I am taking this too far though. Usually the peak voltage across the driver itself (at fs) is about 1V or slightly below. Should I be using more signal?

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