Single sheet TH challenge

[Djim]

Originally Posted by Brian Steele

That's probably the case for every alignment simulated by a program that doesn't take BL nonlinearity into consideration. Most assume that the driver behaves at large signal levels the same way it does at small signal levels, which is simply not true.

Even if the non-linearities would try to make the excursion go beyond its prediction in reality at Xmax (+/- 70% BL) a PA driver already suffers from 2dB-3dB power compression. Adding another few dB's in power and it will rise to 4dB-6dB. That means the excursion will be kept under control. But temperature in the voicecoil can start to rise rapidly from this point and that is something you should worry about.

[4pyros]

Pyros, you need a detailed drawing from your ‘custom’ SS15 otherwise all this good help is for nothing. That way you can translate your cab back to a corresponding HornResp prediction and find the points in your design that can benefit from a little re-arranging. Also from a corresponding HornResp you can calculate exactly the max power you can use and as long your amplifier doesn’t go over that max you can eq as much as you like at any point in the bandpass!

That was done way back in this thread. I had to blow stuff up today. More testing soon.
Andy

[4pyros]

Originally Posted by 4pyros

I am using a PAA3 meter for the testing and the weighing is off. Its a pain to read the meter from behind the speacker. I am going to try and hook it up to a lap top for further testing. Andy

Jim; Did you have any weighing in your tests? I did mine flat and will be retesting soon. I have A, B, and flat. Witch should I use? Andy

[weltersys]

Originally Posted by 4pyros

Jim; Did you have any weighing in your tests? I did mine flat and will be retesting soon. I have A, B, and flat. Witch should I use? Andy

Andy,

Jim used flat, as you should.

You can see the difference in weighting in the chart in post 886, using "A" or "B" weighting would make your cabinet look like it has very little bass.

If you check excursion while you are testing at 28.3 volts, you will find out if your cabinet's low corner is actually lower than the standard SS15.

As I mentioned before, a lower corner will be accompanied by less output in the same volume box.


Art

[weltersys]

Originally Posted by Djim

True, but give me an example where excursions in a TH was higher then predicted, just one Art?! Which means the calculated excursion is safe. But I would agree with you if you say in reality some TH's can be powered way beyond predicted max safe power.

Nevertheless, it still doesn't matter how much and where you EQ as long you don't feed your cab with more watts then its max safe power (from predictions or real life measurements).

I don't have examples of excursion being higher than predicted, in fact suspension rigidity will make for less excursion below Fb than predicted.

That is why I suggest measurement of the actual speaker, rather than relying on a sim for proper setting of the HP filter.

[AndrewT]

Originally Posted by weltersys

in fact suspension rigidity will make for less excursion below Fb than predicted.

VAS is a measure of suspension rigidity.

Reduced excursion would be due to a non linear suspension that becomes less compliant with travel, i.e. more rigid.

[4pyros]

My test tone CD was messed up. I converted the MP3s to WAVs that could be read by the player on a USB stick. I used the smallest amp to set the 2.83VRMS.
and stood the meter up so I could read it better from the side.

Not the best day for testing but I knew the box would go lower and boy did it.

97db at 20Hz
102db at 25Hz
105.5 at 30Hz
106.5 at 35Hz
105.5 at 40Hz
106 at 45Hz
106 at 50Hz

Thats all I did for now. I will try and rerun the full range agin soon.
Andy

[AndrewT]

so F-3dB is just above 25Hz.
That's a mighty good LF frequency response !

[weltersys]

Originally Posted by AndrewT

VAS is a measure of suspension rigidity.
Reduced excursion would be due to a non linear suspension that becomes less compliant with travel, i.e. more rigid.

As most suspensions are, fortunate for those who don't employ proper HP filters.

[Djim]

Originally Posted by weltersys

I don't have examples of excursion being higher than predicted, in fact suspension rigidity will make for less excursion below Fb than predicted. That is why I suggest measurement of the actual speaker, rather than relying on a sim for proper setting of the HP filter.

Okay Art, for a minute I thought you suggested higher excursions did occur.

As far predictions and low cut filters, as long the 1/3 wavelength of the design (HornResp prediction) aligns perfectly to real life SPL measurements like Jbell’s there is no problem to use calculated low cut settings. In other words, Oliver has proven already his latest HornResp from March aligns perfectly to Jbell’s SS15. Therefore it’s absolutely safe to use predictions as guideline for setting out the Low-Cut filter. So it’s not necessary to measure the excursion physically for that.

And for those who ;-) still believe excursions can be higher then predicted:

Power compression: Since most PA drivers have less then 5% efficiency almost all of the rest of the input power is converted into heat. The more input power the more this heat will rise and therefore the resistance of the voice coil.

Dynamic compression: When a PA speaker cone reaches the limit of its excursion the mechanical 'elastic' resistance becomes higher. In the latest generation low frequency PA drivers this dynamic compression is minimised by the extension of the (linear) physical excursion and therefore its Xlim.