Powersoft Digam 5000 on T48-3015LF

[Bruce Weldy]

I must say I like to discuss this kind of things on a forum like this, where contributions make sense and not just bash the OP or any other comments .

You're ugly and your mother dresses you funny....




Sorry, you were just getting too comfortable.....

[Grant Bunter]

I'm struggling now...

I've tried to explain, as best I can.

nick reckons I'm lecturing, so I'll just stay out of it.

[thijs666]

I'm struggling now...

I've tried to explain, as best I can.

nick reckons I'm lecturing, so I'll just stay out of it.

And I appreciate your efforts

I just had the idea I didn't get across what my questions were and what information I was after. That's why I kept on trying to explain. Not speaking English as a mothertongue didn't help with that either .

I didn't think you were lecturing, but I think Nick did point out my question.

So now there are two ...

[thijs666]

I must say I like to discuss this kind of things on a forum like this, where contributions make sense and not just bash the OP or any other comments .

You're ugly and your mother dresses you funny....




Sorry, you were just getting too comfortable.....

I guess I had that coming

[Bill Fitzmaurice]

I'm trying to find out what factor limits the 3015LF to 60V..

Xmax and Pe, as the displacement and thermal power limits for the 3015LF are the same. A few volts more won't result in instant destruction, but there's little to be gained with more than 60v, and much to be lost, namely the driver.

[thijs666]

Xmax and Pe, as the displacement and thermal power limits for the 3015LF are the same.

That's what I was looking for . Thank you.

A few volts more won't result in instant destruction, but there's little to be gained with more than 60v, and much to be lost, namely the driver.

Agreed, there's much to be lost, especially with the latest Neodymium prices .

This corresponds with what I was expecting (luckily ). So above 60V the coil is (partially) leaving the linear magnetic field, resulting in severe power compression and subsequent heating of the voice coil. The question of course now is: when the average power stays under the thermal limits of the voice coil, what is the expected maximum voltage peak that will drive the cone to just below 17 mm. If the answer is 78V (or higher, up to 85V for 900W), than I think the driver will be safe with the built in bungee cord limiter in the Digam5000 (amp is rated at 750W/8 Ohms).

But I guess that's for me to find out in practice and I'm not sure I'm willing to take that €250 risk .

[Bill Fitzmaurice]

what is the expected maximum voltage peak that will drive the cone to just below 17 mm.

You don't want to know, because that would result in a dead driver from the coil bottoming out. Staying to xmax gives room for overshoot, and since Pe is also at 60v you don't want to exceed that except for short transients anyway.

[SirNickity]

I'm struggling now...

I've tried to explain, as best I can.

nick reckons I'm lecturing, so I'll just stay out of it.

No I don't. The thread was taking a "don't do that" turn, which isn't helpful if you're trying to understand the mechanics. When I asked to avoid lectures, it was to point out that no one is looking for permission to throw caution to the wind, so there's no need to convince otherwise. That's it, and that's all.

This group is very good at saving folks from themselves. Sometimes too good. It's OK to talk about what's past 60v, guys. Really.

[thijs666]

what is the expected maximum voltage peak that will drive the cone to just below 17 mm.

You don't want to know, because that would result in a dead driver from the coil bottoming out.

Now I'm confused . Isn't 'bottoming out' the same as the coil hitting the backplate? Which is not going to happen before 17 mm of excursion according to the datasheet , since that is the stated mechanical excursion limit before damage?

Staying to xmax gives room for overshoot, and since Pe is also at 60v you don't want to exceed that except for short transients anyway.

Agreed 100%. And it's that short transients that are cut off by the brick wall limiter of the DCX2496 and not by the amps built-in limiter (which is limiting only at the maximum amps output voltage of 78V, but does limit the average power delivered to the speaker) that make the latter sound cleaner and louder.

... Soooo... in theory would it be safe to conclude that if the average power isn't exceeding Pe AND peaks stay below the level where Xlim/Xmech would exceeded, the driver should survive? Or am I overlooking something?

[Bill Fitzmaurice]

in theory would it be safe to conclude that if the average power isn't exceeding Pe AND peaks stay below the level where Xlim/Xmech would exceeded, the driver should survive?

Yes, but that limit for the 3015LF is 60v.

[thijs666]

in theory would it be safe to conclude that if the average power isn't exceeding Pe AND peaks stay below the level where Xlim/Xmech would exceeded, the driver should survive?

Yes, but that limit for the 3015LF is 60v.

You mean both average Pe and Xlim/Xmech are at the same voltage limit? I'm sorry, I do not follow .

[Bill Fitzmaurice]

You mean both average Pe and Xlim...are at the same voltage limit?

They are. Most drivers have an Xlim voltage well below Pe, the 3015LF does not.

[thijs666]

You mean both average Pe and Xlim...are at the same voltage limit?

They are. Most drivers have an Xlim voltage well below Pe, the 3015LF does not.

Hold on, I think some terms are getting a little mixed up for me now . Before I loose track:
With Xmax I meant maximum linear excursion; 9.6 mm for a 3015LF.
With Xlim/Xmech I meant maximum excursion before damage; 17 mm for a 3015LF (I encountered both terms, Xlim and Xmech, in datasheets).

If I understand correctly you are saying Pe and Xmax (9.6 mm) are the same for the 3015LF in the T48 (probably at 35Hz or so?).
Then there would -in theory- be some headroom for small peaks, as you indicated (up to 17 mm excursion absolute max, which you don't want to drive at since there's absolutely no room for error left).

Am I correct?

Pardon my perseverance

[Grant Bunter]

Since Bill has chimed in, something has become clearer to me. Almost like a light bulb moment lol.
I didn't fully understand the TS parameter Pe (and perhaps still don't), but I did some research.
It turns out that Pe isn't measured at low frequencies, the figures would not be so "palatable".

I copied this from wikipedia (Yeah I know, Wikipedia isn't the definitive on anything at all):
"Pe: Specified in watts. Frequently two power ratings are given, an "RMS" rating and a "music" (or "peak", or "system") rating, usually peak is given as ~2 times the RMS rating.
Loudspeakers have complex behavior, and a single number is really unsatisfactory.
There are two aspects of power handling, thermal and mechanical.
The Thermal capacity is related to coil temperature and the point where adhesives and coil insulation melt or change shape.
The Mechanical limit comes into play at low frequencies, where excursions are largest, and involves mechanical failure of some component. A speaker that can handle 200Watts thermally at 200Hz, may sometimes be damaged by only a few Watts at some very low frequency, like 10Hz.
Power handling specifications are usually generated destructively, by long term industry standard noise signals (IEC 268, for example) that filter out low frequencies and test only the thermal capability of the driver. Actual mechanical power handling depends greatly on the enclosure in which the driver is installed".

The way I read it, the part I made bold tells the true story.
For the 3015 (in this particular case), based on what Bill is saying, Xmax and Pe at the lowest frequency in the T48 is identical. Hence the voltage setting.
The manufacturers published/quoted Pe of 900 and something Watts is obviously measured at some frequency well above 35Hz. More like 200Hz (or some other figure), where cone excursion is less.
It is Pe at 35Hz though that becomes most significant.
Since, in this case, Pe and xmax are the same voltage wise at the lowest frequency, there is no room for more volts (other than the 1 or 2 volts brief transients that Bill suggested earlier), as you are then taking the driver beyond either thermal or mechanical limits.

Bill says most driver manufacturers figures are, to put it bluntly, false and misleading, and relate to sales hype.

I hope this is on the right track.
It does answer your question, in a round about fashion.
If the question is "what fails in the driver when you go beyond 60V for the 3015?"
The answer would be, "Due to Xmax and Pe at the lowest frequency, either the voice coil due to overreaching the thermal limit, or the cone due to exceeding the mechanical limit, which ever occurs first". Both could happen at the same time.

If I have misunderstood the question and the question is in fact "Is the bungee cord limiter in my amp adequate to protect my 3015 driver in a T48?"
The answer is is then "No, due to Xmax and Pe at the lowest frequency, if it allows the 3015 to exceed 60V (other than perhaps a 1-2V brief transient only). Certainly not if the limiter allows a constant extra 1-2 volts rather than brief transients".

Sorry for the essay, just trying to express my thoughts accurately...

[Bill Fitzmaurice]

Take xlim off the table. You don't want to fool with approaching it. Always limit to Pe or xmax, whichever is lower. With the 3015LF they're the same.