Trouble Shoot a Woofer Buttom Out

[parodielin]

The situation is I am helping someone trouble shoot a woofer bottom out situation. Because it is remote and it is difficult to re-produce the environment.

What I did was I used the exact same tune played, the same woofer with the same tuning frequency, same crossover, and same box volume. Speaker impedance is 8 ohm and the lowest point is 6 ohm.

The difference are the amplifiers, pre-amplifers, source equipment (CD Player), and the room.

In my room (23' x 16' or so, closed, carpeted), I can do a pair producing 100 dB measured using OmniMic without bottom out the driver. Actually, this is the loudest volume with amplifer volume at maximum (250W into 8 ohm). As you can imagine, in the room, I wear ear plugs b/c I value my hearing.

I do not know my friend's listening volume. I doubt he has a SPL meter. He said a few other similar volume/configuration speakers he had did not show any sign of bottom out.

If the problem is the woofer, would it show on the impedance sweep? Since both woofers are showing the same bottom out situation, it would be really lucky to get two defect woofers.

Thoughts?

[johnnyrichards]

Does your friend have a heavy hand with the bass boost/EQ?

[parodielin]

Does your friend have a heavy hand with the bass boost/EQ?

I doubt it but I can ask. How would this help?

[billfitzmaurice]

If the problem is the woofer, would it show on the impedance sweep? It would show up on the maximum power chart when modeled in a program with that capability, such as WinISD Alpha Pro. Shy of that, there's a simple cure to woofers bottoming out: turn it down.

[johnnyrichards]

I doubt it but I can ask. How would this help?

If the driver alignment and source material are the same, and if your friend is running the same or less power, the only difference would be volume or the signal.

Bass boost fills in the bottom end nicely, but it also demands much more excursion capabilities.

[fbov]

...I can do a pair producing 100 dB measured using OmniMic without bottom out the driver. Actually, this is the loudest volume with amplifer volume at maximum (250W into 8 ohm). ...

Are you sure you're pulling 250W? There's a difference between gain and power; you have the amp set at maximum, but you've adjusted gain, not power. Turn up your input sources and I bet you can bottom the sub.

Another way to look at this is sensitivity. If 250W truly achieves 100dB, your sensitivity is about 76dB@1W. Mine's rated more like 87dB, so this really looks like a low input voltage issue.

HAve fun,
Frank

[parodielin]

The source is turned to maximum (Preamp). It's a buffer so it doesn't add any gain. I doubt it is truly output 250W because it depends on the content played.

The speaker is rated 86-87 dB. It is crazy loud at max. I won't survive without ear plugs.

I wanted to know if there is better way to figure out what went wrong in my friend's system. Could that be a bad woofer? Would that be his volume requirement is too high? The same tune played on my system at 100 dB in a 23"x14" closed room does not have issues. Why would that be an issue on his system? Could that be a bad amplifier?


Are you sure you're pulling 250W? There's a difference between gain and power; you have the amp set at maximum, but you've adjusted gain, not power. Turn up your input sources and I bet you can bottom the sub.

Another way to look at this is sensitivity. If 250W truly achieves 100dB, your sensitivity is about 76dB@1W. Mine's rated more like 87dB, so this really looks like a low input voltage issue.

HAve fun,
Frank

[CokewithLime]

Just a thought, does your friend know what the actual sound of a driver bottoming out sounds like ??

It could be that he is mistaking severe amplifier clipping as a driver bottoming out sound.......

[parodielin]

Just a thought, does your friend know what the actual sound of a driver bottoming out sounds like ??

It could be that he is mistaking severe amplifier clipping as a driver bottoming out sound.......

He saw the driver being pushed to a point where it stopped. He has Usher Be-718. And under the same condition the Be 718 won't bottom out, understanding Be-718 is in a slightly larger enclosure.

[Jeff B.]

He saw the driver being pushed to a point where it stopped. He has Usher Be-718. And under the same condition the Be 718 won't bottom out, understanding Be-718 is in a slightly larger enclosure.

Some equipment has subsonic highpass filters built into it, some do not. Some amps have a higher damping factor, some do not control motion nearly as well. I think the details are too vague to answer the question right now. Many years ago I had 35 Watt receiver that would send my woofer cones bouncing all over the place. Then I replaced it with a 200 Watt per channel, much higher quality, power amp and preamp, and although it would play louder the cone motion control at very low frequenies was much better. This surprised me at first, but as I looked into it I found the change was due to both of the items I mentioned above - A subsoinc filter in the preamp and much higher damping factor in the power amp.

By the way, if vented, I am assuming the ports are tuned to the same frequency? This can dramatically change the excursion of the woofer.