NatP Crossover Question

[jdp]

I think I've bottomed the drivers on my NatPs. I'm testing the crossovers, and with a T-amp, there is no problem. The bass is slightly thin, but I attribute that to the T-amp.

However, when I switched to the Onkyo TX-SR505 that I plan to use to power them, several seconds into Bach's Toccata and Fugue in D minor, I heard a thump, the woofers moved a lot, and the music stopped for a moment. This happened at a crossover of 200Hz, so I'm assuming it's a crossover problem, not a full-range problem.

Is that "bottoming the drivers?" If so, I assume it's disastrously bad. What might I have done wrong, and what should I do to fix it?

I'll attempt to post some photo-bucket photos below - I hope this is the correct photo posting etiquette.

Images not available

[Ray_D]

Can not access your pictures.

[geno742]

Whoa.....
I cross my Nat. P's at 80hz.

Have heard of others crossing at 60hz, but none at 200hz.

Tried it once at 120 hz just to see how they sounded.
I think they sound best at 80hz with my system.

Emotiva LMC/LPA-1 driving Nat.P's, 15" dvc LLT subwoofer and chris' center.
Oh how sweet it is....

[jdp]

200Hz was an experiment to see whether a higher crossover would stop the bottoming.

It turned out that it was an air pressure problem - I was using weatherstrip to seal the woofers, and in one area I let it slip into the woofer hole, so the seal was bad. When I fixed that, the bottoming stopped.

[fbov]

Actually, that doesn't make sense. Bottoming is reaching Xmech, the mechanical limit of cone motion.

My NatP's are ported, so I have a big hole in the box. I designed it for full-range bass extension a the risk of reaching Xmech at full power (I never expect they'll actually see 100W at 20Hz). At 85dB, I'm not seeing much movement in the cone, although the low bass is both prodigous and deep. That's how ports work.

If you had a small leak, it would be hard to hear, much less causing max excursion.

Have fun,
Frank

[cheno848]

have you ever looked at your receiver when this happens? Sounds like your onkyo could be going into protect mode. Maybe cranking up the sound on the 4ohms is just too much for it.

[---k---]

When I fixed that, the bottoming stopped.

:T
I hope you got it.

[JonP]

have you ever looked at your receiver when this happens? Sounds like your onkyo could be going into protect mode. Maybe cranking up the sound on the 4ohms is just too much for it.

Yeah, it does sound more like overload protection. Bottoming should sound like a harsh CRACK or POP... or other horrible noises on sound peaks. And sometimes noise forever after... if you did some damage.

Check your manual for the amp, and see if you are rated for 4 ohm speakers, or have a setting on the amp for lower impedance speakers. I have a later Onkyo model that needs a settings change for that. Should help the amp be more comfortable when driving more power to them.