Axiom Home Page Forums General Discussion Technical Questions M80ti Crossover Problem (I think)

So I picked up a soundcraft mixer for some of the recording I do and decided to do an A/B comparison between it and a tube preamp that I've been using. Using the same signals to both preamps I drove one speaker with one and the other speaker with another.

What I immediately noticed was that one of the speakers had a punchier bass than the other and running specific audio tracks with extended low frequency showed an even greater difference. Out of curiosity, because my tube pre was literally kicking the soundcraft mixer's behind, I swapped the left and right channels.

Interestingly, the problem switched between the mixer and pre but not speakers. Thinking that it might be a problem with my stratos amp I switched channels at the amp, but the problem still persists in the same speaker.

Since all the drivers in the speaker work I really believe that the culprit here is the builtin crossover. Does anyone know where the crossover is located inside the m80ti speakers? I'm considering rebuilding it from new components to see what happens.

I believe it's directly behind the input jacks, but I've never actually looked.

You're right, I found pictures online which show that the crossover is directly behind as well. I'll take a look tomorrow to see if there' any obvious physical/electrical damage.

On a different note, I wonder if Axiom would be willing to upgrade my speakers with a newer crossover, for example I read somewhere that the original ti's don't even have a high pass filter on the tweeters.

You can buy a new crossover from them. I suspect that your info is wrong on the high pass filter, though.

Yeah, a tweeter would definitely need a HP filter or it would blow! I think you are mistaking the tweeter with the (midrange) woofers in regards to the lack of HP in the crossover on the ti's.

Rob, all the Axiom speakers have(and have always had)high-pass filters on the tweeters in their crossover networks.

In the case of the M3s that's all they have. Axiom wisely uses the mechanical roll off of the driver instead of a cross-over.

Sorry guys, I found the report (http://www.ninjasreview.com/forum/showth...-for-all-of-you) and it's the mid-range drivers that don't have a high pass filter and are allowed to just roll off.

I'm not entirely sure if it really is the crossover, but my cable lengths are the same to both speakers and since I've never played them extremely loud I can't imagine there being any damage to the drivers.

Perhaps I should call axiom directly.

Cable lengths wouldn't make any difference whatsoever. Did you put your ear up to all the drivers and make sure they're all working?

Yes, I've verified that all the drivers are working. The best way to describe what they sound like would be "muddy" and "hollow." Mind you, I was not aware of it until yesterday when I decided to A/B the preamp/mixer.

While the difference isn't extremely noticable it's evident when panning with the same material (mono signal) between the left and right channel.

Intricate,

To make the comparison fair, you should place your two speakers side by side. It could be that one of the speakers is in a location where boundary reinforcement emphasizes the bass output more.

Moreover, a tube preamp's frequency response is rarely linear or smooth, especially compared to solid-state, so unless you measured the frequency response of the tube preamp, it could well be the contribution of the tube preamp that's emphasizing bass. Typically, the generous amounts of harmonic distortion from tube gear sometimes adds a "warmth" to bass reproduction.

By the way, you can ignore that Ninja site. The info there is simply wrong. And as kcarlile pointed out, cable length will have no influence at all.

Regards,
Alan

Hi Alan,

I was awaiting your response. At this point I have eliminated the tube-pre entirely and am using a single channel on my mixer and panning between the left and right channel. I have isolated the problem to be with the speakers as I've swapped the cables to and from the amp one between the other.

Furthermore, playing with the EQ on the mixer I'm 99% sure that the tweeter and mid drivers are responding identically. It is just the low frequency drivers that are contributing to this problem - although they are working.

To start with the troubleshooting, how hard would it be to swap the crossovers from one speaker to the other? Are the drivers plugged in or soldered onto the board?

So I removed the screws on the back of the input and visually examined the crossover. (The cables to the drivers are soldered btw)

There doesn't seem to be any damage, I'd like to swap the units between speakers to see what happens but I'll wait for Alan's response first.

Some additional information.

Doing a 100hz cut in the material makes the problem indistinguishable.

Hi Intricate,

I don't see a problem in switching one crossover to the other speaker if you're confident of your soldering skills. It's rare, but sometimes there can be a defect in a crossover board or a cold solder joint.

Are you using a mono test signal to each speaker? Is each speaker receiving the same signal (i.e. not a stereo signal) because there is no assurance using a stereo signal that bass is mixed equally into both channels.

I would say you need to confirm all the drivers are working before you get too involved with the possibility of the crossover as a bad woofer will certainly make a huge difference both in spl and it may have a muddying effect by reverberating with the good drivers(just a possibility).

I think it would be easier to swap all the drivers over than to desolder the crossovers and swap them around. The drivers have push on terminals.

Rob, as Adrian and Jason pointed out, it would appear to be simpler for a "start with the trouble shooting" to switch the bass drivers rather than the crossovers. The simple fact that they're working to some extent doesn't answer the question.

That will definately make life a lot easier (considering the drivers have push on terminals). I wasn't really up to resoldering the crossover at this point.

I'll try swapping the drivers over next weekend or if I get some free time during the week and report back. I appreciate all of the comments, ideas and feedback.