Speaker Distortion

[jim1961]

Need some help. I am getting a sudden distortion peak around 470hz. As I bring up the volume, its suddenly there. Its not there at any lower SPL, and is ever-present at higher. I dont see it in the other speaker.

Things ive tried:

1) Changed amp channels driving the speaker
2) Made sure all the mounting screws are tight
3) Tested both near field and far field.
4) Eliminated anything that could vibrate near the speaker

The graphs were taken near field (about 10" from cone) with tweeter running as well.

Has anyone seen this type of thing before? Ideas?





The driver in question is a Seas W18NX001

[jim1961]

Problem solved. I tightened the midrange mounting screws just a bit more and wha la, all peachy now.

Was going to delete the thread, but on second thought, someone else may have this issue and my post may help them diagnose it.

[wkhanna]

With DIY speakers especially, periodic tightening of driver mounting hardware is part of my regular preventative maintenance routine.

Your post is a good reminder for everyone, IMHO.

Glad to hear you got things all sorted out. :T

[jim1961]

With DIY speakers especially, periodic tightening of driver mounting hardware is part of my regular preventative maintenance routine.

Your post is a good reminder for everyone, IMHO.

Glad to hear you got things all sorted out. :T

Along the lines of reminders, for those that take measurements, be sure to occasionally take them at fairly high listening levels (higher than 80-85SPLdb). This problem didnt show itself until about 90-95SPLdb at the LP

[---k---]

Never would have thought...

Some questions to satisfy my curiosity now. Could you hear the distortion or was it only in measurements? Was the screw allowing air to leak and that was the distortion or was it causing a rattling? Do you use a foam gasket or anything and what type of screws/wood?

When my speakers come out of storage this weekend, I'm going to be checking all of them.

[jim1961]

Never would have thought...

Some questions to satisfy my curiosity now. Could you hear the distortion or was it only in measurements?

No. But the distortion came into being suddenly around 92SPLdb at the LP. I dont always turn it up that loud.

Was the screw allowing air to leak and that was the distortion or was it causing a rattling?

A vibration. During slow sweeps, there would just suddenly be extra harmonics once the sweep got to 470hz or so.

Do you use a foam gasket or anything and what type of screws/wood?

This you would have to ask my brother. He may chime in and tell you. He did the actual build. But this pic may answer your question.

When my speakers come out of storage this weekend, I'm going to be checking all of them.

Good idea

[BobEllis]

Seems to reinforce the philosophy of giving the drivers a solid mount on a stiff baffle.

I noticed some distortion at higher levels recently. Guess it's time to check the mounting screws. Thanks for this.

[benthe8track]

Could always use one of these guys:

[sdl2112]

Never would have thought...

Some questions to satisfy my curiosity now. Could you hear the distortion or was it only in measurements? Was the screw allowing air to leak and that was the distortion or was it causing a rattling? Do you use a foam gasket or anything and what type of screws/wood?

When my speakers come out of storage this weekend, I'm going to be checking all of them.

The wood is MDF with Parts-Express barbed inserts as shown in the pic. I used their speaker foam gasket tape as well.

[---k---]

Thanks for the answers.

I usually use wood screws with marine weather stripping (From home depot, next to the regular weather stripping. I think it has better adhesive is all). But I also have a roll of PE gasket tape I use. I usually have the problem that even after taking the screws out, the drive is stuck firm to the weather stripping. I have to pound on the back of the speaker and use a wire hook through the screw hole to try and pull the driver out. A few months back, I was taking my subs apart and had to just prop the sub up face down and let it sit for about five minutes before gravity did it's job and the drive fell out.

[Steve Manning]

Thanks for the answers.

I usually use wood screws with marine weather stripping (From home depot, next to the regular weather stripping. I think it has better adhesive is all). But I also have a roll of PE gasket tape I use. I usually have the problem that even after taking the screws out, the drive is stuck firm to the weather stripping. I have to pound on the back of the speaker and use a wire hook through the screw hole to try and pull the driver out. A few months back, I was taking my subs apart and had to just prop the sub up face down and let it sit for about five minutes before gravity did it's job and the drive fell out.

Ryan, I found this to work very well, because sooner or later you will need to take a driver out and I've gone though what you described and a few other tricks that did not work very well.

[JonMarsh]

And some folks still question or wonder why someone would use LBL bamboo for speaker construction, with it's hugely stiff and well damped behavior, and the way it taps out and locks fasteners in solid... :W

Thanks for keeping the thread up and not deleting- it could certainly be helpful for some others!

Any chance of posting distortion plots from AFTER the fix is in? That would be cool, and educational.

[jim1961]

Any chance of posting distortion plots from AFTER the fix is in? That would be cool, and educational.

Just for you Jon :lol:

I recreated the same measurement at the same level and mic placement. Only difference is the high distortion (pre-fix) graph has all the stuffing out of the mid cabinet and the new one has the stuffing in (I dont feel like removing all the stuffing again).





I also put the pointer on the frequency of interest so the distortion numbers at the bottom show the data difference at the frequency where the problem was.

[Steve Manning]

And some folks still question or wonder why someone would use LBL bamboo for speaker construction, with it's hugely stiff and well damped behavior, and the way it taps out and locks fasteners in solid... :W

Thanks for keeping the thread up and not deleting- it could certainly be helpful for some others!

Any chance of posting distortion plots from AFTER the fix is in? That would be cool, and educational.

Jon, have you used threaded inserts with LBL? I was wondering how much more difficult, if at all, installing them would be.

[dar47]

Just as easy as say mdf and would hold the screw type insert better but just a coarse screw in the bamboo facilitates taking drivers out maybe 5 times compared to mdf maybe 2 times. The screws squeak nice and tight.

[Jonasz]

Just for you Jon :lol:

I recreated the same measurement at the same level and mic placement. Only difference is the high distortion (pre-fix) graph has all the stuffing out of the mid cabinet and the new one has the stuffing in (I dont feel like removing all the stuffing again).

[ATTACH=CONFIG]24035[/ATTACH]

[ATTACH=CONFIG]24034[/ATTACH]

I also put the pointer on the frequency of interest so the distortion numbers at the bottom show the data difference at the frequency where the problem was.

Hi Jim,
is the high 3rd order distortion between 1.2-2.2 kHz detectable in listening?

[jim1961]

Hi Jim,
is the high 3rd order distortion between 1.2-2.2 kHz detectable in listening?

No. I suppose you would have to take it away to be sure. It is over 50db down, so I am not worried about it.