North Creek Borealis Problem

Tim K

Member
2001-10-26 10:01 pm
I'm new here, but I'm hoping someone can help. I recently purchased and built a pair of North Creek's Borealis speakers. I built them per the manufacturer's instructions with the exception that I used MDF for the internal braces instead of plywood.

The problem I have is that the speakers seem to "ring" my ears on some vocal passages, and also on brass instruments. The sensation is like my eardrums being excited at their resonant frequency. On some music, the vocals are very forward. This occurs at moderate to high volume levels. It makes them almost unlistenable at anything but low volumes.

These units now have over 100 hours on them, so I'm thinking that whatever break in is required for Scan Speak drivers should be complete. I have tried 4 different CD players, 2 amps, and have bypassed the pre-amp and gone directly from the cd to the amp. The room is quite large with a vaulted ceiling. There is carpeting on the floor and lots of upholstered furniture. I have fooled with all the different combinations of position of the speaker and listener I can think of. The speakers are on stands about 15" tall, angled back 3 degrees. At North Creek's suggestion, the speakers are screwed to the stands and the stands are spiked to the floor.

I'm really hoping I didn't waste $800. Any suggestions?

Thanks!

Tim
 
How well damped is the inside of the cabinet? The tweeter could be giving off an ringing sound due to box resonances. Only other non-crossover related thing I can think of would be room resonances, but as you said, they were well damped. Are there any glass tables/shelves in your room? I had an incredibly annoying ringing sensation at an earlier point in time, and it proved to a cluster of glass mugs. Have you e-mailed North Creek regarding this problem yet?
 
Those speakers have reputation for sounding quite good. If the cabinets and XO's were assembled and wired correctly the difference in bracing materials is insignificant

Do you have a Radio Shack SPL meter? If you do and can send a audio signal from your computer to the 'stereo', download the Swift Sound NCH tone generator program and do a sinewave 'sweep'. Look for peaks in the FR response. Then contact North Creek.

Something else to consider is if the new speakers have less distortion than the ones you were using before, you might be running them at higher SPL's and not realize it. That could certainly cause the issue you describe
 
I have heard the Borealis and they did not exhibit any "ringing" and the midrange where vocals reside was lively and detailed but very smooth.

Have you double checked your crossover wiring, especially the large inductor? That may be where the problem lies.

George Short of North Creek should be your first resource to solve these problems, I have dealt with him and he is a class act.


Tony D.
 

Tim K

Member
2001-10-26 10:01 pm
I have checked with North Creek, and poor George has given up on me. He helped as much as he could from a distance, but was unable to solve the problem.

Super, the inside of the boxes are very well damped. North Creek specifies an interesting mixture of a soft glue and drywall mud that you slather around the inside of the box. There are no glass or other hard surfaces in the immediate vicinity, but I will definitely look around again. The actual fronts of the boxes are very smooth and hard. I have considerable experience generating high gloss black finishes, and I used that experience on the front panels. Any possibility of that being a problem?

Thomas, I think a buddy has the SPL meter you describe. I'll try what you suggest. I was also wondering about your second comment, and you could possibly be right, but for a different reason than you mention. I sold a pair of ancient Magneplanars to buy this kit. I think distortion was probably low, but the sound from that style of speaker is so different from what comes out of these that my ears may just need re-calibrating.

Tony, wiring was George's first suspicion. I haven't checked yet, in part because I was pretty compulsive when I hooked them up, and also because the drivers have adhered themselves to the gasket and I can't seem to get them out. Since I can't identify any other problems, I think I need to check that next.

Thanks to you all for the input.

Tim
 

Tim K

Member
2001-10-26 10:01 pm
I'm trying to get set up to do the frequency sweep, but in the meantime, I have been doing some more listening.

What I have discovered is that the problem seems to be isolated to the upper registers of the male voice. It doesn't seem to matter who the performer is, when they sing towards the top of their range, I get the resonating sensation.

This seems like a possible crossover problem. Any thoughts?

Tim
 

ThomasW

Member
2001-10-19 4:53 am
5280'
Does the problem change with different room placement/sound source/cables/etc?

If you're eliminated all the other variables, then it may be that the 'voicing' of the North Creek design isn't suited to your liking. Moving the XO point up or down slightly might solve the problem; but would require rebuilding the XO. And there are no guarantees.

Another idea (but not a good one IMO) is if you can isolate the frequency, a minor notch filter could be used. Experimenting with this it would be easiest if you had a parametric EQ.
 

Tim K

Member
2001-10-26 10:01 pm
Thomas,

I've experimented with almost every combination of equipment I can think of, even going to the point of borrowing a CD player from a local Hi-Fi shop. I haven't fooled with cables, but this effect is so significant that I have a hard time believing it could be cable induced.

I have moved them around in the general area quite a lot, but I have not completely relocated them in the room. I have tried lots of different listener positions. I can try lugging them downstairs and hooking them up to my home theatre set up. That change should be complete, different source, amplification, cable, and room. Good suggestion.

George at North Creek had this to say this AM.
"It occurred to me that perhaps something in your system reverses absolute phase and that may effect the bias on the capacitors. If that is the case, it is just a matter of playing time before the bias goes to neutral, but it
will be a lot of playing time - perhaps 300 hours."

I don't know what biasing a capacitor means, (I'm an ME, not an EE)but this seems like a possibility. I'm just going to let the system run as George suggests.

Tim
 
Dear Tim;

Yes George is a class act. I had some problems as well, but found that tweaking with some resistors will do the trick. If the xover is functioing correctly, then all you will need to do is to bring the tweeter in line with the midbass. Its really a 4 dollar "fix". I used some TRW resistors to do this, and if you wana know more, send me an email at [email protected] and I can give you full details. Trust me, I went nuts and this helped sooooo much on the North Creeks,I have several sets of them.
 
Tim K said:
What I have discovered is that the problem seems to be isolated to the upper registers of the male voice. It doesn't seem to matter who the performer is, when they sing towards the top of their range, I get the resonating sensation.

This seems like a possible crossover problem. Any thoughts?

Tim,

What does the crossover topology look like? That driver has a natural rise in the 500-1kHz range. There really should be an RLC in there to tame it, but I know some designers choose not to. Is there any kind of RLC notch in the woofer circuit? If not, Bingo there is your problem. If there is, you may be able to adjust it with a single resistor value.

John
 
i built a 8546-9900 MTM using just my ears and many hours of listening. i also faced this issue.

points to ponder assumed you've covered wiring, potted the caps and inductors with silicone, etc):

1> Q of the tweeter crossover preferably under 0.7
2> XO freq for the woofer preferably under 2000.
3> if you have a resistor in parallel with the tweeter (as part fo a L pad) keep the value of this resistor above 16 ohms.

If North creek allows you to post your XO design it might help the more senior memeber here.
 
George designs for a flat baffle step compensated response, and usually uses a low crossover point. He has excellent descriptions on his web page:
http://www.northcreekmusic.com/NorthCreekKits.html

There are good reasons why the old BBC dip will sweeten up (reduce harshness) the sound, see here for example:
http://www.linkwitzlab.com/models.htm#H

People want to run their electronics flat, then often purchase flat speakers meaning that levels will have to be very high, to move up the Equal Level Loudness contours or Fletcher Munsen curves.
http://www.webervst.com/fm.htm
You'll hear many speak of how important flat frequency response is in a speaker, yet if you don't listen at the same levels as the original event (few home systems can come close to even an acousitc event) there is no way it is going to sound accurate. It's no wonder that subjectivists tend to select speakers with non flat frequency response, they're probably correcting for the difference in listening level. Many rave about ProAc speakers. I've never heard them by the way just offering them as an example of non flat response, see figures 3 and 4:
http://stereophile.com/loudspeakerr...297/index6.html
I'm not saying this much compensation is the way to go, but many prefer the sound of ProAcs, they're probably easier to listen to/more engaging at a lower listening level.

I've been wanting to have a listen to the Borealis or Rhythm, and also the Madisound Thor, but have not yet had the chance, their on my list.

Pete B.