Wrong size foam causing muffled woofer?

[CosmoK]

I just recapped and refoamed a pair of Yamaha NS-690 II. The tweeters and mid sound great. The woofers seem weak and I suspect the foam doesn't fit right.

I bought the foam from a prominent vendor and it was about 1/2" too wide to fit in the frame. I triple checked my order, but then figured that the vendor new best. When I glued the foam to the frame I pushed it in to fit, which caused it to bubble/wrinkle around the frame, so I kept applying pressure playing whack-a-mole until the glue got tacky enough to hold it flat. In the end, I think shoving the foam into the smaller diameter caused the foam between the frame and cone to bulge outward, pull the cone forward, and make the surround stiffer.

The problem: The woofer sounds like there's a blanket over it. It's quiet and unimpressive. The surround seems very stiff, even outside the sealed cabinet.

(1) I centered the cone using a 30 Hz signal. The cone is not rubbing and the woofer is not distorted.

(2) The cabinet has a tight seal.

(3) Both woofers sound identical and the magnets look okay, although I'm not sure what a shifted magnet would look like.

(4) I took pictures of all the connections before I started and triple checked that they are the same, so I can't see how I could have the switched the polarity.

(5) The woofers are original and the look just like every other NS-690 II woofer on the internet.

(6) The foam I used has an outer diameter of 11.75", while another vendor sells one with a diameter of 11.1".

Question: Could the wrong size foam make the woofer sound bad? Has anyone else experienced something this?

 

[kwayde]

I checked three of the vendors on that auction site who are selling these surrounds. Two say that an eighth of an inch may have to be trimmed from the surrounds depending on which frame size the woofer has. The other vendor, which is the most expensive of the group doesn't explain this possibility. I'm thinking you have the smaller diameter frame that would require trimming the surrounds before placement. Your drivers may be restricted from moving their full excursion.

As far as experiencing this, I haven't. I've most always found the correct size to use. The only time I didn't use a surround that wasn't made for the driver was when there were no surrounds being made, and after taking precise measurements I was able to find a surround that fit nearly perfectly, and it sounded great. Had to search dozens of surrounds to match the correct measurements

 

[BillyTheKid]

Id first check the rest of the speaker over, see if a mistake was made anyplace else or if something changed. After that, try refoaming with the right size. You shouldn't have to struggle to get the foam in place.

 

[CosmoK]

Thanks for your input. I didn't realize these woofer frames could have two different frame sizes. I just assumed the business selling surrounds for the NS-690 II knew they would work, and would tell me something critical like that they might need to be trimmed. Now I know to measure and check the dimensions before ordering... model numbers are unreliable.

This gives me some confidence that if I go through the work to cut the surround off and re-install better fitting ones the sound may improve. You are correct that they woofer is not moving through its full range freely.

 

[CosmoK]

Id first check the rest of the speaker over, see if a mistake was made anyplace else or if something changed. After that, try refoaming with the right size. You shouldn't have to struggle to get the foam in place.

Will do. I don't love refoaming, so I will try to avoid that if possible. But, the surrounds really feel off.

 

[goodolpg]

As I read the original post I was thinking that the surrounds probably should have had some trimming done before gluing. And that may be the issue.

But just in case, maybe this might help someone in the future.
Are the woofers wired correctly?
Drivers wired out of polarity can cause weakness in the bass.
Admittedly this is a long shot...it seems to happen more often with speakers that have dual woofers.
But it has happened with single woofers as well.

 

[CosmoK]

As I read the original post I was thinking that the surrounds probably should have had some trimming done before gluing. And that may be the issue.

But just in case, maybe this might help someone in the future.
Are the woofers wired correctly?
Drivers wired out of polarity can cause weakness in the bass.
Admittedly this is a long shot...it seems to happen more often with speakers that have dual woofers.
But it has happened with single woofers as well.

I'll switch the wires before cutting the surrounds off. That would be an easier fix.

 

[CosmoK]

The vendor is sending me a smaller surround. I will install it next week and report back. The vendor recommended asking questions before gluing in the future. After some thought, it's hard to blame the vendor for not knowing/documenting every variation of every speaker. I think there is a lesson here:

Model numbers are an unreliable way to identify the parts you need. Many models underwent production changes or have inaccurate documentation. Measure and trust your eyes when something doesn't fit.

Of course, I already know this about working on amps: capacitors are often different from what's listed in the service manual and their polarity is sometimes wrong on the silk screen.

 

[sKiZo]

One size fits none, right? ;-}

I got "exact replacement" surrounds from Orange County for my trusty old McIntosh big boxes and did the refoam myself. Real decent results, except ...

Had a coil go open on one woof a bit later, and I figured to leave that to the local pros. Brought both in to the shop for the work, and first thing counter guy says was ... nice job ... too bad those are the wrong surrounds! The profile was limiting cone travel. Short version - Had both done right, and gained a good octave down low as tested in REW with a calibrated mike.

PS - I'd done the lower mids at the same time and those tested out right.

One oft overlooked step - ALWAYS measure the side profile! Providing the width and height of the domed section as well as the OD and ID can save you a lot of grief. Also allow break in time before getting too concerned - it can take a while for the foam to loosen up.

** Blatant plug for Circuit Shop. Dependable work and my first stop for speaker repair. Doesn't hurt they're local for me.

https://circuitshop.com/

 

[CosmoK]

The new surround arrived with a 11.1" outer diameter. This diameter was sufficient to glue to the frame, but did not cover the entire frame surface. The re-re-foamed speakers sound great now. While I had the speaker apart, I also triple checked the cross-over wiring (all looked good).

I can confirm the vendor's glue is strong, as it was a pain in the neck scraping off the wrong size foam.

If I had to do it again, I would buy the larger foam and trim the outer diameter. This is the recommended action in some of the instructions on the auction-site. I also recommend looking at a variety of vendors to identify the small variations in foam sizes and see what matches your speaker best.

Thanks for all the help with my foam questions.

 

[CosmoK]

Just a general follow up on the NS-690 II.

(1) These Gold Binding Post Banana Jack 5-Way Speaker Terminals are a drop-in replacements for the original spring terminals. They look very similar to an auction item that is much more expensive. The actual replacement was slightly complicated because I had to take the entire cross-over out to replace the internal wires to the terminals, which were thin and short.

(2) I recapped the cross-overs with Dayton Audio Polypropylene capacitors ($47 before tax):
2.5 uF => DMPC-2.7 2.7uF 250V (standing on end, jumper wire for far lead)
3.5 uF => DMPC-2.0 2.0uF 250V + DMPC-1.5 1.5uF 250V (laying down on the board, using the holes where the jumper wires used to be connected)
18 uF => DMPC-18 18uF 250V (standing on end, jumper wire for far lead)
33 uF => DMPC-33 33uF 250V (put under clamp and zip-tied closed, jumper wire for far lead)

Notes: The crossover fits very tightly into the speaker cabinet, so when you're done nothing can hang off the side more than about 1/8".
I also found that by clipping only one or two wires, I could lift the PCB off the black frame far enough to solder all the necessary connections.

 

[CosmoK]

Lastly, the sound:

Setup: Schitt Modi DAC, with Tandberg Tr-2075 (80 wpc), and 6" speaker stands with a slight tilt to point the tweeters at my ears.

The sound was sensitive to speaker placement, I ended up with a little extra toe so that the axes cross about 3 ft in front of my chair, which is about 12 ft from speakers. In some configurations there were very clear nodes in the bass (standing waves).

Impression after a couple of weeks: I don't really hear the speakers, just the music. They're just very detailed with low tight bass. The bass depends on the source: quiet and thin in some songs and it rattles the floor in others. These speakers make me crave HiFi recordings. I've heard ADS L810s and JBL 4312s recently, both have more prominent bass than the 690s and sound especially good with rock. I prefer with the NS-690 IIs for their accuracy, which is a good thing, because the ADS and JBL owners aren't interested in trading!

 

[goodolpg]

Thanks for the follow up.
Enjoy the music!