machine screws for hurricane or t-nuts for vintage S series speakers?

printboy

Can anyone recommend which fastener would be best to secure the drivers? The issue is with the screws originally used on this model.

Polk used a totally different screw which has a flat and smaller diameter head than the screws used on the Monitor series. The three screws used to secure SL5000 tweeter recess into the tweeter flange holes and I assume using a hex cap in conjunction with one of these nuts is not recommended as the cap head will extend above the flange and create defraction issues?

Also the MW7000 woofer rubber surround extends to the edges of the driver, unlike the MW 6500, and it appears that the original screws recess into the rubber surround holes to secure the driver to the baffle. Again, a hex cap is probably not be a good choice here either as it will deform the rubber.

Appreciate any thoughts or recommendations on the subject. Thanks.

Gardenstater

The larger head size is superior because it distributes the force over a larger area of the basket flange and there is less chance of deformation. If the head of the screw will bear down on the rubber surround at all you can just take a pointed blade in an exacto knife and trim a little away for the head to clear it, or use a sharpened piece of thin walled brass or steel tubing and a twisting motion. I wouldn't use a hammer or drill with your makeshift tubing drill bit because of the disastrous possibility of human error

I've never heard of anyone bothering with hurricane or T-nuts for the tweeters. There isn't much danger of resonance at the tweeter frequencies and all you need is a cabinet seal there, really. Not a lot of torque should be applied to those screws.

printboy

Thanks Gardestater for your suggestions. Never thought of trimming the rubber. Of the many posts I have read on the subject I assumed that H or T nuts were used on tweeters a well. Just saved me some money.

F1nut

Never use T-nuts.

You use Hurricane nuts with the tweeters in order to use machine screws instead of wood screws, which were never the best idea to use in particleboard or MDF.

printboy

Thanks F1. I thought one could use H nuts on tweeters.

I know H nuts are superior but I just mentioned T nuts in case I coudnt use H nuts with the appropriate sized machine screw head to recess into the tweeter flange holes.

Anyone have any suggestion as to what size machine screw I may need? Here is a picture with the S series screw on the right. I find the sizing of machine screws very confusing.

Gardenstater

I'm not familiar with the drivers in the S Series speakers but you are saying that screw on the right is what Polk used with both the tweeters and the midbass drivers? It looks like a coarse thread drywall screw. It has a bugle head which is what you have on a drywall screw so that it doesn't break through the paper. I could see using that on a plastic tweeter flange if it had a similar shape molded into the plastic but I can't see using that screw with a metal basket frame on a midbass driver. Coarse thread screws are less likely to strip out in particle board. A greater pitch on a wood screw makes it harder to get as much torque on the screw and it doesn't have as much clamping power and also may be more likely to self loosen, but again less likely to ever strip out.

F1nut

printboy wrote: »

Thanks F1. I thought one could use H nuts on tweeters.

I know H nuts are superior but I just mentioned T nuts in case I coudnt use H nuts with the appropriate sized machine screw head to recess into the tweeter flange holes.

Anyone have any suggestion as to what size machine screw I may need? Here is a picture with the S series screw on the right. I find the sizing of machine screws very confusing.

The machine screw thread pattern will be dictated by the thread pattern of the Hurricane nut.

Gardenstater

printboy wrote: »

Thanks F1. I thought one could use H nuts on tweeters.

I know H nuts are superior but I just mentioned T nuts in case I coudnt use H nuts with the appropriate sized machine screw head to recess into the tweeter flange holes.

Anyone have any suggestion as to what size machine screw I may need? Here is a picture with the S series screw on the right. I find the sizing of machine screws very confusing.

Well the way I would do it would be to measure the diameter of the holes molded into the plastic tweeter flanges. You can measure a hole by using various sizes of drill bits until you find the one that is a slip fit. If you know the size of the drill bit you can look up the appropriate size of machine screw in a chart of machine screw sizes. They are in # sizes and each # corresponds to a certain decimal inch size. You also need to get one that has the appropriately shaped and sized head. The reason you wouldn't use a T-nut is really because the little tangs that are supposed to penetrate a soft wood are way too large and long to work with something as dense as particle board or MDF. I have used them in the past before I knew about hurricane nuts, by grinding down the little tangs so that they are much smaller and able to penetrate and still be large enough to keep the T-nut from slipping, especially with a little bit of epoxy applied.

I still don't see the need for machine screws on the tweeters due to the lack of need for torque or clamping power. Another reason for machine screws would be if you were going to repeatedly and frequently disassemble and re-assemble.

printboy

Thanks guys.

Yes the S series screw does appear to look like a dry wall screw. S/LS series brochure even has a photo of the screw and says they were custom made for these speakers. Marketing!

Great idea Gardenstater... why didnt I think of using a drill bit as gauge? A 7/32 drill bit just fits the holes in the tweeter flange with a tiny bit of room. OK will see if I can find the appropriate machine screw for H nuts.

Much appreciate all your input.

xschop

I used an 8-32 countersunk on my last set SL5000s I installed. Just had t use a countersink bit. Be vvvvvery careful on that plastic.