Primus 360 Mod

[Alex2507]

This is like my thesis from the Computer Class thread.

Trim rings removed. T20 Torx screws.

Mid range wires disconnected at crossover. They are fixed in the non removable housing within the cabinet.

Bottom of stock cabinet. Completely undamped.

Ready for glue. I ran a light stream at can/basket connection and on the outer edge of the can where it resembles the top of a tuna can. Lots of dry time needed. Glue reapplied to make sure any chance of rattling was removed.

1" duct liner installed on back, top and bottom. Lining is toward the inside of the cabinet. Another layer was placed on top of this layer with linning toward the cabinet walls (not shown in pic)

Formaldahyde free thermal insulation adhered with 3M 77 spray adhesive. Pre cut veil like fabric ready to go in.

Mid range housing stuffed with insulation. Fabric installed. A 4"x6" piece of double sided adhesive rubber roofing membrane was used the adhere the fabric to the underside of the midrange housing. Crossover installed with 2-1/2" coarse threaded drywall screws. Stock damping material rubber banded to port as insulation filter.

Echo effect was reduced when speaking into a driver-less cabinet. Placing my ear to the top and sides of cabinet while playing music made me think that less sound was comming through the cabinet.

The real objective was to get the magnetic shields glued up. Everything else is a temporary measure. I figured it couldn't hurt and I was sick of stock piling insulation products in my utility closet.

TIP: Lubricate the grill pegs.

The feet were removed. The speaker was placed on a contraption I thought might decouple it from a resonant floor. I made it with rubber vibration isolators on the top and bottom of some lumber core ply sandwiching some gum like stuff tin knockers use. The only thing I had to pay for was the Super Glue.

Edit: The titles and descriptions didn't make it from Photobucket.

 

[jamie2112]

I get it, I just don't understand why people are buying these speakers just to do your own mods on them. Why hasn't Infinity done this themselves? Good job by the way there Alex......

 

[mike c]

are your changes audible?

i assume (from the pics) you only did one speaker ... can you A/B the damped and undamped speaker?

thanks in advance

btw, if you need an edit to your first post ... let me know.

 

[Matt34]

I get it, I just don't understand why people are buying these speakers just to do your own mods on them. Why hasn't Infinity done this themselves? Good job by the way there Alex......

I think it boils down to the cost involved in constructing a properly braced and resonance free cabinet.

These particular speakers can be found at Frys occasionally for $99/ea which is an absolute steal for what you get. This is backed up by 3rd party measurements that the drivers are of great quality but it still suffers from cabinet resonance like most commercial speakers do.

So for a little of your time and very little money you can lessen the mid-range coloration cause by the cabinets.

 

[Alex2507]

are your changes audible?

i assume (from the pics) you only did one speaker ... can you A/B the damped and undamped speaker?

thanks in advance

btw, if you need an edit to your first post ... let me know.

I did both speakers. I cut material for both at the same time to insure that they both got the same treatment. Then I installed that material in one speaker at a time. I had to get the project off the table. My girlfriend didn't like eating her meals standing up in the corner. Having 2 speakers spread out in 3 rooms of a small condo for a whole weekend isn't her idea of a good time. No time for A/B testing and what would I have thought that I was hearing? An improvement? I could hear the improvement before I took out the first screw. In my head anyways. I was going to put DeoxIT on the electrical connections but reached my 'enough already' point before I got to it.

Of course the changes are audible. After all that work, even if they were inaudible they would be audible to me.

 

[WmAx]

Just to help out; you should put about 5" of dense packed material on the bottom. This, coupled with the top boundary of the cabinet, acts as a relatively low frequency resonator. But if you cut off one of these ends, virtually, in an acoustic sense, it will no longer be able to resonate between these points. A high density fiber glass or fiber rock(rockwool) is needed, with minimum density of 3-4lbs/ft^3, to effectively kill this lower frequency resonance. If you only have low density material at the moment, you can use say, 8-9" of this on the bottom. But of course, be aware that you are going to lose some bass extension.


-Chris

 

[mike c]

please check if I edited your post correctly ...

 

[Alex2507]

please check if I edited your post correctly ...

Much appreciated.

 

[Alex2507]

Just to help out; you should put about 5" of dense packed material on the bottom. This, coupled with the top boundary of the cabinet, acts as a relatively low frequency resonator. But if you cut off one of these ends, virtually, in an acoustic sense, it will no longer be able to resonate between these points. A high density fiber glass or fiber rock(rockwool) is needed, with minimum density of 3-4lbs/ft^3, to effectively kill this lower frequency resonance. If you only have low density material at the moment, you can use say, 8-9" of this on the bottom. But of course, be aware that you are going to lose some bass extension.


-Chris

The time will come for me to do a couple of DIY subs to go under these speakers turned upside down. I'll have the speakers plane out with the top of the TV. Before that happens I have an in wall entertainment center to finish up to get all that stuff out of my living room. The point is that by then I'll have the rockwool for subs and speakers. That's when I plan to start cutting them open for further modifications.

The thing I like listening to is material crossed over at 80Hz. Unless I miss my guess the only bass affected by all that rockwool would have already been routed to the sub. I also read that the port tuning frequency is around 42Hz but I'm not sure how that would be affected by reducing the net volume of the cabinet with high density rockwool.

Thanks,
Alex

 

[Spkr_Bldr]

Just to help out; you should put about 5" of dense packed material on the bottom. This, coupled with the top boundary of the cabinet, acts as a relatively low frequency resonator. But if you cut off one of these ends, virtually, in an acoustic sense, it will no longer be able to resonate between these points. A high density fiber glass or fiber rock(rockwool) is needed, with minimum density of 3-4lbs/ft^3, to effectively kill this lower frequency resonance. If you only have low density material at the moment, you can use say, 8-9" of this on the bottom. But of course, be aware that you are going to lose some bass extension.


-Chris

Exactly, a speaker that height would have a standing wave from top to bottom right about 150-160 hz which is tough to kill. Owens Corning 705 would probably be the best material, but like Chris says you will loose not only some bass extension but overall output level. I'd guess that enough damping to kill that wave will drop overall woofer output by close to a full db.

And don't overdamp the midrange. It's hard to tell just how much you have in there from the pic, but it looks pretty well packed. The midrange chamber isn't going to need that much. I'd just line the walls and leave open space behind the midrange driver.

After it's all done, I'd expect the tweeter will sound a bit hotter due to slightly decreased output from the other drivers. You might need to add a padding resistor across the tweeter terminals to bring it back in balance. Although if you could post a big close-up shot of the tweeter network, both front and back side of the board, we could probably tell you what to replace ... assuming it does sound a bit bright.

 

[Alex2507]

Exactly, a speaker that height would have a standing wave from top to bottom right about 150-160 hz which is tough to kill. Owens Corning 705 would probably be the best material, but like Chris says you will loose not only some bass extension but overall output level. I'd guess that enough damping to kill that wave will drop overall woofer output by close to a full db.

And don't overdamp the midrange. It's hard to tell just how much you have in there from the pic, but it looks pretty well packed. The midrange chamber isn't going to need that much. I'd just line the walls and leave open space behind the midrange driver.

After it's all done, I'd expect the tweeter will sound a bit hotter due to slightly decreased output from the other drivers. You might need to add a padding resistor across the tweeter terminals to bring it back in balance. Although if you could post a big close-up shot of the tweeter network, both front and back side of the board, we could probably tell you what to replace ... assuming it does sound a bit bright.

I still don't understand why I would worry about bass extension when I cross it at 80Hz.

The insulation in the midrange chamber isn't really well packed. It's just really white. I just replaced what Infinity had in there (plus a little extra) with non compacted (fuffy) fiber glass.

I wouldn't know if it sounds bright really due to a lack of listening experience but some graphs I have seen and had explained to me suggest that due to a drop in impedance above 9kHz or so, most receivers are not going to make the tweeters blare. That coupled with the fact of the tweeter having a diminished off axis response doesn't allow for a lot of reflections to get to the listener (me ) either. Besides all that, if my girl sees me trying to remove a driver and crossover in the near future, it's not gonna matter whether they're bright or not. Not from the dog house.

 

[Spkr_Bldr]

I still don't understand why I would worry about bass extension when I cross it at 80Hz.

Because like I mentioned it's extension AND overall woofer output level. The woofers in a 360 run up to something like 350hz, so if they're attenuated over the whole range you will notice. Read this to understand more:

http://sound.westhost.com/articles/boxstuff.htm

The insulation in the midrange chamber isn't really well packed. It's just really white. I just replaced what Infinity had in there (plus a little extra) with non compacted (fuffy) fiber glass.

Well that's good. About all I'd suggest then is push it in a bit to give the mid room to breathe. Of course a cross brace from 1/2" wood dowel rod would be a nice addition too

I wouldn't know if it sounds bright really due to a lack of listening experience but some graphs I have seen and had explained to me suggest that due to a drop in impedance above 9kHz or so, most receivers are not going to make the tweeters blare. That coupled with the fact of the tweeter having a diminished off axis response doesn't allow for a lot of reflections to get to the listener (me ) either. Besides all that, if my girl sees me trying to remove a driver and crossover in the near future, it's not gonna matter whether they're bright or not. Not from the dog house.

Sounds like you're trying to convince yourself it won't be a problem, and it might not be. But don't assume it won't. That tweeter has a pretty normal off-axis behavior, you're getting plenty of reflections. But that's not the point - point is if the woofer output is attenuated 1db then your midrange and tweeter output will be 1db higher in relation. Of course that's a theoretical result, the actual result only you will know.

 

[Rickster71]

I had to get the project off the table. My girlfriend didn't like eating her meals standing up in the corner. Having 2 speakers spread out in 3 rooms of a small condo for a whole weekend isn't her idea of a good time.

Nice job Alex!

I got the same grief, have to put a DVD / VCR combo unit back together.
My wife uses to do her morning exercises.

I almost bought the same speakers a few weeks ago when they were on sale at Fry's for $99.
Just to experiment with, like you are.
The shipping was too much for the pair. (for some reason the shipping was less if I did two separate orders for single speakers, than if I'd ordered the pair)
By the time I realized it, the sale was over.

Rick

 

[Alex2507]

Nice job Alex!

I almost bought the same speakers a few weeks ago when they were on sale at Fry's for $99

The shipping was too much for the pair.

Thanks Rick. You mean nice job on the mod or figuring out how to post pics? Both?
(Elvis Voice) Well thank you, thank you very much.

I think most of us know who is to thank for the modification ideas. Anybody considering a Primus Mod should read this:

http://forums.audioholics.com/forums/showpost.php?p=332680&postcount=14

Here is a list of Harman Audio's completed eBay sales on individual P362 louspeakers. They are factory refurbs that come with a full warranty. I had a problem with an item once and they sent me a shipping label for the return.
It took time to sort it out but what's time to a pig? I just like saying that.
They have the speakers on and off (not now though). Usually they go for a little over $100 shipped.

http://completed.shop.ebay.com/items/__Infinity-P362-3Way-Dual-6-5-Floorstanding-Loud-Speaker_W0QQLHQ5fCompleteZ1QQ_nkwZInfinityQ20P362Q203WayQ20DualQ206Q2e5Q22Q20FloorstandingQ20LoudQ20SpeakerQQ_in_kwZ1QQ_scZ1QQ_sopZ15QQ_udhiZQQ_udloZ

mike c, Adam and MDS helped me get the pic posting business sorted out. They have created a monster.

 

[Spkr_Bldr]

Here is a list of Harman Audio's completed eBay sales on individual P362 louspeakers. They are factory refurbs that come with a full warranty. I had a problem with an item once and they sent me a shipping label for the return.
It took time to sort it out but what's time to a pig? I just like saying that.
They have the speakers on and off (not now though). Usually they go for a little over $100 shipped.

http://completed.shop.ebay.com/items/__Infinity-P362-3Way-Dual-6-5-Floorstanding-Loud-Speaker_W0QQLHQ5fCompleteZ1QQ_nkwZInfinityQ20P362Q203WayQ20DualQ206Q2e5Q22Q20FloorstandingQ20LoudQ20SpeakerQQ_in_kwZ1QQ_scZ1QQ_sopZ15QQ_udhiZQQ_udloZ

Those are good prices. I bought a damaged Beta 40 off Ebay awhile back just to test the drivers, and they're definately worth working with at those prices.

The drivers did well btw, with just some rising 3rd and 5th harmonics starting at about 800hz - 2000hz. I have a friend who can do Klippel testing, and it appears any issues are motor related. But that was the CMMD cone, I'd like to test some MMD drivers too.

 

[Alex2507]

I bought a damaged Beta 40.

Do you know of any 3rd party measurements done on the Beta series? I know it doesn't always mean better quality but those are the next series up. A pair of 50's use to go for around $500 I think but I'm not sure if the CMMD drivers measure out as nice as the MMD ones do. The cherry Beta's sure look nicer.

Here's a review on the 360's with a link to measurements at the bottom of the page:

http://www.stereophile.com/floorloudspeakers/605infinity/

 

[mike c]

no 3rd party measurement, but i did use my ears to A/B the 360 and the Beta 40.

the 40's sure sound a lot nicer. so i bought the 50's blind.

(as in, these ears of mine can barely hear differences between speakers, but i heard that one loud and clear)

 

[Alex2507]

so i bought the 50's

I take it the 50's are nicer than the 40's.

When I first joined AH I recognized the 50's in one of your threads with pic's and thought, "man I bet those sound nice, but what's he doing with all those subs?"

 

[mike c]

I take it the 50's are nicer than the 40's.

When I first joined AH I recognized the 50's in one of your threads with pic's and thought, "man I bet those sound nice, but what's he doing with all those subs?"

i wouldn't know. i'm not that picky with speakers.

i've never A/B'ed the 50's with anything.

 

[WmAx]

Exactly, a speaker that height would have a standing wave from top to bottom right about 150-160 hz which is tough to kill. Owens Corning 705 would probably be the best material, but like Chris says you will loose not only some bass extension but overall output level. I'd guess that enough damping to kill that wave will drop overall woofer output by close to a full db.

If the chamber was severely over-damped, the response drop, is not accurate to say, would be an overall flat drop, because that's what it almost sounds like with that wording. For the information of the OP, the drop would increase as you lowered in frequency if over-dampened. In effect, you can over-dampen(in extreme conditions) an enclosed speaker cabinet to have nearly identical response as an infinite baffle loaded speaker; that is, no effective resonant system would exist so far as the driver is concerned. With the 6.5" mid-bass speakers, this could primarily be a problem, due to the gradual slope having the potential to act as an inverse on the baffle step, causing lower output, especially, under this point, which would lead to subjectively 'thinner' sound.

Now, with the 4" mid in that Primus 360, I do have measured data for that unit, and with the particular xover point is uses, and it's T&S parameters, it should not have much impact at all, if it is over damped or lightly damped, so far as it's over-all amplitude level is concerned.

-Chris