Modding the Primus series speakers

[Alex2507]

In most cases, you are correct. However, some low cost pre-built speakers, though rare, have superb quality drivers and good crossovers, but are held back by very poor cabinetry systems. One such example is the Primus 360. It has a superb driver set and an excellent crossover. On and off axis response is superbly linear. Energy decay of the drivers is superb. The cabinet, however, is a pile of horse doodoo. Like most cabinets, the thing is resonant, and if that is not enough, it does not even use acosutic dampening material internally that is sufficient to absorb reflections/standing waves in the bandwidth of relevance. You could go so far as to put lesser quality drivers in a high quality cabinet, and end up with higher quality sound as compared to higher quality drivers in a low quality cabinet. The cabinet has that much influence. Ideally, the cabinet should have no influence(be neutral/inert) overall, but that is not the case with the vast majority of speaker systems, and that includes high cost 'audiophile' speakers.

-Chris

At the risk of souding dumb I'm going to ask about your thoughts on beefing up an enclosure form the outside. Lets say with a layer of 1/2" rubber contact cemented on like a formica job and then 3/4" MDF with a veneer and hardwood nosing.

I am interested that list of speakers you said had good drivers and weak enclosures. I own a pair of Primus 250's. I think I'd like to get a pair of the 360's and mod both pairs of them, and your thoughts on a nice center would be?

All righty then, I feel like maybe I'm hijacking a thread.

 

[jagxtype]

At the risk of souding dumb I'm going to ask about your thoughts on beefing up an enclosure form the outside. Lets say with a layer of 1/2" rubber contact cemented on like a formica job and then 3/4" MDF with a veneer and hardwood nosing.

I am interested that list of speakers you said had good drivers and weak enclosures. I own a pair of Primus 250's. I think I'd like to get a pair of the 360's and mod both pairs of them, and your thoughts on a nice center would be?

All righty then, I feel like maybe I'm hijacking a thread.

Your alright, good questions in relation to my thread.

But i would think that it would be useless to mod from the outside other than make it sturdier. The sound deadening material wouldn't be ver sound deadending if there was a layer of wood on the inside to still resonate. Just my opinion though.

 

[Alex2507]

I was thinking about using the insulation and bracing on the inside.

 

[jagxtype]

I was thinking about using the insulation and bracing on the inside.

Im not so sure if there is such a thing as overkill in the speaker enclosure world, but i am thinking this would be excessive for such a speaker.

 

[Alex2507]

Im not so sure if there is such a thing as overkill in the speaker enclosure world, but i am thinking this would be excessive for such a speaker.

All I can think of is rivaling $6000 pair of speakers for around a grand. I feel like I could come up with a grand and maybe spend less time here to offset the effort of actually doing this project.

 

[jagxtype]

I highly doubt that it would cost a grand. The project seems like a challenging one.

I was wondering, do you put this insulation on the front (speaker deck) of the enclosure too (on the inside of course)? If so, how would it be secured or whatnot. Would it be hard to make the openings arouns the speakers? Also, in a tower speaker, how is one to gain access to the lower half of the box? It seems like a rather tedious project.

Also, i am confused about the mineral board. At one point you say it comes in shrink wrapped packs. Is this stuff compressable? Does it come 2" thick or do you have to layer it? It makes me nervous to think i might ruin these speakers.

 

[WmAx]

Further along in that thread a suggestion is made for an active x-over, amp and subs all totaling in the $1000 range. A claim is made that the SQ would rival speakers in the $6000/pair range. That's all the reason I need to mod speakers.

With very specific low cost speakers, it can be done, with the right modifications. But do not underestimate the time you will have to invest. It will take more than just a few hours to do it right.

-Chris

 

[jagxtype]

thats why i am asking so many questions. It looks like a tedious project to pull off.

 

[WmAx]

At the risk of souding dumb I'm going to ask about your thoughts on beefing up an enclosure form the outside. Lets say with a layer of 1/2" rubber contact cemented on like a formica job and then 3/4" MDF with a veneer and hardwood nosing.

I am interested that list of speakers you said had good drivers and weak enclosures. I own a pair of Primus 250's. I think I'd like to get a pair of the 360's and mod both pairs of them, and your thoughts on a nice center would be?

All righty then, I feel like maybe I'm hijacking a thread.

While your above idea would virtually remove all external cabinet resonance if done correctly -- it is not as simple as one would like to think. A regular rubber would not work -- it will couple the enclosures. You will have to use a low durometer soft rubber in small blocks for key support areas; or use a highly durable 1/2" sheet of latex foam between the channels. In addition, you have to keep air breaches from occurring from this trapped channel out to the external air. For example, you have to keep the external cabinet from having direct physical coupling with the internal one around the driver mount with no air breach. This would require attaching the driver to the internal cabinet. Then having about a 1/3"-1/2" gap between the internal cabinet and external one around the driver, and then filling this gap with a very soft silicone caulking to prevent air breach. Now, there is one last issue: if the internal cabinet is still highly resonant, it may still produce substantial amplitude internally to radiate out from the driver.

-Chris

 

[WmAx]

I highly doubt that it would cost a grand. The project seems like a challenging one.

It would cost at least a grand to do it right. Remember, as part of the process, you have to use stereo subs and pass all LF to the subs, and have access to an active crossover to split the signal correctly. Ideally, you should use a powerful DSP unit such as a Behringer DCX2496, which would allow you to have far greater control over perceived sound quality relative to personal preference(s), as well as provide a means of bass correction in the room. The 1k estimate would presume lower quality subwoofers, as well. You would have to up this budget to include high quality subwoofers, preferably in DIY kit form(as to maximize value/minimize cost).

I was wondering, do you put this insulation on the front (speaker deck) of the enclosure too (on the inside of course)? If so, how would it be secured or whatnot. Would it be hard to make the openings arouns the speakers? Also, in a tower speaker, how is one to gain access to the lower half of the box? It seems like a rather tedious project.

To do this right, one really has to do what I referred to as Level 2 modification. This requires removal of the rear cabinet wall and removal of all internal bracing. I outlined how to do this in the post that has been linked in this thread already. Level 1 modification will yield improvement, but not to the level that you seem to want. Level 1 is the easy modification that can be done in a couple of hours.

Also, i am confused about the mineral board. At one point you say it comes in shrink wrapped packs. Is this stuff compressable? Does it come 2" thick or do you have to layer it? It makes me nervous to think i might ruin these speakers.

You can not compress the #8 mineral board. It is rather dense. It comes in 2" thick pieces that are 24" W x 48" H. A pack of them is usually a count of 6, that comes shrink wrapped as a single bundle.

-Chris

 

[WmAx]

thats why i am asking so many questions. It looks like a tedious project to pull off.

I will gladly answer any questions in detail if you decide to do it in order to help you execute the modification successfully.

-Chris

 

[jagxtype]

i appreciate it. I just posted elsewhere on my intentions.

 

[Alex2507]

With very specific low cost speakers, it can be done, with the right modifications. But do not underestimate the time you will have to invest. It will take more than just a few hours to do it right.

-Chris

Anything I do takes forever. I like my stuff to look good.

While your above idea would virtually remove all external cabinet resonance if done correctly -- it is not as simple as one would like to think. A regular rubber would not work -- it will couple the enclosures. You will have to use a low durometer soft rubber in small blocks for key support areas; or use a highly durable 1/2" sheet of latex foam between the channels. In addition, you have to keep air breaches from occurring from this trapped channel out to the external air. For example, you have to keep the external cabinet from having direct physical coupling with the internal one around the driver mount with no air breach. This would require attaching the driver to the internal cabinet. Then having about a 1/3"-1/2" gap between the internal cabinet and external one around the driver, and then filling this gap with a very soft silicone caulking to prevent air breach. Now, there is one last issue: if the internal cabinet is still highly resonant, it may still produce substantial amplitude internally to radiate out from the driver.

-Chris

Okay, sounds like this just modifying it the way you suggested is 1. enough of a chore and 2. produces good results. Thanks a bunch.

 

[jlohl]

Back to the topic of primus 360 mods, has Wmax finished his work ?
And what are the results before/after ?

I'm asking this because I also have Primus 360. I did some tests with RplusD and here is the average of 24 measurements around listener place. I did many others but this one shows what I'd like to speak about. It shows some response peaks around 400Hz, 700Hz, 1.25kHz, 4.2kHz (some of these also appear on Stereophile measurements)
Just would like to know if anybody has got same peaks measured.
Maybe the 1.25 and 4kHz are due to diffraction.
Wmax uses a DCX2496, did he EQ something on his Primus ?

 

[jliedeka]

Chris, do you know if the Primus 162 is a good candidate for this treatment? I would actually consider just saving the baffle and building new cabinets. I would make them deeper to preserve the internal volume. Does that sound workable?

Jim

 

[WmAx]

Back to the topic of primus 360 mods, has Wmax finished his work ?
And what are the results before/after ?

I should clear this up: I do not have a Primus 360. I was responding to another user on possible ways to modify them, or build new non-resonant cabinets of certain types.

Now, it just does happen, that I am currently doing an extensive re-engineering of a Primus 362 for someone right now, but it's far more than just a modification. It involves new drivers, new crossover, extensive cabinet modification and a new external finish.

-Chris

 

[WmAx]

Chris, do you know if the Primus 162 is a good candidate for this treatment? I would actually consider just saving the baffle and building new cabinets. I would make them deeper to preserve the internal volume. Does that sound workable?

Jim

Not with the stock crossover, IMO. The Primus 162's crossover and driver integration is not nearly as good as the one designed for the 362 or 152 and the response characteristics are much worse, overall. Also, even with a new crossover, I can't really recommend it for far field use, because it's off axis response is not that good. But if you were using near-field or semi-nearfield(like 4-5' distance maximum) and not near side walls, then the off axis response would not be a big deal.

I did use a Primus 160 for a near field application, but this involved not only extensive re-design of the internal part of the cabinet, but a new crossover.

-Chris

 

[jliedeka]

What about the 152? They sell for $80 apiece which would be a great deal for decent drivers and a crossover. I'd be using it in a small to medium sized room about 8 feet from where I sit.

Jim

 

[WmAx]

What about the 152? They sell for $80 apiece which would be a great deal for decent drivers and a crossover. I'd be using it in a small to medium sized room about 8 feet from where I sit.

Jim

The 152 would be worth modifying. However, you would need to use it with 2 high quality matching subwoofers, one near each mid-treble module, if you are to have seamless bass extension. This will require a proper active crossover, also. Optimum crossover frequency is about 100Hz with the Primus 150/152 if ideal dynamic range is to be had, in order to keep the Primus 5" from have excessive movement which would result in substantially increased non-linear distortion. The Behringer DCX2496 is the crossover that I recommend to make all of this come together perfectly. You can fine factory refurbished ones for as low as $200 shipped.

-Chris

 

[WmAx]

Johl, I thought you would want to see the following image files. This is the diagram showing the Primus 362 mods I am currently doing:

Here are some images of the actual modification in progress. The rough cut out made quickly with a router, as seen on the inner wall where the plywood is clamped, on the last image, is just for clearance of the huge subwoofer frame, and this entire back will be covered in another sheet of material. The plywood is to give a strong and secure medium to screw into to hold the W7 woofer, as I don't want to leave support only up to some 0.75" MDF, which is to be the back material.

http://www.linaeum.com/productinfo/other/infinity_primus362_ultra/01.jpg
http://www.linaeum.com/productinfo/other/infinity_primus362_ultra/03.jpg
http://www.linaeum.com/productinfo/other/infinity_primus362_ultra/05.jpg
http://www.linaeum.com/productinfo/other/infinity_primus362_ultra/07.jpg
http://www.linaeum.com/productinfo/other/infinity_primus362_ultra/09.jpg
http://www.linaeum.com/productinfo/other/infinity_primus362_ultra/10.jpg

It must be stated that this is not a regular modification. In fact, this is a complete re-working of the system. Besides extreme cabinet modifications, the unit is getting a new tweeter (Fountek ribbon tweeter will be used) and an extraordinary 8" woofer is being installed(8" JL W7). The system will be a full active 4 way system. Off axis response will be superior to most monopolar speakers by a considereable degree. The cabinet is getting a real wood veneer as a last step.

-Chris