Ok, time for something sacrilegious (maybe)

FestYboy

So.... I was thinking last night (dangerous I know), but bigger is better sometimes, and everyone loves the 7s and 10s, why not bump it up a notch? I started researching potential drivers and think I found suitable 8s and a 15 passive...

I told you this was a dangerous thought.

The drive behind this was clean SPL ala the SRT discussion for my HT setup. Since Polk doesn't make the SRT and getting a set is near impossible or stupendously expensive why not dream up a good compromise?

I'll likely be banned for this.

codycatalist

You want to remake the Monitor line with 8 inch active and 15 inch passive drivers?

FestYboy

Dang Cody, I didn't even get to finish writing the first post and you're all over it. Lol

But yes, that's the idea. I come from a live sound background and 8" mid woofers are small in that world but very large in HT or Hi-Fi.

codycatalist

FestYboy wrote: »

Dang Cody, I didn't even get to finish writing the first post and you're all over it. Lol

But yes, that's the idea. I come from a live sound background and 8" mid woofers are small in that world but very large in HT or Hi-Fi.

8 inch drivers are great in my opinion but how are you tying them into the Monitor line? Gut the cab? Use the crossover and tweets?

Intrigued by how you want to pull it off.

tonyb

Buy a different speaker, by the time you modify the cabinets, rework the crossovers to accommodate the new drivers, your crossing your fingers on if you'll like the outcome.

F1nut

Wrong cabinet volume. Like Tony said, buy a different speaker.

[Deleted User]

or learn and experiment.
Then, buy a different speaker.

FestYboy

Haha, no I think you have the wrong impression. I mean to make a new cabinet to house the new drivers. I'm well aware that the 10a box is way too small to work with a pair of 8s, let alone fit them. Think 10a x 1.5. Everything is bigger to accommodate the larger drivers.

Conradicles

Do it and post pictures and results. Great idea if you do it right.

FestYboy

I'm hoping the same thing. The only thing I haven't decided on is which tweeter, and where/how to mount it. Could go 10A, or 12b with it...

Ideas?

mhardy6647

Do you (the OP) understand how passive radiators "work"? They are surrogate bass reflex (Helmholtz resonator) ports -- the important variable is the moving mass of the PR. Actually, I've gotta admit, I am not at all sure how the size (diameter) of the PR figures into its characteristics (if at all)!

https://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture3 /ho_helmholtz/ho_helmholtz.html

This being said, there are a couple of differences in the LF performance of a PR-loaded vs. bass reflex box:



I am not knocking the concept, although I guess I'd strongly encourage the OP, if he (or she) hasn't heard the Polk Audio Monitor series 5,7, 10 and 11 and/or 12, try to listen to 'em all and decide where the "sweet spot" is in terms of overall sound quality (performance).

I can say that, for me, it's not the biggest one(s)

xschop

I can 2nd what Mhardy says as I prefer the 5B over the 7B specifically in the upper bass lower midrange. The 5Bs sound more accurate to me.

Will you try and keep all Polk brand drivers?

For lobing remedy, look to the Monitor 11 crossover design. IMO Polk should have kept this crossover in the Monitor 10s

I'll be watching this/your progress and commend the initiative.

FestYboy

Mhardy, the OP (he/me) happens to own all of the above listed, plus 5JRs.
The PR I'm looking at comes with the ability to tune with added mass. And the volume of air displaced by the active drivers comes into play as well as the mass. Changing the mass moves the natural resonant frequency of the PR.

Xschop, I'm not aware of an appropriate Polk driver in 8" to sit this potential build.

tonyp063

Fest,
Correct me if I am wrong, but you are looking to do a polk-esque speaker using non-polk components you will source.
And you are planning on doing a copy of the basic polk design( tweet, mid/bass, passive) in a cabinet you will design/source elsewhere.

You are not taking an existing Polk speaker & modifying it with those components.

If true; interesting.

If false; good luck.

FestYboy

Correct, seeing as Polk doesn't make any components in the size and style I'm postulating, I'll need to source elsewhere. Think of it as an homage to a classic, only larger.

Now if I could source Polk components in those sizes and they had complimenting sonic qualities, I think I'd likely go that direction.

For now, it's still in the rough planning stages. Need to figure box dimensions, and design a XO, build both and then fiddle with EVERYTHING so it MIGHT sound OK. Then duplicate another one.

Easy!

Nightfall

Passive radiators aren't exclusive to Polk though. Call it a Fest Audio build.

pkquat

This might be better suited for the DIY section.

IMO you really need to find a pre-designed or specified MW / PR combo that also includes recommended cabinet dimensions. Then find a tweeter to work with the crossover frequency of the MW. There may be better software today and translations from ported recommendations to PR recommendations. As I recall there was a bit of a black art to PR's.

Porting is often used because it is easier for the home builder. Their are some basic formulas for porting, and easier methods to tune the port. Aside from the port dimensions, box design, even for the same volume, can still have a significant effect on the sound. Bracing and baffles can play a big part in the final sound as well.

I've heard two similar sized ported cabinets that used the similar, or maybe the same, 8" peerless MW. One was quite flat, tight, deep, and rich. The other had better "thump" but was not near as deep or tight. It was a little boomy, had a peak, and somewhat of that ported bong sound. Both were stand alone bass boxes with different separate mid/high pass combinations.

Parts express has some pre-designed speaker combos, plans, and kits. I think that would be a good start. There was a speaker design bible a ~30 years ago with some great information, tips, and tricks. There maybe better ones now, along with new design software.

[Deleted User]

Or just buy a pair of B&W speakers that have multiple 8's in them and be done with it.

VSAT88

Lol, doubt you will get banned but I would not try this with your money and tools. No not me. But keep in mind that I am old and have not attempted a speaker cabinet built an over 30 years. I hope you luck though and it would be cool if you did this and it came out good for you !

FestYboy

Unfortunately, the two suggestions above (Slapaho and pkquat) defeat the purpose of the build...

My goal here is to recreate the look and "feel" of a Polk monitor 7, 10, or 12, only on a larger scale. Admittedly, as you move up the series, the maths involved get a bit more complex, but I'm treating this as a learning experience.

And also as suggested above, this should probably be moved to the DIY/build section.

lawdogg

mhardy6647 wrote: »

Actually, I've gotta admit, I am not at all sure how the size (diameter) of the PR figures into its characteristics (if at all)!

Do you think it could affect the propensity of the radiator to be affected by the motive force? The resulting force of pressure applied over a surface is proportional to the area of the surface I think. P = F*a. Can we tie that relationship between into our knowledge of inertial mass to come up any deeper an understanding of how the PR works? Maybe if we know what acceleration we needed (resonant frequency?) it would help find the right diameter? All ears.

FestYboy

I'm thinking it (PR) may wind up being a half or quarter of the resonant frequency of the active driver(s), so that there is sympathy between them, and then build the box to suit the PRs tuning Rf??? I have more research to do.

pkquat

FestYboy wrote: »

My goal here is to recreate the look and "feel" of a Polk monitor 7, 10, or 12, only on a larger scale.

I hope "Sound" is included too, otherwise pair an 8" MW with a 10" passive for a larger M5, a 12" passive for a larger M7, and a 15" passive for the M12 and scale the boxes.

I am not trying to defeat the process, and I wish you success. You might just have a new product line.

I would check out the information and some of the builds done at https://www.parts-express.com/. For reference http://salksound.com/ uses some 8" MW and PR combos effectively, but they also incorporate a midrange because it is hard to get an 8" MW to cross over high enough and work well with a PR.

http://audiojudgement.com/passive-radiator-speaker-design/
has some really good info on the advantages and disadvantages of PR's, of which crossover design and speaker specifications are discussed. It may be vey hard to find an 8" MW that will do everything. This is why many designs are ported.

This added info on the Polk 6.5" MW is very good. http://forum.polkaudio.com/discussion/comment/2107275/#Comment_2107275
(Spooky that the thread and comment numbers are the same)

Along with the rest of the thread.
http://forum.polkaudio.com/discussion/comment/2107275

FestYboy

Oh my yes! Sound is of the utmost importance, and I have a few tricks to achieve that. Otherwise what's the point of the build? Anyone could throw together what I've proposed and it would make noise, but that wouldn't pay proper homage to Mr Polk and his designs. If it can't sound right, then I won't build.

K_M

FestYboy wrote: »

Oh my yes! Sound is of the utmost importance, and I have a few tricks to achieve that. Otherwise what's the point of the build? Anyone could throw together what I've proposed and it would make noise, but that wouldn't pay proper homage to Mr Polk and his designs. If it can't sound right, then I won't build.

I would try joining "Parts express's" Tech talk forum. They specialize in DIY speakers, and designing Crossovers, cabinets and have access to many hundreds of driver parameters.

If you tell them you are trying to "Emulate" a vintage Polk Speaker from the 1980's, you may get several questioning you as to why, but just tell them what you are wanting to do, and Passive Radiators are important to you, and you will get several offering to help.

FestYboy

Yes, been a member for 2 years. And you're correct, I should inquire about passive integration over there for this type of build.