Monitor 10B Redesign...

goldcrown4

Hello all... I'm new to this thread, but not new to Polk Audio Monitor 10B's. I've owned a pair since 1986 and don't really think I'll ever 'part' with them... at least in a manner of speaking anyway.

I'm interested in redesigning the bookshelf cabinets to a modern tower design. I've thought about buying a used pair of Mon 10's off of Ebay and using those drivers in their new configuration but haven't quite got started yet. I figured I'd ask forum members first what they think of this:

1. Maintain same internal air volume
2. Consider T-M-M, or M-T-M layout for tweeter and mid-bass drivers
3. Passive radiator mounted on the side.

It's as simple as that. Basically, the cabinet depth would have to be deep enough to support adequately mounting a 10 inch passive radiator. Another option would be to simply port the cabinet, but I'd rather use all the original components.

My main concerns are:

1. Which layout would be ideal without doing specific driver testing? TMM or MTM?
2. Would the existing crossover be adequate or require modification?

Has anyone ever tried to do something like this with Polks or any other existing above average speaker? I have no way to test the drivers, determine their existing frequency response curves on or off axis, etc. In fact, I need to obtain the original driver specs, especially the roll off frequencies. Does anyone have those?

heiney9

This is rarely a good idea unless you are EXTREMELY knowledgeable about building DIY speakers. Why take a perfectly good pair of working speakers and turn them into Franken-Polks? There are many sites with DIY kits you can build if you have a little understanding and want to experiment.

I've always wanted to do a DIY bookshelf, but with my very limited knowledge I always found it more feasible (monetarily and time-wise) to purchase from a well known company already assembled.

What you are proposing is basically the same as an RTA-8 or RTA-11 which would have been from that era and used the similiar drivers as the Monitor 10. You can get those on e-bay and audiogon much cheaper than DIY.

FWIW

H9

goldcrown4

Heiney9... If it doesn't work out, I can always put the drivers back in their original cabinets. I don't want to do this necessarily to my existing Mon 10's because I want to be able to do A/B comparison tests. These would be listening-tests-only due to lack of test software and other equipment. You mentioned the RTA-8 and 11 series... I've never had opportunity to listen to those... now you got me curious about their cabinet dimensions.

One of the other design considerations has to do with safety around my toddler. Once he starts to go mobile, I have basically four options: 1. Anchor speakers to floor or wall without somehow adding audible resonating Hz...preferably in a tower configuration that doesn't require a stand; 2. Replace the Mon 10's with satellite drivers with bullet proof subwoofer disguised as furniture; 3. Put an impenetrable cage around each existing speaker; 4. Anchor existing Mon 10's.

None of these options present 100% toddlerproofing, but some get close. What bothers me most about the mon 10 cabinets is the sharp corners... they are eye gougers for a young'un, and sitting loosely atop the stands make them tipsy.

hoosier21

Get a pair of RTA 8's (or copy the design) same drivers with a front port, floor standers.

burdette

You can't "simply" substitute a port for a passive radiator. You'll need a complete redesign of the cabinet based on the parameters of the bass drivers involved, and a resulting port design. And for that you'll need the T/S parameters - which, I know, Polk will NOT give you (I've asked). If you have the means, you can measure the parameters first-hand (or have it done).

To duplicate the original design, yes, you'll have to keep the internal volume the same (including 'net' of bracing).

Theoretically, it shouldn't matter whether the PR is mounted on the front or the side. Sonically, however, I think it would depend a little on the tuning frequency of the PR - you're obviously going to dilute the front-firing output. I would THINK if the PR is tuned pretty high, you could get an audible difference in overall sound in that frequency region compared to the 10Bs.


If you're just wanting to experiment, I may have some components you might want to buy... I own the complete works from a pair of RT8s (no cabinets). I may want to hold on to the tweeters as backups for my Monitor 7Cs... email me if you want to discuss any of this. Otherwise, no big deal.

heiney9

I certainly understand your concern, but no speaker is toddler proof. You really have to know what you are doing if want to redesign something that's already an existing unit. If you have the knowledge, math skills, wood working/assembly skills, tools, time, etc. go for it. But if you don't have all these skills I will say it won't turn out to sound good even in the slightest. Building speakers that sound good (especially as good as Polks) takes alot of knowledge and money (for good parts and wood for enclosures/baffles/terminals etc.). Sure you could get by with cheap cabinets and cheaper drivers, but they'll never sound like Monitor 10's.

I seriously checked into buying a kit and assembling it myself. When all was said and done I would have had $1200 in cabinets, drivers and accessories. I could buy 2-3 times the speaker with that kind of money compared to the ones I could have built. Sure it would have been cool as hell to say I built those speaks, but in the end it just wasn't worth it. This was a tried and true design, not just a "let's see what I can experiment with" type project.

If you think you can spend the time and money and have a thorough understanding, then go for it.

Just my .02 c

Here's the reference link to RTA-8t's

http://www.polkaudio.com/forums/showthread.php?t=30583&highlight=rta8t

H9

VR3

If you want to rebuild them - you need to rebuild them exactly the same...

I am in the process of rebuilding my mains (for fun) - anf i have about 60 measurements to follow... its not an easy task - measuring is by far the hardest part...

goldcrown4

(Interestingly, I just checked EBay and have already found passive radiators and 6.5 inch drivers... this project might be easier or cheaper than I thought.)

Burdette, thank you for your post... I never wanted to use a conventional port anyway... always liked the 10" PR. I'm not sure why I didn't consider the reduced "front-firing output" if positioned on the side... I guess I was thinking old school 'non-directive-in-nature bass...it is a radiator afterall, and not powered. It's amazing how much movement the PR's can make, and how low it can get. Remember an old Aldo Nova track "Fantasy"? with the helicopter in the beginning? If not, dig up that ol' speaker killer.

I hear ya about holding onto spare tweeters... I've destroyed a couple myself years ago, with Blue Oyster Cults, "Take me away", and Mannheim Steamroller's "Taccata". I have a better amp now. (NAD) I'll email you off line if I go forward with this design. I still have to price out the cabinet materials.

burdette

If you're interested, I have the following:

Four (4) 6510 drivers;
Two (2) SL2000 tweeters;
Two crossovers (including input terminal) from RTA8s. I also have the engineering drawing from Polk of the crossover network. The crossover was designed for two 6510s and an SL2000.
Two (2) port tubes that are pretty close to what the RTA8 used.

I used half of this equipment for a center channel speaker to use with my Monitor series mains and surrounds.

My original intent was to build cabinets and have another set of speakers to use. But (and I know this is sacrilege), I just don't need another pair of speakers.

goldcrown4

Heiny9 Many thanks for the link because I couldn't find pics of the RTA8T's elsewhere on the Polk website (found the RT8, but not RTA8). I've never seen or heard this model before... I'm interested to know how the ported version compares to the 10s' Passive Radiator during listening tests.

The 10's cabinets have an approx volume greater by 1572.75 cubic inches (5040 cu in minus 3467.25 cu in). *If* the RTA8T's were magnificent sounding (i need some feedback here on how they sonically compared to the 10's for soundstage, low end, separation, etc.), then basically, I'd be creating a cabinet that is simply deeper than the 8's, enough to facilitate the 10" PR, without exceeding the 10's 5040 cu inches (internal bracing will certainly be addressed). Then I'd have to buy or craft a sturdy stand with spikes, similar to those used for the RTi70 due to the dense Kuristan carpet they would stand on. Personally, I think the redesign will sound fabulous. Burdette made a good point about reduced bass because the PR would no longer be front firing, but that doesn't sway me from wanting to try this.

burdette

http://www.polkaudio.com/forums/showthread.php?t=11279

I don't know the actual specs.. but my guess is the 10Bs were tuned a little lower than the 8s. I'm sure Polk could tell you for sure.

Acutally.. the RTA8 specs are in the linked thread....

HBombToo

burdette wrote:

http://www.polkaudio.com/forums/showthread.php?t=11279

I don't know the actual specs.. but my guess is the 10Bs were tuned a little lower than the 8s. I'm sure Polk could tell you for sure.

Acutally.. the RTA8 specs are in the linked thread....

The 10B's definetly dig deeper and are a fantastic speaker.

heiney9

Disclaimer: I have no hands on with trying what you are proposing. All I have to go on is my many years selling audio, what I’ve read here on CP (from very knowledgeable folks) and several thousand articles over the past 10-15 years.

From a pure speaker designers POV the Monitor 10 is a bit flawed. It’s not very customary or ideal to design a speaker that has mid-bass drivers in a side by side configuration. The main problem is a blurred soundstage and general muddiness of mid-range frequencies. Simply, the radiating patterns from the drivers overlap at several freq and thus are not ideal. I’ve said it before, Polk got away with this design as it was probably the most popular selling speakers of the 80’s. Does it give acceptable sound, absolutely!! Is it ideal, not really. The Monitor 7’s and even the (Monitor 5’s) are a much more coherent sounding speaker.

That being said you will face some challenges in redesigning a speaker using the components from a Monitor 10. Mainly the 10” passive absolutely needs to be mounted forward as the “fluid coupling” from the mid-bass drivers will most definitely suffer (a lot IMO) if you mount it sideways. So the front baffle is going to be as large as the original M10 as I don’t think it can be mounted in a smaller baffle. So you aren’t saving any space there, and believe me the smaller the front baffle the better a speaker will sound when you consider it should (must, IMO) be a MTM design using a TRUE D’Appolito array with the parts you have.(more on the D’Appolito array later).

So if the front baffle is the same dimension (width wise) and you mentioned wanting to make the cabinet deeper, also for the MTM design it should be taller. By my estimations your internal volume has just increased by a pretty substantial amount. What now? The type of enclosure the drivers and x-overs were designed for has changed. Also you need to see if you can use the M10 x-over since the mid-drivers won’t be side by side anymore. IMO, Polk probably had to do work some magic on the M10 x-over to get it to sound good, maybe not. If you have the knowledge to compensate then that’s great, move forward.

The RTA8 and RTA11 and RTA15 all use what’s called an MTM design (mid-tweeter-mid). The best design of an MTM config. is called a D’Appolito array. In a true D’Appolito array the top and bottom mid’s are crossed over at exactly the same frequency the benefit of this is explained in the following definition:


D'Appolito
A loudspeaker configuration developed by and named for Joe D'Appolito, in which a high frequency driver, or tweeter, is positioned between two midrange or low frequency drivers that each cover the same frequency range. Depending on the exact implementation the speakers can be positioned with a vertical and/or horizontal orientation. In either case the two midrange drivers serve a couple of purposes: they combine to create a larger effective woofer or midrange driver size, and they also serve to control the dispersion of the tweeter. The tweeter's output is somewhat corralled or contained by the sound coming from the midrange drivers in a similar way to how two parallel surfaces control dispersion. There are some variations on the design where two same sized woofer/midrange drivers may cover slightly different frequency ranges, however those aren't considered true D'Appolito designs. (Input from an inSync Reader:) The D'Appolito design specifies a third order crossover network. �The tweeter is coordinated with the woofer so that at the selected crossover frequency, the drivers all have similar horizontal dispersion. �(This is not easily accomplished because many drivers behave badly at the extremes of their range.) The advantage of doing it all correctly is one of the most seamless blending of drivers possible. �The result is an absence of any sudden change in directivity with frequency. �This may not mean much for monitors where there is a limited listening area, but in a typical room where a large percentage of the sound is reflected by the room, the effect is dramatic.

So if you don’t have a proper x-over for a true D’appolito array then you are presented with another challenge. Again if you have specific knowledge to overcome this then move forward.

This is the difficulty I was speaking of about doing it CORRECTLY. You could scrape the tall monitor MTM design and do something similar to a Polk Monitor 7, but you’d have to build/buy the correct x-over. The x-over out of the M10 won’t work unless it’s modified. Basically the M7 is the M10 minus the 2nd mid-woofer. But IMO, your original intent was too make it toddler proof and there really isn’t much diff between the M7 and M10 size wise. If you can pull it off the M7 does sound noticeably better than the M10.

You could certainly try to build the RTA8’s but by the time you get the correct parts and build the cabinets, you could buy a used pair and have much $$$ left in your pocket.

Sorry for the long post---hope this helps.

H9

heiney9

HBombToo wrote:

The 10B's definetly dig deeper and are a fantastic speaker.

Ever owned a properly set-up pair of RTA-8's? They are superior in many ways to the M10. The side-by-side mids is really what limits the M10's sound. Don't get me wrong the M10's sound good, the RTA's are superior in many ways. I've owned both the M10's and RTA11 and there is no comparison. IMHO .

H9

HBombToo

heiney9 wrote:

Ever owned a properly set-up pair of RTA-8's? They are superior in many ways to the M10. The side-by-side mids is really what limits the M10's sound. Don't get me wrong the M10's sound good, the RTA's are superior in many ways. I've owned both the M10's and RTA11 and there is no comparison. IMHO .

H9

I have a pair of RTA8T's in the Bomb shelter and a pair of RTA15TL's and they are both absolutely amazing. The 8T's were my first pair of "real" speakers I purchased back in ~1990. Spent a lot of time in front of 10's and they are very impressive but as you suggest... I also prefer the RTA line.

HBomb

goldcrown4

A couple of comments... first, many-many thanks to all the posts regarding this design concept. I know technical posts can take a lot of time, so thank you for yours.

Second, regarding the bass response of the 8's... the difference in the low Hz response isn't that much on paper, and in fact, most adults only feel the 20-45 Hz range rather than hear it. What I'd really like to do, is audition a pair of 8's if anyone around the Greenville SC area has them. That will help me decide if the difference in the low end is audibly significant enough to thwart me, but from reading the posts, no one has anything negative to say about the 8's. HBomb said the 10's "definitely dig deeper", so that means it is audible enough for him to remember and comment on.

I would be really interested to contrast & compare the actual crossovers (more so for the mids on up)... the low Hz cutoff is obviously different than the 10's, but what about the mids and highs?

I just don't think there would be a drastically signficant difference in the overall listening experience with the two design concepts. Transparency, coherency, accuracy, etc. would agreeably be theoretically better with the 8's, but I sure would like to do an A/B comparison with all my favorite tracks. I need to get my garage cleaned up for shop duty.

heiney9

goldcrown4 wrote:

A couple of comments... first, many-many thanks to all the posts regarding this design concept. I know technical posts can take a lot of time, so thank you for yours.

Second, regarding the bass response of the 8's... the difference in the low Hz response isn't that much on paper, and in fact, most adults only feel the 20-45 Hz range rather than hear it. What I'd really like to do, is audition a pair of 8's if anyone around the Greenville SC area has them. That will help me decide if the difference in the low end is audibly significant enough to thwart me, but from reading the posts, no one has anything negative to say about the 8's. HBomb said the 10's "definitely dig deeper", so that means it is audible enough for him to remember and comment on.

I would be really interested to contrast & compare the actual crossovers (more so for the mids on up)... the low Hz cutoff is obviously different than the 10's, but what about the mids and highs?

I just don't think there would be a drastically signficant difference in the overall listening experience with the two design concepts. Transparency, coherency, accuracy, etc. would agreeably be theoretically better with the 8's, but I sure would like to do an A/B comparison with all my favorite tracks. I need to get my garage cleaned up for shop duty.

First off, gald we could be of help. Second, your current approach seems very logical about auditioning a pair if possible. Third, there really is a fairly significant difference in the design of the 2 (M10 vs. RTA8) and all the concepts you mention (coherency, transparency, accuracy, freq resp) the RTA8 (to my ears and many others) are the clear winner. The M10's are no slouch by any means, but the RTA8 is just a better approach.

One small negative to the RTA line is the sweet spot is pretty focused. They still sound very good off axis, but outside the sweet spot there is a noticeable collapse of soundstage. All the intsruments, vocals, bass is still there it just becomes less dimentional. The M10's don't suffer as much, but then again they never were able to acheive the same 3-d soundstage the RTA's could. Hope it makes sense and I'm trying real hard not to dump on the M10's as they are a very capable speaker.

Then go listen to a pair of SDA's and those blow the RTA's out of the water....maybe not clear out of the water, but the SDA's are much better, but again a completely diff design.

All there is to do now is get YOUR LISTEN on and decide for yourself.

H9

goldcrown4

I always thought the M10's had an unconventional design, but i couldn't dispute the sound my ears were hearing. I can only imagine how the Monitor 12's sounded to many back then. Too bad I never heard the MTM design of the RTA8's. Now I want to hear the 8's more than ever. If i had a pair of 8's, I'd still have to get a stable spiked platform/stand and even then, will have trouble keeping Luke from tipping them over onto himself. (We do have a spare leash however... it would conveniently connect to Luke's beltloop.)

I may still proceed with the design challenge anyway if nothing more than to satisfy my curiosity. I would certainly report on the results, and take some pics of the progress.

thanks again!

joelll

I have a pair of Monitor 12's (more often called RTA-12's around here), and I like the way they sound, side-by-side mid-bass drivers and all. The tweeter-on-top design works quite well, IMHO.

With regard to the toddler thing: a more solid pair of stands (bought or built) is probably a much better idea. If you get a pair of hollow metal stands and fill them with sand, then they'll be much more stable.

My dad has had a pair of AR3's sitting horizontal on one-foot wooden stands since before my siblings and I were born (I was born in 1966). We toddled around them, but never knocked them off the stands or anything. The grills are nearly impossible to remove for service, so there wasn't the issue of prying little fingers.

My younger sister now has four sons, the oldest is eight and the youngest is 18 months. I recently gave her a set of Ohm Model D's I found on the curb a while ago. No stands, they're just on the floor, and the grills were nailed on at the factory, so little fingers can't get into the drivers. She's very happy with the speakers, though I think they should eventually be on at least one-foot-high stands to get good sound.

I might suggest getting creative with some way to hold the grills on tight on stock M10's. It may not be practical to nail the grilles on, but if you're handy with sewing, get some 1.5-inch wide black elastic band at a fabric store, and sew it into loops that will stretch all the way around the speaker. This should keep the kidlet from pulling the grills off easily, without altering the cabinet. M10's are heavy enough such that if you put them onto a pair of sand-filled hollow metal stands that have a fairly large area of support to the speaker, they'll be very stable.

markmarc

Goldcrown:
I have thought the idea of converting 10B's to an mtm would be fun as well. I always thought of mounting the passive radiator in back. The keys would be to make sure you have a good tight seal when mounting the components.

I say go for it, as long as you keep the original cabinets, no harm no foul!

goldcrown4

thanks again for the posts...

re: toddler safety -- I may have to come up with a stand that is immovable when placed on top of precisely placed floor-mounted steel pins. (drivers can most always be replaced if dented, but I just don't want the speaker to fall over). The reason this approach is feasible for me is because there is only one wall my entertainment center can be on, and the M10's are on either side of it, away from the wall.

re: M10 cabinet redesign -- I did some rough calculations using the RTA-8's EXterior dimensions to get an idea of how much "extra" cabinet would be necessary, should I proceed, for side mounted PRs but otherwise using the MTM arrangement for the RTA-8's (without the port of course)... I came up with a depth change from the 8's 11.5 inches to 16.716 inches which is ~ equal to the externally measured volume of the M10's (5040 sq inches or 2.92 cu ft).

Volume = HWD
M10: 28.0 H x 15 W x 12.0 D = 5040.00 in sq
RTA8: 33.5 H x 9 W x 11.5 D = 3467.25 in sq

so, 33.5 x 9 x ___ = 5040
301.5 x = 5040
5040/301.5 = 16.7164 in.

Should the PR not be front mounted, Heiney9 reported "fluid-coupling from the mid-bass drivers will most definitely suffer" . I'm sure you're referring to the PR's effective ability to be moved by the mid-bass driver's compression, (whether or not it would move the same volume of air as when front mounted). I wonder if the 6.5's would handle less power in this configuration.

Hmmm... compression dynamics in a sealed enclosure... I'll think of it as this... the closer ones mouth is when blowing soap bubbles the more impact there is when you blow out the bubbles, whereas the farther away the pressure source is, the less impact there would be. But that isn't in an air tight environment. And since bass is, generally speaking, non-directive in nature, what impacts the audibility (i'm referring to it's dB and bass 'quality') of that theoretical relative same air movement would be close-by reflective objects like an entertainment center, or another wall, or my marble fireplace, and of course, one has to consider absorptive materials. Only one way to find all of this out I guess.

It makes me wonder about something else then too... whether or not a T-M-M configuration would be the choice here because at least then the mid-bass drivers would be physically closer to the PR should the compression be audibly that noticeable and the power handling characteristics significantly changed, but now I feel like I'm REALLY 'experimenting'. But!... ya got to wonder.

This would of course open another can of 'dispersion' worms... and may only be better than M-T-M if it had a waveguide??? I'm not prepared in the least to toy with this concept, but an old friend of mine has experimented with waveguided domes (http://www.zaphaudio.com/Waveguidetmm.html) which is well documented as are many of his other projects.

If the RTA-8's 6.5 in drivers are crossed exactly the same, and, assuming the M10s mid-bass drivers are crossed over the same, I wonder how their crossover Hz compare. Does anyone knows what those Hi and Lo Hz are?

heiney9

I say knock yourself out, but again to do this correctly, better yet, to get even remotely satisfactory results you need to have some knowledge.

There maybe other speaker builders on here that may dispute my opinion of NOT mounting the PR sideways. I've never seen a design like that and still feel it will not work as the drivers should be on the same plane as the PR. The driver arrangement is like that for a reason. If you can come up with a preceding design to follow then go for it. Active drivers can be monted sideways, but that's a completely different animal because they don't need to interact with other drivers.

Going with the MTM design is going to be manditory(if using the RTA8T x-overs; most likely the M10 x-over is the same type as well) unless you plan to completely re-work/scrap the current x-over. Even in the D'Apolitto array (MTM) the drivers must be mounted in a very exacting way. The center of each mid have to be exactly equi-distant from the center of the tweeter. There is a formula for this so as to minimize destructive interference.

A T-M-M is a totally different animal and has all sort of issues to overcome. The biggest concern is destructive interference between the two low frequency drivers. Lobing error issues (desc. as: the dispersion of treble sounds from a different vertical axis than the mid and low frequencies). Phase displacement issues ( desc. as: if the same frequency is propagated by two separate sources, the signals will be superimposed on each other. Depending on the timing of the oscillations, the amplitudes will either add to each other or cancel each other out. This is called phase displacement. At 0° phase displacement, the waves complement each other and at 180° they cancel each other out. Any other combination is possible in between). Time alignment errors will most likely be great (desc as: frequencies on the same axis reaching the listening position at slightly different time intervals).

M-T-M can have some of these same issues but by careful placement of drivers and proper x-over characteristics they can be minimized. Same goes for T-M-M, but you'd have to build and test a proper x-over to get it to work and that will take much time, knowledge and effort.

Again if you are just going to mount some drivers and experiment, go for it. But I think the results will be much less than satisfactory. Seems like an awful lot of time and effort to just experiment w/o atleast having some knowledge about what the outcome should/will be. When dealing with large enclosures, mutliple drivers, and PR's it tends to complicate things far beyond a simple 2-way ported bookshelf speaker.

I'm trying to be helpful and not a negtive Nancy, but then maybe you are much more adventurous than I am.

Good luck

H9

P.s. Hopefully some speaker builders will chime in on this. Maybe post this link in the DIY forum simply asking for opinions. My guess is this is uncharted territory by the lack of many responses.

heiney9

Goldcrown,
Here's a link that might be of interest. A low cost fairly easy MTM bookshelf design that is explained pretty well. You already have the drivers and a possible x-over that would work. This would allow you to forget about the PR and it's related complications. These could easily be put on stands filled w/ shot or sand and be made very sturdy for the toddler.

http://www.speakerbuilder.net/web_files/Projects/D3/dayton3.htm

H9

joelll

Epicure made the EPI 500, which had a tweeter, midrange and 10" woofer on the front of each speaker, and two 12" passive radiators on the sides. I don't know how they sound, though, because they were expensive then, and hard to find now. More information at http://www.humanspeakers.com

Flash21

I'm not sure I agree that the passive has to be on front...I think this is true in the existing 10B configuration, but for a tower with vertically stacked midbass drivers I suspect it will be preferable if the passive is placed at the same height vertically as the midbass drivers so that the impulses inside the cabinet arrive at the passive simultaneously. Could get crowded, depending on how deep the cabinet is.

I suspect you will not have enough cabinet volume to work with to make a true floorstanding tower. Of course, a small stand could do the trick.

It would be interesting to see how the vertically stacked configuration affects imaging...most of the imaging information comes from the tweeter, though.

burdette

There are plenty of examples of passive radiators located on the sides and even backs of cabinets from very popular speaker manufacturers - including Polk. The smallest SDA speaker.. is it the CRS or CRS+? Anyway.. single tweeter and two 6.5 inchers on front, 10" PR on the back.

The movement of the electrical driver(s) changes the pressure inside the cabinet, which moves the PR. I don't quite understand what the concern is regarding the location of the PR assuming the cabinet is an open space inside containing both the powered driver(s) and the PR.

The concern I expressed was about the output volume. A PR facing rearward MIGHT produce a lower perceived output towards the front of the speaker at certain frequencies. But whether it is noticable.. ?? Afterall... PRs extend bass response.. and you can design a sub with a front-firing.. or side-firing.. or down-firing driver.

I've done a LOT of reading and research on subwoofer and bass driver enclosure design. I admit I have NOT done a lot of reading specifically on PRs in NON-subwoofer applications. But based on what I do know, and the physics involved - I'm not saying there can't be a problem, I just don't know what it would be..and it can't be a universal problem because there are a lot of marketed speakers with PRs on the side and back.

goldcrown4

Burdette... there is a concept called "baffle step compensation" that is an issue with my plan, but, though I don't have specific details and math to show, the only concern would be the width the front baffle. Specifically I was told "the baffle step compensation differences could be too different between the old and new cabinets."

It has been recommended that because of this unknown, that I do not use a narrow, slim-line MTM configuration because of this issue, rather, add a couple of inches. Because part of the plan is to mirror 2 of the 3 dimensions of the RTA-8T, I asked that particular designer if the RTA-8T's already had sufficient width at 9 inches but i've had no response. I think the RTA-8Ts width will be just right. I'm not exactly sure how high up from the bottom of the cabinet I should mount the PR, but it might be best if mounted midway between the bottom and the lower mid-bass driver. I don't really know one way or another what would be best when dealing with Hz that low.

Something I'm still researching is trying to find the crossover freqs for both the RTA-8's and the Mon 10s to find out if both designs had the same hz for each of their respective mid-bass drivers. I'm sure the low pass hz are different when compared to the two designs (one ported and one PR), but what about those two midbass units?

Will Polk give me the schematic for their crossovers?

burdette

goldcrown4 wrote:

Will Polk give me the schematic for their crossovers?

They gave me the schematic for the RTA8. However, they would NOT give me the T/S paremeters of the 6510 drivers, and without those you can't completely analyze the circuit.

duaneage

burdette wrote:

They gave me the schematic for the RTA8. However, they would NOT give me the T/S paremeters of the 6510 drivers, and without those you can't completely analyze the circuit.

You say they won't give you the T/S parameters? Who cares, just measure the drivers yourself. It's not that hard really.

Audax made the 6510 anyway. Polk probably can't give out TS because the specs are covered under an NDA and all that. The 6510 is a high qts midbass that worked well in a REALLY big cabinet that used a 10 inch PR instead of a vent.


That being said you will face some challenges in redesigning a speaker using the components from a Monitor 10. Mainly the 10” passive absolutely needs to be mounted forward as the “fluid coupling” from the mid-bass drivers will most definitely suffer (a lot IMO) if you mount it sideways.


"Fluid Couping" is marketing BS for a PR. There is no fluid and there is no coupling. Just so everyone knows, a port or PR can be front, back, or side. It does not matter since LF waves are so big they travel out in waves. anyway. As long as the port or PR is not blocked against a wall it does not matter.

This is rarely a good idea unless you are EXTREMELY knowledgeable about building DIY speakers.

Not true really. Trying new things is better than feeling it is a waste of time. I happen to be EXTREMELY knowledgeable about building speakers and have a few dozens projects behind me already. Not all of them turned out well and others were truly great. Discouraging tinkerers leaves us with the same old bowl of spaghetti instead of something new. I can understand your point of not wanting to fail at redesigning the M10 but so what? Drivers are available used and it's not like your trashing anything.

My redesign will be finished in a few weeks. I will test an original M10 for response, impedance, dispersion, etc alongside an MTM design and see how it goes. If anybody needs TS on the 6510 drivers I can provide that as well.

duaneage

Oh, another thing... Crossovers can be analyzed with equipment like o-scopes for phase and pass capabilites without caring what the TS parameters of the drivers are. Looking at the current and voltage phase relationships tells you more than calculating the values. In the end a RTA analysis of the speaker's output is the only real test that matters.

heiney9

Hey guys......don't forget your WHITE LAB COATS :rolleyes: