Monitor 70 subwoofer crossover frequencies

wboffthelake

Hello all. Does anyone know what frequency the bottom two "subwoofer" drivers crossover to the top two "woofer/mid" drivers on the Monitor 70? Also, as I'm unsure regarding the exact crossover design, do the top two woofer/mids produce all of the bass frequencies, or just the frequencies at and above the subwoofer crossover? I sent an e-mail to Polk customer service asking this question but they did not respond.

I am new to HT and just bought the M70s, CS2, M30 surrounds and a Pioneer VSX-919AH-k receiver. I have an ED A2 300 on the way and would like to know the above information for when I calibrate my HT when the sub arrives.

One other thing, the website says the M70 is a 2 1/2 way design. This doesn't seem to make any sense, as the subs crossover to the mid/woofers, which in turn crossover to the tweeter, and you have the cascade tapered design, wouldn't that make it a 3 1/2 way?

Thanks.

cnh

I'm not sure on this one myself because the Polk stats are indistinct listing just ONE crossover at 2.6Khz. My understanding is that the upper two (one?) midwoofs are coupled with the tweeter in a different manner than the way the bottom 2 speakers are crossed over. But there is an overlap between the 4 drivers? They all play some common range of the frequency continuum?

Do get back to us when Polk responds. They WILL respond to your email it takes a few days some time but they are good about it!

In the meantime does anyone else know?

cnh

wutadumsn23

No clue here either, bur I would also like to know the answer to this question since I own the 70's as well. Be intresting to find out the answer, to a very intresting question, and welcome to Club Polk wb.

wboffthelake

It has been several days so I resubmitted my question, in a more detailed fashion where I also asked, with respect to the cascade-tapered array, at and above what midrange frequency is only the upper midrange is sent to the top driver. I'll let you know when they respond.

The M70 crossover really seems like quite a complex design. There has been a big debate over M70 vs Tsi500. Where the M70 has this complex crossover, the Tsi500 is clearly a straight 2-way design without the cascade-tapered array. Since the TSi500 has 4 6.5" drivers producing midrange, I can see it being a strong HT speaker, with the M70 being more musical, although I wouldn't know for sure because I have never heard the Tsi500. I'm am quite puzzled though as to how, according to the specs, the Tsi500 goes 2Hz lower than the M70, as each of it's drivers are producing a wide frequency range (28Hz-2.5Khz) while the M70 has two dedicated low frequency subwoofer drivers. Given the use of subs and it's crossover configuration, it seems to me the M70 has more in common with something between an Rti A7 and A9 than it does the Tsi500.

I'll post again when I get Polk's response.

rru2s

I'm interested in the response, too, although not sophisticated enough to do a good job evaluating how to build my own speakers and crossovers. I googled cascade crossover speakers and read a bunch of articles written by DIY companies and other speaker company design professionals. I'll guess the high pass of the first crossover goes to the tweeter, and the "cascade" means that the low pass of the first crossover is sent to the second crossover, so the midrange 6.5 inch speakers see a low end rolloff output of the first crossover at 2.6K, while the other two 6.5 inch bass drivers in the m70 experience a steeper rolloff curve at 2.6K compared to the midrange speakers, but with roughly the same starting frequency for the cutoff. It would great to be able to simultaneously visualize the 3 divided component outputs (tweeter, midrange, and low end) in an overlayed graph showing speaker decibel response across the frequency spectrum.

cnh

wboffthelake wrote: »

It has been several days so I resubmitted my question, in a more detailed fashion where I also asked, with respect to the cascade-tapered array, at and above what midrange frequency is only the upper midrange is sent to the top driver. I'll let you know when they respond.

The M70 crossover really seems like quite a complex design. There has been a big debate over M70 vs Tsi500. Where the M70 has this complex crossover, the Tsi500 is clearly a straight 2-way design without the cascade-tapered array. Since the TSi500 has 4 6.5" drivers producing midrange, I can see it being a strong HT speaker, with the M70 being more musical, although I wouldn't know for sure because I have never heard the Tsi500. I'm am quite puzzled though as to how, according to the specs, the Tsi500 goes 2Hz lower than the M70, as each of it's drivers are producing a wide frequency range (28Hz-2.5Khz) while the M70 has two dedicated low frequency subwoofer drivers. Given the use of subs and it's crossover configuration, it seems to me the M70 has more in common with something between an Rti A7 and A9 than it does the Tsi500.

I'll post again when I get Polk's response.

I agree completely and have written pretty much the same thing in a number of other posts. But without confirmation...it has always been guesswork. Do tell us when you find out.

cnh

cnh

rru2s wrote: »

I'm interested in the response, too, although not sophisticated enough to do a good job evaluating how to build my own speakers and crossovers. I googled cascade crossover speakers and read a bunch of articles written by DIY companies and other speaker company design professionals. I'll guess the high pass of the first crossover goes to the tweeter, and the "cascade" means that the low pass of the first crossover is sent to the second crossover, so the midrange 6.5 inch speakers see a low end rolloff output of the first crossover at 2.6K, while the other two 6.5 inch bass drivers in the m70 experience a steeper rolloff curve at 2.6K compared to the midrange speakers, but with roughly the same starting frequency for the cutoff. It would great to be able to simultaneously visualize the 3 divided component outputs (tweeter, midrange, and low end) in an overlayed graph showing speaker decibel response across the frequency spectrum.

That also sounds like a possibility--or at least a good guess. Let's see what Polk says!

cnh

wboffthelake

It's been two weeks and no response to either of my e-mails.

I originally e-mailed the questions to Polk because this involved multiple interrelated technical questions that I felt would best be answered if the questions were submitted in a clearly written form, since a technical person would probably need to be consulted before a phone representative could answer the questions, meaning they would probably have to "get back" to me anyway if I called.

I'll try and call them next week, but their phone support is only available during standard business hours, the time when most everyone is at work. Because of this, it seems reasonable to assume that their e-mail support would be quite responsive, as it allows their customers to submit a question at any time. Given this, the fact that two of my e-mails have gone unanswered is unacceptable.

wboffthelake

One other thing, according to this webpage:

http://www.polkaudio.com/education/tech_article.php?id=23

"multi driver LSi, RTi towers, Monitor towers, TSi towers and high end CSi models use "Cascade Tapered Array" crossovers"

The 2008 Lsi and Rti catalogs mention Cascade Tapered Arrays, but the Tsi catalog does not mention it anywhere. Seems strange.

So, I guess the question is, does she or doesn't she?:D

I'd e-mail Polk about it, but we know what that would get me.

wboffthelake

I was finally able to contact Polk via phone (again, their hours coincide with most business hours, making this difficult). As I suspected, they are getting back to me because the rep didn't know the answer. Also, when I told the rep about my sending two messages to them asking this question via their website, he told me they answer all questions submitted and "sometimes they (the answers) just end up in cyberspace somewhere." Lame answer. Lame answer.

cnh

That's really surprising. I've never had more than a week wait for an email response from Polk?

I wonder if something happens...summer hours?....vacations..etc...

It does sound like you're making 'some' progress with dogged determination.

Let's hope they get back to you sooner..

cnh

dnoyeB

Nice. This is the exact set of questions I am looking to have answered. I guess that means Polk plans to keep this under the vest...

slammin86

I would like to know this also. I can tell the upper mid seems to be the only one that puts out the higher midbass frequencies.

MentalNomad

I've seen the crossover diagram on these (and I own them), I'll see if I can turn that up again... but basically, it's a 2 1/2 - way design because:

The first split in the crossover has a traditional 2-way design; highs pass to the tweeter, and lows pass to the bass side.

On the bass side, the full signal goes through two woofers (these produce all bass and mids), and the signal goes through a low-pass filter and into the last two woofers (so these two produce bass only.)

So all four woofer produce very low bass, but only two of them produce mids.

Hence 2 1/2 way:
one way: tweeters doing highs
second way: two woofers doing lows
last bit: two more woofers doing half of the lows (the lower lows)

MentalNomad

wboffthelake wrote: »

I'm am quite puzzled though as to how, according to the specs, the Tsi500 goes 2Hz lower than the M70, as each of it's drivers are producing a wide frequency range (28Hz-2.5Khz) while the M70 has two dedicated low frequency subwoofer drivers.

As I noted above, all four of the M70's speakers produce the very low frequencies. It's just that only two are DEDICATED to those frequencies.

The difference between the Tsi500 and the M70's response with lows comes more from the cabinet design. The Tsi500 is a substantially larger cabinet. It's just an inch here, there inches there... but when you multiply the dimensions to get the cabinet volume, there's a huge difference from those couple of extra inches (can somebody check spec and run the math?) Also, on the Tsi500, the port is moved off the front of the speaker - so none of the bottom woofer's lows are getting sucked into the port. The port is apparently on the bottom, now.

Cabinet design result: the Tsi500 is more efficient at the very low frequencies. The overall efficiency is better than the M70's (91 versus 90), and the Tsi500's bass gets down to a lower frequency before the it rolls off below spec.