Convert Monitor 70 to Center (crazy mod)

MentalNomad

So with Monitor 70's on super sales lately, I bought a set as mains AND surrounds AND center.

Yeah, center. I'll be bi-amping them all shortly.

Anyway, am looking for advice on converting one 70 into a center channel. I've thought of the following options, after removing the feet:

1. Raise the TV. I can stand all three front monitors and have the TV suspended higher. This doesn't quite look right, and the soundstage will be below the display. No likey.
2. Invert a Monitor 70 (upside-down), raise the TV so that the the tweeter and two woofers of the 70 are exposed. Two woofers and the port will be blocked by the TV, but there will be a few inches of air space; some degree of low bass will be lost, but not all. Overall, it should still sound better than a CS2, no? And the TV will still be between the tweeters of the L/R monitors. I can actually incorporate the center monitor as a pillar in the DIY TV stand (not worried about stability; I'll build it to be stable.)
3. Lay a Monitor 70 sideways, stand TV on top. The monitor will need to be way off to one side to keep the tweeter near the center of the TV, so I'll build a dummy box to place at the other end to balance the appearance.
4. Lay a Monitor 70 sideways, but modify the driver arrangement: re-wire the woofers so the two outer woofer are the subs, and the two middles are the mid/upper woofers. Further, remove the tweeter, drill new hole between the center woofers, and plant the tweeter there. Not worried about cosmetics; I can make it look nice (using the cut plug from the center to fill the original tweeter hole), plus I usually have the grilles on.

Thoughts? Other ideas?

I'm not sure if option 4 is confounded by the internal design of the speaker; am assuming a single chamber inside, but it's feasible that that bottom portion (with the sub woofers and the port) are a separate enclosure from the top. Anyone know?

spock 2054

What kind of television is it? Is it in the wall?

mdaudioguy

I use 3 RTi10 towers for mains and center - all upright, with a PJ screen that comes down to within a quarter inch of the top of the speakers. Sounds great.

MentalNomad

I have a flat panel; 46". Currently standing on a custom stand. Have an unused wall mount that I can do some construction with for a custom overhead rig... have DIY skills and a creative mind.

MentalNomad

Mdaudioguy... you don't notice the soundstage below the display? That's great!

That would mean no mods to the speaker... but totally new av rack. Need a pair of racks, speaker in middle with TV ON TOP.

And must asses SAS...

Pappy1

Hi MentalNomad!

You are doing exactly what I wanted to do, but I bought my speakers in March before all of the great sales. I was thinking of doing your Option 3 (my TV stand would allow for it). Extrapolating from my current setup, in my space, I felt that it would be an excellent way to go once I could have added an external amplifier of at least 200wpc.

What will you use for amplification? This will be exciting.

Please let us know what you do and how it sounds.

Best Wishes!

Pappy

AVR - Pioneer VSX 9040TXH
TV - Samsung HL-T6756W DLP
BD - Panasonic DMP-BD605
Cable - CableOne HD DVR
Fronts - Polk Audio Monitor 70s
Center - Polk Audio CS2
Rears - Polk Audio Monitor 60s
Subwoofer - Polk Audio PSW 505

MentalNomad

Right now I'm running a Marantz SR5000. Am considering buying a used upgrade receiver and using pre-outs into the Marantz to bi-amp the five speakers. The likely upgrades will be higher wattage, so the Marantz will be driving the tweeters...

I'm leaning toward doing a modified sideways Monitor 70 to improve SAF.

Face

Don't lay it on it's side, it's dispersion will be all wonky.

mdaudioguy

Face wrote: »

Don't lay it on it's side, it's dispersion will be all wonky.

+1.
There are some speakers that are designed to disperse sound properly in either vertical or horizontal orientation, but these are definitely not designed for this. They will compromise the sound due to a phenomenon known as lobing, however, wonky will also suffice. On the other hand, it's free to try it. But, I'm also positive that it will not only sound wonky, but it would also look pretty dang wonky, too.

mdaudioguy

MentalNomad wrote: »

Mdaudioguy... you don't notice the soundstage below the display? That's great!

Nope, not at all, but hey, now that you've got me thinking about it, I'll probably be all distracted while watching my next movie... not. The screen is 120" and the mains sit below each corner. The soundstage created by a trio of towers is massive. No one has ever complained about the sound emanating from below the picture. Everything seems to come right from where it should. Essentially, it's no different than most TVs.

MentalNomad wrote: »

And must asses SAS...

You got me with that one.

MentalNomad

mdaudioguy wrote: »

+1.
compromise the sound due to a phenomenon known as lobing... look pretty dang wonky, too.

Good point on the lobing. I was initially thinking the lobing/combing would be no worse than the Polk CS2, which is also a pair of woofers with tweeter between, and might actually be less bad because of the cascade array... and the overall sound would be better matched because the CS2 crossover points don't match the 70's.

I discounted lobing from the two other woofers, which work as subs, writing it off as "lows are non-directional," but that's just about perception... the sound is still subject to lobing, and at the wider width, it's a bigger issue.

I still believe it would sound better than a CS2, but it's certainly true that the best sound will come from a vertical 70.

So I'm down to two options: tv above the center, or an inverted center with a TV in front of it blocking one or both of the woofers and the vent...

MentalNomad

mdaudioguy wrote: »

You got me with that one.

Typo. Mean SAF: Spousal Acceptance Factor.

MentalNomad

mdaudioguy wrote: »

The soundstage created by a trio of towers is massive. No one has ever complained about the sound emanating from below the picture. Everything seems to come right from where it should. :

This makes more sense to me today than the other day, for some reason... we have very good stereo placement which is left-right, like our ears, but we don't really place sounds vertically based on their source, but rather, other qualities of the sound. So why would people notice the height of the soundstage?

Now, which way to go... either way, I have a construction project...

mdaudioguy

Let us know how it goes... Good luck!

FTGV

MentalNomad wrote: »

Good point on the lobing. I was initially thinking the lobing/combing would be no worse than the Polk CS2, which is also a pair of woofers with tweeter between.

The severity of the lobing would be dependant on the actual listening axis.If you were within say + or -15 degrees or so then it may not be apparent.As you move farther off the tweeters axis it will get progressively worse.

mdaudioguy

MentalNomad wrote: »

Good point on the lobing. I was initially thinking the lobing/combing would be no worse than the Polk CS2, which is also a pair of woofers with tweeter between, and might actually be less bad because of the cascade array... and the overall sound would be better matched because the CS2 crossover points don't match the 70's.

Also, to comment on your above point, you are ignoring the fact that the CS2 was designed to be oriented horizontally, so one might assume that Polk at least accounted for lobing in some way in the design. Although I'm admittedly not knowledgeable enough to verify this assumption. To my way of thinking, it would not be so reasonable to assume that Polk in any way accounted for lobing in the event someone wanted to orient their Monitor 70 horizontally.
In such instances I'm a proponent of using things as they were designed, although I realize that standard design doesn't always match reality, and there's always the chance that an alternate usage might result in a more pleasing experience, so by all means, experiment and report back what you've learned!

mrbigbluelight

It's kind of neat to see people try things which, by all accounts, shouldn't work too well; can't help but think of "FrankenPolks".

I'd say, "Go for it".
If it works, awesome !
If it doesn't work, don't be afraid to say, "Dang, that didn't work worth a hoot !" and then try something different.

I have to admit that I don't see the 70 working horizontal as a center, but give it a whirl.

MentalNomad

Just to close off the thread - ended up not doing any interesting experiments. I ripped my entertainment center in half, did some finishing, and added enough casters to have two separate racks (lost about 12" of total width in the process). I mounted the TV on the wall, high enough to be 1" above the center Monitor 70 speaker. So my arrangement is TV on top, and below I have: LF Monitor 70, audio rack, C Monitor 70, HTPC rack, RF Monitor 70. (Plenty of space for extraneous equipment like PS3 and network equip in the two racks.)

MentalNomad

Further update:

I moved. I ditched the split rack and did, in fact, do this crazy mod.

It looks and sounds great.

Moving the tweeter within the cabinet turned out to be too daunting to try. The spacing between the upper woofers is different than the spacing between the rest of the woofers, and the carpentry would be non-trivial. Instead, I removed the tweeter and installed it into a small box housing on top of the now-sideways speaker. I drilled one small hole through the side of the speaker to feed the wires up, and I patched over the hole where the tweeter used to be with modified steel can lids, screws, and silicone.

The result is reminiscent of many high-end center-channel designs with a pyramid shape, or where the tweeter up above the axis of the two woofers.

I also shifted the woofer connections to the crossover, so that the mids come out of the two center speakers, and the extreme right and left woofers only handle the sub freqeuencies. I needed to bring in extra wire only for one of the woofers; all the rest of the cables were sufficiently long.

I've done some listening tests and cannot detect any combing or lobing effects. I'm sure they are there, to some degree, but they are certainly subtle across my listening positions.

I find that a great deal of content is still mixed stereo, anyway, and since I don't like the sound of most "synthesized" surround sound, I let it play through the left and right channels. It's hard to find material with center content which might be susceptible to the combing and lobing, let alone hear it - and I've tried to hear it with test tones.

I'll try to get some pics up if anyone is interested... am still working on getting my receiver and PC down into the the new furniture, so I'm not happy with the overall look, but I've got the L/R speakers mounted on the wall, the TV wall-mounted between them, and the center channel is underneath. These all look and sound great!