More Monitor 10 questions... Cabinet Rebuild

dc55110

As stated in a few other posts, I’m going to be building new cabinets for some 10A’s I recently pick up. A decade or two in a damp basement has left the original cabinets warped and horribly musty smelling. I intended to keep the cabinets’ internal volume and dimension the same. Some changes I’m curious about… flush or recessing of the drivers? Placement of the tweeter, is higher on the cabinet ok? Tweeter orientation, is horizontal optimal or is vertical ok/better? Can you add too much mass to the cabinet?

jon s

Normally, flush mounting of the drivers would reduce diffraction and improve the image, but the Polk 6.5" mid-woofers and passive radiators have a "lip" which would make it seem useless. The tweeter should be flush mounted, but veritcal or horizontal placement is non-critical for a domed driver, in fact, some SDAs have it mounted vertically.

One item you might want to consider is to mount the two mid-woofers vertically as it should improve imaging. The current side by side placement probably compounds crosstalk interference between the drivers, reducing the imaging accuracy. If you are considering to mount the drivers vertically, you also might want to consider mounting the drivers in a D'Appolito configuration, where the HF driver is placed between the two mid-range drivers. Also, the width of the cabinet also affects imaging. Another idea would be to mount the passive radiator on the side of the cabinet to reduce the width of the front.

Don't know how far up you want to place the tweeter, but you should not make it too far from the mid-woofers, or a hole may be apparent in the sound. Also, it would probably be best if you keep the tweeters in a sealed section to prevent any interference from the mid-woofers.

If you increase the cabinet size you also might want to consider using the 12" passive radiators from the Polk RTA-12Cs to improve the bass.

Regarding mass, the denser the cabinet, the less resonance which affects the sound. Of course, this makes the speaker heavier and harder to handle. In either case, make sure you put cross braces inside the cabinet to reduce resonance. I always wondered how much improvement there would be if you laminated two 3/4" MDF boards together to increase rigidity.

Good luck.

dc55110

jon s wrote: »

Normally, flush mounting of the drivers would reduce diffraction and improve the image, but the Polk 6.5" mid-woofers and passive radiators have a "lip" which would make it seem useless.

I had intended to mount them so the lip would be flush with the face.

jon s wrote: »

One item you might want to consider is to mount the two mid-woofers vertically as it should improve imaging. The current side by side placement probably compounds crosstalk interference between the drivers, reducing the imaging accuracy. If you are considering to mount the drivers vertically, you also might want to consider mounting the drivers in a D'Appolito configuration, where the HF driver is placed between the two mid-range drivers.

I the thought of mounting the drivers vertically hadn't crossed my mind. I had orginally invisioned something the marginally held true to the orginal cabinets. But now that you have put this bee in my bonnet...
thanks for the input.

Dan

Face

I wouldn't change the driver arrangement, you're just asking for problems. If you want a narrower and taller speaker, part out the M10 drivers and buy a RTA.

Nothing wrong with flush mounting or adding mass to the cabinets though as long as you keep the internal volume the same.

zingo

I agree with Face. If you want to rebuild Monitor 10s, that's great. But to make frankenpolks is just asking for trouble unless you want to spend lots of time and money getting them right; then you might as well just get a pair of RTAs at Face also suggested. But, to each his own.

scootchu

If it were me, and I do have a set of 10's, I would match the layout of the present 10's you have. I gotta believe the guys at Polk kinda knew what they were after when they designed them.