dumb question replacing drivers in a vintage 3-way cab

[exabrial]

I have some "MCS 3-way" vented cabs that I'm replacing the drivers in. I'd just build new speakers altogether, but the cabs are hefty 5/8" construction and weigh about 30-40lbs each. They have a 10" woofer, 2" dome midrange, and 3" tweeter.

They have a 5-3/8" cutout for midranges. I was thinking of replacing them with some 6" midbass drivers, but it occurred to me that the existing dome midranges are "sealed back".

Now the cabs have a 4.5" x 1.125" x 6" vent for tuning. Am I limited to sealed back midranges or can I use something like a Dayton Audio Dayton PK165-8?

Thanks for answering, I'm a complete noob and I couldn't find this questions asked elsewhere in on the boards.

[wintermute]

whilst you don't necessarily have to limit yourself to sealed back midranges, you will need to come up with a way of giving the mids you do buy it's own enclosure of suitable size for the driver. This could be rather tricky if you only have the hole for the 10" woofer to work through (ie assuming all baffles are glued in place.

With respect to the tuning of the port, you have a couple of options.

you could simply seal it up. or you can try and find a woofer that will work well in a vented enclosure of the same volume (minus whatever you need for the mid enclosure) and then replace (or modify) the existing port to get the correct tuning.

Some simulation software such as unibox or winisd will help in this regard.

Tony.

[Moondog55]

Something like this is what could work.

Midrange Enclosure 3 Litre'

Personally I would keep to a 4 or 5 inch mid.

Coffee cans ( or a Milo tin in Australia ) can work as an enclosure using epoxy glue tp hold it in place, the plastic is easier as it inserts from the front

[exabrial]

So it sounds like the answer to my question is "yes, you do hava to isolate the mid in it's airspace." Thanks!!! The coffee can idea is brilliantly cheap solution... I'm going to give that a try.

Picture of similar cabs: http://www.fasttrackauctionpictures....ta1173/51t.jpg

As far as tuning the pre-existing vent to the new woofer... well the woofer I'm looking at is a Goldwood GW-10PC-8 because of good reviews and moderate-ish price. I calculated the interior volume of the empty cabs to be 1.445 ft^3... I'm rounding down to 1.25ft^3 because that sounded like a more realistic estimate. The nice thing is when I put that vent size and cubic volume into windISD, I get a nice smooth line with a rolloff beginning at +1db @ 80hz and a -3db point around 42hz! Shortening the vent to 4" would extend the lower bass shelf, but causes the response to drop off like a rock rather than a nice smooth rolloff... So all in all, I don't think i'm going to mess with the port tuning unless I put it in and it sounds like utter crap.

Thanks for the patience and advice both of you! Much appreciated!

[AllenB]

If you can connect an output of your soundcard to a largish resistor, then run that to both your driver and a soundcard input, then you can see the impedance and identify the peaks.