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Young Croc
Young Croc


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    Posted: 20 November 2019 at 8:38am
Just acquired two volt rv4504 that have been liberated from some fairly knackered mdf boxes.

Has anyone any suggestions to a reflex design that would suit, I plan on running then up to 150/250hz max for home use with a plate amp.

cheers
purple monkey dishwasher
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DMorison View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2019 at 6:46pm
TS parameters suggest it's happy in quite a modest box volume for any given tuning, so that'd be useful in a home situation.
Below are a few options depending on how you want to trade off loud vs low - these are all driven to Xmax within the operating bandwidth FWIW.
The smallest of these is likely to work out pretty similar in total size to a d&b Q-Sub, if you want a commercial cab as a point of reference.
HTH,
David.



Edited by DMorison - 20 November 2019 at 6:47pm
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cyklist Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2019 at 11:46pm
Fantastic, thanks David.

Ideally lower extension to compliment a pair of fairly big studio monitors I have.

As I wont be driving the shyte out of these at home, am I right in assuming I can just opt for smaller box and boost eq on low end to compensate for smaller volume? ie - Run it through smaart then eq flat to 30 ish for lower volume application?

Given I have two are there any benefits to running two drivers in a small sealed enclosure?
thanks for your help!!


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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 21 November 2019 at 12:37pm
Quote Fantastic, thanks David.

Ideally lower extension to compliment a pair of fairly big studio monitors I have.

As I wont be driving the shyte out of these at home, am I right in assuming I can just opt for smaller box and boost eq on low end to compensate for smaller volume? ie - Run it through smaart then eq flat to 30 ish for lower volume application?

Given I have two are there any benefits to running two drivers in a small sealed enclosure?
thanks for your help!!

To an extent, yes you can reduce box size & make up for that with EQ, though there are limits to how much it's practical to do.
Firstly, as you reduce box size for a given tuning, the required vent length gets longer to maintain that tuning, so it will start eating up more space within the box, somewhat negating the volume reduction and requiring more complicated construction (eg bending it around 2 sides of the box rather than just one).
Secondly, the driver will be operating at higher average power for any given listening volume, meaning it may be closer to thermal or mechanical limits and distortion may be a little higher too. If you have enough headroom (ie listening at lower volumes) that shouldn't be a problem but is something to bear in mind.

In theory yes you can extend the principle to using a sealed box instead with even more EQ to flatten it, but the amount of boost is going to be a lot higher and you will run out of excursion quicker, so you'd have to be sure that a lower maximum listening volume was acceptable.

Putting both drivers in one box gives you the option of push-pull mounting then which can reduce distortion a bit though that shouldn't be all that likely to be a problem for you at lower volumes. It also gives the option of dual opposed mounting for force cancellation within the box (drivers on opposite sides of the box so any mechanical vibration transmitted from driver to panels cancels out).
However, depending on your room acoustics having all the bass come from one location may mean it's harder to get an ideal position as you may find yourself in an all or nothing position wrt nulls and peaks from room modes.

Putting the drivers in separate boxes allows you to move them independently giving the option of using positioning to smooth out room response issues.

Below is a comparison of one sealed and one vented option.
The sealed is only 65l net internal, which is tiny for an 18" - it'd be approx 47cm w x h and 36.5cm deep internally, but needs a total of 8dB net boost in the EQ to get that response.

The Vented is 110l net tuned to 29Hz and as you can see it goes a full 10dB louder, albeit taking 4dB more power to do so, so it is effectively 6dB more efficient.
The vent, if built as a shelf with one central divider, would be 86cm long, so as said above would have to fold up the back of the cab as well as running along the base of the cab.

I've modelled each with a generic crossover in place as that does slightly impact excursion within band (mostly for the vented option), obviously you'd tweak that to suit your mains so don't take these models as 100% exact.

Cheers,
David.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cyklist Quote  Post ReplyReply Direct Link To This Post Posted: 21 November 2019 at 2:39pm
Thanks for the very detailed response!!

Great that gives me plenty to work with now Thumbs Up
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