Open back/rear vented midrange driver, ideas?

[flyingtele]

I'm currently working on a 3 way design, with a 10" side mounted woofer, a 5" Zaph Audio aluminium mid driver and a 1" Vifa silk dome tweeter.
I was thinking about running the mid in an open back setup, simply a diagonal partition starting from just below the woofer, and running at an upwards angle towards the rear of the cabinet with say a 10 cm or so opening, so it may possibly be a transmission line type setup. I have included a simple diagram for simplicity. I intend to crossover to the woofer at around 150 Hz or so.

How will this type of enclosure react and does it need to be tuned? Or is that not going to be of any concern? Any ideas or suggestions would be appreciated as I haven't played around with this type of cabinet before.

[ScottG]

MathCad Computer Models : Upgraded Versions

[planet10]

I refer to this configuration as a mid-TL. Stuff it such that it starts light behind the driver and gets progressively denser towards the terminus. You are attempting to flatten the impedance peak as much as possible. I did something similar in Tysen.

dave

[mlise]

The tweet is sealed, so it doesn't care. The mid probably only wants a couple of liters. He could live in a little sono tube (cardboard tube for forming concrete) or ABS sewer pipe with a wood disc plug and a chunk of fiberglass. I'm not sure what metric sizes are available for sewer pipe, but something with 120 mm or so inside diameter would be perfect.

Cheers

[flyingtele]

I plan to run the mid quite low, to around 100-150 Hz so I would rather not use the typical small sub-enclosure and I like the idea of having it open backed. The woofer is side facing, so if I cross the woofer too high then directionality could be an issue with the side radiating sound becoming more noticeably from the side. I realise that this will still happen to a degree, but I am trying to minimise it without having to put the midrange into its own bass reflex cabinet which would likely cause more problems than it would solve.

Is there any formula to work out the ideal terminus area or the length of the pipe? I thought about maybe putting in alternating baffles to increase the effective length and possibly make it into a 1/4 wave pipe tuned to the crossover frequency.
Or would it be okay to simply have the partition opening to a rear terminus and fill it with stuffing without special focus on the dimensions etc?

[tvrgeek]

Tried it once. Was not happy with the results. Wound up with a large chamber stuffed instead. I found round chambers to be especially bad. Pay attention to Dave if you are looking at this. You will need to consider this in the crossover, and it may require some of the same compensation as an OB.

[phivates]

What Stubbie said. I don't care much for 5" drivers crossed that low unless steep slopes are involved and then...

[mlise]

Hi,
You've kind of got three options. 100 Hz is pretty low, so just treat it like a woofer project and your 10" is a sub. As a woofer, it could be in a closed box, a bass reflex box or horn loaded. Your idea of an open enclosure really wants to be a horn loaded driver. Look at the single driver website for info about horn loading and a couple of calculators Single Driver Website Even if you plan on the speaker being in the corner of the room (size factor=8), this'll get to be a little large. The mouth of the horn ends up being about 30 cm X 39 cm. The length of the horn will be 87 cm long for a tractix. You can fold this about once and have it work well. The mouth size is dictated by the lower frequency you choose and the length is dictated by how beefy the motor of the speaker is and you can't really fight much with the physics there. The upside is you can't get more from your driver than horn loading and the poor 10" may not get you much unless it'll handle a kilowatt.
The simple options are closed and bass reflex. WinISD is free and comes up with 3.3 liters for a closed box or 7 liters for a reflex with a port tuned to 60.21 Hz which would be a 2" tube 7.8" long. You can play with the numbers in WinISD.
A random sized box with a mountain of fiberglass will be a little hit or miss. If you start with one of the calculators for an exact solution, then cheat it a bit to fit the space, things will be a bit more deterministic.

Cheers

[Moondog55]

Also two 10 inch woofers side mounted are better according to Dave, see his posts on that subject.
I would be using digital and bi-amping to cross to a 5 that low, an octave higher tho should be no problem, would you consider a 150 or 165mm driver, Vifa P-17 would work well like that

[mlise]

Er,
You're changing horses in the middle of the stream. If you're just looking for a dirt cheap awesome driver, try the Eminence 'Red White and Blues'. It has the wide range of the little 5's and 6's you're looking at, but with way bigger cojones. Way, way more efficiency too. The aluminum guy is 88dB, the Vifa is 90 dB, but the RW&B's is 101dB.

Cheers