full range in an existing small cabinet

[mda1]

Hi all,

This is my first post here after trying to read all the threads that already brought me a bunch of answers (and many new pages to read in the infinite knowledge that one can find on the internet).

My challenge is as follows: I inherited a pair of beautifully designed but quite badly sounding design speakers from the 70's. The enclosures are spherical brushed aluminium with a diameter of about 20cm diameter (8 inches). The driver inside is about 5 inches (133 mm BCD, slightly smaller baffle) and a tiny tweeter in front. Both straight from the 70's and well... sound as such . After a bit of research I have decided that I would like to replace this combination with a single full range driver as I like the simplicity and philosophy of the single driver.

The full range driver has to fit in this existing enclosure, so I am limited to something between 4 and 5 inches. The air volume in the (closed enclosure) is about 1 or 2 liters (depending on the driver one puts in there).

I understand that in these conditions I will not be able to have a very much in the lower freq range... but there is not much I can do about that I think (right?)

I listen all kind of music, but almost no jazz and no classical music.

I driver my speakers with a rotel pre-amp and a NAD 216 amp.

Now the question: which driver should I choose?

I have been doing some research already and ended up on the likes of TangBand and Fostex. How do these compare?

As this is my first build project (well, for speakers at least), I would be happy with any advice I can get.

[planet10]

How thick is the Al? How big a sloce off the end to mount the driver. a 10 cm R sphere os about 4 litres.

When one has 2-2.5 litre to play with i immediately think of Fostex FF85wk. If it is at the large end of that volume, A6.2m or A6.2p are candidates.

Can you post pictures?

dave

[mda1]

thanks for you reply. I'll get some pictures tomorrow.
The slice that comes off the sphere is about 1/2 to 1 liter so I don't lose too much there. Then comes the volume of the driver itself. So I am indeed left with something like 2-2.5 liters depending on the driver chosen.

This FF85WK you recommend is smaller than what I could mount in there. What is the reason that you recommend this one in particular? (note: i don't doubt your choice, I just want to learn...)

[planet10]

Every driver requires a certain volume to work its best, with the given volume those 3 drivers are what i know works. A larger driver would need greater volume, there are quite a few 5" that can work in 4.5-4.7 litre, but that is as small as i'd put them in.

The 3 mentioned drivers, althou somewhat bass limited are no slouches in the range they do work in.

dave

[talaerts]

If you can neatly attach a round plate to the hole in the speaker then in the middle of the plate you can put the FF85WK. Or put it excentric with room for a bass reflex opening below it.
This driver has qualities, but it is not a bass monster. You may want to add a subwoofer to it for complete music enjoyment, possibly also filtering the FF85WK to protect it from the lower frequencies so it can focus on what it does best. To my own taste, a speaker with the FF85WK will not have enough bass on its own.

If you prefer to keep it with 1 driver without sub, then a 3" Tangband is probably a better choice. Since these speakers offer lower efficiency, they can go lower in bass - at the expense of loudness.

[planet10]

Originally Posted by talaerts

If you prefer to keep it with 1 driver without sub, then a 3" Tangband is probably a better choice. Since these speakers offer lower efficiency, they can go lower in bass - at the expense of loudness.

Same with Alpair 6.2s. Also the Fountek FR88ex

FF85wk with helper woofers are pretty amazing.



dave

[mda1]

Thanks again for all the answers and advice

The aluminium is 2mm thick. Here are some images of the spheres in original state and after partial disassembly:






(the last one is just to show the part that is 'sliced off')

I was not really planning on adding a filter. It adds more complexity to my first project, and because placing the filter inside these spheres will 1) take away even more volume, and 2) be a real challenge to mount / fix in a proper way. Additionally: isn't the beauty of full range that you don't need filters?

As the original way these were made is just a sealed volume, I was planning on doing the same, so I had not thought of a BR design... would you indeed recommend this?
With these speaker I would rather consider adding a subwoofer than pushing the lows on the spheres themselves. And I value a clean sound over volume for this project.

[mda1]

No comments on the sealed vs BR choice?

[GM]

It would really depend on the sealed system's Q [sysQ]. In such a small cab though, a damped vented alignment [semi-aperiodic] is often the best overall compromise.

An easy test for vented is to gap [space] the driver to create a leaky seal with the greater the gap, the higher it begins rolling off in the bass.

Adding foam or similar in the gap can also change its tone, creating an increasingly aperiodic alignment with increasing density, so worth experimenting with also.

GM

[mda1]

Sounds cool... Can you give me a ballpark idea of how 'leaky' my seal has to be? i.e. how much of a gap I should leave between the driver and the board it will be mounted on (there are no drivers with the exact mounting pattern of the old drivers, so for sure I will have to do some woodwork...).

Is it mm's? or rather cm's? (assuming I will use a 3 inch driver).