Use old enclosure for new speaker

Dear all

I've been searching the web for info on my project of "renewing" a set of old speakers - and while I've learned alot, I still have some questions that I cannot seem to find the answer to.

In the following I will describe my current project, which may get a bit lengthy, but it will include photos to make the reading easier :)

I have an old pair of Bang & Olufsen type-K speakers that I acquired because my wife liked the look of them (WAF-factor guaranteed =BONUS :D) - this is the reason I want to stick with this enclosure instead of just making a new one to fit the drivers. Below are a few photos and data on the enclosures:

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[model photo - mine are the same type/veneer]

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[The inside of the speaker from the back. It is a 3-way speaker from around 1964]
The inside dimensions (excluding stuffing and drivers) are:
Width = 44.5cm
Height = 61.5cm
Depth = 35.0cm
And the bats are 5cm thick and are glued to all sides except the front baffle. There is also an extra loose piece of stuffing at the back of the speaker making the total thickness here 10cm (it may have been added later?)
The rear plate is a relatively thin light board, and is simply screwed into place.

I want to update the speakers for 2 reasons:
1) There is currently a serious problem with one of the drivers (I think it is the mid-range) which rattles considerably during play, and considering the age of this speaker I imagine replacements may be hard to acquire.
2) The sound quality is not up to todays standard (as expected), and I therefore hope to get a better sound quality from updating the drivers/XOs than from renovating the aged drivers.

Here are my own thoughts on the "new" speakers:
*I want to keep this fairly "cheap" as I am currently low on cash - I expect to do a better update in the future when I have more money available.
*I don't have alot of time (two small kids), so the less work the better.
*I am fairly used to DIY'ing on the house etc., so I have basic tools available and I am not afraid to use them ;)
*I am confident in my soldering skills, thus as long as I have a schematic available I should be fine doing any required cross over soldering.
*They will be placed in a living room with fairly strict placement requirements (e.g. 50cm from rear wall is not an option).
*Number of drivers: I like my speakers to cover the lower octaves, but considering the cost of extra drivers required + XO, I have seriously considered going the "fullrange-driver" route (the enclosure is almost 100L without the bats, so it should be possible to get the required volume to give a single driver optimal working conditions.

My current choice is to use a Cube F180 in each, as I may currently purchase them for around 100 dollars (for both). I am thinking of using a closed enclosure for simplicity (the problem of distance to the rear wall may also be exaggerated with a bass reflex design?) I have a few questions about this setup though:
*I expect to basically line the entire enclosure with a layer of e.g. 19mm MDF to improve rigidity of the enclosure - is this a good idea?
*Is there something I should be aware of regarding location of the driver (e.g. symmetric/asymmetric) - I was thinking of placing it towards the top of the enclosure to bring it closer to ear-height?
*Does the batting (same stuff you use for insulating e.g. a loft) reduce the internal volume of the enclosure? And should I leave it in or maybe get a thinner bat?
*Is it true that a larger enclosure does not significantly lower the lowest frequency of the driver in a closed enclosure?
*Should I just make the internal volume equal to Vs (39.4L) - if yes, I guess it would be wise to reduce it by introducing non-parallel walls inside (to avoid standing waves)?

*I have also considered partnering a fullrange driver with a bass to get a wider frequency response without the need for 6 drivers and a complicated XO - is this a viable route?
*Lastly, I will be driving them with a Luxman 5L15 which, I have read, really doesn't like low impedance speakers, so any design should aim for 8Ohm, or at least 6Ohm (if I am wrong about this, pleas let me know).

I will appreciate any response to my questions, as I am eager to learn more about this topic (and revise any wrong impressions :) )

Regards
Jakob
 

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if you're going full range (my preference) then you need to place the driver at ear height, else you're going to be missing out on the higher frequencies, that's just the reality of a large radiating diameter, if you can't do that, then go for a dome tweeter of 25mm or preferably 19mm, keep the crossover simple crossover, design is a dark science and you can spend a lot of time driving yourself crazy, unless you enjoy doing that keep it to 1st order and two-way (in my experience), unfortunately that does limit your choice of driver combination, and size of woofer.
The thick damping is great, keep it, putting more timber in there is likely a waste of time. volume needs to match the woofer but I wouldn't lose too much sleep about getting it exactly right.
My suggestion is get an 8" and a 1" dome, cross at 3500, one coil on the woofer a really nice capacitor on the tweeter, then spend some time building a pretty cabinet for your full range driver and maybe incorporate a sub.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
Those are beautiful!
I would try to find a new mid and leave them as they are. You might stiffen the back if really thin, but those are best left unmolested, IMO. Make some small boxes for your fullrangers and place them on top if you must have something newer, it will keep other things from being set on top and ruining the finish.
 
Hi Horst and Ron - sorry for the late reply, we've all been ill in shifts here for the past few weeks...

thank you for the great input - I had read about the poor dispersion of treble from a large radiating source, but thought that room reflections would make it less of a problem...this kinda rules out a full-range speaker design as the speaker height is too low to put the drivers at ear height (even when sitting).
Simply building a new pair of speakers is not really an option, as I don't have the time (or money) to complete them now - furthermore, it would defeat the purpose of having acquired a set of enclosures, which are "wife approved", in the first place.

The two options are then to either keep the original design, or do a 2-way design.
As I am not really impressed with the sound quality of the current design (they sound muddled/muffled/wooly with little detail) I am leaning towards replacing drivers. But could the SQ simply be due to e.g. deteriorating XOs?
Also, Horst you mentioned "unfortunately that does limit your choice of driver combination, and size of woofer" - how do I ensure that they match? I can ofc. compare specs and ensure that they have about the same SPL, but how do you get the "sound signature" to match (if possible)? is it enough/preferred to buy drivers of the same brand?

And again - thank you for the great help guys.

/Jakob