Transfering good drivers to new cabinets

[nightflier]

I have a pair of speakers from college that have totally beat-up cabinets. These are old Philips speakers that had the typical wide front / narrow depth look popular in the 80's. However, the drivers look to be in very good shape with large 10" woofers. These speakers were never abused sound-wise, but from all the moving around the corners are completely destroyed and the vinyl is so badly worn that even the MDF is falling appart.

Would it make sense to purchase new cabinets from parts express or someplace similar and mount the drivers in there? These cabinets will likely not have the wide / narrow size that the old speakers had, but as long as the interior space is about the same, they should still be listenable, right? Or are these drivers only good in the old 1980 cabinets?

I'm not doing this to save money or anything. I'm just interested in easing my way into learning about speaker-building w/o having to worry about building cross-over networks and all the advanced stuff (at least not yet).

[bjornb17]

i think the internal volume is the most important factor. I think since older speakers had larger drivers, they tended to have wider cabinets, and therefore they did not have to be as deep to achived the same volume.

If you look at some of the floorstanders available today with the woofer on the side of the base (http://www.polkaudio.com/homeaudio/products/individual/floorstanding/lsi15/ like these for example), its the same idea as what was present in the 1980s. If you look from the side, it would be a wide cabinet with shallow depth. However they speaker is designed in such a way that the front of it still has the sleek narrow look which is very common today.

[kexodusc]

Wide baffle design actually has a few advantages and disadvantages. Primarily, you lower the frequency where baffle step loss (rise) occurs...this is where sound radiates from 2 pi to 4 pi or half space to full space. What happens is a loss of 3-6 dB at a frequency related to the width of the front baffle (and frequencies below). It's not an instand loss in dB, but gradual slope.
Point here is, a narrow baffle will lose mid bass/midrange earlier and could sound a bit funny, especially if the crossover incorporated that into the design.

Only one way to find out...give it a shot. Port them in the front and place them within 12 inches of a wall to mitigate the effects of baffle step loss.

A great kit for getting introduced to speaker building is the BR-1 kit from Parts Express. At $140, I'd take them over my Axiom M3Ti's or old Paradigm Mini Monitors anyday.

[jocko_nc]

Hmmm.... Normally, I'd say take an old cabinet and fix it up with new drivers.

Considering how reasonable top quality drivers are these days (and crossover parts) I'd say it is a losing proposition. MDF doesn't just rot away, however, particle board does. Many respectable speakers in the past used particle board. I have torn apart many old speakers, it is amazing how much better you can do.

I'll take any good old cabinet. Old drivers aren't so great.

jocko

[nightflier]

MDF doesn't just rot away, however, particle board does.

You're probably right. It does look like particle board.



A great kit for getting introduced to speaker building is the BR-1 kit from Parts Express. At $140, I'd take them over my Axiom M3Ti's or old Paradigm Mini Monitors anyday.

Yes, I still have a parts express kit that I have yet to start on. The cabinets are much smaller than what I would need for these drivers, though.

Very interesting analysis on the speaker volume and cabinet width, by the way.

We'll see what I can get to over the holiday break.

[2bluechris]

Nightflier , many of the old Philips' drivers were quite good , both compared to many other drivers of that era and to the current or recent Philips drivers which are less good as Philips no longer specialize in driver technology . If you have the time and the budget , then do build some new cabinets . Keep the internal volume the same , or very slightly larger than that of the original cabinets . Also , ensure that no 2 internal dimensions are simple multples of the smallest , that is no X2 ; X3 ; X4 ; etc ... Try the ratio 1:1.618 for the 2 smallest internal dimensions and choose a non-mutiple of those for the largest dimension to avoid co-incident resonances inside the cabinet - to some degree , there will always be internal resonances but with careful choice of ratio of dimensions the resonances will be spaced in frequency , hence not "add" to each other .
Also , replace any electrolytic capacitors in the cross-over with new plastic film capacitors of the same capacitance value and of at least 100 volt rating . Electrolytic capacitors deteriorate with age and thus the cross-over frequency will shift . Plastic film caps will last longer than you and I , unless overheated by your soldering or by excess current through them or over-voltage - thus my rec. for 100 volt minimum rating . Polypropylene capacitors are best , but if you can't find any then Polyester or Mylar types will work OK and better than bi-polar electrolytics . Plastic film caps are much larger size than Electros , thus for the large value caps that may be in the bass to mid section of the cross-over you may have to connect several plastic caps in "parallell" to equal the total required value . If you do not understand electronics and not know what I'm on about here then ask for some-one knowledgeable at an electronics components store that sells capacitors to explain "parallell" , etc ... to you . I have done all the above for various people . best wishes , Chris .

[nightflier]

OK,

I have some more news about this project.

I was originally going to try and build a three-driver tower with the bass drivers mounted on the sides. I always wanted to see what that would do to the imaging - sort of similar to the Audio Physic speakers. The difficult thing about this would be building the cabinets.

Well... my brother is a sculptor (he does large-scale industrial pieces made of steel). So over the holidays he said he could build the cabinets out of steel. This would allow me to come up with a very solid cabinet custom-built to my specs. We will be using SolidWorks (sort of like AutoCAD) to calculate the internal volume and correct dimensions. I can even have these chromed to add a little pizzaz. I'm still thinking front-ported towers with the woofers on the sides, but I now have the option of making the speaker sides curved or making the rear panel narrower than the baffle. I suppose I can get much more creative too.

While I am guessing that there are real advantages with steel such as that it is very solid, especially if I use thick sheets, there are probably sonic qualities I need to take into account. I've heard some of the less expensive metal-encased speakers and I could definitely make out these problems. So my question is: what can I do to treat the sheetmetal internally?

Chris, I will definitely consider upgrading the electrolytic capacitors.

[2bluechris]

You are certainly undertaking an ambitous project there ! - I wish I had that brother , etc ... For damping the steel panels try the stick-on bituminous damping pads sold by some Car / Auto accessory shops . These are used inside car body panels to reduce vibration noise , etc ... They are flexible , hence will fit to curved side panels if you use such in your design . [INDENT] Rather than make the back panel narrower than the baffle , I would make it wider so that the sides flare outwards towards the back and thus reflect internal sound away from the drivers and towards the back panel where you can install cut edge out fibreglass strips cut from insulation batts . Cut at least 3 inch wide strips , or one quarter the internal depth of your cabinets if they will be deeper than 12 inch . With flared out sides and 3 inch or greater absorbsion on the back panel you will not need absorbsion on the side panels . Calculate one quarter the internal height and cut fibreglass strips to that and then cut from those strips 3 inch wide for under the top panels and use the remaining , wider, strips for in the bottom . There will be some type of adhesive available that will stick fibreglass to metal or to the bituminous pads - inquire at Boating supplies shops if none at general Hardware shops or Auto shops . That is the type Of cabinet I will be building when I eventually get time , but probably from woods . With metal it is possible to make wide radius curves instead of sharp corners for the baffle to side panels' edges . This is acoustically good - reduces diffraction - as well as visually attractive . [INDENT] For side firing woofers to work they need to be bass frequencies only - below 160 hertz . When "low midrange" frequencies above such fire inwards - or outwards - instead of forewards with the higher mids and treble the sound becomes peculiar and can sound quite unbalanced - such may ruin the tone and projection of you recordings . Listen to your speakers with your ear close to the woofer then move slowly your ear towards the midrange driver and hear where the "cross over" is occurring before you decide your design . I find "all forwards" sounds more punchy . For wider imaging - if one has hard surface flat side walls in listening room - some types of speakers sound good if pointed outwards to relect off the side walls and back from there to your listening position . This does limit the position best sound balance can be heard from though . best wishes , Chris . P.S. - sorry the layout is so cramped - the "indent" fuction does not work today !

[nightflier]

Well my brother also works on cars and boats so I'll ask him if he knows what stick-on bituminous damping pads are.

We did discuss the speakers some more. We've decided to forgo the side-firing woofer and instead put the drivers in a conventional array with the woofer front-firing at the bottom. The enclosure will be a half-round pyramid-type structure with a flat front and shopped off top. It will be very heavy apparently, and will take some time to design properly. The most difficult part, ironically, will be getting the internal volume to be identical to that of the previous speakers.

[2bluechris]

Have a look at the damping pads at their thickness before you finalise your internal dimensions - particually if you decide to use a lot of pads . If you can't find bituminous pads , then for flat surfaces you can use Fibreboard - that soft board made of wood fibre that is often used for noticeboads as it is easy to push thumbtacks into to hold paper on , etc ... It often comes painted white on one side , but you can sandpaper that off easily . It does not resonate and is heavy enough to use in 1/2 inch thickness on small panels . For curved panels , cork tiles can be glued on , but as they are light you will need to buy the thick ones - the thickest that can be bent sufficiently . Look in Hardware stores and DIY Home Improvements stores . -------------------------------------------------------------------------------- Keep any fibreglass or other soft internal absobtive filling at least 2" - 3" away from the in-cabinet end of the port , as the air velocity is high there and needs to be for the port to work properly . If you want to try a "damped" port , roll up the absorbtive and put it inside the port tube . ---------------------------------------------------------------------------------------------------- As for calculating internal volume - any "shape" can be divided into parts that are shaped to allow geometry formulae to be applied to calculate each individual volume , and then add all together for the total - yes , it is time consuming ! best wishes , Chris .