Speaker build?

70chevelle

70chevelle

Active Member
OK, here's the background. I have very good woodworking skills and a shop. I have a pair of Boston Acoustic T930's that I really enjoy. The surrounds went on the woofers and I ordered a new set from BA. I also refoamed the original woofs and have them stored away. I've found BA tweeters on Ebay and am considering purchasing a 6.5" midrange and 3 way crossover from Parts Express. So, basically, I want to put the 10" woofs to work in new cabinets. Being new to this, I'm looking for suggestions on the 2 purchases (mids & crossovers). I would basically build the cabinets to the same dimensions as the originals, but they will look a lot nicer! Any hints, tips, or suggestions would be appreciated.
 
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what he said

i agree with what Face said

You can't just buy a crossover and expect it to match your drivers. I tried it once and the speakers sounded horrible. The cabinet was solid. The drivers were all good quality. The crossover was an off-the-shelf 8 ohm 3-way crossover. The people who sold it to me (not PE) didn't bother telling me that you can't simply put parts together like that to make a good sounding speaker.

An "8 ohm" driver, for example, is only NOMINALLY 8 ohms. Its impedance will vary a lot from 8 ohms and will also vary at different frequencies. Near the upper end of its frequency response its impedance can rise dramatically. Manufacturers carefully match crossovers to fit their drivers. There is probably no driver on earth that is exactly 8 ohms across its useful frequency response.

With your wood working skills I would suggest an exact clone of your BA speakers using your own cabinet- same dimensions and vent size (if there is one) but use the exact same drivers as in your current BA's. This assumes that you will be able to reverse engineer the crossover since you have one to look at and/or measure. It is OK (recommended - search some threads here) to replace electrolytic caps in the signal path with poly, and those you can get at PE. (I love Parts Express) But that is the only practical improvement or modification I would attempt with the crossover.

Good luck
 
What I've done for years is run an active crossover until I have it tweeked, then build the xover to those settings and order.
 
djnagle said:
What I've done for years is run an active crossover until I have it tweeked, then build the xover to those settings and order.
Click to expand...
Honestly, that's a not a great method. That's as accurate as using a crossover calculator.
 
No, I meant what I said.

There are other issues to deal with when switching from active to passive. Passive components and drivers don't always worth together as they should.

For example, I tried crossing a Vifa XT-19 over @ 5800 with a first order slope. According to the crossover calculators I was using, A 6.8uf cap would work. Well, it wasn't even close. Even with a smaller cap, it still wasn't close either, and I would have blown the tweeter if I didn't use a mic to test the FR. LR2 response was way off also, by over 1,000hz.
 
It's always worked for me. Although, to be frank, I can't tell the diff between a 1st, 2nd, 3rd, or 4th order xover.
 
a first order XO has one component (e.g., high pass, a series capacitor) and a slope of 6 dB per octave.
a second order XO has two components (e.g., high pass, a series capacitor and an parallel inductor) and a slope of 12 dB per octave.
a third order XO has three components (e.g., high pass, series cap, parallel inductor, series cap) and a slope of 18 dB per octave.
there's a pattern developing...
wanna know the nominal phase shifts as a function of XO order?

(EDIT these are all Butterworth filters [I think]...)
 
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mhardy6647 said:
a first order XO has one component (e.g., high pass, a series capacitor) and a slope of 6 dB per octave.
a second order XO has two components (e.g., high pass, a series capacitor and an parallel inductor) and a slope of 12 dB per octave.
a third order XO has three components (e.g., high pass, series cap, parallel inductor, series cap) and a slope of 18 dB per octave.
there's a pattern developing...
wanna know the nominal phase shifts as a function of XO order?

(EDIT these are all Butterworth filters [I think]...)
Click to expand...
Butterworth, LR, Bessel, the components are the same, just the values(ratios) are different.
 
Thanks for all the input. Seems that the best route would be to get a quote on tweets, mids, and crossovers from BA and see if it's worth doing. Then at least I have a reasonable idea that everything should work together.
 
here's another idea

You said in your opening post: "So, basically, I want to put the 10" woofs to work in new cabinets."

You have good woodworking skills and tools. You want to build something. And you want to improve your sound.

Here is an idea for your consideration: What about using your extra woofers as dedicated subs? At Parts Express (and other places, no doubt) you can get lots of different subwoofer plate amps that could be built into the cabinets:

http://www.parts-express.com/wizards/searchResults.cfm?srchExt=CAT&srchCat=505

If budget is an issue there is a 70 Watt plate amp on sale for $53: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-784

You probably would not want to go below 70 watts as a minimum. If money isn't an issue you could get more power.

You would need two amps and two cabinets for the simplest execution of this plan. Simply copy the size and venting (if any) of your original BA's. Allow for any internal volume consumed by the plate amp by making your sub cabnet that much larger and subtract volume for the mid and tweeter that will not be there. (actually, precise volume matching is not really that critical - stay within +/- 5% and you'll be OK). Be sure to make the new sub cabinets very solid, even adding bracing or wall thickness, especially on the baffle (where the driver is mounted) that the original BA's may not have.

Make sure that whatever plate amp(s) you buy have variable crossover setting. Set the crossover to reinforce ONLY the lowest frequencies, say 70-75Hz and below. Of course you will experiment with that setting, the goal being to make the bottom more solid without muddying up the mid-bass (as would happen if the crossover setting is too high).


Optional:

While matching original cabinet volume and venting is the safe and sure way to approach this, other options do exist although with added complexity. If you have access to a means of measuring the TS parameters of your spare woofers with something like this:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-804

Then you could get design software, free or otherwise, which uses the TS parameters as a basis for designing sub cabinets that may actually improve upon using clone cabinets. It would also be possible, once you know the TS parameters of your drivers and have design software, to create a sub which utilizes BOTH woofers in one cabinet. Various configurations are possible some of which may require less internal cabinet volume (isobaric?). In a dual-woofer sub you would be able to use only one, higher powered plate amp instead of two.

The negative side of the "Optional" plan: If you go to the trouble and expense of buying the TS measuring device and software, there are probably drivers designed specifically for subwoofer use that would be better than your spare BA 10" drivers. But if you can get TS parameters measured for you, or if they are available from BA tech support or online then the option of exploring alternate designs makes sense financially. Free software is obtainable.


Stuff to think about...
 
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