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Drivers for existing cabinet

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Posted on May 1, 2024 at 09:27:07
Bill the K
Audiophile

Posts: 8448
Joined: June 3, 2006
 My old Boston Acoustics bookshelf speakers CS 26 have lost their old drivers which sounded very good for the last 12 years. The cabinet looks is a favorite of mine, classy and elegant. I would like to use two six and a half full range drivers in them, some better sounding ones. Sorry for bothering but if you don't mind please suggest a make from your experience which I can order online. I don't think I enjoy high frequencies any more ( maybe I can't hear them) but a very clear voice and tuneful bass would be loved.

I bought a new Boston speaker A25 and was very disappointed.

Thanks and Regards

Bill

 

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RE: Drivers for existing cabinet, posted on May 1, 2024 at 10:52:20
Bill the K
Audiophile

Posts: 8448
Joined: June 3, 2006
 Sorry forgot to give the size. 12×8.25×8.75 inches. One port in the back at tweeter level.

Thanks

Bill

 

RE: Drivers for existing cabinet, posted on May 1, 2024 at 11:30:57
tomservo
Manufacturer

Posts: 8615
Joined: July 4, 2002
 The low end "knee" or corner is tied to the sensitivity and interior cabinet volume. So the LF -3 point, box volume and 1w sensitivity are tied together by the wall of science aka Hoffman's iron law, not a suggestion haha.
While your HF response may be rolled off, you have also adjusted to that and will notice if what was is no longer. But a woofer that gives you lower bass also doesn't go up high and a 6.5 inch driver is too large to go up all the way without a wacky radiation pattern.

Before you decide what to do, consider dipping a toe in the speaker building water.
Take one of your speakers your considering working on and put it on the table or living room floor and look at the woofer.
Examine the mounting screws and carefully remove them. They might be wood screws -or- machine screws with fine thread and a"T-nut" or threaded insert in the wood.

The woofer may well be kind of stuck to the baffle board, good speakers have a back gasket to seal that connection. If the woofer seems stuck, get a couple small blocks and position the speaker front down raised at the corners by the blocks. Usually gravity will free the driver after a little while.
If not, use a small wood block on the baffle to protect it and use a flat blade screw driver to pry up the edge of the driver, you may have to pry up in several places if it's really stuck (there was a speaker in the old days that actually caulked the drivers in).
IF your cabinet happened to have a port in the right place on the back, if you can push on the magnet with a stick that can pop one out too.

With the driver out, you have "it" in your hands and now you can look at your mounting hole diameter and bolt circle for if/when you look at drivers. Hopefully the driver has push terminals or push on removable connection but note which wire went where.
Hope that helps
Tom

About how far is the closest edge of the lf cone to the center of the tweeter?



 

RE: Drivers for existing cabinet, posted on May 1, 2024 at 13:39:05
hahax@verizon.net
Audiophile

Posts: 4431
Location: New Jersey
Joined: March 22, 2006
 Putting new drivers in an old cabinet is almost as bad as throwing a dart blindfolded when all you know is the direction to throw. Bass response, both quality and roll off point is totally linked to cabinet type(reflex or closed box), cabinet volume, driver Vas and driver Vts. All of these need to be coordinated to get the kind of bass you are looking for and without proper design you can be so far off you'll never listen to those speakers again. Normally you choose your drivers first and then design the box to enclose them.

 

If not for the need for truncated frame, simple task, posted on May 1, 2024 at 14:28:29
Edp
Audiophile

Posts: 4609
Joined: September 23, 1999
 The simple fact of initial model has truncated frames that use entire front baffle and that is issue

Tweeter faceplate size is also limiting factor. Possibly Wavecore, but guessing at size from photo.

A 1/2 cube foot box in 6 1/2 " 17 cm drivers is probably the most used versatile configuration you could want to upgrade. Literally many dozens upon dozens of designs. Even full kits from multiple sources.

Few if any use truncated drivers anymore, been awhile since I looked for that detail.

I have ground down round to fit truncated but not recommending for someone new to the process.

For the cost involved you maybe better off buying a ratty box set used and swap drivers

But if you want Togo ahead with your "use better drivers questions to gain experience, willing to help.




 

RE: Drivers for existing cabinet, posted on May 2, 2024 at 05:36:50
Bill the K
Audiophile

Posts: 8448
Joined: June 3, 2006
 The distance between the edge and the centre of tweeter is 1.75 inch

Bill

 

RE: Drivers for existing cabinet, posted on May 3, 2024 at 06:10:39
tomservo
Manufacturer

Posts: 8615
Joined: July 4, 2002
 Hi
Ok that small space means that your choice of crossover points is pretty wide open.

OTH, your thought about using a full range driver also has merit.

About 15 years ago at work i designed a small "fill" speaker that used a Fostex 126 full range driver with two small woofers.
Yesterday i had to see how the new version of the Fostex 126nv2 measured in that same cabinet.

There is a property the late Dick Heyser measured called Energy/Time Curve or Envelope which shows how fast the sound stops radiating from the driver after the signal ends.

The 126 has an unusually good ETC, at 10 inches distance the energy from the driver fell more than 50dB in just a few ms (50dB = 100,000:1 energy ratio) .
That is a very good sign as the biggest issue loudspeakers usually have is all the sound they produce and arrives that isn't directly tied to the input signal. That's the stuff that lets your ears triangulate on the speaker distance AND disrupts the acceptance as real of the illusion in the recording

This driver is large compared to 20KHz (wl about 5/8 inch) and I have not measured the polar pattern (it will have significant directivity up high) but on and near on axis, on a nice baffle (that doesn't cause re-radiations) that driver should provide an excellent stereo image. Like i said, that ETC property is a very good indicator so far as imaging.

At a modest distance, in the right bass tuning, this would be very satisfying speaker.

OTH, it will not produce much bass and if used in your box, you would want to model that driver in your box volume to see what port length gave the best results.

Your other options would be to use a tweeter that went down low and use a 6.5 inch woofer. That old speaker i was working on has 2x 5 inch woofers and the fostex .
For that you will need a new crossover. IF you have a lot of overlap, and drivers less than 1/4 wl at crossover, a first order crossover can sum into a "no phase shift" crossover like a single driver, unlike all the other named slopes 2nd order and above.
Alternately, if your boxes went down into the 60's alone, you would be able to hid a small subwoofer the do that bottom octave or more.
I have not looked at that driver so far as bass in many years but the measurements yesterday I thought were worth mentioning.
Subwoofers are the easiest speakers to make and with a low enough crossover can blend in.

 

RE: Drivers for existing cabinet, posted on June 1, 2024 at 14:16:14
oranda
Audiophile

Posts: 91
Location: So. California
Joined: October 16, 2005
 I agree in that you shouldn't choose replacement drivers at random. However, for a recycled, ported cabinet, if you get a Q somewhere in the 0.5 and 0.7 range, I don't think it's going to be all that terrible. Ports can often be altered and there are enough compromises made along the way in designing a cabinet that there is some degree of leeway in cabinet-driver matching. Certainly a cabinet can be made too small, but you can always add something to occupy the internal volume if it's too large.

If what you were saying was universally true, there would be one ideal cabinet for each driver which we know is not the case. As long as you are careful in your driver selection and can make some alterations, seems like it can be made to work.

Happy to hear other opinions on this matter.

 

RE: Drivers for existing cabinet, posted on June 2, 2024 at 11:11:19
Bill Fitzmaurice
Industry Professional

Posts: 5390
Location: New England
Joined: October 20, 2002
 Of course you shouldn't stick any driver in any cabinet, but it's not at all difficult to use speaker modeling software to see how any given driver would work in any given enclosure.

 

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