Starting with the enclosure, not the drivers

[paean]

Hello all,
It seems so many people here start their DIY loudspeaker designs with the driver selection, but I found some old floorstanders my father had buried in the basement. Upon closer examination, I saw one of the midbass drivers had a finger sized hole through it. (Yep, I was the curious critter who destroyed it.)

The cabinets look pretty good. A little cleanup and I think I can make it shine. Sounds an opportunity to experiment.

So let me throw this out there. How does one pick drivers after he has already picked his enclosure?



NB: Please excuse the innocence of this request for help. I have searched the forums, but I'm just getting into home audio so direct advice would really help me on my way. Thanks!

[Dryseals]

That's really not a tough thing to do, I've done it's many times for myself and other folks, but will some time take some research.

The first thing is to inspect the cabinet to see if you can gain access to the internals. Most cabinets were glued together, so the only access is through the speaker holes. Measure the internal space you have available to work with. Then download something like winisd or a few of the spread sheets floating around out there.

Then you go to somewhere like partsexpress and find something that will fit in and work. Run the numbers and look some more

It's a good lesson on speaker building, just remember that you can always make the cabinet a little smaller by adding more wood. Some older sealed enclosures where big, so you might want to go ported, and then again, you can some times close the port and shrink the internals for a sealed box.

[bjorno]

Sounds an opportunity to experiment.

Yes but….
Your question is of a too general nature to be answered.
Narrow down and specify your question to be more manageable.

1.What kind of enclosure are the floorstanders and the existing driver brand? Are they of closed or ported type?

What are the speakers internal and external dimensions and seizes, you have to make accurate measurements.

A scaled drawing with all drivers should be provided, calculate the internal volume and measure eventual port length and internal diameter and preferably post a picture or write down all measurements you can get hold of.

Estimate the amount of box damping material and where it’s located in the box.

2.What is your total speaker driver budget the filter included?

3.You must first estimate your expectation of speaker performance and tell us how you will use them, close to a wall or as floorstanders away from any wall a couple of feet.

4.What sensitivity SPL at 1m/1W are you aiming at (85-95)? How low do you expect the speakers to go, estimate the low frequency extension needed?

Be serious and you will have corresponding answers in return.

b

[stokessd]

Also take a serious look at the speakers in question, are they worth the time and effort? If you replace one driver you will have to rework the crossover. Are the other drivers and the enclosure nice enough that when all the effort is over will you be ahead vs. selecting drivers and building from scratch. Don't forget that over the last decade or so, drivers have gotten a lot better.

An example: A friend of mine was given a set of Theil 3.6's without tweets (and woofers). The cabinets were just OK, but not amazing (buy our DIY standards). The tweeter hole was a non-standard diameter, and there was something funky about the woofers. Anyway he tracked down the original parts and refinished the cabinets and frankly spent a whole lot of time and effort on a project that in the end wasn't nearly as good as his other projects, and cost more in time and effort than starting from scratch. He sold the speakers as part of a fun-draising effort for a friend who died from cancer, so it went for a good cause.

My view of old speakers is that they are old, and probably not as good as you could do today if you started from scratch. Not all old is good. Example: Old tube amps are usually quite good, old tube preamps are usually not. Old speakers are typically not particularly good either.

[Dryseals]

Originally posted by stokessd
Also take a serious look at the speakers in question, are they worth the time and effort? If you replace one driver you will have to rework the crossover. Are the other drivers and the enclosure nice enough that when all the effort is over will you be ahead vs. selecting drivers and building from scratch. Don't forget that over the last decade or so, drivers have gotten a lot better.

An example: A friend of mine was given a set of Theil 3.6's without tweets (and woofers). The cabinets were just OK, but not amazing (buy our DIY standards). The tweeter hole was a non-standard diameter, and there was something funky about the woofers. Anyway he tracked down the original parts and refinished the cabinets and frankly spent a whole lot of time and effort on a project that in the end wasn't nearly as good as his other projects, and cost more in time and effort than starting from scratch. He sold the speakers as part of a fun-draising effort for a friend who died from cancer, so it went for a good cause.

My view of old speakers is that they are old, and probably not as good as you could do today if you started from scratch. Not all old is good. Example: Old tube amps are usually quite good, old tube preamps are usually not. Old speakers are typically not particularly good either.

One thing to remember, is that this guy is wanting to learn something about speakers. The strive for perfection often drives folks away and most folks could really careless about it being perfect.

But given an opportunity to experiment, often leads one to dig a little further. Take a good look at the first speaker you ever built and compare it to what you have today. Each time we go for a bit better than last time.

[AKN]

Hi paean,

I saw one of the midbass drivers had a finger sized hole through it

It means that one of them is ok, right?
Post some pics of the driver in question.
It should be possible to measure TS parameters of the driver that's ok.

[paean]

First off, I appreciate the offers of help. I honestly didn't think anyone would take a second look at my request for assistance.

I will have to pull apart this cabinet to get most of the information that's been requested, but here's the best I can start with.

This is my first effort so I can tell you up front it won't be exacting or up to the respectable benchmark many of you stand by. That said, I would very much like to build on what I learn and attempt better loudspeakers with more specific goals.

The general idea is to make a budget setup with minimal complexity. Remember, this is my first go. Perhaps $250-300 in materials, if its possible. I'm not looking for anything loud, but these will likely be used in a small room, so that should be fine. I have an old HK amp I'd like to play with, but its only 25w rms aside, so I'm guessing there aren't many speakers efficient enough to play ball. And yes, I would like to replace all drivers, if possible.

After having a once over, I can tell you that the cruddy dampening materials are falling apart and will need to be stripped and replaced. The MDF is 3/4" all around. Here are the internal measurements of the box, not including dampening.

h=19.25", w=11.5", d=6.0"

Dryseals is correct about the cabinet being glued together. This is going to be interesting. I'm not quite sure where to start. O =

After doing my measurements of the enclosure, I pulled the grill off of the mid and tweeter. I'm assuming the top speaker is a tweeter, but I've never seen a tweeter that looks like this. Here are the measurements of the speakers.

Tweet - 3 3/8"
Mid - 4 3/8" surround, 3" cone fabric
Mid bass - 8 3/8" outer MDF surround, 7 1/8" speaker surround, 5 3/4" cone fabric

As you can see from the photo, there is a port on the front and a port on the back. Here are those measurements.

Front port - 2 1/4" across, 5" deep
Back port - 2" across, 3/4" deep


Sorry about the photos. I didn't even clean the cobbwebs off the cabinets. Haha...



Please let me know if closeups would be of any benefit.

[paean]

Oh, and I'm not sure how important it is, but the brand on the cabinet is Vega Linear, and the model is VL 12. I did a little snooping around and found that these are no-name speakers that were sold in Alberta in the early 80s. They were sold with HK amps and cassette players... which explains the other equipment sitting in my father's basement.

[sreten]

Hi,

The hole in the bass driver is relatively easy to fix, if your not ham-fisted.
Search on author "sreten" and text "PVA", request any explanations needed.

Crossover details would be nice .........

/sreten.

[audiobomber]

Not worth the time, effort or expense IMO. Not trying to be a dick, I just don't see anything worth saving here. The cabinet has weird dimensions, isn't attractive or well-built or anything. The crossover's only going to work for those exact drivers, and the drivers are nothing special at all (judging by the 49 cent tweeter).
If I were you I'd clean up the cabinets, patch the damaged woofer and call it a done deal.

You'll learn as much and have a more rewarding result if you build new speakers from scratch (i.e. follow one of the DIY recipes online). For example the Zaph budget MTM fits your price range, and will look and sound way better than anything you'll achieve with your dad's old speakers.

http://www.zaphaudio.com/BAMTM.html