re building speaker cabinets

[davestradamus]

i have some white van speakers that were given to me by a friend. i was thinking about adding some soundproofing in the cab, then replacing the drivers and crossovers with higher quality units. the cabs take 2 8" drivers and a tweeter. they are 4.5' tall and about 1.5' deep. the cabs are constructed from 3/5" mdf so they should sound decent right?
thanks
-david

 

[GregS351]

The box size depends on the speaker, just make sure the speakers you buy will work with the dimensions of the box you have already.

 

[davestradamus]

are you referring to the ratio between the volume of the cabinet versus size of the speakers/ movement of air in the cab?

 

[annunaki]

The T/S parameters determine the cabinet alignment (vented/sealed) as well as the size. It is all dependent upon the woofers used.

 

[jliedeka]

You can get WinISD for free to model the cabinet. You need to know the T/S parameters. You can get those from the driver spec sheet but it's better if you can find independent measurements from somebody like MarkK or Zaph.

You don't have to be exact with volume but you should be close. I'd measure the internal dimensions less any bracing, drivers and ports. You can probably guesstimate about a liter each for the woofers but a more accurate number might help.

A lot of DIY speaker builders will use a lower port tuning than the default you get from WinISD. (And a lower box tuning for sealed). The theory is you will get some room gain for the mid bass.

Also, you'll probably want to look for a tweeter that can be crossed fairly low to the 8" woofers. Some candidates would be the the Seas 27TDFC and 27TBFC and the Dayton RS28A.
Jim

 

[davestradamus]

WinISD is the next step then. i am not experienced with the crossovers used in speaker cabinets. are you saying since i have 2 8" woofers, the tweeter needs to be crossed over low to compensate for a the lack of a midrange speaker?
thanks for your help!
david

 

[davestradamus]

soo close....

on second thought...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=275-070

 

[TLS Guy]

soo close....

on second thought...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=275-070

Why do you have two different woofers on that order? You need four the same, with the right T/S parameters to fit the box. It needs to be a two and a half way speaker not a three way.

Crossovers need to be customized to the speakers. I never heard anything any good using off the shelf crossovers.

You did not give us the internal width of the box. If you post the internal volume we might be able to find you suitable drivers.

 

[jliedeka]

WinISD is the next step then. i am not experienced with the crossovers used in speaker cabinets. are you saying since i have 2 8" woofers, the tweeter needs to be crossed over low to compensate for a the lack of a midrange speaker?
thanks for your help!
david

It's actually the 8" woofer that would be the issue. It will depend on the driver but generally you don't want the woofer to cover very high frequencies.

The actual crossover point will depend on the driver and your baffle width. To get the best sound, you really need a Zobel (impedance leveling circuit), the crossover, baffle step compensation and possibly an L-pad to lower the tweeter level.

You may be able to find an existing design for a TMM system with 8" woofers. Then you can just order the same drivers and copy their crossover design.

Jim

 

[TLS Guy]

It's actually the 8" woofer that would be the issue. It will depend on the driver but generally you don't want the woofer to cover very high frequencies.

The actual crossover point will depend on the driver and your baffle width. To get the best sound, you really need a Zobel (impedance leveling circuit), the crossover, baffle step compensation and possibly an L-pad to lower the tweeter level.

You may be able to find an existing design for a TMM system with 8" woofers. Then you can just order the same drivers and copy their crossover design.

Jim

That will be his problem, there are very few eight inch drivers suitable to crossover to a tweeter. The ones that are available are costly, and then I bet his box will be the wrong size.

I think the OP will find out it is not good to start with a white van box.

I have a really good design using 7" woofers.

 

[TLS Guy]

That will be his problem, there are very few eight inch drivers suitable to crossover to a tweeter. The ones that are available are costly, and then I bet his box will be the wrong size.

I think the OP will find out it is not good to start with a white van box.

I have a really good design using 7" woofers.

I have looked at a lot of 8" drivers. Most have dreadful off axis response and terrible waterfall plots.

This one shows promise. They have good off axis response, and could be crossed over in the 1.8 to 2 kHz range. They would still need a notch filter in the crossover. However they are $212.00 each. So he would have $850 in woofers before selecting tweeters and crossover components. This would be a $1000 + reconstruct. Those white van cabinets are not worth it.

He would be into it for far less money he he starts from scratch. If he does not have carpentry skills he should by new speakers and send those cabinets to the dump.

 

[jliedeka]

I was thinking about suggesting he make a new baffle. He could probably turn them into a floorstanding Modula MT or maybe a Natalie P if the baffle isn't too wide.

Jim

 

[TLS Guy]

I was thinking about suggesting he make a new baffle. He could probably turn them into a floorstanding Modula MT or maybe a Natalie P if the baffle isn't too wide.

Jim

By the time you do that it is usually easy to start again. If he can get it out neatly though it would be an option. If the enclosure is too big, he can add bracing and a walled off compartment full of sand at the base.

We still do not know what volume we are working with.

 

[davestradamus]

wow, thanks for keeping me from making a terrible mistake! i really need to buy 3 matching front channels for my system. why am i so cheap??

 

[jliedeka]

You can get more bang for the buck with DIY but building speakers takes some work and designing speakers is hard. I'm in the process of building a bunch of speakers but I didn't design them. There are a lot of really smart people like Jon Marsh on the HTGuide forum that publish their design and assist builders.

I should qualify bang for the buck. You can build a speaker for a couple of Benjamins that will blow away anything the average guy could buy. OTOH, there are some pretty good speakers that can be bought for not a lot of money like the Infinity Primus series.

Jim