Need help understanding this crossover, then choosing speakers for mystery cab - Page 1
Forum section: electronics / projects

author: mkiijam
author_rank: Regular Contributor
timestamp: February 16, 2024, 03:13:33 am
content: I have these 3-way cabs. They have 15" woofers. The mids and tweeters are horn type. They were given to me with not only the mids blown, but the mids and tweets replaced at some point with random speakers. I would like to get back to something that is closer as the one cab that is still working sounds bad, like way out of balance.I figured that maybe the crossover specs would reveal something about the mid drivers and tweeter specs? I believe the original drivers were 8Ohm woofer, 8 Ohm Mid, and 6 Ohm tweeter.

author: CaptDon
author_rank: Super Contributor
timestamp: February 16, 2024, 03:31:57 am
content: Are you kidding me, the woofer has no low pass high cut circuit? It is direct to the input jacks?? What brand is it and what model number? You could probably find the original direct replacement drivers online and examine the specs. If I read correctly you have one cabinet totally dead and one cabinet that sounds bad? Much like the BOSE Tandem Tuned 100 pound subwoofer, the cabinets may be useful as kindling for winter heat. Your schematic shows respectable crossovers for the mid and high but without low pass / high cut in the woofer circuit I doubt these cabinets ever sounded 'good'. Woofers are often spec'd as 40Hz to 3000Hz but anything fed to the woofer above about 400Hz will sound like hammered dog poop totally lacking in definition and interfering with the mids causing a muddy low mid and mid. If you got them for free you may have already paid to much considering what I may cost to replace the drivers and still get poor sound.

author: mkiijam
author_rank: Regular Contributor
timestamp: February 16, 2024, 04:06:17 am
content: YQuote from: CaptDon on February 16, 2024, 03:31:57 amYep! sure looks like it to me. I didn't believe my eyes, but they are BI-amp - TRI-ampable so I think the idea was to send them a woofer type signal.TurboSound Prague TPZ153/64I should have drawn the schematic with the separate woofer input as it is totally isolated from the rest, My bad:-(

author: mkiijam
author_rank: Regular Contributor
timestamp: February 16, 2024, 04:11:27 am
content: speakers - Schematic.pdf(11.62 kB - downloaded 69 times.)

author: GLouie
author_rank: Regular Contributor
timestamp: February 16, 2024, 05:11:11 pm
content: I'm not familiar with the speaker, but Turbosound was bought by Behringer. These are live sound speakers, the general specs are on the Behringer (musictribe) site:https://mediadl.musictribe.com/media/sys_master/h2f/h33/8848066805790.pdfBehringer has a poor reputation sometimes for supplying repair parts and service info. You might find similar replacement parts, but in the end you'll probably end up with a poor performing speaker and spending too much money.

author: donlisms
author_rank: Frequent Contributor
timestamp: February 16, 2024, 06:17:55 pm
content: The corrected schematic makes more sense, and I would say is perfectly normal for such a cabinet. Bi-amping over three drivers.I think the original schematic might have sounded a little whack in the lower middle when the mid driver started kicking in, but it wouldn't have been any screaming disaster. Just a little... "off".A little math would give the crossover frequencies for the high-end driver pair, and I can't read it well in my phone, so I'm not going to be helpful there. :-). There are, however, many crossover calculators online; maybe one of them will help.Once the frequencies are split, there is still the issue of the driver efficiencies, which are going to effect the overall balance between them. So... either two drivers with very close efficiencies, or... just pop in a shelf filter at the mixer output, if you can do that.And then, of course, the lower limit of each driver, which is where the power handling matters because it's where we're asking the most cone excursion, and it's as the natural balance of power in music goes up so dramatically. (I think it's to the 4th power or something; don't remember.) So you don't want a mid that handles 1kHz at its low end if the crossover is going down to 500.Another issue with cabinet design is dispersion, where as the frequency goes up, a driver's pattern gets narrower and narrower. So you kinda have to match the driver sizes with the crossover frequencies, to try to keep the dispersion similar between all the drivers - when one starts to get narrow, you hand it off to the next smaller driver. This is a little different than just making each driver has its own power-handling range and such. What it implies is that since you're going to be using the same size drivers, you should probably stick with the same crossover frequencies. Which, I guess, is the natural flow of things in your project, since there's probably no reason to change the crossover.So... do some filter math, and find drivers that have proper low-end power limits, and similar efficiencies, and there you go. And of course you want both cabinets the $ame.Tri-amping is an alternative that puts the control of all the parameters outside the cabinet and easy to tweak, but it's kind of a pain. Potentially higher quality, but probably not worth it for a cabinet like this.