Raise crossover point?

[alexclaber]

If it's a 3rd order 6kHz HP, as has been guesstimated by others, then it would be -18db at 3kHz.

That entirely depends on the the impedance curve of the tweeter - the response will only be definitely 18dB down at 3kHz if the tweeter has a totally flat impedance curve. In reality the tweeter is likely to have at least one resonant peak below 5kHz, each of which will change the filter response.

Alex

 

[David Jayne]

Since you can zoom in on it using your EQ, wouldn't it make just as much sense to find it, then cut it hard to remove the quack you don't like?
Seems easier than modifying the Xover.

You'd think so, but the Q on the control is too wide for this and so eliminates too much above and below it's center.

 

[billfitzmaurice]

You are correct, Bill- some of the offending quack is coming from the speakers, but the vast majority is coming from the tweeter. I can zero in(roughly) on these frequencies using the EQ on my amp. Boosting Hi Mid control and sweeping the frequency center, I land here, the quack zone. The range of the control is 700hz to 6kHz, so this would be, what, 2-3K?

Could be. The tweeter can be receiving a fair amount of power at 3kHz, and that quack is its way of telling you that it doesn't like it. The main reason why most manufacturer's use such a high crossover point is that the inexpensive tweeters they use have to be crossed that high or they'll blow, and in some cases even 3rd order won't allow them to perform as well as possible. If your problem is 3kHz raising the crossover point would help, but only at the expense of response where you do want it. A 4th order filter is a better route, as is using a better tweeter.

 

[BassmanPaul]

Seems to me to be a complete waste of time and effort. If you don't like what the cabinet is doing for you that's fine. Before you alter the crossover and negatively impact the cabinets resale value, sell it and buy something you do like. All of us, at some time or other, have gone through similar situations. To "fix" what you consider to be a problem entails a complete redesign of the crossover if you are to do it properly. Just put the money towards something else.

Paul

 

[megadan]

You'd think so, but the Q on the control is too wide for this and so eliminates too much above and below it's center.

Hmm.

Maybe a good rack rack or pedal could be a better tool for that. Might be just as cheap as changing the Xover, taking into account resale value, and easily reversable!

 

[David Jayne]

Seems to me to be a complete waste of time and effort. If you don't like what the cabinet is doing for you that's fine. Before you alter the crossover and negatively impact the cabinets resale value, sell it and buy something you do like. All of us, at some time or other, have gone through similar situations. To "fix" what you consider to be a problem entails a complete redesign of the crossover if you are to do it properly. Just put the money towards something else.

Paul

I knew it was just a matter of time before someone said that. But I'd like to fix it, because no one else makes a cab like this, you see. I may swap the crossover out of my Goliath and see how that works.

 

[will33]

Hmm.

Maybe a good rack rack or pedal could be a better tool for that. Might be just as cheap as changing the Xover, taking into account resale value, and easily reversable!

To be effective you'd need a fully parametric eq so you could set the Q very narrow, a useful tool but it'd probably be cheaper to make a new HPF.

Would a narrow notch filter remedy this? More of a band-aid than a fix and with the parts count you're probably back to building a new filter again. Sorry to answer my own question....sort of.

 

[greenboy]

That entirely depends on the the impedance curve of the tweeter - the response will only be definitely 18dB down at 3kHz if the tweeter has a totally flat impedance curve. In reality the tweeter is likely to have at least one resonant peak below 5kHz, each of which will change the filter response.

Yep. A lot of the compression drivers on cheap horns have a pretty obvious primary resonant peak, and a couple of related secondaries, and one of those can be fairly hot too. It's not unusual to see the primary one be audible in spite of a higher crossover point unless the crossover has a tank filter for it.

In decent PA boxes, the crossovers seem to take this into account and also work in some CD compensation which can have the net effect of moving that ouput a few dB lower yet. But in bass cabs the rudimentary crossovers and cheap driver/horn combinations seem to have some output down lower that shows through in a bad way.

 

[Rick Auricchio]

I may swap the crossover out of my Goliath and see how that works.

Don't try that without first posting the impedance of the cabinet! You can damage the tweeter or the amp.

Of course, blowing the tweeter would solve part of the problem...

 

[will33]

Just make sure the 2 tweeters are the same impedance, if not switch the tweeter out of the goliath along with the filter. The 10's in either cab will be wired to a main line coming from the jack and let play as high as they'll go, the tweeter is HPF only, there is nothing cutting the top of the 10's off, they don't go that high anyway.

 

[David Jayne]

OK, I went ahead and did it(I did verify the horns are both 8ohms first).
Mixed results. The unpleasant noise was gone, but it was too much of a good thing- the SWR X-over cut too much off the bottom of the horn, leaving a too-large hole in the upper midrange. It sounded sweet, but there was no grit left, only sparkle. My guess is I want something in-between these two X-overs. Anybody want to help me build it? Here's a pic of the SWR unit. The choke reads .17mH:

 

[David Jayne]

Or maybe I should look for a better horn, or other tweeter?

 

[will33]

You can use the 2-way crossover calculator at that link I posted at the beginning of the thread to find something in-between those two. Only pay attention to the top half of the crossover as you're not cutting the top of the 10's off. Problem is I've never come up with a 3rd order filter where the 2 capacitors are of the same value before and after the inductor. If those 2 capacitors on the swr filter are wired together on the back side of the board it could be a 2nd order but that would put the crossover point pretty low for a tweeter on a little horn like that, something's weird there.

Best bet might be to let this thread ride through tomorrow and see what the real guru's have to say about it.

This http://www.talkbass.com/forum/showthread.php?t=160091&highlight=avatar+tweeter+mod might be the thread about the tweeter mod on the avatar but not sure, I thought they replaced the tweeter with something like this [Invalid or Expired Link Removed] .

The main point was getting the tweeter to play as low as it could and still sound pleasant to take up as much of the response gap as you could, then chop it off sharply with a 4th order HPF to keep the quack out.

 

[Stumbo]

How about a 31 band 15db cut/boost e.q.?

 

[will33]

Another good tool but still likely more expensive than the parts cost of building a good passive HPF and one more piece to carry around. IMO of course. 31 band EQ belongs in the PA.

 

[DukeLeJeune]

I may swap the crossover out of my Goliath and see how that works.

A tweeter will have a particular frequency response curve, impedance curve, and efficiency, as well as thermal and mechanical power handling capacities. The crossover designer would have taken all these factors and more into account - but only FOR THAT TWEETER. Give that crossover a different tweeter, where all of these factors are probably different, and at best you've got a roll of the dice. At worst, the new tweeter will be inadequately protected.

I would not undertake to modify an existing crossover without having comprehensive spec sheet on the drivers, nor without being able to make my own frequency response and impedance measurements, nor without a LOT of motivation. Modding a crossover is easy; doing a good job of it is not.

DIY speakerbuilding can be great fun and even highly rewarding, but trying to second-guess a professional crossover design is not where I'd recommend someone start.

 

[KJung]

A tweeter will have a particular frequency response curve, impedance curve, and efficiency, as well as thermal and mechanical power handling capacities. The crossover designer would have taken all these factors and more into account - but only FOR THAT TWEETER. Give that crossover a different tweeter, where all of these factors are probably different, and at best you've got a roll of the dice. At worst, the new tweeter will be inadequately protected.

I would not undertake to modify an existing crossover without having comprehensive spec sheet on the drivers, nor without being able to make my own frequency response and impedance measurements, nor without a LOT of motivation. Modding a crossover is easy; doing a good job of it is not.

DIY speakerbuilding can be great fun and even highly rewarding, but trying to second-guess a professional crossover design is not where I'd recommend someone start.

This makes sense and +1.

Also, just as a reminder to those reading this thread, the OP is looking for a very specific response from the high end of his cab. The SWR circuit is, IMO and IME, unique, in that the tweeter seems to carry only the upper, upper treble sizzle, so there is a wider 'hole' between the response of the tweeter and the top end of the woofer. For certain tone goals this sounds beautiful with a bass guitar.

The Epi tweeter, while more 'airy' than most (i.e., that steep roll-off slope and relatively high crossover point), is not nearly the 'super sizzle' tone profile of the SWR circuit.

So, again, if you read through the EpiUL mega thread, the crossover and tweeter design of the EpiUL's is one of the things that most of us simply LOVE about the UL's. However, if you are a player like the OP that, from my understanding, is trying to get that classic SWR sizzle from an Epi, that's a bit difficult.

While I moved from the SWR sound to the Epi tone a while back, part of the reason was that I tired of that 'SWR super top end sitting way above the woofer' sort of tone. However, in general, I still like that tone universe, and to my ear, the Epi does this more musically and evenly than the SWR circuit (i.e., not quite as extreme).

So again, for you cab designers/tinkerers, there is NOTHING wrong with the Epi circuit at all. It just doesn't seem to fit the OP's tone goal. Nothing wrong with that, and I believe the OP will find his solution when he gets the new SWR GoLight 410 (i.e., the SWR tone he loves in a much lighter weight package).

IMO!

 

[David Jayne]

A tweeter will have a particular frequency response curve, impedance curve, and efficiency, as well as thermal and mechanical power handling capacities. The crossover designer would have taken all these factors and more into account - but only FOR THAT TWEETER. Give that crossover a different tweeter, where all of these factors are probably different, and at best you've got a roll of the dice. At worst, the new tweeter will be inadequately protected.

Yes, I know, you're right. I'm listening. If I can't do it, well, I won't do it. Just thought it was worth a shot, but I do understand that it's complicated.
It's in my blood to tweak stuff. I don't believe I own anything that's still factory spec, with the exception of my mower, and TV. Edit: modified the mower, forgot.

 

[KJung]

I don't believe I own anything that's still factory spec, with the exception of my mower, and TV. Edit: modified the mower, forgot.

I think you passed me on the highway riding that mower the other day

 

[David Jayne]

I think you passed me on the highway riding that mower the other day

Red Toro? It's fast, huh? "More Power! Uuurrrhhhh!!!"