studio monitor xover

[luker]

In my studio I have custom studio monitors: Peerless 7" exclusive, SEAS 27TDFC, professionally built boxes, and a xover design from madisound. The projected response from madi was awesome, like +-1db. But something is seriously wrong with the design. I have an auto eq processor and it corrects 12db dips and peaks in the speakers. I have triple checked everything and explored all suggestions given by the designer. Any thoughts? Thanks.

[daryl]

Provided Link: Daryl's Speaker Stuff.


Get a power inverter and go to a deserted parking lot at night.

Hook your equipment up in your car and put the speaker on top of a 10' board and suspend the measurement mic 3' in front of the speaker and try it again.

[billfitzmaurice]

> Get a power inverter and go to a deserted
> parking lot at night.

> Hook your equipment up in your car and put
> the speaker on top of a 10' board and
> suspend the measurement mic 3' in front of
> the speaker and try it again.

What he's saying is that predicted response is in an anechoic environment, half-space, not a real room.

[luker]

> What he's saying is that predicted response
> is in an anechoic environment, half-space,
> not a real room.

Ok...I can see that. But there is still a big problem with the speakers. The response drops off after about 2k about 12db. It's not a picky thing, it is a blatant flaw. I just don't understand what the problem is. Hmm...

[dthomas]

> Ok...I can see that. But there is still a
> big problem with the speakers. The response
> drops off after about 2k about 12db. It's
> not a picky thing, it is a blatant flaw. I
> just don't understand what the problem is.
> Hmm...

It could be a reflection especially it is a small room and the speakers are on a shelf close to walls etc... Or it could be the tweeter polarity needs to be reversed. Where did they cross the tweeter to the woofer. If it is at around 2K you could just have the tweeter in the wrong polarity.

Dave

[billfitzmaurice]

> Ok...I can see that. But there is still a
> big problem with the speakers. The response
> drops off after about 2k about 12db. It's
> not a picky thing, it is a blatant flaw. I
> just don't understand what the problem is.
> Hmm...

How wide is the cabinet? Around 7-8 inches? That places the baffle step in the vicinity of 2kHz, explaining 6dB of that drop. How do you have them placed? Improper placement would explain the other 6dB, as would series wiring the woofers instead of parallel and a number of other scenarios. Knowing all the exact particulars would help.

[luker]

> It could be a reflection especially it is a
> small room and the speakers are on a shelf
> close to walls etc... Or it could be the
> tweeter polarity needs to be reversed. Where
> did they cross the tweeter to the woofer. If
> it is at around 2K you could just have the
> tweeter in the wrong polarity.

> Dave

The xover point is around 2k. The dip is from 2k and all the way up. I will reverse the ploraity though. I haven't tried that yet.

[luker]

> How wide is the cabinet? Around 7-8 inches?
> That places the baffle step in the vicinity
> of 2kHz, explaining 6dB of that drop. How do
> you have them placed? Improper placement
> would explain the other 6dB, as would series
> wiring the woofers instead of parallel and a
> number of other scenarios. Knowing all the
> exact particulars would help.

The baffle is 10" wide and 15" tall. I gave the baffle deminsions to the designer and he said it was taken into account when designing the xover, however it is just a simple two-way 12db/octave. The speakers are placed about 5 inches away from the wall on a desk top, so nothing on the sides of them or above. The side walls are around 48 inches from each speaker. The woofers are wired in parallel with the tweeters if that is what you meant. And I have triple checked to makes sure the xover is properlly wired. Thanks alot for your help in this.

[dthomas]

> The xover point is around 2k. The dip is
> from 2k and all the way up. I will reverse
> the ploraity though. I haven't tried that
> yet.

If the dip runs from 2K all the way up then I doubt it is a reverse null from improper polarity on the tweeter. That should not be any wider than a few thousand hertz depending on the measurement axis and distance.

It sounds more like something odd like a mis-wired network or a component with a mis-labeled value. Can you post the crossover schematic?

Dave

[billfitzmaurice]

> If the dip runs from 2K all the way up then
> I doubt it is a reverse null from improper
> polarity on the tweeter.

I misunderstood the original post, took it to mean that the woofers were down 12dB from the tweeter level. If the tweeter is down 12dB from the woofer level that's quite odd. A 12dB phase dip at the crossover would be expected with a 2nd/2nd crossover if the tweeter polarity isn't reversed, but that dip should be only 100Hz or so wide. A 12dB sensitivity loss across the entire tweeter bandwidth points to an error in the wiring and/or components of the crossover.

[dthomas]

> I misunderstood the original post, took it
> to mean that the woofers were down 12dB from
> the tweeter level. If the tweeter is down
> 12dB from the woofer level that's quite odd.
> A 12dB phase dip at the crossover would be
> expected with a 2nd/2nd crossover if the
> tweeter polarity isn't reversed, but that
> dip should be only 100Hz or so wide. A 12dB
> sensitivity loss across the entire tweeter
> bandwidth points to an error in the wiring
> and/or components of the crossover.

I agree... it sounds like one of those "oh crap why did I not notice that the first 12 times I looked at this" problems. My first guess would the be the cap and coil in the high pass are in the wrong positions. Or if there is a 2 resistor zobel the resistor values might be reversed. Just guessing without thinking much but it sounds like one of them pound you palm against your forehead problems.

We have all done it once... or if you are like me more than you can care to admit.

Dave

[luker]

Provided Link: http://webmail.rmc.edu/exchange/LMcG...9.pdf?attach=1


> If the dip runs from 2K all the way up then
> I doubt it is a reverse null from improper
> polarity on the tweeter. That should not be
> any wider than a few thousand hertz
> depending on the measurement axis and
> distance.

> It sounds more like something odd like a
> mis-wired network or a component with a
> mis-labeled value. Can you post the
> crossover schematic?

> Dave

This should work. The schematics are on the fourth page.

[dthomas]

> This should work. The schematics are on the
> fourth page.

It wants a user name and pass code?

If you have a pdf just email it to me at the address above.

Dave

[luker]

> In my studio I have custom studio monitors:
> Peerless 7" exclusive, SEAS 27TDFC,
> professionally built boxes, and a xover
> design from madisound. The projected
> response from madi was awesome, like +-1db.
> But something is seriously wrong with the
> design. I have an auto eq processor and it
> corrects 12db dips and peaks in the
> speakers. I have triple checked everything
> and explored all suggestions given by the
> designer. Any thoughts? Thanks.

You guys were right. After the tenth or so check I realized my tweeter pad was wired backwards. I can't believe it! I have been messin' with this thing for months! Ahh...I am very relived though. Wow, haha. Thanks for all the help.

[flexus]

hi luker,
sorry to get back to such an old thread, but i´m working on a sealed 830883 / 27tdfc kombi and would be very interested in seeing the crossover schematics. maybe you could post it here.

greets,
flexus