Crossover challenged

[tommytolson]

If I use a 3500 Hz crossover in a 2-way cabinet, does the woofer play beyond 3500 Hz? Does the tweeter play below 3500 Hz? How do I have both playing the maximum amount of time? Thanks.

Tommy Tolson

[marlboro]

> If I use a 3500 Hz crossover in a 2-way
> cabinet, does the woofer play beyond 3500
> Hz? Does the tweeter play below 3500 Hz? How
> do I have both playing the maximum amount of
> time? Thanks.

> Tommy Tolson

yes but how much depends on the slope of the cross. 6 db(1st order) slopes drop the sound requires by 6db per octave, which would be 7000hz one octave up from 3500.

Its part of the reason why all these designs have to be completely thought out beforehand, rather than just thrown together.

Marlboro

[dthomas]

> If I use a 3500 Hz crossover in a 2-way
> cabinet, does the woofer play beyond 3500
> Hz? Does the tweeter play below 3500 Hz? How
> do I have both playing the maximum amount of
> time? Thanks.

> Tommy Tolson

Yes... but as marlboro says it depends on the slope of the crossover and the acoustic output of the driver. 1st order crossovers have a 6db per octace slope, so the acoustic output of the speaker will be reduced by 6db for each halving or doubling of the frequency depending on whether it is a lowpass or highpass circuit.

Second order (12db), 3rd order (18db) or 4th order (24db) are seen more commonly and have progressively steeper slopes or more attenuation. And remember these are the electrical slopes the amount of attenuation from the circuit is completely dependant on the drivers acoustic output and impedance. So modeling the driver/crossover together is very important if you expect a reasonable result.

If you post or email the drivers you are intending to use I would be glad to assist you in doing an appropriate crossover circuit.

Dave

[marlboro]

Since they are electrical slopes, if you use an electrical crossover, what you see is what you get since you are using low voltages right out of the pre-amp.

You probably wouldn't do that, but there is a small group of us here that are real fans of electrical crosses, and wouldn't use anything else. Unfortunately that also requires a pre-amp, and a separate amp for each speaker range, plus the electrical cross. You can buy a new digital Behringer for about $230, or an analog USED Rane AC 22 or AC 23 for about $95 to $120 US$ on ebay, if you wait.

Marlboro

[damkor]

> Since they are electrical slopes, if you use
> an electrical crossover, what you see is
> what you get...

The response still depends on the raw response of the driver.

[dthomas]

> Since they are electrical slopes, if you use
> an electrical crossover, what you see is
> what you get since you are using low
> voltages right out of the pre-amp.

> You probably wouldn't do that, but there is
> a small group of us here that are real fans
> of electrical crosses, and wouldn't use
> anything else. Unfortunately that also
> requires a pre-amp, and a separate amp for
> each speaker range, plus the electrical
> cross. You can buy a new digital Behringer
> for about $230, or an analog USED Rane AC 22
> or AC 23 for about $95 to $120 US$ on ebay,
> if you wait.

> Marlboro

Uhh... I was referring to a passive crossover as I think that is what the first poster was asking about. A passive network has an electrical slope and that is imposed on the drivers acoustic output so depending on the driver it may or may not follow the electrical slope.

I think you are referring to line level active crossovers. But even they are are dependant on the drivers acoustic output. In the end the driver has the final say so in how it behaves to the signal. Crossing at line level is no guarantee that your driver will follow the assigned slopes it will be totally dependant on the drivers acoustic output.

Either method requires modelling/measurements to assure a reasonable result if a flat acoustic output is your goal.

Dave

[Andy_G]

There are not that many drivers that can really successfully be used with first order slopes, those that do tend to have poly or paper cones.

If you wish to use 1st order slopes you MUST choose your drivers very carefully from the start of the design process.

[tommytolson]

Thanks for the kind offer of help. I think Dayton DA175-8 woofers (8 ohm, 35-10000 Hz) and Morel MDT-20 tweeters (8 ohm, 1300-23000 Hz)as that takes me beyond the original frequency response range of the Infinity RS 2001s but to avoid cutting on the cabinets (to who knows what effect) I'm thinking Pioneer AHE60-51F horn tweeters (8 ohm, 2000-20000 Hz). Thanks again.

Tommy Tolson

> Yes... but as marlboro says it depends on
> the slope of the crossover and the acoustic
> output of the driver. 1st order crossovers
> have a 6db per octace slope, so the acoustic
> output of the speaker will be reduced by 6db
> for each halving or doubling of the
> frequency depending on whether it is a
> lowpass or highpass circuit.

> Second order (12db), 3rd order (18db) or 4th
> order (24db) are seen more commonly and have
> progressively steeper slopes or more
> attenuation. And remember these are the
> electrical slopes the amount of attenuation
> from the circuit is completely dependant on
> the drivers acoustic output and impedance.
> So modeling the driver/crossover together is
> very important if you expect a reasonable
> result.

> If you post or email the drivers you are
> intending to use I would be glad to assist
> you in doing an appropriate crossover
> circuit.

> Dave

[dthomas]

> Thanks for the kind offer of help. I think
> Dayton DA175-8 woofers (8 ohm, 35-10000 Hz)
> and Morel MDT-20 tweeters (8 ohm, 1300-23000
> Hz)as that takes me beyond the original
> frequency response range of the Infinity RS
> 2001s but to avoid cutting on the cabinets
> (to who knows what effect) I'm thinking
> Pioneer AHE60-51F horn tweeters (8 ohm,
> 2000-20000 Hz). Thanks again.

> Tommy Tolson

Tommy,

The DA175 is good to tops 2000Hz with 1500Hz being better upper limit. The morel tweeter might get you down to 1500Hz but my recollection is that will struggle to go that low.

Rule #1 is don't believe the manufacturer's claimed frequency response. If you look at the reponse graphs on the DA175 you will see that it is quite rough above 2000Hz.

Dave

[tommytolson]

Hi, Dave,
Before I learned that I didn't know what I was doing, I ordered Goldwood GW-6028s because they fit the hole in my cabinets but I'm considering sending them back. Usher 8945As fit the hole and have a wider frequency range than the others that are close to fitting, Dayton RS180S-8s and Vifa PL18W0-09-08s. I'm thinking Pioneer AHE60-51Fs, so the GW-6028s might accidentally work as there's a bit of an overlap between the woofer and tweeter for the crossover to deal with, if that's what I'm looking for.

> Tommy,

> The DA175 is good to tops 2000Hz with 1500Hz
> being better upper limit. The morel tweeter
> might get you down to 1500Hz but my
> recollection is that will struggle to go
> that low.

> Rule #1 is don't believe the manufacturer's
> claimed frequency response. If you look at
> the reponse graphs on the DA175 you will see
> that it is quite rough above 2000Hz.

> Dave

[dthomas]

> Hi, Dave,
> Before I learned that I didn't know what I
> was doing, I ordered Goldwood GW-6028s
> because they fit the hole in my cabinets but
> I'm considering sending them back. Usher
> 8945As fit the hole and have a wider
> frequency range than the others that are
> close to fitting, Dayton RS180S-8s and Vifa
> PL18W0-09-08s. I'm thinking Pioneer
> AHE60-51Fs, so the GW-6028s might
> accidentally work as there's a bit of an
> overlap between the woofer and tweeter for
> the crossover to deal with, if that's what
> I'm looking for.

The Usher, Vifa and RS180 are all good drivers and in my opinion in that order. Not sure about the Pioneer.

It is not very likely that the crossover in your existing cabinet will work well with any of these driver though. Crossover must be designed to fit the drivers parameters and it would be only by chance that you would get very good results trying to put any of these drivers into your existing cabinet with its crossover.

Dave

[tommytolson]

Hi, Dave,
No, if I were going to simply replace the 6 ohm speakers in my cabinets, I would, I think, buy Audax AP170Z0s and, if the tweeters don't work, either Vifa D27TG-35s or Tang Band 25-1372SCs. If I go 8 ohm, though, I run into the crossover issue right away. The RS 2001 6 ohm crossover is 4800 Hz. That seems pretty high, but I'm not sure I know enough about it to make a determination like that. I never dreamed what an adventure buying a pair of speakers in a thrift store could become. My first effort is going to be to replace the foam surrounds on the Infinity woofers to see if that fixes them. If that $20 effort doesn't work, I decide whether to stay 6 ohm or go 8 ohm. 4 ohm? I don't know. I want them to sound good as or better than Infinity speakers, so I have this ugly educational process to deal with, only it's not so ugly. Ignorance has a solution. Thanks for your help.

Tommy

> The Usher, Vifa and RS180 are all good
> drivers and in my opinion in that order. Not
> sure about the Pioneer.

> It is not very likely that the crossover in
> your existing cabinet will work well with
> any of these driver though. Crossover must
> be designed to fit the drivers parameters
> and it would be only by chance that you
> would get very good results trying to put
> any of these drivers into your existing
> cabinet with its crossover.

> Dave

[dthomas]

> Hi, Dave,
> No, if I were going to simply replace the 6
> ohm speakers in my cabinets, I would, I
> think, buy Audax AP170Z0s and, if the
> tweeters don't work, either Vifa D27TG-35s
> or Tang Band 25-1372SCs. If I go 8 ohm,
> though, I run into the crossover issue right
> away. The RS 2001 6 ohm crossover is 4800
> Hz. That seems pretty high, but I'm not sure
> I know enough about it to make a
> determination like that. I never dreamed
> what an adventure buying a pair of speakers
> in a thrift store could become. My first
> effort is going to be to replace the foam
> surrounds on the Infinity woofers to see if
> that fixes them. If that $20 effort doesn't
> work, I decide whether to stay 6 ohm or go 8
> ohm. 4 ohm? I don't know. I want them to
> sound good as or better than Infinity
> speakers, so I have this ugly educational
> process to deal with, only it's not so ugly.
> Ignorance has a solution. Thanks for your
> help.

> Tommy

I understand. If you can't repair your woofers then you probably want to scrap the internal crossover and have one done for the drivers you choose. You can easily equal the sound of the Infinity speakers. With the right drivers you should be able to exceed the sound quality.

There are plenty of folks here that will help you and feel free to email me if you run into problems.

Dave