# passive crossover



## snapvalonia (Jun 29, 2010)

Does anyone know where I can find a good range of crossovers. Diy build is ok. For small hifi speakers. About 75 watts. Thanks in advance.


----------



## robbo266317 (Sep 22, 2008)

Crossovers need to be designed for the individual drivers used. Do you have a list of drivers you are considering?


----------



## snapvalonia (Jun 29, 2010)

im using a Peerless 830860 HDS 134 PPB MidWoofer Speaker
and a Peerless Vifa XT25SC90-04 Tweeter


----------



## robbo266317 (Sep 22, 2008)

The MidWoofer you have chosen is an 8 Ω unit whereas the Tweeter is 4 Ω. Typically these need to be the same impedance.
I would recommend either finding a suitable 8 Ω Tweeter, or a 4 Ω MidWoofer.


----------



## snapvalonia (Jun 29, 2010)

the problem is that these 2 drivers have been chosen as part of the box design. Im sure a crossover design could compensate for these ohm numbers to give a more satisfactory ohm reading in total.


----------



## robbo266317 (Sep 22, 2008)

snapvalonia said:


> the problem is that these 2 drivers have been chosen as part of the box design. Im sure a crossover design could compensate for these ohm numbers to give a more satisfactory ohm reading in total.


I personally would consider adding a second MidWoofer in parallel with the first to achieve a 4 ohm nominal impedance. 

However, here is a *simple* first order crossover using the stated resistance of the two drivers of 5.7 and 3.2 ohms and a crossover frequency of 2 kHz. (From http://www.diyaudioandvideo.com/Calculator/XOver/ )









You will need to add a level matching circuit to balance the output from each driver and this is best done by measuring the finished system.

Note: There are more complex crossover design calculators but it depends on what you are trying to achieve.


----------



## snapvalonia (Jun 29, 2010)

I cant add a second woofer as these are small bookshelf boxes that are designed with a separate sub box. It should be fine with a slightly strange ohm rating. Thanks for advice.


----------



## snapvalonia (Jun 29, 2010)

Im looking for a crossover that is clean as possible yet simple. The speakers are very good quality
So sound is everything


----------



## joebertin (Jul 21, 2013)

Put a 4 ohm resistor in series with the tweeter. That will give you your 8 ohms.


----------



## Kiwilistener (Apr 5, 2010)

You're not asking the right questions, or supplying the right info. As robbo has said, each speaker combination needs to have a crossover designed for it.

First off the drivers you are choosing and specifically the woofer don't really work all that well together ( or at least not in the modelling I've done ). The woofer has a very low Vas which means it should be good for a small enclosure but in reality anything under about 15 liters is going to sound horrible.
I ran the specs through a number of scenarios with uni-box and 15 liters appears to be optimum, in a vented enclosure. This yields good numbers in general all though at max SPL it is possible theoretically to exceed xmax. You wanted 75 watts but the limit will be whatever the woofer provides, in this case 50 watts appears to be the limit.

I ran a number of models for the crossover as well. Best result without huge expense comes when the drivers are crossed at 3000 kHz, as seen in the first image. The graph shows how the crossover matches and the 3rd image shows why it is almost never a good idea to just put a resistor in series with speaker in an unequal setup. The graph shows a really nasty rise in the tweeter which would sound horrible. To demonstrate this I simply zeroed RP2 and changed the value of RP1 to 4 ohms. Even when impedance equalisation is added back to the crossover the hump remains from the 4 ohm resistor.


Both the tweeter and woofer need to have impedances equalized and there needs to be a 5 dB L-pad on the tweeter with the polarity reversed as well. This design assumes a vented 15 liter enclosure.

If I were using these drivers this is how I would have them running. You can then look at the drivers graphs and see if there are any really large dips in the frequency response graphs and perhaps add a contour/notch/zobel circuit if needed. As it stands the crossover below may well yield a pleasant result and no further tweaking may be necessary. I generally try to arrive at that scenario as start point, then adjust after a couple of hundred hours of run in time. This allows new drivers to settle in. Measuring at this point is always a handy thing but I generally tune to my ear and leave it at that. The purist wouldnt recommend this but unless you have a dedicated listening room accurate measurements can be very difficult to achieve.


----------



## Kiwilistener (Apr 5, 2010)

This is what happens to the crossover when a 4 ohm resistor is placed in series with the tweeter to (equalize) the load seen by the amp.


----------



## robbo266317 (Sep 22, 2008)

Thanks for the great input Kiwilistener, it highlights the need to research the drivers to be used and how they interact. 
After choosing drivers you need to model them to see how they work together and, if unsatisfactory, look at what else is available.


----------



## Kiwilistener (Apr 5, 2010)

robbo266317 said:


> Thanks for the great input Kiwilistener, it highlights the need to research the drivers to be used and how they interact.
> After choosing drivers you need to model them to see how they work together and, if unsatisfactory, look at what else is available.


Agreed. Choosing drivers that match well is without doubt the most important first step once one has decided on the type of speaker they want to build.


----------



## snapvalonia (Jun 29, 2010)

Thanks for all the info guys. Went back to the drawing board on this. 
Decided to order Harris techs crossover design program to help me along.
Hopefully I can post some results later this year.


----------



## Kiwilistener (Apr 5, 2010)

Good luck with the project and if you have the time a build progress thread would be cool too.


----------



## snapvalonia (Jun 29, 2010)

Ye no problem


----------



## PlanoDano (Aug 30, 2013)

Troels Gravesen has a published design using these drivers. I hear he is pretty good
http://www.troelsgravesen.dk/Peerless_HDS830860.htm


----------



## Kiwilistener (Apr 5, 2010)

PlanoDano said:


> Troels Gravesen has a published design using these drivers. I hear he is pretty good
> http://www.troelsgravesen.dk/Peerless_HDS830860.htm


Yes he is a good designer, I'm currently building a slightly modified version of his PMS. Build thread here.

The drivers Troels used for his design , differ slightly from the mid-woofer the OP is using, however its interesting to note that the crossovers, both his and mine put the sweet-spot at about the same frequency. His x-over is interesting as he uses a combination of factors to arrive at the best result. The crossover I suggested for the OP to view is not necessarily the final iteration but rather a starting point. The really interesting thing is the differing method the software packages use to basically arrive at the same point. I've run the sim through PCD and its very close to both x-overs. I generally don't use PCD for crossovers as I find its somewhat overkill for smaller builds, and is a little too complex for most DIYer's. :dontknow:

That said I note the output power for these speakers is 50watts RMS max, which is also a little lower than the OP was looking for, however on a mid sized amp they should work well combined with a small sub as they dont have a great deal of bottom end, and if you build to the size Troels did I'm not sure how much bass they would produce.

To be honest I don't design anything under a 15 liter enclosure size, and don't use drivers smaller than 6 inches as there isn't generally enough bottom end with smaller drivers. ( as always there are exceptions to this ) but for most Hi_Fi reproduction that's generally the smallest I go.


----------



## PlanoDano (Aug 30, 2013)

Kiwilistener
I took a look at your PMS thread. That is a very ambitious project and looks like you are pulling it off wonderfully. I do not have the wood working skill (patience) to pull off any of Troels Gravesen's designs but admire his contributions. I also agree with the point you made on woofer size for Hi-fi listening.


----------



## Kiwilistener (Apr 5, 2010)

Hi Dano.

I built my first set of speakers circa 1974, using Plessy Davred 8 inch paper cone drivers. For the tweeter this was a paper cone 2 inch unit. The crossover was a capacitor for the tweeter and a coil ( transformer style) for the woofer, if memory serves. These came as a kitset with a book on speaker building. One of the comments in the book was that the bigger the room the bigger the drivers should be.

Thats a little simplistic but it generally holds true. A good quality 8 inch woofer should out perform one or even two 6 inch drivers. There are of course six in drivers that can go toe to toe with some of the eights, hence my comment regarding six inch drivers. My lounge is reasonably large and is also my listening room, at 8 x 6 x 3.5 or 25' x 18' x 10' . That's a good volume to fill and my latest version of the "Pettites" are 15 liters using a 6.5 driver and do very well, but for the same power output from the amp through my Mains, blows them out of the water without breathing hard.

Bass response is good in the smaller speaker but is much more room filling and effortless for the same power from the larger speakers. We had both running using the Sugden 21se amp recently. At 35 watts rms it not a big amp, but the sheer quality of sound from the big speakers was lightyears ahead of the Pettites.


----------



## Danny Richie (Jul 12, 2009)

Hey guys, 

Just a few things to think about...

Designing crossovers is something that I have been doing professionally for a long time. Most of you know who I am or even own some of our products or products from companies that I have designed for in some way. 

Software like Harris Tech bases its figures on electrical parameters. They are what is know as textbook designs. Sometimes they get you in the ballpark but usually not. 

Crossovers really need to be designed based on acoustic output. This is not limited to a measured response of the drivers used either. It really involves the output of the drivers used in the cabinet that you are using them in. And the cabinet design and surface reflections of the cabinet will have a dramatic effect on the response. Time and phase must also be accounted for. Break up mods have to be minimized. Impedance's need to be matched. Output levels matched. etc. 

If it were only as easy as a mathematical calculation...

For me to design a crossover for anyone I have to have the speaker here in a cabinet that is identical to the one that will be used in the final product. Without that I won't even attempt the job.


----------

