Design for a cheap two way for use as rear speakers in 5.1 setup

[Dissi]

Originally Posted by DrNick

I also modelled the box effects, and this has dropped the bass a fair bit once the baffle step comes in.

Just a hint:
It's very important to consider the baffle step in a crossover design. But in case of your woofer it's better not to model the box effects. Why? The frequency response of the driver is measured in a Seas test cabinet having almost the same baffle dimensions (310x210 mm) as your cabinet. Thus the measurement published by the manufacturer already includes the baffle step. Don't do it twice!

[Siggma]

Originally Posted by DrNick

Thanks! I can get this woofer from Conrad Electronic UK. I'll have to make my own enclosures though, I've looked for the Dayton kits before and they do not seem to be distributed over here (UK). Shipping things over is usually very expensive, if you want to be sure they'll arrive.

Is the crossover diagram in the pdf file? I could see the image of the driver and the title text.

Please let me know how you get on with this one, thanks.

This is the PCD graph I have but it's the old baffle. I need to move the woofer forward a little and move it down, then re-valuate the crossover. It's not bad the way it is but the tweet is mounted on the edge of the top of the baffle. Plus, if I move the woof forward a little the phase tracking will be closer in time. Right now it's 21mm behind the tweet. With the new baffle it will be very close to zero Z axis. That will make the phase lines almost line up in the graph which should sound better as well. But, as with anything in reality it might change other things as well so I'll need to re measure and go over it again a few time, then assemble and listen and ...

THIS IS NOT INTENDED AS A FINISHED CROSSOVER
Woofer second order electric
1 mh coil
7.8 cap

Tweeter third order electric
12 mfd = 10 mfd + 2.2 mfd in parallel in series
.15 = .18 mh parallel to ground
90 mfd electrolytic or 80 mfd electrolytic plus 10 mfd plastic bypass to sweeten it up a bit. I would never put an electrolytic in series but in this case it's parallel and probably won't have any ill effect since it will be passing very little signal. Bypassing it with a good plastic will reduce or eliminate any harshness.
L-Pad
Series 7.5 Ohm resistor
Parallel 8.5 Ohm resistor

As you can see from the plot I have a ways to go to get the slopes the way I want them but phase is tracking over most of the usable range. The woofer phase crosses the tweeter about 200 Hz and track it till about 6K, but I can do better. I just didn't put the time into this version because I'm going to re cut the baffle. My version won't have any BSC and for sats you probably won't want any either. I'll get better measurements when I can set up over at the shop where we have a 40' ceiling.

Tom

[Bob Richards]

David Griesinger, top engineer at Lexicon, made the point in one of his papers that the lower in frequency you go, the more effective side or rear channels will be at creating a sense of envelopment. That suggests that the side or rear speakers should have a good lower mid and bass response. Personally I've found that side speakers up at the ceiling, half way between the listening position and the front speakers, aimed directly across at each other sounds real good to me. I found that full surround gets tedious to listen to after a while with music, so I don't bother with those.

[DrNick]

Originally Posted by Dissi

Just a hint:
It's very important to consider the baffle step in a crossover design. But in case of your woofer it's better not to model the box effects. Why? The frequency response of the driver is measured in a Seas test cabinet having almost the same baffle dimensions (310x210 mm) as your cabinet. Thus the measurement published by the manufacturer already includes the baffle step. Don't do it twice!

Ah! It might not be such a bad result then. Thanks! I did look at the final model and wonder if the reinforcement from the wall behind would make a difference and decided 'not enough' but you're quite right of course, if there is already a baffle effect then the bass won't be so bad. The profile published does fall off from 1 kHz so that does make sense.

I'll load this up tonight at home and have another look. I really want to see if I could make a whole family of units from the same tweeter and woofer to give me a 5 speaker set up, if that is possible.

[DrNick]

Originally Posted by tuxedocivic

Thanks for taking my advice and not misunderstanding it as a put down. I get that often it seems. And I'm glad a major problem was solved before expensive parts were purchased.

I'm always happy to have my errors pointed out to me! Peer review is pretty much the main reason to post stuff like this on the web, and I really appreciate anyone taking time to read anything I've posted.

Originally Posted by tuxedocivic

Also remember that using response modeler gives minimum phase. You'll need to enter the driver x, y, z coordinates if you're not measuring the drivers. For z, you'll just have to take a stab in the dark. I suggest -0.025 for the woofer and 0 for the tweeter. You won't be far enough off that it matters. You are, after all, using them as surrounds. So you'll likely rarely be on axis vertically.

Good luck

Thanks again. I'm going to revisit this tonight and see what I can do with the phase minimised, but without the baffle step, taking into account Dissi's comments about the cabinet that the measurements were taken in.

As for the alignment, I was wondering about orienting the units with the tweeter and woofer in the horizontal plane, so the dispersion will be wide vertically, but narrower in the horizontal plane. The reason would be that they will be located higher than ear level, and I can rotate the speakers easily around the vertical axis to point at the listening position, and then I would not have to rotate them to point down.

[DrNick]

Originally Posted by Bob Richards

David Griesinger, top engineer at Lexicon, made the point in one of his papers that the lower in frequency you go, the more effective side or rear channels will be at creating a sense of envelopment. That suggests that the side or rear speakers should have a good lower mid and bass response. Personally I've found that side speakers up at the ceiling, half way between the listening position and the front speakers, aimed directly across at each other sounds real good to me. I found that full surround gets tedious to listen to after a while with music, so I don't bother with those.

I found the paper http://www.davidgriesinger.com/objmeas.pdf, I take it that was the one? It's very interesting.

I feel like I have just finally entered the world of proper bass, after building a sub, and I'm currently working on the basis of buildling complementary speakers to work down to the sub. I'm currently experimenting with the crossover frequency, 80 Hz seems to work well with my current two way main speakers, although the 60 Hz frequency discussed in the paper as a target is perfectly possible to use, if I can design the rear speakers to work that low. Thanks for pointing this out to me!

[mondogenerator]

in surround arent the rears already high passed at the decoder? i always thought they were. Or are you using THX? i dont wish to criticise but if they are HP'd at the decoder, then your efforts may be wasted.

[Siggma]

Originally Posted by DrNick

I'll load this up tonight at home and have another look. I really want to see if I could make a whole family of units from the same tweeter and woofer to give me a 5 speaker set up, if that is possible.

That was the design goal with the Visaton / Vifa pair. At under $100 it's a decent deal. Make your own boxes and you can make them even cheaper. Did you say you already have drivers or were you working from factory data?

I like the finished Visaton HT, very revealing tweeter for it's size and that little woofer has very nice bass but I found a really good deal on the Aurum Cantus so I bought 6 of them. I'll be using the Vifa XT25TG30 for the AC-130's. The Aurum Cantus is much smoother and crossed down low will have excellent off axis response with that tweet. I bought mine on eBay and he probably won't ship out of country. He's in California. Holler if you decide to go this route and I'll post the final crossover. If you do decide to go the Visaton/Vifa route the boxes need to be .25 for .7 Q, I'm using a .23 and the roll off is so close it's nearly identical.

Tom

[DrNick]

Originally Posted by mondogenerator

in surround arent the rears already high passed at the decoder? i always thought they were. Or are you using THX? i dont wish to criticise but if they are HP'd at the decoder, then your efforts may be wasted.

I have an Arcam AVR300 AV amp, which accepts a digital feed and does the decoding from DVD formats (it does not have support for the latest blu-ray formats, but the LG player I have can resample to 192 kHz Dolby DTS format). It can set the crossover between the sub and the rest of the system anywhere from 40-130 Hz so I'll be able to choose based on whatever works best for the system. I'm thinking of crossing at about 60-80 Hz based on keeping the front speakers smaller. If I can make the rear speakers so that they can play down to that range then that would be ideal.

With the AVR300 you can also choose to send the unfiltered signal to either the front, or all of the speakers if you want their crossovers to do the work, and you can also set it up to use the sub channel for HT but just use the front speakers for stereo signals, if you have full range main speakers. I can't help but think this feature is also for those whose subs play explosions better than music. However, given that I have a miniDSP in the sub, I could just play full range to all the speakers and set the sub up to fill in below where the speakers roll off. This could give a gentler crossover slope than the one in the amp, which appears from measurements to be around fifth order.

[DrNick]

Originally Posted by Siggma

That was the design goal with the Visaton / Vifa pair. At under $100 it's a decent deal. Make your own boxes and you can make them even cheaper. Did you say you already have drivers or were you working from factory data?

I'm just playing with spreadsheets at the moment. I'm just beginning this!

Originally Posted by Siggma

I like the finished Visaton HT, very revealing tweeter for it's size and that little woofer has very nice bass but I found a really good deal on the Aurum Cantus so I bought 6 of them. I'll be using the Vifa XT25TG30 for the AC-130's. The Aurum Cantus is much smoother and crossed down low will have excellent off axis response with that tweet. I bought mine on eBay and he probably won't ship out of country. He's in California. Holler if you decide to go this route and I'll post the final crossover. If you do decide to go the Visaton/Vifa route the boxes need to be .25 for .7 Q, I'm using a .23 and the roll off is so close it's nearly identical.

Tom

So you have built a pair with the Visaton drivers? Can I ask what you use for measurement equipment and software? I think I'll need to invest in some testing equipment if I'm going to do this properly.