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Multi-Way Conventional loudspeakers with crossovers

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Old 11th January 2013, 12:56 AM   #51
DrNick is offline DrNick  United Kingdom
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Quote:
Originally Posted by Siggma View Post
SIGGMA-VV51-HT update.

I glued up the boxes and took a measurement this morning. Not good. I'm seeing a 5 db peak in tweeter response around 1.5K that's either from baffle edge diffraction or the woofer ring. Note the blue tweet response in the second image matches the predicted peak in the third image.

On the plus side, from the tweeter position my tweet and woof are only 2mm apart in time. The woof is actually ahead of the tweeter now. But that's at the new tweeter position.
It's not an electrical effect to do with the tweeter impedance peak there is it?
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Old 11th January 2013, 10:29 PM   #52
Siggma is offline Siggma  United States
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The rest of this build is over here on Tek Talk if you want to follow. No need to register to read.
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Old 13th January 2013, 02:11 PM   #53
DrNick is offline DrNick  United Kingdom
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Default Trying the Peerless 830860 and Vifa BC25TG-15-04

After modelling the system using the Seas U16RCYP, I wanted to see if it was possible to spend a bit less, so I have modelled a possible build using the Peerless 830860 5" midwoofer and the Vifa BC25TG-15-04 12 soft dome tweeter which retails for about 37 and 14 respectively. The woofer seems to model well in only 7 litres of volume, and the narrowed sides mean the baffle can be 164 mm wide by 296 mm high, with 15 mm left around the units so the edges can be radiused by 12 mm or so.

I've used the response modeller spreadsheet to include the baffle step and diffraction, and generate the phase information for the final driver response in the cabinet. The crossover for the woofer is just a second order with a 2 mH inductor and 10 uF cap. The crossover for the tweeter is third order electrically, with a 12 uF cap first, a 0.15 mH inductor and a total of 2 ohms resistance in parallel, and then a 5 uF cap. The tweeter level is then controlled by a 3 ohm resistor in series after the crossover and a 5 ohm resistor in parallel. This gives a crossover at 2.7 kHz, but this really could be higher or lower. The phase tracks pretty well from 300 Hz to 5 kHz. I'm choosing 2.7 kHz rather than going lower as this is a cheaper tweeter and I don't want to stress it. Also, this value worked well with the values of the inductor to give baffle step compensation for the woofer. There is 1/12th octave smoothing on the frequency responses, which I traced from the manufacturer's pages using SPLCopy. Some retailers seem to have out of date specifications on their web sites.

The overall response here is within +/- 1.5 dB of 84 dB over the range 160 to 13 kHz, which seems fair given the modest cost.

The system response is as shown here

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

The costings are

Peerless 830860 37.61
Vifa BC25TG-15/04 14

Terminal for speaker cable 3.50

2 mH coil 0.15 Ohms (JANTZEN-5156) 6.92
10 uF cap (Solen 10.00uF 400V 2% tol) 5.17

12 uF cap (Solen 12.00uF 400V 2% tol) 5.80
0.15 mH 0.5 Ohm (JANTZEN-1816) 0.70
1.5 Ohms (10W ceramic) 0.80
5 uF cap (Solen 12.00uF 400V 2% tol) 3.24

3 Ohms, and 5 Ohms (10W ceramic) 0.80 each

So the total per speaker will be 79.34, plus a few pounds for the cabinet.

This compares with about 135 per speaker for the Seas U16RCYP design I tried first off. The trade off is that this design rolls off earlier in the bass. Whether this will really be so bad in its role as a rear channel speaker I'm not sure. There may be a little reinforcement from being placed on a wall, but I've not attempted to include this. It seems as if up to 5 db of gain may be given between 100 and 150 Hz from the rear wall depending on exact placement. I've heard all sorts of speakers sound annoying when booming away because they are too near a wall, and seeing as that is where the rear spoeakers must go, I'd really rather they were too light than too heavy in the bass.

So, I am going to look around and see if there are other drivers I should consider, but for the moment, this looks like a distinct possibility.
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Old 16th January 2013, 05:28 PM   #54
Siggma is offline Siggma  United States
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I finally have the crossover for the Visaton HT / Vifa speaker. After listening to it without BSC it sounded thin and horrible so I had to go back and add BSC (Baffle Step Correction) plus a notch filter for the tweeter. Below is the final expected response. Ignore the peak at 200 Hz, it's a measurement anomaly. The crossover has 11 components the largest being a 2mh coil on the woof so even though it uses a lot of parts it will be easy to build and fit in the box.

Nearfield measurements place f3 at about 83Hz in this .23 enclosure so it goes down quite a bit lower than what you're modeling. I'd build a .25 for an expected F3 of about 81hz.
Attached Images
File Type: png 11 comp XO.png (53.4 KB, 68 views)
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Last edited by Siggma; 16th January 2013 at 05:31 PM.
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Old 16th January 2013, 09:48 PM   #55
DrNick is offline DrNick  United Kingdom
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Cool. Looks nice and flat but why is it at 65 db though? Is your measured frd file not at 1W, or can you normalise it to 1W?
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Old 16th January 2013, 11:26 PM   #56
Siggma is offline Siggma  United States
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Cool. Looks nice and flat but why is it at 65 db though? Is your measured frd file not at 1W, or can you normalise it to 1W?
It's not measured at 2.83 at 1 M. That's a simulation from PCD. I haven't measured the speaker yet and when I do I'll have to splice it together. I'll take a gated response down to 200 then take a nearfield below that and splice it together. Actually that crossover is OK but probably excessive for this speaker. It's better to just correct the glaring issues and get on with it. This is nearly as good and it only requires 6 components. It's a toss up whether a $50 worth of drivers is worth $30 in parts to make changes that are, in the end, barely audible.

But will post them if you want.
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Old 17th January 2013, 12:46 AM   #57
Siggma is offline Siggma  United States
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Just got it wired up and starting measurements. First is Gated measured very near 1 meter. Sensitivity will end up being about 82 or 83 db 1w/1m, maybe higher.

Second is nearfield on woofer showing slope. I'll bop into Excel and patch them together later tonight or tomorrow. Actually, after all the hassle I had with this it's a decent little speaker. It could use another ohm or two of padding on the tweeter which I'll do tomorrow but it's a decent deal for $100. As odd as it seems most speakers that measure flat on the tweeter sound hot and/or harsh. This doesn't sound harsh but it does have a slight edge. A little more padding, probably 2 db will fix that. I've listened to it before this version and its OK once it's padded down enough.
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File Type: jpg Gated Finished XO.jpg (94.9 KB, 15 views)
File Type: jpg Nearfield Finished XO.jpg (96.1 KB, 13 views)
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Last edited by Siggma; 17th January 2013 at 12:49 AM.
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Old 17th January 2013, 10:39 AM   #58
DrNick is offline DrNick  United Kingdom
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Thanks for posting the frd files. I just wonder if you have some resistance in series with the woofer in the PCD crossover model, to drop the sensitivity so much?
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Old 17th January 2013, 12:34 PM   #59
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Originally Posted by Siggma View Post
You might check out the Visaton AL-130 Aluminum cone driver. It probably fits your specifications. It's a tad more expensive but has been successfully used in several projects. Paired with one of the less expensive Vifa tweets if I recall correctly, so there is a crossover designed for it somewhere. Yea, here's a goo link: TQWT Visaton AL130 & G20SC Finished!




yes that is the crossover I posted a couple of years ago in the build thread of my main speaker system using the AL130 and G20SC.

I cant really take any credit for it though, as it was a re-hash of the 'Vib130TL crossover on the visaton site. All I did was add a 47uH choke to attenuate the breakup peak better than the original.

Some of the original photos of the build and sim pictures have vanished mysteriously since the gallerys disappearance a while back. Most of the links in my thread arent working in all probablilty.

Heres what IS still here on the site:

Click the image to open in full size.

Click the image to open in full size.

The LP C1 was reduced to 5uF in the end, as it stressed the tweeter resonance a little (system7 alerted me to this, I actually didnt realise that I had forgotten to change it earlier!)

When im at home Ill dig out the original pictures and re-post them, should you (or Dr. nick?) be interested.

I also have the .frd and .zma on file, if those are handy to anyone.
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Last edited by mondogenerator; 17th January 2013 at 12:37 PM.
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Old 17th January 2013, 01:49 PM   #60
Siggma is offline Siggma  United States
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Thanks for posting the frd files. I just wonder if you have some resistance in series with the woofer in the PCD crossover model, to drop the sensitivity so much?
No I was measuring them at very low levels. Probably around 1 volt. I don't have a volt meter on the output although I probably should. I don't want to cook my tweets, it takes 7 days to get a replacement and they cost $18 plus shipping.

I have a very high noise floor here, it's about 50db avg all the time. I can set the mic with the SPL meter and measure a nearly constant 45-60 db background rumble. I'd have to really hammer the tweeter to get a clean measurement over that noise. Omnimic uses a CD for it's excitation. Optionally you can use the sound card directly but you can't choose which track you want when you use the sound card. There is a track on the CD with a frequency limited sine sweep 500hz and up I think, that I could use but I'm lazy and didn't use the CD. I really should try it. But it won't make any difference in terms of noise.

I just rented a small space downstairs below me in the laundry room. It's below ground in the concrete foundation so it should be much quieter.
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