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Multi-Way Conventional loudspeakers with crossovers

Active MTM with 18W/8531G00 and some tweeter
Active MTM with 18W/8531G00 and some tweeter
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Old 1st May 2018, 07:10 PM   #1
elagil is offline elagil
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Default 2.5 way 18W/8531G00 and D2608/913000 with Hypex FA123

Hello!

I plan on building a two-way speaker that is powered by the new Hypex FA 122/123 amplifiers. I have been listening to Zaph ZRTs for close to 10 years now, and I wish for the capability to listen at higher levels without the bass drivers reaching their limit at low frequencies. Also, I want to build something new and different, which is probably even more important.

The speakers are currently using these drivers:

18W/8531G00: http://www.scan-speak.dk/datasheet/pdf/18w-8531g00.pdf
D3004/660000: http://www.scan-speak.dk/datasheet/pdf/d3004-660000.pdf

one on each side.

I want to add another bass driver to each cabinet (total of around 70 L, tuned to 30 Hz-35 Hz or so) and also swap the tweeters, as one of them is giving me constant problems after I changed a broken diaphragm. Air now comes in from the back, so the bass driver influences the treble, when it moves.

Sadly, the availability of replacement parts is not great, as even diaphragms are hard to get now (Germany). So, I would like to sell the two D3004/660000 and get other tweeters. The idea is to use R2604/833000 ring radiators, even though these may seem like a step back in quality. Crossover frequency would be around 2 kHz:

Link to datasheet: http://www.ase-scanspeak.de/chassis/...604-833000.pdf

Now I have a deciding question, as to how good the concept is: Is the chosen crossover frequency too high for the 18W? Off-angle, they drop hard at 2 kHz. If I choose a lower crossover frequency (say, 1.7 kHz), the R2604 significantly degrades in distortion performance. I could also use the D2604, which has much better distortion characteristics, but I would like to try a ring radiator. Generally, the linearity of the X2604 looks nice to work with.

In any case, the holes in the box (104 mm diameter) will fit any tweeter that I may want to use. The Hypex modules will give me the flexibility to adjust.

I do have access to measurement equipment and have some experience in building original designs with passive crossovers, as well as active (with DCX2496).

I would be happy to hear your comments on the concept! A little drawing is attached.


Here are some measurements of the XT25TG-30/04 which is very similar to the R2604 but lacks the double magnet: Test Peerless / Tymphany XT25TG-30/04 (Vifa XT-300/K4) Heissmann Acoustics
Another link to measurements: Test Bench: Scan-Speak Discovery D2604/833000 1″ Wide Surround Silk Dome Tweeter | audioXpress
and of the D2604: Test Scan-Speak Discovery D2604 / 833000 Heissmann Acoustics

Sorry that some of this is in german.

Thanks for your suggestions,
Adrian
Attached Images
File Type: png drawing.PNG (73.6 KB, 427 views)

Last edited by elagil; 16th August 2018 at 11:33 AM. Reason: title
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Old 2nd May 2018, 04:58 PM   #2
elagil is offline elagil
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After a bit of reading, I am thinking about adding an actual mid-driver, due to the compromise of using the 18W well into high frequencies. The 12MU looks very nice but is also quite expensive, so I could be using something like this instead:

http://www.scan-speak.dk/datasheet/pdf/10f-8414g10.pdf

This now looks a lot like an Ekta Grande, but a bit cheaper. The FA123 will allow me to drive three ways, too.
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File Type: png Unbenannt.PNG (18.4 KB, 398 views)
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Old 3rd May 2018, 10:25 AM   #3
TMM is offline TMM  Australia
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The R2604/8330 is the same as the XT25BG60-04 if i'm not wrong. There are measurements of the single (TG) and double magnet (BG) here:
Measurements and compare | HiFiCompass

The double magnet version is a little better than the single magnet but both are a step backwards from the 6600 IMO. The only thing the XT25 does better is the frequency response from 10kHz up.

I would not worry much about the woofers off axis response. It is acceptable as long as you cross around 2.5kHz or below. What will be far more of a problem is the centre-to-centre spacing with the tweeter. If you increase the crossover frequency, the vertical polar response gets worse. If you increase the spacing between woofer and tweeter, it gets worse. If you use an MTM configuration, it gets MUCH worse. Go have a look at it in Zaph's ZRT article.

If it were me, i'd modify the ZRT into a 2.5way design and retain the 6600.
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Old 3rd May 2018, 12:32 PM   #4
elagil is offline elagil
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Yes, the R2604 and XT25 are the same (mostly). They may have differences in airgap size, as far as I have read.

I am also certain that the 6600 is of better quality, but one of them is slightly defective (sometimes scratches, not airproof, probably related) and I cannot get replacement parts, which is a bit sad. Buying a new one is certainly possible, but not my favourite choice. I will need to do measurements on them to see how they do.

Let's say, I use a middriver (like the 10F fullrange, a 12m, 12mu ...) that I cross over to the tweeter at 3-3.5 kHz and to the woofers at around 500-1000 Hz. I am hoping that the higher distortion of the R2604 vs the D3004 at lower frequencies becomes irrelevant.

I saw that the 10F has rather high distortion in comparison with the 12M and especially 12MU. This driver also looks very adequate for use as a mid driver and offers low distortion:

http://www.scan-speak.dk/datasheet/pdf/12w-8524g00.pdf

A 2.5 way is also nice but contrary to my own initial concept, I would rather build a speaker with less compromises that I would use for longer (maybe 10 years again, or even more).

Last edited by elagil; 3rd May 2018 at 12:44 PM.
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Old 3rd May 2018, 02:10 PM   #5
TMM is offline TMM  Australia
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In the ZRT the C2C spacing between the woofer and tweeter is 15.2cm. If you use the 12M below the tweeter instead of the 18W, the C2C only becomes 11.9cm. Therefore just to equal the ZRT in polar response you can't cross higher than 15.2/11.9*1700hz = 2171Hz. To realise the polar benefit of using a smaller mid, you need to pick a tweeter with a smaller faceplate. Then you have to juggle the fact that tweeters with smaller faceplates typically don't have as good non-linear distortion. That's all part of multi-way speaker design.

I'm not sure that the 12M actually beats the 18W/8531 in midrange distortion either. The ZRT is quite a good execution of a 2-way because it uses exceptional drivers - a woofer which has no problems with distortion on the top end, and the tweeter which has no problems on it's bottom end. It will require an above average 3-way design to beat it.

Last edited by TMM; 3rd May 2018 at 02:14 PM.
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Old 3rd May 2018, 02:51 PM   #6
elagil is offline elagil
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Quote:
Therefore just to equal the ZRT in polar response
I am guessing, vertical polar response? That did not cross my mind yet
Extending the ZRT to 2.5 way seems more and more sensible. I could even rebuild the Zaph crossover in DSP and correct for the room.

I found a test report of the 18W/8531G00 and you are right, the distortions are indeed quite low:

http://www.audiocomponents.nl/downlo...i%202002-3.pdf

The 12M is quite a bit worse above 1 kHz:
http://www.audiocomponents.nl/downlo...i%202003-2.pdf
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Old 3rd May 2018, 05:17 PM   #7
elagil is offline elagil
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Since the original idea seems pointless now, I will just stick with what I have for the tweeter and midwoofer and try to repair that tweeter. The remaining options are:

2.5 way enhancement
3 way with a larger woofer, like a 22W or 26W of some series. This would give me something similar to this:

Jensen-1071

A 22W seems to make no sense, since two 18W have more surface area (300mm^2) than one 22W (220mm^2). A 26W has around 320mm^2. Both larger drivers offer more excursion, though.

I wonder if 125 W on a large woofer may clip on peaks
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Old 4th May 2018, 09:55 AM   #8
elagil is offline elagil
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I think I have decided to go with the drawing of the first post and implement a 2.5 way speaker with MTM configuration and two 18W/8531g00. This is, so I can compare 2.5 way and 2 way by switching profiles on the Hypex module. Also, I prefer it optically over TMM.

Are there any objections with regard to a 2.5 way MTM, where the bottom woofer handles mids?

Thanks!
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Old 15th August 2018, 09:56 PM   #9
elagil is offline elagil
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I finally received the FA123 modules and built a speaker (pictures to follow).

Some facts:
2.5 way (two 18W/8531G00, tweeter in use is now the D2608/913000 because of the defects of the old tweeters)
Volume of around 60 L with 33 Hz tuning
2 kHz crossover between mid and tweeter

I noticed a stupid mistake that I made with tweeter placement. It is centered on the baffle which results in a diffraction dip of around 5 dB on axis at 2.8 kHz. Consequently, I designed the crossover with measurements from 15 and 30 degrees off axis, where the interference is not so visible.

Find the measurements attached. One measurement shows the on-axis measurement (0) with the complete crossover, another shows the 30 measurement (with individual drivers) and the last one contains both (0 and 30) for comparison. The measurements are strongly gated, so please ignore low frequencies. The bass region was tuned by means of nearfield measurements that I am not showing here.

The dip on axis is still bothering me. Should I ignore it, since it vanishes off axis anyway?

Presuming that I made a different baffle, where the tweeter is off-center (so that on-axis frequency response is linear), would I get problems off-axis instead?

Thanks for any feedback!
Attached Images
File Type: png 0deg.png (27.1 KB, 286 views)
File Type: png 30deg.png (51.6 KB, 281 views)
File Type: png both.png (35.3 KB, 281 views)

Last edited by elagil; 15th August 2018 at 09:59 PM.
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Old 16th August 2018, 12:41 AM   #10
TMM is offline TMM  Australia
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Looks good to me! Just toe them a little in/out from your listening position to smooth the diffraction ripple. Add some boost to the top octave if needed to account for this.

When running an MTM as 2.5way, it can often be better to run the top woofer as the 0.5-way. If the bottom woofer is the 0.5way then the midrange droops when you stand up.
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