Is this up-fit of my speakers viable or am I just throwing away my money? - diyAudio
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Old 27th June 2014, 06:32 PM   #1
reine73 is offline reine73  Sweden
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Default Is this up-fit of my speakers viable or am I just throwing away my money?


At first I was thinking of building myself a set of three-way speakers, but then I come to my senses and thought that maybe I should try to fix my old set instead. A good start at least, you never know what happens later

Just as a clarification, what I want to accomplish is to get a descent set of speakers that works ok with a descent crossover. There are most likelly alot of drivers out that handles things better but in some cases one of them costs as much as the complete set that I have found, but there are certainly alot of drivers out there that I have not seen... and I realise that there are alot of compromises made when trying to squeeze the budget and are trying not to adapt the box to much...

I have a couple of old Sonab speakers (A-120) 2-ways, most likely from their dark times when they produced crap... according to the person that had them last, one of the woofers are most likely blown/broker or just plain bad (or maybe they have always been )

I couldn't find any information about the woofers at all (only thing I found on them was RD20EU71 which didn't give any hits on google) but the tweeters are of model DT-4817 ASZR which I actually can find data about, one is replaced long ago and they are most likely not identical even if they have the same type number (the identification differs even if both have number 4817 on them). The "crossover" consists of a capacitor and a resistor in series between the woofer and the tweeter (3.3uF and 6 Ohm).

So for the tweeter the mounting rim/hole is 10cm/6cm (not sure that I am using the correct words here, hope you understand)
And for the woofer it is 21cm/18.5cm

So I thought that I try to locate drivers that will fit the box... and came to the conclusion that those might work ok
Tweeter: SCAN-SPEAK DISCOVERY R2604/832000
Woofer: Dayton RS225-4 8" Woofer

They will fit the box holes ok (will have to adopt a bit for the tweeter though), which is a plus. With WinISD I calculated the box volume for the woofer to 27.5 liters in a closed box and the boxes I have is about 25.5 liters, and changing the volume in WinISD shows only slight changes in frequency response so I assume it would work quite ok, also I have read that padding/stuffing actually "increases" the volume when it comes to the speakers (ok, the volume is the same but something happens that I haven't bothered to try to understand just yet ).

And also, they are not to expensive so they will not dig a hole that is to big in the pocket either.

And also, if I read the datasheets correctly, they could be quite ok paired with a crossover at around 1250Hz...

So using this nice guide: Introduction to designing crossovers without measurement

I designed the following crossover for it:
To flatten the impedance of the woofer, a resistor 3.625 Ohms (3.9 closest) and a capacitor at 36.8uF (33uF closest)

The woofer crossover coil ended up at 0.423mH and 0.42 is a good standard value.

To flatten the impedance of the tweeter I choose the highest value in the examples, 20Ohms as the tweeter only is 4 Ohms and I don't want to go to low

Tweeter crossover a coil at 0.70mH and a capacitor at 15uF, and a resistor in series at 0.4 Ohms to dampen it one decibel (the "new impedance" of the tweeter multiplied by 0.12 for dampening it one dB)

So, what is the verdict, am I completely lost pairing those drivers?

Does the slightly lower actual box volume just have a slight impact as I think or will it be a disaster?

Did I get it all wrong when looking at the datasheets? would they work ok together and also to crossover at 1250Hz?

Is this project completely futile and just render me a set of completely crappy speakers (which I already have one pair of )?
Or will I end up with something that possibly would be quite ok to listen to?


Last edited by reine73; 27th June 2014 at 06:44 PM. Reason: Added links to the drivers datasheet
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Old 27th June 2014, 07:07 PM   #2
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Dayton make paper version of these drivers. With this metal driver, you'd need a notch filter. If you insist on metal drivers, I'd choose seas over dayton for a two way system. Seas has a single break-up peak to deal with and dayton rings all-over high frequencies.
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Old 27th June 2014, 08:32 PM   #3
reine73 is offline reine73  Sweden
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Good catch!
I actually didn't notice it was aluminium cone. Looking at the paper version of of the driver the frequency response was a bit nicer
Also it had a little bit higher sensitivity, 91dB, which matches the tweeter so I can remove one resistor from the crossover.

Doing a new calculation with this one gives me a box size of merely 16.9 liters for a closed box, or 32.6 for a vented box, so either I seal of a bit of the box to make it smaller.

Or... I just put vents in it... looking at the graph in WinISD I would get an extra bass response of +0.16dB at most but I would get down to about 50Hz instead of 75Hz.

So looking at the graphs in WinISD, there it seems like the volume isn't really that big issue... sure... I get an overshoot of the bass a little bit... but is there more to it that I miss? (I assume it is, it can't be that small difference between 25 and 32 liters... or can it?

Obviously I will have to check the filter numbers again... to some extent... haven't done that quite yet...
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Old 27th June 2014, 08:58 PM   #4
system7 is online now system7  United Kingdom
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I can't even find a picture of the Sonab A-120. Is it a regular front firing two way? What is the box volume in litres? Is there a reflex tube? A picture would help.

Like this:
Click the image to open in full size.

The tweeter looks like a mylar dome type @ 100mm diameter, 60mm cutout working above 2.5kHz. The bass looks pretty standard at 210 mm diameter and 185mm cutout. Is the 210mm outer diameter rebated to fit very exactly in the front panel, or does the bass just flush mount? The diameter of the circle that goes through the fixing bolts is useful too. It's called the PCD.

W 200 S - 8 Ohm

The original was a 210mm or 8" paper bass I would guess. Quite a lot to choose from, and quite easy. A metal bass will need a complex filter as mentioned, and that very low 1250Hz tweeter crossover is not going to work with a Vifa or Scanspeak ring radiator tweeter.

So a rethink needed. Below is a typical simple 3.5kHz filter for 8" bass.

Visaton even make it for you, but you won't want the 10uF capacitor here, and you'll need to adjust some tweeter resistors for correct loudness. With ring radiators you usually add 3.3R in series with the tweeter too, because they are low 3R resistance.
Attached Images
File Type: png Typical Commercial Crossover 3.5kHz XO.PNG (5.8 KB, 323 views)
Well, there it is! Best regards from Steve in Portsmouth, UK.

Last edited by system7; 27th June 2014 at 09:16 PM.
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Old 27th June 2014, 09:34 PM   #5
system7 is online now system7  United Kingdom
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If there is a rebating issue on the 100mm tweeter, it is easy enough to fit some smaller 94 or 98mm types:
G 20 SC - 8 Ohm
H1283-06 22TAF/G

I'm fairly sure Monacor do 100mm tweeters too. Just can't remember which ones.
Monacor: Products

Something around or above 88dB sensitivity should be OK.

I found a polycone bass that fits exactly too:

Don't know anything about it, but shouldn't be hard to look up. Dissi even did a crossover for it, which looks easy enough:
hello. what am I doing?

I don't suppose the values are all that critical.
Well, there it is! Best regards from Steve in Portsmouth, UK.

Last edited by system7; 27th June 2014 at 09:43 PM.
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Old 27th June 2014, 09:38 PM   #6
sreten is offline sreten  United Kingdom
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You have lost something in trying to use that article.
FRD Consortium tools guide

The x/o design for those two drivers is far more complex,
and the tweeter distortion is far more complex than just
looking at Fs, it does not predict the x/o point well at all.

In the UK I'd recommend this :
" =item35d78e3626"

It will work well enough in a sealed and stuffed 25L box.

rgds, sreten.
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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Old 27th June 2014, 11:04 PM   #7
reine73 is offline reine73  Sweden
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sreten: Thanks for those links, I will read through that tomorrow, even as the metal cone wasn't intentional (didn't notice it), I wasn't aware of the need of the notch filter, so I will look for a paper woofer instead, no need to make things more complicated then needed, but I still want to build it myself, even with some help to calculate it...
And also, I knew there was a catch to it, you read and read and thinks, "that wasn't very complicated" and... well... it wasn't as you expected thanks again!

Thanks for the information, looked quickly and it seems like both tweeters and the woofer should fit ok (especially the woofer )
I will look through it better tomorrow when I am awake...

I will also try to get a quick photo of the speakers, but in the meantime:
The boxes looks quite like the one you linked to, standard box speakers, 2-way forward firing, closed box so no reflex tubes, around 25-26 liters (measured the outside, and made some guesses)

Thank you!
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Old 27th June 2014, 11:53 PM   #8
OllBoll is online now OllBoll  Sweden
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Designing a set of speakers without measuring is risky business, it's risky as you might not end up with good speaker at all and then it's hard to troubleshoot. If you cant burrow a measurement microphone and don't want to buy one then I'd recommend you to avoid trying to design a speaker yourself at all, the stock measurements of drivers are rarely accurate and the box you choose impacts the response too so it's hard to simulate.

Have you already bought the drivers? If not I'd suggest building a pre-designed speaker instead. Say one of troels designs for example. If you are open to building dipoles ( which sounds awesome compared to normal speakers! ) then the Nao note II RS or the Linkwitz LX521 are very good speakers.

That way you'd be sure your money is well spent getting an upgrade that actually is an upgrade =)

Personally I have a speaker similar to the LX521, but if I didn't love tinkering and trying stuff I'd probably just have built a LX521 instead of cloning and modifying it.

ADDITION: While it is possible to design without measuring for sure the problem is that it probably won't be perfect on the first try: if you have lots of different crossover components you easily can connect and thus build the crossover by ear then that's alright but if you don't then you have to buy new components for each iteration. As you are just guessing you would spend a lot of money on this which is why measuring and then calculating the component values you need is likely cheaper unless you are impossibly lucky and guess the perfect values on the first try.

Last edited by OllBoll; 28th June 2014 at 12:01 AM.
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Old 28th June 2014, 12:04 AM   #9
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For those of us with limited pocketbooks, there's a "mini" LX521 now: LXmini Challenge

Or, consider one of the Zapf kits: Zaph|Audio
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Old 28th June 2014, 12:22 AM   #10
system7 is online now system7  United Kingdom
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I'm always disappointed to resort to a kit design. It's not really my idea of DIY.

I have found the secret of good DIY is to get drivers that are easy. And 8" or 210mm bass is quite an easy one for the beginner to tackle IMO.

Here's a couple of lovely bass units I'd like to try:
H1471-08 CA22RNY
H1659-08 U22REX/P-SL

See, they both don't need much doing to them to get near 4th order acoustic LR4 slopes. Me and Dissi kinda agree that some shunt RC filtering helps them rolloff smoothly. Because harsh cone breakup and an overdriven tweeter is what ruins a speaker.

Then you can pick easy tweeters too. A lot of them will work well enough on a simple second order, because they have some rolloff built into them mechanically that gets you near the theoretically good LR4 slopes.

Click the image to open in full size.

The last thing you need to know about 8" bass is that the time alignment sucks, but comes to your rescue the possibility of wiring them out of phase.

Nothing in loudspeakers is perfect, but I can assure you that the 8" bass and tweeter idea can sound very good indeed. Enough to have a go with a crossover that will work better than most commercial designs.
Well, there it is! Best regards from Steve in Portsmouth, UK.
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