I have built some speakers by combining parts of two others, using SEAS and Vifa drivers. First impressions were quite positive, however after a while they can be a but tiring/harsh. I'm interested in thoughts on my approach.
I started with some Interdyn P32's with blown tweeters and melted crossovers. These use a SEAS 25 F-EW 10" woofer. It's a small-ish sealed box which appears similar to Dynaco A25 and has fibreglass insulation. I decided that keeping this box would ensure the right parameters for the driver.
Separately, I had some Sony SSU-280 speakers that were missing the 10" woofer. These are unusual for Sony in that they used scandinavian drivers, a Vifa K10MD-18 mid range and D19TD-05 tweeter. I'm almost certain the original driver is a Peerless 830668 based on the size of the cutout and what was around at the time they were made, but I can't be 100% sure.
In any case, what i did was pulled the tweeter, midrange and crossover from one box, to make sure the cutoff frequencies were right, and put them in the other box that had the woofer matched to the enclosure. Should work ok, right?
I started with some Interdyn P32's with blown tweeters and melted crossovers. These use a SEAS 25 F-EW 10" woofer. It's a small-ish sealed box which appears similar to Dynaco A25 and has fibreglass insulation. I decided that keeping this box would ensure the right parameters for the driver.
Separately, I had some Sony SSU-280 speakers that were missing the 10" woofer. These are unusual for Sony in that they used scandinavian drivers, a Vifa K10MD-18 mid range and D19TD-05 tweeter. I'm almost certain the original driver is a Peerless 830668 based on the size of the cutout and what was around at the time they were made, but I can't be 100% sure.
In any case, what i did was pulled the tweeter, midrange and crossover from one box, to make sure the cutoff frequencies were right, and put them in the other box that had the woofer matched to the enclosure. Should work ok, right?
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Unlikely. Your assumption is that the woofer and box responses are identical between the swapped cabinets and woofers; and that the woofer low pass integrates as the crossover intends between the Seas woofer and Vifa midrange. The parameters of the woofers are unlikely to be identical, the swapped woofer came from a sealed box, and the baffle widths are also unlikely to be the same.
The frequency response and impedance curves look similar. The only concern is that the sensitivity on the Peerless is 87.9 dB whereas it is 89dB on the SEAS. In theory that would mean my ones are slightly more bass- heavy ??
You'll also have to consider the baffle step. You may want to bring the tweeter down more than you can see from the sensitivity alone.
To be clear, the woofer is in the same box as it was originally. I added the midrange and tweeter from another box, and used the crossovers that were designed for the midrange and tweeter. My understanding (which I guess is wrong) was that the high pass for the mid was the most important bit, as long as the woofer freq response was flat up to that point. The good thing is that I can get specs for all the drivers that I do have, and that in theory the box has been matched to the woofer parameters, so I just need to do a crossover design and then see how close the one I have is to that. Not quite sure how I will measure the existing inductors, but I'm sure there's a way.
I think I've followed what you've done. Photos of the speakers and crossovers would help.
The XO should have both a bass driver low-pass and midrange high-pass. It would have been designed for a different woofer and box.
I mean, since you don't truly know the differences between the original Interdyn woofer + the Seas, it is weak to assume the crossover will still work well.
Equally, you're saying that you find the highs fatiguing, so maybe the original XO needs tweaking in that regard in any case.
The XO should have both a bass driver low-pass and midrange high-pass. It would have been designed for a different woofer and box.
I mean, since you don't truly know the differences between the original Interdyn woofer + the Seas, it is weak to assume the crossover will still work well.
Equally, you're saying that you find the highs fatiguing, so maybe the original XO needs tweaking in that regard in any case.
I did a little research - the 25 F-EW may be the grand dad of the A26RE4 - which may allow the natural rolloff of the driver to work with no low-pass elements.
The new box is smaller than the old box because you have taken away the volume of the small sub-enclosure for the Vifa midrange, but it's only a couple of litres and some extra polyfill would fix that. With the Fs of that little Vifa being 110Hz it should be crossing over at around 400. Do you know the value of the coil inline with the woofer?
I've rebuilt one of those; a while ago; I thought it had decent bass for a small box
I've rebuilt one of those; a while ago; I thought it had decent bass for a small box
Get a multimeter with the ability to measure caps and coils
Cheap enough
https://www.jaycar.com.au/true-rms-...ec6e569bb61f2a1a871863ac977a4c&sort=relevance
Cheap enough
https://www.jaycar.com.au/true-rms-...ec6e569bb61f2a1a871863ac977a4c&sort=relevance
I’ve done some more research. The original woofer has a SEAS D037 crossover, operating at 1500 Hz and with a 8 mF cap, a 2.2 Ohm resistor and ?? Inductor.
I’ll have to pull the other one out of the cabinet to have a closer look.
I’ll have to pull the other one out of the cabinet to have a closer look.
Probably need to trace the schematic and see the back of the PCB - I don't want to guess what the Sony XO is doing.
It looks like the Interdyn crossover used an inductor on the woofer and just a cap and resistor for the tweeter.
I like they used the vintage Seas-type tube cylinder for the midrange chamber; about 0.5 cu liter 😎
Are you in AUS / NZ? Lots of members there could probably measure your speaker and drivers.
Otherwise, if we assume your Seas can be proxied from the A26RE4 datasheet, we have the D19 datasheet, and the K10 datasheet, I feel this would be a good candidate to follow @allenb's sticky on designing a speaker w/o measurements sticky thread, with driver TS parameters to hand.
I'd do a new XO - bass-mid @ 700hz LR2, mid-tweeter @ 3.5khz LR2-BW3
It looks like the Interdyn crossover used an inductor on the woofer and just a cap and resistor for the tweeter.
I like they used the vintage Seas-type tube cylinder for the midrange chamber; about 0.5 cu liter 😎
Are you in AUS / NZ? Lots of members there could probably measure your speaker and drivers.
Otherwise, if we assume your Seas can be proxied from the A26RE4 datasheet, we have the D19 datasheet, and the K10 datasheet, I feel this would be a good candidate to follow @allenb's sticky on designing a speaker w/o measurements sticky thread, with driver TS parameters to hand.
I'd do a new XO - bass-mid @ 700hz LR2, mid-tweeter @ 3.5khz LR2-BW3
The one I worked on only had a cap on the tweeter with a padding resistor, it went through several iterations of XO and tweeter apparently.
ok, have redrawn it, but with 2 multimeters, neither can measure inductance so I’m a bit stuck. I think it’s safe to assume the crossover between tweeter and mid range will be ok, so maybe it’s the resistor I need to look at re levels. Updated schematic is attached.
Is Aranmar Acoustics in Melbourne still around - I understand they built several speakers in Interdyn's range; they certainly built my 'Pee Wee Monitors'. If they are around, they might be able to assist if you ask nicely.
Geoff
Geoff