Hi folks
My Sanyo speakers (from their late 70's OTTO range of higher-end equipment) are in need of some work as one of the tweeters has developed a bit of a rasp.
I was thinking that the best thing is just to replace them with a modern tweeter, but given the large amount of free space in the cabinets, I have all kinds of options. I could make them a 3-way speaker, I could install horns, there is a ton of room to do all manner of mods.
At the same time, I'd like to replace the spring loaded terminals with modern binding posts and perhaps rebuild/upgrade the crossovers to allow bi-amping.
Here's the specs and some pics:
method 2-way, 2-speaker, NRB system, bookshelf type
Unit used For low frequencies: 25 cm cone
type For high frequencies: 5 cm cone type
Impedance 8Ω
Maximum allowable input 50W
Output sound pressure level 94dB / W / m
Frequency characteristic 40Hz-20kHz
Crossover frequency 2.5kHz
External dimensions Width 300 x Height 590 x Depth 318 mm
weight 13.1kg
I think they are ported, there are three holes about one inch in diameter at the bottom which I think are the ports for the 'NRB system' as described in this text:
"A bookshelf type speaker system that uses the newly developed NRB method.
The newly developed NRB system is adopted as an enclosure.
In the NRB method, the part corresponding to the duct of the bass reflex is made into a horn shape, and the so-called bass reflex resonance is eliminated by utilizing the fact that the sound pressure is changed to the air flow below the cutoff frequency. This has acquired the high efficiency and straightforward low-pass characteristic.
In addition, the weight of the system has reached 13.1 kg with sufficient plate thickness (15 m) and reinforcing rod.
The 25cm cone type Woofer is carried in the low-pass.
The frame squeal is suppressed by using aluminum die-casting for the frame.
The 5cm cone type tweeter is carried in the high region.
This unit suppresses extra parasitic vibration by the edgeless structure.
Punching metal is used for the front grille. "
My Sanyo speakers (from their late 70's OTTO range of higher-end equipment) are in need of some work as one of the tweeters has developed a bit of a rasp.
I was thinking that the best thing is just to replace them with a modern tweeter, but given the large amount of free space in the cabinets, I have all kinds of options. I could make them a 3-way speaker, I could install horns, there is a ton of room to do all manner of mods.
At the same time, I'd like to replace the spring loaded terminals with modern binding posts and perhaps rebuild/upgrade the crossovers to allow bi-amping.
Here's the specs and some pics:
method 2-way, 2-speaker, NRB system, bookshelf type
Unit used For low frequencies: 25 cm cone
type For high frequencies: 5 cm cone type
Impedance 8Ω
Maximum allowable input 50W
Output sound pressure level 94dB / W / m
Frequency characteristic 40Hz-20kHz
Crossover frequency 2.5kHz
External dimensions Width 300 x Height 590 x Depth 318 mm
weight 13.1kg
I think they are ported, there are three holes about one inch in diameter at the bottom which I think are the ports for the 'NRB system' as described in this text:
"A bookshelf type speaker system that uses the newly developed NRB method.
The newly developed NRB system is adopted as an enclosure.
In the NRB method, the part corresponding to the duct of the bass reflex is made into a horn shape, and the so-called bass reflex resonance is eliminated by utilizing the fact that the sound pressure is changed to the air flow below the cutoff frequency. This has acquired the high efficiency and straightforward low-pass characteristic.
In addition, the weight of the system has reached 13.1 kg with sufficient plate thickness (15 m) and reinforcing rod.
The 25cm cone type Woofer is carried in the low-pass.
The frame squeal is suppressed by using aluminum die-casting for the frame.
The 5cm cone type tweeter is carried in the high region.
This unit suppresses extra parasitic vibration by the edgeless structure.
Punching metal is used for the front grille. "
Attachments
Mmmhh...25 cm cone and a tweeter is no good news ( for the midrange band)
There are some moder tweeters that may allow a lower Fc, but still a big waveguide (not a horn)is needed to make the DI ( directivity index) similar when the signal passes from the woofer to the tweeter.
So, for me, it seems a waste to search for a low Fs tweeter ( and possibly 1mm excursion) when still corrections need to be done ( oh, well, the crossover ....).
Those Sanyo are similar to Altec Model 3, but the woofer has inverse surround....interesting! The absence of the external surround helps in reducing diffraction in the mid-treble, so the 2kHz crossover poin might be reached without problems...what?! 2k5 Hz ? Whooaa, 500 Hz in that region is dramatic, isn'it?
There are some moder tweeters that may allow a lower Fc, but still a big waveguide (not a horn)is needed to make the DI ( directivity index) similar when the signal passes from the woofer to the tweeter.
So, for me, it seems a waste to search for a low Fs tweeter ( and possibly 1mm excursion) when still corrections need to be done ( oh, well, the crossover ....).
Those Sanyo are similar to Altec Model 3, but the woofer has inverse surround....interesting! The absence of the external surround helps in reducing diffraction in the mid-treble, so the 2kHz crossover poin might be reached without problems...what?! 2k5 Hz ? Whooaa, 500 Hz in that region is dramatic, isn'it?
I would first check the tweeter if it still holds its value sound wise. Either repair or replace with a similar one, then update the npe's (capacitors) to original spec, then evaluate its electrical/acoustical performance and further adjust if necessary. It could be improved by becoming a 3 way classic style loudspeaker and the drive units of comparable quality are affordable. 94 dB output spl at 1W/1m appears a little too optimistic, perhaps 88-89.
As there is a lot of room in the top of the cabs, I thought I could use a compression driver and horn flare in place of the tweeter as I see there are moderately priced compression drivers that are specc'ed at 1-2kHz-20kHz.
Or there are tweeters like these Skytronics ones that are 2khz-20kHz:
QTX 100MM (4") TITANIUM DOME TWEETER 40WATTS RMS 8715693994766 | eBay
I have never messed with speaker design/repair before, so I'm in need of advice and guidance as I'm sure there are many pitfalls.
I happen to have a pair of bi-ampable crossover units from a pair of Mission 780 mkII speakers, which are also 2.5kHz, so would likely be a suitable drop-in upgrade for these Sanyos so I could bi-amp them when I finally finish building my DIY power amps.
Or there are tweeters like these Skytronics ones that are 2khz-20kHz:
QTX 100MM (4") TITANIUM DOME TWEETER 40WATTS RMS 8715693994766 | eBay
I have never messed with speaker design/repair before, so I'm in need of advice and guidance as I'm sure there are many pitfalls.
I happen to have a pair of bi-ampable crossover units from a pair of Mission 780 mkII speakers, which are also 2.5kHz, so would likely be a suitable drop-in upgrade for these Sanyos so I could bi-amp them when I finally finish building my DIY power amps.
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I shall take the speaker apart, is the value of the tweeter I need to measure it's resistance in ohms?
I am not adverse to rebuilding the existing crossovers, but I think the Mission crossovers I have would likely be an upgrade.
Judging by how loud these speakers are, I agree that 94dB/W/m is a little optimistic, they are louder at the same volume setting than my Linn Index MkIIs that are rated at 86dB/W/m, so I think your guess of 88-89 is probably realistic.
Actually I am very fond of such projects because the financial risk is minimal and the prospect of a success is fair because drive units being in good working order means that half of a job is already done. I don't ever touch a loudspeaker without performing at least two sets of measurements, impedance and frequency response. Without a soundcard, dedicated software, amplifier, impedance jig, microphone, you are basically in the dark.
That sky tronic tweeter off ebay is something I'd be very reserved abut taking into consideration, instead there is enough decent budget tweeters like Monacor DT99 (14.92), Monacor DT100 (23.03), Monacor DT-28N (20.84) all at CPC Farnell UK, Peerless (Vifa) DX 25 TG59 (Falcon Acoustics GBP 22.92).
I don't mind giving Mission crossover a test drive.
That sky tronic tweeter off ebay is something I'd be very reserved abut taking into consideration, instead there is enough decent budget tweeters like Monacor DT99 (14.92), Monacor DT100 (23.03), Monacor DT-28N (20.84) all at CPC Farnell UK, Peerless (Vifa) DX 25 TG59 (Falcon Acoustics GBP 22.92).
I don't mind giving Mission crossover a test drive.
I have a good soundcard (mAudio Audiophile 24/92) and a good condenser mic (Auna CM600), but no experience of anyaspect of speaker construction or repair. I guess it's time to learn!
There's such a huge variety of tweeters available, I just have no idea what is most suitable for this application.
There's such a huge variety of tweeters available, I just have no idea what is most suitable for this application.
BTW, I found out that the original tweeters are made by CTS and are a phenolic ring type, used by many manufacturers such as Bose, Fisher, Marantz etc.
A modern reproduction is available, so it might be sensible to just buy one of these:
Looking for a GRS PRT-8 tweeter? - SoundImports
A modern reproduction is available, so it might be sensible to just buy one of these:
Looking for a GRS PRT-8 tweeter? - SoundImports
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After more listening, I'm not sure the tweeter is the problem as the highs are perfectly crisp and clear, the problem is some distortion in the mid range, it's only slight, and is probably around 4kHz if I were to guess.
So I'm wondering if the issue is the crossover and a recap would fix it?
So I'm wondering if the issue is the crossover and a recap would fix it?
I removed the woofer to have a look at the innards and the crossovers are rather basic, just a couple of coils, a couple of wire wound resistors and two bipolar caps, the wire used looks pretty thin and crappy to me too. To remove them is just a case of removing six screws.
So, I'll remove these crossovers, enlarge the hole in the wood slightly and fit the Mission crossovers in their place, they have polypropylene caps and are set up for biamping, should be a quick and easy job.
Can anyone figure out from looking at the Mission crossovers which wires go to which driver?
If the distortion is still present after fitting the new crossovers, I'll have to look at replacing the tweeters.
So, I'll remove these crossovers, enlarge the hole in the wood slightly and fit the Mission crossovers in their place, they have polypropylene caps and are set up for biamping, should be a quick and easy job.
Can anyone figure out from looking at the Mission crossovers which wires go to which driver?
If the distortion is still present after fitting the new crossovers, I'll have to look at replacing the tweeters.
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Speakers are fixed, upgraded and working fine again. Turns out it wasn't a tweeter, it was the electrolytic capacitors in the crossover, after 44 years of use they had dried up and stopped working. So I ripped out all the electronics and wiring and replaced it with the Mission crossovers and thicker wiring so now they have gold plated binding posts instead of the nasty spring loaded plastic clips, and they are now bi-ampable. I even gave them a good clean and polish. Should be good for another 40 years now.
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Interestingly, since I replaced the crossovers, the bass has become a lot punchier, listening to a ZZ Top album and the basslines are really slamming, taut and punchy. I guess this is how they should have sounded and the knackered capacitors were masking that. I'll stick the Prodigy's The Fat of The Land on next and really see just how much bass these newly restored things have. Apologies in advance to the neighbours. 🙂
After a few more hours listening, the speakers do sound considerably improved. However, one interesting side effect is that I need to turn the amp up a little more to get the same volume as previously. The amp (Apart Concept1) has digital volume control, and the scale for the volume goes from -1 to -99 with -1 being the loudest. I need to use a setting of -32 to get approx the same volume as -36 gave before I changed the crossovers. I have no idea why this is, but I can now drive the speakers hard without any distortion so I am pleased with the result of the refurbishment/upgrade.
When I thought the tweeter was shot, I bought a pair of NOS tweeters that came from the old Castle Acoustic factory in Skipton. It's unknown who made them, perhaps Minebea in Japan, and the specs are unknown, but they will be be high quality units as castle only used high quality parts.
They don't appear to be a dome type, I think they are ring radiators, but it's hard to tell.
Anyone encountered these tweeters before? Looking at pictures online, I can't see any Castle speakers that have this tweeter, so I have no idea about it's origins or specs.
I'm wondering if these would likely be an upgrade from the old CTS phenolic ring tweeters in my Sanyo speakers? Or is it a case of I'll have to fit them and find out for myself?
They don't appear to be a dome type, I think they are ring radiators, but it's hard to tell.
Anyone encountered these tweeters before? Looking at pictures online, I can't see any Castle speakers that have this tweeter, so I have no idea about it's origins or specs.
I'm wondering if these would likely be an upgrade from the old CTS phenolic ring tweeters in my Sanyo speakers? Or is it a case of I'll have to fit them and find out for myself?
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The extent of the sound damping material in these speakers is two pillows of a fibreglass like material just loosely stuffed inside, I think I can do better.
Yesterday I salvaged some nice thick carpet underlay from the dumpster behind the local carpet store,
I'll use it to line the inside of the cabinets. I'm still hunting for some bituminous roofing felt, I'll use that underneath the carpet underlay. Sheep shearing season is coming, and a friend who is a professional shearer is going to give me a load of Herdwick wool, I'll stuff the cabinets with that, it's said to be the best material for the purpose due to the random alignment of the fibres.
Yesterday I salvaged some nice thick carpet underlay from the dumpster behind the local carpet store,
I've obtained a pair of compression driver/horn tweeters but have no idea who made them or what model they are as they have no markings on them. Does anyone recognise them? I'm debating whether to use these to upgrade my speakers rather than the other tweeters I showed a couple of posts ago.
