I've got a pair of mission 762s in custom cabinets.
I know nothing about the thiele small parameters of the 8" woofers but I know the frequency response of them in the custom cabinets falls rapidly below 100Hz 🙁 however above that frequency the response is pretty flat within about 10dB which is good enough for me. The cabinets have an internal volume of no more than 64 litres each and are made of 1" thick MDF, they are sealed.
My question is: can the lower response be improved by adding two 8" passive radiators to each cabinet or will it make things worse? If so, can I get away with buying unbranded Chinese ones as the thiele parameters are unknown?
Thanks for taking the time to read my question, all answers are appreciated.
I know nothing about the thiele small parameters of the 8" woofers but I know the frequency response of them in the custom cabinets falls rapidly below 100Hz 🙁 however above that frequency the response is pretty flat within about 10dB which is good enough for me. The cabinets have an internal volume of no more than 64 litres each and are made of 1" thick MDF, they are sealed.
My question is: can the lower response be improved by adding two 8" passive radiators to each cabinet or will it make things worse? If so, can I get away with buying unbranded Chinese ones as the thiele parameters are unknown?
Thanks for taking the time to read my question, all answers are appreciated.
The 762 was a reflex 30L design, IIRC. Easy 8" polycone bass on a simple 2nd order filter.
64L is quite large in closed box, but I'd think refitting a port might help. Ports can add an extra octave to bass.
Monacor :: Monacor MBR-70 PS4.51 IN STOCK (18 Aug 2017)
I used a drill and a jigsaw last time I fitted one. If you work near the bass, you can usually get enough access for the frame of the jigsaw.
Be worth checking the crossover too. It may have been modified ineptly. Don't forget that if the speakers are wired out of phase, the bass gets a bit vague too. 🙂
The simple test for correct woofer phase is to place the speakers face to face and touching. If the bass disappears when you do this, they are out of phase.
64L is quite large in closed box, but I'd think refitting a port might help. Ports can add an extra octave to bass.
Monacor :: Monacor MBR-70 PS4.51 IN STOCK (18 Aug 2017)
I used a drill and a jigsaw last time I fitted one. If you work near the bass, you can usually get enough access for the frame of the jigsaw.
Be worth checking the crossover too. It may have been modified ineptly. Don't forget that if the speakers are wired out of phase, the bass gets a bit vague too. 🙂
The simple test for correct woofer phase is to place the speakers face to face and touching. If the bass disappears when you do this, they are out of phase.
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Thanks for the reply Steve, I checked the polarity of the woofers and tweeters, they were all wired up correctly.
Would the port in the link be the right one for a cabinet for this volume to get the same response or a better response than the original cabinets? I used to have the cabinets rear ported with ports taken from the Tannoy eyris however they made things worse.
I understand there are lots of numbers to consider when tuning with ports but as these numbers aren't available, could there be a rule of thumb that could apply to my situation to find the right port e.g. if the volume is doubled could the port sizes be doubled?
Can passive radiators be used as an alternative or do they also require specs of the woofer? I heard somewhere that you can have two PRs of the same diameter of the woofer in each cabinet for it to work well?
Thanks once again for your time.
Would the port in the link be the right one for a cabinet for this volume to get the same response or a better response than the original cabinets? I used to have the cabinets rear ported with ports taken from the Tannoy eyris however they made things worse.
I understand there are lots of numbers to consider when tuning with ports but as these numbers aren't available, could there be a rule of thumb that could apply to my situation to find the right port e.g. if the volume is doubled could the port sizes be doubled?
Can passive radiators be used as an alternative or do they also require specs of the woofer? I heard somewhere that you can have two PRs of the same diameter of the woofer in each cabinet for it to work well?
Thanks once again for your time.
This is all a bit desperate IMO. I'm not even sure what the problem is.
Firstly, I'm not knowledgable about ABRs, which are quite exotic. I thought they were a heavy passive cone tuned lower than the main bass unit. So they make it behave like a deeper bass. But, IIRC, end up in a similar place to a reflex.
Let's just do a review. Somebody has ditched the 30L reflex cabinet in favour of 64L of closed box. That's easy enough to model with a typical reflex unit: W 200 S - 8 Ohm
Shouldn't lack bass at all. I think you just don't like the closed box sound, albeit it is what is called overdamped here.
Adding a port, well, I thought 2.5" by about 6" would be about right. But the port is adjustable. It can't be far away from the SEAS Njord, in fact. For sure that would get you even more bass than the 30L reflex original. But who knows what your particular room is going to add in terms of room gain, and also affected by positioning near the wall or floor.
My own preference is bass light but then placed near the wall.
The electronic answer for more bass is a bigger bafflestep coil, which reduces the midrange by 2-3dB. This is what I adjust to my taste. You can see from the frequency response of something I built, I prefer a lifted midrange giving LESS perceived bass, so I'm not in the thunderous bass camp at all.
All in all, I'm a bit surprised you want more bass... this must be what they call, an INTERESTING problem. 😕
Firstly, I'm not knowledgable about ABRs, which are quite exotic. I thought they were a heavy passive cone tuned lower than the main bass unit. So they make it behave like a deeper bass. But, IIRC, end up in a similar place to a reflex.
Let's just do a review. Somebody has ditched the 30L reflex cabinet in favour of 64L of closed box. That's easy enough to model with a typical reflex unit: W 200 S - 8 Ohm
Shouldn't lack bass at all. I think you just don't like the closed box sound, albeit it is what is called overdamped here.
Adding a port, well, I thought 2.5" by about 6" would be about right. But the port is adjustable. It can't be far away from the SEAS Njord, in fact. For sure that would get you even more bass than the 30L reflex original. But who knows what your particular room is going to add in terms of room gain, and also affected by positioning near the wall or floor.
My own preference is bass light but then placed near the wall.
The electronic answer for more bass is a bigger bafflestep coil, which reduces the midrange by 2-3dB. This is what I adjust to my taste. You can see from the frequency response of something I built, I prefer a lifted midrange giving LESS perceived bass, so I'm not in the thunderous bass camp at all.
All in all, I'm a bit surprised you want more bass... this must be what they call, an INTERESTING problem. 😕
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Thanks again for the help. I'll order a pair of those adjustable ports and give an update when they're in use!🙂
Update: The ports have been fitted and the bass sounds much better 😀. Is there any way other than trial and improvement to get the right length of the port? Thanks
I'm really just guessing 2.5" x 6" is about right for a 30Hz Fs 8" woofer in 63L.
The W 200 S - 8 Ohm box data comes up with something like that.
Troels did some stuff with a 7" 28Hz reflex scan woofer too:
vent tuning
Port Calculation
Maybe the port is a bit long, and maybe 10cm or 4" would be better. But I really don't know. If it was me, I'd just leave it alone. Once you cut it, there's no going back! Anyway, there isn't any correct single bass tuning. Just variations. You can even fill a port with drinking straws or line it with felt or carpet for the damped aperiodic approach too. That ends up between reflex and closed box at 18dB/octave.
Edit: I just looked up the Vifa polycone P21WO-20-08 sheet which I have on file. Qts 0.33, Fs 28Hz. They recommend 10cm dia x 17 cm long for 60L and Fb of 35Hz. Well, that's saying you could fit two 6cm dia ports really. But all a moveable feast. LOL
The W 200 S - 8 Ohm box data comes up with something like that.
Troels did some stuff with a 7" 28Hz reflex scan woofer too:
vent tuning
Port Calculation
Maybe the port is a bit long, and maybe 10cm or 4" would be better. But I really don't know. If it was me, I'd just leave it alone. Once you cut it, there's no going back! Anyway, there isn't any correct single bass tuning. Just variations. You can even fill a port with drinking straws or line it with felt or carpet for the damped aperiodic approach too. That ends up between reflex and closed box at 18dB/octave.
Edit: I just looked up the Vifa polycone P21WO-20-08 sheet which I have on file. Qts 0.33, Fs 28Hz. They recommend 10cm dia x 17 cm long for 60L and Fb of 35Hz. Well, that's saying you could fit two 6cm dia ports really. But all a moveable feast. LOL
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Could I cut the main piece to 4" and leave the adjustable sliding part off? Then if it doesn't work I could maybe put it back on. I'm asking because I'm not sure if having the sliding part off would change anything because it goes over the main part but it has a wider diameter on the end - the side inside the cabinet. I might try putting the straws in as well once I get some! Thanks
I wish someone who understands reflex more would help me out here. 😱
I'm a bit of a closed box fan myself. TBH, and this might be my own opinion, a big box in a small room is a boomy disaster. All down to a thing called room gain.
I used to have a pair of BBC Chartwell PM400 monitors, which never lacked in the bass department. This was the early days of reflex. I bought them just because of their amusing ability to blow a cigarette lighter out when placed in front of the simplistic damped holes in the baffle and hitting a deep bass note! 😀
Pretty fine polycone speakers, as it goes. But no reflex tubes whatsoever. So even try this without any tubes at all. AFAIK, if the volume of a big magnet Qts=0.38 reflex driver in a cabinet approaches the Vas, the port becomes very short. Which is what Chartwell did. Simple holes in the baffle lined with rubber damping foam.
I suspect you could cut the port length to 4" and see how it goes. For sure you can then add back the extra tube. I seem to remember it was then a good idea to fix the extension with insulating tape to stop rattles.
No doubt that a reflex driver in a big cabinet sounds better with a port. It goes deeper. But only in a big room. Otherwise the bass becomes a bit excessive.
I'm a bit of a closed box fan myself. TBH, and this might be my own opinion, a big box in a small room is a boomy disaster. All down to a thing called room gain.
I used to have a pair of BBC Chartwell PM400 monitors, which never lacked in the bass department. This was the early days of reflex. I bought them just because of their amusing ability to blow a cigarette lighter out when placed in front of the simplistic damped holes in the baffle and hitting a deep bass note! 😀
Pretty fine polycone speakers, as it goes. But no reflex tubes whatsoever. So even try this without any tubes at all. AFAIK, if the volume of a big magnet Qts=0.38 reflex driver in a cabinet approaches the Vas, the port becomes very short. Which is what Chartwell did. Simple holes in the baffle lined with rubber damping foam.
I suspect you could cut the port length to 4" and see how it goes. For sure you can then add back the extra tube. I seem to remember it was then a good idea to fix the extension with insulating tape to stop rattles.
No doubt that a reflex driver in a big cabinet sounds better with a port. It goes deeper. But only in a big room. Otherwise the bass becomes a bit excessive.
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Wow, they must have really been pushing the air! :O
I'll cut the port and update you on the results.
If the bass is excessive I'll move them to a larger room, ATM they're in a medium sized room. I heard somewhere that 'if the shoes don't fit, change the horse' 🙂
I'll cut the port and update you on the results.
If the bass is excessive I'll move them to a larger room, ATM they're in a medium sized room. I heard somewhere that 'if the shoes don't fit, change the horse' 🙂
Ooh, I wasn't far off the money there! 🙂
This design is a big cabinet like yours with an 8" polycone. Lots of tuning options, but all in the same ballpark as I suggested. 6cm port. 4-12 cm long.
TUNING KLS-9
Long ports go deeper, for sure.
This design is a big cabinet like yours with an 8" polycone. Lots of tuning options, but all in the same ballpark as I suggested. 6cm port. 4-12 cm long.
TUNING KLS-9
Long ports go deeper, for sure.
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