I am considering making new cabinets for some very knocked around JBL 4612Bs those are the Baby cheek 2404 tweeter with a pair of 2118H 8" 16 ohm drivers in series.
My use is home theatre/ music and my idea for the cabinet is to make it taller but significantly narrower by firing one driver out the back and one forward. Crossover will be Marchand Electronic 4th order.
This would result in an easier to live with cabinet and I am not certain how the dipolar nature will sound. Will I need a rear firing tweeter too? I will be integrating these with a pair of Subs that I am yet to source.
How will this work? Thoughts?
Regards Onslo
My use is home theatre/ music and my idea for the cabinet is to make it taller but significantly narrower by firing one driver out the back and one forward. Crossover will be Marchand Electronic 4th order.
This would result in an easier to live with cabinet and I am not certain how the dipolar nature will sound. Will I need a rear firing tweeter too? I will be integrating these with a pair of Subs that I am yet to source.
How will this work? Thoughts?
Regards Onslo
"Dipolar" would mean you wire the rear woofer reverse polarity from the front.
That would result in a "figure of 8" pattern with nulls on either side, a signifigant reduction in low frequency output, and sound very dependent on the reflected sound from the rear wall.
If wired in polarity, the output would be monopole, but sound very dependent on what is reflected from the rear wall. The distance from the room walls will determine the peak and null frequencies.
If you want the reflected sound to have much content above ~4.5kHz, yes.
The 2402's really shouldn't be crossed much below 4kHz, it's acoustic response drops off below 5kHz, ~-12dB @3kHz. It's (expensive) tiny aluminum annular diaphragm will shatter at relatively low SPL if crossed lower. Below 2 kHz it's input power should be limited to 5 watts (6.3 V RMS) or less.
The 4612B was designed more towards stage use than HiFi..
The 4612B runs one of the 8" "full range", no crossover at all, the second has a series coil to roll off some of it's highs, a "2.5 way" crossover of sorts.
I'd suggest running the rolled off 8" below the "full range" 8" on the front of the cabinet for a home theater or music presentation similar to what it was mixed for, whether you use active or passive crossovers or not.
Anyway, you could wire one of the cabinets reverse polarity (swap leads on a 1/4" plug) and point it backwards to get a rough idea of dipole radiation sound in your room. Cover the tweeter with some foam or a pillow to hear without.
Art
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Dipole/bipole loudspeaker needs two complete pairs of woofer/tweeter combos - one in frot, the other behind.
But dipole/bipole loudspeakers are not good solution for front LCR loudspeakers in a home theatre setup - you need a conventional, front-firing loudspeaker, with two woofers in front (vertically one over other), plus the tweeter in front.
Thanks Art, this is great information and I appreciate the effort you have gone to help. I think I will abandon the idea of rear firing one driver and try them as a 2.5 way vertical cabinet. It is still a fairly small enclosure. Any suggestions for subs? I am thinking I might go with a pair of isobarik subs to keep the cabinets small.
No need to go isobarik for small subs with the speaker parameters easily available this century.
Decide how loud and how low you want the subs to go to determine the displacement required.
Small boxes will require more power and equalization to extend down low.
The pair of 4612B could do around 114dB SPL at 100Hz with only ~10 watts each.
Small subs will require a lot more power (+10 to +20dB, 100 to 1000 watts each) to achieve that SPL.
This piston excursion calculator makes it easy to see how much displacement is required (disregarding room gain) for sealed subs:
http://www.baudline.com/erik/bass/xmaxer.html
It is surprising to hear how much musical content there is below 40Hz, and movie soundtracks often extend into the single digit range.
As you can see, takes about eight 12" drivers to equal the SPL of two if your goal is 20 Hz rather than 40 Hz, while a pair of 21" could do the same SPL at 20Hz with a bit more excursion.
That said, 3 or 4 smaller subs spread around the room can often give much smoother in-room response than a pair of larger subs.
Art
Decide how loud and how low you want the subs to go to determine the displacement required.
Small boxes will require more power and equalization to extend down low.
The pair of 4612B could do around 114dB SPL at 100Hz with only ~10 watts each.
Small subs will require a lot more power (+10 to +20dB, 100 to 1000 watts each) to achieve that SPL.
This piston excursion calculator makes it easy to see how much displacement is required (disregarding room gain) for sealed subs:
http://www.baudline.com/erik/bass/xmaxer.html
It is surprising to hear how much musical content there is below 40Hz, and movie soundtracks often extend into the single digit range.
As you can see, takes about eight 12" drivers to equal the SPL of two if your goal is 20 Hz rather than 40 Hz, while a pair of 21" could do the same SPL at 20Hz with a bit more excursion.
That said, 3 or 4 smaller subs spread around the room can often give much smoother in-room response than a pair of larger subs.
Art
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Thanks Art and Sonce. It's been a while since I visited this forum. Used it a Loy when I was doing my Purifi speakers but have been absent since. It is great to have so much good advice.
I am on the hunt for four 12" subs to complement these. Maybe since Arts advice I will not go isobarik but stick with sealed and some eq. Starting my research now. I guess high sensitivity long throw is the go for a match. I don't care too much for getting down to 20hz, fast responsive bass with some slam is more important to me.
Many thanks Onslo
I am on the hunt for four 12" subs to complement these. Maybe since Arts advice I will not go isobarik but stick with sealed and some eq. Starting my research now. I guess high sensitivity long throw is the go for a match. I don't care too much for getting down to 20hz, fast responsive bass with some slam is more important to me.
Many thanks Onslo
If you actually 'have your hands on' a pair of 14mH inductors as indicated in the circuit diagram above >
I have a very adventurous project for you to try >
1. You separate the "Lower (sub) Woofer" and its 14mH inductor from all other crossover components. This means the 'sub' will be its own independent
circuit connected to the amplifier. [ with the possibility of a series resistor needed ]
2. You mount the 'sub' Face to the rear of the speaker box. In this way, you slightly add some volume to the enclosure, rather than subtracting.
3. You add a 'blanket of 1cm felt' > glued to the interior of the wood cut-out > this makes the 'sub' think it is seeing a larger box.
This scenario could be called "an actively assisted rear port" OR "an actively assisted rear passive radiator" but with far more output >
Giving you SUB output
When such a design is located in the region of a room corner, a horn-loading effect can come into play greatly increasing Low Bass output.
[ a resistor or EQ may be required to customize/tame things ]
The Phase orientation/wiring of the rear driver WILL be immediately obvious when you get it right.
PS.
I have used this design, and it is quite amazing. [ driver & enclosure obviously dependent ]
I have a very adventurous project for you to try >
1. You separate the "Lower (sub) Woofer" and its 14mH inductor from all other crossover components. This means the 'sub' will be its own independent
circuit connected to the amplifier. [ with the possibility of a series resistor needed ]
2. You mount the 'sub' Face to the rear of the speaker box. In this way, you slightly add some volume to the enclosure, rather than subtracting.
3. You add a 'blanket of 1cm felt' > glued to the interior of the wood cut-out > this makes the 'sub' think it is seeing a larger box.
This scenario could be called "an actively assisted rear port" OR "an actively assisted rear passive radiator" but with far more output >
Giving you SUB output
When such a design is located in the region of a room corner, a horn-loading effect can come into play greatly increasing Low Bass output.
[ a resistor or EQ may be required to customize/tame things ]
The Phase orientation/wiring of the rear driver WILL be immediately obvious when you get it right.
PS.
I have used this design, and it is quite amazing. [ driver & enclosure obviously dependent ]
I should have stipulated that this 1cm 'felt blanket' should hang like a curtain being attached/glued only at its top.
Attachments
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Thanks Audio>X I am not sure I fully comprehend this approach. Would the extension still not be limited to the Fs of the driver, which is pretty high ( can't recall exactly what). Do you have any links to arcticles on this or any sketches images? Very interesting I love to try something unusual. Onslo
The bottom part of my main 'twin tower' speakers is a sealed bass & sub box.
The front firing woofer is 12", and the specially driven rear 15" sub is rear reverse mounted.
This way box volume is increased a bit and the 'ugliness' is out of eye shot
The front firing woofer is 12", and the specially driven rear 15" sub is rear reverse mounted.
This way box volume is increased a bit and the 'ugliness' is out of eye shot
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Yes, I do understand that your drivers do have rather high Fs and are identical.
I was really just re-posting 'Food for Thought'.
I was thinking that you could use both your 8" 16ohm drivers in parallel on a front baffle [ maybe too loud ? ] and then also incorporate a
rear mounted 10 or15" sub that has reasonably high efficiency and low Qts.
There are actually quite a few Car Subs @ reasonably low cost that can work well, so long as you use a very high value inductor with useful DCR.
Of coarse, you need an amplifier that is happy with a 4ohm load.
PS.
If your 8"s are too loud, then series wiring could be the way to go 🙂
Thanks Audio>X I think I follow. I do have a pair of these, no longer used. Never known what to do with them. https://www.wagneronline.com.au/nak...RBIj-iTNa6Xlyx8rEC_m_kHS5xHYb6y71M1EHoJNPGM4f
Any use?
Any use?
WOW !!!
I never even knew Nakamichi made speakers 😳
I think you probably have the right components for a very interesting speaker project.
I'll be watching with interest.
Keep everyone informed 🙂
I never even knew Nakamichi made speakers 😳
I think you probably have the right components for a very interesting speaker project.
I'll be watching with interest.
Keep everyone informed 🙂
Yes Audio>X they are monstrous drivers but doesn't look like they will suit this application as the ported enclosure calls at 200l and sealed box over 2000l. I am wanting a small enclosure so need to explore other options. However two of these in an isobarik install in 100l box would be useful.
Hi there Onslo,
I was just looking at the specs. of your JBL 8"s. They are pretty amazing drivers > with super high efficiency of 97dB/W/m.
With their Continuous Program Power of only 50 watts, series wiring would be a great way to go > increasing things to 100 watts.
Also, with their HIGH ENERGY 'motor' giving a Qts of .35 they are ideally suited to a small enclosure > which is exactly what you want 🙂
PS.
I am now interested to read more about your thoughts regarding the 'rear mounting' of one (?)
I was just looking at the specs. of your JBL 8"s. They are pretty amazing drivers > with super high efficiency of 97dB/W/m.
With their Continuous Program Power of only 50 watts, series wiring would be a great way to go > increasing things to 100 watts.
Also, with their HIGH ENERGY 'motor' giving a Qts of .35 they are ideally suited to a small enclosure > which is exactly what you want 🙂
PS.
I am now interested to read more about your thoughts regarding the 'rear mounting' of one (?)
Hi Audio>X yes I think they are pretty interesting. A bit louder than I need in this application actually which makes it harder to integrate with a woofer or sub below them. I could use only one but then it's an impedance issue being 16ohm. I am thinking I will build a 3 way with them. I am trying to keep my cabs as small as possible so looking for some reinforcement below them as they roll of early without a huge cabinet. I have a pair of the old HIVi D10Gs which also don't go super low either but would help in the sub 100hz to 35 ish. https://www.swanspeakers.com/product/view?id=481 I might make a cabinet with the 4612 drivers vertically stacked and a space for about 70l below which I can put the D10Gs in for now while I find something to swap out with a bit more depth. Need some out of the box ideas, so keep them coming. Hmmm maybe OB 😊
Do not complicate. Build slim and tall enclosure with two JBL woofers vertically, with the same internal volume as original 4612B, with the same port and the same original crossover.
With your two D10G (in parallel!) make one 90 liters closed box active subwoofer. Mount one sub plate amplifier with 300-400 Wrms/4 ohms and enjoy. For serous home theatre setup with 25-30 Hz ability you have to build much larger vented enclosure sub.
Interesting suggestion thanks heaps Sonce. I assume you are suggesting mono bass so summing the low from both channels. I would like to understand the reason for running both into one box rather than keeping them seperate? Certainly less work.
Summing below 80 Hz is the duty of the sub plate amplifier.
Low frequencies below 80 Hz generally can not be detected by ear, so you can easily find the most appropriate place for one box only. 90 liters sub volume is small enough - there is no need to cut in two halves. Also, if you mount the two D10G at opposite sides of the sub enclosure, vibrations will be canceled.
But if you want to build vented sub with killer low frequency response, than the volume per each D10G must be large - about 140 liters, so two separate enclosures seems appropriate. One plate amplifier for both subs in parallel also.
What you have is a 97db efficient, 8", 85hz FS, with 3mm of xmax, 100W power rating.
It is a midrange driver as it says in it's manual.
Use both, or don't play too loud/low.
IF you overdrive them, the cone will fold/crease along the first corrugation, and you will need a new recone kit.
That is what kills 2118's usually.
A simple TS box calculator, will not take such things into account.
Also why the 2119, and M209 is what is used today.
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The reason I suggested wiring two [per box] in series is because this would mean that each driver would receive HALF the amplifiers output voltage.
Also, you would achieve an output level reduction of 4.2dB [ some say 3dB, but that is a debate ]
Of coarse, if you are crossing over to a tweeter using a passive filter you would need to take into account driver impedances for correct component values.