Thanks Arez and Audio>X I will proceed with a box for these drivers and decide if I use the D10G as a sub or three way bass driver as an interim as I have it to hand.
Wattage received by each driver is the main point.
Two in series: each driver will receive half of the max amplifier wattage output (at 32 ohms).
Two in parallel: each driver will receive half of the max amplifier wattage output (at 8 ohms).
I can't see any justified reason why anyone would want 6 dB lower sensitivity or lower SPLmax from the loudspeaker?
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Well I am rather gutted. I pulled the drivers from the 4612 boxes and found both tweeters have been replaced by Eminence tweeters. They are attached to the horns by two bolts. One of the horns is broken and ideally need replacing but could be repaired. Can't see any numbers on the Eminence tweeters to know if it's an upgrade or more likely downgrade after some PO blew the originals. Decision time. Wise words appreciated. Onslo
YES @Sonce - I made a significant error in stating a reduction of 4.2dB volume level with series wiring. You are correct that it is 6dB.
The reason I suggested series wiring is because, the JBL 8"s have a sensitivity of 97dB/W/m [ but only 50 watt Program Power ]
Series wiring would not only make it easier to match to 'regular sensitivity' tweeters but also help the JBL's cope with much higher amp voltages.
PS.
Series wiring for level reduction of an 8" mid is better than using resistors.
The reason I suggested series wiring is because, the JBL 8"s have a sensitivity of 97dB/W/m [ but only 50 watt Program Power ]
Series wiring would not only make it easier to match to 'regular sensitivity' tweeters but also help the JBL's cope with much higher amp voltages.
PS.
Series wiring for level reduction of an 8" mid is better than using resistors.
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The JBL 2404 diaphragms when they were available (only aftermarket imitations are available now) cost considerably more than a complete 1" exit Eminence driver, the PSD 2002 the most common.
The PSD 2002 can be crossed much lower than the 2404, but it's response above ~ 10kHz is generally not very smooth.
Eminence does not make any drivers with a similar response to the 2404H, and even if they did, the 2404 throat is only 1/2" diameter, and Eminence does not make any 1/2" throat drivers. Putting a 1" exit driver on a 1/2" horn causes terrible response, even if the crossover would be correct, which it wouldn't be due to the impedance mismatch.
Photos of the horns and drivers would help identify what you have, and what might be usable.
Thanks Weltersys. Yes I agree looks like I got duped agaIn. It's the risk you take with old gear especially Pro stuff that has been potentially hammered and treated rough.
The good news is I got four very nice 2118 midranges that look and sound to be perfect at still reasonable price.
I am now looking at tweeter options. I have a CNC router so might try one of Joseph Cowles bi radial horn files or a ring radiator. Open to hear suggestions...
Also another question. The 4612 enclosure is about 40 litres with two holes about 50mm round as ports. No port tubes. If I was using these drivers in a new enclosure as part of a 3 way what do you suggest I do? Use a similar ported enclosure? I could save them some power handling by rolling them off at 100-150 and handing that over to subs.
Love to hear suggestions.
The good news is I got four very nice 2118 midranges that look and sound to be perfect at still reasonable price.
I am now looking at tweeter options. I have a CNC router so might try one of Joseph Cowles bi radial horn files or a ring radiator. Open to hear suggestions...
Also another question. The 4612 enclosure is about 40 litres with two holes about 50mm round as ports. No port tubes. If I was using these drivers in a new enclosure as part of a 3 way what do you suggest I do? Use a similar ported enclosure? I could save them some power handling by rolling them off at 100-150 and handing that over to subs.
Love to hear suggestions.
Depends on what crossover range they cover and how loud you plan to listen.
JBL's response graph gives you an idea of what to expect with just 14L per driver:
If volume isn't top priority, I usually opt for sealed for its better transient performance in the woofer to mid range transition.
If you decided to build a 'all in one box' 3 way speaker, and used the JBL 8" as mids in parallel, it would be very expensive and near impossible
to find a woofer that could match the very high output of mids. You basically would have to go with an active base system.
If you wired the JBL's in series, bringing them down 91dB sensitivity, you would open-up a 'whole new world' of woofer & tweeter selection/choice.
You would also have the possibility of very broard & coherent midrange with 'near indestructible' power capacity 🙂
Thanks Weltersys and Audio>X.Very good information.
Just showing my ignorance here but how would it go as a 2.5 way with the higher channel in a sealed 15l and the lower channel in the ported?
Another question... Why does the ported enclosure roll off so much earlier than the sealed?
I have ordered a Celestion CDX1-1425 Neo and paid for the Joseph Crowe matching horn CNC file which I will make. Horn Lens No.2332 Looks like sensitivity in that horn and frequency range and dispersion should be promising with those drivers.
I think the impedance might be getting up a bit with them in series Audio>X don't you? I might have to look at some sort of horn loaded sub to match them as you rightly note it's going to be a sensitive upper frequency system. There goes my nice small system. What WAF?
Just showing my ignorance here but how would it go as a 2.5 way with the higher channel in a sealed 15l and the lower channel in the ported?
Another question... Why does the ported enclosure roll off so much earlier than the sealed?
I have ordered a Celestion CDX1-1425 Neo and paid for the Joseph Crowe matching horn CNC file which I will make. Horn Lens No.2332 Looks like sensitivity in that horn and frequency range and dispersion should be promising with those drivers.
I think the impedance might be getting up a bit with them in series Audio>X don't you? I might have to look at some sort of horn loaded sub to match them as you rightly note it's going to be a sensitive upper frequency system. There goes my nice small system. What WAF?
Absolutely. You would find that the impedance response would be higher in the midrange, however there is no 'golden rule' that states
the impedance response of speaker systems needs to be flat. Using tube amps with low damping factor is really the only exception.
In fact, when using transistor amplifiers, there is even the possibility that a higher impedance can actually result in lower distortion.
It seems that you're on exactly the right track using the Celestion's with a horn 🙂
I am sure that a clever & smart member WILL respond clearly & concisely regarding your question about 'Ported vs Sealed' roll off.
When the two woofers have different rolloffs through the bass, they will compete with differing phase. You may lose out this way.
I'm a little late into this but I have some concerns. I can't be sure without seeing details. The larger cabinet may have been holding the baffle step low enough to cover down to the room frequency. Sometimes in these conditions the baffle step is not accounted for.
By using a narrow box you might be introducing a baffle step. By going 2.5 way you are addressing the baffle step.
If this is so, I might imagine a couple of things. One is that the tweeter would need to be padded down. The other is the lower midrange will get mixed up in the room, needing careful placement for smoothness (like any narrow speaker would).
If this change is important to you I can imagine you want to do a little equalising.. whether it is used to teach you what you have, or simply gives you back a usable response while you do your measurements and work it all out.
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Original JBL 4612B is 2.5 way, although in a wider cabinet. In narrower cabinet it might call for a smaller value of the coil (low-pass filter) for the lower 8" driver.
I am still recommending ported enclosure for the two 8" midbass drivers (as a 2.5 way) with total internal volume of 24 liters, plus additional subwoofer.
Ported enclosure has faster roll-off and in the larger enclosure will reach lower frequency than closed box. it is the nature of the beast.
Thanks for the replies. I am gaining a lot of knowledge here. Some further questions...
Sonce - can I ask why you would port the enclosure if there will be a subwoofer in the mix? To me sealed looks to deliver better at the top end with these drivers and the bass extension would not be needed anyway ?
Thanks AllenB your insights are valuable. What can I expect sonic differences of a 2.5 way on its side as these were to orienting it vertically in a living room sitting close.
Thanks again too Audio>X , you were right I got an answer, AllenB gave some good info.
Sonce - can I ask why you would port the enclosure if there will be a subwoofer in the mix? To me sealed looks to deliver better at the top end with these drivers and the bass extension would not be needed anyway ?
Thanks AllenB your insights are valuable. What can I expect sonic differences of a 2.5 way on its side as these were to orienting it vertically in a living room sitting close.
Thanks again too Audio>X , you were right I got an answer, AllenB gave some good info.
The top end of the driver's response is identical sealed or ported.
The upper rolled off response in the "average" response curve in post #28 is the 45 degree off axis response.
The JBL 2118's actual response has peaks and dips rising ~+/-2dB above and below the average curves.
It's response is -6dB at ~2kHz 45 degree off axis. Above that frequency, the driver may be considered "beamy".
The port increases output between the 70Hz Fb (box tuning) and ~300 Hz.
A higher Fb in a similar size box (~14L per driver) will have a "flatter" response.
The JBL 2118 woofers are 229mm wide, baffle cutout of 179mm.
The Crowe Horn No.2332 is only 200mm wide, it's round over is designed for a cabinet of that width to reduce edge diffraction.
Vertical alignment of the horn over the woofers improves horizontal dispersion.
Art
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Because the original vented box JBL 4612B has low cut-off frequency of 80 Hz - which is optimal for a subwoofer. In closed box the same JBL 8" drivers will have much higher ow cut-off frequency.
Since the 0.5 way woofer is dealing with the range of frequencies that are not acoustically seeing the box, the orientation may not be the most significant difference. By using a smaller baffle you're likely to increase the frequency up to where the sound goes around it. This is why the 0.5 is going to need to play a little higher up, and half that energy is going to go behind the speaker into the room.
Thanks people. I do have some more questions if I may...
Art you mentioned the Crowe horn being rounded over for a narrower baffle than I will need (about 15mm per side) Is that likely to be audible and could some chamfering of the baffle to blend into the horn overcome this? Conversely if I decide to build a wide cabinet and mount the drivers side by side like the original 4612 cabinet can I mount such a horn on a flat wide baffle above the woofer pair?
The 4612 cabinet is 40litres. I cannot understand why JBL used that size but don't publish it and how it performs in their literature. How is the smaller recommended size enclosure ever going to deliver the bass of the original 4612 vented enclosure?
Many thanks
Art you mentioned the Crowe horn being rounded over for a narrower baffle than I will need (about 15mm per side) Is that likely to be audible and could some chamfering of the baffle to blend into the horn overcome this? Conversely if I decide to build a wide cabinet and mount the drivers side by side like the original 4612 cabinet can I mount such a horn on a flat wide baffle above the woofer pair?
The 4612 cabinet is 40litres. I cannot understand why JBL used that size but don't publish it and how it performs in their literature. How is the smaller recommended size enclosure ever going to deliver the bass of the original 4612 vented enclosure?
Many thanks