Pretty cabinet and it would be a shame to dump it, so .... would you consider buying another pro woofer that would work in a cabinet of your size? Off the top of my head I can't name any, but there should be something out there that would be more appropriate for your cabinet.
Did you put the mic directly pointing at or even slightly inside the port? There seems to be a lot of driver output bleeding over.
The bass reflex resonator seems to work just fine, according to your impedance plots.
Pro drivers mostly have a raising response with frequency (strong magnets) and when tuned low the strong upper bass and midrange response will mask the bass. So you don't hear much difference with open or sealed ports.
Did you compensate/equalize the response with your x-over?
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Also the positioning of speakers has a great influence on the bass response! Moving the speakers near the walls helps
At 87 litres @ 30 Hz, the Eminence LAB 15 doesn't look bad at all.
How large is the port cross-sectional area?
How large is the port cross-sectional area?
I never wanted to tune to 30 Hz — I’m actually trying to avoid that. My goal was 40–42 Hz. But it looks like even for that tuning, the enclosure is too small. So most likely, my task now is to find a driver that fits this box, because rebuilding the cabinet would be much more complicated.
I do not want to tune to 30 Hz. My target tuning is 40–42 Hz, but I still can’t get it to work — the port just doesn’t function. Even at that frequency, the bass reflex system fails to resonate.
There are drivers that work well in almost 90 litres with a tuning of 40 Hz, for example the BMS 15N850v²:
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Here I have shown the Deltalite II 2510 (green) with the same volume and tuning:
How did you even get the idea that this could fit? Or did you have massive EQ in mind? If I had been looking for a 15-inch subwoofer driver, this driver wouldn't have come to mind, because, as far as I know, this is not his area of application.
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Here I have shown the Deltalite II 2510 (green) with the same volume and tuning:
How did you even get the idea that this could fit? Or did you have massive EQ in mind? If I had been looking for a 15-inch subwoofer driver, this driver wouldn't have come to mind, because, as far as I know, this is not his area of application.
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If you look at the impedance plot it does indeed resonate. You just expect much too high bass boost from the resonance.
I didn’t think I’d need a subwoofer driver just to hit 40–42 Hz. This driver was actually recommended to me by a very well-known person — though I won’t name names. I guess we just misunderstood each other.
Low frequency measurements are hard to make. Your microphone may not be flat at low frequencies. If you seal the box and your mic measures fairly close to the predictions (assuming you measured the T/S parameters) when you close mic the woofer you can sort of believe the microphone. To close mic the woofer you place the microphone like 1/4" away from the driver and take a measurement at a very low signal level.
I see someone else has addressed it, but the box is rather small for the woofer. When you jam a woofer in a small box, you reduce port output. A "Correct" QB3 box for this woofer (assuming those parameters are correct) would be around 160 liters tuned to around 43Hz or so accounting for a little series resistance. Cutting box size in half from that means port output would be 6dB less than the optimum box..
Your port is sort of like what another old school designer used to call a "diffuser port". I seem to remember reading about it in Weems that he did one so he could do a downfiring port in a bookshelf speaker and ended up not using a tube 😉
I see someone else has addressed it, but the box is rather small for the woofer. When you jam a woofer in a small box, you reduce port output. A "Correct" QB3 box for this woofer (assuming those parameters are correct) would be around 160 liters tuned to around 43Hz or so accounting for a little series resistance. Cutting box size in half from that means port output would be 6dB less than the optimum box..
Your port is sort of like what another old school designer used to call a "diffuser port". I seem to remember reading about it in Weems that he did one so he could do a downfiring port in a bookshelf speaker and ended up not using a tube 😉
I didn't want to exaggerate it that much. I'm not talking about drivers whose surround area is almost as large as the area of the actual diaphragm. I mean drivers that are specially optimised for such an application.
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And do not underestimate 40 Hz.....😉
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I have read the start post again more carefully. So you're looking for a woofer for a large 2-way speaker.
It will probably be difficult to find a 15-inch driver that is not only optimised for a good midrange, but also for an f3 around 40 Hz in such a small cabinet. In order to achieve an f3 of 40 Hz in such a small cabinet, the cone has to be quite heavy, which is not normally what you want for the midrange.
On the other hand, examples such as the GedLee Summa show that there are drivers that can apparently be used in such a wide bandwidth, even if they initially appear to be subwoofer drivers *edit" Here, however, the 15NBX100 is used somewhat unconventionally in CB and then seemingly only from 80 Hz upwards.
Btw: which horn do you want to use with the DE250? And where do you want to set the crossover frequency?
It will probably be difficult to find a 15-inch driver that is not only optimised for a good midrange, but also for an f3 around 40 Hz in such a small cabinet. In order to achieve an f3 of 40 Hz in such a small cabinet, the cone has to be quite heavy, which is not normally what you want for the midrange.
On the other hand, examples such as the GedLee Summa show that there are drivers that can apparently be used in such a wide bandwidth, even if they initially appear to be subwoofer drivers *edit" Here, however, the 15NBX100 is used somewhat unconventionally in CB and then seemingly only from 80 Hz upwards.
Btw: which horn do you want to use with the DE250? And where do you want to set the crossover frequency?
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I’m planning to use a Joseph Crowe horn that’s designed to work up to 1000 Hz. I was planning to set the crossover at 1600 Hz. Based on my measurements, it performs quite well. The only issue is the low-frequency section. I’ve already realized I made a mistake there, but now I need to find a way to salvage the situation — ideally by finding a woofer that can perform well from around 40 to 1600 Hz and costs under $300.
In the picture I see a large, slightly widening, rectangular port. Is it closed and are there two round ports, each 70 mm in diameter, somewhere where you can't see it in the photo?
Two tubes of 70 mm each result in a port cross-sectional area of 77 cm². I usually aim for about 1/3 of the diaphragm area (SD), SD for 15-inch drivers is around 800 cm².
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I also believe that for achieving a smooth Radiation pattern 1.6 kHz is too high for a 15-inch driver to be separated from a horn with a comparatively wide dispersion pattern (As far as I know, Joseph Crowe is aiming for horns like that, isn't he?).
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What do you think about the Eminence Kappa-15LFA?
It seems to be the only driver available in the U.S. that more or less fits the parameters for my situation.
It seems to be the only driver available in the U.S. that more or less fits the parameters for my situation.
Let’s start by figuring out the driver first. I can always drill larger holes later.
Unless you want to run a subwoofer to fill in the bass it doesn't possess in that cabinet, yes. Either live with it as is, and add a dedicated subwoofer, or choose another driver / driver ~ enclosure combination.
You haven't mentioned what sort of power amplifier reserve you have for these. If you do have power to burn you can always shorten the ports and EQ the response, but you still have a high efficiency woofer, which doesn't go low unless placed in a large cabinet.
Kind of a pickle, that woofer has to meet the DE250, which doesn't go very low either, so the woofer has to have low inductance, and well behaved suspension and cone up high.