Can anyone give a rough estimate for the sensitivity of two like 15”, 16 ohm, 97 dB 1W/1m, mid-woofers wired in parallel? The configuration is TMM, 2.5-way. The high frequency roll-off for the .5 woofer will begin around the BS of 250Hz or less. Cabs are base reflex est. 18”W x 40”H. Not looking for the sensitivity of the overall TMM 2.5 speaker, just the two 16ohm woofers wired in parallel. Thanks.
you must have missed the 'search' function at the top right.
Brief answer: +3dB for speakers in parallel; another +3dB because you're halving the amplifier load
Brief answer: +3dB for speakers in parallel; another +3dB because you're halving the amplifier load
Last edited:
You have given the manufacturer's rating of the sensitivity already. Should be at 1kHz, half sphere (2π) radiation. That means baffle step is included on a IEC baffle.
I'd say with a 2.5-way you end up with the sensitivity of one driver, max. The second driver won't contribute much at 1kHz, system sensitivity will be no more than 97dB/W/m, half sphere.
I'd say with a 2.5-way you end up with the sensitivity of one driver, max. The second driver won't contribute much at 1kHz, system sensitivity will be no more than 97dB/W/m, half sphere.
Thanks all for your answers. Lojzek, the drivers are JBL 2226 Js. PeteMcK, have searched the archives, but I’m still not clear, may be my limited experience. However, 2 of the responses so far, one 103 dB & the other 97 dB, you can see there’s some room for confusion. I’ve got the basics, +3dB parallel & +3dB load, but also the .5 woofer BS offset should impact in some fashion.
Also, I’m not clear… TMM 2.5-way (2 like 16 ohm mid-woofers in parallel) with say a TM Xover point around 1.5k Hz and a BS of 250Hz. Top mid-woofer handles from 1.5k Hz down & bottom woofer blends in around 0 -200 Hz. Seems like the combined impedance for the 2 woofers will be 8 ohms from 0 - 200 Hz and 16 ohms from 1.5k - 200 Hz. Correct?
Also, I’m not clear… TMM 2.5-way (2 like 16 ohm mid-woofers in parallel) with say a TM Xover point around 1.5k Hz and a BS of 250Hz. Top mid-woofer handles from 1.5k Hz down & bottom woofer blends in around 0 -200 Hz. Seems like the combined impedance for the 2 woofers will be 8 ohms from 0 - 200 Hz and 16 ohms from 1.5k - 200 Hz. Correct?
Measured under 4V of input, the sensitivity is 97dB/1m 2 pi. Referenced to 2.83V/1m this is 94dB/1m. Decrease by 3dB for baffle step and two of these in parallel, I'd guess 97db/2.83V/1m should be an estimate about right.
Thanks Lojzek and all for helping. Kinda what I figured. I was hoping to increase sensitivity while maintaining a relatively flat 8 ohm nominal load for my SET amps. I'm not sure there's enough benefit in combining the two 16 ohm woofers to make it worth my while. Again... thanks.
There is benefit. Unless you’d opt for e.g. an in-wall solution or corner woofers. The baffle step essentially is a transfer from 4pi to 2pi radiation. If you want the high efficiency on -say- 1kHz, you need more sound energy on lower frequencies where radiation is more like 4pi. Doubling the cone surface helps you out here.
It´s a murky issue because everybody quotes everybody else without actually measuring.
Measuring RULES.
Feed 4V proper bandwidth pink noise into one 16 ohm speaker, measure SPL.
Now connect second in parallel, lower noise signal to 2.83V , measure again.
(needed because keeping 4V signal is cheating, not a real "sensityivity" increase, simply doubled power)
You will find SPL increases by somewhat over 1 dB , not reaching 2dB.
3 dB real increase?
Never *measured* that, only found on paper and simulations 😉
And part of it comes from increased directivity, so SPL increases on axis.
Measuring RULES.
Feed 4V proper bandwidth pink noise into one 16 ohm speaker, measure SPL.
Now connect second in parallel, lower noise signal to 2.83V , measure again.
(needed because keeping 4V signal is cheating, not a real "sensityivity" increase, simply doubled power)
You will find SPL increases by somewhat over 1 dB , not reaching 2dB.
3 dB real increase?
Never *measured* that, only found on paper and simulations 😉
And part of it comes from increased directivity, so SPL increases on axis.
Measure swept sine. You will find efficiency higher on low and low-mid frequencies. As long as the phase is relatively coherent, efficiency rises.
Using pink noise and measuring broad band is pretty useless as long as you have no crossover applied.
Using pink noise and measuring broad band is pretty useless as long as you have no crossover applied.
Agreeing with Mark. For proper additive driver sensitivity measurements, the two signals must be fully correlated, 100% in phase sine waves. Using pink or white noise with random phases results in a noise sensitivity measurement, yielding lower results.
Last edited:
- Home
- Loudspeakers
- Multi-Way
- Help with Sensitivity Estimate