Thinking of building 7" wide mini-towers with 106 db/w sensitivity

[Aijan]

I'm thinking of building a pair of 7" wide mini-towers with a sensitivity of 106 db/w, using the following drivers (chosen for their smooth frequency response):

• 4x Lavoce FSF041.00 4" full-range drivers (88 db/w)
• 1x Lavoce DF10.142LM 1" compression driver (106 db/w)
• 1x Lavoce HD1004 horn (1200 Hz cutoff frequency)

The crossover between the full-ranges and the compression driver will probably be around 1500 Hz. I will also be using subs, crossed over at 100 Hz.

The full-range drivers, placed in close proximity, should act like a line array up to approximately 1600 Hz (the space between driver cone centers will be about 105 mm). This assumes that the 1/2 wavelength rule for line arrays applies in my case. If I need to use the 1/4 wavelength rule, I can switch to smaller 3-inch full-range drivers with little loss in sensitivity.

Do you think this is doable, or am I missing something?

Driver specs:

• 4" full-ranges
• Compression driver
• Horn

 

[LTig]

The sensitivity of the FSF041.00 is only 88 dB. You won't reach 106 dB with them in a line array, except when adding a large bass horn.

 

[PatentLawyer]

Yeah, and those all wired in parallel will present a really low impedance....

 

[alex-z]

Even if you run all 4 woofers in parallel that only gets you to 94dB sensitivity, and you will lose 5-6dB for baffle step compensation.

If you really want to push the sensitivity up then switch to 6" mid-range, and do side-mounted low profile woofers crossed at 200-300Hz. Here are some example drivers you could use.

FaitalPRO 6FE400 6" Professional Woofer 8 Ohm

FaitalPRO 6FE400 6" Professional Woofer 8 OhmThe bigger brother of the 6FE400, FaitalPRO's open back 6FE400 6" professional midrange speaker is purpose-built to cover the critical midrange in three-way speakers, but also works great as a door speaker in car audio applications. With 400 watts of...

www.parts-express.com

Dayton Audio LS10-44 10" Low Profile Subwoofer Dual 4 Ohm

Dayton Audio LS10-44 10" Low Profile Subwoofer Dual 4 OhmDayton Audio's shallow subwoofers let you put more bass into less space! The new LS10-44 Low Profile Subwoofer from Dayton Audio provides over 10 mm of controlled excursion, for bass that hits hard and goes deep -- even in places ordinary...

www.parts-express.com

 

[voodooless]

How about XT120? It’s a bit more modern design without diffraction slot.

 

[Hayabusa]

Even if you run all 4 woofers in parallel that only gets you to 94dB sensitivity, and you will lose 5-6dB for baffle step compensation.

If you really want to push the sensitivity up then switch to 6" mid-range, and do side-mounted low profile woofers crossed at 200-300Hz. Here are some example drivers you could use.

FaitalPRO 6FE400 6" Professional Woofer 8 Ohm

FaitalPRO 6FE400 6" Professional Woofer 8 OhmThe bigger brother of the 6FE400, FaitalPRO's open back 6FE400 6" professional midrange speaker is purpose-built to cover the critical midrange in three-way speakers, but also works great as a door speaker in car audio applications. With 400 watts of...

www.parts-express.com

Dayton Audio LS10-44 10" Low Profile Subwoofer Dual 4 Ohm

Dayton Audio LS10-44 10" Low Profile Subwoofer Dual 4 OhmDayton Audio's shallow subwoofers let you put more bass into less space! The new LS10-44 Low Profile Subwoofer from Dayton Audio provides over 10 mm of controlled excursion, for bass that hits hard and goes deep -- even in places ordinary...

www.parts-express.com

2x2series/parallel will give you 94dB
you would need 64 to get 106dB

 

[Aijan]

Ok, achieving 106 dB sensitivity doesn't seem realistic, even with a line array. How about wiring two of these 94 dB/W 6.5" mid-woofers in parallel to reach 100 dB and calling it a day? I'll be crossing the towers to quad 12" subs at 100 Hz, so low bass won't be a problem.

LAVOCE WSF061.52

 

[Devnull]

Not gonna hit your f3 or your desired SPL. F3 will be 115 Hz best case. 2 in parallel is realistically going to get you 95 dB and that's with an under 3 ohm impedance.

You should probably think about stepping up to a decent pro sound 8 inch driver and even then it will probably take 2 of them to hit a 100dB/W.

If I could make a suggestion, learn to use some simulation software. Boxsim from visiton, vituixcad and winisd are available for free.

 

[Aijan]

Not gonna hit your f3 or your desired SPL. F3 will be 115 Hz best case. 2 in parallel is realistically going to get you 95 dB and that's with an under 3 ohm impedance.

You should probably think about stepping up to a decent pro sound 8 inch driver and even then it will probably take 2 of them to hit a 100dB/W.

If I could make a suggestion, learn to use some simulation software. Boxsim from visiton, vituixcad and winisd are available for free.

I've done a quick calculation in WinISD, and above 300 Hz, I can achieve 100 dB with two drivers at 2.83V to accommodate the low impedance of parallel connection. Am I missing something? At 1 watt, though, the output is around 96 dB.

 

[Devnull]

That's above 300 Hz you can hit 100 dB. I thought you wanted 100dB/W. And did you take into account the baffle step of the enclosure? You still need to address the crossover to your subs. Your box F3 is above your stated sub crossover frequency, 100Hz, so you will not have a flat frequency response.

 

[Aijan]

That's above 300 Hz you can hit 100 dB. I thought you wanted 100dB/W. And did you take into account the baffle step of the enclosure? You still need to address the crossover to your subs. Your box F3 is above your stated sub crossover frequency, 100Hz, so you will not have a flat frequency response.

Good points. Keeping the width of the towers narrow is important to me, so I can't really use two 8-inch drivers to achieve 100 dB/W sensitivity. I think I can live with 96 dB/W sensitivity (or 100 dB/2.8V). I might be able to boost the low-end of the towers with DSP a bit, since they don't need much power to get loud.

 

[voodooless]

Maybe also horn load the midranges of you want better sensitivity. Like this:

 

[tmuikku]

driver datasheet sensitivity is either from 1kHz or some average on some bandwidth on mids, basically every manufacturer define it how they want, if I've understood correctly. So, if 6" driver says its 96db sensitive it's likely that around some kilohertz. If one looks datasheet of the 6fe400 for example, it's perhaps 86db at 100Hz. To get high sensitivity around 100Hz, look for +10" drivers. 10fe400 for example, seems to get to more than 90db at 100Hz. Most 15" drivers should be able to pull 96db 100Hz. There is no way to cheat physics, so perhaps less sensitivity is fine. If not, then more and bigger drivers is must.

 

[D!sco]

I think there's been a little confusion on the part of the OP on some of the terminology. Do you want a speaker that can play to 105dB, or one that only needs a watt to play 105dB?

The "one watt, one meter" test determines system sensitivity. Doubling power adds three decibels to playback output, increasing logarithmically until something fails. The Max SPL of a unit is that output with a safety margin of usually another 3dB, so half output power. Lots of drivers are capable of reaching 105dB with enough power, but almost none can do that with a tickle of electricity.

You can see the LaVoce's have a sensitivity of ~91hz. This means one watt outputs 91dB of sound power in your direction! It should only take a few watts to reach studio reference levels. They are also capable of playing at concert venue levels, with a 100W continuous power rating. This comes at the cost of extension. The LaVoce resonates at 103dB, making it difficult for the woofer to play lower. Most HiFi drivers sacrifice sensitivity for low range extension and better damping, which requires a lower box volume. This allows them to play linearly and low, at the cost of output. Using this 6.5" will require a subwoofer, or even a bass woofer between to extend linearly and loudly.

 

[tmuikku]

Yes, it is not too hard to make high sensitivity on mids, or highs. Hard part is to get ~linear frequency response from the whole system for whole bandwidth, from low bass up, let alone to some target response like harman where bass is 10db above highs. To get full bandwidth system even with 91db sensitivity, the bass system needs to be quite substantial. Single 15" could make ~90db 1W down to perhaps 40-50Hz in ported box. To get lower than this, say ~91db/30Hz/1W requires 18" woofer or several smaller ones, with quite a large box volume. Good thing is these could be separate from mains and possibly hidden into house structure or furniture.

Sensitivity is very important feature on a system if one has very low watt amplifier which must be there. Sensitivity is important anyway to reach some kind of SPL target but sensitivity is not free due to very long wavelength on low frequencies, which means big size. Small system just cannot do it, so either size must go up, or sensitivity requirement down to more realistic Small slim systems just ain't very sensitive but that might still be fine.

It might be that high sensitivity mid/high system makes less distortion, perhaps provides desirable directivity and so on, and thus sounds better as low sensitivity one, but it might be just waste of money. So, careful there, not just got with high sensitivity, figure out what's the goal for your system and what kind of a system then fits. In general, driver sensitivity number in datasheet isn't very helpful, it's basically just cone size wavelength ratio that matters. Small drivers are sensitive on short wavelengths, large drivers are sensitive on bit longer.

I find it easier to think in terms of max SPL capability. How loud you want to listen and with what bandwidth, from 30Hz up? To be able to listen reference level say 85db at listening spot which might be 2m away from speakers the system needs to be able to do 91db + peaks say 15db. So system capability with nice sound needs to be around 105db or so, not 1W capability. 40W makes about 15db of gain, so if system sensitivity is 91db it can do the dynamic peaks with 40W amp, but one could use 400W if the transducers can handle it and are top shelf stuff with high excursion low distortion, to get system size down some. Anyway, this kind of stuff, reference level from 30Hz up is 15" woofer territory, perhaps multiple 10" or 12" would be enough, so quite a big system.

Have fun

 

[Aijan]

Thank you for all the suggestions. My original idea was to use a line array of small-diameter drivers coupled with a compression driver to minimize vertical cancellations, but that sacrificed too much sensitivity. So, I entertained the idea of using two high-sensitivity 6.5" woofers in an MTM configuration to reach 100 dB/2.83V (before baffle step compensation). Unfortunately, even with a crossover frequency of 1 kHz or so, the vertical directivity isn't to my liking in VituixCAD simulations. I do plan to use subwoofers crossed over at 100 Hz to handle the low-end.

As much as it pains me to admit, if I wish to have coaxial-like horizontal and vertical directivity, it appears that I need to ditch the second woofer. The final sensitivity is now only 90 dB/1W (after BSC), but thanks to the high-sensitivity drivers, the speaker can reach 110 dB/1m with only 100W. The compression driver will do hardly any work, and that's a good thing since the crossover will likely be quite low at around 1 to 1.2 kHz.

Here are the simulated horizontal and vertical polar maps (based on my quick-and-dirty in-room measurements of the B&C ME10 horn) if anyone is interested:

 

[Devnull]

I'd rethink your horn and compression driver choices. Your proposed crossover frequency is half an active below the horns cutoff frequency. The compression driver's not meant to be used that low either. The recommended x-over is 2200Hz twice what you want. Using the recommended x-over the output is down at least 12+ db. You can't use the frequency response graph published because it's not using the same horn that you want to choose. Rule of thumb is half power max below a compression driver's peak impedance and that's usually around a half octave below the peak.

Small compression driver's just aren't made to perform that low, you should really think about stepping up to a 1.4 inch driver

 

[Aijan]

Thank you for the tips @Devnull,

I think the manufacturer's crossover recommendation is for pro audio use where they commonly power drivers at their limits. I doubt the compression driver will ever see more than a couple of watts in a domestic environment. The horn rolls off at 1400 Hz according to my measurements. The 1200 Hz crossover I intend to use is about half an octave below the impedance peak of around 1700 Hz.

I'm trying to keep the speaker fairly compact, so using larger horns or compression drivers isn't really possible. However, I might switch to an alternative compression driver with a recommended crossover frequency of 1200 Hz, such as this one: Lavoce DN10.142, but I don't really like its frequency response over 15 kHz.