Yet another near-field project beginning

Sooo.. I've been dithering about for quite some time... asking different questions and starting/testing different ideas for a while now. This is my latest attempt at making something final from that. I like near-field listening, by which I personally mean being close enough to the speakers that room effects are much reduced. The direct sound is dominant, reflections from the room are there so things don't sound dead, but they're later and lower in SPL so don't compete with or mask the direct sound very much.

Anyway, I tried tiny speakers, round and then egg-shaped designs, and then slightly larger desktop speakers. But finally realised that however wierd and wacky, I'm not going to be satisfied with anything basically less capable than the decent two-way bookshelf speakers I've been using for decades.

One aspect of this is the bass. So I've decided the woofers are going to be decent for small speakers: a pair of SB23MFCL45 that I have. Technically called subwoofers but small (for such things) and in my estimation able to go up to several hundred hz. Not very sensitive of course, but fine for a close listening situation. Physically just over 9" wide so could be used front mounted in a small cabinet, or side facing if the crossover were low enough, which might allow a 6" wide cabinet.

sb23mfcl45-4.jpg


They won't need to reach a tweeter, as I want the important mid-range covered in one driver. That exact range is contested, but a few (maybe several) hundred hz up to maybe 5khz or so is my verdict. It may even be a widerange driver with no tweeter, however that is undecided yet and somewhat secondary IMO, so I'm purposely posting this in the multi-way forum (I have no problem with crossovers at several khz, but some wide-range drivers might suffice for someone in their 50s).
 
These are subs rather than woofers. Crossing at 200 Hz to a largish lower midrange should be OK but crossing higher to a midrange or upper midrange driver will place a wonky response in the crossover region. They are inefficient likely requiring a pair to get a reasonable response w.r.t. efficiency and clean SPL. I have some for small subs but dropped the idea of temporarily using them as woofers crossing to a small midrange.

If a wideband driver with it's low SPL and ragged response is considered acceptable then that could be a better match than a midrange. I think this is referred to as a Woofer Assisted W-something and is a thing on the fullrange forum.
 
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Andy made some goood remarks, you may use two woofers on the sides in a push-push config and create a small line array with four small fullrangers on the front baffle. There are nice linear 3" fullrangers for this purpose. I designed such a speaker for a friend. The downside was that you need a stable amp as it is not very sensitive. For really close listening, I am not shure if lobing may become a problem in the high freqs though. Just an idea.. good luck with finding a solution!
 
Looking at response curves & SPL ratings at frequency...the Tang-band W3 1878, a three-incher FR seems to be a decent match...crossed over at 600-650 hertz to your specific eight inch, should work out fine.


------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
 
For your SB eight-inch, by simming, in a vented enclosure, I get 45.7 liters, an fb of 26.7 hertz...and a final -3 DB@25.44 hertz....rather great performance. For sealed, it's virtually half size at 21.7 liters...but not quite reaching down very far at --3.02Db@ 46.8 hertz.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rick...
 
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Thanks everyone. Yes they call the SB23MFCL45 subwoofers, but I agree they should make it up to a couple of hundred herts if wished. IMO perhaps a bit more (I've actually listened to them higher and they do very well). Though it is interesting (and useful) to hear that you dropped the idea, Andy - perhaps I need to evaluate them a bit more carefully before deciding what and where to cross over to.

Thanks for doing the sims, Richard; those numbers are around what I had thought too. My initial thought is to take advantage of their potential for a small sealed cabinet, as they reach low enough for me like that. Though they are small and inefficient, their SPL will be sufficient for close listening distances with one each side (one left, one right).

I just found a short thread by Graham in which he kindly shows a couple of frequency and distortion plots for these drivers in just 16L enclosures.
sb23cubes-measurements-jpg.1072174

sb23cubes-distortion-jpg.1072175

he was making subwoofers of course, but I find his results encouraging for my purposes too.

So I'll need to decide what drivers to pair them with, next. Through listening and looking at FR and distortion plots, the idea of crossing at a couple/few hundred herts to a wide-range driver as a mid looks possible, and is quite tempting. But I'm most interested in the midrange driver, and might want something smaller in that role than I would choose for crossing directly to 8" woofers, in which case an additional/intervening mid-bass unit (maybe around five or six inches) would be worthwhile considering; I suppose ultimately it might depend on how high I feel comfortable crossing the SB23s.

Thanks for the thoughts everyone, they have already been helpful!
 
Sounds good , your almost there.
Desktop 3 way with side facing woofers.

find a 3 or 4" mid and cross to 3/4" tweet.

but yes about 180 to 200 Hz is about all the
8" has. Its fine, the woofer will be close
to the mid regardless, just on the side.

basically a really deep bookshelf
 
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Thank you, very much; yes this would indeed be the kind of thing I was aiming for. Depth of the speaker cabinets can certainly be more than for a typical bookshelf speaker. Comfortable legroom dictates a decent depth of desk, whilst I want the drivers/baffle fairly close to the listening position, so there is going to be plenty of space behind.

Perhaps I expected a slightly higher crossover from the (sub)woofer driver, but only slightly and you're now the second knowledgeable person to suggest 200hz as the upper limit so I'll quite happily go with that. Lower would probably be no bad thing for side-facing the drivers, too. At 200hz the wavelength of sound is about 67.5 inches, so the radiation from any likely baffle should be 4pi and the ideal quarter wavelength driver spacing would still be over 16 inches.

There must be plenty of 3"-4" drivers that'll do 200hz to 5khz. Certainly most 'full range' types and small midbass drivers have no problem if any nasty break-up is high enough. Not sure about dedicated midrange drivers, it'd likely depend on their linear excursion at 200hz; some might. I also don't mind a gently narrowing directivity, in fact I'd prefer it, so 3" or 4" would be perfect.

There might be an argument for no tweeter with some full-range drivers used as the midrange. Personally I'm starting to go away from that because I seem to be able to (very easily) localise higher frequency sounds from them when listening up close. Unless the drivers are fairly tiny anyway, which can work but in my intended enclosure size and SPL would be asking too much IMO down at 180hz. So, I'm much more likely to settle on a tweeter, both for the above reason and to avoid cone break-up from the 'mid-range' driver. I don't believe that by five or six khz we're really able to discern things that'd make a crossover more undesirable lower down. Depending on the size of driver I might consider a waveguide for it to manage directivity and also reduce influence of baffle edges.

Early days, but after a few false starts I suspect this direction is one that I'll stick with and so complete; it really appeals to me. :)
 
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