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Most HE drivers seem to be for ported enclosures. Anything available that will work well in a sealed enclosure? TIA
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Yes, you can do this, and maybe you should.
The tradeoff is: no bass. A sealed design with a hi-eff cone will roll off around 100-150hz typically. But, that is OK in today's world of cheap and easy powered subs.
A lot of speaker configurations today reflect the realities of the 1950s and 1960s. They wanted high efficiency because they had low power amps. Also, they didn't have the cheap sealed sub with 500 watts of power. So, they needed high efficiency, and the ability to go low. This translated into large cones and large ported boxes. Even the horn speakers of the time e.g. Altec 210 bass cabs transitioned to a ported box for the low end.
Today, you can get readymade subs at Parts Express for really not much money. There are cheapie versions and also some pretty nice sealed versions. They cost more than a box with a hole in it, and are more complicated, but it might be better than what amounts to a one-note organ pipe.
Yeah, I tried to go the.....sealed box route, and you're absolutely right.....NO bass.
However, I am NOT a fan of subwoofers (powered or otherwise), because.....IMHO, they rarely integrate well with your main speakers.
That said, I ended up building a pair of rear-ported cabinets, that worked well with the FR drivers (E-V SP8C) I eventually installed in them.
I've had good results with Eminence Basslite Neo in a 3 cuft sealed cab.
Rolls off below 60 Hz, and a second order lowpass blends nicely with horns.
I'm having very good results with TAD 1601b in the same cabinets.
Here a first order lowpass works very well.
I love the drivers blending deep into each other.
Just have to set the crossover points really far apart.
According to the calculator, I am at 200 and 700, but it sounds flat.
The TAD's reach down a little lower, and to my ears and heart,
the pleasure of Alnico magnets is great.
Driving this channel with a nice tube amp seems to set the tone for the whole system.
Mats
I have 2 pairs Utah V12RXC21 which come up on Ebay frequently and, according to legend, were made by Utah for Altec, or maybe the other way around.
Anyway, as measured with a P.E. DAT, the specs are
Re 3.6
Fs 27
VAS 237.9 L
QTS .31
QMS 2.50
SPL 94
WinISD graph for 2 Cu Ft sealed
I have had them in a smaller cabinet that was on hand and played around with ports and KLH type vari-vent then sealed. Boomy with a port, nucely balanced sealed. After I got the DAT thingy and had some T-S specs, I got serious. Vifa DX25GT09 will cross at 2500 Hz first order for an overall 95 dB Sensitivity. Not, strictly speaking, High Efficiency, but not bad.
For a while I had some vintage Utah 12" fullrange in large homemade sealed cabinets. They sounded a lot like Dynaco A25's but where much more efficient. At the time, I had A25's to compare. I would recommend them.
Dave
I'd look for big drivers with Qts of about .4-.5 and lowish Fs
Not many pro / HE drivers fit this. 15-18" PA / instrument drivers with relatively low (95-96dB) sensitivity are sometimes candidates.
Punch the specs into an efficiency calculator, (see the link)
Punch the specs into a sealed box calculator (same site)
E.g. P-Audio P-18N "designed with a vintage voicing" (I look to P-Audio first mainly due to local availability)
3.03% efficient (96.8dB / watt)
-3dB at 72.62Hz in a ~120 litre box
It works in a reasonable box, but with a relatively high Fs. Depending on your room and tastes, that may be low enough.
Eminence DELTA-15LFA, which is only $100 in the USA:
2.62 efficient (96.2dB / watt)
-3dB at 57.45 in a ~210 litre box
If something like this looks like a reasonable compromise to you, go for it! They are easy systems to get right, and forgiving - it doesn't matter so much if the drivers don't exactly match advertised specs, or if you make the box 10 litres too large or small.
I have an all sealed system (using 6*15" drivers) and rather like it.
I wouldn't call them high efficiency (87db - 92db) but you can get reasonable efficiency in a sealed box and a decent f-3, with some of the 15" woofers at Parts Express (if their specs are to be believed). If you have room for multiple drivers in a giant pox, you can have it all!
Dave
The quick check is to calculate fs/QT. You can get 0.707 of that for a Butterworth alignment, or 0.577 for Bessel alignment. But you can't really get below about 1.4 times the free air resonance fs without impractically large boxes. In the fifties people would mount speakers in heavy closet doors, using the coats and hats as damping material. Some even used fireplaces for the ultimate transmission line design!
You are correct. One reason is that a sealed box must usually be larger (2 to 3 times greater volume!) to get the same -3dB bass extension, so nobody wants a speaker designed for a sealed box.
A second reason is the one that hitsware referred to. For a given cone and voice coil mass and resonance frequency, the optimum magnet for a sealed box is much smaller that that for a ported box, so the driver is less efficient.
A third reason is that the excursion required to get a given loudness at the lowest frequencies is much larger for a sealed box.
A fourth reason is that a good design for a sealed box has a loose and floppy suspension, so it is easily damaged when ignorant dorks pour hundreds of watts into the driver mounted in the wrong box - then they complain about the manufacturer.
Nevertheless, I am also very attracted to the idea - the smoother rolloff and reduced ringing are very attractive aspects, as is the immunity to uncontrolled sub-resonance excursions like record warps. The most interesting candidate I've run across is the Fostex FW305, though I have not actually heard one yet. One approach that helps is to design for a Bessel filter response, QT=0.577, or even a critical QT of 0.50. If the resonance is low enough, room gain can bring the bass levels up enough to sound right.
This may be a fundamental mistake I have had for all these years. I thought the AR guy developed sealed designs to get the air to act as a spring and needed only smaller cabinets. So the AR speakers were all small and the bass went down deep but not efficient. You have stated that the sealed cabinets should be much bigger.Have I totally misunderstood the concepts? Thanks.
Cheers
Bill
There are several variables playing against each other, so it's really hard to make sense of any simple rule such as the ones I posted above. I intended them as examples rather than rules but that's really too much subtlety for a forum post - I apologize if I've sowed unnecessary confusion.Edgar Vilchur was the AR guy. In order to make the box serve spring duties, it is necessary to reduce the suspension stiffness or increase the box air stillness so that the box air stiffness dominates. There are limits to how floppy a suspension can be and still keep the voice coil well centered in the gap. So another way to do that is to use a smaller box to increase the box air stiffness. But then the resonance, which is the low frequency cutoff, becomes high - no deep bass. To get deeper bass, you have then to make the cone mass greater. The greater cone mass is harder to move, so the efficiency goes down. These are qualitative remarks, but djk has distilled the mathematics to put numbers on the effect.
edit: I'll leave the following paragraph, but note that it's incorrect - see the post by djk below for the correct information
> > > "Vilchur originally made a pretty efficient compromise - I don't remember the numbers but the AR-1 must have been around 94dB in a 3 cubic foot box with a ~50Hz resonance. But just at that time, solid state amps were making high power affordable, so smaller speakers with deeper bass and much lower efficiency became the cost-effective standard. Efficient speaker well matched to huge sealed boxes do not make cost-effective speaker systems, which is why it's hard to find suitable drivers on the market." < < <
Edits: 03/28/14
"Efficient speaker well matched to huge sealed boxes do not make cost-effective speaker systems, which is why it's hard to find suitable drivers on the market."
"To get deeper bass, you have then to make the cone mass greater."
The DIY-er can try this too.
I've never rigorously experimented with adding mass to a speaker's cone, but have been tempted, to get an almost suitable driver over the line.
AR-1, 25" x 14" x 11" made of 3/4" stock, about 1.615 cu ft gross.While 92dB/2.83V, they're 4Ω, so they are actually 89dB/1W/1M.
Edits: 03/28/14 03/28/14
could a cheap Visaton BG20 be used to make a knockoff? - wonder how the ~1K crossover sounded? - are there suitable modern woofers that won't rot?
Karlson Evangelist
Thanks for the correction, I was way off. I do remember the WE755 "tweeter" though!
Efficiency and size are directly related.
For any given cut-off frequency the box size will have to double for each 3dB higher efficiency.
2 cu ft 30hz = 84dB
4 cu ft 30hz = 87dB
8 cu ft 30hz = 90dB
16 cu ft 30hz = 93dB
32 cu ft 30hz = 96dB
The multiple drivers will also need to be close to each other to fully couple.
Thanks PJ. Just finished reading your response to my question on the Bottlehead forum, you do get around. My concept would be that of a large sealed box crossed over at around 200Hz. After that problems diminish, could even use a wide-range driver on an open baffle crossed over to a ribbon tweeter.
Your observation about a smoother rolloff is precisely what I find objectionable about ported designs, only took me about 30 years to come to that realization(insert smiley-face thing here). Bessel filters will be "googled" very soon. Hopeful that I will be able to listen to Mahler and Shostakovich on a 300B amp without cringing. Thanks.
FWIW, the FW305 is only 95dB. You might need two of them for the Mahler Eighth :^) Bessel filter with a 300B gives resonance at about 40Hz, in a ~6 cubic foot box. Internal volume. Per driver. No free lunch.
Seems like the big magnets that contribute
to efficiency detract from the necessary Q
for sealed .
hey hits - instead of using my Peerless of India W-12p for S.L.O.B. woofer duty, I think I'll go with this guy's arrangement with a compression driver and waveguide for a two-way sealed box with "some" efficiency
Karlson Evangelist
Please tell me more, although I am philosophically opposed to paralleling things I like to be open-minded.
that was a close-out 8 inch woofer from Parts Express with a reasonably low free-air resonance and a nominal impedance of 12 ohms so 4 drivers could be paralleled and used with amplifier's happy with a nominal 4 ohm load. The response was pretty good and in his description, the builder used a 3500Hz 12dB/oct. lowpass & 5000Hz 2nd order high pass to the waveguide
fwiw - the woofer specs
http://www.parts-express.com/peerless-india-w8-12t-12p-8-paper-cone-woofer-12-ohm--299-068
Karlson Evangelist
Q I take to mean resonance, but what this has to do with driver performance in a sealed enclosure I don't understand. I'd love to be enlightened. It does seem to me that some designs from the era when watts were not free used drivers such as what I am enquiring about, please correct me if I am wrong. Many thanks!
Q means many things, but where sensitivity is concerned the primary Q considered is Qes. Drivers that work well in sealed enclosures tend to have high Qes, but high Qes also translates to low sensitivity. Very low Qes will usually give high sensitivity, but at the cost of low frequency response, especially in a sealed alignment.
Thanks, so would you say that a high efficiency sealed enclosure is a sort of mutually exclusive terminology?
> Thanks, so would you say that a high efficiency sealed enclosure is a sort of mutually exclusive terminology?
Pretty much, certainly as far as low frequencies are concerned. You can use a very low Qes driver, like a JBL E130 (0.21), to realize 101dB sensitivity from a sealed box, but the f3 will be around 150Hz.
A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).
fantastic paper."Marketing Considerations
The biggest problem with the sixth-order vented system (V6TH) is the rather anemic looking 200 mm (8 in) driver in the 2 ft3 box (the marketing department won't like it).
But now lets look at that 380 mm (15 in) driver in the closed-box system (Wow, we can really sell that one !). Well, maybe we can put a 300 mm (12 in) or 380 mm (15 in)
passive radiator with that 200 mm (8 in) driver in the vented sixth-order system and come up with a sellable package (this system is quite close to the Electro-Voice Inc. system
described by Newman in (6.,7). "
Karlson Evangelist
Edits: 03/25/14 03/25/14 03/25/14
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