Which is the best 7" mid/woofer around?

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Hi,

I have built a 16 liter vented speaker using the Scanspeak 8545k and the 9300 tweeter. I have been struggling for years to get the crossover satisfactory, and now I have basically given up. I want to find a nice sounding mid/woofer without any need for crossofer wizardry. I am not the guy who designed the Wilson Watt5 or the Proac 2.5 (evidently). I'm just an average audio geezer who wants to make my speakers sound OK.

My question to you guys: Which 7" mid/woofer is the best around for a small vented box? Money is not an issue. :)


The history is this... I worked with passive crossover back and forth and came up with a pretty nice and balanced design. I abandoned it, though, due to the harsch midrange. I have instead built my own active 24dB cossovers with state of the art op amps. My latest endeavour has been to build my own measurement microphone. SPL measurements look more or less OK (hard to judge due to room acoustics), but the speakers are still as harsch as ever. They only allow me to play soft acoustic music. If I put on a rock record I just want to go hang myself in one of my ripoff-over-prized-speaker-cables.

The 8545k has a 3-4dB bump around 500-1000 Hz which I have of course attenuated with different types of notch filters over the years. I have also, of course, compensated for the difference in driver sensitivity. Now that I have active crossovers, phase problems can be ruled out.

Well, there you have it... I want a new mid/woofer. Which one should I go for?
 
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Look for a driver (any driver) that is free of peaking in the 1~5 kHz region; these are very rare, but do exist. The measurements posted from the manufacturer are not to be trusted unless they were made on a IEC or larger flat baffle; you are not interested in replicating the diffraction patterns of the particular small box that was used to measure the speaker, but want to see the real response of the driver mounted on a flat plane.

Of course, your box will not be a flat plane, but it can use large-radii curved edges, at least on the left and right sides (2" or greater radii suggested). This not only simplifies the crossover design, but makes the driver sound better. (It's bad practice to try and solve a time-domain problem like diffraction with frequency-based equalization, as in the crossover.)

If your driver is flat and the box has low diffraction, you'll be surprised how little coloration the overall system has. You can preview the sound of the driver by listening to it full-range with no crossover at all; if it sounds bad, get rid of it, since even the most complex crossover can only disguise, but not eliminate, the inherent sonic character of the driver.

If listening to the driver full-range reveals a smooth, but slightly dull, sound, that's what you want. The tweeter is there to take care of sparkle. If the driver sounds harsh with no crossover, get rid of it, no matter how good it measures or how many rave reviews you've seen on the Internet.

My experience with notch filters is they are only advisable as a last resort. They can get rid of annoying and irritating peaks, true, but the resulting filtered sound can be dull and drab, with an odd absence of tonal color in the region that's being filtered-out. My guess is what's happening is that there's still a substantial increase in IM distortion in the region being filtered, and this is audible as a shift in tonal color in the filter region. By contrast, drivers that don't need extensive filtering usually have tonal colors are bright and vivid over the working range of the driver, and the crossover is simpler too.
 
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..but the speakers are still as harsh as ever..

Well, there you have it... I want a new mid/woofer. Which one should I go for?

Avoid paper and hard materials and composites..

Look to a *good* poly woofer.

At the high-end (price) there are the Audio Technology drivers (poly with mineral-loading), which can be custom made to your needs. Also, there is the previously mentioned Tang Band W6-1721, and the at lower end the Peerless 830874.

Dynaudio, Morel, and Dynavox also produce poly woofers, but their Voice Coil diameter tends to be overly large which usually produces a cavity resonance with a "peak" in the treble response (..it's the 3" VC's you need to be wary of, 2" is usually OK).

Frankly the Tang Band sounds about right for your needs at a decent price. Of course any given driver might not be what you need with respect to your cabinet volume, so you'll need to do some modeling.

At a slightly larger size look to the Vifa 8" poly which is now re-branded as the ScanSpeak Classic P21WO20.



Remember that with a small baffle the response will need to be corrected, both for pressure-loss below the baffle's support region, and pressure gain near where it peaks due to multiple edge-sources of diffraction.

Home of the Edge
 
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How about a Hivi 6.8?

That's one of the 3" VC drivers based on the Dynaudio design..

You can see the resonance/peak in response near 3 kHz:

http://www.parts-express.com/pdf/297-444g.pdf


This one manages to push the resonance up higher and suppress it a bit more than usual:

http://www.parts-express.com/pedocs/manuals/297-101-morel-tiw-638ft-manual.pdf

Hopefully this newer model has better non-linear performance than older models..

http://www.parts-express.com/pe/showdetl.cfm?partnumber=297-101
 
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He wants a small cabinet, I guess studio monitor size - the smallest box the TB will work is around 25 litres ported.

Another driver with a v smooth response is the Jantzen 6004 /6006, but don't cross too high as U'll lose detail.
It will work ok in 16 litres
 
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Thanks!

Thank yo all for your insights!

I have decided to go for a completely new box. It will be too hard to match the current diameter of the hole in the baffle. Also, i think the edge diffraction might be a culprit.

I am consideribg building a floor speaker using one of the midwoofers suggested by you and my scanspeak 9300 tweeter.

I think a poly cond will be my choice. The SB Satori and the Morel seem really nice.

My current active crossover (ESP board) crosses at 1700 Hz which should be ok for both these woofers.

I'm thinking maybe a 9" rounded baffle and a vented box with an adjustable bottom plate for fine tuning box volume.

Any thoughts on that?

/k
 
What do your measurements look like?
You're already using quality parts; I have a hunch that the problem is the frequency response, not the woofer.
I can get a good measurement in any room down to 500hz with a proper gate. Its only hard to measure low frequencies indoors. What program is being used for measurement?
 
Vance Dickason uses the Scan Speak 18w/8545K00 woofer in his LDC6 Studio Monitor (Loudspeaker Design Cookbook 7th edition) with the Scan Speak D2905 Revelator tweeter. I'd be very surprised if he published a design that sounded harsh, so i'm sure the harsh sound is crossover related.
 
If I was picking a 6-7 inch woofer for a two way system to be used with that tweeter you already have and like (I used to have that one), I'd look for a vented flat spider, rubber surround suspension (polyurethane foam disintegrates over time). Polypropylene cones seem to have the smoothest frequency responses when you need to go above about 1kHZ. It's a rare 1 inch dome tweeter that sounds good below about 3kHZ, so I'd be careful there. If you have an active 4th order crossover some can go below 2kHZ (Seas Millenium, some Scanspeakes, for ex.), but then the off axis response (and thereby "room response") jumps right where the ear is most sensitive (2kHZ - 4kHZ). An abrupt change draws attention and is never good. I like vented pole pieces, I don't care what the driver frame is made of since the mass of a ceramic magnet dampens that considerably.

Since you are rebuilding the box, I'd go 3 way, so the dispersion change at the crossover frequency wouldn't be so severe. Arrange the drivers vertically tower style so the tweeter at the top is at least 36 inches off the floor. Put all three drivers as close to each other as is practical.

A peak in the upper midrange is arguably the very definition of harshness generation. Harder cone drivers do better at low frequencies, below say 400HZ, but they always have severe resonant peaks in the upper midrange. Hammering these peaks down with notch filters (Zobel?) doesn't fix the time smearing property (ringing) of any resonant mechanism, and could even make it worse if not perfectly calibrated and stable over time.

Paper cones are often a paper substrate saturated with some brew of harding material (usually some variation of plastic - often with a filler such as nomex fiber or carbon fiber, for ex.). They're not all the same. Poly cones often have fillers or whatever too, so there's a lot of variation within each catagory. Look to the frequency response graph for the final decision. Polyprop is usually the smoothest, then paper, then many different types of hybrids/multilayers etc. then kevlar, then metal or ceramic (ring-a-ding-ding).

Rounding the baffle corners to minimise diffraction helps significantly. Personally I glue 1/4 inch or thicker wool felt to the front baffle surface, keeping it at least an inch away from the tweeter dome so I don't create a cavity effect there. Glue any variation of 3/8 inch or thicker synthetic wool felt to all internal surfaces of the enclosure. Especially a midrange sub-enclosure. Absorbtive material glued to internal walls is much more effective than the same material just thrown in there loosely.

Personally, I'd use the Peerless 6.5 inch (#830875) or 8 inch version Nomex cone up to 600HZ (very well vented flat spider, good Xmax), then a Peerless 3 inch TG9FD10-08 (glass fiber cone, well vented flat spider, shorting ring on end of pole piece) in it's own subenclosure from 600 - 6kHZ (keeping crossover phase anomolies out of the sensitive imaging frequency range (1kHZ - 6kHZ)). I'd use a Dayton 3/4 inch ND20FB-4 dome ) or a Fountek 1.5 inch NeoCD1.0 ribbon for above 6kHZ. Not only would I rebuild the active crossover, but I'd put the big driver in a sealed box (which will be significantly smaller than a vented box) and use active EQ to make it flat to whatever low end I'd want (40HZish for a 6 or 8 inch driver operating as a woofer) (you want to use a topology that rolls off the response sharply below that 40HZ peak). I'd possibly use a 1 pole passive crossover between the 3 inch and the tweeter, but higher order is worth it at the lower crossover, although with these drivers and those xover frequencies (600 and 6kHZ) you could go 1 pole passive in both places and do well. I'm actually using these drivers I've mentioned above, and am very happy with them. I don't see that you get anything better by spending huge amounts of cash on brands lie Scanspeak, Seas, Dynaudio, Fostex. Been there done that too. Baffle Step as it's called needs to be addressed as well. That's where the baffle stops reinforcing the acoustic output due to it's physical size in relation to the size of the wavelength being produced. It will typically cause a rolloff below about 500HZ with an enclosure about this size. If the speaker is close to a wall baffle step will be more of a shelf than a full rolloff. Go to linkwitzlab.com for more on this, or just measure what you end up with before building the active xover, so you can add it in there. Put the speaker where you plan to put it, when measuring for baffle step response.

16AWG AC Line Cord stranded copper wire from any hardware store at 20-50 cents per foot is just as good as any wire out there for up to 12 ft. and arguably twice that (you'll lose a little power on a really long skinny wire - nothing else really). It's the connectors that are possibly a weak link. I use gold alloy plated Banana connectors and solder all wire connections. The set screws in many male Banana connectors (on the speaker cable itself) can become a weak/distorting connection over time.
 
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