So what to put under a midrange dome....M74T in my case? I am planning a wide baffle, 52cm or 20.5", with large radii (perhaps 4"), picture the Grimm LS1 with a little more depth. This gives a baffle step frequency of ~250Hz.
My first thought was, well, you haven't spared expense so far, so go for it, Purifi 8" or 10" and call it good. Then I was struck by their poor sensitivity v the M74T (Re 5.6R, 95.5 @ 2.83V/1m) and T34B (Re 3.3R, 97.5 @ 2.83V/1m). Certainly not a huge deal if crossed-over electronically, but still...and not to mention the expense (especially when I considered a second PTT8 crossed at the baffle-step so as not to drive down sensitivity even further (3.5 way), that is just simply too much $$$ when I am building 3- L,C, and Right).
I also thought a lot about the crossover frequency of 500Hz and C-C spacing the wavelength. The currently recommended C-C distances seems to be within 1/4λ or 1.2λ. Whereas typically the former is almost never achievable and the latter is used, in this case 1/4 wavelength spacing is possible and 1.2λ is 82.3cm or 32.4"........
Staying within 1/4λ sounded very appealing in terms of making it easier on a relative rookie to do the XO, particularly if the driver was nice and flat well beyond 500Hz. So I did some math.
The M74 chassis diameter is 12.1cm. So a woofer chassis (max) of 22.2cm is within 1/4λ C-C at 500Hz. That opens the possibility of 6 1/2" up to 8" drivers.
Still thinking about sensitivity, I began searching and modeling tons of drivers, hi-fi and pro. This is the power region, I want an effortless sensation of power, but also drivers that start and stop fast by CSD, are well-behaved above XO, don't have ripples in the impedance response in the intended frequency range, etc. I learned a lot, including:
I also realized that if 2 of the midbass drivers' C-C was < 1/4λ at 500 Hz I could possibly put them side-by-side under the mid-dome, increasing sensitivity, SPL, etc.
After all of that, here is a list I have come up with. If anyone has gotten this far and has any thoughts, I would love to hear them. I am ready to purchase and put this decision behind me. I am thinking of these drivers covering 80-120Hz up to 500Hz (the Satoris would extend deeper). One more driver will go below. And I have 5 JBL sealed 10" studio subs distributed in the room.
Thank you,
Bill
My first thought was, well, you haven't spared expense so far, so go for it, Purifi 8" or 10" and call it good. Then I was struck by their poor sensitivity v the M74T (Re 5.6R, 95.5 @ 2.83V/1m) and T34B (Re 3.3R, 97.5 @ 2.83V/1m). Certainly not a huge deal if crossed-over electronically, but still...and not to mention the expense (especially when I considered a second PTT8 crossed at the baffle-step so as not to drive down sensitivity even further (3.5 way), that is just simply too much $$$ when I am building 3- L,C, and Right).
I also thought a lot about the crossover frequency of 500Hz and C-C spacing the wavelength. The currently recommended C-C distances seems to be within 1/4λ or 1.2λ. Whereas typically the former is almost never achievable and the latter is used, in this case 1/4 wavelength spacing is possible and 1.2λ is 82.3cm or 32.4"........
Staying within 1/4λ sounded very appealing in terms of making it easier on a relative rookie to do the XO, particularly if the driver was nice and flat well beyond 500Hz. So I did some math.
The M74 chassis diameter is 12.1cm. So a woofer chassis (max) of 22.2cm is within 1/4λ C-C at 500Hz. That opens the possibility of 6 1/2" up to 8" drivers.
Still thinking about sensitivity, I began searching and modeling tons of drivers, hi-fi and pro. This is the power region, I want an effortless sensation of power, but also drivers that start and stop fast by CSD, are well-behaved above XO, don't have ripples in the impedance response in the intended frequency range, etc. I learned a lot, including:
- graphic demonstrations of Hofman's iron law- if I want sensitivity in the midbass I won't get deep extension and am looking at a 4-way(!)
- low Qts pro drivers roll off very high in sealed enclosures...
- finding good measurements of pro drivers isn't as easy as going to hificompass.com...
- B&C seems to have good correlation with their datasheets, 18Sound is somewhat hit or miss, and I don't have much confidence in Faital Pro.
I also realized that if 2 of the midbass drivers' C-C was < 1/4λ at 500 Hz I could possibly put them side-by-side under the mid-dome, increasing sensitivity, SPL, etc.
After all of that, here is a list I have come up with. If anyone has gotten this far and has any thoughts, I would love to hear them. I am ready to purchase and put this decision behind me. I am thinking of these drivers covering 80-120Hz up to 500Hz (the Satoris would extend deeper). One more driver will go below. And I have 5 JBL sealed 10" studio subs distributed in the room.
Thank you,
Bill
You could add one of the SB Audience Nero 10 or 12mwn700d drivers to the mix, even tho they don't go that low. All of the mwn700d series (including the 15") appear to have the same motor. High efficiency & power handling, fairly light paper cone, Fs 40~55 Hz, 7mm Xmax, robust motor & frame. Modest cost for what you get. The 12 is a very nice, neutral, dynamic driver.
I used well braced 2cf 44 Hz ported boxes lined with 1.5~2" thick foam. Near the wall & mounted high in a ~5000cf room, they go deeper than they should even near 110 dB spl. Live voices speaking into ordinary stage mics are produced with startling clarity. Extremely dynamic. Probably more so than any home HiFi woofer I have used.
Do you think that it could partly be that the speaker system designers were really talented and did a great job with the overall design, that allowed the great mid-drivers to really shine? I say this partly because it seems that really expensive speakers don't always live up to their inflated price tags, and some more modest ones seem to get things right. It seems like careful overall design is a big factor. Not trying to be contrary, just hope to provide some perspective.
They are a 10" sealed design, right? Do you know the woofer/mid cross point?
I have had a pair of those around for a while. One mid is dead. I might replace both mids with HIVI DMB-A. Since I have already suffered the learning curve with regard to the DMB-A, maybe the new crossover will not be too hard. The woofers need surrounds, and I would probably use new tweeters. The walnut cabinets are nice, but need new finish. It would be good to protect the DMB-A dome somehow; a typical round wave-guide for it is a no-go according to my experiments---it will only accentuate the problematic 4300hz null.
Maybe another, better behaved mid, could be made to mate with the existing Phillips wave-guide?
That's a shame ...
I've got perfect working pair in storage. I know they're pretty good within their power range and wonder what project I might use them in (?)
Sadly > don't be surprised if the tweeters are damaged and 'buzzy' also. These drivers strictly need second or third order crossovers.
As you will find in this thread, you have a wonderful range of choices for replacement.
Absolutely, I do think that. My ear can, however, decipher between which driver is playing the mids in a speaker system. He did say he had to work with the driver manufacturer and specifically develope that waveguide to get the right sound out of it. He had a hand in the driver design himself. He was impressed I could tell the dome was what stood out. He spent most of his time with the dome and the mids. He didn't even really mention the woofer or the tweeter. It was clear where his efforts were focused
Certain drivers specifically stood out at the show. Wharfendale's large AMT tweeter was top notch for example.
It's not like you cannot tell which drivers are best out of a system when you listen to system after system in a row for 9 hours
I probably will in the future. I just got the PMC domes though and ordered drivers for my kitchen 2.5 way. I'm a ways off from beginning that engineering project
Does Wharfendale manufacture their own AMT or do you know which tweeters they use?
I am 90% sure that they do. Or, at least, they are built to their specification.
I spoke with one of their engineers there outside the rooms and inquired about acquiring a set of the tweeters. He said it wouldn't be any issue at all. Considering they cross them with a 7-8" driver I would say they cross pretty low for an AMT.
I will try to buy a set soon here and likely cross them with the PMC dome.
Going to be a Frankenstein build using all the best drivers from the systems i heard. Though the Accuton 8" drivers are a bit out of my price range. But my goodness, the dynamics of those things were incredible.
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I heard the Bliesma dome 1 weeks go: M74B and M142P 7" with T34B. Impressive mids. The M142P was xo at 250Hz.
I'm convincing myself to jump onto M142T, which can go to 2 to 3kHz very well. And I like AMT/ribbons. Have a Beyma TPL that will likely be replaced down the road as I won't need the lower xo capability. Hence I was interested in your comment.
I would highly recommend the BliesMa dome mids for anyone interested in top dome mids.
I'm convincing myself to jump onto M142T, which can go to 2 to 3kHz very well. And I like AMT/ribbons. Have a Beyma TPL that will likely be replaced down the road as I won't need the lower xo capability. Hence I was interested in your comment.
I would highly recommend the BliesMa dome mids for anyone interested in top dome mids.
Are they available to the public? How are you going to buy them?
No idea. Probably going to call and ask for a replacement set. It didn't seem like it would be that big of deal.
Most companies are happy to take you money. They don't really care what you're going to do with the product
Yes, the M142T are very expensive. That is why it’s a significant decision for me. But what I heard was very significant too.
The M74 is less expensive, but not cheap. I thought you mentioned these above, but upon revisiting I see it was Bill Brown who did.
"Best" and "cheap" rarely happen together though. Best for a given price range is another story.
Definitely not cheap. I got a pair of the M74B. Ambitious build for a friend. Retails CA$2000 at Solen.ca
Sometimes more expensive doesn't mean more better.
I assume you have a lot of tools if you're into this hobby. Check out "Project Farm" on YouTube. He tests tools from all different price points. Sometimes more expensive definitely means better. Like drill bits. Sometimes though, the cheaper options turn out far better.
I don't deny what you heard but I, like you, would need to hear them before placing down that amount of money on a set of drivers.
Above referring to the vintage Phillips 2" paper domes from the Phillips 477 3way, the(AD 0210)? It is interesting that the same basic shape of the response curve (attached scan above by Audio-x ) seems to be common to various mid-domes that I have seen measurements for. I think that it was in another thread where Profiguy said (corrections welcome) that the strong dip at about 4300hz was likely caused by cancellation at that frequency, inside the dome from one side to the other. I interpret that as being something similar, as the phenomena that a "phase" plug on a cone driver is supposed to help reduce. Might not be quite right about that though.
In the inexpensive HIVI DMB-A that I have been working with lately, this dip is only accentuated by adding a circular wave-guide----due to raising the on axis area centered at about 2500hz. But it might be OK with the right crossover design. As it is, the bell-shaped response of the DMB-A (with my crossover) has it covering just 800-3000hz or so. It does sound good, and have very low distortion, especially considering the price. It does need a few "extra" crossover parts, though a few of those doing shunt/conjugate duty can be electrolytic, if we are not being too picky.
As far as expense goes some drivers are worth it.
For example my grandparents bought three EV drivers in 1964. 15W for about $78. T250 and T350. I do not know the retail prices on the mid and tweeter in 1964.
I could sell the T350 for about $350 currently.
I first remember hearing the 15W woofer when I was four years old. I now have another 15W for stereo and listen to them daily.
A pair of Eton 4-203 midranges I bought about 1990 are about to go into some speakers for one of my kids. Was expensive then but still in use over the years.
For example my grandparents bought three EV drivers in 1964. 15W for about $78. T250 and T350. I do not know the retail prices on the mid and tweeter in 1964.
I could sell the T350 for about $350 currently.
I first remember hearing the 15W woofer when I was four years old. I now have another 15W for stereo and listen to them daily.
A pair of Eton 4-203 midranges I bought about 1990 are about to go into some speakers for one of my kids. Was expensive then but still in use over the years.