Help with tower upgrade

[wlg]

Hi all,

I've spent the last few days searching the interwebs for the best way to upgrade my towers (8" TMM/TWW), but I'm no closer to a final decision . At first I was hoping to keep the cabinets exactly as they are but I don't think that's going to be possible so I'm prepared to cut the baffles off and make new ones, then re-paint. Don't want to build new if I can get away with it. Current woofers are unknown, they have a 230mm overall diameter. Unknown dome tweeter also. Cabinets are 900mm high, 275mm wide and 380 mm deep for around 70L net volume.

Current thoughts - I would like a 3-way setup, mostly to make it easier to deal with BSC. I also want to keep the budget down so mostly looking at Dayton and PRV stuff. I'm leaning towards a waveguide tweeter, not real sure why, just like what I've read. The main restriction is my AVR which will only do 100x5 @ 6ohm, so the total impedance will have to be 8. Some woofers I've shortlisted are the Dayton PM220-8 and the RS225P-4A (2 in series). Also in contention is the Eminence Delta Pro 8B (2 in parallel) but at 99db it's hard to find a matching mid. Maybe the Dayton PM180 but would a 6.5" mid work with 2x8" woofers?

I'm just really lost and confused at the moment. I'm almost ready to buy a couple of Fusion-8 Alchemy Tower kits and hope for the best. Any suggestions on driver choice would be greatly appreciated. I listen to music mostly, but the room does get some HT use as well, not that I care too much what a movie sounds like. I have a Dayton 15" sub to take care of the lows, so the towers only need to get down to say 80-100hz. Room size is quite small at 4mx4.5m and the towers have to sit just off the wall. I only run 2.1.

Please help?

 

[wlg]

I think I have made a choice on woofer and mid at least. Here's what I have so far

Woofer - Eminence Delta-10A, 98.8db 1w/1m
Mid - Eminence PRO 5MRN-8 Neo 5", 93.1db 1w/1m
Waveguide - FaitalPRO STH100 1"
CD - ??

Woofer in 30l(1cu.ft) tuned to 80hz with 80hz high pass from reciever gives an F3 of 80. Higher efficiency of the 10" should minimise BSC requirements. Crossovers at 400 and 2k or higher. Definitely won't be the prettiest of towers, but could it sound ok?

 

[jrh0516]

Unless you are planning to design your own enclosure and crossover it's probably better to ask what existing designs fit your requirements.

Your room is small enough where many 2-way designs with a subwoofer would work quite well.

 

[wlg]

Thanks John. I already have enclosures I built years ago that I'd like to re-use. Regarding crossovers, while I have no problem soldering I just don't have the time to design and put one together, so will probably buy pre-made. I'd like to stick to a simple 2 way but I keep hearing about how important BSC is, so I'm trying to design something that factors it in.

 

[jrh0516]

If you are not designing the x-o then it's not possible to account for the baffle step. Any properly designed 2-way or 3 way will account for the baffle step.

Take a look at the resources ribbon on the right side of this link https://sites.google.com/site/undefinition/diy

 

[system7]

wlg, we are in the business of putting old heads on young shoulders here.

8" bass plus 1" tweeter can sound pretty good. Doubling basses into the MTM style isn't a big change, as it goes. And an amp doesn't usually mind a higher impedance, just hates low ones.

I happen to spend a lot of time on this combination. By merest fluke of circumstance. I just got interested in it when I bought a rough old pair of speakers second-hand.

Here's the Graham Audio Rogers LS5/9 clone:
Journeys in Audio Subjectivism ? Part Five - Positive Feedback

I have my own solutions that work with almost any well-behaved 8" bass. But the one I currently like the most is the BBC approach:
Rogers Loudspeakers › LS5/9

Before we go into a wild, exotic chase of three ways, I think you should just seek simple ways to improve your current speaker. Usually the crossover is some simplistic poor design. You should trace the crossover schematic, measure the actual cutout holes on the baffles to determine what else might fit, and identify the drivers you currently have. They must have some markings on them.

Some photos would help.

 

[wlg]

Thanks again for the replies. Just pulled one of the drivers to double check and definitely not a mark on them. I took a couple of pics to show you. Baffle cutout is 190mm, these drivers are 230mm overall diameter so I'm limited in driver choice to the larger 8's. I'm not against removing the baffle and adding a new one.

I put the fluke across the terminals and one driver measures around 7ohms, the resistance for the whole cabinet is 4. That's about right for a Z of 6 I think.

I don't want to bother drawing up the crossover as I know it won't work well with anything else. Might be able to re-use the board though. If you think a 2 way will be fine as opposed to a 2.5 or 3 way (which I'm pleased about by the way), I will look at finding some 16ohm 8" drivers to run in parallel. I have already been looking at the Eminence Delta Pro-8B's. They might even just be large enough to cover the existing holes.

 

[system7]

If that isn't a "Mickey Mouse" crossover, I'll eat my hat. Second order bass, and a near-useless first order tweeter.

The woofers look quite decent, as it goes. Can't identify them right at this moment. But I'll mull it over.

 

[danielwritesbac]

If the cabinet specs are known then the Parts Express forum would be a good resource.

 

[wlg]

Thanks Steve! Don't stress too much, I've all but made up my mind to replace them.

Daniel, not sure what you mean? I built these cabs 10-15 years ago. I bought a kit from ebay back then and built them according to the kit design.

 

[jrh0516]

If you want to keep your boxes and can redo the baffle there are several designs here that have the correct baffle width. Speaker Design Works

 

[system7]

That crossover board has room for some upgrades. Certainly a coil on the tweeter to take it to second order.

The woofers really look fairly standard fare from China:
W 200 S - 8 Ohm

This is just the sort of speaker I like improving.

I'd need to see some resistor values, because I can't read them, and some measurements of driver DC resistances to go further. And to know if my guess on the schematic is right. Parallel or series wired woofers?

But don't let me stop you spending a fortune on something else.

 

[wlg]

Wow good job finding those woofers! That's them for sure.

Since you've helped me out so much I did a schematic for you, I couldn't find a value for the coil though. I mentioned the DC resistance earlier, the woofers are 7 ohm and they're in parallel. Seems I might have been pushing my little Yamaha receiver too hard all these years, although it's never complained

Question - what is the purpose of the 6.8 ohm resistor in parallel with the woofers?

 

[wlg]

John, thanks for the link. I see a few I like already. The Anthologys are almost identical in size and as a bonus, looks safe enough to run on a 6 ohm amp.

 

[system7]

wlg, we ought to get on first name terms. I always find internet nicknames a bit odd.

This sort of thing, which has to be modified for impedance, is high inductance paired 8" woofers with a bit of voicecoil damping added by the 6.8R and 22uF.

Probably about 2.5kHz crossover. The problem with very high efficiency here is it puts a lot of strain on the 1" tweeter. Which leads to distortion, and might cause some issues under fault conditions. Because it's always worth considering what might happen if the tweeter blows, taking HF impedance low, and what that might do to your amp.

I had a look at the Fusion-8 Alchemy MTM Centre:
Alchemy Center Channel DIY Sound Group

It's doable, for sure, provided the woofers and CD waveguide fit.

Another approach, availability allowing, is to fit a big loud 95dB 1.5" tweeter with or without a waveguide:
www.audioexcite.com Monacor DT-300 + WG-300

Since you live in the land of Australia, with all its terrible import issues, you might get in touch with Joe Rasmussen for some of his waveguides and tweeter ideas too:
Elsinore Speakers DIY

Joe's a great guy with many fun ideas. If it was me, I'd try a bare 1.5" 95dB tweeter first. Once you move into the horns idea, you are building a disco speaker which is highly directional.

But really, I see no reason to ditch the woofers. I've used Eminence B 8" with a 1.5" Audax TW034, and it works well, but woofers are woofers, IMO. Though we should mention that the efficient (and low Le 0.6mH inductance, which tends to affect the crossover...) Eminence will have less bottom end than lower efficiency woofers. I think the reason people like them is the low mechanical loss from the Kapton formers and corrugated surrounds. Current theories say that low mechanical loss makes for great micro-detail in the sound.

BTW, I'd get those speakers off the floor and out of the corners. Here's the MT Fusion-8 Alchemy Eminence B crossover and a MS 737 Decca Ribbon cabinet. Do you get the idea?

 

[wlg]

Once again thanks for your advice Steve. It's Wayne by the way

Ah man, this wasn't supposed to be so hard! Whack some new drivers and crossovers in - done. You've swayed me to leave them be, maybe a tweeter upgrade and some crossover tweaking could help. Can you please check my tweeter crossover calculations? With the 8ohm resister in parallel and a single series resistor for the l-pad gives a total impedance of 6.2 ohms, therefore a 5.6uF capacitor would result in a high-pass frequency of around 4.5k?

Oh and I can't bring them out from the wall as I just don't have the room. I don't know how everyone can do that. Perhaps I should look into something designed to be on wall...

 

[system7]

I don't think it's hard, exactly, Wayne. But a hobby, by definition, is an interesting waste of time. So we shouldn't be surprised if it leads us down interesting paths.

Pleased to meet you, BTW.

Having been round the block a few times, I can tell you that big speakers in a small room tend to get problematic. This is down to a thing called "room gain". It means that if you put a big speaker in a small room, it sounds terribly bassy.

Then you move on to the basic sound quality. There is good reason to think that higher order crossovers sound cleaner at high level than simple ones like single capacitor tweeter ideas. If speakers behaved like 6 ohm resistors, it would all be terribly simple. But they don't.

mh-audio.nl - Home

We deal with something called cabinet bafflestep, and rising speaker inductance and even the Fs resonance at low frequency.

Back to your speakers.

I would like to know the DC resistance of the tweeter to be most precise, but in general, I would say the weakest link to good sound here is the 1" tweeter and its single capacitor crossover.

It would be simple enough to just change to a 95dB ferrofluid 1.5" dome and a near 3.9uF capacitor and 6.2R resistor, and it ought to go louder with less distress. But really, I would go a bit more complex on the tweeter filter. Tweeters are best protected from low frequencies. Then they sound nicer, because the other factor that causes distortion is driver excursion.

 

[wlg]

Sorry I thought I gave the tweeter resistance earlier, It's 8.3.

Say I do the tweeter upgrade and add a coil to the xover for 2nd order high pass, what about the mids then? For example sometimes in movies a male voice can be muffled and hard to make out the words. I don't have any EQ applied to my system, either on the HTPC or the receiver. Perhaps I could turn down the bass a db or two.

 

[system7]

You can reduce effective bass level by getting speakers up on stands and out of corners. You can also stuff the ports with a pair of socks.

You can also reduce the bass coil and adjust elsewhere for 1-2dB less bass. Male voices are actually in the 500-1000Hz range, so entirely from the woofer which must be crossing over around 2.5-3kHz.

I'm a bit surprised the tweeter is keeping up at all here. That 8 ohm resistor across it is reducing level a lot. I would be expecting something like below to work better. The 7.5R 0.68uF zobel is optional. Just something I like to do. The red resistor adjusts tweeter level.

 

[danielwritesbac]

Probably about 2.5kHz crossover. The problem with very high efficiency here is it puts a lot of strain on the 1" tweeter. Which leads to distortion, and might cause some issues under fault conditions. Because it's always worth considering what might happen if the tweeter blows, taking HF impedance low, and what that might do to your amp.

For the tweeter, perhaps an added series capacitor, located on the opposite pole from the series parts of the crossover.

Yes, that does result in series capacitance on the + and more series capacitance on the -; however, then the tweeter lasts.

I've done it quite a few times, and the only bother was having to use rather decent quality caps for it. Even so, it was still less expensive and more satisfactory than the alternative involving tweeter replacements.