A decent sub for minimus 7's

[Stocktone]

Hi there,

This is my first post, but I've been reading the forums, and I haven't really found the answer to my question.

I recently suffered a disaster of sorts, and I need to replace much of my equipment. I have put together on the cheap a somewhat decent HT receiver and a few pairs of Minimus 7's.

My question is, what sort of sub will go well with these? Much of what I have was purchased off eBay (kinda hard to scoff at a pair of 7's for $20, unless you've gotten a pair your friend was tossing out), so I'm looking to continue the low-cost/doesn't-totally-suck performance trend. I would like to do a decent passive sub, but I'm not sure what the response is on the 7's, so I don't know what sort of crossover point I should use. And if they need to crossover high, should I then have a pair of subs?

Whatever help I get is appreciated.

Thanks,

Eric

[Cal Weldon]

How much power do you have?
How big is your room?
Do you like bigtime whoopass bass?
Where in the room can this (these) be placed?

If you are running 7's, I would guess that a single 10" is all you need.

Cal

[rdf]

If my mental way-back machine still works the fundamental resonance of a Minimus 7 (haven't owned one in at least a decade) is 120 - 130 Hz. Think woofer instead of subwoofer and x-over as high as placement permits.

[Stocktone]

Hey, thanks for the info!

The entertainment room is rather small, maybe 15 feet deep by 13 feet wide. The receiver puts out 100 watts RMS per channel, but I never crank it.

As for my taste in bass, I prefer it balanced all the way down. In fact, I'd be willing to sacrifice the very lowest 20 or so hertz (say, 20-40Hz) just to keep it nice and tight (as far from flatulent as you can get).

I currently have the fronts about 5 feet apart, and two feet from the front wall. They're toed in very slightly. I have the center on a cobbled together shelf above the tv because they're not shielded. The surround channels are on the wall a couple of feet above and about a foot behind the listening position. I'm still playing around with those.

All told, I'm really surprised at how good the little beggars sound, especially once you factor in the price. All I'm lacking is a couple of octaves at the bottom end.

Now if they're good down to about 120-130 hz, shouldn't I be able to run a decent single sub and cross it over at 180 hz, and not worry too much about it sounding localized? As you can tell, I don't have loads of room to play with, so is there a decent sub I could cobble together myself that would fit the bill?

Thanks again for the replies,

Eric

[rdf]

I don't run subs and haven't played with 7's in at least a decade so take this with rocks instead of grains of salt. 180 Hz sounds way too high. It's into male vocals, and don't forget the sub will still have significant output at least an octave above for typical x-overs.
I do recall a pair of 7's surviving abuse at the hands of 200 watt SAE when we were bored one day, so I doubt power handling will be an issue for a room that small. I also recall that the 7 was tuned to a fairly high Q, meaning a rise at resonance. If it were me I'd start at ~ 140 for the satellites and, on the assumption the rise in speaker response will result in slightly more extension, stagger the sub x-over to 120 or less. A lot will depend on placement too.

[TerryO]

I've still got two pair of 7's which I bought for my cars back about 1977 or '78. I used mine in-house with a 10 inch driver xo'd about 100Hz or so. Please don't forget to modify the 7's if you want semi-decent sound. I have a pair that I modified and a stock pair. There is a great deal of difference (and improvement!) involved.

For this system, try PE's Quattro 10 inch driver and the ApexJr "junior" plate amp. It's been independantly tested in excess of 130 watts into 4 ohms. Neither of these components are expensive and give good bang-for-the-buck value.

If you need a better Sub, then go for one of the Adire Audio drivers and an Apex "Senior" amp.

Best Regards,
TerryO

[Stocktone]

Hey, thanks for the replies! Now let me respond:

Please don't forget to modify the 7's if you want semi-decent sound. I have a pair that I modified and a stock pair. There is a great deal of difference (and improvement!) involved.

What sort of modifications are you referring to? I've spent hours on Google trying to find tips, but what I've come up with so far includes "painting" the cone on the woofer with puzzle coat (a thinned PVA glue?), replacing the existing electrolytic cap with a polystyrene type, soldering the speaker wires, and further dampening the interior of the cabinet with something (I guess to lower the resonance, but that's my ignorance showing). What would I use to dampen the cabinet? I would love to hear all the tricks!

I'll have to look through the forums again, but are there any driver replacement recommendations? Just in case, you know...

For this system, try PE's Quattro 10 inch driver and the ApexJr "junior" plate amp. It's been independantly tested in excess of 130 watts into 4 ohms. Neither of these components are expensive and give good bang-for-the-buck value.

So I took a peek at partsexpress.com, and I found the speaker, but not the amp. I was able to pull up plates amps in general. So the idea looks good, and it would be something worth sacrificing my morning mocha for, but my 5.1 integrated amp output only has a mono line-level LFE out (no left/right RCA jacks), and I'd have to spend quite a bit more money than I like to get a plate amp with a single LFE input (direct). I'll just have to keep looking.

The nice thing about the amp is the fact that it has a built-in x-over. Should I try to match the amp and sub x-over, or should I pad either one?

I don't run subs and haven't played with 7's in at least a decade so take this with rocks instead of grains of salt. 180 Hz sounds way too high. It's into male vocals, and don't forget the sub will still have significant output at least an octave above for typical x-overs.

Thank you; that's excellent information. I wasn't sure whether the 180Hz point was too high or not.

If it were me I'd start at ~ 140 for the satellites and, on the assumption the rise in speaker response will result in slightly more extension, stagger the sub x-over to 120 or less.

Are you referring to room lift? Thanks for this as well, since I hadn't even considered it.

I do recall a pair of 7's surviving abuse at the hands of 200 watt SAE when we were bored one day, so I doubt power handling will be an issue for a room that small.

I thought the power rating was a bit on the conservative side. They're fairly sturdy speakers. Not that I'll be shoving 200 watts into them anytime soon.

Thanks again!

Eric

[TerryO]

You asked:

What sort of modifications are you referring to? I've spent hours on Google trying to find tips, but what I've come up with so far includes "painting" the cone on the woofer with puzzle coat (a thinned PVA glue?), replacing the existing electrolytic cap with a polystyrene type, soldering the speaker wires, and further dampening the interior of the cabinet with something (I guess to lower the resonance, but that's my ignorance showing). What would I use to dampen the cabinet? I would love to hear all the tricks!
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Ok, I'll tell you what I did and let anyone else add their ideas.

First, I coated the woofer cones with 3 coats of Latex wallpaper border adhesive, applied one thin coat at a time. You can add acrylic craft paint to it at a ratio of 1 part paint to 3 parts latex if your cones are that parchment color and you want ,for instance, black.

Second, I replaced the electrolytic capacitor with the same value polyprop. Increased the wire guage to 18 awg and soldered to drivers.

Third, I used non-hardening oil based modelling clay rolled into a thin layer (1/8th inch or so) and applied these "sheets" to the inside of the cabinets for damping.

Fourth, I used 1/4 inch thick self adhesive weather stripping foam to cover the entire area around the tweeter dome. I imagine that layers of felt would work as well, but I haven't tried it.

With the grills off and the foam in place, there was a great improvement, a little less with the grill installed. The midrange was improved a great deal, voices sounded more natural and smoother, not bright and "edgy" as the unmodified 7's sound. I A/B'd them with my second pair of stock 7's and just switched back and forth on the speaker selector knob on my receiver while playing music that I was familiar with.

I noticed that you couldn't find the Apex Jr. amps. They are available from Apex at: www.Apexjr.com

Anyhow, I hope this will get you started, it's an interesting project.

Best Regards,
TerryO

[Stocktone]

This is great... I'm getting all sorts of ideas here! Thanks for the info.

I went to the Apex website, and the amp looks perfect, except for one thing: it has left and right input jacks. My amp only has one RCA output jack for the sub. Does anyone know how this works? Does it sum the bass and push it down a mono pipe, and what sort of sub amp should I use with this? I was thinking I might just kludge a single to double-end cable, but I don't know whether this might screw things up. The reason I don't want to use the crossover on the plate amp is because I already have one box with a load of wires hanging off of it, I don't want another one.

Also I discovered while playing around with my amp that the internal sub crossover only goes up to 120Hz. I just hope that the sats go low enough to avoid a big dip in the freq response around that point. Will some of the mods help to alleviate that?

All told the tips have been very handy. I've already removed the grilles (I like the look better as well), and I'll go and pick up some spare parts soon. Thank goodness there's a Radio Shack nearby; I should be able to procure the wire and caps easily. Hey, they even have an art supply section at the college bookstore... modelling clay!

[Cal Weldon]

Your amp will be fine with only one output.

The high level ouput is an 8 ohm 125Hz 6 dB high pass. It will be fine to use it or to run the speakers straight from the amp. It does seem like a lot of amp for matching the minimus 7's though.

Read the literature again on the amp. It tells you about mono operation and when to use high level or low level.

Most of all enjoy.

Cal