Using Unibox and MCM 55-2185 8"DVC Woofer

[bobhowell]

I am trying to design a sub with Unibox for a MCM 55-2185 8" DVC woofer mentioned on Zaph's site. He is happy with his so I thought I could use Unibox to come up with the design own my own. Problem is I don't know how to get an optimum volumn. Ray Alden says that is the first step and gives a little formula for it but I can't solve for the value. I thought Unibox would do it, but how.

Help

Bob

[---k---]

Thomas once did a picture tutorial about how to design with Unibox. But I can't seem to find it in the FAQ section. I'm probably not searching hard enough.

But, real quick, this should get you started: After you get all the driver parameters in

For Sealed:
1) "Damping pull" down menu set to "Heavy Fill"
2) "Leakage pull" down menu set to "Minimal Leaks"
3) "Wanted Qtc" set it to 0.6 and click the "Start" button and then the "Graphs not updated, OBS!" button.
4) Your done! Review the right side to check the box volume (the Help tab has conversions to customary U.S. units).
5) Revise to better suite your needs. If you raise your Wanted Qtc, you'll get a smaller box and more slam, but less extension. Make Qtc=1.0 for bloated bass. Lower your Wanted Qtc, and you'll get more extension with a bigger box. The bass may be a bit drier for some tastes. ThomasW typically recommends a Qtc=0.5, but anything between 0.5 and 0.7 is probably good.

I'll do a quick vented next.

[---k---]

Vented is more difficult, because you can change 3 variables: box size, port diameter, and port length.

1) "Damping" = "Walls Covered"
2) "Leakage" = "No Leaks"
3) "Port Type" = set this to what you're using.
4) "No of ports" = generally 1
5) Inside diameter = 15.24cm for a 6" port, which usually work really well for big 12" and 15" drivers.
6) "Wanted tuning peak" = set this to ~18hz.
7) Click "Start" and then the "Graphs not updated, OBS! " button.
8.) Review the frequency response. And move the Wanted tuning peak up and down until it is reasonably flat. Note, that a tuning between 15hz - 18hz seems to protect the driver well from bottoming, but is not a guarantee. Tunnings around 20hz or higher should probably have a highpass filter (not always economical to buy) to protect the driver from bottoming.
9) Check to make sure your port length will fit inside your box. If it won't, you're going to need to either raise your tunning or figure out how to make it fit.
10) Click the "Vented Box" tab and Check to make sure the port velocity is less than 25-30ms once you get over say 20 hz. If your velocity is higher than this, you could get chuffing. Try a larger port diameter. Also make sure you're going to be building with flared ends, at least a 3/4" roundover.

I think that is a quick overview to get you started. Try that and we can go from there.

[ThomasW]

Thomas once did a picture tutorial about how to design with Unibox. But I can't seem to find it in the FAQ section. I'm probably not searching hard enough.

http://www.htguide.com/forum/showthread.php4?t=23273

[bobhowell]

I see no way to solve for box size. Do I just start plugging in estimates? Also, with 40 L I get impedience of 6 to 30-40, below 100hz, where I will be using it. I will be using the PE 70 watt Plate amp. But with those impedience numbers the actual watts will be, say, in the 20-50 range. Do I have this right?

I just plug in volumne numbers till I get an F3 I like. Is that it?

Now I see this may not be wattage enough.

Thanks

Bob

[ThomasW]

There is no 'optimum volume'. The volume is what you want or it's calculated after you choose "Q", Fb, or whatever else is the priority.

[HareBrained]

I see no way to solve for box size. Do I just start plugging in estimates? Also, with 40 L I get impedience of 6 to 30-40, below 100hz, where I will be using it. I will be using the PE 70 watt Plate amp. But with those impedience numbers the actual watts will be, say, in the 20-50 range. Do I have this right?

I just plug in volumne numbers till I get an F3 I like. Is that it?

Now I see this may not be wattage enough.

Thanks

Bob

A single SA70 per driver would be fine. The driver is capable of handling more (200W max) but you're not going to need more.

With Unibox, you're looking at the predicted response for what's going to suit your environment. In a small room, you'll get some room gain that's going to offset the roll-off of the sub & enclosure response. Sealed subs are preferred in such situations because the gentle roll-off combined with a 6db/oct rise, you can get a net flat response. If you design for a flat response, most likely, you'll still be happy. If the response is bowed or has a hump/bump/spike/etc. you should probably keep twiddling. No that those conditions are bad in all situations, they're just not optimal for all types of listening.

So, finding an acceptable sealed configuration is fairly simple. Just be aware that the volume is an airspace volume and you have to add the woofer, plate amp and wood volumes to determine the final box size. This can be >120% of the airspace volume, which can be significant.

For vented, I like to start with the Fb = F3 of the driver as I'm always limited in the amount of space I can devote to a sub (yes, I'm married). Very low Fb requires very long ports which is also added to the airspace for final box size determinations. Net result is that final vented enclosure can be >175% of the airspace volume. So, I set my volume to something I think I can put in my room and work backwards thru the Fb. The port diameter is typically fixed by the available pipes and the determined from the woofer size. Bigger drivers require bigger port diameters, which in turn require longer port lengths (compared to a fixed Fb) and thus more space. But in the end, it's still the predicted response that's going to tell me if the driver is going to work for me. So finally, I'll alter the tuning to see how the driver responses. I've found that some drivers like large boxes while other can work in smaller ones. I've not found a reason to tune below 25Hz.

Running a quick sim in Unibox, I wouldn't use this driver sealed. I like the looks of 23L@35Hz w/ 7.68cm port dia (3"). It would work well in a small to moderate sized room. This looks like a good little woofer for the money. On paper, I think I like the SD215-88 a little better but without a side-by-side, it'd be difficult to say one's better than the other.

[ThomasW]

Bob,

Regardless of the text posted on the MCM website there's no way that driver for use as a 'subwoofer', it's a woofer.

Why?

Fs 45Hz
Xmax 4.1mm

And HB is correct with regard to his recommendation of the SD215-88 (PE p/n 295-480) being a better choice if the goal is not to spend more than $30.

[bobhowell]

This will be used for music along with a pair of Zaph's ZBM4's. I bought it 3 months back. I got it for $20 to experiment with as part of a larger order. I also got a TB 6-1/2 Neo sub with the 70 w Plate amp to make the small sub on Roman's site, Cerberus.

I will cross over at about 100 to 150hz.

I need another Plate amp and am looking at what size. I am going to test with one.

I will work on it in a few days.

Thanks

Bob

[JonP]

There ya go, got two to compare. Always better to have more than one to decide upon...

I can say from experience that a Cerebus is a good match for a pair of ZBM4's...
I would steer you in the direction of a 2" port vs the 1.5"...

[bobhowell]

I got this woofer because Zaph mentioned a sub he use it in as good for music. Since he has posted more info on it.

I have read Roman's writeups on his various 3 way speakers. I guess I am trying to get the effect of a 3 way by using a small MT and crossing over to a sub at 150. The small MT like ZBM4 blend in the room with a much better WAF.

I built 60L sealed sub with RS 10" HF driver and a PE240 plate amp. I pared it with two ZBM4 speakers alternated with a pair of BAMTM. Crossing over at 150 both setups sounded about the same, great!!

The Sub is designed like an end table and just disapears in the room.

I set up the Home theater in the livingroom with our 50" plazma. The ZBM4's are so small the WAF sores when they are used over the BAMTMs. I really could see little difference between the sound of the two. Now she wants a set in the den for music and radio, so I am working one up. This MCM 8" looks like a good start, but I did put a crease in it with my thumb. Most of it came out but I don't know if it will be the same.

I see a lot of 8" -10"woofers on clearance now but don't know which are good for my purpose.

Peerless 85136 8"-$39
Audax Aerogel AP210z0 8"- $25

I could use two Peerless for 4 ohms, but I also see the RSS210hf-4 8" sub is $80. I am so happy with my 10", I don't see how I could get any better. Seems it takes more amps. Maybe that is the key.

The 6 ohm Audax with a 75w PE Plate amp might be all I need.

I ramble, but I do enjoy working all this out and would appreciate any comments on my plans. I am looking for another woofer to pair with a 75w plate amp. PE has the Audax and the SD215-88 about the same price. How would they compare for me?

Thanks for your input.

Bob

[alias2]

The important thing to realise with the MCM driver is that Zaph tuned the
port low and used a subamplifier with built in bass boost, +5dB (at 30Hz ?).
Designing for an amplifier with bass boost moves the goalposts a lot.

[bobhowell]

The important thing to realise with the MCM driver is that Zaph tuned the
port low and used a subamplifier with built in bass boost, +5dB (at 30Hz ?).
Designing for an amplifier with bass boost moves the goalposts a lot.

I have been playing music from my computer with Windows Media Player. It has an equalizer function that lets me boost centered on 31Hz. I think I am getting a similar effect when I use the BAMTM with no sub.

Any one doing this?

[HareBrained]

Regarding the main speakers, if you're looking for something in between the ZBM4 and the BAMTM, I've designed a MTM using the MCM 55-3853 (4" cast frame woofer from the ZBM4) and the Vifa DQ25SC16 (tweeter from Zaph's ZVM5). Initial write-up will be posted in 2 weeks but for the teaser, the baffle is 6"x13", vented enclosure with front port and decreased BSC for "proximity" placement, and 2100Hz Fc. The lower Fc (compared to the ZBM4) decreases the impact of the increasing distortion in the 3853 above 2000Hz. The xover topography is the same used by Zaph in both the ZBM4 and the ZVM5

The Audax Z woofers are not subwoofers and they're generally accepted as a failed experiment with Aerogel (cool stuff though).

The SD215-88 is a highly respected subwoofer. It's incredibly versatile regarding the enclosure. Look at the Triska in the PE showcase. It can be tuned to just about any frequency you want and can be used sealed if you want. Trade off is that it's inexpensively built with stamped frame and lower power handling. Still highly recommended.

The RSS210HF is really several steps above the others under consideration and would do wonderful for what you're doing. The SA70 would still be a good match as it'll still have good output levels. If you hurry, the driver and amp total $133 and you can use the $20 incentive.

Another, yet to be mentioned alternative is the RS225S-8. This can play quite low, vented or sealed, and has similar output predicted output to the HF in identical sealed enclosures with more efficiency but lower potential maximum output (due to lower max power handling.) Not to mention, they're half the price of the HF.

Note that a pair of HF or SD drivers on the SA70 would mean 45W of total power max because it's a net 8-ohm load. There will be very little noticeable change in output over a single driver unless you use 2 amps, at least two channels of power, or the amp is 2-ohm stable. This is where the RS225 would be better.

You're software EQ is doing the same as the boost function. There are other factors such as the Q of the boost but essentially, it's the same.

[bobhowell]

Regarding the main speakers, if you're looking for something in between the ZBM4 and the BAMTM, I've designed a MTM using the MCM 55-3853 (4" cast frame woofer from the ZBM4) and the Vifa DQ25SC16 (tweeter from Zaph's ZVM5). Initial write-up will be posted in 2 weeks but for the teaser, the baffle is 6"x13", vented enclosure with front port and decreased BSC for "proximity" placement, and 2100Hz Fc. The lower Fc (compared to the ZBM4) decreases the impact of the increasing distortion in the 3853 above 2000Hz. The xover topography is the same used by Zaph in both the ZBM4 and the ZVM5

The Audax Z woofers are not subwoofers and they're generally accepted as a failed experiment with Aerogel (cool stuff though).

The SD215-88 is a highly respected subwoofer. It's incredibly versatile regarding the enclosure. Look at the Triska in the PE showcase. It can be tuned to just about any frequency you want and can be used sealed if you want. Trade off is that it's inexpensively built with stamped frame and lower power handling. Still highly recommended.

The RSS210HF is really several steps above the others under consideration and would do wonderful for what you're doing. The SA70 would still be a good match as it'll still have good output levels. If you hurry, the driver and amp total $133 and you can use the $20 incentive.

Another, yet to be mentioned alternative is the RS225S-8. This can play quite low, vented or sealed, and has similar output predicted output to the HF in identical sealed enclosures with more efficiency but lower potential maximum output (due to lower max power handling.) Not to mention, they're half the price of the HF.

Note that a pair of HF or SD drivers on the SA70 would mean 45W of total power max because it's a net 8-ohm load. There will be very little noticeable change in output over a single driver unless you use 2 amps, at least two channels of power, or the amp is 2-ohm stable. This is where the RS225 would be better.

You're software EQ is doing the same as the boost function. There are other factors such as the Q of the boost but essentially, it's the same.

Glad to hear about the MTM. I am very interested and will watch for details. The size is very good for WAF. I would tend to do a sealed and cross over to this sub at the appropriate level.

I am leaning towards the RSS210 HF. Glad to hear you think the PE 70w Plate amp will drive it. The 240 watt drives the RSS HF10" beyond what we need for HT and certainly music.

I have been looking at the Aerogels for months wondering why they were sitting there.

The 4 ohm version for the RS225 8" is interesting. Not on sale but still $25 less.

Decisions!!

Thanks for the help.

Bob

[HareBrained]

Glad to hear about the MTM. I am very interested and will watch for details. The size is very good for WAF. I would tend to do a sealed and cross over to this sub at the appropriate level.

I am leaning towards the RSS210 HF. Glad to hear you think the PE 70w Plate amp will drive it. The 240 watt drives the RSS HF10" beyond what we need for HT and certainly music.

I have been looking at the Aerogels for months wondering why they were sitting there.

The 4 ohm version for the RS225 8" is interesting. Not on sale but still $25 less.

Decisions!!

Thanks for the help.

Bob

I did look at sealed for the MTM but in a low Q configuration, power handling is a problem, and in a higher Q (smaller enclosure), the roll-off begins around 200 Hz. Even vented, woofer volume is only 7.5L and the port volume is <0.5L.

If you're going with 2 RS225-4's, powering them with a single SA70 will not be very much power (22W per driver). It also doesn't play a low as the -8 version, that is on sale and would receive 35W per.

Another interesting option might be the DC200-8. It's not a sub but output is fairly good all things considered. The DC160s-8 is a very well loved driver, and the DC200 appears to be more of a kin to it then the RS225-4 (Fs=41) is to RS225S-8 (Fs=33).

As an experiment, in Unibox, I compared the DC200, RS225S-8, SD215-88, RSS210HF, eD 9kv.2, and HiVi M8N. All in sealed enclosures of ~25L at 80W (60W for the DC200 because it the rated max). All were within +/-2db max output and crossed the 90db level within +/- 2Hz, and 80db within +/-4Hz. The similarity in predicted output was astonishing. I believe the differences will be the amount of distortion and I think you're essentially going to get more of it, the less you spend. With the possible exception of the RS225, which has constantly been touted as a very low distortion driver. But I also believe that if you're not doing side-by-side comparisons, all will be enjoyable and you won't know what you're missing. Each of these drivers are supposed to have different targets. The HF and 9k are high excursion, high power subs. The SD is a sub but of lesser capacity. The other 3 are traditional woofers with low Fs but different constructions. And all have their predicted ideal enclosure to be "sealed" or have successfully used as such. Overall, I think it would depend on price, available power and room size, more so than the woofers themselves.

[bobhowell]

I did look at sealed for the MTM but in a low Q configuration, power handling is a problem, and in a higher Q (smaller enclosure), the roll-off begins around 200 Hz. Even vented, woofer volume is only 7.5L and the port volume is <0.5L.

If you're going with 2 RS225-4's, powering them with a single SA70 will not be very much power (22W per driver). It also doesn't play a low as the -8 version, that is on sale and would receive 35W per.

Another interesting option might be the DC200-8. It's not a sub but output is fairly good all things considered. The DC160s-8 is a very well loved driver, and the DC200 appears to be more of a kin to it then the RS225-4 (Fs=41) is to RS225S-8 (Fs=33).

As an experiment, in Unibox, I compared the DC200, RS225S-8, SD215-88, RSS210HF, eD 9kv.2, and HiVi M8N. All in sealed enclosures of ~25L at 80W (60W for the DC200 because it the rated max). All were within +/-2db max output and crossed the 90db level within +/- 2Hz, and 80db within +/-4Hz. The similarity in predicted output was astonishing. I believe the differences will be the amount of distortion and I think you're essentially going to get more of it, the less you spend. With the possible exception of the RS225, which has constantly been touted as a very low distortion driver. But I also believe that if you're not doing side-by-side comparisons, all will be enjoyable and you won't know what you're missing. Each of these drivers are supposed to have different targets. The HF and 9k are high excursion, high power subs. The SD is a sub but of lesser capacity. The other 3 are traditional woofers with low Fs but different constructions. And all have their predicted ideal enclosure to be "sealed" or have successfully used as such. Overall, I think it would depend on price, available power and room size, more so than the woofers themselves.

I was actually thinking one RS225 4 ohm, but did not notice it had a higher Fs.

I think the RSS210HF is the one for me. I look forward to your new MTM writeup.

Thanks

Bob

[bobhowell]

Another, yet to be mentioned alternative is the RS225S-8. This can play quite low, vented or sealed, and has similar output predicted output to the HF in identical sealed enclosures with more efficiency but lower potential maximum output (due to lower max power handling.) Not to mention, they're half the price of the HF.

I have been running sims on the RS225-8 and understand it better. It seems to be all I need, even at 8 ohms. Can you explain why Unibox suggest closed. Everyone seems to use it vented and Qts is under .40. I would like tight bass like sealed is noted for, but Roman used vented in Astorius, as have others, with good reports.

I plan to use this in a den/kitchen, 16x24, for music.

Thanks

Bob

[understandin]

Check out the MCM 55-2185 in an MTM setup. Can it be done with a 1,500 hz cross?

[jkrutke]

Bob,

Regardless of the text posted on the MCM website there's no way that driver for use as a 'subwoofer', it's a woofer.

Why?

Fs 45Hz
Xmax 4.1mm

Yeah, at one point I actually had this project posted as a subwoofer. The reason I took it down is basically because you're right. In any reasonable use as a sub, people are generally going to be unhappy with insufficient output. And this comes from me, a guy who really doesn't ask much from a sub, if anything at all.

I got this woofer because Zaph mentioned a sub he use it in as good for music.

And to this day I still use it as a sub - nearfield from 3 feet away at my computer. It would not be enough for any usage intended to fill any room. It is a decent woofer for the price however. It's distortion profile and response curve would even work in a 2-way with a tweeter of sufficient low end power handling.

[HareBrained]

I have been running sims on the RS225-8 and understand it better. It seems to be all I need, even at 8 ohms. Can you explain why Unibox suggest closed. Everyone seems to use it vented and Qts is under .40. I would like tight bass like sealed is noted for, but Roman used vented in Astorius, as have others, with good reports.

I plan to use this in a den/kitchen, 16x24, for music.

Thanks

Bob

There's a simple formula, Fs/Qes, that provides a suggested box alignment BUT (big "but") that doesn't mean it won't work in another alignment. For a result:
<50 --> sealed
>50 & <70 --> sealed or vented
>70 --> vented.
This is what Unibox is reporting. And most people will say that there are as many exceptions to this rule are there are conformers.

Note that a well designed vented enclosure can sound as tight as a sealed box. With the RS225S-8, you simply have compare the simulations to see what the tradeoff is. Vented, you'll get better extension (lower F3) but sealed will give you a lower F10. In such a large space, you're not going to have much room gain (which can lead to a boomy vented sound) so if you don't mind having a high F10, vented should be a very good alignment for your situation (assuming the volume isn't too big for your wife.)

[bobhowell]

There's a simple formula, Fs/Qes, that provides a suggested box alignment BUT (big "but") that doesn't mean it won't work in another alignment. For a result:
<50 --> sealed
>50 & <70 --> sealed or vented
>70 --> vented.
This is what Unibox is reporting. And most people will say that there are as many exceptions to this rule are there are conformers.

Note that a well designed vented enclosure can sound as tight as a sealed box. With the RS225S-8, you simply have compare the simulations to see what the tradeoff is. Vented, you'll get better extension (lower F3) but sealed will give you a lower F10. In such a large space, you're not going to have much room gain (which can lead to a boomy vented sound) so if you don't mind having a high F10, vented should be a very good alignment for your situation (assuming the volume isn't too big for your wife.)

I don't know anything about F10, so, better go read.

She hasn't seen it yet.

Thanks

Bob