Help me commit sacrilege -- modify a Zaph design (ZMV5)

[echrisconnor]

No, I really don't want to be a zealot, but I've had this idea kicking around and wanted some help. I'm planning on building a pair of Zaph's ZMV5s but have been thinking about how to reinforce the low end on them. Yes, I could go with a sub, or a pair of subs, but I want to run this with my old-school line level preamp/power amp with no sub amps, xo, etc. So what I'm thinking about doing is to create a pair of passive bass modules to support the ZMV5s.

I'd like to do this with a RS270 on each side. I'd not modify the original Zaph design in any way, but would want to add a high-pass component to the bass module which removed everything below 150hz from getting to the ZMV5s. Then have a low pass for the bass modules to add the low end. The woofers would also need to be padded, since the effeciency of the zmv5 is lower than the woofers.

Here's a crude schematic of what I'm thinking about doing. I'm a very novice designer, but have built several of the commonly build designs out there.

Thoughs?
Chris

[tubbsbright]

I say go for it, but I would call it a Zapp or a Zaff.

http://blog.wired.com/gadgets/2007/0...-spot-a-f.html

[depthsounder]

My first thought is do you have the drivers in hand? I ask because the MCM woofer is sold out, and the lead time is claimed to be 90+ days.

I can't do it this week, but if you want me to measure the response of the ZMV5 in the standard size enclosure with those passive components in the circuit I will.

-David

[echrisconnor]

Ouch! 90+ day backorder. No I don't have the drivers yet. I figured it would be a good project to get rolling after the holidays, but I didn't figure it would be spring before I could get rolling. Well I'm still eager to get it going and I can still do most all the cabinet and XO work without drivers in-hand.

David If you'd be willing to measure things and let me know what you think of these components that'd be great. No hurry.

Chris

[depthsounder]

Yeah it is a bummer about the lead time, but chin up, the lead time may be inaccurate. You should call a MCM representative to see what they say. I was hoping to purchase another pair of these woofers with my MCM rewards cash back at the end of the year, so I'm hoping that they will be in stock sooner than later!

I checked and I don't have a 5.0mH inductor on hand, the closest I have is a 6.5mH. I'll dig around more later. This week's going to be really busy.

-David

[Wolf]

No, I really don't want to be a zealot, but I've had this idea kicking around and wanted some help. I'm planning on building a pair of Zaph's ZMV5s but have been thinking about how to reinforce the low end on them. Yes, I could go with a sub, or a pair of subs, but I want to run this with my old-school line level preamp/power amp with no sub amps, xo, etc. So what I'm thinking about doing is to create a pair of passive bass modules to support the ZMV5s.

I'd like to do this with a RS270 on each side. I'd not modify the original Zaph design in any way, but would want to add a high-pass component to the bass module which removed everything below 150hz from getting to the ZMV5s. Then have a low pass for the bass modules to add the low end. The woofers would also need to be padded, since the effeciency of the zmv5 is lower than the woofers.

Here's a crude schematic of what I'm thinking about doing. I'm a very novice designer, but have built several of the commonly build designs out there.

Thoughs?
Chris

I have to point out that your schematic probably has the wrong value-labels on the inductors, as they are normally "mH", not "micro-H".
Later,
Wolf

[Taterworks]

mH = millihenries = 1x10^-3 henries
uH = microhenries = 1x10^-6 henries

mF = millifarads = 1x10^-3 farads
uF = microfarads = 1x10^-6 farads

[Dirk]

Don't pad woofers if there's any way around it. Ucky Ucky. You'll be wasting about 1/4 of your amplifier power doing nothing but generating heat.

You know, given the cost of XO components, you could probably pick up the 70W plate to run the RS-225s for about the same price. Run them in parallel off of a single plate and I bet you'll have plenty of SPL...

[echrisconnor]

Yup, I got my symbols screwy. Thx for the clarification.

Regarding padding the woofer. Would it be better to run a less sensitive driver over padding? The RS225 is a few db less sensitive than the RS270 and seems to go just about as low. I'm not so much after high spl, as I am extending the frequency range lower. The zmv5s are not terribly effecient to begin with so one way or another I see burning some unnecessary power if I go passive.

Finally, I'd rather not go the plate amp route but if I were to, is there an elegant solution to the crossover? I plan not to use a HT receiver and have never had good luck with the XOs in the plate amps.

[jbruner]

Passively crossing a woofer below 200Hz usually causes a peaking (boomy) response unless an expensive resonance control filter is also employed.

There are other pitfalls in trying to convert a two-way to a three-way, but for now suffice to say what others already said- active is the way to go.

[jbruner]

.

Finally, I'd rather not go the plate amp route but if I were to, is there an elegant solution to the crossover? I plan not to use a HT receiver and have never had good luck with the XOs in the plate amps.

I have used satellites full range with plate amped subs with very good results. The key is to have your mids in a small sealed box. A 5-1/4" mid works well, because the rolloff starts at the right place (90-100Hz) and the small box controls the excursion. You still will be limited to about 15-20watts on the mids.

[echrisconnor]

I'm still intent on the passive route, but what's the best way to do this actively if you're not using a HT receiver and you (possibly foolishly) assume the XO in the plate amp is crap. I don't doubt the XO in the amp will let you adjust what fequency the sub comes in at, but how do you best remove the lows from the main speakers? I don't trust the line level filter in the plate amp in my signal path but maybe I'm wrong... Any suggestions?

I'd really just like something I can just run my amp into and have it be reasonalby well balanced.

Chris

[Dirk]

As mentioned, reduce the volume on the monitors until mechanical over-excursion would become a difficult act of torture (ie, more power than you expect to use). Run the monitors full-range and the roll-off on the bottom end will be 12dB/oct. That dovetails nicely with the 2nd order lowpass of your average plate amp.

[echrisconnor]

Dirk,

I'm missing something in your response. I don't understand the part about reducing the volume on the monitors, nor where the roloff for the monitors would be coming from. Sorry, but could you clarify for me?

So, this really can't be done well passively?

[depthsounder]

Dirk is referring to the box volume. By reducing the box volume (and making it a sealed system), you are passively forming a high pass crossover with a 12 dB/oct slope at the box tuning frequency.

Reducing the box volume of a sealed enclosure increases the power handling (at least in terms of driver excursion) of the driver, due to the increased air spring constant.

This would work acceptably with the built in adjustable 2nd order low pass crossover built in to most plate amps.

-David

[echrisconnor]

LOL, I was interpreting volume (db) as the level of sound the emit, rather than internal box volume. Hmm, I need to consider this. I would rather keep the monitors vented and able to be run as full range per the original design if used without my crazy bass modules.

Thanks for clarification.

c

[echrisconnor]

So, I've been thinking about this project over the last week. I'd still like to build the ZMV5s and leave them true to their original design and leave them in a ported box. I'd still like to roll them off on the bottom end with a passive filter though. From there, I guess the best way to integrate the bass modules is with a plate amp which I can adjust the XO frequency to dovetail them together.

Three questions:

1. Given that I want to roll the bottom end off passively, is my original high-pass filter a good design?

2. Does throwing a big cap and inductor in there alter the performance of the original design?

3. Is there a better, and fairly inexpensive, way to roll off the bottom end actively if I'm not using a HT receiver?

[HareBrained]

Just to take this in a slightly different direction, have you considered going with a 2.5-way TMM conversion? The MCM 55-3870 isn't a bass monster but you could definitely firm up the bottom octaves this way. You could start by modeling the existing ZMV5 in PCD, and then change the alignment. It'd be real simple.

Playing around in Unibox revealed that the performance of a paralleled pair of these drivers in a common box is different than a single driver, and a F3=35Hz (30L @ 41Hz) is easily attained.

[echrisconnor]

John,

I think the approach of changing woofers is just a littel beyond my comfort zone. A lot of why I want to go with the ZMV5 in its unaltered form is that I have confidence in Zaph's designs and that he's gotten the details sorted out from flat response to correct phase relationships. If I go monkeying about and swapping woofers even with re-modeling it, I suspect my end result will not be as good as what was originally designed.

I would like to add to the low end though.

chris

[critofur]

I'd be happy to model up a 2.5 if somebody would supply accurate measurement files for the ZMV5. Too bad Zaph won't give his out.

I might even build a pair of 2.5 ZMV5s, but, my measurement setup isn't so great (mic not calibrated).

I've got 4 of the woofers and the tweeters should arrive in the mail tomorrow.

I want to do basically the same thing that you want to do: run ZMV5s with passive bass bins.

I bought a 10 lb spool of 16 AWG magnet wire and have some "Micro Metals" brand ferrous bobbins to wind it on so I'll make my own inductors. If the sub is more efficient than the ZMV5s, then it's ok if my inductor isn't the most expensive lowest resistance 14 AWG type... I am thinking about getting a spool of 15 AWG wire maybe...

EDIT: Too bad the x-over on these is 3Khz, I wonder if it's easily modifiable: http://www.parts-express.com/pe/psho...number=300-774