Using ZBM4 with PE 70 watt Plate amp crossover

[bobhowell]

I want to use 2 ZBM4's with the Cerberus sub and PE 70w Plate amp and the incorporated crossover. My understanding of crossovers has developed as I progressed with this project and Now I see a hitch.

F3 for the ZBM4 is 44hz and for the sub 35hz. Not much coverage for the sub. I am using sonic T amp to power the speakers, so I have no active crossover. I have fiddled with different sealed volumes in Unibox, but nothing improves the roll off of speakers and improves their power handling. Do I need to add crossover components to get them to drop off at 120HZ or so? Is this feasible? Is the sub not practical for them?

Thanks for looking

Bob

[peter_m]

bob,
as long as you keep the ZBM4 running full range and don;t filter out part fo the base, the benefits of having a sub are minimal. You will need either an active x-over or a passive one to filter out what s only intended for your sub.

If you want to go active, this might help: http://www.htguide.com/forum/showthread.php4?t=28300

Peter

[bobhowell]

bob,
as long as you keep the ZBM4 running full range and don;t filter out part fo the base, the benefits of having a sub are minimal. You will need either an active x-over or a passive one to filter out what s only intended for your sub.

If you want to go active, this might help: http://www.htguide.com/forum/showthread.php4?t=28300

Peter

This would be too expensive. I bought an AV receiver, Onyko 505 refurb from Shoponkyo for $110 with all discounts. HT 7.1 Receiver with, amp,sub-crossover and other. Small is only so good.

Seems I read somewhere you can cut down on box size for some drivers and get them to work better.

[peter_m]

...I bought an AV receiver, Onyko 505 refurb...

...Do I need to add crossover components to get them to drop off at 120HZ or so? Is this feasible?

If your receiver is a TX-SR505, click here for the user manual: http://63.148.251.135/redirect_servi...X-SR505_En.pdf

It has a built in x-over and you need nothing else. Go to page 56 and follow steps all the way to step 9 where you can set the desired 120hz. The Onkyo will do everything for you. You don;t even have to use the low-pass filter in the sub's plate amp.

Peter

[bobhowell]

That was for another Daughter; this one needs small,for bedroom.

Thanks for the help'

Bob

[alias2]

I'm confused. Sonic T amplifier or HT reciever ?
HT is easy, there is a way of doing it with the Sonic T.

For the sonic T reduced the input capacitor to form a high pass filter.
Drive the subwoofer from the amplifier out via a speaker level to line
level converter than includes an inverse function to the high pass filter.
This way you can adjust the nominal subwoofer/satellite c/o point.

[JonP]

I want to use 2 ZBM4's with the Cerberus sub and PE 70w Plate amp and the incorporated crossover. My understanding of crossovers has developed as I progressed with this project and Now I see a hitch.

F3 for the ZBM4 is 44hz and for the sub 35hz. Not much coverage for the sub. I am using sonic T amp to power the speakers, so I have no active crossover. I have fiddled with different sealed volumes in Unibox, but nothing improves the roll off of speakers and improves their power handling. Do I need to add crossover components to get them to drop off at 120HZ or so? Is this feasible? Is the sub not practical for them?

Thanks for looking

Bob

To sum up, you want to avoid running the 4" speakers at 44hz if you can. Zaph was reccomending 100-150hz with a sub. Then, the sub covers a lot of range.

I was going to reccomend a Reckhorn F1 active crossover, $50 for a complete unit, that would have done it with your seperate amp, but you got the AV amp with built in crossover.

With the AV amp, you have the required highpass and lowpass filters. Set them appropriately, turn your plate amp lowpass all the way up, or above the AV amp's setting, and you're good to go...

[bobhowell]

Please forget the AV amp for this solution. It will be across town in another house. I need to understand how to do this with only the T Amp and maybe the PE 70w plate amp.

The plate amp has a 1st order lowpass filter that, from what I understand effects the sub input. It has no effect on the speaker signal passed on. I need to put in some sort of component to have that siginal fall off. The Reckhorn F1 unit seems to be viable.

The cost of this project is mushrooming.

Reading Roman's writeup on the sub I see it was designed for speakers that have an F3 of 115hz and don't go into distortion at operating levels.

The ZBM4 just does not fit well for this application, so I must search for another.

Lou's Amethyst is 4 ohm and might just work with no sub.

Also Madisound has a 4", 4 ohm Aura Sound full range on sale for $21. Anyone have experience with it?

I think 4 ohms may be necessary for the T Amp.

Thanks

Bob

[bobhowell]

I'm confused. Sonic T amplifier or HT reciever ?
HT is easy, there is a way of doing it with the Sonic T.

For the sonic T reduced the input capacitor to form a high pass filter.
Drive the subwoofer from the amplifier out via a speaker level to line
level converter than includes an inverse function to the high pass filter.
This way you can adjust the nominal subwoofer/satellite c/o point.

This sounds good. Will it work with the PE70W plate amp.

Just where do I reduce the input cap. In the speaker crossover? To what Value? Not sure I have a picture of what to do.

[BobEllis]

The input cap to reduce is at the input of your T amp. However this will give you a first order filter. The low pass on the plate amp is 2nd order. You should try to match the acoustic slopes, which in this application means matching the electrical slopes, meaning you want a bit more of a crossover for best results.

That Reckhorn F1 active crossover is tough to beat for the price. You could build something on prototype board with a single op amp and 3 legged regulators, but to power it and put it in an enclosure you'll be around $50 anyway.

[kevinp.]

cant you just reduce the enclosure volume to the point where the driver starts to roll off where you want it to? What is the woofer in that system again?

I know some drivers will give you a high -Q hump here, but couldn't hurt to try

[BobEllis]

Until you get the enclosure so small that the response peaks several dB, the F3 does not change significantly. If you go that route, you'll still need eq unless you want disco peaky response and the enclosure depth would likely get so small you'd likely have reflections off the back wall coming out through the cone, so why not spring a for the Reckhorn XO?

Sorry for sounding like a Reckhorn salesman. I have no ties to the company or its products.

[Dennis H]

You could always use an F-mod before the T-amp. I think PE carries them but their search engine sucks today.

http://www.hlabs.com/products/crossover/

[kevinp.]

Until you get the enclosure so small that the response peaks several dB, the F3 does not change significantly. If you go that route, you'll still need eq unless you want disco peaky response and the enclosure depth would likely get so small you'd likely have reflections off the back wall coming out through the cone, so why not spring a for the Reckhorn XO?

Sorry for sounding like a Reckhorn salesman. I have no ties to the company or its products.

Disco peaky response?? Now I have to try it!!

Ok, maybe it wasn't such a good idea....

[HareBrained]

Personally, I don't think there's any issue integrating the ZBM4 with a the subwoofer without any additional components. The 15W amp is not going to overdrive the speakers and the bass output will be minimal. I say, build the sub, hook it up and listen as is. You're not in Carnegie Hall. The environment is going to contribute far more "issues" than having a little overlap between 50 and 100 Hz. If needed, just plug the port on the ZBM4 and go from there.

[alias2]

The input cap to reduce is at the input of your T amp.
However this will give you a first order filter. The low pass on the plate
amp is 2nd order. You should try to match the acoustic slopes, which
in this application means matching the electrical slopes, meaning you
want a bit more of a crossover for best results.

Personally, I don't think there's any issue integrating the ZBM4 with a the
subwoofer without any additional components. The 15W amp is not going
to overdrive the speakers and the bass output will be minimal. I say, build
the sub, hook it up and listen as is. You're not in Carnegie Hall. The
environment is going to contribute far more "issues" than having a little
overlap between 50 and 100 Hz. If needed, just plug the port on the
ZBM4 and go from there.

The purpose of decreasing the amplifier input capacitor is two-fold,
mainly bass distortion reduction but also to allow a little more voltage
swing at maximum levels (i.e. reduce the bass level effect on clipping).

The ZBM4's could be built smaller and sealed. In this case with the
amplifier you would end up with an overdamped 3rd order roll-off,
vented you end up with an overdamped 5th order roll-off.

The subwoofer is driven by its line inputs via an inverse network.
This network is driven by the amplifiers speaker outputs.
The network does the opposite of the amplifier input, a 1st order
lowpass network. In the low bass it will return bass response to
flat. Higher up you can leave it as a filter or return the response
to flat. So in combination with the plate amplifier the roll off
can be second or third order depending on the inverse filter.

[Just realised that whilst this normally works the sonic-T is a
BTL amplifier ? Which would mean the network connection is
a little more complicated to sort out the line input ground ?]

[Quwiksilver]

Please forget the AV amp for this solution. It will be across town in another house. I need to understand how to do this with only the T Amp and maybe the PE 70w plate amp.

The plate amp has a 1st order lowpass filter that,...Bob

Actually, I don't think that's correct. I'll be doing something similar to you and was also eyeing the PE 70W Plate Amp (300-784). I talked to a tech at PE today, and he said that the plate amp has a fixed 1st order (6db/octave) high pass filter on the speaker high level outputs and the variable 2nd order (12db/octave) low pass filter for your bass driver. I believe the fixed high pass filter on the plate amp is a 100uF capacitor.

Have a look at the section on subwoofer integration on Zaph's writeup for the B3S single driver system. He advises not to use your plate amp in that particular application because of that particular speaker/box impedance behavior. The impedance behavior in the ZBM4 is quite a bit different (peak is at 90 Hz). I think the plate amp's high pass filter is supposed to combine with the speaker woofer's natural roll off to make something resembling a match the 2nd order filter on the sub driver. Obviously, this doesn't always work as planned, as in the case of the B3S. It might work better with the ZBM4. I'm not sure. Zaph would be the best person to tell you but I think he's on speaker building vacation.

Perhaps someone else could comment?

[bobhowell]

Update on Unibox and Sims

I discovered something was wrong with Unibox and it has been giving me false data. I was running sims on other drivers and saw something was wrong, so I deleted it and downloaded another copy.

Now I get different output on everything.

On this issue I now find that if I reduce volume to 3L, I get a F3 of 121hz with sealed box. Distortion starts at 96 hz, but its down 5 db at that point. How will this sound, and will it hurt driver?

[HareBrained]

I discovered something was wrong with Unibox and it has been giving me false data. I was running sims on other drivers and saw something was wrong, so I deleted it and downloaded another copy.

Now I get different output on everything.

On this issue I now find that if I reduce volume to 3L, I get a F3 of 121hz with sealed box. Distortion starts at 96 hz, but its down 5 db at that point. How will this sound, and will it hurt driver?

Same thing happened to me with Unibox.

By "distortion", you mean "over excursion" which may, or may not, result in greater distortion, it depends on the suspension construction but I doubt it'll hurt the driver. Sound shouldn't be that bad. The modeled excursion does not go exponential. It reaches a peak (barely above the xmax) and flattens out. Of course, you could just turn it down. :roll: :B

Also, Unibox has a xmax factor ("Linear Cone Overdrive") that defaults to 1. Some people will tell you that most drivers are linear to 1.15, or 15% over xmax. I've seen this stat for years, from many different sources. I think it may vary by manufacturer but it's something to consider.

[bobhowell]

Hairbrained,

Thanks for the help. Now I am seeing results that make sense and give many good options, including your MTM in the works.

Bob

[alias2]

It might work better with the ZBM4. I'm not sure.
Perhaps someone else could comment?

Download the demo version of Basta! from www.tolvan.com
Put in the MCM parameters and a say a 4L sealed box.
Choose the passive filter and 100uF 1st order highpass.
Observe disabling and enabling the filter .........

[JonP]

The purpose of decreasing the amplifier input capacitor is two-fold,
mainly bass distortion reduction but also to allow a little more voltage
swing at maximum levels (i.e. reduce the bass level effect on clipping).

The ZBM4's could be built smaller and sealed. In this case with the
amplifier you would end up with an overdamped 3rd order roll-off,
vented you end up with an overdamped 5th order roll-off.

The subwoofer is driven by its line inputs via an inverse network.
This network is driven by the amplifiers speaker outputs.
The network does the opposite of the amplifier input, a 1st order
lowpass network. In the low bass it will return bass response to
flat. Higher up you can leave it as a filter or return the response
to flat. So in combination with the plate amplifier the roll off
can be second or third order depending on the inverse filter.

[Just realised that whilst this normally works the sonic-T is a
BTL amplifier ? Which would mean the network connection is
a little more complicated to sort out the line input ground ?]

Yep, the Sonic-T's have around +6V on the speaker output leads, you can't get that tied to ground of the input or you short the amp. The shields of the inputs may get back to the speaker outputs thru the plate amp, or other places. Gotta watch for that, or you cook your amp.... May make it impossible.

Another thing, if you do some kind of line level highpass (the T-amp mod or one of the F-mods) you are forced to fixed amp and sub settings, and have to control system volume by changing the line level in. If you turn down the amp, the sub stays playing at a fixed level, change the amp volume and the sub isn't balanced anymore, etc. So you need a preamp volume control, or computer source, just plugging into a CD player or other fixed out won't work gracefully. Unless you play at only one volume all the time...

Using the single cap 6db/oct passive highpass in the plate amp (actually, I don't think the 70W one has that?? No caps in mine!) is only a marginal rolloff, and you may get that peaking effect that Zaph mentions. To roll them off steeper gives you more of the bass unloading effect, and you would be more able to play louder, cleaner.

Otherwise, yep, I agree with much of what's said. I can say a Cerebus matches pretty well with a pair of standard ZB4M's. If you plug the port (standard size cab's) it rolls them off about 70-80hz, which helps, though smaller sealed enclosures might be better if well chosen.

That did pretty well for me, and adding an active highpass in the F1 helped a bit more as well. Steeper lowpass than the PE 70W plate, too.

I guess that puts me in the Reckhorn sales camp as well... :B No affiliation!!

Uh, talk to Bob about active filter boards, or check Marchand for their low end active filter board, if you're up for a bit of kit building. See, I'm not a single brand sales guy!! :W

[alias2]

Yep, the Sonic-T's have around +6V on the speaker output leads, you can't get that tied to ground of the input or you short the amp. The shields of the inputs may get back to the speaker outputs thru the plate amp, or other places. Gotta watch for that, or you cook your amp.... May make it impossible.

The speaker out to line level in should (if its BTL) be able to be derived from
either of the speaker outputs referenced to the actual common ground, i.e.
you use only one of the the two "balanced"/ "opposite phase" outputs.