M&K V-1250THX 125W Subwoofer Wanted!

[riverwolf]

Can you tell me how these second order and fourth order crossovers differ from one another as I know next to nothing about crossovers? My THX amp didn't even have a bypass, so I guess the receiver and THX amps crossovers were both active.

The THX mode shown in your picture is a crossover bypass. In THX mode, the amp bypasses its internal lowpass and depends upon the processor to provide the lowpass. Most likely, it also engages a high pass filter to increase output at the expense of a little bit of extension. If you're using your processor for bass management, as you should be, then the order of the low pass filter in the sub amp doesn't really matter, assuming your processor implements the de facto standard 4th order lowpass at 80Hz.

The OAudio 300 TLS recommended is also available as the BASH300 from Parts-Express. PE also has the BASH500...should be the same amp platform as the OAudio 500, minus the custom rumble filters and PEQ. Actually, the BASH500, with its relatively high (for a sub) default rumble filter might be a good match for an older THX sub that was focused on output >30Hz. ApexJr, as I think was mentioned in one of your AVS threads last year, also has old stock M&K USA amps from the VX-1250. Like your SB-1250 amp, it has a 2nd order lowpass, but that shouldn't matter since you're using your processor for BM, right? ;-)

-Brent

 

[TLS Guy]

The THX mode shown in your picture is a crossover bypass. In THX mode, the amp bypasses its internal lowpass and depends upon the processor to provide the lowpass. Most likely, it also engages a high pass filter to increase output at the expense of a little bit of extension. If you're using your processor for bass management, as you should be, then the order of the low pass filter in the sub amp doesn't really matter, assuming your processor implements the de facto standard 4th order lowpass at 80Hz.

The OAudio 300 TLS recommended is also available as the BASH300 from Parts-Express. PE also has the BASH500...should be the same amp platform as the OAudio 500, minus the custom rumble filters and PEQ. Actually, the BASH500, with its relatively high (for a sub) default rumble filter might be a good match for an older THX sub that was focused on output >30Hz. ApexJr, as I think was mentioned in one of your AVS threads last year, also has old stock M&K USA amps from the VX-1250. Like your SB-1250 amp, it has a 2nd order lowpass, but that shouldn't matter since you're using your processor for BM, right? ;-)

-Brent

For some reason he uses the filters cascaded.

 

[Techlord]

For some reason he uses the filters cascaded.

What are you talking about, cascaded? Back when I bought my Denon THX Ultra receiver and speaker system there was no such thing as adjustable Bass Management crossover settings in a THX Ultra Certified product. The M&K THX speaker system was designed to run on Variable and 80Hz/24 db octave, the same signal sent by the receiver. Setup this way I experience the best sub/sat integration that made the M&K 750THX speaker system so popular, the bass was so fast and tight it blended-in with the super fast transient response of the 5.25" woofers.

-Techlord

 

[TLS Guy]

What are you talking about, cascaded? Back when I bought my Denon THX Ultra receiver and speaker system there was no such thing as adjustable Bass Management crossover settings in a THX Ultra Certified product. The M&K THX speaker system was designed to run on Variable and 80Hz/24 db octave, the same signal sent by the receiver. Setup this way I experience the best sub/sat integration that made the M&K 750THX speaker system so popular, the bass was so fast and tight it blended-in with the super fast transient response of the 5.25" woofers.

-Techlord

If you use the low pass filter in the receiver and sub, then that constitutes two cascaded filters. Generally not a good idea and certainly not THX spec.

You should just use the receiver filter 80 Hz fourth order low pass, that is the THX spec. The sub filter should be bypassed.

 

[Techlord]

In THX mode, the amp bypasses its internal lowpass and depends upon the processor to provide the lowpass. Most likely, it also engages a high pass filter to increase output at the expense of a little bit of extension.

-Brent

riverwolf what you have said makes perfect sense, my V-1250THX never really went deep and that didn't bother me one bit! The V-1250THX blended-in with the rest of the speakers so well it disappeared into the main five sats being truly non-directional! I miss that increase output even at the expense of bass extension!

Techlord

 

[Techlord]

If you use the low pass filter in the receiver and sub, then that constitutes two cascaded filters. Generally not a good idea and certainly not THX spec.

You should just use the receiver filter 80 Hz fourth order low pass, that is the THX spec. The sub filter should be bypassed.

Using both low pass filters in the receiver and sub wasn't even possible since both receiver and speaker system were both THX spec'ed, I think riverwolf already explain it best. Back then I didn't have any option to just use the receivers filter 80 Hz fourth order low pass since both systems were fixed meaning no adjustment of any kind regarding the 80Hz crossovers were possible. The THX spec back then didn't want anyone adjusting anything that would take the components out of THX specs.

Techlord

 

[TLS Guy]

Using both low pass filters in the receiver and sub wasn't even possible since both receiver and speaker system were both THX spec'ed, I think riverwolf already explain it best. Back then I didn't have any option to just use the receivers filter 80 Hz fourth order low pass since both systems were fixed meaning no adjustment of any kind regarding the 80Hz crossovers were possible. The THX spec back then didn't want anyone adjusting anything that would take the components out of THX specs.

Techlord

But you must have had that option, as your picture shows a switch, which you have shown set to low pass filter.

If you switch it to THX, then the crossover in the sub is bypassed. It is pure conjecture whether there is a high pass filter or not, but the O audio amps have parametric Eq so you can limit low frequency extension if you want.

The low pass crossover though should be the one in the receiver, not the sub.

 

[riverwolf]

{snip}
If you switch it to THX, then the crossover in the sub is bypassed. It is pure conjecture whether there is a high pass filter or not, but the O audio amps have parametric Eq so you can limit low frequency extension if you want.
{snip}

No conjecture involved. Sadly, I no longer have the periodicals from the '90s where this common design practice was discussed; they're long gone to the recycling center. Fortunately, HomeTheaterMag does still have a graph showing the 350THX's frequency response with THX Mode on/off. Notice how it drops like a rock below 40Hz in the 'on' setting. They also have a graph of the 1250THX, but only with THX mode=on, showing a similar response.

The Oaudio500 has a user adjustable highpass/subsonic/rumble filter (pick your preferred label) with settings at 12/16/20/25Hz; no reason to waste the PEQ in the effort. This highpass filter has a fairly high Q, introducing a decent amount of boost right above cutoff that makes this amp a relatively poor choice for ported alignments.

The OAudio 300 does not have PEQ. Since it appears to be the same stock BASH design as P-E's BASH300, it does have a fixed highpass at 18Hz with a Q of 1 (you can see it in the response graphs in the manual). The frequency and Q can be adjusted by changing the values of 2 resistors; instructions can be found on P-E's web site.

-Brent

 

[riverwolf]

What are you talking about, cascaded? Back when I bought my Denon THX Ultra receiver and speaker system there was no such thing as adjustable Bass Management crossover settings in a THX Ultra Certified product. The M&K THX speaker system was designed to run on Variable and 80Hz/24 db octave, the same signal sent by the receiver. Setup this way I experience the best sub/sat integration that made the M&K 750THX speaker system so popular, the bass was so fast and tight it blended-in with the super fast transient response of the 5.25" woofers.

-Techlord

It really sounds like you're not configured properly. The 5700 has settings for small/large for the mains as well as subwoofer on/off. You should be running "small", which activates the bass management system to redirect bass below 80Hz to the subwoofer. THX's filter was chosen to complement the natural 2nd order rolloff of sealed mains, combining for acoustical 4th/4th slopes in room. Checking the 5700 and 1250 manuals, I think this is pretty well explained. BTW: Denon *chose* to only implement one xover frequency, this was not a THX requirement. THX only required the presence of a 4th/2nd low/hi filter at 80Hz, the mfg could/should have provided adjustable frequencies, especially in a flagship product.

Similarly, your subwoofer amps, THX or not, should be set to bypass the onboard lowpass filter and let the 5700 handle it. THX Mode=bypass on the 1250THX amp. With cascaded filters, you're creating a frequency hole between the subwoofer and the mains by rolling off the subs at 48dB/octave instead of the 24dB/oct needed to complement the highpass to the mains.

In all honesty, your money would be better spent upgrading your subs than trying to chase down another 1250THX amp. For starters, the 1250THX was only Select, not Ultra. It's using driver technology from the '90s that's probably below average by today's standards in both distortion and excursion. You could reuse the 1250 cabinets and just replace the drivers and amps for a semi-DIY project. My short list of drivers based on guestimating the 1250 cabinet at 2.5 ft^3 internal would be the Dayton 315HF-4 ($140), Creative Sound's Trio12 ($150), and DIYCable's Shiva-X2 ($195). You could try using these drivers with your existing amp, but ideally you'd be better off going with one of the BASH amps TLS and I have mentioned. There's a decent chance the M&K amps contain some additional response shaping EQ (fairly common practice) that's not needed with these DIY drivers ...ApexJr says their surplus VX-1250 amp has 6dB of boost.

The 315HF with 300 watts will have 4dB more output at 20Hz than a 350THX v.2 based on AVTalk's measurements. The 350 is essentially a dual driver version of your 1250 so the gap would be that much bigger. The Trio12 and Shiva have even more excursion than the 315HF...feed them with a 500 watt amp and the performance gap grows even more. They're advantage is not just with output either, all 3 use motors designed from the ground up with low distortion/inductance as a focus.

-Brent

 

[TLS Guy]

No conjecture involved. Sadly, I no longer have the periodicals from the '90s where this common design practice was discussed; they're long gone to the recycling center. Fortunately, HomeTheaterMag does still have a graph showing the 350THX's frequency response with THX Mode on/off. Notice how it drops like a rock below 40Hz in the 'on' setting. They also have a graph of the 1250THX, but only with THX mode=on, showing a similar response.

The Oaudio500 has a user adjustable highpass/subsonic/rumble filter (pick your preferred label) with settings at 12/16/20/25Hz; no reason to waste the PEQ in the effort. This highpass filter has a fairly high Q, introducing a decent amount of boost right above cutoff that makes this amp a relatively poor choice for ported alignments.

The OAudio 300 does not have PEQ. Since it appears to be the same stock BASH design as P-E's BASH300, it does have a fixed highpass at 18Hz with a Q of 1 (you can see it in the response graphs in the manual). The frequency and Q can be adjusted by changing the values of 2 resistors; instructions can be found on P-E's web site.

-Brent

Thanks for the info on those speakers. All of the response curves are perfectly dreadful and not what you would want in a decent sub. In fact from those curves they don't even fit the definition of sub, but bass module.

They are one note subs if ever I saw them. I suppose the module has a reasonably tight because of the Q of the peaked response.

That is not the performance I would be looking for in any type of bass system.

The rest of the system has a fair response. Roll off of the main speakers is fourth order at 90 Hz. What that speaker system really needs is a sub rolling off fourth order low pass at 90 Hz, and with smooth extended response to the 20 to 30 Hz range. Then the OP would have a much better speaker system.

I would not be putting any money into those subs. He can do a lot better.

 

[Techlord]

Forgive me, I just looked at my signature regarding my home theater components and I realised that I didn't change my specs after I upgraded. I no longer have the M&K 750THX speaker system, I upgraded to MKSound's 950THX Select2 speaker system for which the MK 350THX is a pefect match, I just don't care to spend that much money for a subwoofer that with drive my neighborhood crazy living in a condo! I will say that when I did own the 750THX Select speaker system including the V-1250THX Select subwoofer I detected no such frequency hole as everything sounded perfect in transitions between sub and sats, but that system no longer applies to me.

I did manage to take quite a few free M&K sub enclosures when Deep Surplus gave them away for nothing, I've got several dual and single VX-1250, MX-2500/5320 enclosures!

-Systemlord

 

[TLS Guy]

Forgive me, I just looked at my signature regarding my home theater components and I realised that I didn't change my specs after I upgraded. I no longer have the M&K 750THX speaker system, I upgraded to MKSound's 950THX Select2 speaker system for which the MK 350THX is a pefect match, I just don't care to spend that much money for a subwoofer that with drive my neighborhood crazy living in a condo! I will say that when I did own the 750THX Select speaker system including the V-1250THX Select subwoofer I detected no such frequency hole as everything sounded perfect in transitions between sub and sats, but that system no longer applies to me.

I did manage to take quite a few free M&K sub enclosures when Deep Surplus gave them away for nothing, I've got several dual and single VX-1250, MX-2500/5320 enclosures!

-Systemlord

As far as I can tell the MX250 was designed to mate with the speaker system you now say you own.

If you don't want to buy a new sub, I would just buy a plate amp or pro amp and be done with it. The chances of finding a good used MK amp are remote.

By the way enclosures without their speakers are useless as a rule, hence the price you paid. It is almost always impossible to reverse engineer a speaker.

 

[Techlord]

As far as I can tell the MX250 was designed to mate with the speaker system you now say you own.

If you don't want to buy a new sub, I would just buy a plate amp or pro amp and be done with it. The chances of finding a good used MK amp are remote.

By the way enclosures without their speakers are useless as a rule, hence the price you paid. It is almost always impossible to reverse engineer a speaker.

I didn't pay any price as the enclosures were "free", MKSound sells the same equivalent 12" woofers that M&K did and they sound indistinguishable from one another. MKSound's SB-1250 amp is an exact copy of the VX-1250 amp, just the name plate change, I own both SB-1250 and VX-1250 amps. MKSound didn't change things much, they went with what worked. I have an SB-1250 subwoofer and the dimensions are EXACTLY the same as my V-1250 sub enclosure, thats right same enclosure, same spec'ed woofers with same amps! Thats beside the point though as I intend to run a different amp altogether, the only difference between the MX250 and the MX350 is one is THX Certified thats it. If I remember correctly the 950 system was reviewed with the MX350 and the blending was quite spectacular according to the review. There is no reverse engineering when you have the same woofers/amplifiers to choose from with the exception of the V-1250THX amps.

-Techlord

 

[TLS Guy]

I didn't pay any price as the enclosures were "free", MKSound sells the same equivalent 12" woofers that M&K did and they sound indistinguishable from one another. MKSound's SB-1250 amp is an exact copy of the VX-1250 amp, just the name plate change, I own both SB-1250 and VX-1250 amps. MKSound didn't change things much, they went with what worked. I have an SB-1250 subwoofer and the dimensions are EXACTLY the same as my V-1250 sub enclosure, thats right same enclosure, same spec'ed woofers with same amps! Thats beside the point though as I intend to run a different amp altogether, the only difference between the MX250 and the MX350 is one is THX Certified thats it. If I remember correctly the 950 system was reviewed with the MX350 and the blending was quite spectacular according to the review. There is no reverse engineering when you have the same woofers/amplifiers to choose from with the exception of the V-1250THX amps.

-Techlord

I know you get them free. The point I was making is that the enclosures are worthless unless you have the correct drivers to put in them.

 

[riverwolf]

{snip}
By the way enclosures without their speakers are useless as a rule, hence the price you paid. It is almost always impossible to reverse engineer a speaker.

I have do disagree since we're talking subwoofers. Matching a driver to a subwoofer cabinet that will use an electronic xover is fairly easy, especially for sealed alignments...all you need to know is the net volume and tuning frequency if ported...the tuning frequency can be calculated from the net volume and port diameter/length. All 3 of the suggestions I offered would work quite well in the 1250's cabinet using a "flat" amp...Qs would be in the mid .6 range with better distortion, output, and frequency response than the original M&K drivers.

-Brent

 

[riverwolf]

Forgive me, I just looked at my signature regarding my home theater components and I realised that I didn't change my specs after I upgraded. I no longer have the M&K 750THX speaker system, I upgraded to MKSound's 950THX Select2 speaker system for which the MK 350THX is a pefect match, I just don't care to spend that much money for a subwoofer that with drive my neighborhood crazy living in a condo! I will say that when I did own the 750THX Select speaker system including the V-1250THX Select subwoofer I detected no such frequency hole as everything sounded perfect in transitions between sub and sats, but that system no longer applies to me.

I did manage to take quite a few free M&K sub enclosures when Deep Surplus gave them away for nothing, I've got several dual and single VX-1250, MX-2500/5320 enclosures!

-Systemlord

What doesn't apply? You have THX speakers, which are intended to be used with a 2nd order highpass at 80Hz. As a system, they're expected to be matched with a subwoofer using an 80Hz 4th order lowpass. THX speakers are designed to have a 2nd order acoustic rolloff at 80Hz, effectively a natural 2nd order highpass. This combines with the 2nd order electronic highpass in the processor to produce a 4th order highpass to the satellites to complement the 4th order lowpass to the sub. Doesn't matter what model number you're currently using.

How would you know if you're missing something? Since it sounds like you've always run it this way, you have no point of comparison. The most effected area will probably be the 60-120Hz range. The content will still be produced, but will be recessed relative to what it should be with a proper 4th order slope instead of 8th order. The satellites rolloff is supposed to be reinfoced by what information the sub plays above the 80hz point since xovers aren't brickwalls. By reducing the sub's output twice as fast as intended, you reduce the output in this overlap region...it'll still be there, but not at the relative level it was recorded at.

-Brent

 

[larmat]

Re: MK V-1250 thx sub-woofer

Just curious if you are still looking for a MK V-1250-THX sub-woofer? I have one that has been barely used and in new condition, just to large for my entertainment center. Made in 1999 and bought from MK in Culver City.

 

[larmat]

Just curious if you are still looking for a MK V-1250-THX sub-woofer? I have one that has been barely used and in new condition, just to large for my entertainment center. Made in 1999 and bought from MK in Culver City.

 

[Techlord]

Just curious if you are still looking for a MK V-1250-THX sub-woofer? I have one that has been barely used and in new condition, just to large for my entertainment center. Made in 1999 and bought from MK in Culver City.

As a matter of fact I am still on the lookout for a M&K V-1250THX subwoofer, I live in the US and some pictures would be appreciated. I would prefer to buy it on eBay if your still interested in selling it. I'm looking to buy March - April time frame.

--Techlord

 

[mikkelc15]

Here You see one for sale in Denmark! http://www.dba.dk/subwoofer-miller-kreisel/id-1029985086/