MCM 55-2421 8” driver VS everything

[Tom Smit]

Yup, I think that is a quite sufficient recovery.

[ACUA]

I have not been on here in a while , but I have been using my Tuba 45 sub horn in my truck almost daily . I found that this 18.5" wide horn fits nicely in the back seat of my 06 dodge with the rear seat folded up. There is about 62-65ish inches between the doors for about 20 inches between the horn mouth and the closed door. I have been running this set up for at least a year now and have been playing it as hard as I could while maintaining that it sounds good. I believe I can hear distortion of some kind at the last few notches on the volume knob. The max volume level reads 40 on the display and I get about a doubling of voltage about every two notches of adjustment. I find that for most music volume 36-38 is peak output with full clarity. At volume 38-40 I detect no loudness gain but a muddiness in the sound occurs. The amplifier is a Rockford Prime 750.1. I adjusted the gain structure to match the rest of the music to my liking, certainly not up past half gain as I recall. The drivers are paralleled for a base 2ohm load and the amp should be capable of 500w at 2ohms according to spec sheet.

I have said this before but there is something special about these horn-loaded subwoofer enclosures when compared to a direct radiator configuration. I noticed this way back when I built and started testing my first tuba45. At the time, I had a basic Behringer single 18" passive pa subwoofer in my possession for comparison as well as a 12" home theater sub in my house. I remember being able to test each and use an SPL meter to set the level equal and I would get very different effects beyond the sound/timbre. With the horn the sound energy seemed focused at my ears and did not interact with the environment that much, where either of the direct radiator designs that I was testing would often make things in my house rattle audibly before I felt like I was hearing the same level of sound as with the horn. I notice something similar with a horn set up in my pickup truck. I had to put a lot of work into sound deadening the cabin of my old truck to fix the tin can echo and rattles. I had multiple layers of deadening mat in the roof and doors and back panel wall to make it sound good. I have done nothing to doctor the cabin of my current truck, and I hardly get any rattling even at war level. The mirrors shake like crazy, but I don't hear rattles like I would expect. This has always fascinated me and been a major factor why I endorse these horn-loaded designs. If were to go the conventional car stereo route to achieve what I have, I would have to spent upwards of $4000-6000 for electrical upgrades, acoustical treatment, amps and subs to be as loud as my truck currently is. As it is now, I can play the system with the engine off for a long time and never hardly drag on the batteries. I only have a few hundred invested for the entire system.

I had never put a meter on the system to measure voltage output of the amp until now, I just sent it as hard as it sounded good and wondered just what these little 8" drivers could handle. For the average car audio bass head enthusiast, I am not ashamed at the output. It digs just about as low as I care to go and for the cost it just can't.

In conclusion; I measure amp voltage output at max volume(40), to be at 22.3vac. When I back the knob down to around 36-38 I get 12-15vac. If I remember correct, the recommended voltage peak on one of these MCM 8" drivers is 22-25vac. I initially wanted to compare a dual 8" setup to a lab12 which can take 50vac and series configuring two MCM 8"s gets the same power handling and roughly same cone displacement for 1/8th the cost. I was hoping that I was going to get to report that I was pushing closer to 35-40vac into the drivers but alas I am feeding them exactly what they should be able to handle. What is that then, 23v into a starting 2ohm load 250watts total peak power? Oh the money I could have saved if I had gotten into these horn-loaded designs years ago!

[himhimself]

Welcome back, ACUA! I've been out of the loop for a hot minute too, but just set up the whole rig in the backyard because that was a birthday request of one of my kids - hey papa, teach me how to set up/tear down and everything you know about sound reinforecment
Damn, the tubas sound soooooo good. We played all afternoon until the cops showed up about 8p. All cool, they said they "had to" show up due to the complaints, but we weren't violating any ordinances. I said we were planning to shut down at 9, and they said feel free to run til 10, it sounds great.
Had a couple neighbors come over with beers and hang out. And for reference, one was mowing about 1/4 mile away, with ear protection on, and could feel/hear the thump. Woohoo!!!
I realllllly want to build a couple more tubas but still trying to figure out if there is any way I could fit them into my little enclosed trailer. We shall see. But a pile of 6? Oh yeah.
Got my son looking for an indoor venue we can play around in like we used to do at the climbing gym. With indoor room gain, the tubas are ominous.
Every now and then I wonder if I should have gone with titans, but given the dj content we end up pushing, I don't think the tubas can be beat.
thanks again, Bill!!!!!!!!!!!!!!

[ACUA]

This might be an annoying question.
I really wanna ask though.

With regard to my tuba 45 18.5” wide dual MCM55-2421 8” loaded horn, I would like to consider upgrading the drivers for the most ridiculous option on the market.

I realize the relationship between wide and narrow cabinets for a given driver size has to do with particle velocity and the efficiency relationship between laminar flow and turbulent flow, or something like that!!! To small a path and there is a restriction, to big and the coupling goes away. My 18.5” wide cab is on the small side meaning to me that two 8” drivers moving at 8mm of excursion/displacement may be about all the horn can handle, and increasing the power and excursion with beefier drivers may not yield much more output. I still want to pose the question.

How much more spl could I get with two of these little monsters?

https://www.audioaceinc.com/product-page/str8-nst

These are SPL subwoofer drivers, the entire focus is to withstand a lot of electrical power and mechanically handle a lot of movement. Fidelity and sonic accuracy is hardly considered!

Also another question, with an Fs of 54hz might I get away with running this configuration with the door removed from the sealed chamber? This is a slightly expensive experiment to preform at nearly $500 for a pair. I really want to know how much peak spl I could squeeze out of this horn when placed in my truck! I am tempted to buy a set of drivers like this to test! My curiosity is spiked!!

[Bill Fitzmaurice]

Output is more or less linear with respect to Xmax. But those 'monsters' have high Qes as well as Fs and the surrounds are silly. If you want maximum output use a twelve. The PRV 12W1600 will beat two eights. As to no door that's a no-no.

[ACUA]

You wanna see silly…. Look up the Sun Down Audio z8:

https://sundownaudio.com/products/z-ser ... woofer-z-8

https://youtube.com/shorts/FwkcB1JbwA4? ... LGeV-B5sef

https://youtube.com/shorts/zobmONvfEg8 ... K8I5k1IHAd

Now that thing is silly!

As for things that are considered a “no-no”, well so was running the pathetic little MCM55-2421 8” drivers in a tuba 45, but here we are!

[ACUA]

I finally hatched one of the MCM 55-2421 8” drivers yesterday. I was able to replicate the event and took a voltage reading and set to peak hold the meter climbed to 22.66vac. Looking at the coil it was thermally within the limits, but mechanically it Marty McFly style yeeted the coil out of the hole and through the cone. The spider ripped at the former as well as the cone. The dust cap I found part way down the horn throat. I have not inspected the other driver yet as it has not failed but I imagine it is pretty fatigued. I would like to find some stronger drivers to use in this enclosure and see what it can do.

[ACUA]

I have tried many things in my Ram pickup truck in order to achieve good bass response. I have manipulated prefabricated enclosures with different driver configurations and I have achieved some good results. I took one enclosure that was supposed to be about 0.9 ft.³ internal volume per side that was ported to a predicted 48hz frequency designed for 10inch drivers, this as you can imagine was peaky above 50 Hz and had no low frequency extension. I made adapter rings and installed 8inch drivers and then installed some foam in the ports to lower the port tuning frequency to an estimated 36Hz. the result was a much smoother flatter response with some low frequency extension. I would report it sounds great that way. I also acquired and tested a sealed enclosure that is supposed to have a total net volume of 1.2 ft.³ this enclosure is designed for 12 inch drivers which sounds terrible and is peakier above 50 Hz and worse than the other enclosure with even less low end extension, I optioned to install a passive radiator in this enclosure, which I predict had a tuning frequency of about 26 Hz. This configuration has good low end extension and seems to sound very good to me. Although I have improved the response of these set ups they just fall short of greatness.

I would like to express with solemn conviction that nothing I have ever done has been able to compare to the sound signature of these horn loaded enclosures. Nothing sounds as good, or has as much control of air molecules. Nothing is as smooth, plays as low, or is as tight as these horn loaded enclosures are. yes they are big. Yes, they are annoying to build, but if efficiency and sound quality is your focus there is likely never going to be an equal.

I have recently gotten back into the car audio scene and even competed in a formal car audio competition recently I have had the ability to share and demo my truck with this horn loaded enclosure in it, now for pure SPL output it is lacking compared to other configurations with similar enclosure form factors, but everyone agrees for sound qualities sake, the set up I have is truly impressive. I just want to share this information for anyone who is skeptical I assure you there is something special about the sound signature that these horns produce without a doubt.

[ACUA]

I picked up a set of very beefy 8” drivers that I am going to test out in this enclosure. They already do not fit through the side cover holes. The am going to have to trim some of the side cover plating to get these guys to fit!

[ACUA]

I had to carefully smash/fold the bubble surround of these drivers to squeeze them through the cover window but they fit with no modification and lucky me they fit snuggly, literally touching each other but the original screw holes lined up. Initial test suggests that the MCM 8”s seem to have a smoother softer timbre/tonality. These drivers are stiff and there is a slight oddity to the sound signature to my ear. I am not sure how loud these drivers will go but I know that they have much more in them than the MCM8”.

If you wanna know these are DS18 ZXI8.4D 8”

https://ds18.com/products/ds18-zxi8-4d- ... wvR0Zu2w5M

THIELE & SMALL PARAMETERS
Equivalent Volume Vas
6.75L / 0.238ft3
Free Air Resonance Fs
45Hz
Mechanical Factor Qms
5.318
Electrical Factor Qes
0.791
Total Factor Qts
0.689
Moving Mass Mms
87.65g
Compliance Cms
0.135mm/N
Bl Factor Bl
8.073
Voice Coil Inductance Le
0.476 mH
Diaphragm Area Sd
188.69cm2
DC Resistance Re
4.0+4.0 ohms
Efficiency Bandwidth Product EBP
58.4
Internet says- xmax : 18.5mm

The whole point of this thread was to capture my experience using the MCM55-2421 8” drivers, back then they were cheap and considered a budget option today the price has nearly doubled making them much less appealing. I used mine for two ish years no issues but in the end the driver is just not strong enough for the abuse I put it through. This may mark the end of this thread for me as I have moved onto a much different style of driver that seems much much more capable at sustaining high spl. I shall report back later, side note I generated 132.6dbspl at roughly 23vac at 36hz in my truck at the competition. I’m curious what it will do now!

[Tom Smit]

I'm grateful for the praise that you gave to the horn. I am looking forward to your report on the new drivers, for my curiosity's sake

[Seth]

I pounded the piss out of my MCM's. I had a pair of them in a Tall Auto Tuba and another pair in a Truck Tuba. I had years on the pair in the TAT, no issues. The pair I had in the TrT, both spiders separated from the coil/cone. Obvious damage from over excursion by playing too low of frequencies at full rated power in testing. I used to say not to sweat the highpass filter for automotive applications. But, the fact is, below the shoulder frequency of the horn, excursion increases sharply. Which is why it's mandatory for pro audio.

I look forward to hearing about your experience with these new drivers in your T45's. Please keep the thread going, who cares if it takes on a new life... it's about the cab now.