Hello bob540,
Each of your ML 60XT speakers have rated bass output from their dual 8" woofers of 35 Hz +/- 3 dBs. Humans are capable of hearing bass frequencies down to 20 Hz. Virtually all commercially available recorded music (CDs, LPs and digital music files) have all of the left and right channel bass picked up by the recording mics, that are below about 100 Hz, summed to mono during the recording’s mixing process. This is done because humans generally cannot localize (determine exactly where bass sound tones are coming from) on bass frequencies below about 80 Hz.
In practical terms, the above means there’s no such thing as true stereo deep bass because we can’t determine where bass frequency sounds below 80 Hz are coming from and, even if we could, virtually all of the recorded music we play on our systems is summed to mono below 100 Hz anyways. So, it makes no difference whether we setup our playback systems for true stereo deep bass or mono deep bass reproduction since we’re going to perceive deep bass as mono either way. It’s also important to know that we get progressively better at determining exactly where sounds are coming from as the sound frequency gets higher, from about 80 Hz all the way to our audible high frequency sound limit of about 20,000 Hz.
But it gets more complicated than this and all hope is not lost due to our remarkable brains and the fact that that all deep bass fundamental tones have overtones or harmonics that are at frequencies that reach frequencies well above 100 Hz, are recorded in true stereo, are played back through our main L+R main speakers and that we are able to localize (determine exactly where these bass overtones/harmonics are coming from).
Fortunately, our brains are able to associate these bass overtones/harmonics that are at frequencies that reach well above 100 Hz, we are able to localize, that are played through the main stereo speakers, with the deep bass fundamental frequency tones that are below 80 Hz, that we are not able to localize, that are played through the subs and, therefore due to our brains sound processing power, we are effectively able to determine specifically where deep bass tones below 80 Hz are coming from.
This cerebral association process is very relevant to audio because it allows us to perceive exactly where in the stereo sound stage illusion that deep fundamental bass frequency tones are coming from. For example, the upright bass can be properly perceived as being located at the front left of the sound stage and the deep bass drums can be properly perceived as being located at the center rear of the sound stage. I’m sorry for all the detail but I think this information is essential in understanding how to attain improvements in bass performance quality in our domestic sized rooms and systems.
As I mentioned at the beginning of this post, your ML 60XT main speakers are rated to have bass extension down to 35 Hz, which means you’re currently not hearing or feeling any of the deep bass content on any of the music you play from 20 Hz to about 35 Hz.
This is basically the entire bottom 2 octaves of the musical spectrum, that forms the solid foundation of most musical genres and that I’m not even sure you realize has been completely absent from every track you have ever played or will play on your current system. But I believe your interest in adding a pair of subs is likely based on your sense that a large and critical portion of the audible frequency spectrum has been missing in action from your system and musical enjoyment. So we’re in absolute agreement that your system needs a pair of good quality subs like Trump needs a brain and a soul.
My opinion that a pair of HSU uls-15 MK2 subs you linked to are a very good choice. They have high quality deep bass extension down to the audible limit of 20 Hz, have the 3 required controls (volume, crossover frequency and continuously variable phase.) and each has the proper line level rca ’Sub In’ input for connection to your P5’s line level rca ’Sub 1’ and ’Sub 2’ outputs, respectively.
I also think your P5 is an ideal preamp to use when adding a pair of subs to one’s system since it has dual line level rca mono sub outputs with a built-in adjustable low pass cutoff frequency that controls the range of bass frequencies sent to both connected subs. The P5 also has line level rca L+R main speaker outputs with a built-in adjustable high pass cutoff frequency that controls the range of bass frequencies sent to your
A21 amp first and then on to your main speakers. These are both very useful controls that we can discuss how to best utilize and set on future posts.
Just one more opinion, I think you might want to consider paying the extra $150 per sub for the rosewood finish. You’re going to be seeing these subs in your room on a daily basis for probably at least a few years. I think the fact that you didn’t pay the relatively small extra money to have them better match your ML main speakers may nag at you long after you’ll remember or care about saving a bit of money in the short term. Just something to think about since it’s your money and decision.
The last thing I want to mention is you’ll need 2 single mono male-to-male line level cords to connect each sub to your P5 preamp. If you use the crawl method to optimally position each sub in your room in relation to your designated listening seat, and begin your search at the right front corner of your room and proceed counter-clockwise around the perimeter of your room as recommended, I strongly suspect you’ll discover that the bass sounds best at your listening seat with both subs positioned along your front short 14’ wall. It could be with one in each corner but my experience makes me think they’re most likely to sound best with both subs along the front wall with one about 1-2’ away from the right front corner and the other 1-2’ away from the left front corner.
I still suggest you just faithfully follow the crawl method and position them precisely where they sound best to you. But this means it’s best to buy one 8-12’ mono rca cable for Sub#1 and the one for Sub#2 much longer, at least to start with. If I’m correct about sub positioning, you could probably just exchange the extra long cable for another 8-12 footer or just buy another. But if I’m wrong, you’ll probably need it because the optimum position may be along your left long wall with the windows and you’ll need to avoid positioning Sub#2 directly over an hvac vent.
Later,
Tim
