Necesssity is the mother of invention
Hi,
- If I was in a similar situation ( blessed with an over abundance of midbass woofers such as the 515-8HP / but land-locked within Norway & therefore having little to access to "flipping the originals for a more desired bass-woofer" ) I'd be looking to find a way to turn those 515s into a driver that'll produce more bass .
- An idea ( such as this ) is only for the adventerous, & those who have the required tools to measure a woofers TS parameters ( & those who understand the relevance to woofer/enclosure alignments that the new numbers will offer ) .
- One way ( to turn a midbass woofer into a bass woofer ) is to add weight to the cone to increase its' MMS ( moving mass ) up to a value ( more conducive to producing convincing bass ) . My calcs. show that you want to get the 515-HPs "MMS" up to at least 100 grams .
- This is accomplished by adding weight to the cone . I'd start with 20 to 30 grams ( in a unconnected ring of non-ferric/non-magnetic metal ) temporarily glued to the joint between the dustcap & the cone .
- The advantage of adding cone weight in this way ( as opposed to just gooping up the cone with aquaplas ) is that the originals' midbass response is mostly retained .
- This is the very approach that JBL used when they decided to create the 2231/5 from their standard "Sound-Reinforcement" woofer; the 2205 or 2225 .
- They glued a 35 gram, lead-like "mass-ring" to the top of the voice-coil to increase the "MMS" . They kept the originals' paper cone and voice-coils .
- JBL also increased the compliances ( looseness ) of the spider & surround ( which is admittedly hard for the "hobbyist" to do ) .
- FWIW, typically, by not changing-out any of the original compliances ( spider or the surround ) / the Qts will rise some (ie; sacrificing a bit of cone control for better bass reproduction ) . Vas will increase .
- Depending on the resilience of the stock Altec parts, Fs "may/or may" not drop very much ( one would need to monitor the trend as more & more cone weight is added ) .
- Once a reasonable new moving weight is arrived at / it would be best to permanently glue it just over the voice-coil ( but under the dust-cap ) . Obviously removal of the cap & it's reinstallation will be necessary .
- Just a thought, mostly for those "hooped" by geographical ( &/or ) economic circumstances . ;)
>< cheers :)